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193 Cards in this Set

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  • Back
Describe the role the immune system plays in health and disease?
Immune system has defense against microorganisms and other potentially noxious substances, elimination of abnormal host cells, and clearance of dead and dying cells => carried out by both innate and adaptive immunity
Identify cells and soluble mediators involved in innate and adaptive immunity and briefly describe their functions?
Inflammation is characterizied by vascular changes and activation of leukocytes. Tissue mast cells, phagocytes, platelets. Soluble mediators include histamine, arachidonic acid metabolites, plasma enzyme cascade.
What is the first barrier to infection?
What types? give exp.
First barriers are nonspecific and can be chemical like acid pH, lysozyme and or physical (Skin, mucus). Most of defenses against infection are nonspecific.
What do pathogens in common that are integral to their survival but different from host structural elements?
Gram- bacteria =?
Gram positive bacteria?
What are molecules called?
Cell wall and capsules of bacteria and fungi.
Endotoxin of gram negative bacteria
Lipoteichoic acid of gram positive bacteria.
Specialized for defense, but does not possess immunological specificity.
Pathogen associated pattern molecules.
How have eukaryotic species evolved to combat common pathogen structural elements?
Examples of defenses?
Evolved receptor molecules that recognize Pattern Associated Pattern Molecules and trigger vigorous cellular responses when pathogen is encountered.
Mannose receptors, endotoxins receptors on the macrophage (which recognizes fungal and gram negative bacterial surfaces), C-reactive protein (recognizes polysaccharide capsule of pneumococcus), mannan binding lectin, and alternative complement pathway.
What do you call non-clonal, non-specific defense strategy?
Innate immunity because recognition mechanisms are inherited, non-adaptive yet can differentiate pathogen from non-pathogen. Rapid response, fixed, limited number of specificities, constant during response. (no improvement w/time)
Third or altered second response to pathogen is called?
When transferred from one individual to another with serum it is called?
Adaptive Immunity.
Humoral Immunity when transferred via serum.
Other adaptive responses can be transferred only with viable lymphocytes - cellular immunity.
Humoral immunity is mediated how?
Humoral mediated by antibodies produced by plasma cells, cellular immunity is mediated by T lymphocytes and their products ==> allergies, accidental immune response. clonally expressed. specifically recognize self from non self.
White Blood Cells are also called?
What is derived from them?
Leukocytes.
Lymphocytes, Monocytes, Polymorphonuclear Leukocytes.

Monocytes ==> IDC -> mature dendritic cells / macrophages

Granulocytes (PMN) => Neutrophil, Eosinophil, Basophil
What do lymphocytes differentiate to?
T Cells => CD4+ or CD8+ ==> CD4+ Th0 helper CD4+ differentiates to Th1 or Th2.

B Cells => Plasma Cells => Ab

NK cells
What are some effector molecules for adaptive immune response that recognize and bind to foreign substances/antigens in the environment?
Antibodies. The are one arm of the humoral response of the adaptive immune response. The antibody proteins are immunoglobulins --> heterogeneous group of glycoproteins that are 20% of total plasma proteins.
Where are antibodies?
Present in free circulation and on B-lymphocytes.
What is the basic structure of an antibody?
What kind of bond links them?
What is the exception to symmetry rule?
Four polypeptide chains, 2 identical heavy chains, 2 identical light chains.
Covalent disulfide bonds as well as non covalent bonds in bilaterally symmetical arrangement links the two chains.
Ig4 is unique in that one IgG4 molecule can exchange one heavy chain and one light chain molecule (one half of the antibody molecule) with a heavy chain and a light chain module of a second IgG4 molecule.
What does each polypeptide chain contain?
How many aa. acids are in each region?
How many domains per/light chain
or per/heavy chain?
Each polypeptide chain contains domains which are compact globular regions containing 100-110 amino acids formed by intra-chain disulfide bonds.
Light chains contain 2 domains
Heavy chains contain 4-5 domains
In an immunoglobulin which domain has more variability?
What exhibits little diversity?
N-terminal domain of each heavy and light chain display more variation in amino acid sequence.
N terminal domain of each polypeptide chain has a variable domain and remaining domains are designated as constant domains.
Constant regions exhibit little variation in amino acid sequence and have similar secondary and tertiary structures.
All immunoglobulins are ____proteins.
Amount of ______ varies with Ig.
Where are most oligosaccharides attached?
All immunoglobulins are glycoproteins but the amount of carbohydrates varies with the immunoglobulin. Most of the oligosaccharides are attached to the constant domains of the heavy chain.
Carbohydrate may play a role in Ig secretion by plasma cells.
What cleaves in Ig, the first and second constant domains of the heavy chain (CH1 and CH2)?
What is the region name?
What does it cleave into?
The protease sensitive region is more exposed than other portions and more flexible and can be cleaved by papain.
It is called the hinge region.
It cleaves the antibody molecule into two Fab fragments (univalent 1 ab site) and one Fc fragment (Effector response).
What does Fc from Ig do?
What is Fab composed of?
Fc portion initates biological activities subsequent to antigen binding.
Fab is composed of a light chain + one variable and first constant domain of the heavy chain. Each Fab fragment is composed of the carboxy-terminal portion of heavy chains and initiates activity.
What acts on the hinge region to cleave the molecule into one F(Ab')2 fragment and a degraded Fc fragment?
Pepsin. Each F(ab')2 contains 2 covalently linked Fab fragments that are bivalent.
What are the classes of light chains?
What differentiates these light chains?
What is the ratio?
What does one Ig have?
Kappa and Lambda.
Differ structurally in the constant domain. Both types of light chains display an equal ability to associate with heavy chains.
Kappa to lambda : 2 to 1.

One Ig molecule contains two identical kappa or two identical lambda chains.
What are the classes of heavy chains?
What differentiates these heavy chains?
Heavy chains are in 5 classes,
gamma, alpha, mu, delta, epsilon.
5 classes differ structurally in their constant domains. The structure that determines class of antibody chain.
What % of total serum is IgG in adults?
How many subclasses? Rank order and what differentiates?
What is unique of IgG?
What does IgG activates/which classes?
75% in adults. Consists of 2 heavy chains (gamma) and 2 light chains.
IgG1>IgG2>IgG3>IgG4. Defined by differences in their constant regions.
Major antibody formed during the secondary response.
Only antibody able to cross the placenta and provides immunity in newborns.
IgG 1-3 activate complements, are opsonins (molecules that mediate the binding of particles to phagocytosis.)
What effector mechanism of cell mediated immunity does IgG activate?
Which classes for IgG on monocytes and macrophages bind in monomeric form to Fc receptors?
What is unique about IgG4
Antibody dependent Cellular Cytotoxicity (ADCC) .

IgG1 and IgG3 bind to Fc receptors.

IgG4 is unique in that one IgG4 molecule can exchange one heavy chain and one light chain module with half of antibody molecule with a second IgG4 molecule. Most IgG4 molecules recognize 2 different antigens and is functionally monovalent.
What is unique about IgM?
What is the attached protein?
What is IgM function?
Where is IgM found on B lymphocyte surfaces?
What is the valence ?
Pentameric structure of 5 monomers making up 10% of serum Ig containing a additional heavy chain domain.
Larger than gamma heavy chain and the pentamer is enclosed by the J chain.

J chain is a glycoprotein that covalently links two monomer subunits together.

IgM is the major Ab class formed in primary immune response, the most efficient activator of complement, expressed on B lymphocytes -> mediates antigen specific B lymphocyte activation.

IgM is found as a monomer, and is the antigen receptor for the B cell.

Valence of 10. Can recognize 10 molecules at a time.
What is unique about IgA, where is it predominantly found?
Whats structure of IgA?
What structure links IgA monomers?
What does the component do?
Valence?
IgA is present in serum and predominant antibody in seromucous secretion. 15-20% of serum Ig and >80% in a monomeric structure analogous to IgG.

Serum IgA is formed in dimers. Heavy chain class is alpha class and has two subclasses: IgA1 and IgA2.

Secretory IgA present almost exclusively in seromucous secretion and exists as a dimer.

Two monomers are linked covalently by a J chain (Same as for IgM). Each secretory IgA molecule also has a secretory component which is a 70 kD polypeptide fragment of a receptor for polymeric immunoglobulin on the basal surface of mucosal epithelial cells.
Secretory component facilitates transport of secretory IgA across mucosal epithelium into the lumen and protects secretory IgA from proteolysis.
Responsible for immunity at mucosal surfaces has a valence 4.
Binds Ag, neutralizes virus, toxins, blocks bacterial adherence.
What is IgD?
Predominant Ig with IgM on B lymphocytes that comprises < 1% of total serum Ig. Like IgM, IgD can mediate B cell activation.
What is unique about IgE?
What does it mediate?
IgE like IgM contains an additional constant domain.
.004% of total serum Ig, but binds strongly to Fc receptors for IgE on basophils and mast cells.
IgE mediates hypersensitivity reactions, mediates allergies, host defense against parasites.
What are on the surface of memory B lymphocytes?
IgG IgA IgE are on surface of memory B cells where they serve as antigen receptors, membrane bound form of IgA is a monomer.
Membrane form of Ab is anchored by lipophilic segment at carboxy-terminus of heavy chain.
What does isotype signify/which specific region of Ig?
What is each isotype encoded by?
Isotype defines structural differences in constant regions that distinguish class and subclasses of heavy chain and the class of light chains within a single species.

Isotype is encoded by a specific gene. Humans have 9 different heavy chain isotypes and 2 light chain classes. Also differentiate between human and animal Ab.
What defines small structural variations in the constant region of the heavy /light chains of an Ig of same isotype within the same species?
Allotype. Notably the genes encoding the heavy chains IgG and light chains are polymorphic.
Structural variations encoded by different alleles result from substitution in one or two amino acids. Allotypes exhibit Mendelian form of inheritance.
What defines structural differences within the variable domains of heavy and light chain?
What does it dictate?
Idiotype. Each clone of Ab producing lymphocyte synthesizes an Ig molecule with a unique variable region amino acid sequence.

The sequence dictates the antigen specificity of the antibody.
What are Igs synthesized by a single clone of a malignant plasma cell called?
Free light chains found in urine of patients with multiple myeloma are called?
Myeloma proteins. It is monoclonal (derived from single clone) and has been observed with all Ig classes.
Bence-Jones proteins found in the urine of patients.
What defines immunogenicity?
What can induce an immune response and what reacts specifically with immune system?
Capacity to react with immune system.
Immunogens are substances that induce an immune response and antigens are substances that react specifically with the immune system. ALL IMMUNOGENS ARE ANTIGENS BUT NOT ALL ANTIGENS ARE IMMUNOGENS (haptens)
True/False Antigens arise from external sources only.
False. Antigens arise from both external and internal sources.
Externally derived antigens - soluble molecules such as bacterial toxins, components of more complex structures such as bacteria. Endogenously-derived antigens expressed on cell surface of virus-infected cells or tumor cells. Antigens may be: proteins (toxins, allergens, proteins); polysaccharides (bacterial cell walls and ABO blood group antigens).
What are the criteria for immunogenicity?

Homopolymers of single amino acids are strongly immunogenic?
Foreign - self from non self

Molecular size - minimum size is necessary but no specific threshold. < 5 kd is weakly immunogenic if at all whereas molecules > 100 kD are strongly immunogenic.

Chemical complexity - immunogenicity increases with complexity.



False - homopolymers of single aa. are poor immunogens whereas polymers of repeating units 2 or 3 amino acids may be immunogenic.
What portion of antigenic molecules interact with antibody?
Antigenic determinants or epitopes are areas which interact with antibody. Number of distinct antigenic determinants varies with size and complexity of molecule.

A given individual may respond to only a subset of determinants. Epitopes that induce an antibody response in the majority of individuals are IMMUNODOMINANT EPITOPES.
Where are antigenic determinants for Ab interactions located?

True/False - Conformation and sequence are each important to antigenicity of proteins and polysaccharides.

Denaturation destroys which determinant on an antigenic molecule?
On most hydrophilic region of molecule, and usually 5-7 amino acids for proteins or 5-7 monosaccharides for polysaccharides.

True. Conformational determinant is based on overall structure of a substance. Specific sequence of amino acids or monosaccharides define a sequential determinant.

Denaturation of the antigenic molecule destroys a conformational determinant, but not a sequential determinant. Denaturation may sometimes uncover a new sequential determinant not from native molecule.

Linear epitope - Denaturation has no effect.

Discontinuous epitope - Relies on conformation for antigenicity.
What are antigens but not immunogens?

What is their valency?

What is an example of a hapten?

What is importance of protein carrier?
Haptens, are small chemically defined molecules that are not immunogenic but that can react with antibody of appropriate specificity.

Haptens are univalent molecules in contrast to multivalent proteins or polysaccharides.

Haptens, dinitrophenol, DNP, act as a partial or complete antigenic determinant when coupled to a protein carrier.

Protein carrier has its own inherent antigenic determinants. Some antibodies made against the hapten-carrier complex will be specific for hapten. Any chemical structure may act as a hapten if coupled to a protein carrier.
At the antigen binding site, where is the greatest variability?

Where are the framework regions?
Greatest variability are termed the hypervariable regions.

Relatively constant sequences between the hypervariable sequences. Light chains have 3 hypervariable regions and heavy chains have 3 or 4 hypervariable regions.

A SPECIFIC VARIABLE DOMAIN MAY BE LINKED TO ANY CONSTANT DOMAIN OF A HEAVY CHAIN CLASS OR A LIGHT CHAIN TYPE.
What forms the antigen binding site?

What are important for the framework regions?

What kind of bond links the antigen binding site and antigenic determinant?
It is the variable domains of the heavy and light chains aligned to bring together the hypervariable regions of each chain that form the antigen binding site

The framework regions are important in the folding and proper orientation of the binding site.

Molecule dimensions of antigenic determinants and antigen binding site must be complementary to each other.
COMPLEMENTARITY-DETERMINING REGION.

Strong multiple NON-covalent bonds form. Strength of noncovalent bonds is inversely related to the distance between interacting groups.
What is cross reactivity?
Antibodies made against one antigen or hapten may in some cases reach with another antigen or hapten. This phenomenon is called cross reactivity and reflects shared antigenic determinants by the two antigens.
Generally an antibody binds less strongly to a cross-reacting antigen than to the antigen that induced the antibody formation.
Antibody-antigen complex is irreversible true or false?
False. The reaction between an antibody and an antigen is reversible, but the dissociation of Ab-Ag complex is slow that it is essentially irreversible under normal conditions.
What do you call that is a measure of the strength of interaction between a single antigen epitope and a single antigen binding site (Fab) of an antibody?

What do you call a measure of the strength of binding between a multivalent antibody and a multivalent antigen?
Affinity. The interaction follows law of mass action and allows affinity to be measured experimentally. Calculation holds for a hapten (univalent interaction) and Fab.

Avidity. IgG, serum IgA, IgD, IgE each have 2 Ag binding sites whereas IgA and IgM have 4 and 10 binding sites respectively.
Aividity is dictated by the affinities of the individual interactions, but the avidity is greater than simpley the sum of individual affinities.
What is another name for antigen antibody complexes?

What is formation of a precipitate a function of?
immune complexes. The form taken by Ag-Ab complex depends on nature of antigen and ratio of Ag and Ab concentrations.
Ab interactions with particulate antigen result in agglutination of cells.
Binding of Ab to soluble antigens forms immune complexes that may precipitate.

Formation of a ppt is a fxn of antigen and antibody conc.
When you increase antigen with constant amount of antibody what happens?

As you increase amount of antigen, what happens?
Can see a precipitation of an immune complex.

Amount of precipitate increases then decreases. 3 zones of precipitation ==> antibody; equivalence; antigen excess.

Antibody excess - most Ab bound in univalent fashion to antigen
Antigen excess - conc. of antigen is excess relative to Ab. One Ab will bind and crosslink two antigen molecules.

Equivalence - antigen and antibody are equivalent, IgG binds bivalently to form insoluble lattice with multivalent antigen. --> Antigen must be at least bivalent for insoluble lattice and ppt to form.
What clears immune complexes after initial stage following antigen exposure?

What can larger complexes activate via Fc?
Phagocytic cells in the reticuloendothelial system clear larger immune complexes from blood via recognition of Fc portions of the antibody molecules.

Larger immune complexes can also activate complement and phagocytic cells in the circulation via the Fc. Conditions where exposure persists, such as in autoimmune system disease, formation of the immune complexes can overwhelm the reticuloendothelial system and lead to tissue damage.
What are some ways to use foreign antibodies such as those from mice?
(1) Graft variable domains of mouse heavy and light chains onto the constant domains of human IgG (chimeric monoclonal antibody)
(2) Grafting hypervariable domains of mouse heavy and light chains onto a human IgG humanized monoclonal antibody.
Define role of MHC class I and MHC class II molecules in antigen recognition by T cells?
T cell receptor only recognizes peptide antigens presented in the peptide binding groove of an MHC class I molecule (Cytotoxic T cell) or MHC class II molecule (Helper T cell). The MHC molecules present their antigens usually on Antigen Presenting Cells (APCs).
How are proteins for MHC class cells processed?
Proteins are processed by proteolytic enzymes into peptides and transported to site of association with MHC class molecule and then transported to surface of APC.
How does T cell antigen receptor derive its antigenic specificity?
Which molecules are expressed on T cell surfaces during maturation?
T cell antigen receptor derives specificity through gene rearrangement similar to B cell antibody diversity.
Cellular Differentiation molecules include CD3, CD4, CD8 expressed on T cell surface and play an essential role in both selection of the T cells that reach maturity and subsequent recognition of foreign antigen.
Describe the structure of a T cell receptor?
T cell receptor is a 2 chain molecule. TCR chains are alpha, beta, gamma, delta expressed only as alpha + beta or gamma + delta.
All T cell receptors have domain structure simliar to Ab Fab fragments, have variable domain w/ hypervariable loops and one .
constant domain.
T cells are rigid and lack the hinge region, have a valence of ONE and are not designed to be secreted molecules.
What is the specificity of T cell receptors?
Each T cell recognizes one antigenic determinant ==> one antigen receptor specificity ==> unique idiotype

Only one alpha chain variable region is expressed by each a/b T cell and only one beta chain.
How many different genes are there that encode the variable region of each chain for TCR?
They have a leader sequence, variable gene sequence, diversity gene sequence (beta and delta chains only), and a J joining region, and a constant region that has extracellular, transmembrane, and cytoplasmic domains.
Why are all the delta chain gene sequences found between the Valpha and J alpha genes?
This arrangement assures that each T cell will express only one of two antigen receptor isotypes: alpha beta or gamma delta.
A rearrangement of the alpha gene deletes the entire delta chain gene region
Differences between Ab and T cells?
Antibody binds free, soluble UNPROCESSED antigen usually through determinants exposed on surface of antigen molecule (Linear or Conformational).
T cell recognize only peptides bound in groove of MHC class I or class II cells. T cell epitopes mainly hydrophobic and are always linear determinants.
What do TCRs associate with to enact effector functions?
Noncovalently associated molecule complexes called CD3 are on the surface of T cells and composed of several membrane-bound polysaccharides called gamma, delta, epsilon, zeta and eta. CD3 is a signal transduction part of the antigen receptor. It undergoes a conformational change when TCR binds to the MHC-antigenic peptide complex. This activates intracellular protein tyrosine kinases that activate effector functions.
B cell receptor has how many idiotypes?
What are the isotypes?
Secretions possible? Valence? Mobility? Antigen recognized? Associated Signal transduction molecule?
B cell receptors have 1 idiotype, 2 isotypes of Igm and IgD, They can be secreted, have a valence of 2, have a flexible hinge region, and recognize soluble unprocessed antigen. Associated surface molecule are CD19, CD20,CD21.
What is TCR? Valence? Isotype? Idiotypes? Mobility? Antigen Recognized? Associated molecules?
They have 1 idiotype, 1 isotype of alpha+beta or gamma+delta.
No secretion possible have a valence 1 and the mobility is rigid. They only recognize processed peptides on presented MHC molecules.
CD3 is the associated signal transduction molecule.
What is another name for MHC gene products in humans?

What chromosome are they found on?
HLA or Human Leukocyte Antigens.
THey are found on chromosome 6 in humans and are divided in 3 classes which are expressed on different tissues and have very different functions.
What are the diff types of class II HLAs?

What are the diff types of Class I HLAs?
HLA - DP, DQ, DR for Class II have restricted tissue distribution. Found only on B lymphocytes, monocytes, macrophages, dendritic cells, Langerhans cells, activated endothelial cells, and activated human T cells.
HLA-DM is found only within endosomal compartment and plays a role of transferring peptides to other MHC Class II molecules. Catalyzes exchange of CLIP for processed exogenous peptide.
HLA- B, C, A for Class I found on all nucleated cells in the body and platelets

Antigen binding groove is hydrophobic environment and has internal determinants of protein.
What do class III MHC genes encode?
They encode secreted plasma proeins which do not participate in direct antigen recognition by T cells. They include TNF alpha and beta and some complement proteins C2, C4, and Factor B
What is the structure of class I MHC molecule?

What is the function of MHC 1 cells?
Consist of a heavy chain that has transmembrane anchor near carboxyterminal end and peptide binding groove near aminoterminal end.
Light B chain called B2-microglobulin that is found on chromosome 15 in humans, function of B2-microglobulin is to transport MHC Class I molecule with peptide bound to alpha chain to cell surface.

Fxn of class I MHC molecules is to act as the target for the limination of abnormal host cells.
What characterizes a abnormal host cell?
A abnormal host cell is one that is
- infected with intracellular agent, virus, intracellular bacteria, intracellular protozoal parasites, intracellular fungi.
- mutate or transformed to produce an abnormal cellular gene product (oncogenes activated in tumor cells)
Whats the pathway of MHC Class I degradation?
intracellular antigen ingested -> proteasome digests antigen processing begins in cytoplasm -> peptide transport into rough endoplasmic reticulum for loading peptide into groove of MHC I class molecule (TAP) -> transport to ER and peptide binding by MHC class I -> MHC class I presents peptide at cell surfaces.

Class I MHC molecules carry out fxn by binding to peptides that are actively synthesized by host cell. Very nonspecific pathway so both self peptides and abnormal peptides are bound and then arried to cell surface.
What recognizes abnormal peptide bound to class I molecule?
Cytotoxic T lymphocytes recognize abnormal peptide that is an essential signal that triggers release of cytotoxic molecules from cytotoxic T cells resulting in destruction of infected host cell, and elimination of infecting agent.
What is function of class II molecules?

What is the name for remnant peptide that remains in peptide binding groove of MHC II until HLA -DM in endosome catalyzes exchange for processed exogenous peptide?
Function of class II molecules is to present exogenous peptides to helper T lymphocytes.

Proteins from outside APC cells are nonspecifically internalized by endocytosis. In the endocytic vacuoles in these cells, enzymes process proteins into small peptides. Class II MHC molecules are synthesized by cells then transported into same vacuoles where they bind to peptides -> at time of synthesis, the alpha and beta chains of class II molecules are bound to INVARIANT chain and prevents peptide binding to MHC class II molecule.

CLIP or Class II associate Invariant Chain Peptide. The low pH of endosome permits proteolytic degradation of invariant chain and facilitates exchange of CLIP for processed peptide.
What do the surface molecules of CD4 and CD8 in terms of T cell - MHC interaction?
CD4 and CD8 are involved in the stabilization of the T-cell receptor-antigen-MHC interaction. CD3 T cell surface molecule is associated with TCR and transduces the signal that is effected upon binding of antigen by TCR
What is the function of lymphoid organs?
Their function is to optimize the recognition of the immune system. Job of lymphoid system is to recognize presence of intruder, and respond in very specific fashion to eliminate intruder.
What are the primary lymphoid organs?

True/False Lymphoid organs are where foreign antigen is directed to the immune system.
Primary lymphoid organs are where the lymphocytes develop immunocompetence and the ability to specifically recognize foreign antigen and become tolerant to self structures (specifically unresponsive).
Bone marrow and Thymus.

False. Organs are NOT the sites where foreign antigen is directed to the immune system. They have the ability to recognize foreign antigen and to distinguish self vs. non self by random genetic rearrangement BEFORE contact with foreign antigen. Only self antigens are present in lymphoid tissue and where they become tolerant or unresponsive to self structures.
What is the role of hematopoietic development for lymphocytes?

What are 2 important cytokines for early developmental stages?

What is responsible for antibody synthesis? where do they develop immunocompentence?
Begin in the yolk sac then later carried to fetal liver --> taken over by bone marrow where pluripotent self renewing stem cells give rise to erythroid, myeloid, and lymphoid precursors which differentiate under influence of cytokines or hormone like growth factors.

IL- 7 is produced by stromal cells in bone marrow and important in lymphoid development.
IL - 3 and variety of colony stimulating actors are essential for myeloid development. (Granulocytes, monocytes)

B cells, Bone Marrow
What subset of lymphocytes exit bone marrow at undeveloped stage?
Where are they headed?

At what age does it shrink?
T cells. They require further differentiation at thymus. T cell differentiate along diff pathway from B cells and recognize antigen only when it is presented with MHC. They do not synthesize antibodies.

5 years of age thymus involutes.
Describe structure and how thymus works?

What cells are essential in T cell maturation?
Thymus is a bilobed organ with an outer cortex and an inner medulla. The T cell precursors from bone marrow are transported in thymus via the blood, migrate to the cortex, and with maturation move deeper into medulla.

Intimate contact with thymic epithelial cells, macrophages, and dendritic cells is essential in T cell maturation.
What are two important functions in T cell development?
1) Secretion of thymic hormones that direct T cell differentiation and play no direct role in selection process carried out in thymus.

2) Education, Thymic epithelial cells, dendritic cells, macrophages present self-antigen but NOT foreign antigen to developing T cells in the cortex.
Those that recognize self MHC positive get positive selection signal to continue dividing and establish clone that mature in medulla --> exit into periphery to populate secondary lymphoid organs. Low or weak binding due to T cells that fail to recognize self MHC molecules will die. (Failure of positive selection)

High or Low affinity binding = death
Where does positive selection of TCR occur?

Where does negative selection of TCR occur? Those that fail to do so can cause what?
By cortical epithelial cells in thymus positively select alpha+beta TCR

Negative selection of TCR are by dendritic cells, macrophages, and other cells in the thymus. T cells that express Ag receptors that bind too well to self MHC if leave thymus cells would recognize and be activated by self antigens.
They can cause autoimmune disease.
Thymus induces these autoreactive T cells to committ suicide and negatively select them. Only 1% of T cell precursors can ever leave.
What is the structure of lymph nodes?
Lymph nodes are collecting points in an open circulatory network where lymphocytes systematically monitor body's extracellular fluids for presence of foreign antigen.Afferent lymphatic vessels with lymph fluid that bathes cells bring antigen into lymph node. Has a lymphoid follicle in cortex with a paracortex area with Tcells that then go to medulla where memory cells leave through.
Where are the immunocompetent B cells found in the lymph node?
They are mainly found in the follicles of the lymph node where mature T cells are found in the paracortex which is the T-dependent region of the lymph node.
Macrophages pick up T cell, T cell activate cytokine, T cells proliferate and undergo clonal expansion.
Antigen In -> Antibody out.
What serve as initial, nonspecific traps for antigens as they enter from afferent lymphatics?
Dendrites and macrophages. When b cells get activated they migrate to paracortex where T cells meet w/ B cells and B cells proliferate at germinal centers --> migrate to medulla
What secondary lymphoid organ is the major antigen trapping site in the immune system?
Lymph nodes. They collect and sample the lymph draining from a particular area of the body. Soluble antigens carried by afferent lymphatics are picked up non-specifically in lymph node by macrophages and dendritic cells which are presented to lymphocytes.
What type of cells in the follicles divide?
What is the region called in the follicle?
B cells are stimulated to divide and produce clones of cells that make Ab specific for intruding antigen.
A germinal center that is called a secondary follicle. Stimulation of B cells by antigen induces their terminal differentiation into plasma cells. Plasma cells migrate to medulla of lymph node where they spend rest of lives secreting Ab.
What do lymph nodes do for long term immune defense?

T/F. These cells and plasma cells leave lymph node to peripheral tissues.
Lymph nodes also participate in establishing immunological memory. Some B cells differentiate into memory cells which provide host with long lived memory for antigen.

False. Only memory cells can leave lymph node unlike plasma cells. They exit via efferent lymphatic vessels and find way to blood stream via thoracic duct to spread to other secondary tissues.
How is the recirculation of memory lymphocytes accomplished?
By homing receptors on cells, when lymphocytes in blood pass through capillaries of another lymphoid tissue, they encounter HEV, or high endothelial venules which express surface ligands that homing receptors will bind.

Stimulation of lymphocytes in one lymph node results in the dispersion of memory cells specific for an antigen throughout the body.
What carries out secondary lymphocyte activities for blood?
Spleen. Spleen has B cell dependent areas (follicles or marginal zone and T cell dependent areas (Periarteriolar lymphoid sheath, PALS). During antigenic stimulation, follicles develop germinal centers, just like lymph node.
During antigenic stimulation, follicles develop germinal centers.
What is name for collection of lymphoid tissue in submucosa and lamina propria?
MALT, mucosa-associated lymphoid tissue (MALT) They are prominent in the gut where they include Peyer's Patches and in the bronchioles. Sample Ag that enters host through mucosa, sites of constant antigenic exposure. they make up the secretory immune system.
What is the purpose of secondary lymphoid organs?
To maximize contact between APC, B cells, T cells, and antigen molecules.
Effective immune response.

Recirculation of lymphocytes among different lymphoid compartments assure benefit of immunological memory avaible where Ag appears in future challenge. Circulation is selective directed by particular adhesion molecules.
Cells stimulated by Ag in particular system recirculate exclusively to other sites of like system. Cells stimulated in nonsecretory system such as spleen and lymph node, recirculate to lymph node and spleen
What are the stages of T lymphocyte development and what are the expressed markers?
1. Prethymic, bone marrow precursors. Express Terminal deoxyribonucleotidyl transferase. TdT is involved with recombination.
2. Stage I. Thymic cortex. Immature and express CD2 or sheep RBC receptor, and begin to rearrange TCR genes. Beta chain rearranges first but is not expressed on cell membrane yet. Cells are unresponsive to antigen.
3. Stage II. Intermediate thymocyte. TCR alpha chain is rearranged and CD3+, CD4/8+
4. Stage III. Thymic medulla. Cells become mature thymocytes CD4+ and CD8+ are distinct subsets commited to helper or cytotoxic t cell functions.
What is always rearranged first in TCR gene chains?
Gamma+delta chains are always rearranged first and produces an in-frame functional molecule. If the rearrangement is not successful, cell rearranges to differentiate into an alpha+beta T cell.
Gamma+delta T cell found mainly in sub-epithelial and sub-mucosal sites, where antigen first penetrates the nonspecific (physical barriers).
How are T cells educated?
Interactions of developing T cells with thymic epithelial cells and dendritic cells expressing a high level of both MHC class I and class II are important in educating the T cell in self/non-self recognition.
Foreign antigen is not present in thymus, so it seems that self reactive T cells are eliminated or inactivated in this organ.

CD4+ helper T cells enter circulation and migrate to secondary lymphoid tissues where they encounter antigen.
Antigen recognition by naive helper t cells (TH0) results into what?

How are they distinguished?
Differentiation intwo two subsets of Th1 and Th2 helper T cells.

Cannot be distinguished by surface markers. All express CD3, CD4, TCR. They are differentiated by cytokines produced.
What do Th1 helper T cells secrete?

What do Th2 helper T cells secrete?
IFN-gamma, IL-2. Essential for stimulation of cell mediated immunity.

IL-4, IL-5, IL-6, IL-10. Play a major role in B lymphocyte differentiation and antibody production.

TH0 can secrete both types of cytokines.
If TCR has affinity for MHC I what is retained and what does it become?
If CD8 marker is retained, CD4 will stop being produced and cell will become a mature cytotoxic T cell. They migrate to periphery and secondary lymphoid tissues.

When CD8+ cells encounter antigen AND are activated by Th1 cytokines, they develop into cytotoxic effector cells and kill target cell that they reognize.
Where is CD3 expressed on?

Where is CD2 expressed on?

Where is CD40 ligand expressed on?

CD28?
CD3 - all T cells, T cell receptor associated signal transduction molecule.

CD2- All T cells adherence to other cells binds LFA-3.

CD40 LIGAND - Activated helper T cell that binds to CD40 on B cells. Essential for Ab isotype switching.

CD28 - Helper T cells and Mostly Cd8+ T cells. Costimulatory molecule needed for T cell activation. Binds B7.1 and B7.2 for
What is the sequence of B cell development?
1. Precursor B cell (Germline / Found in bone marrow)
1a. Pro-B cell (progenitor) TdT expressed. Ig Heavy chain rearrangement begins
2. Pre-B Cell Only Heavy Chain V region rearranged (V/D/J) at random to begin making an intact mu chain of defined specificity. Not able to recognize antigen and marker is the cytoplasmic IgM only in cytoplasm. TdT expressed
3. Immature B cell. Heavy and light chain V regions rearranged (V, J, and kapp or lambda). IgM expressed on surface membrane. Antigen is response and easily tolerized.
4 Mature B cell. Heavy and LIght chain V regions are rearranged and IgM and IgD are expressed on surface membrane. Short-lived, difficult to tolerize.

No antigen is required to reach mature B cell stage. Ag specific recognized by B cell receptor stimulate cell division and further differentiation ==> plasma cell
True/False. B cells differentiate from lymphoid precursors in Bone marrow and can leave the bone marrow with full ability to recognize and respond to antigen.
True. They can then migrate to secondary lymphoid organs to await the arrival of antigen. B cells also express CD markers which are useful in their identification. Best markers of B cell development are the Ig chains they make.
What are some important B cell markers?
CD19, CD20, CD21, CD40

CD19/20 Signal transduction
CD21 - Complement receptor type 2. Binds cleave C3 (C3d) fragment and is a receptor for epstein Barr Virus
CD40 - Costimulatory molecule required for memory and class switch signals from T cells.

CD19/MHC II not expressed on plasma cells
What happens with Memory B cells?
They have a heavy chain constant region rearrangement, class switch.
Express IgG, IgA, IgE on surface but needs help of T cell.
They begin differentiating to plasma cell but not completely. They are long lived. Antigen stimulus conc dec. stop diff.
How many antibody specificities are there?
There are about 10^8 possible antigenic structures due to the cross-reactivity of the antibody combining sites. It has been estimated that the immune system can produce at least 10^8 different antibody molecules.

All chains are on autosomal chromosomes.
Heavy and light chains are INDEPENDENTLY REGULATED on different chromosomes.
How can limited amount of DNA encode for all possible structural variations that an antigen binding molecule can recognize?
1. Limited size of an antigenic determinant
2. Cross Reactivity between antigens limits requirement.
3. Inheritance of multiple V region gene segments encode some specificities. Germ Line genes are inherited gene segments that encode for variable domains of heavy chains, light chains, and T cell receptor chains.

For antibody molecules, there are btwn 100-300 of germ line V region gene sets for each of the heavy chains, kappa light chains, and lambda chains.
4. Mutations in B cells that divide in germinal centers. Mutations that increase Ab affinity are preferentially selected, mutations thus play a role in affinity maturation of B cell clones. This DOES not occur in generation of T lymphocyte antigen receptor diversity.
5. Recombination of variable region gene segments. Genes that encode for variable domains are split into a group of 100-300 V gene segments that encode for first 95 aa of variable domain. Domain is 110 amino acids so DNA base pairs that encode last 15 amino acids of domain are found in linked DNA segments along the chromosome, For light chain, one of four possible J gene segments for joining, these DNA sequences encode for the amino acids that join the rest of the variable domain to the constant domain, randomly selected.
6. Recombinational inaccuracies that occur when exons fuse increase variability. Heavy chain variables are undergoing recombination D with J first vollowed by V with DJ. TdT is active.
Which proteins are involved in recombination activating and rearrangement of genes for germ line DNA?
RAG genes or recombination activating genes. Light chain only rearranged DNA can be expressed if V and J genes are not together.
(Somatic recombination)
Light chains have VJC segment
Heavy chain have VDJC. 10-20 D region gene sequences even though they only encode 1-2 amino acids, each VDJ combination gives a different structure in hypervariable regions of the heavy chain and a different specificity to the antibody produced.

Germline DNA --> Rearranged DNA in an Antibody producing B cell --> Expressed mRNA
What does TdT do?
What are the additions called?
Enzyme inserts bases rnadomly without a template on the complementary chain at the junctions of J with D and D with V. These N-region additions because aNy base can be inserted in this process. Creates additional diversity in the mRNAs transcribed from this B cell DNA.
This mechanism generates variability ONLY in heavy chains, as light chains rearrange later. Recombinational inaccuracy also occur at splice junctions when coding sequences are fused, with one or two bases pairs.
What is the order for recombination for B cells?
Heavy chain are first rearranged then light chains, between V and J there are short exons in he heavy chain, coding region called D Diversity segments.
Light and Heavy chains are not linked, so variable regions are selected at random for each cell, since any light chain can bind with any heavy chain, reassortment of heavy and light chains further increases variability.
How are do T cell mutations affect diversity?
Somatic mutation only works for B cells not T cells, rapid division of B cells may result in mutation which can enhance binding of Ab to antigen cells that are preferentially selected. T cell mutations are automatically deleted in thymus --> they do not contribute to diversity because if they do you have autoimmunity.
What are some exon rearrangement effects on alleles?
Exon rearrangements occur at random and spontaneously during B cell development. If they produce functional antibody molecule, B cell will express IgM monomers on its surface, making it responsive to antigen.
When one heavy chain gene rearranges to produce functional gene product, it shuts off rearrangement and expression of allele. This happens in light chain and is called ALLELIC EXLCUSION.
What does allelic exclusion insure?
Allelic exclusion is essential to assure that each B cell synthesizes only one heavy chain variable domain and only one light chain--> makes only one antibody specificity.

All progeny of B cell will express same VH and VL sequences even if class switches occur during differentiation. Also applies to synthesis of TCR chains. Will express only one alpha and one Beta chain or one gamma and delta chain.
What does RNA processing do to Ig expression?
Splicing out of introns, of mRNA produces an RNA that decides whether Ig is secreted or membrane anchored molecules based on amino acids encoded at carboxy terminal end of the heavy chain..

Determines whether protein eventually translated from primary nuclear RNA transcript will be secreted or membrane anchored. Alternative RNA splicing determines whether B lymphocyte will express surface IgM or IgD or both.
What needs to occur for Ig class switching?
Cytokine signals from helper Th2 cells

IL-4, IL-5, IL-6, IL-10, CD40 surface molecule, signal the B cell to switch class.
Does so by rearranging the DNA that encodes for constant region of heavy chain. Loop is formed in DNA between homologous switch regions of the 5' end of non-coding DNA near each heavy chain constant region.
Mechanism for class switch between IgM , IgG, and IgA, or IgE.
Information is excised and degrade so information is lost. IRREVERSIBLE Class switching does NOT affect variable region of heavy chain and light chain.
In class switch isotype/allotype/idiotype remains the same?
IDIOTYPE stays the same. Specificity of antibody stays the same while ISOTYPE is affected.
A loss of RAG enzymes, or no recombination events results in?
SCID, or severe combined immuno deficiency disease. No B cells No T cells.
What are the four phases of serum antibody response primary antigen sensitization?
Lag
Log Phase,
Plateau
Decline
What does the lag phase vary with and represent?
Lag phase represents the initial challenge with the antigen and appearance of first detectable antibody in serum. Length of lag phase varies with dose and solubility of antigen, route of injection, presence of an adjuvant, species, and sensitivity of assay for detection of antibody.
What characterizes a secondary response?
Lower threshold of antigen, shorter lag phase, greater rate of synthesis, higher amounts, and longer persistence of antibody.

More antibody produced, lag phase is shorter, and less antigen required to trigger secondary response.
What appears in primary response?
What appers in secondary response?
IgM always appears First
IgG is predominant antibody. For antigen via mucosal route, IgA is predominant antibody isotype.
What do you call changes during immune response where antibody for IgG affinity also changes?
Antibody Maturation. In immune response many B lymphocytes may respond to an antigen. While IgM affinity for some might be high, others will be lower. All will be stimulated to produce antibody but average Ab affinity will be low, as Ag levels decrease, competition for diminishing Ag assures that only the B cells with highest affinity for antigen will continue to be stimulated as long as antigen presence is around. This increase in average antibody affinity with time occurs for the IgG antibody and is called affinity maturation.
What determines clonal selection?
Number of clones stimulated depend on the number of different antigenic determinants presented by the antigen and a single antigen may simultaneously activate multiple B cell specificities producing a monospecific, polyclonal response.
How does clonal selection solve problem with no prior knowledge of antigens in future?
One B cell One Ab specificity, One T cell, one T cell antigen receptor specificity. Individual B cell is committed to making an Ab with single idiotype prior to any exposure to antigen.

All specificities are made all the time by random selection of hypervariable region structures.

Antigens selects the cell that have complementary receptors by binding to them, and only cells that undergo clonal expansion and differentiation.
What happens in lifetime of B lymphocytes?
Antigen stimulated B cells undergo several rounds of cell division generating a clone of cells, all members which express Ag receptors with same antigenic specificity as original cell that was stimulated. If antigen is continuously present to stimulate them, cells differentiate into plasma cells.
Plasma cells divide T/F?

When do they die?
False, they are non dividing and have a lifetime of 4-6 weeks during which they synthesize an enormous about of Ig with identical structure, isotype, and idiotype.

Plasma cells during decline phase of primary immune response, they die but are not replaced due to absence of antigen stimulation. B and T cells begin to differentiate into memory cell
What kind of antigens do Antibody recognize?

What kind do T cells recognize?
Antibody recognizes foreign antigen in its free state, and has its main function the elimination of extracellular antigen: bacteria, soluble toxins, extracellular fungi or parasites, viruses in the extracellular environment.

Cell-mediated immunity is involved with the limination of abnormal host cells and intracellular pathogens. T cells recognize foreign antigen only when it is presented by MHC on surface cell. CTL sees intracellular parasites, including intracellular bacteria, viruses, and tumor antigens presented by Class I MHC.
Class II MHC molecules bind what type of antigens and present it to?

Class I MHC molecules process what and present to?

Which effector mechanism of CMI is specific/nonspecific?
Class II MHC bind antigens from the extracellular environment and present it to CD4+ helper T cells

Class I MHC molecules process antigens found within the cell and present it on their surface they then become targets of CD8+ cytotoxic T cells. Effector mechanisms can be specific or non-specific.

DTH is non-specific while CTL effector cells are antigen specific.
What activates DTH Mediated CMI? which type of lymphocyte?
CD4+ T lymphocyte when presented with antigen by APC can activate DTH response. Involves primary and costimulatory signals. Antigen specific and MHC Class II restricted.
Activation leads to: proliferation of the CD4+ cells, expression of CD40 ligand, IL-2, IL-3, INF-gamma TNF-Beta, GM-CSF, Fas ligand, CXCL2.
Cytokines induce and amplify an inflammatory response and activate macrophages.
What happens when macrophages are activated by interferon gamma?
Macrophages exposed to INF-gamma differentiate to activated state and: increase surface expression of MHC II and I, TNF receptors, B7 molecules, CD40.
Secrete TNF-alpha, IL-1, IL-6, chemokines, PGE2, reactive oxygen metabolites, and enzymes that cause nonspecific damage to tissues.
Cytokines are a major source of what in DTH?
Inflammation. Activated macrophages are more efficient in killing ingested organisms. They can also kill some tumor cells and virus-infected cells but killing mechanisms are NOT ANTIGEN SPECIFIC AND NOT MHC RESTRICTED.
What do macrophages fuse into when they encounter particulate antigen?
What is the final stage formation due to chronic local CMI reactions?
They develop into epithelioid cells and fuse into multinucleated giant cells that attempt to surround and wall off antigens that resist killing and degradation.
Final stage is formation of a granuloma which is a characteristic of chronic local CMI reactions.
FROM AN ACTIVATED TH1 CELl:
What does: IFN gamma and CD40 ligand do?

Fas ligand or LT?

IL-2?

IL-3 +GM-CSF?

TNF-alpha + LT?

CXCL2?
Activates macrophages to destroy engulfed bacteria.

Kills chronically infected macrophages, releasing bacteria to be destroyed by health macrophages.

Induces T cell proliferation, increasing number of CTL cells

Induces macrophage differentiation in the bone marrow.

Activates Endothelium to induce macrophage adhesion and exit from blood vessel at site of infection.

Causes macrophages to accumulate at site of infection.
How are CTL mediate CMI dependent on CD4+ T cell?
CD8+ T cells are antigen specific and MHC restricted. In primary response, they need CD4+ T cell help to differentiate from precursor -> effector killer cells. Th1 help is NOT MANDATORY for secondary memory CTL response.
What leads to target cell death with CD8+ cells?
Cell to cell contact (conjugate formation) leads to target cell death. CD8+ T cells and helper CD4+ T cells may be activated by different APCs or same APC.
How does IL-2 affect DTH?
IL-2 is released as a cytokine from CD4+ helper Th1, it acts on itself to expand and cause T cell proliferation as a autoreceptor then releases more IL-2. Simultaneously, CTL makes contact with APC and upregulates IL-2 receptor which upon binding IL-2 from helper TH1 cells proliferates, and increases effector cytotoxic function. Not necessary for memory CTL response.
Cytotoxic cells posses pore-forming molecules (perforin) which are secreted during cell-cell contact and polymerize into channel of membran eof target cell. As well as granzymeswhich are esterases.
What are NK cells and where are they found?

T/F. NK cells require antibodies
NK cells are a subset of lymphocytes and found in blood and lymphoid tissues such as spleen and lympho nodes.
Are responsible for earlier response to infection and play a important role in controlling viral infections before effective CTL cell response can be generated.
False. Do not require antibody
What can NK cells destroy? where?
NK are 5-20% of peripheral blood lymphocytes that are found in gall bladder, liver, intestines, lungs, resp tract, uterus and differentiate from bone marrow straight to blood circulation
Do not require thymus maturation an specificity is broader than that of CTL but not random.
NK cells can kill tumor cells and normal cells infected with some, but not all viruses, and will not kill uninfected cells.
Differentiated from T cells, monocytes, and B cells by unique array of CD antigens.
What CD antigens are expressed:
On NK cells:

On T cells:

On Monocytes:

On B cellls:
CD16,CD56,CD57, CD8, CD2, CD11a CD11b, CD11c, CD18

TCR/CD3, CD2, CD4, CD8, CD57, CD56, CD11a, CD18

CD14, CD16, CD11a, CD11b, CD11c, CD18
(CD14 detects gram negative LPS)

Surface IG, CD19, CD20, CD21, CD24, CD11a, CD18
What is another name for larger granular lymphocytes?

What is CD16+?
NK cells, also known as CD16+CD56+ lymphocytes.

CD16 is a receptor for FcgammaIII

NK killing does not require Fc receptor or complement.
-has 2 functions, cell killing and secretion of cytokines.
What two type of receptors are involved in NK mediated killing?
Recognition receptors such as NKR-P1, NKG2D, DAP12 that recognize cell surface oligosaccharides transmits a postivei kill signal and enable them to see virus infected or a tumor cell.

Inhibitory receptors that prevent normal cells from being killed which are KIR2, KIR3D, CD94/NKG2A that bind to MHC class I on a normal cell and prevents it from being killed.

NK cells provide defense against abnormal virus infected or tumor cells which may escape destruction by cytotoxic T cells if these target cells are inhibited in their expression of MHC class I molecules.
Cytokines activate which NK cells?

Individuals with NK cell deficiences are more likely to have ?
IFN-alpha, IFn, b, IFN-gamma, IL-12 all activate NK cells.

IL-12 activates secretion of cytokines.

IFN-alpha, IFN, beta, IFN, gamma and TNF-alpha all activate killing

NK cell deficient patients are more likely to have early problems with viral infections. These individuals are susceptible to infection with HERPES VIRUS.
LAK+ IL2 vs LAk displayed ?
Cells with Lymphokine activated killer cells were derived in vitro by culture of peripheral blood lymphocytes in high dose of IL-2. Resulting cells exhibited markedly enhanced and NONSPECIFIC capacity to kill tumor cells. Majority of cytotoxic cells were NK phenotype.

Tumor infiltrating lymphocytes or (TILS) were isolated from site of melanoma and expanded in culture in IL-2. TILs grew out of culture were T cells with LAK like activity but immunotherapy proved to be more effective, required fewer cells and lower doses of IL-2 than LAK cell therapy to achieve tumor regression.
By virtue of CD16 or FcGammaRIII, NK cells along with monocytes, macrophages, neutrophils, eosinophils can express what?
ADCC. Antibody dependent cellular cytotoxicity. Mechanism of ADCC killing by NK cells is similiar to non-antibody dependent killing, ie granule exocytosis, perforins, and granzymes.

Monocytes, macrophages, and neutrophils mediate ADCC by non-perforin-dependent mechanisms of killing involving secretion of nitric oxide and oxygen radicals, TNF alpha and proteases.


Eosinophil ADCC also may be medaited by IgE and Fcepsilon R
True / False involvement of 3 different cell types participate in primary or secondary response to strong immunogen.
True. Three major cell types cooperate in the production of a specific antibody in response to a T dependent antigen.
APC are due to macrophage
T lymphocytes due to helper T lymphocytes
B lymphocytes from which main antibody secreting plasma cells arise.
What are the three rules for production of a secondary IgG response to a hapten?
1. There must be B cells that have been exposed to hapten twice.
2. There must be T cells that have been exposed to carrier twice
3. There must be a covalent bond between hapten and the carrier that is recognized by T cell.
What is the order of the APC helper T cell activivation sequence?
Helper T cell bind antigen, a TH0 cell expresses IL-2 Receptors and secretes IL-2 which induces cell division of T and B lymphocytes. Costimulatory molecules such as CD40L are upregulated on T cell by CD3 which then bind to APC CD40R. This CD40 interaction upregulates expression of B7.1 and B7.2 on APC which then bind CD28 .
What is the essential costimulatory signal?
CD28 is the essential signal to the T cell to secrete sytokines as IL-2, IFN-gamma, and IL-4.

IL-4 activates B cells
while IL-2 activates macrophages.

Macrophages in turn secrete IL-1, IL-6, IL-12, IL-15 and TNF-alpha

If no costimulatory signal such as those from B7.1 and B7.2, T cell is deactivated.
What is essential for class switching?
CD40 and CD40 ligand are essential for B cell differentiation.

Ag bind to B cell receptor delivers signal first to B cell where the binding of antigen is antigen specific and can recognize and bind, and internalize free unprocessed antigen. Process and present them on B cell in MHC II cells. When activated helper T cell specific for peptide MHC class II complex on B cell surface comes along, it binds to B cell.
B cells are same as APCs, except?
B cells are same as APC cells except antigen is endocytosed, degraded, and fragments are presented on MHC and antigen-specific.
Which cytokines are secreted by macrophages?
IL-1, act on T cell and B cell
IL-6, act on B cell and T cell for activation and differentiation (acute phase proteins)
IL-8 act on neutrophil and activate vascular endotehlium for chemotaxis.
IL-12 act on Helper T cell TH1 and NK cell. - Activation of NK cells and TH1 cells
TNF-alpha act on endothelial cells for inflammation and toxicity
What cytokines are released by Helper TH2 cells?
IL-4,5,6,10,13 TGF-Beta

IL-10 inhibit TH1 cellular immunity
IL-13 activates B cell IgE synthesis
TGF-Beta activates B cell IGA synthesis
What are Ab that activate B cells in absence of significant T cell help called?
T-independent antigens induce primarily an IgM with the kinetics of a primary response even on repeated exposure. T independent antigens are generally large polymers with repeating antigenic epitopes such as polysaccharides. Multiple identical epitopes can crosslink surface of Ig of B cells and stimulate proliferation and IgM production.
What are the general properties of immunologic tolerance?
Is immunologically specific, tolerance to self is learned or acquired, immature or developing lymphocytes are more susceptible to tolerance inductino that are mature or functionally competent cells.
Tolerance to foreign antigens can be induced even in mature lymphocytes when these cells are exposed to Ag under inadequate activation (lack of costimulatory signals) clonal anergy
Difference between clonal tolerance and peripheral tolerance?
Clonal tolerance occurs in deletion of self reactive clones of T helper and cytotoxic cells in thymus. Clonal deletion

Peripheral tolerance occurs by clonal anaergy in immature B cells which are anergized by binding Ag w/o T cell ,help or costimulatory signal (APC, CD40, B7.1. 7.2, LFA-3)
What are factors that affect tolerogenicity of an antigen in an adult?
1. Route of administration of antigen - intradermal or intramuscular injection is best route for inducing immune response; intravenous antigen is poorly immunogenic. oral administration of antigens can induce tolerance.
2. Structure of Ag. Aggregated or particularte Ag is immunogenic but not monomeric, disaggregated antigen.
3. Dosage of Ag, extremes of Ag conc. Low doses or very high doses can induce tolerance.
How do pathogen associated pattern molecules affect antigen-specific T helper cell responses?
B7 is not expressed constitutively on APC but is induced by recognition of pathogen associated pattern molecules by APC. Since self antigens do not possess PAPM, their ingestion by APCs fail to upregulate B7 resulting in T cell tolerance rather than autoimmunity.

Some PAPM (innate immunity markers)-
endotoxin - gram negative bacteria
teichoic acid - gram positive
mannan - fungus
T regulatory cells are ones differentiated from CD4+ cells, what do they do?
Treg cells constitutively express alpha chain of IL-2 receptor or CD25and express the transcription factor FoxP3 and CD4+. Can inhibit lymphocyte response.
What is CTLA-4?
CTLA4 is an alternate receptor for the costimulatory B7 molecule expressed on T cells that appear late after antigen activation on the T cell, and outcompetes CD28 for binding to B8.
When B7 binds to CTLA-4 the CTLA-4 produces a negative signal that turns off the activated T cell.
What kind of proteins are C1r and C1s?
Serine Proteases that are dependent on calcium to maintain C1 complex.
Removal of calcium via chelators such as EDTA, EGTA dissociates complex and prevents classical complement pathway.
How is classical complement pathway initiated?
When IgM, IgG1-3 bind to an antigen, expose Fc portion of antibody which can bind to C1q. C1qrs cleaves C4 to C4b which cleaves C2 to C2a--> C4b2a (C3 convertase) cleaves C3 --> C4b2a3b (C5 convertase) --> C5 to C5b which activates MAC.
How do you clear immune complexes ?
C3 fragment deposition or opsonization coating with C3b interact with specific receptors on phagocytic cells, neutrophils, eosinophils, monocytes, macrophages.-> triggers adherence and then particle ingestion.

Also mediated by C3b breakdown fragments, iC3b and C3dg.
What causes vascular hereditary angioedema?
C1-esterase inhibitor defects. GEnetic abnormalities but acquired C1-INH def. has been describe in patients with lympoproliferative diseases accompanied by monoclonal gammopathy. Defects permit uncontrolled fluid phase activation of C2 and C4, lowering levels of both.
C2b released from C2 duing activation is further degraded by plasmin to release a small peptide with kinin like activity in increasing vascular permeability, edema, and pain.
Generating too much kinin like substance in plasma causes recurrent episodes of angioedema in skin, viscera, and larynx (hereditary angioedema)
What are some indicators that come along with C1-INH defects?
C proflie indicates decreased levels of C4 and C2 and Ch50 activity, levels of C1 are low. C3-C9 anad alternative pathway components are unaffected.

Tx: modifiend androgens (danazol, stanazolol) significantly increase C1-INH and C4 levels and control attacks.

C1-INH is show to be an inhibitor of plasmin and of bradykinin generation via fibrinolysis as well as C4 activation.
What are the anaphlyatoxins?
C3a, C4a, C5a interacp with receptors on basophils and tissue mast cells causing granule release. Granules contain a variety of vasoactive and inflammatory mediators such as histamine and heparin. Cells also synthesize prostaglandins and leukotrienes which mediate inflammation. Net effect is smooth muscle contract, and increased vascular permeability.
What is the major chemotactic factor in complement for all pathways?
C5a is the major chemotactic factor that causes directed cell movement. C5a cause leukocytes to migrate towards higher concnetrations of molecules, accumulate at sites of infection, inflammation, or immune reactions.
C5a also able to trigger degranulation of endothelial cells, mast cells, and phagocytes.
C5a activates WBC by increasing avidity for WBC integrins and upregulating Lipooxygenase pathway. Too much can mediate shock though.
Which organisms are resistant to MAC complex of complement?
Gram positive organisms (peptidoglycan) as well as fungi (Carbohydrate) and protozoal parasites. Only some gram negative bacteria can be killed (Shigella, E. Coli, Salmonella, Heliobacteria). Neisseria species often requires MAC to kill them
What is special about the alternative pathway that differs from other 2?
May be activated by antigens without the requirement for specific antibodies, provide innate immunity like defenses in early stages of infection before appearance of significant amounts of antibody.
-Activated by pathogen surfaces
-LPS gram + / i bacteria, complex polysaccharide cell walls of fungi, virus, and virus infected cell parasites. Some Igs can also activate pathway when they are aggregated. Broad range of activators ensures that most extracellular fungal or bacterial pathogen will be able to activate pathway.
Give the steps to the alternative pathway:
Hydrolysis of C3 is a spontaneous reaction
C3 + H20 -> C3(H20)
C3(H20) + Factor B -> C3(H20)B + Factor D -> C3(H20)Bb + Ba
Factor B cleaved by factor D

C3(H20)Bb cleaves new native metastable C3

C3 --C3(H20)Bb--> C3b + C3a
C3b + surface --> C3bsurface (Antigen surface)
This forms C3b +B+D+Mg2+ --> C3Bb is very reactive but binds to P which stabilizes it to
C3BbP
C3 --C3BbP--> C3b + C3a.
This is an important amplification point or positive feedback loop generating a lot of C3b.

C3bBbP + C3b -> C3bBbP3b is C5 convertase

C5 -- C3bBbP3b --> C5a +C5b.
What initiates the MAC?
C5b initiates membrane attack sequence and then lysis.
What controls alternative pathway?
Which factor helps accelerate decay?
Decay loss of Bb even with properdin stabilized enzymes helps prevent over consumption of C3. Decay is accelerated by Factor H.
Factor H also works in concert with Factor I or (C3b inactivator) to cleave C3b into inactive fragments of iC3b, C3c, C3dg.
What is the determining factor in alternative pathway activation?
The nature of the surface of which C3b is bound. The hydrolysis of C3b is slow spontaneous process that generates low levels of C3(H20)Bb. Rapidly inactivated by Factor H and I in non-activator surfaces (RBC, host cells, some viruses)
But if it is an activator, strucutres protect C3b from control proteins and leave it free to bind Factor B to generate amplification C3 convertase
C3bBbP
What are control mechanisms for complement?
1. Decay of C3 and C5 converting enzymes, C4b2a, C4b2a3b, C3b(H20)Bb, C3bBbP, C3bBbP3b decay by loss of C2a or Bb by dissociation.
2. Labile binding sites - covalent binding of C3b or C4b must react quickly or thioester bond will react with water molecule to inactive fragment. C5b must bind to C6 and must C5b67 complex must bind to a hydrophobic surface within .1 sec or they too will be inactivated.
What are the control proteins on cell surfaces for complement control mechanism?
Affects C3 convertase - CD55 - Decay accelerating Factor which dissociates C2a and Bb from bound C3 convertases

CD35 - complement receptor Type 1 (CR1) - dissociates Bb from bound enzymes and acts as a cofactor for I cleave of C3b (ALTERNATIVE PATHWAY ONLY)
CD46- MCP or membrane control protein like CR1 is a cofactor for I cleavage of C3b.
CD59 - HRF, or Homologous restriction factor binds to C8 and C9 prevents the assembly of C5b-9 on homologous cell surfaces, protecting host cells from lysis.
What are some control proteins in plasma that regulate the classical pathway?
C1 inhibitor - binds c1r and c1s irreversibly, inactivating these enzymes and dissociating C1r and C1s from C1q.

C4 binding protein competes with C2 for binding to C4b. Also acts like a cofactor for the breakdown of C4b by Factor I
What are the actions of factor H?

What are the actions of Factor I
Factor H or B1H acts as a cofactor for Factor I in breakdown of C3b to iC3b. H also competes with factor B for binding to C3b.

Factor I or C3b/C4b inativator breaks down C4b and C3b.
What does properdin do?
Positive regulator that stabilizes C3 and C5 cleaving enzymes of ALTERNATIVE PATHWAY.
C3(H20)Bb , C3BbP, C3BbP3b
What acts like homologous restriction factor or CD59?
What does carboxypeptidase N do?
S protein vitronectin, C8 and lipoproteins all bind C5bC67 preventing its attachments to membranes.

Carboxypeptidase N inactivates anaphylatoxins C3a, C4a, C5a by cleaving off carboxy arginine. C5a des arg still have some chemotactic and leukocyte activating activity.
What are some important complement receptors?
Receptors for C1q and MBL are opsonins mediating phagocytosis of particulate antigens, thus protecting against bacterial infection.
C5a receptor on phagocytes mediates chemotaxis
Receptors for C5a, C3a, and C4a on basophils and mast cells mediate granule release for cells, promoting inflammation.
Receptors for large fragments of C3, C3b, iCrb, C3d and C3dg are expressed on many cell types
What are the classifications of C3 receptors?
CR1 (CD35) is expressed on RBC (clearance of immune complexes), phagocytes (opsonization), and B cells (enhanced immune response) and bind to C3b, C4b

CR2 (CD21) - one of major markers for B cells are on B cells, for enhanced immune response, signal transduction, EBV receptor, and Follicular /dendritic cells for antigen trapping. ligands are iC3b/C3d/C3dg
CR3 and CR4 are on phagocytes and bind to iC3b for opsonization
CR3(CD11b/CD18)
CR4(CD11c/CD18).
Which C system deficiency gene is not autosomal codominant inheritance like most deficiencies?
Properdin deficiency which is X-linked.

Genes for C2 and C4 deficiency have been linked to certain HLA alleles along with genes for factor B mapped on chromosome 6.
What does deficiency of a classical pathway component lead to?
Incidence of C-mediated dermatitis, IBD, anaphylactoid purpura arthritis, nephritis, sytemic lupus erythematosus, lupus like disease, -elevated in patients lacking an early acting classical pathway component (C1,C4, or C2). C in cleranace of immune complexes or in ealingw ith certain infectious agents
What does deficiency of C1q and C2 and C3 cause?
Increased susceptibility to infectio by encapsulated bacteria resulting from decreased serum opsonic activity.
What do patients with selective inborn deficiency of Factor I and Factor H show?
Patients with C3 nephritic factor , an acquired autoantibody to the alternative pathway C3 convertase, C3bBb impedes the function of Factors H and I, this auto antibody is described in patients with glomerulonephritis but also is detected in large proportions of individuals with partial lipodystrophy.

Hypercatabolism of C3 results in recurrent pyogenic bacterial sepsis or glomerulonephropathy. Treatment is same as C3 defciency
How do you treat C3 deficiency?
Prompt diagnosis and aggressive antibiotic therapy for infections, antibiotic prophylasix in some caes, and for glomerulnephritis, treatment with prednisone or other anti inflammatory agent.
Deficiency in Factor H leads to ?
Repeated infections, hemolytic uremic syndrome.
Deficiency of CD59+CD55(DAF)
Paroxysmal noctural hemoglobinuria, defect in GPI complement induced anchor. Condition exacerbated by acidosis, sleep blood becomes more acidic.
What is expressed by CD54?
I CAM-1 which is a intercellular adhesion molecule or ICAM distributed on transmembrane protein present on leukocytes, endothelial cells, epithelial cells and upregulated by many of the interleukins.

Has 5 Ig domains.
What is the major ligands for integrins CR3 and CR4?
CR3 which is CD11b/CD18
CR4 which is CD11c/CD18
the major ligand is iC3b.
What does rhinovirus use to gain entry into cell?
Rhinovirus which causes common cold uses I-CAM1 to gain entry to the cell.
What is exhibited in LAD?
Leukocyte Adhesion Deficiency occurs when patient's leukocytes are deficient in CD18. Patient are susceptible to recurrent and often fatal bacterial infections, clinical hallmarks are infections of soft tissues such as skin, mucous membranes and intestinal tract with a spectrum of bacteria and fungi, but usually devoid of leukocytes.
Infusion of normal phagocytic cells into deficient patients indicate deficiency was attributable to an abnormality in the cells of the patients. Patients phagocytes showed marked defects in adhesion-related functions such as chemotaxis, aggregation, phagocytosis, and ADCC reactions.
What are VLA? and what differs from them from CD18?
Very late antigens are leukocyte integrins that are evolutionarily related to the integrin receptors that mediate cell adhesion to the ECM during development and wound healing. There are three subunits of integrins, each defined by common beta subunit, beta-1,beta-2,beta-3.
Beta -1 subunit shared by VLA antigens after stimulation
B - 2 leukocytes integrins
B3 - vitronection receptor and platelet glycoprotein.
What does the interaction between LFA-1 and I-CAM1 represent?
Interference with either surface receptor is associated with inhibition of CTL killing of target cells as well as inhibition of other T cell functions, the inhibition is at the level of cell conjugation. Anti-LFA-1 mAB also blocks NK and ADCC killing.

Antigen/mitogen proliferation, T and B cell aggregation, adhesion to endothelium, and helper activity for primary in vitro IG production also inhibited anti-LFA-1.
Where is CD58? Where is CD2?
Blocking either one leads to?
CD58 is distributed on Lymphocytes and APCs and also known as LFA-3, its ligand is CD2.
CD2/LFA-2 is distributed on T cells, NK cells and its ligand is CD58 or LFA-3 .

Blocking either molecules with mAb blocks T-cell cytolysis.
What is the role of CD62 E?
CD62E or E-selectin is distributed on activated endothelium and activated by IL-1, IL-8, and TNF-alpha and its ligands are carbohydrates or lectin on PMNs, monocytes, and lymphocytes. Initially binds to endothelium.
What is the role of CD62L?
Is distributed on leukocytes and its ligands are CD34, vascular carbohydrates.
What is the role of P-selectin ?
CD62P, its tissue distribution is activated endothelium, platelets and its ligand are carbohydrates on PMNs, monocytes, and lymphocytes. Function is for leukocyte migration to inflammatory sites.
What are three characteristic of acute phase changes?
(1) RBC sedimentation rate or ESR, settle more quickly by decreased resistance to gravity due to fibrinogen and other proteins of blood which alter RBC surface charge to favor rouleax formation. RBC surface negative charge is neutralized and allows settling.
(2) C reactive protein or CRP
(3) Amyloid related proteins.
What represents the presence of inflammation and tissue necrosis?
CRP and ESR, but CRP levels rise more rapidly upon cessation of inflammation than does ESR. It binds to pneumococcal C polysaccharide and phophorylcholine, which is exposed on damaged cells.
Has unclear constituents and cationic polymers, C1q activate classicaly pathway Fc gamma receptors on phagocytes mediate particle uptake
What is synthesis of CRP ?
CRP is synthesized in lover by hepatocytes in response to cytokine IL-6 augmented by IL-1 released from macrophages stimulated by products of inflammation and tissue necrosis.
CRS binds to cell membranes altered during the inflammatory process, and is found at sites of tissue injury.
What are actions of CRP?
CRP activates classical complement pathway and induces complement consumption, complement-dependent phagocytosis, generation of complement derived biologically active peptides, complement dependent cytolysis.
CRP also reacts with phagocytic cells to promote and enhance phagocytic responses and induce platelet aggregation and secretion.
CRP breakdown products modulate leukocyte and platelet responses.
What are some clinical applications of CRP?
1.Screen for inflammatory disease, infections, cancer and tissue injury
2. Detect and evaluate inflammatory disorders
3. Detect and manage certain infections
4. Detect and evaluate tissue injury neoplasia
5. Aid in certain differential diagnoses.
Which cytokine is most directly associated with class switching to IgA?
TGF-Beta