Mcb 150 Immunology Midterm #1

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Pathogen

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microbe that causes disease

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antigen

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any substance that is recognized by the immune system but that does not necessarily elicit an immune response

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innate (natural immunity)

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rapid, non-specific immune response

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adaptive (acquired) immunity

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slower, specific immune response

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leukocytes

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blood cells

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lymphocytes

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specialized blood cells that mediate adaptive immunity

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thymus function

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primary lymphoid organ for T-cell development

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bone marrow function

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primary lymphoid organ for B-cell development

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lymph nodes

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collect antigens from tissues

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spleen

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collects antigens from blood stream

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cytokines

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small secreted peptides that are used for intracellular communication between cells of the immune system

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chemokines

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subset of cytokines that specialize in regulating cell motility

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inflammation

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a complex series of events induced by tissue damage (characterized by redness, pain, swelling, and heat)

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what are some diseases associated with immune system dysfunction?

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1. autoimmunity - SLE, arthritis, Myasthenia gravis, Graves disease
2. immunodeficiency
3. allergy
4. cancer

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defensins

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small polypeptides secreted at mucosal surfaces; insert into biological membranes leading to target cell lysis

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What are the benefits and hazards of TLR signaling?

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Benefits: less chance of septic shock from infection with gram-negative bacteria
Hazards: more sensitive to infection with a gram-negative bacteria

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what are the four forces that hold antigens and antibodies together?

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1. Electrostatic forces
2. Hydrogen bonds
3. Van der waals forces
4. Hydrophobic forces

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epitope

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the three-dimensional face of an antigen which makes contact with the antibody

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what are the three main ways that antibodies provide protection?

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1. neutralization
2. opsonization
3. complement activation

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IgG

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Predominant Ig in serum, 4 subclasses, important for opsonization, complement activation, antibody-dependent cellular toxicity, crosses placenta to protect fetus

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neutralization

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toxins bind to cellular receptor -> endocytosis of toxin-receptor complex -> dissociation of toxin to release active chain which poisons cell -> antibody protects cell by binding of toxins

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antibody-dependent cellular toxicity (ADCC)

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antibody binds antigen on the surface of target cells -> Fc receptors on NK cells recognize bound antibody -> cross-linking of Fc receptors signals NK cell to kill target cell -> cell dies by apoptosis

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IgM

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pentameric, first Ig produced in response to infection, good at complement activation

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IgA

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dimeric (tetravalent) predominant Ig in secretions, transported across epithelial cells via poly-Ig receptor, 10 g of Ig secreted/day, found in breaks milk and supplies passive immunity to baby

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IgE

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low amounts in serum, binds to Fc receptors present on mast cells/basophils, levels increase in setting of parasitic infection, can transfer allergy between individuals

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immunogen

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substance that elicits an immune response

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hapten

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small molecule that by itself cannot induce an immune response but can be an antigen

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what are the characteristics of immunogenicity?

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1. size
2. foreignness
3. complexity
4. susceptibility to phagocytosis
5. genotype of host
6. route of administration
7. dose

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adjuvant

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something that enhances the immunogenicity of antigens by triggering the innate immune system, slowing release of antigen, and promoting phagocytosis of antigen

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When do antibody-antigen lattices form?

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Form with polyclonal antibody and antigen with multiple distinct epitopes

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Isotypic determinants

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secondary antibodies that recognize portions of the constant regions that are characteristic of a particular antibody isotype

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allotypic determinants

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some secondary antibodies recognize portions of the antibody that are variable between different individuals (different allotypes) in the species

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idiotypic determinants

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some secondary antibodies recognize unique portions of the variable domain of the antibody: the antigen-binding sites (idiotypes). Anti-idiotypic antibodies are rare.

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radioimmunoassay

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very sensistive assay that measures the ability of a test sample to compete for binding with labeled antigen to antibody on dish; quantitative due to use a standard curve; used to measure small amounts of hormones, drugs, microbes, etc. in body fluids

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ELISA

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Enzyme-linked immune sorbant assay
Steps:
1. capture antigen using plate-bound antibody
2. add second specific antibody-enzyme conjugate
3. use a colorimetric assay
Used to measure small amounts of hormones, drugs, microbes in body fluids

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ELISPOT assay

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used to determine the number of cells within a sample that are secreting a particular cytokine

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Western blot

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gel electrophoresis separates proteins by size so Western blot not only provides quantification but also provides info about the molecular weight of antigen
medical example: using western blot to detect anti-HIV antibody in patient serum

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immunoprecipitation

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detects a specific protein form a complex mixture

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immunoaffinity chromatography

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way to separate antibody-antigen complexes -> get specifically bound molecules

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immunofluorescence microscopy

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can provide spatial information about cells or molecules that react with antibodies

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flow cytometry

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used to determine the number of cells within a sample that react with a particular antibody or antibodies

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FACS (fluorescence activated cell-sorting)

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can physically separate droplet based on the markers that are expressed, uses the same technology as the flow cytometer; can physically isolate CELL POPULATIONS

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magnetic beads coupled to antibodies

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another way to purify cells as an alternative to FACS that is useful for processing larger number of cells

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what are the functions of complement?

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1. opsonization of cellular (bacterial) antigens
2. provoke inflammation
3. poke holes in membranes leading to lysis of bacteria

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Southern blot

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restriction endonucleases cleave at specific sequences in the DNA and can be used to generate a physical map of DNA

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promoters

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relatively short nucleotide sequences within ~200 bp of transcriptional start site that initiate transcription in a certain direction

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enhancers

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nucleotide sequences located upstream or downstream of a gene that activated the promoter in an orientation independent manner

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allelic exclusion

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this ensures that most B-cells will express a single-antibody specificity (note: allele definition - two or more alternative forms of a gene) => B-cells only use one of the alleles

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similarities between antigen receptors of T and B cells

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1. both encoded by genes undergoing VDJ recombination
2. both are composed of repeated Ig domains
3. both have N-terminal V domains that contribute to antigen binding site
4. both are disulfide linked heterodimers

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differences between antigen receptors of T and B cells

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antigen receptor of B cells binds directly to antigen while antigen receptor of T-cells binds processed antigen on the surface of an antigen presenting cell
Antibody also exists in both a transmembrane/secreted form while TCR exists only in an transmembrane form.

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Stages in B-cell development and their characteristics

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1. pro b-cells: no HC/LC expression
2. pre b-cells: HC but no LC expression
3. immature b-cell: IgM but no IgD
4. mature b-cell: IgM and IgD

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what are some examples of T-cell independent responses?

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1. simple, reptitive antigens
2. mostly IgM
3. modest affinity
4. no memory
5. B-cells activated by direct BCR crosslinking
6. B-cells can also be activated via TLRs

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T-cell dependent responses

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1. required for antibody response to complex antigens
2. requires direct, physical B/T cell interaction
3. involves multiple cell surface receptors on T and B cells
4. both B and T cell must recognize antigen but not necessarily the same epitope
5. both B and T cells need signal 1 and signal 2 (co-stimulation)

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comparison of VDJ recombination vs. class-switch recombination

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1. VDJ recombination occurs as part of antigen-independent develop in bone marrow while CSR occurs as part of antigen-dependent development in secondary lymphoid organs
2. VDJ requires RAG 1 and 2 while CSR does not
3. VDJ is target precisely though RSS while CSR occurs within simple repetitive DNA sequences
4. both required dsDNA break repair machinery

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affinity maturation

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the increase in average affinity of an antisera that occurs during the course of an immune response with successive immunizations

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what is vaccination

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exposure of an individual to an infectious agent or toxin in a form which doesn't produce significant disease but generates immunity to subsequent infection by the same prganism

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why would it be useful for infected cells to undergo apoptosis?

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to prevent viral replication and spread

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what is passive immunity?

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immunity due to the transfer of Ig or T-cells from one individual to another. It is limited by the half-life of transferred Ig

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what is TLR9?

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TLR9 is a toll-like receptor that recgonizes unmethylated CpG DNA. It is specific for pathogens because it only recognizes unmethylated DNA, common in pathogens but relatively absent from humans since human CpG DNA is methylated

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how can an antigen activate B-cell directly, without T-cell help?

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If it's a polyvalent antigen, it can directly crosslink individual IgM molecules on the surface of the B-cell resulting in cellular activation

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what is receptor editing and why is it more likely in the light chain locus than the heavy chain locus?

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receptor editing is the secondary rearrangement of an already rearranged allele, deleting the previous gene and trying a new one. It is unlikely in the HC locus because all the D segments are deleted from frully rearranged gene and upstream VH genes have the same RSS as downstream JH genes which would violate the 12/23 rule

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The Danger theory

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pathogens cause damage to tissues which leads to the release of alarm signals that trigger immune responses

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pattern recognition theory

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pathogens contain molecular patterns that differ from host cells "pathogen associated molecular patterns" or PAMPs which can be recognized by immune cells using specific receptors

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apoptosis vs. necrosis

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apoptosis: tidy, programmed from inside the cell
necrosis: mess, produced by external insult

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MyD88

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adaptor molecule that interacts with TLRs to active cell signaling

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how is septic shock caused?

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shock is caused by overwhelming production of cytokines and is induced by presence of LPS in the blood stream. Mice lacking TLR4 are resistant to LPS induced shock but more sensitive to infection with gram-negative bacteria

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what is the significance of the myeloma protein?

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it ws the key to determining Ig structure because myeloma paitents have large amounts of one particular Ig molecule in their serum and urine

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heavy chain types

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u, delta, gamma, alpha, epsilon

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neutralization

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binding itself prevents pathogenesis

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opsonization

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enhances phagocytosis

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what are the similiarities between antigen receptors of B and T cells

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1. both are encoded by genes that undergo VDJ recombination
2. both are composed of repeated ig domains
3. both have N-terminal V domains that contribute to the antigen binding site
4. both are disulphide linked heterodimers

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adjuvants enhance the immunogenicity of antigens by:

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triggering the innate immune system, slowing release of antigen, and promoting phagocytosis of antigen

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when do antibody-antigen lattices form?

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polyclonal antibody and antigen with multiple distinct epitopes and with monoclonal antiobdy and antigen with repeating pattern of identical epitopes

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follicular dendritic cell

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present antigen to germinal center B-cells in the form of antibody-antigen complexes