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151 Cards in this Set

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What 2 signals are required for B cell activation and antibody production?
1. co-receptors (CD79 & CD19/CD21 (complement receptor for C3d) to bind antigens and deliver signal 1

2. co-stimulatory receptors to receive signal 2 from T cells
What are the 2 functions of the B cell receptor?
1. antigen binding and signaling

2. internalization
What is required for the Ig molecule to have signaling capacity
Ig MUST associate with Ig(alpha) & Ig(beta), which is actually CD79

The Ig(alpha) & Ig(beta) both contain an ITAM consensus motif that is REQUIRED for signaling
What are some examples of TI-1 antigens?
polyclonal activators such as: LPS, peptidoglycan, lipoprotein, porin

Also called B-cell mitogen- they directly induce the proliferation of the B cell b/c they have repetitive epitopes
What are some examples of TI-2 antigens?
repeating polymers (very large antigens)

polysaccharide antigens (bacterial cell wall)

unmethylated CpG

viral antigens

(CAN ONLY ACTIVATE MATURE B CELLS)
What are the T cell dependent antigens?
Protein antigens
What are the limitations of T-cell independent antigens?
CAN'T induce ISOTYPE SWITCHING, AFFINITY MATURATION, OR MEMORY B CELLS

They are ONLY IgM
What does linked recognition mean?
B cells and T cells must recognize the same antigen, but NOT THE SAME EPITOPE
What is linked recognition important for?
1. SELF TOLERANCE- if B cell recognizes a self antigen it won't get help from a T-cell, because ALL T-cell that self-recognize are killed off in the Thymus

2. VACCINE DEVELOPMENT
How do the T-cells and B-cells find each other?
The recirculating B cells enter into the lymph nodes through high endothelial venules and migrate to the primary follicle...

On their way there, they get trapped at the border between the T-zone (paracortex) and the primary follicle...

This allows the B cells to have a higher chance of being activated by interacting with all those T-cell that are hanging out there!
Where do the B cells go in the lymph node after they are activated?
1. some go to the medullary cords to secrete antibody, which will be then released back into circulationg

2. or they migrate to a nearby follicle forming a germinal center where they undergo rapid proliferation and somatic mutation... (somatically mutated B cells that still bind antigen survive, while others die)
What happens between the Helper T cell and the B cell to further activate the B cell?
1. The helper T-cell adheres to the B cell and begins to synthesize CD40 ligand and IL-4 (a potent B-cell activator)

READY!

2. The T-cell then reorients it's cytoskeleton and secretory apparatus toward the B cell

AIM!

3. IL-4 is released and is confined to the space between the B-cell and the T-cell.

FIRE!!!
What are the important events at the GERMINAL CENTER?
1. Clonal expansion (dark zone)

2. Somatic hypermutation (dark zone)

3. Class switching (light zone)

4. Differentiation to MEMORY CELLS OR PLASMA CELLS
What are Centroblasts in the Germinal Center?
highly dividing B cells in the DARK ZONE (produces many varieties of receptors)
What are Centrocytes in the Germinal Centers?
they intermingle with the T cells and the follicular dendritic cells

***basically- CENTROBLASTS selected for affinity
What are Follicular Dendritic Cells in the Germinal Centers?
they present antigen, but unlike normal APC's they do not need to engulf something... they have long extensions that help retach things that go thru the LN (act as a filter!)
What kind of cells are in the Mantle Zone of the Germinal Centers?
non antigen specific B cells
What is Clonal Expansion?
The production of daughter cells from a single original cell.

B cells proliferate in the dark zone of the GC (centroblasts); at this point they are expressing many different types of receptors (not selected for affinity yet)
What is Somatic Hypermutation?
AFFINITY MATURATION- (Dark Zone' centroblasts; requires the generation of variability in B cell receptors and the selection for those with the highest affinity for the specific antigen in target)

The Immunoglobulin variable region genes accumulate mutations RAPIDLY (HYPERMUTATION)

The mutant receptors are expressed on the centroblasts that become CENTROCYTES
What are the 2 steps in Centrocyte Selection?
1. Interaction with FDC (follicular dendritic cell): centrocytes w/ higher affinity receptors are selected by its interaction with antigen-loaded FDC; low affinity receptors-bearing cells can't compete and are lost to apoptosis and engulfed by tangible body MACs

2. Interaction with T-helper cells and CD40-CD40L interaction: This interaction makes B cells proliferate and become plasma cells
What is Isotype Switching?
DNA arrangements that underlie isotype switching directed by cytokines produced by T-helper cells

Class switching occurs in the LIGHT ZONE

Involves recombination of constant genes in the heavy chain locus
Describe Plasma cell behavior?
They can travel to the spleen, medulla of LN, or bone marrow to secrete antibodies

Short lived (days-months)

Morphology- Ovoid, Cartwheel-shaped nucleus, large Golgi
Describe Memory B cell behavior?
Remain in the LN (IgG BCR or IgM BCR)

No typical morphology

Survive b/c their ability to bind antigen induces CD40L on neighboring T cellls which in turn promotes the expression of anti-apoptotic gene bcl-2

Long-lived (YEARS)

Quickly proliferate w/o further mutation!!!
Can IgD be secreted as an Antibody?
NO... once a B-cell has become a memory cell it can no longer express IgD.
Describe the Gross anatomy of a Lymph Node
Capsule

Cortex

Medulla
Describe the Microscopic anatomy of a Lymph Node
Outer Cortex- FOLLICULAR DOMAINS (B cells; have either primary follicles or secondary follicles--> contain pale germinal centers composed of large actively proliferating B cells that are responding to an antigen (CLONAL EXPANSION), GC contain a network of FOLLICULAR DENDRITIC CELLS and some MACS) separated by PARACORTICAL DOMAINS (T-cells; more CD4+T-helper cell, less CD8+ cytotoxic cells); Post capillary HIGH ENDOTHELIAL VENULES (HEVs) are present ONLY in the PARACORTEX and their morphology is due to T-cell derived cytokines, such as INF-gamma

Inner Medulla- contains MEDULLARY CORDS which are extensions of the paracortex and are separated by MEDULLARY SINUSES
What are the 3 types of reactive lymphadenopathies?
Follicular hyperplasia

Paracortical hyperplasia

Sinus hyperplasia
What are the characteristics of Follicular Hyperplasia?
characterized by the appearance of large follicles with prominent germinal centers

Typical of certain bacterial antigens and autoimmune disease; indicating that the antigen has stimulated mainly B cell responses.

FIV-lentivurs; Lyme Dz
What are the characteristics of Paracortical Hyperplasia?
Expansion of the paracortex may encroach on the follicular domains. The appearance of many T-cell blasts and assoc. tingible body macrophages gives a moth-eaten or "starry-sky" appearance. HEV are prominent and lymphocyte traffic through them is brisk.

Paracortical hyperplasia is characteristic of antigens that mainly stimulate a T-cell response (viral infections and viral vaccine)
What are the characteristics of Sinus Hyperplasia?
Sinus will be distended with macrophages.

Occurs when the corical and medullary sinuses of LN's are draining chronic infection, granulomatous Dz, immube mediated destruction of tissues, hemorrhage, or neoplasia.

This hystiocytic hyperplasia occurs in response to increased particulate antigen load and the sinus macrophages may contain phagocytic debris (RBCs, hemosiderin, melanin)
What is Lymphadenitis?
inflammed lymph node!

occurs when an infectious agent localizes in the lymph node or inflammatory products (fluid and cells) drain into the node from a distant site.
What characterizes ACUTE LYMPHADENITIS?
HYPERMIA, PAIN, HEAT, EDEMATOUS SWELLING (classic signs of acute inflammation)

Necrosis and liquefaction with abscess formation or cessation are possible depending on host/agent factors.

In contract, rapid lysis and LYMPHOCYTE DEPLETION with very little inflammatory response is characteristic of some acute viral infections (feline and canine parvovirus).
LYMPHOID DEPLETION is a common response to severe stress with elevated cortisol levels leading to apoptosis!
What characterizes CHRONIC LYMPHADENITIS?
LESS hyperemia and edema and affected nodes are ENLARGED and FIRM.

Nodes often dominated by reactive hyperplastic changes, and medullary cords may be expanded by plasma cells.

The connective tissue septa and capsule may be thickened by fibrosis.

EXTRACELLULAR (higher bacteria and fungi) or INTRACELLULAR infectious agents (e.g. Leishmania, Histoplasma capsulatum, Neorickettsia salmincola, Mycobacterium paratuberculosis)
What are the types of Neoplastic Diseases of Lymph Nodes?
Lymphoma- usually firm, nonpainful, and fixed in position due to inflitration of neoplastic lymphocytes through the capsule into adjacent tissues.
***Dogs with T-cell lymphoma have a higher risk of relapse and early death compared to dogs with B-cell lymphoma

Leukemia- Neoplasms of either lymphoid or myeloid hematopoietic stem cells that originate in the bone marrow and later flood the peripheral blood and may invade lymphoid tissues secondarily; animals usually have hepatosplenomegaly while lymph node involvement is less pronounced.

Histiocytoses- represents proliferation of dendritic cells and phenotypic differences can distinguish between distinct syndromes (1. Canine Cutaneous Histiocytoma 2. Cutaneous Histiocytosis 3. Systemic Histiocytosis 4. Histiocytic Sarcoma

Metastatic Neoplasia- metastatic neoplasms often spread via lymphatics to regional lymph nodes (generally, carcinomas) The closest lymph node to the primary tumor is not always infiltrated first ("skip metastasis") so patients with negative lymph node biopsies are often subjected to follow-up chemo or radiation therapy
What is the function of the RED PULP in the slpeen?
functions in defense against bacterial sepsis by opsonized phagocytosis mediated by both Fc and complement fragment receptors.

Add'l fxns: maturation of reticulocytes, pitting of erythrocytes, and removal of senescent cells; also stores significant number of erythrocytes and platelets
Characterize disease of the WHITE PULP in the spleen
the spleen is relatively sheltered from antigen by the innate immune system, while regional lymph nodes and Kupffer cells efficently filter antigen.

THUS, REACTIVE HYPERPLASIA IN THE SPLENIC WHITE PULP IMPLIES SYSTEMIC ANTIGENEMIA
Characterize disease of the RED PULP in the spleen
Diffuse ENLARGEMENT of the spleen; AN ENLARGED SPLEEN IN ALMOST INVARIABLY A DISEASED SPLEEN.

Enlarged spleens are prone to THROMBOSIS & INFARCTION

"Pulpy" vs "Meaty"
What does "Pulpy" Spleen mean?
PASSIVE SPLENIC CONGESTION (oozing out BLOOD)

Thombosis of the splenic vein, which can accompany inflammatory diseases such as traumatic reticuloperitonitis in cattle or necrotizing pancreatitis in dogs (CAN't GET BLOOD OUT)

Immune mediated hemolytic anemia may induce thrombosis to the splenic vein

TORSION occurs when spleen twists on its mesentery.

Most often caused by BARBITUATES, used in ANESTHESIA or EUTHANASIA

ANTHRAX
What does "Meaty" Spleen mean?
A fleshy to firm consistency in an enlarged spleen indicates DIFFUSE RED PULP involvement.

Usually has a DRY SURFACE

RED PULP MACROPHAGE HYPERPLASIA arises in response to prolonged particulate ANTIGENEMIA such as blood borne parasites or chronic hemolytic anemia.
MYELOID METAPLASIA (bone marrow failure and chronic anemia; predominates in INFECTIOUS TOXEMIAS such as pyometra)
LEUKEMIAS of all types may infiltrate the splenic sinusoids as a secondary site of involvement
What are isotypes of immunoglobulins determined?
By the PRIMARY SEQUENCE of AA in the CONSTANT REGION OF THE HEAVY CHAIN of an immunoglobulin.

Different ISOTYPES have DIFFERENT STRUCTURES, FUNCTIONS, and DISTRIBUTIONS
What is special about Plasma cells that make IgA or IgM?
They also make a J chain (JOINING chain).

J chain mediated polymerization of IgM and dimerization of IgA has important functional consequences and impacts distribution.
Where is IgG found?
BLOOD and TISSUES

Readily escapes the vessel because it is VERY SMALL; only immunoglobin that can cross the PLACENTA
Where is IgM found?
LIMITED TO BLOODSTREAM
(because its so big)
Where is IgA found?
MUCOSAL SURFACES
(due to transepithelial transport by secretory component; GUT, URINARY TRACT, RESPIRATORY SYSTEM, SALIVA, TEARS, MILK)
Where is IgE found?
On the surface of MAST CELLS and in very low concentration in serum in physiologic conditions.

INCREASED IN ALLERGY and NEMATODE INFECTIONS (ANAPHYLAXIS)
Where is IgD found?
mainly functions as BCR (INSOLUBLE!)
How is IgA transported from the lamina propria of the epithelial basement membrane to the lumen of the gut?
1. The IgA dimer bound to the J chain diffuses across the basement membrane.
2. The IgA (w/J) is bound by the POLY-Ig receptor on the basolateral surface of an epithelial cell (of the gut) (Binding is via the Ch3 constant domains of the IgA heavy chains)
3. The bound complex undergoes transcytosis across the cell in a membrane vesicle and is finally released onto the apical cell surface (of the gut).
4. There the poly-Ig receptor is cleaved, releasing IgA from the epithelial cell membrane while still being bound to a fragment of the receptor called the secretory component.
5. Carbohydrate of the secretory component binds to mucus at the epithelial surface, thus preventing IgA from being washed away into the gut lumen.
What are the Fab dependent functions of an antibody?
VIRUS NEUTRALIZATION- IgG & IgA

TOXIN NEUTRALIZATION- IgG & IgA

INHIBITION OF BACTERIAL ADHESION- IgA
How does Fab dependent functions work in TOXIN NEUTRALIZATION?
High affinity IgG (b/c of it's diffusibility) & IgA (because it is secreted) work to BLOCK BINDING OF TOXIN!
How does the Fab dependent function work in VIRUS NEUTRALIZATION?
High affinity IgG, IgA can BLOCK THE VIRUS BINDING SITES
How does the Fab dependent function work to BLOCK BACTERIAL ADHESION?
By blocking COLONIZATION AND UPTAKE OF BACTERIA.

IgA is important because bacteria have ADHESIONS, which is a mechanism in MUCOSAL INVASION (the bacteria NEED to ADHERE to the wall or else they will get washed away by peristalsis, mucocilliary app., or just by the movement of mucus)
What are the Fc RECEPTOR dependent functions of Antibodies?
OPSONIZATION

MAST CELL ACTIVATION

ADCC (Antibody dependent cellular cytotoxicity)

***Antibodies can activate effector cells that bear receptors for Fc: all phagocytic cells, NK, mast cells and eosinophils. These cells are triggered to secreted mediators when their Fc receptors are engaged.
What are the Fc dependent functions of Antibodies?
COMPLEMENT ACTIVATION!
What does OPSONIZATION of the Fc dependent functions do?
Phagocytes are activated by the Fc receptor of IgG antibodies (esp. IgG1 and IgG3) to:
1. increase the rate of PHAGOCYTOSIS, and fuse phagosomes and lysosomes.

2. increase RESPIRATORY BURSTS

3. induce EOSINOPHIL DEGRANULATION


ALSO, IgM can opsonize by complexing with C3b!!!!
How does the Fc receptor dependent function work on MAST CELL ACTIVATION?
The Fc receptors on MAST CELL are bound with HIGH AFFINITY to IgE molecules. When IgE is cross-linked on a mast cell, the mast cell is STIMULATED TO RELEASE MAST CELL GRANULES containing INFLAMMATORY MEDIATORS into the surrounding tissues.

Involved in Allergy and Parasitic Infections
How does the Fc receptor dependent function work on ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (ADCC)?
The Fc receptor on NK cells recognize bound antibody to antigens on the surface of target cells.

The cross-linking of Fc receptors signals the NK cell TO KILL THE TARGET CELL! (TARGET CELL DIES BY APOPTOSIS)
What in the Fc function in relation to complement activation?
Once the antibody has bound to the antigen on the bacterial surface; the Fc portion of the antibody (IgM***, IgG1, IgG2, IgG3, IgA) binds C1q and stimulates the COMPLEMENT CASCADE!!!!!!!!

COMPLEMENT ENHANCES IgG-MEDIATED OPSONIZATION!!!
Again, how is the classical pathway of complement initiated?
BY BINDING OF C1q to the Fc portion of IgM or IgG!!!
How does the immune system overcome the fact that ENCAPSULATED BACTERIA CANNOT BE ENGULFED BY NEUTROPHILS?
1. antibody bound to bacteria activates complement and binding of C3b to bacteria

2. Engulfment of bacteria by neutrophils is mediated by Fc receptors and complement receptors.

3. Granules use with phagosomes, releasing toxic oxygen metabolites that kill bacteria.

***ENCAPSULATED BACTERIA ARE PHAGOCYTIZED MORE EFFICENTLY IF THEY ARE ALSO COATED BY COMPLEMENT!!!***
How does ERYTHROCYTE CR1 help to clear immune complexes from the circulation?
1. small antigen:antibody complexes form in the circulation and activate complement

2. Immune comples is coated with covalently bound C3b

3. Bound C3b binds to the receptors CR1 on ERYTHROCYTE SURFACES

4. In the SPLEEN and LIVER, phagocytic cells remove the immune complexes!
What is the structure of the MHC class I molecule?
composed of one membrane-bound heavy (alpha) chain (with three alpha domains) and a noncovalently bounded beta-2 microglobulin

The peptide binds in the groove between the alpha1 and alpha 2 subunits of the alpha heavy chain
What is the structure of the MHC class 2 molecule?
Composed of 2 membrane bound chains:
an alpha chain & a beta chain

The alpha1 and the beta1 resemble each other in structure and form the peptide binding site.
How are antigens processed by MHC class 1 molecules?
1. The pathogens are degraded in the CYTOSOL into peptide fragments

2. These peptides then bind to MHC class 1 molecules

3. Presented to CD8+ cytotoxic T-cell leading to CELL DEATH
How are Intravesicular pathogens processed by MHC class 2 molecules?
1. The intravesicular pathogens are degraded in (low pH) endocytic vesicles to peptides.

2. The peptides bind to the MHC class II.

3. They are they presented to CD4+ T-cells, which are then activated to kill intravesicular bacteria and parasites
How are extracellular pathogens and toxins processed by MHC class II molecules?
1. The extracellular pathogens and toxins are degraded in (low pH) endocytic vesicles to peptides.

2. The peptides then bind to MHC class II molecules.

3. Then presented to CD4+ T cells, which activates B cells to secrete Ig to eliminate extracellular bacteria/toxins
What are the functions of the MHC?
Clinical Organ Transplantation

MHC & Mate Choice

MHC Disease Assoc.

Fetal-Maternal Immunological Relationship

Viral Evasion of Host Immune Response

(Natural Killer Cell Role)

Tumor Evasion or Host Immune Response
How does a fetus survive without being attacked by the maternal immune system?
1. There is down regulation of MHC class I expression on equine trophoblasts

2. MHC I and MHC II is suppressed on the outside of the placenta; so that the immune system CAN'T SEE THE PLACENTA!!!
How does the Equine Herpes Virus evade the host's immune response?
MHC class I expression is down-regulated following EHV-1 infection.
How does a NK cell know not to kill a HEALTHY CELL?
The INHIBITORY RECEPTORS interact with MHC class I molecules, which are present on virtually all healthy cells.
How does a NK cell KNOW WHEN TO KILL A CELL INFECTED with an INTRACELLULAR PARASITE (i.e. Virus)?
Infection of a cell with an intracellular parasite MIGHT change the EXPRESSION or CONFORMATION of the MHC class I molecules such that the interaction of the cell with the receptors on the NK cell generates a stimulatory signal that causes the NK cell to kill the infected cell.

***Basically, virus (intracellular parasites) infected cell don't express the same MHC I molecule, therefore it can't bind to the INHIBITORY RECEPTOR on the NK cell!
How does stress reduce immune functions?
Can depress T cell responses to:
MITOGENS
NK ACTIVITY
IL-2 PRODUCTION
and expression of IL-2R on lymphocytes.

Early Weaning in piglets reduces IL-2 production, which decreases T-cell effector function.
How do lipid mediators control aspects of inflammation?
Initially you have the production of PROSTAGLANDINS (PGE2) & LEUKOTRIENES, which are PRO-INFLAMMATORY MEDIATORS, but PROSTAGLANDINS also activate 15-lipoxygenase in neutrophils, which lead to dissociation and production of lipoxins from arachidonic acid (which has anti-inflammatory fxn)

So now we have undergone CLASS-SWITCHING to anti-inflammatory lipids (cyclopentenone PG (cPG), lipoxins & resolvins)
What are the endogenous mediators that actively promote the RESOLUTION OF INFLAMMATION?
Amines: Andrenaline, Noradrenaline

Lipid Mediators: PGJ2, PGA1/2, lipoxins

Complement: C1q receptor

Cyclic nucleotides: cAMP

Adhesion molecules: some integrin, TSP receptor, PS receptor

CYTOKINES: TGF-beta1, IL-10

Steroid Hormones: glucocorticoids
How does ASPIRIN have ANTI-INFLAMMATORY effects?
Aspirin-mediated acetylation of COX-2 switches enzyme catabolism to generation of LIPOXINS!!!!!!!
Name some ways that LIPOXINS regulate INFLAMMATORY RESPONSES
1. Potent chemoattractant for monocytes

2. Induce macrophage maturation by NOT respiratory bursts

3. Stronly ENHANCE uptake of APOPTOTIC CELLS by Macrophages

4. Inhibits chemotaxis, adhesion and transmigration of PMN cells

5. Inhibition P-selectin mobilization in Endothelium
How do pathogens exploit lipoxins?
Examples:

T. gondii infected Macs produce LXA4, which prevents DC migration and IL-12 (pro-inflammatory cytokine) production (can't produce effector T-cells)--> This all secures the SURVIVAL OF THE PATHOGEN AND THE HOST CELL

T. gondii induces upregulation of host-5-lipoxygenase, also releases its own 15-LO homologue in the cytosol, which is an anti-inflammatory mediator.
What is the BASIC coordinated process in RESOLVING INFLAMMATION?
1. Suppression of pro-inflammatory gene-expression

2. Suppression of Leukocyte migration and activation

3. Apoptosis of inflammatory cells

4. Phagocytosis and clearance!
What are the negative effects of Necrosis (as cell death)?
Necrosis- death of cells or tissues due to chemical or physical injury.

NEGATIVE- EXTENSIVE CELLULAR DEBRIS and INDUCES INFLAMMATION (upregulates TNF, IL-1beta, IL-8 and downregulates TGF-beta1)
Why is APOPTOSIS the preferred mechanism for cell death?
PROGRAMMED CELL DEATH- cell activates an interanl death program.

Characterized by nuclear DNA degradation, nuclear degeneration and condensation, and the phagocytosis of cell residua.

POSITIVE b/c:
1. cell contents will NOT be released into the environment
2. phagocytosis of apoptotic cells has ANTI-INFLAMMATORY EFFECTS (upregulates TGF-beta1, downregulates pro-inflammatory mediators such as, TNF, IL-1beta, IL-8)
Apoptotic PMNs are removed by PHAGOCYTOSIS... what else happens to regulate the inflammatory response?
1. Recongition of apoptotic cells by macs and DC ('eat-me' signal)

2. Phagocytosis and digestion in endosomal/lysosomal pathway

3. Inhibition of pro-inflammatory mediator production (TNF-alpha, IL-1, IL-6, IL-8, IL-12) by phagocytic cells

4. Release of ANTI-inflammatory mediators (TGF-beta, IL-10)

5. NO respiratory burst by phagocytic macrophages

6. Tolerance induction
What happens if there is defective clearance of apoptotic cells?
RISE OF AUTOIMMUNITY

-defect in C1q promotes systemic lupus erythematosus (SLE)

-there is often high titers of antibodies against apoptotic cell surface molecules (PS) in autoimmune patients
What are the different types of regulatory T cells?
Natural Treg (Thymus derived)

Induced Treg Tr1- Derived from periphery from activated effector T cells by anergizing with IL-10

Induced Treg Th-3: Derived from periphery induced in the GALT by low doses of antigen (oral tolerance) produces TGF-beta
What are some examples of newly emerging antibiotic resistant bacteria?
Important foodborne pathogens

most common acquired nosocomial infections

community-acquired infections

(PUBLIC HEALTH ISSUE)

Salmonella Newport (cattle and human infections; shows resistance to expanded-spectrum cephalosporins)

Campylobacter spp. (most important foodborne pathogen in US)- emergence of fluoroquinolone resistances, there is also a high prevalence of C strains resistant to tetracycline, erythromycin

Staphylococcus aureus- methicillin resistant strains (infection w/ these strains is increasing)
How is ANTIMICROBIAL RESISTANCE AQCUIRED?
1. EVOLUTIONARY CHANGES
-selective point mutations
-transposons (recombination events can allow a resistance gene to insert itself just downstream to an efficient promoter.

ACQUISITION OF DNA FROM OTHER SPECIES
-Conjugative plasmids
-Phages
-Transformation
Where do antibiotic resistant genes come from?
1. Antibiotic producing organisms

2. Cryptic embedded genes (genes that are either not expressed or expressed at very low levels)

3. Precursor genes (genes that encode proteins with modest resistance or antibiotic binding function, which might evolve into bona fide resistance elements given the appropriate selection pressure

4. Most bacterial genomes include resistance genes, even in bacteria that are normally susceptible to the antibiotic
Give examples of antibiotic producing organisms or naturally resistant microbes
-Spore-forming soil bacteria sythesize antimicrobials

-Soil bacteria possess mechanisms of resistance to antimicrobials

-A large number of soil bacteria are resistant to fully synthetic antimicrobials
What are the targets of ANTIMICROBIALS?
Cell membrane: lipopeptides

Cell wall sythesis: beta-lactams, glycopeptides

Folic Acid Synthesis: trimethoprim, sulfonamides

DNA gyrase: fluoroquinolones

RNA polymerase: rifamycins

Protein synthesis, 30S inhibitors: tetracyclines, aminoglycosides

Protein synthesis, 50S inhibitors: macrolides, lincosamides, streptogramins, phenicols
What are some of the mechanisms of ANTIMICROBIAL RESISTANCE?
Modification of target

Protection of target

Degradation of drug

Modification of drug

Efflux pumps

Decreased permeability
What is CROSS-RESISTANCE?
When a single mechanism confers resistance to an ENTIRE class or to MULTIPLE classes of antimicrobials

EX. non-specific efflux pump
overlapping targets
What is CO-RESISTANCE?
When an organism harbors several mechanisms, each conferring resistance to a GIVEN CLASS of antimicrobials

-frequently occurs via co-selection when multiple resistance genes are located within the same integron or on a plasmid
How do you get resistance to FLUOROQUINOLONES?
Modification of target by mutation

Protein that protects DNA gyrase from quinolones

Efflux pump

Decrease permeability of bacterial outer membrane
How do you get resistance to TETRACYCLINES?
Modification of target by mutation

Cytoplasmic proteins that promote release of tetracycline from the ribosome

Efflux pumps

Inactivation of drug by hydroxylation
How do you get resistance to MACROLIDES?
Modification of target by methylation of ribosomal RNA

Modification of target by mutation

Efflux pumps

Inactivation of drug by degradation or modification
How do you get resistance to BETA-LACTAMS?
Modification of target by mutation

Inactivation of drug by cleavage
-2 major groups of beta-lactamases (serine proteases or metaloprotease)
-over 100 different enzymes
What are the problems assoc. with the use of antibiotics at sub-therapeutic doses?
Selection of low resistant strains

Potential increase in bacterial VIRULENCE:
-increase motility (tobramycin)
-trigger expression of type 3 secretion system (tetracycline)
-induce BIOFILM formation (tobramycin, tetracycline, norfloxacin)
What are the innate mechanisms of mucosal immunity in the respiratory tract?
PHYSICAL BARRIERS:
-tight junctions
-flushing action: cough, saliva
- mucus and turbulent flow
- mucociliary elevator

ANTIMICROBIAL PEPTIDES AND PROTEINS:
-lysozyme
-lactoferrin
-secretory phospholipase A2
-defensins
What are the innate mechanisms of mucosal immunity in the GI tract?
PHYSICAL BARRIERS:
- tight junctions
- flushing action (peristalsis; saliva)
-low pH environment
- commensal bacteria in gut

ANTIMICROBIAL PEPTIDES AND PROTEINS:
-produced by paneth cells in gut (present in crypts in herbivores and omnivores) (CATS DON"T HAVE PANETH CELLS)
- PC's produce lysozyme, secretory phospholipase A2, and defensins
What are the role of Nod2 proteins in the innate mucosal immune mechanism in the gut?
regulate the production of defenins. Nod2 proteins are PRRs that recognize PAMPs (peptidoglycans) in the gut
What is the function of Adaptive Immunity in the mucosa?
IgA production!
**primary fxn of all "ALT"'s
MALT- mucous associated lymphoid tissue
GALT- gut associated lymphoid tissue
BALT- bronchiole associated lymphoid tissue
What is the gut lymphoid architecture?
Inductive site- Peyer's patches (contains germinal centers making proliferating B cells)

Effector site- Lamina Propria (where IgA is presented to the antigen's that were taken up by M cells)
Who does the antigen sampling of the lumen of the gut?
M cells (microfold cells)- very good at phagocytosis & they are very prominent in the lymphoid region of the gut

Intraepithelial Dendritic Cells- can sample antigens directly from the lumen of the gut and present them to B cells or TH2 cells.
Once antigens are released beneath the M cells and taken up by antigen presenting dendritic cells, where do they go?
Can go to either the:

LYMPHOID FOLLICLES: Peyer's Patches

MESENTERIC LYMPH NODES
What happens in Peyer's Patches?
Primary site of IMMUNE INDUCTION

DC's present antigens to T-cells/B-cells

B-cells specific for those antigens divide in germinal center undergoing somatic hypermutation and class-switching to produce IgA (the B cells interact with T-cells or DC's specific for their antigen)

Class-switching to IgA is regulated by the presence of specialized regulatory T-cells and dendritic cells that produce IL-4, IL-5 and TGF-beta.
What happens with IgA's after they are produced in the Peyer's Patches?
IgA+ cells leave the Peyer's patches and migrate to mesenteric lymph nodes where they proliferate further and differentiate into plasmablasts

IgA+ producing plasmablasts then leave the MLN's and home back to the mucosa via the thoracic duct and blood vessels
- effector sites in the mucosa have high endothelial venules
- B and T-cells primed in the mucosa express specific homing receptors.
What keeps gut effector B-cells in the gut?
binding of MAd-CAM-1 to the epithelium of the gut.

The CCL25 chekmokine is produced by the epithelium of the gut which also acts to HOME the B-cells to gut epithelium.
Can IgA-producing B cells seed distant mucosal sites?
Yes, they can seed the respiratory tract, urogenital system, and mammary glands.
How is IgA transported to the lumen of the gut?
-IgA is produced mainly as dimers or larger polymers (linked w/ J chains)
-IgA reaches the intestinal lumen via TRANSCYTOSIS
-IgA binds to Poly-Ig receptor on the basal side of the epithelium
-It is then carried in an endosome (secretory vesicle)
-Then there is enzymatic cleavage of a portion of the poly-Ig receptor and the IgA remains bound to the other portion of the poly Ig receptor, which may prevent degredation of IgA by food, proteases, etc, by binding to the MUCUS LAYER OVERLYING THE GUT EPITHELIUM.
What does IgA do in the gut?
-Neutralizes pathogens and their toxins

-Restricts penetration of commensals to low levels and prevents gut inflammation

-Potential to act intracellulary against viruses present in enterocytes

-Binds macrophages, neutrophils and eosinophils via low affinity Fc receptors--> opsonization can trigger phagocyte activation

-Can potentially excrete foreign antigens to the lumen

-In some species (rats, rabbits, chickens) it reaches the intestinal lumen via the bile
What else do the mucosa do to provide a highly tolerizing anti-inflammatory environment?
-ORAL TOLERANCE (if introduce an antigen orally will get tolerance not a response)

-Production of ANTI-INFLAMMATORY Cytokines IL-10 and TGF-beta by:
-T regulatory cells
-tolerizing dendritic cells

-Disregulation of inflammation can result in autoimmune inflammatory disease and food allergires (IBD, CHRONES Dz)
What type of response should a vax elicit to be effective against an EXTRACELLULAR PATHOGEN?
Humoral antibody response: activation of CD4+ T-cells.
What type of response should a vax elicit to be effective against an INTRACELLULAR PATHOGEN?
Cell-mediated response: activation of CD8+ T-cells.
What is the difference b/w LOCAL vs. SYSTEMIC immunity?
-local- mucosal immunity required for pathogens that gain entry via the mucosa

-systemic- sytemic immunity required for paraenteral and disseminated infections
What are the categories of vaccines?
Live vaccines

Killed vaccines

Subunit vaccines
Why are live vaccines the best generally?
Induce long term; cell-mediated, humoral, and mucosal/systemic immunity!
Why can live vaccines induce both humoral and cell-mediated immune responses?
Because LIVE VAX generate CD4+ and CD8+ responses because the live vax stimulate APCs to present to both MHC classes?
Why can live vaccines induce local (i.e. mucosal) immunity?
Because LIVE VAX can gain entry to sites of immune induction in the gut and resp. tracts.
What are some of the negative things about KILLED and SUBUNIT Vax?
-get degraded in the GUT

-get sampled as food

-RESULT in ORAL TOLERANCE
How do live vax elicit MEMORY?
-Persistence of LIVE AGENTS- restimulation of T-cells (at the point of infection or in draining lymph nodes may be extremely important in inducing long-term memory.)
What are some DISADVANTAGES of LIVE VAX?
-RESIDUAL PATHOGENICITY- SIDE EFFECTS: Fever, pain, swelling, malaise, abortion, encephalitis, anaphylaxis

-PATHOGENICITY in non-host species (jump species)

-IMMUNOSUPPRESION OF THE HOST

-BIOLOGICAL INSTABILITY

-CONTAMINATION (could make really bad viruses)
-oncogenic viruses
-prions

-REVERSION TO VIRULENCE-
-back mutation/recombination (w/ wild tyes to get emergence of new strains)
-emergence of new strains
How can we overcome the disadvantages of live vaccines?
-TYPE 3 recombinant and DNA vaccines

-Killed and subunit vaccines
What are Type 3 recombinant vaccines?
-NON-PATHENOGENIC viral and bacterial vectors that can deliver protective antigens from a pathogen (not taking pathogen itself)

-because they are LIVE, they can induce CTL, memory, and possibly mucosal responses (but not likely)
What are DNA vaccines?
(take naked DNA) gene from pathogen--> put into plasmid DNA w/ promoter in front of it; inject into muscle and that DNA will get taken up and antigen gene will get expressed.

-Clone gene for protective antigen
-Incorporate gene into plasmid expression vector
-Introduce "naked" DNA plasmid into host
-Results into protein expression and immune response to vector-encoded antigen
What are some ADVANTAGES to KILLED and SUBUNIT VAX?
-no potential for reversion ot virulence
-fewer side effects
-killed vax are relatively easy to make
-subunit vax can be administered at high antigenic mass and do not require growth of large amounts of pathogen
How can we overcome the problem of killed and subunit vax with LOW ANTIGENICITY?
ADJUVANTS

IMPROVED DELIVERY METHOD
What do ADJUVANTS do and what are some examples?
Adjuvants boost immunogenicity of co-administered antigens.

Contain carrier substances (alum, mineral oil), an IMMUNOMODULATORY SUBSTANCE (mycobacteria) or both.
What do IMMUNOMODULATORY SUBSTANCES do and what are some examples?
Directly stimulate immune response to co-administered antigens.
EXAMPLES:(PRRs, interact with TLRs)
-mycobacterial cell wall components
-bacterial DNA- CpG oligos
-derivatives of LPS and peptidoglycan
-yeast mannans (beta-1,3 glucans)
-imidazoquinolones (imiquimod)
How does stimulation thru TLRs by ADJUVANTS increase efficacy of VAX?
Antigen + Adjuvant stimulates TLR's and B7 to be upregulated, these are co-stimulatory molecules that are needed to increase binding of Th cells and APCs as well as Th cells and B cells to make antibodies!
What are CARRIER SUBSTANCES and give some examples?
Carriers are vehicles for the delivery of antigen; they also all boost the immune response.
EXAMPLES:
-alum
-oil (mineral oil)
-lipid or detergent spherules
-latex beads/biodegradable polymers
-large proteins
Why do we use CARRIERS?
-provide a depot for SLOW RELEASE of antigen (potentially increasing memory responses)

-can induce local inflammation that can potentiate responses to the co-administered antigen

-particulates are more readily taken up by APCs (
What are some PARTICULATE CARRIER VEHICLES?
polyactide/polyglycolide microspheres

chitosan nanospheres

powdered-sugar glasses (trans-dermal FeLV vax)
Why is a TRANSDERMAL VAX delivery BENEFICIAL?
Because the particulate antigens stimulate the high density of dendritic cells that are hanging out in the skin.
What are the 5 stragies to diagnose INFECTIOUS DISEASES?
1. CLINICAL HISTORY: clues to exposure or risk factors

2. SMEARS OR HISTOLOGICAL SECTIONS: morphology of agent/host response

3. CULTURE: definitive identification/Interference by antibiotic therapy

4. SEROLOGY: exposure vs. vaccination

5. MOLECULAR TECHNIQUES (PCR, FISH): Limited availability/false positives
What are included in "very small" classes of infectious agents?
Prions
Viruses
Chlamydia
Rickettsia
Mycoplasma
What are included in the "bacteria" class of infectious agents?
Pyogenic bacteria
Enterobacteria
Gram - anaerobic bacilli
Clostridia
Actinomycetes
Spirochetes
Bacteria w/ complex walls
What are included in the "fungus" class of infectious agents?
Cutaneous
Systemic
Opportunistic
What are included in the "protozoan parasites" class of infectious agents?
Coccidia
Toxoplasma
Amoeba
Giardia
What are included in the "metazoan parasites" class of infectious agents?
Nematodes
Trematodes
Cestodes
Acanthocehalans
Pentastomes
Arthropods
What are the SIX MAJOR HISTOLOGIC patterns of tissue reaction in inflammatory response to infectious agents?
1. Spongiform encephalopathy
2. Non-suppurative
3. Suppurative
4. Necrotizing
5. Granulomatous
6. Eosinophilic
What are the characteristics of SPONGIFORM ENCEPHALOPATHY?
PRIONS
-invariably fatal neurodegenerative diseases due to the accumulation of an altered protein.
-may be hereditary or acquired through the ingestion of neural tissue--> travel to lymphoid organs and replicate in Follicular Dendritic Cells.
-Eventually PRIONS accumulate in the sympathetic nerve endings in lymphoid organs--> travel up the nerve via retrograde axonal flow to reach neurons in the CNS.
-Abnormal prion protein accumulates and eventually leads to neuronal cell death and spongiform VACUOLATION of the brain.
-SINCE prion contain NO ANTIGEN that are recognized by the host, there is NO INFLAMMATORY RESPONSE.

CLINICAL EX. (Scrapie, BSE, Chronic Wasting Disease, Transmissable Mink Encephalopathy, Feline Spongiform Encephalopathy)
What are the characteristics or NON-SUPPURATIVE INFLAMMATION?
VIRUSES
-obligate intracellular pathogens
-APCs process viral antigens into short peptides and present them via MHC class 2 molecules to antigen-specific CD4+ helper t-cells.
-TH1 cells then stimulate cell-mediated immunity through the elaboration of IFN-gamma.
-In addition, virally infected cells display viral peptides complexed to MHC 1 molecules to CD8+ cytolytic t-cells, which directly kill the infected cells

MAJOR CLINICAL PRESENTATION (Viral cytopathic effects)-
- Cell necrosis
- Inclusion bodies (intranuc. or cytoplasmic)
-Syncytia (polykaryons)
- Vesicles
- Cell proliferation

VIRAL MIMICS?
- some intracellular bacteria and intracellular parasites stimulate cell-mediated immunity (i.e. SPIROCHETES-Helicobacter, Borreila burgdorferii, Leptospira)

CLINICAL EX.
Parvovirus enteritis
Canine Distemper
BRSV pneumonia
Squamous papilloma
What are the characteristics of SUPPURATIVE INFLAMMATION?
"PYOGENIC" BACTERIA (extracellular, GM+ cocci, GM- bacilli)
-tissue damage results in acute inflammatory reactions
-increased vascular permeability and recruitment of neutrophils leads to the generation of SUPPURATIVE EXUDATES.
-GM stains of exudate is an effective and simple method to demonstrate bacteria dn differentiate them into GM+ and GM- varieties.

CLINICAL PRESENTATIONS-
-Abscess
-Bacteremia (disseminated microabscesses)
-Cellulitis (fasciitis- acute inflammation spreading along fascial planes)
-Empyema (acummulation of pus in body cavity)

CLINICAL EXAMPLES-
Equine STRANGLES- Streptococcus equi
Cat-bite abscess- Pasteurella Multocida
Canine prostatic abscess- coliforms
Abscess in cattle- Arcanobacterium pyogenes
What are included in the "metazoan parasites" class of infectious agents?
Nematodes
Trematodes
Cestodes
Acanthocehalans
Pentastomes
Arthropods
What are the SIX MAJOR HISTOLOGIC patterns of tissue reaction in inflammatory response to infectious agents?
1. Spongiform encephalopathy
2. Non-suppurative
3. Suppurative
4. Necrotizing
5. Granulomatous
6. Eosinophilic
What are the characteristics of SPONGIFORM ENCEPHALOPATHY?
PRIONS
-invariably fatal neurodegenerative diseases due to the accumulation of an altered protein.
-may be hereditary or acquired through the ingestion of neural tissue--> travel to lymphoid organs and replicate in Follicular Dendritic Cells.
-Eventually PRIONS accumulate in the sympathetic nerve endings in lymphoid organs--> travel up the nerve via retrograde axonal flow to reach neurons in the CNS.
-Abnormal prion protein accumulates and eventually leads to neuronal cell death and spongiform VACUOLATION of the brain.
-SINCE prion contain NO ANTIGEN that are recognized by the host, there is NO INFLAMMATORY RESPONSE.

CLINICAL EX. (Scrapie, BSE, Chronic Wasting Disease, Transmissable Mink Encephalopathy, Feline Spongiform Encephalopathy)
What are the characteristics or NON-SUPPURATIVE INFLAMMATION?
VIRUSES
-obligate intracellular pathogens
-APCs process viral antigens into short peptides and present them via MHC class 2 molecules to antigen-specific CD4+ helper t-cells.
-TH1 cells then stimulate cell-mediated immunity through the elaboration of IFN-gamma.
-In addition, virally infected cells display viral peptides complexed to MHC 1 molecules to CD8+ cytolytic t-cells, which directly kill the infected cells

MAJOR CLINICAL PRESENTATION (Viral cytopathic effects)-
- Cell necrosis
- Inclusion bodies (intranuc. or cytoplasmic)
-Syncytia (polykaryons)
- Vesicles
- Cell proliferation

VIRAL MIMICS?
- some intracellular bacteria and intracellular parasites stimulate cell-mediated immunity (i.e. SPIROCHETES-Helicobacter, Borreila burgdorferii, Leptospira)

CLINICAL EX.
Parvovirus enteritis
Canine Distemper
BRSV pneumonia
Squamous papilloma
What are the characteristics of SUPPURATIVE INFLAMMATION?
"PYOGENIC" BACTERIA (extracellular, GM+ cocci, GM- bacilli)
-tissue damage results in acute inflammatory reactions
-increased vascular permeability and recruitment of neutrophils leads to the generation of SUPPURATIVE EXUDATES.
-GM stains of exudate is an effective and simple method to demonstrate bacteria dn differentiate them into GM+ and GM- varieties.

CLINICAL PRESENTATIONS-
-Abscess
-Bacteremia (disseminated microabscesses)
-Cellulitis (fasciitis- acute inflammation spreading along fascial planes)
-Empyema (acummulation of pus in body cavity)

CLINICAL EXAMPLES-
Equine STRANGLES- Streptococcus equi
Cat-bite abscess- Pasteurella Multocida
Canine prostatic abscess- coliforms
Abscess in cattle- Arcanobacterium pyogenes
What are the characteristics of NECROTIZING INFLAMMATION?
CLOSTRIDIA ssp
FUSOBACTERIUM NECROPHORUM
BACTEROIDES NODUSUS
- organisms are commensals living in the GI or on MM
- can also survive as free-living soil saprophytes and are distributed widely in the soil
-because they are ANAEROBES, they typically invade and multiphy only in an ANAEROBIC environment created by PREVIOUS TISSUE DAMAGE.
-Thus, these bacteria are freq. opportunists as part of a mixed infection
- Elaboration of powerful toxins can cause RAPID AND SEVERE NECROSIS, which creates a favorable env. for further spread.
-FOUL ODOR and clostridial infections in particular may be accompanied by gas production in tissues (emphysema).
-because of RAPIDITY of ONSET and the loss of blood supply due to necrosis, FEW INFLAMMATORY CELLS are typically present and the lesions may resemble infarcts.

CLINICAL PRESENTATIONS:
Myonecrosis
Gangrene
Enteric Necrosis

CLINICAL EX.
Blackleg- Clostridium chauveoi
Enterotoxemia- Clostridium perfringens
Foor rot- Bacteroides nodusus
What are the charateristics of GRANULOMATOUS INFLAMMATION?
"HIGHER" BACTERIA- MYCOBACTERIA
ACTINOMYCES, NOCARDIA, RHODOCOCCUS
FUNGI
PARASITES
- macrophages predominate in the response to infectious agents that resist eradication and stimulate strong cell mediated immune responses.

CLINICAL PRESENTATIONS:
"HIGHER BACTERIA"- GRANULOMATOUS inflammation; some bacteria induce PYOGRANULOMATOUS inflammation characterized by macrophages accompanied by suppuration.
-macrophages then may form an organized mass -GRANULOMA (may be intact or the center may undergo CASEOUS necrosis) -> Tuberculosis

FUNGI- (2 distinctive forms) YEASTS- single-celled organisms that reproduce by budding & MOLDS, which form filamentous structures termed- HYPHAE.

COCCIDIA- most commonly encountered protozoa

GRANULOMATOUS MIMICS: Foreign-body type reactions & Histiocytic proliferative disorders

CLINCIAL EXAMPLES:
Johne's Dz (Mycobacterium avium ssp. paratuberculosis)
Rhodococcus equi pneumonia
Lumpy Jaw- Actinomyeces bovis
Caseous lymphadenitis- Corynebacterium pseutotuberculosis
What are the characteristics of EOSINOPHILLIC INFLAMMATION?
METAZOAN PARASITES
-parasites that are in greater contact with host tissues, esp. blood, typically invoke a greater eosinophillic infiltrate than other parasites.
- a significant eosinophil response may accompany infestations with hookworms, lung worms, stonglyes, flukes and ectoparasites.
-under physiologic conditions, eosinophils are located in the GI tract but not in other tissues; eosinophil mobilization from the bone marrow is under the control of IL-5 and eotaxin (CCR-3)

EOSINOPHILIC MIMICS: Immediate type 1 hypersensitivity may occur as either a systemic disorder (anaphylaxis) or as a localized reaction.
-EOSINOPHILIC GASTROENTERITIS- idiopathic disease where large numbers of eosinophils accumulate in the wall of the stomach.

CLINICAL EX.:
Heartworm Dz
Lungworms
Scabies
How does the Immune system provide Innate Immunity against viruses?
Foreign nucleic acid sensing is used to initiate defenses against viruses.

1. RNA SILENCING
2. RIG-1, MDA5 and viral RNA SENSORS
3. NUCLEIC ACID SENSORS: the Toll-like receptors (TLR's)
4. MEDIATORS: alpha and beta interferons
5. IFN-INDUCED EFFECTORS OF THE ANTIVIRAL STATE
6. NK cells
How does the immune system provide Adaptive Immunity against viruses?
1. ANTIBODY- counteracts viruses in several different ways (virus neutralization, opsonization)
2. ANTIBODY-DEPENDENT CELLULAR CYTOTOXICITY (ADCC)
3. CYTOTOXIC T CELLS