Immune-Mediated Tissue Damage

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superantigen

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binds to outside surface of an MHC class II molecule and outer surface of T-Cell

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superantigens activate

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large percentage of CD4 T lymphocytes.

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Consequences of superantigen activating CD 4 T lymphocytes

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release of cytokines and systemic inflammatory response ie toxic shock syndrome

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Hypersensitivity represents

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altered sensitivity or sensitivty to harmless antigens
immune mediated tissue injury/damage

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All hypersensitivity reactions result from an

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adaptive immune response.

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hypersensitivity reactions occur after

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sensitization

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The hypersensitivity response is

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elicited on re-exposure to offending antigen

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Antigens enter the body via what 2 methods

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delivered at low doses across mucosal surfaces(pollens, molds, foods.
injected percutaneously- insect venums, drugs, vaccines

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Most IgE synthesis occurs where

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mucosal tissues (plasma cells in lamina propria

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High levels of what cytokine promotes Ig class switching to IgE

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IL-4 from Th2 lymphocytes

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IgE sensitizes what 2 cells

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mast cells and bsophils by binding to the FCe receptors

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The mechanism of damage of Type I hypersensitivity is

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Mast cell activation (IgE bound and ready)

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When activated Mast Cells

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release histamine, prostaglandins, and leukotrienes

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Characteristics of Type I Hypersensitivity reaction

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rapid onset <15 min
miscrovascular response (wheal and flare)
Muscosal responses: increased mucus and smooth m. contraction

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The mucosal response for Type I hypersensitivity includes

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increased mucus secretion and contraction of smooth muscle

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With Type I Hypersensitivity leukocytes do what?

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do not accumulate except in Late-Phase response

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LPR occurs when and is characterized by

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in some animals
delayed onset 3 - 24 hours
Mast cell cytokines recruit leukocytes (eosin, monon, T-cell, neutrophils.

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Late-phase response significance

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1) antihistamines are ineffective
2) presence of the late phase response is associated with more severe reactions

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Chronic type I hypersensitivity reaction

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continuouse stimulation results in chronic inflammatory reaction. Canine atopic dermatitis

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Anaphylaxis

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systemic form of Type I hypersensitivity

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Mild anaphylaxis is characterized by

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generalized edema

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Severe anaphylaxis is characterized by

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systemic hypotension and collapse, edema in the lungs

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Anaphylaxis is characterized in horses, pigs and cats _____ and in dogs _____

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with intestinal tract edema
hepatic vein congestion

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Canine atopic dermatitis may also include

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Type IV hypersensitivity

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Canine atopic dermatitis is characterized by lesions

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most commonly on the paws, axillary, and inguinal areas, and the face.

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Equine Recurrent Airway Obstruction is also called ____ and affects _____

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COPD
type I with some type III
affects the alveolar walls.

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Antigens for Equine RAO are typically

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spores from dust and molds in stalls and barns.

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Vaccine reactions are true _____ and are characterized by ____

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Type I hypersensitivity reactions
facial swelling and wheals

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Arthropod parasites can elicit a Type ____ HS reaction

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Type I hypersensitivity reaction

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Cattle and Horse arthropod parasites include

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bites of midges, black flies, stable flies, mosquitoes

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Dog arthropod parasite reactions include

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sacroptes scabiei, flea saliva (also type IV)

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Cat arthropod parasites include

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otodectes cynotis

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Immunotherapy is also called ____ and is practiced when _____

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hyposensitization or desensitization
offending allergens can be identified

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Immunotherapy works by

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shifting IgE to IgG. and shifting from an TH2 to a Th 1 response.

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Recently, immunotherapy has focused on

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induction of treg cells

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Type II Hypersensitivity intrinsic antigens include

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1) most blood group antigens of erythrocytes ( e.g. blood transfusion reactions)
2) autoantigens in autoimmune disorders

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Type II Hypersensitivity extrinsic antigens include

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1) some microbial antigens
2) certain drugs or products of drug catabolism

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Mechanisms of Damage: cytotoxicity 3 methods

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1) complement
2) opsonization and cell destruction
3) agglutination

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Mechanisms or damage Type II HS: altered cell signaling 2 methods

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1) antibody-mediated cell activation
2) antibody-mediated cell inactivation

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Antibody-mediated cell activation includes

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1)Ab binding physiologic receptor mimics binding or natural ligand
2) cell is activated to perform some action
3) activation mech causes normal regulation to be absent
4) results in unregulated action by the cells

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Antibody-mediated cell inactivation characteristics (Type II Hypersensitivity)

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1) antibody binding to a physiologic receptor prevents natural ligand binding
2) Cell unable to respond and perform

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example of antibody-mediated cell activation (Type II Hypersensitivity)

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immune-mediated hemolysis, transfusion reactions, neonatal isoerythrolysis, AIHA, hemoparasites, IMT, pemphigus

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example of antibody-mediated cell inactivation (Type II Hypersensitivity)

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Myasthenia gravis - blockade of acetylcholine receptors at the motor endplate

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Blood Group antigens

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Membrane antigens that can induce antibodies in other animals of same or other species

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Blood Group antigens characteristics

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1) polysaccharide antigens
2) complex mode of inheritance
3) multiple systems of blood group antigens

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Natural antibodies to blood group antigens are called ___ and are _____

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isoantibodies
pre-formed antibodies w/o prior exposure to RBC's

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Natural antibodies to blood group antigens are induced by and are typically Ig?

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1) cross-reactive antigens of normal microbial flora
2) IgM

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Canine blood group antigens are called and there are _____ groups

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Dog Erythrocyte Antigens (DEA)
8 blood groups

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The most important antigen for dog blood transfusions is

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DEA 1

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What are the alleles of DEA 1

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DEA 1.1, DEA 1.2, DEA 1.3

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Characteristics of DEA 1.1

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33- 45 % of dogs
no isoantibodies
high antigenicity
in-clinic kit

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Characteristics of DEA 1.2

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4 - 22% of dogs
No isoantibodies
moderate antigenicity
reference lab

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Sensitization to canine blood group antigens requires

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prior transfusion with mismatched blood.

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Reactions are usually observed in ________ transfues with ______

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DEA 1.1 negative
DEA 1.1 positive

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Sensitization to canine blood troup antigen prevention includes

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type and cross-match
use DEA 1.1 negative blood for transfusion

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DEA 1.1 positive transfused into DEA 1.1 negative would have what reaction

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1st sensitization to DEA 1.1.
2nd: transfusion reaction is likely

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DEA 1.1 negative transfused into DEA 1.1 positive would have what reaction

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reaction is unlikely

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Feline blood group antigens

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AB blood group system

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Feline blood group antigens: 3 blood types:

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Type A, Type B, Type AB

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Feline blood group antigen system classification

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Type A is dominant to Type B (Type A/B cats are type A, not type AB)

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Almost all cates in the USA are type

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Type A

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Feline blood group Type A characteristics

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75 - 95% overall
95% of DSH and DLH
Weak isoantibodies (IgM, IgG anti-B)
in-clinic kit

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Feline blood group Type B

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5 - 25% overall higher frequency in Rex, British shorthair, himalayan, abyssinian
strong IgM anti-A
In-clinic kit

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The reaction to type A blood when given to a type B cat on first transfusion would

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be a severe transfusion reaction: 1 mL can cause shock within minutes

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The reaction to Type B blood when given to a type A cat on transfusion would be

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a mild transfustion reaction

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Prevention of blood transfusion reactions is accomplished by

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type and cross-match

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Blood group Major cross-match is carried out by

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Testing for Ab in the recipients blood
Recipient serum
Donor RBC's

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Blood group Minor cross-match is carried out by

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Testing for Abs in the donor blood
Recipient's RBC's and donor's plasma

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Cross-matching detects

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antibodies, regardless of their specificity, that might cause a transfusion reaction

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Neonatal isoerythrolysis or hemolytic disease of the newborn occurs

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when hemolysis caused by maternal antibodies to blood gorup antigens of the newborn

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NI occurs after

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absorption of maternal antibodies in colostrum

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NI occurs in what species

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equids, cats

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Equids blood group antigens associated with NI

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horses:Aa negative mare to Aa positive sire
Mules" doneky sire, horse dam (unique antigen of donkeys)

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Sensitization of equid NI

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mare bred to a mismatched sire.
Aa-neg mare, to Aa pos sire
Aa negative mare to Aa-positive sire
mare to donkey

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NI occurs when

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small placental hemorrhases allow fetal erythrocytes to enter maternal circulation. Not apparent in all mismatched breeding

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In Cats Ni may occur when a type ___ queen is bread to type ____

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type B queen
Type A tom
All kittens A

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In NI the neonate _______ and receives

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ingests colostrum
natural antibodies

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Type III hypersensitivity reaction antigens

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soluble antigens (Type II are cellular antigens)

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Type III Hypersensitivity reaction mechanism of damage # 1

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Immune complex formation and deposition

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Type III HS immune complexes may form

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1) locally at sites where the antigens enter
2) in circulation when antigen is present in the blood stream.

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Type III HS large immune complexes

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are phagocytosed by macrophages in the spleen and liver and do not cause damage

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Type III HS small and medium complexes deposit in

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blood vessel walls of 1) renal glomerulus 2) dermal arterioles
3) small blood vessels in other sites

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Type III HS mechanism of damage # 2

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activation of complement,
tissue macrophages, and mast cells

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The immune complexes of both types cause

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inflammation.

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Immune complexes activate

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1) complement:C3a, C5a, C3b
2) cells that express Fc receptors: macrophages, mast cells

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Type III HS reaction inflammation is induced by

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activated mast cells and macrophages

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The key feature of type II HS reaction is

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the accumulation of neutrophil due to C5a and neutrophil chemokines

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In type III HS reaction neutrophils

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attempt phagocytosis of immune complexes via their Fc receptors and C3b receptors (frustrated phygocytosis)

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In type III HS reactions, phagocytes release

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lysosomal enzymes and reactive O2 intermediates and damages host tissue

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In type III HS reaction neutrophils

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attempt phagocytosis of immune complexes via their Fc receptors and C3b receptors (frustrated phagocytosis)

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In type III HS reactions, phagocytes release

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lysosomal enzymes and reactive O2 intermediates and damages host tissue

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glomerulonephritis Type III HS

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infectious agents that cause persistent infections expecially virus and HWA, idiopathic

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Bovine hypersensitivity pheumonitis Type III HS

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inhaled mold spores from hay, immune complexes form in walls of alveoli and bronchi (may involve Type I HS too)

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Purpura Hemorrhagica Type III HS

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sequela of streptococcus equi (strangles)
cutaneous edema, small mucosal hemorrhage and sometimes glomerulonephritis

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Blue Eye in dog Type III HS

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reaction of CAD1 or CAD 1 vaccine.
immune complexes form in the ciliary body and inflammation occurs, cornea is edematous and hazy.

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Blue Eye does not occur after

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vaccination with CAV2

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Type IV HS reaction antigens

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1) intracelllar parasites (bacteria, protozoa, fungi ) eg. tuberculosis
2) haptens
3) foreign MHC molecules in transplants

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Haptens include

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formaldehyde
urushiol
foreign MHC molecules in transplants

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Type IV HS reaction mechanism of damage

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1) Th 1 mediated
2) Tc medicated (organ transplant

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Activated Th1 cells secrete cytokines that

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recruit momcytes from blood and mcrophages

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Th1-mediated type IV hypersensitivity includes

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memory Th 1 cells migrating to the site of antigen entry

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Activated TC lymphocytes action includes

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killing cells of the transplant
releasing IFN - g to activate macrophages

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Type IV HS examples

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1) contact sensitivity/hypersensitivity, allergic contact dermatitis (poison oak)
2) granulomas
3) tuberculin reaction

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Test procedures for type IV hypersensitivity

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intradermal inoculation or antigen
read test at 72 hours
positive test: firm swelling at injection site;T-cells macrophage