Lecture Two

Question 1

What is the definition of a hypersensitivity reaction?

Answer 1

undesirable/harmful responses produced by normal immune system mechanisms. They are evolved to protect against infection but overact and react to harmless things (e.g. environmental allergens) and react to self (part of autoimmunity) causing tissue injury and serious disease.

Question 2

What is meant by the term autoimmunity?

Answer 2

Refers to an immune response directed against self tissue due to failure of self tolerance

Question 3

What is immune mediated disease (also called auto-immune disease)?

Answer 3

Inflammation, tissue damage and resultant clinical signs that result from auto-immunity

Question 4

What is a primary autoimmune/immune mediated disease?

Answer 4

Something that has no obvious triggers is called idiopathic

Question 5

What is a secondary autoimmune/immune-mediated disease?

Answer 5

Suspected secondary to a known trigger. The trigger causes an upset of the balance. Sometimes removing the trigger solves the disease

Question 6

What are the protagonists of type 1 hypersensitivity reactions?

Answer 6

Involve Th2, IgE and mast cells

Question 7

What is the mechanism involved in type 1 hypersensitivity?

Answer 7

1. Exposure to allergen
2. Activation of TH2 and cells and IgE class switching in B cells
3. Production of IgE
4. Binding of IgE to Fc on mast cells
5. Repeat exposure to allergen
6. Activation of mast cell and release of mediators

Responses:
Immediate response causes release of histamine, proteases, prostaglandin and leukotrienes. These cause an immediate response of vasodilation, vascular leakage and smooth muscle spasm.
A late phase reaction causes leukocyte infiltration, epithelial damage and bronchospasm

Question 8

What types of symptoms are seen with local type 1 hypersensitivity reactions?

Answer 8

Symptoms depend on the portal of entry - e.g. inhaled allergens (pollens) cause upper respiratory tract infection

Question 9

What type of symptoms are seen with systemic type 1 hypersensitivity reactions?

Answer 9

Anaphylaxis, generalised hives, hepatobiliary signs - increase live enzymes (ALT)

Question 10

What is the mechanism of action of type II hypersensitivity reactions?

Answer 10

production of IgG and IgM binds to antigen on target causing damage. The three ways it can cause damage include Opsonisation and phagocytosis of target cell, lysis of target cell complement, antibody dependant cell cytotoxicity (ADCC)

Question 11

What might that target cells of type II hypersensitivity be?

Answer 11

Self (e.g. autoimmunity)
Self - but reactive antibodies from colostrum (neonatal isoerythrolysis)
Foreign - incompatible blood product (haemolytic transfusion reaction)

Question 12

What is the main difference between type II and type III hypersensitivity antigens?

Answer 12

Type II = cell or matrix associated antigen

Type III = soluble antigen

Question 13

What is the mechanism of action of type III hypersensitivity reactions?

Answer 13

deposition of antigen-antibody complexes. This is caused by complement activation, recruitment of leukocytes by complement and Fc receptors and the release of enzymes and other toxic molecules

Question 14

What are the pathogens responsible for type III hypersensitivity reactions?

Answer 14

Bacterial infection (e.g. Streptococcal infection), viral infection (FIV, FeLV, FIP)

Question 15

Provide an example of a type III hypersensitivity reaction and the clinical signs that are evident:

Answer 15

Glomerulonephritis (GN) - causes protein loosing nephropathy (PLN), nephrotic syndrome, high blood pressure

Question 16

What is the mechanism of action of Type IV hypersensitivity?

Answer 16

Activated T-lymphocytes leads to release of cytokines, macrophage activation. This leads to T-cell mediated cytotoxicity. This originates from normal immune response to infection with intracellular pathogens (Mycobacteria, Leishmania).. Pathology occurs from a protracted infection or repeat exposure