Hypersensitivity

Question 1

Type I hypersensitivity

Answer 1

IgE mediated

• Allergy
• Does not involves complement
• Immediate response within minutes
• Has 2 phases
• Response may be to food, pollen, dust, chemicals
• e.g. Anaphylaxis, atopic dermatitis

Question 2

Type II hypersensitivity

Answer 2

Antibody-mediated cytotoxic reaction

• Usually IgG mediated (IgM possible)
• Reaction maximal within 5-10 hrs
• Antibody recognises molecule/antigen on host cell or tissue
• Sources of these antigens/molecules can be intrinsic or extrinsic
  
  • e.g. Intrinsic: body’s own blood cells (haemolytic anaemia)
  • e.g. Extrinsic: drug metabolite
• Cells can be destroyed by complement, phagocytosed by innate immune cells, or by toxins from NK cells

Question 3

Type III hypersensitivity

Answer 3

Immune complex mediated

• IgG/immune complex mediated
• Reaction maximal at 4-8 hrs
• Antibody/antigen complexes escape the normal route of clearance (i.e. phagocytosis)
• e.g. Equine Recurrent Airway Obstruction (RAO)

Question 4

Type IV hypersensitivity

Answer 4

Delayed type hypersensitivity

• T cell mediated;
• Involves primed (memory) T cells and also macrophages/dendritic cells
• Reaction maximal at 24-72 hrs
• T cells recruit and activate mononuclear cells e.g. monocytes, tissue macrophages
• Inflammation at the site of the DC/T cell interaction occurs
• e.g. Johne’s disease

Question 5

Which type of hypersensitivity is shown here?

Answer 5

Type III - immune complex mediated

Question 6

Which type of hypersensitivity is shown here?

Answer 6

Type IV

Question 7

Why is the reaction maximal of Type I hypersensitivity shorter than that of other hypersensitivity reactions?

Answer 7

Type I only involves IgE-mediated effects rather than activation of the complement system.

Question 8

Outline how Type II and III hypersensitivity differs

Answer 8

• Both Type II and Type III can be IgG mediated
• Type II involves IgG and IgM directed against cellular antigens/molecules → leads to cell damage mediated by other immune system effectors
• Type III reactions involve IgG, IgM and occasionally IgA1 antibodies forming immune complexes

Question 9

Outline the difference between cell mediated and antibody mediated hypersensitivity

Answer 9

• Type I, II and III hypersensitivity reactions are antibody mediated, whilst Type IV is cell-mediated.
• Cell mediated reactions take longer than antibody-mediated responses because they take longer for cells to be recruited to the site of exposure.

Question 10

Outline how the antigens involved in Type II and Type III hypersensitivity differ?

Answer 10

• Type II = antigens are bound to cell surface
• Type III = antigens are soluble

Question 11

Which condition is pictured here and which type of sensitivity is it?

Answer 11

Myasthenia gravis

Type II hypersensitivity

Question 12

What structure is shown here? Which disease could it be associated with? What type of hypersensitivity is this?

Answer 12

Granuloma

Bovine TB

Type IV

Question 13

What condition is shown here? What type of hypersensitivity is it?

Answer 13

Canine blue eye

Associated with canine adenovirus

Type III hypersensitivity

Question 14

Give some examples of Type I hypersensitivity

Answer 14

• Anaphylaxis
• Atopic dermatitis
• Asthma
• Allergic rhinitis

Question 15

True/false: you can be genetically susceptible to hypersensitivity

Answer 15

True

e.g. could have high levels of circulating IgE or specific MHC genes

Question 16

Give some examples of Type II hypersensitivity

Answer 16

• Autoimmune haemolytic anaemia
• Pemphigus
• Myasthenia gravis

Question 17

Give some examples of Type III hypersensitivity

Answer 17

• Polyarthritis
• Systemic Lupus Erythematosus (SLE)
• Nephritis
• Post-infection reaction

Question 18

True/false: Type I hypersensitivity reaction could occur after vaccination

Answer 18

True

Question 19

True/false: Type I hypersensitivity reaction could occur after vaccination

Answer 19

True

Question 20

Give some examples of Type IV hypersensitivity

Answer 20

• Granuloma formation in TB, Brucellosis, Johne’s
• Tuberculin skin reaction