Hypersensitivity

Question 1

Type 1

Answer 1

• Immediate hypersensitivity/fastest type- minutes
• Anaphylactic/atopic
• Antibody mediated- IgE
  MOA
  1. Exposure to allergen
  2. TH2 cells stimulate b cells to produce IgE antibodies
  3. IgE antibodies attach to Fc receptors for which they have a high affinity on mast cells and basophils
  4. Exposed to allergen for second time
  5. IgE cross linking on mast cells which results in immediate release of vasoactive amines which are the mast cell mediators e.g. histamine and heparin
  6. They can cause vascular leakage, bronchoconstriction, inflammation
  7. histamine= arteriolar vasodilation= increased blood flow

Question 2

Type 1 examples

Answer 2

1. Anaphylaxis allergens= bee sting, food like nuts, drugs and excipient allergy , insect bite
2. Asthma allergens= inhaled materials
3. Allergic rhinitis allergens= animals and trees
4. Atopic dermatitis= rash
5. Allergic conjunctivitis

Question 3

Type 2

Answer 3

• Slower than type 1- hours
• Cytotoxic
• Cell bound antigens which are extrinsic or intrinsic
• Antibody mediated- IgG or IgM
  MOA
  1. Antibody directed to and binds to IgG or IgM on cell surface causing
  2. Complement activation
  3. Cell lysis
  4. Opsonization
  5. Cytotoxicity by NK cells
  6. IgG mediates ADCC with cytotoxic T cells, NK cells, macrophages, neutrophils, eosinophils and polymorphonuclear cells
  7. Impair cellular function

Question 4

Type 2 examples

Answer 4

1. Penicillin induced drug reaction
2. Myasthenia gravis
3. Haemolytic anaemia
4. blood transfusion reactions

Question 5

Type 3

Answer 5

• Slower than type 2- hours
• Antibody mediated- IgG
• Immune complex mediated
• Against Soluble antigen
  MOA
  1. Soluble immune antigen antibody complexes form in circulation (IgG and IgM antibodies)
  2. Deposit in tissues
  3. This causes complement activation to occur or FC mediated inflammation
  5. Leave circulation and trigger inflammation locally or systemically mediated by neutrophils

Question 6

Type 3 examples

Answer 6

1. Serum sickness

2. Lupus

Question 7

Type 4

Answer 7

• Cell mediated
• Delayed type
• Slowest= days
• CD8 cytotoxic t cells
• CD4 t helper cells
  MOA
  1. CD8 t cells kill target cell directly
  2. T helper cells sensitised
  3. They release cytokines interferon gamma and INLK 2
  4. They activate macrophages or cytotoxic t cells
  5. These mediate direct cellular damage and cause inflammation

Question 8

Type 4 examples

Answer 8

1. Type 1 diabetes
2. Contact dermatitis
3. Tuberculin test
4. Transplant rejection