Case 1 - Peanut Allergy

• What type of hypersensitivity is a peanut allergy?

  Type I
• What are the risk factors of a peanut allergy?

  Genetics (atopic phenotype)

  Often unknwon why the allergy is intially triggered in some individuals
• Mechanism behind Type I hypersensitivity.

  Foreign but harmless antigen

  IgE mediated crosslinking of FceRI -> mast cells become activated & degranulate -> release of histamine & leukotrienes -> smooth muscle contraction & increased vascular permeability

  Histamin can also activate nerve endings directly -> itching

  Eosinophils recruited -> release mediators (e.g. MBP) which are very damaging

  Basophils -> important in systemic anaphylaxis

  Th2 cells infiltrate tissue (chronic) -> release cytokines (IL-4, IL-5 & IL-13)
• Treatments

  Adrenaline -> bind to adrenergic receptors (esp. b2 on bronchial smooth muscle) -> bronchodilation & prevents asphyxia (complete lack of O2)

  Chlorphenamine -> H1 receptor antagonist (SC, IM or IV) -> provides relief of itching & swelling

  Hydrocortisone -> corticosteroid -> suppresses inflammatory response -> reduces inflammation in later phase & reduces chance of subsequent severe reaction (e.g. anaphylaxis)
• What are the signs & symptoms of allergy?

  Itching

  Swelling

  Airway constriction

  Pulse & BP changes (in anaphylaxis, systemic vasodilation & increased vascular permeability -> hypovolaemic shock)