Information about different types of Hypersensitivity

Types of Hypersensitivity

Type I

  • It is immediate type of Hypersensitivity
  • Immune reactant is IgE
  • Antigen form is Soluble antigen
  • Initiation time is 2-30 minutes
  • Mechanism of activation: Allergen- specific IgE Ab Bind to mast cells via their Fc receptor. When specific allergen bind to IgE, cross linking of IgE induces degranulation of mast cells
  • Example;
    • Food allergies like;
    • peanuts
    • egg
    • fish

Type II

  • Immune reactant is IgG or IgM
  • Antigen form is Cell bound antigen
  • Initiation time is 5-8 hours
  • Mechanism of activation: IgG or IgM Ab Bind to cellular antigen, leading to compliment activation and cell lysis. IgG also mediate ADCC with cytotoxic T cells, NK cells, macrophage and neutrophils
  • Example;
    • Erythroblastosis foetalis

Type III

  • Immune reactant is IgG or IgM
  • Antigen form is Soluble antigen
  • Initiation time is 2-8 hours
  • Mechanism of activation: Ag – Ab Complexes are deposited in tissues. Compliment activation provides inflammatory mediators and recruits neutrophils. Enzymes released from neutrophils damage tissue
  • Example;
    • Arthus reaction,
    • Serum Sickness,
    • Blue eye condition in dog

Type IV

  • It is Delayed Type Hypersensitivity
  • Immune reactant is T-cell
  • Antigen form is Soluble or cell bound antigen
  • Initiation time is 24-72 hours
  • Mechanism of activation: TH1 cells secrete cytokines, which activate macrophage and cytotoxic T cells
  • Examples;
    • Tuberculin test (Diagnosis of tuberculosis)
    • Johnin test (Diagnosis of Johnes disease)
    • Mallein test (Diagnosis of glander)
    • Brucellin test (Diagnosis of Brucellosis)
    • Mantoux test (Diagnosis of tuberculosis)

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