Hypersensitivity Reactions

The Gell and Coombs classification divides hypersensitivity reactions into 4 types:

Type I - Anaphylactic or immediate

• antigen + cell surface IgE on mast cells and basophils (mediated by IL-2)
• anaphylaxis, atopy (e.g. asthma, eczema and hayfever)

Type II - Antibody-dependent cytotoxicity

• Cell-bound antigen + circulating IgG or IgM
• autoimmune haemolytic anaemia, ITP, Goodpasture's, pernicious anemia, acute hemolytic transfusion reactions, rheumatic fever, bullous pemphigoid, pemphigus vulgaris; *Myasthenia gravis (d/t anti-receptor antibodies); the eosinophil-mediated cytotoxicity against parasites

Type III - Immune complex-mediated or Arthus reaction

• free antigen and antibody (IgG, IgA) combine
• serum sickness, systemic lupus erythematosus, post-streptococcal glomerulonephritis, extrinsic allergic alveolitis (especially acute phase)

Type IV - Cell-mediated or Delayed-type hypersensitivity

• Antigen (with class II MHC) + sensitized (memory) T cells
• tuberculosis, tuberculin skin reaction, graft versus host disease, allergic contact dermatitis, scabies, extrinsic allergic alveolitis (especially chronic phase), multiple sclerosis, Guillain-Barre syndrome

Type V - Stimulatory

• antibodies + cell surface receptors, either stimulating them or blocking ligand binding
• Graves' disease, myasthenia gravis

AEFI