Gell and Coombs classification of immune reactions

In allergy and immunology, as well as a broader range of medical conditions, the Gell and Coombs classification of immune reactions is widely used to categorized specific disorders into four useful categories. It has been improved, however, into subtypes and an additional type has been added.

• Type I, anaphylactic hypersensitivity reactions, mediated by interaction of Immunoglobin E (IgE) antibody and antigen and release of histamine and other inflammatory cytokines; it also can involve mast cells, basophils and mediators that induce muscle contraction
• type II, antibody-mediated hypersensitivity reactions or cytotoxic hypersensitivity reactions, due to antibody-antigen interactions on cell surfaces; host cells are destroyed
• type III, immune complex hypersensitivity reactions, which are local or general inflammatory responses due to formation of circulating immune complexes and their deposition in tissues
• type IV, cell-mediated hypersensitivity reactions, also delayed hypersensivity reaction or cell mediated immunity, initiated by sensitized T-lymphocytes either by their releasing lymphokines or by T-cell–mediated cytotoxicity; modulators here include leukotrienes.

Immediate hypersensitivity reaction encompasses types I-III, while Type IV is the delayed hypersensitivity reaction.