Type II: cytotoxic reactions. Cytotoxic reactions involve the binding of either IgG or IgM antibody to cell-bound antigens. Antigen–antibody binding results in activation of the complement cascade and the destruction of the cell to which the antigen is bound. Examples of tissue injury by this mechanism include immune hemolytic anemia and Rh hemolytic disease in the newborn. Diseases such as autoimmune hyperthyroidism in which thyroid-stimulating antibodies stimulate the thyroid tissue, or thyroid-stimulating hormone (TSH)-binding inhibitory antibodies inhibit the binding of TSH to its receptor; or myasthenia gravis in which antibodies are directed to the acetylcholine receptor blocking this neuromediator from interacting with its receptor are also type II reactions. In this latter group of diseases, cytolysis is not a component of these reactions.
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