type IIa hypersensitivity An inflammatory response resulting in cell death mediated by activation of the classical complement pathway or induction of effector cell phagocytosis or cytolysis mechanisms via complement or Fc receptors following the binding of antibodies to cell surface antigens on a target cell. GO:0001794 biological_process Note that some type IIb hypersensitivity responses (GO:0001795) are referred to simply as type II hypersensitivity in the earlier literature, but are mechanistically distinct from type IIa hypersensitivity. type II hypersensitivity