Hypersensitivity Type II: Cytotoxic and Cytolytic Reactions.
Cytotoxic and cytolytic reactions are type II hypersensitivity reactions involving the direct binding of IgG or IgM antibodies to an antigen on the cell surface.
Antigen-antibody complexes activate the com- plement system, which mediates the reaction. Cellular tissue is destroyed in one of two ways: (1) activation of the complement system resulting in cytolysis or (2) enhanced phagocytosis.
Target cells frequently destroyed in type II reactions are erythrocytes, platelets, and leukocytes. Some of the antigens involved are the ABO blood group, Rh factor, and drugs. Pathophysiologic disorders characteristic of type II reactions include ABO incompatibility transfusion reaction, Rh incompatibility transfusion reaction, autoimmune and drug-related hemolytic anemias, leukopenias, thrombocytopenias, erythroblastosis fetalis (hemolytic disease of the newborn), and Goodpasture syndrome.