Hypersensitivity Reactions: Cytolytic Reactions

Type II hypersensitivity involves IgG and IgM antibodies targeting cell surface antigens, leading to cell destruction. This can occur through complement activation, antibody-dependent cell-mediated cytotoxicity (ADCC), or acting as opsonins for phagocytosis. When excessive, these reactions cause significant tissue damage.

Drug-induced hemolytic anemia is a common example, where drugs like penicillin or cephalosporins bind to red blood cells, forming drug-protein complexes. These complexes trigger the formation of antibodies, leading to complement-mediated lysis of red blood cells and anemia. Withdrawal of the drug usually resolves the condition. Hemolytic anemia can also result from other drugs like methyldopa, used in hypertension, causing antibodies to target red blood cells, leading to their destruction. The Coombs test can detect this reaction, indicating the presence of antibodies against red blood cell surfaces.