Hypersensitivity Reactions: Cytolytic Reactions

Type II hypersensitivity, or cytolytic reactions, involves IgG and IgM antibodies binding to antigens present on the surface of host cells. This binding can trigger the complement system or recruit cytotoxic cells, ultimately resulting in targeted cell death.

In some cases, the antibodies can also tag the cell for clearance through opsonization—a process where opsonins like IgG mark targets to be recognized by phagocytes. The phagocytes then engulf and digest the marked cells.

A classic example of this type of hypersensitivity is hemolytic anemia induced by penicillin. In this condition, the drug binds to red blood cells, forming a drug–protein complex. Antibodies bind to these drug–protein complexes, activating complement components and causing lysis of the RBCs.