In autoimmune hemolytic anemia of the IgG-mediated type II hypersensitivity, what is the general mechanism?

• A. Immune complex deposition
• B. T cell–mediated cytotoxicity
• C. Antibody-mediated destruction of target cells
• D. Delayed-type hypersensitivity

Answer: (C)

Antibody-mediated destruction of target cells is the hallmark of this mechanism. In IgG-mediated type II hypersensitivity, autoantibodies bind to antigens on the surface of red blood cells. This tagging recruits effector systems: macrophages with Fc receptors recognize the Fc portion of the bound IgG and phagocytose the coated RBCs (extravascular hemolysis). Complement can also be activated, causing intravascular lysis in some cases. So the process is antibodies guiding the immune system to destroy the body's own red blood cells.

Immune complex deposition would involve circulating antigen–antibody complexes (type III), T cell–mediated cytotoxicity describes cytotoxic T cells (type IV), and delayed-type hypersensitivity is also type IV.