Incompatible blood transfusions are examples of which type of hypersensitivity?

Incompatible blood transfusions are examples of which type of hypersensitivity?

• A. Type I.
• B. Type II.
• C. Type III.
• D. Type IV.

Answer: (B)

This item tests antibody-mediated cytotoxic hypersensitivity, where antibodies bound to cell-surface antigens trigger destruction of the target cells. In an incompatible blood transfusion, the recipient has antibodies (usually IgG or IgM) against donor red blood cell antigens such as ABO antigens. When these antibodies bind the donor RBCs, they activate complement and promote opsonization, leading to rapid destruction of the donor red cells—either directly by complement in the bloodstream or by phagocytosis in the spleen. This direct attack on cells by antibodies is the defining feature of Type II hypersensitivity. Type I involves IgE-mediated allergic reactions with mast cell degranulation; Type III involves immune complex deposition in tissues causing inflammation; Type IV is a delayed, T-cell–mediated reaction.

This item tests antibody-mediated cytotoxic hypersensitivity, where antibodies bound to cell-surface antigens trigger destruction of the target cells. In an incompatible blood transfusion, the recipient has antibodies (usually IgG or IgM) against donor red blood cell antigens such as ABO antigens. When these antibodies bind the donor RBCs, they activate complement and promote opsonization, leading to rapid destruction of the donor red cells—either directly by complement in the bloodstream or by phagocytosis in the spleen. This direct attack on cells by antibodies is the defining feature of Type II hypersensitivity.

Type I involves IgE-mediated allergic reactions with mast cell degranulation; Type III involves immune complex deposition in tissues causing inflammation; Type IV is a delayed, T-cell–mediated reaction.