Which of the following best describes the role of antibodies in type II hypersensitivity reactions?

• A. Cellular antigens
• B. Immune complexes
• C. IgE-mediated mast cell activation
• D. T-cell mediated cytotoxicity

Answer: (A)

In type II hypersensitivity, antibodies (usually IgG or IgM) mediate effects by binding to antigens present on the surface of cells or in the extracellular matrix. This antibody binding flags the target for destruction or dysfunction through mechanisms like complement activation, opsonization with phagocytosis, or interference with receptor signaling. Because the antibodies are directed against cellular antigens, describing their role as targeting cellular antigens best captures the key action in this type of reaction.

For context, immune complexes drive a different mechanism (type III), IgE with mast cells triggers an immediate type I reaction, and cytotoxic T cells mediate type IV hypersensitivity. Examples of type II include autoimmune hemolytic anemia, Goodpasture syndrome, and myasthenia gravis, where antibodies against cell-surface components lead to cell damage or altered function.