Which hypersensitivity type is involved in myasthenia gravis?

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

Answer: (D)

Myasthenia gravis involves autoantibodies directed against a component on the surface of the neuromuscular junction, most often the acetylcholine receptor. These antibodies bind to the receptor, blocking acetylcholine signaling, promoting receptor internalization, and can activate complement to damage the postsynaptic membrane. The result is impaired transmission at the neuromuscular junction and fatigable weakness. This is the hallmark of an antibody-mediated process acting on cell-surface structures, which defines Type II hypersensitivity.

Other mechanisms in immunology differ in their usual patterns: Type I is IgE-driven allergic reactions, Type III involves immune complex deposition, and Type IV is T-cell–mediated delayed-type hypersensitivity. So the hypersensitivity type involved here is antibody-mediated cytotoxic or antibody-mediated dysfunction targeting a cell-surface receptor—Type II.