Myasthenia gravis is best classified as which type of hypersensitivity?

• A. Type II hypersensitivity (cytotoxic)
• B. Type I hypersensitivity
• C. Type III hypersensitivity
• D. Type IV hypersensitivity

Answer: (A)

Myasthenia gravis is driven by autoantibodies against a muscle cell surface receptor on the postsynaptic membrane of the neuromuscular junction. This makes it an antibody-mediated cytotoxic process—the hallmark of Type II hypersensitivity. The antibodies bind the acetylcholine receptors, blocking acetylcholine binding, promoting receptor cross-linking and internalization, and activating complement to damage or destroy the receptors. With fewer functional receptors, the end-plate potential is insufficient to trigger reliable muscle contraction, especially with repeated use, leading to the characteristic fatigable weakness.

Other hypersensitivity types involve different mechanisms (Type I is IgE-mediated and allergic, Type III involves immune complex deposition, and Type IV is T-cell–mediated delayed responses), none of which describe the receptor-targeted, antibody-driven dysfunction seen in MG. Some MG cases involve antibodies to MuSK, but the pathogenic mechanism remains antibody-mediated disruption at the NMJ, still aligning with Type II characteristics.