Myasthenia gravis involves autoantibodies that target components at the neuromuscular junction, representing which hypersensitivity class?

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

Answer: (C)

Autoantibodies against a cell-surface receptor at the neuromuscular junction mediate the injury in myasthenia gravis, which is characteristic of a Type II hypersensitivity. In this disease, IgG antibodies target the postsynaptic nicotinic acetylcholine receptors, blocking signaling and triggering complement-mediated damage that lowers receptor numbers. The result is impaired neuromuscular transmission and muscle weakness. Type II hypersensitivity involves antibodies directed at cell-surface or extracellular antigens with effector mechanisms like complement activation or receptor loss. This contrasts with Type I (IgE-mediated allergic responses), Type III (immune complex–mediated deposition), and Type IV (T-cell–mediated) responses.