Giant cell arteritis is best described as which type of hypersensitivity?

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

Answer: (A)

Giant cell arteritis is driven by cell-mediated immunity, not antibodies. It shows granulomatous inflammation with multinucleated giant cells in the walls of large arteries, especially the branches of the carotid. This pattern arises from a delayed-type hypersensitivity reaction: CD4+ T cells recognize antigens in the vessel wall, secrete cytokines such as IFN-γ, recruit and activate macrophages, and form granulomas. Because antibodies or immune complex deposition are not the primary injury mechanism here, this is not Type I, II, or III hypersensitivity. Clinically, patients have headaches and risk of vision changes, and biopsy reveals granulomatous inflammation with giant cells; corticosteroids are the standard treatment.