Which type of hypersensitivity is T cell–mediated delayed-type hypersensitivity with no antibodies?

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

Answer: (A)

This is Type IV hypersensitivity, the delayed-type hypersensitivity that is driven by T cells rather than antibodies. When a person first encounters the antigen, sensitized T cells—especially Th1 cells—respond by releasing cytokines that activate macrophages and recruit other immune cells to the site. This creates local inflammation and tissue damage that develops over 24 to 72 hours, hence the delay. Because antibodies are not required for this reaction, it fits the antibody-independent, T cell–mediated pattern of Type IV.

Examples you might recognize include the tuberculin skin test and contact dermatitis from certain metals or plant chemicals, where the reaction occurs in the skin due to memory T cells recognizing the antigen.

In contrast, the other hypersensitivity types involve antibodies: Type I is an immediate IgE-mediated reaction with mast cell degranulation; Type II involves antibody-dependent cytotoxicity against target cells; Type III involves immune complex deposition and complement activation.