What are common symptoms of Type IV hypersensitivity?

• A. Edema, induration, ischemia, tissue damage at the exposure site
• B. Urticaria
• C. Anaphylaxis
• D. Serum sickness

Answer: (A)

Type IV hypersensitivity is a delayed, cell-mediated immune response driven by T cells and macrophages rather than antibodies. After exposure, sensitized T cells release cytokines that recruit and activate macrophages, producing a localized inflammatory environment that grows over 1–3 days.

The symptoms at the exposure site fit this pattern: edema from increased vascular permeability, induration from the dense cellular infiltrate, and tissue damage from activated macrophages and the inflammatory milieu. In severe cases, inflammation can compromise local blood flow, leading to ischemia and further tissue injury. This contrasts with antibody-mediated or immune complex reactions seen in other hypersensitivity types.

Urticaria, anaphylaxis, and serum sickness reflect other pathways: urticaria and anaphylaxis are typical of immediate, IgE-mediated (Type I) responses, while serum sickness involves immune complex deposition (Type III).