Question

Which of the following step is not a part of hypersensitivity type IV reaction?

• A. Sensitization
• B. Antigen presentation
• C. Phagocytosis
• D. All of the above

Answer 1

Answer: (D)

All of the above

Type IV hypersensitivity also called delayed type hypersensitivity is a type of cell-mediated response. CD4+ helper T cells recognize antigen in a complex with Class II major histocompatibility complex. The antigen-presenting cells are macrophages that secrete IL-12. IL-12 stimulates the proliferation of CD4+ T helper cells. These cells secrete IL-2 and interferon gamma, further inducing the release of other Th cytokines, hence mediating the immune response. Activated CD8+ T killer cells then destroy target cells on contact. Hence sensitization, antigen presentation or phagocytosis are not seen in hypersensitivity type IV reaction. Thus the correct answer is option D.