The correct option is B T killer cell
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. Thus the correct answer is option B.