An infiltrate composed of helper T cells and macrophages
DTH is type 4, which involves Tcells, macrophages IFN-g and TNF-a
Type IV hypersensitivity is often called Delayed Type Hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response.
CD4+ helper T cells recognize antigen in a complex with either type 1 or 2 major histocompatibility complex. The antigen-presenting cells in this case are macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ T cells. CD4+ T cells secrete IL-2 and interferon gamma, further inducing the release of other Type 1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.