Interleukin 12 （IL-12） is an interleukin that is naturally produced by dendritic cells, macrophages, neutrophils, and human B-lymphoblastoid cells （NC-37） in response to antigenic stimulation. IL-12 belongs to the family of interleukin-12. IL-12 family is unique in comprising the only heterodimeric cytokines, which includes IL-12, IL-23, IL-27 and IL-35. Despite sharing many structural features and molecular partners, they mediate surprisingly diverse functional effects. IL-12 is involved in the differentiation of naive T cells into Th1 cells and plays an important role in the activities of natural killer cells and T lymphocytes.