Interleukin 12 (IL-12), also known as natural killer cell stimulatory factor (NKSF) or cytotoxic lymphocyte maturation factor (CLMF), is a heterodimeric pleiotropic cytokine made up of a 40 kDa (p40) subunit and a 35 kDa (p35) subunit. The IL-12 p40 subunit is shared by IL-23, another heterodimeric cytokine that has biological activities similar to, as well as distinct from, IL-12.
IL-12 is produced by macrophages and B cells and has been shown to have multiple effects on T cells and natural killer (NK) cells. IL-12 is involved in the differentiation of naive T cells into Th1 cells. It is known as a T cell-stimulating factor, which can stimulate the growth and function of T cells. IL-12 has anti-angiogenic activity and is linked with autoimmunity as well.