Interleukin-12 (IL-12), also known as NKSF, TCMF, CLMF and TSF, is a heterodimeric cytokine composed of p35 and p40 subunits. It is produced by monocytes, macrophages, B cells and dendritic cells in response to bacterial lipopolysaccharides and intracellular pathogens. IL-12 signals throughtheIL-12 receptor complex, which is comprised of IL-12 Rß1 and IL-12 Rß2. IL-12 induces the proliferation and activation of hematopoietic stem cells, natural killer cells and T- cells. It is indispensible during the development of Th1 cells, leading to the production of IFN-gamma and IL-2.