Interleukin 12 (IL-12) is a pro-inflammatory cytokine with a molecular weight of 70 kDa composed of two subunits, IL-12 p35 (35 kDa) and IL-12 p40 (40 kDa), and IL-12 p35 as a p35-p35 homo-dimer with 57?kDa molecular weight and a p35 monomer of 27?kDa molecular weight. The p35 molecule is unique to IL-12, while p40 is shared by both IL-12 and IL-23. IL-12 promotes Th1 T cell responses, while IL-23 promotes Th17 T cell responses.