Interleukin-12, p70 (IL-12 p70) is a disulfide-linked heterodimeric 70-kDa cytokine composed of a 197 amino acid 35-kDA (p35) subunit and a 306 amino acid 40-kDa (p40) subunit. It is naturally produced by dendritic cells, macrophages and human B-lymphoblastoid cells in response to antigenic stimulation. IL-12 stimulates growth and function of T cells, production of interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) from T cells and natural killer (NK) cells, and reduces IL-4-mediated suppression of IFN-γ. IL-12 has been reported to be associated with autoimmune and inflammatory conditions. Increased IL-12 plasma levels may also be detected in patients with neurological disorders such as multiple sclerosis.