|IL12 (p70) is a disulfide-linked heterodimer composed of unrelated p40 (glycosylated) and p35 subunits. IL-12 acts as a growth factor for activated human T and NK cells, enhances the lytic activity of human NK cells, and stimulates the production of IFNg by resting human PBMC. IL-12R is formed by two chains, IL-12Rβ1 and IL-12Rβ2. IL-12Rβ1 is associated with the Janus kinase (Jak) Tyk2 and binds IL-12 p40; IL-12Rβ2 is associated with Jak2 and binds either the heterodimer or the p35 chain. Signaling through the IL-12 receptor complex induces phosphorylation, dimerization, and nuclear translocation of several signal transducers and activators of transcription (STAT) family members (STAT1, 3, 4, 5), but most of the biological responses to IL-12 have been attributed to STAT4. IL-12 has been shown to elicit anti-tumor activity in mice and humans. It is believed that the antitumor effects of IL-12 are mediated, at least in part, by indirect mechanisms. Induction of IFN-γ results in the upregulation of class I and class II MHC molecules, adhesion molecules (ICAM-1), nitric oxide production by antigen presenting cells (APC), and the production of additional cytokines, CXCL9 and 10, which in turn mediate angiostatic effects; Cytokine detection: IL-12, IL-23 and IL-35 share common subunits, utilizing combinations of p40, p19 and p35 proteins. Caution must be used when selecting antibodies and assays when specific identification, measurement, as well as activation state discrimination, is required. 1. Active IL-12 consists of two subunits: p40 + p35. 2. p40 can also exist as a monomer (IL-12 p40) or a homodimer (IL-12 p80). 3. Besides contributing to IL-12, p40 is also found in IL-23, a heterodimer of p40 and p19. 4. Similarly, p35 not only contributes to IL-12, but is also found in the heterodimer IL-35 (p35 and EBI3). Note that assays using antibodies specific for the p40 subunit will be unable to discriminate between the active IL-12, monomeric p40, dimeric p40, and IL-23; likewise, assays using p35 detection alone will pick up both IL-12 (heterodimer) and IL-35.