The interleukins (ILs) are a broad family of well characterized cytokines, primarily of hematopoietic cell origin. As new cytokines are molecularly characterized, they are assigned an IL number to maintain a standard nomenclature. ILs are secreted by immune cells that regulate a wide range of immune system functions. IL-12 is secreted by macrophages and human B-lymphoblastoid cells in response to antigenic stimulation. This IL is responsible for the differentiation of naive CD4+ T cells into type 1 helper T cells that produce interferon-gamma (IFN-gamma). It also activates production of tumor necrosis factor alpha (TNFalpha) from T and natural killer (NK) cells, and it inhibits IL-4 mediated suppression of IFN-gamma. IL-12 also has anti-angiogenic activity since the production of IFN-gamma increases the production of inducible protein-10 (IP-10). IL-12 p40 represents a subunit of IL-12 that is induced by several pathogens. IL-12 p70 is a subunit of IL-12 that is controlled through both the p35 and p40 genes in a cell type-specific fashion.Synonyms: CLMF p40, Cytotoxic lymphocyte maturation factor 40 kDa subunit, IL-12 subunit p40, IL-12B, Interleukin-12B, NK cell stimulatory factor chain 2, NKSF2