Biologically active mouse IL-12 is a disulfide-linked, 70 kDa (p70) heterodimeric glycoprotein that is composed of a 40 kDa (p40) subunit and a 35 kDa (p35) subunit. The IL-12 p40 subunit is shared by IL-23, another heterodimeric cytokine which belongs to the IL-12 cytokine family. IL-12 and IL-23 are important immunoregulatory molecules. They share overlapping but distinct biological activities, which promote cell-mediated immunity. Interleukin-12 (IL-12) is a heterodimeric pleiotropic cytokine that is primarily produced by monocytes, macrophages, and dendritic cells in response to bacterial lipopolysaccharides (LPS), to intracellular pathogens, and to activated T cells. IL-23 is an important part of the inflammatory response against infection. IL-23 promotes up-regulation of the matrix metalloprotease MMP9, increases angiogenesis and reduces CD8+ T cell infiltration. In addition to being secreted as a component of IL-12 or IL-23, free p40 monomers and homodimers are also secreted.This ELISA kit specifically measures the mouse p40 subunit in IL-12 p70, IL-23, p40 homodimer, and p40 monomer.