The MaxDiscovery™ Human IL-23p19/p40 ELISA Test Kit is designed for quantitative determination of the concentration of human IL-23p19/p40, without interference by IL-12p70, p40 monomer, or p19 monomer in serum, plasma, and cell culture supernatant. Human interleukin 23 (IL-23) is a heterodimeric cytokine composed of the p40 subunit of IL-12 disulfide-linked with a protein p19. p19, like p35 of IL-12, is biologically inactive by itself. IL-23 interacts with IL-12Rß1 and an additional, novel ß2-like receptor subunit with STAT4 binding domain, termed IL-23R. IL-23 is secreted by activated dendritic cells. Human IL-23 has biological properties which are less distinct from human IL-12; human IL-23 induces proliferation of memory T cells and induces moderate levels of IFN-? production by naïve and memory T cells, as compared to IL-12. IL-23-dependent, IL-17-producing CD4+ T cells (Th-17 cells) have been identified as a unique subset of Th cells that develops along a pathway that is distinct from the Th1- and Th2- cell differentiation pathways. The hallmark effector molecules of Th1 and Th2 cells, e.g., IFN-? and IL-4, have each been found to negatively regulate the generation of these Th-17 cells. More recently, de novo differentiation of Th-17 cells in the absence of IL-23 has been demonstrated by treatment of naïve CD4 cells with TGF-ß1 and IL-6.