This monoclonal antibody recognizes human IL-23, a heterodimeric cytokine composed of the p40 subunit shared with IL-12 and a specific p19 subunit. This antibody recognizes heterodimeric IL-23, but does not react with the p40 subunit alone or recombinant IL-12(p70) when used as a capture antibody in ELISA. IL-23 is secreted by activated dendritic cells and macrophages and has been shown to enhance IFN-y secretion by memory (CD45RO) T cells in an IL-2 dependent manner. IL-23 may also induce unique Th subset (designated ThIL-17) that secretes the cytokines IL-17, IL-6, TNF and low levels of IFN-y. IL-23 has been shown to promote immunity to mycobacteria and has been shown to be upregulated in response to some viral infections and in psoriatic lesions. IL-23 binds to the IL-23 receptor comprised of a B1 subunit shared with the IL-12 receptor and IL-23-specific subunit.