IL-12 (Interleukin-12) is a secreted heterodimeric cytokine that contains disulfide-linked p35 and p40 subunits. The p40 subunit is also a subunit of the heterodimeric IL-23. IL-12 is produced by macrophages, dendritic cells, monocytes, Langerhans cells, neutrophils, keratinocytes, microglia, and non-germinal center B cells. It acts through a receptor complex that contains the ligand binding IL-12 R alpha 1 and the signal transducing IL-12 R alpha 2. IL-12 can enhance cytotoxic activity and induce Interferon-gamma production in NK cells, T cells and dendritic epidermal T cells. In conjunction with IL-23 and IL-27, IL-12 promotes the development of a Th1 immune response.