IL-12 (Interleukin-12) is a heterodimeric cytokine that consists of a p35 and a p40 subunit. p40 is also a subunit of the cytokine IL-23. IL-12 enhances the cytotoxic activity and induces IFN-gamma production in NK cells, T cells, and dendritic epidermal T cells, and it promotes a Th1 biased immune response. It signals through a receptor complex composed of IL-12 R beta 1 and IL-12 R beta 2. Both homodimeric p40, and IL-23 can bind to the IL-12 receptor, serving as non-signaling antagonists.