A heterodimeric cytokine that plays a role in innate and adaptive immune responses. interleukin-12 is a 70 kDa protein that is composed of covalently linked 40 kDa and 35 kDa subunits. It is produced by dendritic cells; macrophages and a variety of other immune cells and plays a role in the stimulation of interferon-gamma production by t-lymphocytes and NATURAL KILLER CELLS.