Interleukin-12 (IL12) is also known as natural killer cell stimulatory factor (NKSF), cytotoxic lymphocyte maturation factor (CLMF) , is a heterodimeric cytokine encoded by two separate genes, IL-12A (p35) and IL-12B (p40). IL12 is naturally produced by dendritic cells, macrophages and human B-lymphoblastoid cells (NC-37) in response to antigenic stimulation. IL-12 is involved in the differentiation of naive T cells into Th0 cells and plays an important role in the activities of natural killer cells and T lymphocytes.IL-12 also has anti-angiogenic activity, which means it can block the formation of new blood vessels. Interleukin-12 subunit alpha (IL12A) also known as NKSF1, CLMF1 and P35, IL12A shows significant sequence similarity to IL-6, G-CSF, and exerts biological activities only when the IL12B is co-expressed. IL12B deficient mice are resistant to the induction of experimental chronic inflammatory diseases whereas IL12A knock-out mice develop more severe forms, suggesting opposite functions of the two subunits in the outcome of chronic inflammatory diseases.