IL-12B is a subunit of interleukin 12, a cytokine that acts on T and natural killer cells, and has a broad array of biological activities. Interleukin 12 is a disulfide-linked heterodimer composed of the 40 kD IL-12B, and the 35 kD subunit IL-12A. IL-12 is expressed by activated macrophages that serve as an essential inducer of Th1 cells development, and has been found to be important for sustaining a sufficient number of memory/effector Th1 cells to mediate long-term protection to an intracellular pathogen. [provided by RefSeq, Jul 2008, taken from NCBI Entrez Gene (Gene ID: 3593)].