IL12B (Interleukin 12B): IL12B is a gene that encodes the p40 subunit of interleukin-12 (IL-12), a cytokine involved in immune responses. IL-12 plays a key role in activating the immune system by promoting the production of interferon-gamma (IFN-Îł) and stimulating the activity of T cells and natural killer (NK) cells to fight infections and tumors.