M1 macrophages mediate inflammatory responses to a variety of bacterial, protozoal and viral infections and produce many inflammatory cytokines, including TNF, IL-18, IL-12 and IL-23, which mediate immune reactions in several chronic inflammatory and autoimmune diseases, including rheumatoid arthritis, Crohn’s disease, multiple sclerosis and autoimmune hepatitis [40–42]. The gene discussed is IL18; the disease is Crohn disease.