ABSTRACT: The immune system is spread throughout the body and involves many types of cells, organs, proteins, and tissues. Crucially, it can distinguish our tissue from foreign tissue — self from nonself. Dead and faulty cells are also recognized and cleared away by the immune system.If the immune system encounters a pathogen, for instance, a bacterium, virus, or parasite, it mounts a socalled immune response.The immune system includes a range of cell types with different roles in defending the body against infection.Occasionally, the immune system can make a mistake and attack itself, resulting in autoimmune disorders. Many of these cells arise in the bone marrow, circulate in the blood and can migrate into solid tissues1 . The primary parts of the immune system include the bone marrow and thymus. The bone marrow is extremely important to the immune system because all the body’s blood cells (including T and B lymphocytes) originate in the bone marrow. B lymphocytes remain in the marrow to mature, while T lymphocytes travel to the thymus. Immune responses involve interactions between some of these cells and/or their secreted products. B and T lymphocytes specifically react to microbial antigens: activated B lymphocytes secrete antigen‐binding antibodies, and subpopulations of T lymphocytes possess regulatory or cytotoxic functions2