Thymus is known as "throne of immunity" because it is the site of maturation of T-lymphocytes. Thymosin is the hormone produced by the thymus gland. Its job is to nurture the lymphocytes, which is a type of white blood cell that plays an important and integral role in the body's defenses. It promotes proliferation and maturation of T-lymphocytes. If one gets severe dose of radiation, enough to knock down the immune system, thymosin must be life saver, stimulating the spleen and the other organs that had shut down to get back into reproduction.