The thymus produces types of white blood cells called "T-lymphocytes," which help fight infection. This gland functions primarily in infancy and childhood to help build up the immune system. After puberty, the thymus gradually shrinks, reaching only about 15% of its maximum size by middle age.
While the thymus is extremely important to the developing immune system in children, having a thymectomy (surgical removal of the thymus gland) as an adult does not increase your chance of developing autoimmune diseases. If you have a thymus gland tumor or myasthenia gravis, your doctor may recommend a thymectomy.