Thymosin hormones are typically produced by the thymus gland and trigger the creation of T-cells, which are used by the immune system to fight disease. There are different classifications of thymosins, and it is believed that not all thymosins are produced by the thymus.
The thymus gland has a limited time frame in which T-cell production occurs. Once puberty occurs in a human, a normal thymus has created the T-cells needed by the body and begins to shrink, eventually being replaced by fatty tissue. Though it is not needed for T-cell production after puberty, the thymus serves a necessary role in the endocrine and lymphatic systems as aging occurs.