# The Thymus Gland --- The **thymus gland** is an [[endocrine gland]] that secretes some stuff. - secretes hormone (thymosin, thymopoietin) that cause t-lymphocytes to become immunocompetent - size varies with age, it gets smaller and smaller as we age - it functions strictly in [[T-cells|T-cell]] maturation - it does not directly fight antigens **Positive selection and negative selection** *do* recognize MHC II *do not* recognize self-antigen If they survive (only about 2% live!) they lose either their CD4 or CD8 and are now *immunocompetent* but *naïve*. ___