人体胸腺位于胸骨后部,分左右二叶。在胚胎期开始发育,到青春期就开始衰退,25～45岁间降得很快,45岁以后已逐渐消失,并为脂肪组织所代替。在60年代以前,一般认为胸腺是一个退行性器官,有如阑尾一样,因此没有引起足够的重视。60年代以后,由于免疫学的长足发展,人们对胸腺逐渐有所认识,目前认为胸腺是免疫的中枢器官之一。朐腺之所以重要,是因为能产生一族蛋白质和多肽的激素,称为胸腺激素(Thymosin 简称胸腺素)。它能使在骨髓中不具有免疫活性的淋巴干细胞,一部分进入胸腺后,经过与胸腺细胞的相互作用以及受胸腺素的刺激,分化成为具有细胞免疫活性的淋巴细胞,故称“T”淋巴细胞(胸腺依赖性淋巴细胞)。近年来,由于分子生物学的发展,对于胸腺素的结构、氨基酸的数目和排列顺序均已研究得比较详细,并可人工合成。现已了解到胸腺素的活性在第29～41号13个氨基酸所组成的 The human thymus is located in the back of the sternum, divided into two leaves. Beginning in the embryonic development, began to decline during adolescence, 25 to 45 years old dropped very fast, after 45 years of age has gradually disappeared, and replaced by fatty tissue. Before the 1960s, the thymus was generally considered a degenerative organ, appearing as an appendix, and therefore did not attract enough attention. Since the 1960s, due to the rapid development of immunology, people have gradually become aware of the thymus, and the thymus is currently considered as one of the central organs of immunity. The reason why the glandular gland is important is that it produces a family of hormones for proteins and peptides called thymosin (Thymosin). It can make non-immunocompetent lymphoid stem cells in the bone marrow, part of which enters the thymus and then differentiates into lymphocytes with cellular immunity through the interaction with thymocytes and thymosin, so called “T” lymphocytes (Thymus-dependent lymphocytes). In recent years, due to the development of molecular biology, the structure of thymosin, the number of amino acids and the order of the array have been studied in more detail and can be synthesized. It is now known that the activity of thymosin is composed of 13 amino acids at No. 29 to No. 41