An analysis of thymic function and the possible role of the thymus in stem cell production

The thymus is considered to be essentially an organ of the immune system, its purpose being to supply T cells. The role of the T cell is to regulate the immune reaction which it does by liberating lymphokines. The lymphokine function of the T cells was not deciphered in vivo, but in explanted T cells, and it is debatable if explanted cells behave in the same way as their counterparts in the intact animal, so the liberated lymphokines may not represent nature's intent. Adding to the disquiet are those biological properties of the thymus which are difficult to explain on an immunological basis, in particular why the thymus is essential in the child but not in the adult. Thus, there is room for a different approach to the role of the thymus. There is sound evidence that the thymus plays a part in somatic growth and differentiation, and one explanation is that the thymus provides the stem cells for somatic growth. A stem cell role is supported by studies on mastopoiesis and eosinophilopoiesis, and also supported by the way embryonic organs grow after their initial development. From the arguments put forward, the hypothesis is put that the role of the thymus is to store and propagate the stem cells required for the organ growth which takes place subsequent to their initial development. If the thymus is a repository for stem cells, the varied aspects of thymic behaviour, including its role in immunity, can be explained.(ABSTRACT TRUNCATED AT 250 WORDS)