AN ANALYSIS OF THYMIC FUNCTION AND THE POSSIBLE POLE OF THE THYMUS INSTEM-CELL PRODUCTION

The thymus is considered to be essentially an organ of the immune syst em, 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 i n the same way as their counterparts in the intact animal, so the libe rated lymphokines may not represent nature's intent. Adding to the dis quiet are those biological properties of the thymus which are difficul t to explain on an immunological basis, in particular why the thymus i s 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 eviden ce that the thymus plays a part in somatic growth and differentiation, and one explanation is that the thymus provides the stem cells for so matic growth. A stem cell role is supported by studies on mastopoiesis and eosinophilopoiesis, and also supported by the way embryonic organ s grow after their initial development. From the arguments put forward , the hypothesis is put that the role of the thymus is to store and pr opagate the stem cells required for the organ growth which takes place subsequent to their initial development. If the thymus is a repositor y for stem cells, the varied aspects of thymic behaviour, including it s role in immunity, can be explained. In particular, the hypothesis ex plains that aspect which is most mysterious, and that is why the thymu s is essential in the child but not in the adult.