Thymic hormones markers

It is probably unfair to expect that any single thymic polypeptide should have the capability of inducing the full maturation of precursor stem cells into mature functional T lymphocytes. It is perhaps more appropriate to hypothesize that the variety of well-defined thymic polypeptides act sequentially in the thymus to promote selected steps of T-cell differentiation similar to the sequential interactions seen in the complement and coagulation cas-case systems. Thus, the most informative studies concerning the mechanisms of thymic hormone actions are those that have employed prethymic precursor cells or thymocytes and specific assays to detect the influences of the preparation on various intracellular enzymes or cell surface markers that reflect the state of differentiation of the cell. A detailed schematic representation of the different steps in T cell differentiation (in man) was shown in Fig. 10 earlier in this chapter. Figure 10 has been generated from studies performed with both murine and human thymic precursor cells, and on the basis of such studies the hypothesized sites of actions of each of the well-characterized thymic factors are indicated. It would appear from the currently available information that some thymic factors (such as thymosin P3... 

The cause of the T-cell depletion in peripheral blood is not certain. In preliminary unpublished studies Chandra and we (Keusch, Urrutia, Goldstein) have found that thymic hormones will induce the sheep erythrocyte rosette marker in vitro in PEM children with severely depressed T-cell numbers. There is also a suggestion of decreases in the level of circulating thymic hormone. However, the relevance of these findings to the process of T-cell maturation in PEM is uncertain, since the critical events undoubtedly take place within the thymic micro-environment itself and not in the periphery. However, Beatty and Dowdle (1978) have recently demonstrated that mitogenic responses of normal peripheral lymphocytes are suppressed in serum from Kwashiorkor patients compared to normal AB serum.. 

---