Human thymoma lymphocyte mitogenesis: glucocorticoid inhibitory capacity as a function of the size of the more mature T cell subset.

The relationship between the expression of T3 and T6 antigens and the capacity to respond to phytohaemagglutinin (PHA) has been studied in the lymphocyte component of nine human thymomas. It appears that there is a positive correlation between the mitogen responsiveness of thymoma lymphocytes and the relative proportion of T3 positive (T3+), T6 negative (T6-), peanut receptor negative and IgM-Fc receptor positive cells. Moreover we have comparatively investigated the dexamethasone (Dex) inhibitory effect on the mitogenesis of T lymphocytes from thymoma, normal thymus and peripheral blood. In the presence of the macrophage product interleukin 1, the capacity of Dex to inhibit the mitogenesis of peripheral blood purified T cells (PBT) is inversely correlated with the PHA concentration used. Conversely, Dex completely (greater than 90%) inhibits thymocyte mitogenesis irrespective of PHA concentration. The entity of Dex inhibitory effect on thymoma lymphocyte mitogenesis shows a great variability ranging between that observed in normal thymocytes and that observed in PBT. In each thymoma case the degree of inhibition appears to be dependent on the size of the more mature thymocyte pool being positively correlated with the number of T6+ but negatively with that of T3+ cells. Our data demonstrate a high degree of variability among thymomas relative to the phenotypic and functional properties of their lymphocytic component. On the other hand, in some thymomas the phenotypic and functional characteristics of lymphocyte component seem to represent only a narrow span of normal thymocyte maturative pathway. In this respect, human thymoma may constitute a profitable tool for studying the intrathymic T lymphocyte maturative steps.