A comparison of proliferative response to IL-7 and expression of IL-7 receptors in intermediate TCR cells of the liver, spleen, and thymus.

It is well established that IL-7 supports the earliest differentiation of both T and B cells in fetal and adult life. On the other hand, mature lymphocyte subsets tend to decrease the response to IL-7 in case of T and B cells. In a recent study, NK1.1+ T cells in the thymus are also found to efficiently respond to IL-7 and express IL-7 receptors (IL-7R). This population is generated through an alternative intrathymic pathway. A similar population, namely, T cells with intermediate levels of TCR (i.e., int TCR cells) are known to be generated through extrathymic pathways. In this respect, the proliferative response to IL-7 and the expression of IL-7R in int TCR cells of various organs were compared. Whole liver MNC and isolated int TCR cells from the liver were found to proliferate in response to IL-7. Moreover, a considerable population of int TCR cells in both the liver and thymus were found to carry a higher density of IL-7R on the surfaces than high TCR cells. More precisely, the intensity of IL-7R on int TCR cells in the thymus was the highest but those on int TCR cells in other organs were slightly lower (i.e., int TCR cells in the thymus greater than int TCR cells in the liver greater than high TCR cells). Taken together with the result of expression of IL-7 mRNA by hepatocytes and thymic tissues, it is concluded that IL-7 is one of the most important growth factors for int TCR cells both in the liver and thymus.