Selective effects of human cord serum on distinct events of the lectin-induced activation and proliferation of thymic T-cells.

The results of this study demonstrate that human cord serum, but not adult serum, contains a factor(s) which without being by itself mitogenic for unstimulated resting cells, enhances the PHA- and ConA-induced proliferation of rat thymocytes. Dissection of the effects of HCS on the distinct events involved during lectin-induced activation and growth of thymic T cells, revealed the basic mechanisms by which the stimulatory factor(s) exerts its action. HCS does not affect the IL-2-dependent proliferation of ConA-blasts derived from thymocytes. Furthermore, it does not act via macrophages but rather directly on thymic T cells by increasing their capacity to proliferate in response to the activating signals delivered by lectins in conjunction with IL1. Thus, HCS enhances the lectin-induced expression of IL2-receptors as evidenced by both increased responsiveness to IL2 and increased capacity to absorb IL2 of HCS-treated thymocytes. On the other side, HCS also enhances the lectin-induced production of IL2 by thymocytes.