Modulation of T-lymphocyte proliferation by exogenous natural ceramides and sphingosylphosphorylcholine.
Sphingolipids such as ceramide and sphingosine are abundantly present in the stratum corneum of epidermis. In atopic stratum corneum, sphingosylphosphorylcholine (SPC) is present in association with a reduction in the amount of ceramides. We have previously shown that the cellular kinetics of T cells are affected by exogenous addition of sphingosine and synthetic ceramides, raising the possibility that sphingolipids diffusing from the stratum corneum modulate skin-infiltrating T cells. By using two natural ceramides and murine T cells, this study further clarified the conditions under which exogenous ceramides enhance the proliferation of T cells. KLH-specific T cell clones 28-4 and 24-2 proliferated in response to natural ceramides when cultured for 44-48 h in the presence of concanavalin A at 1 microg per ml. Elongation of culture periods adversely inhibited the T cell proliferation, suggesting the existence of an optimal exposure time. Augmentation of DNA synthesis by natural ceramides was more pronounced in tumor necrosis factor alpha (TNFalpha)-sensitive 28-4 cells than in less sensitive 24-2 cells, and TNFalpha-induced proliferation of 28-4 cells was suppressed by the concomitant addition of natural ceramides. Similar to ceramides, SPC augmented the proliferation of resting spleen cells. Our study suggests that ceramide modulation of T cell proliferation depends on the TNFalpha sensitivity and activation level of T cells and that SPC also has a mitogenic potential for T cells.