Sphingosine 1-phosphate is a novel inhibitor of T-cell proliferation

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Abstract
Sphingosine 1-phosphate (S1P) is a pleiotropic lysosphingophospholipid stored and secreted by platelets. Using reverse transcription–polymerase chain reaction and flow cytometric analyses, we determined the expression of S1P receptors (S1P1, S1P3, S1P4, and S1P5) in peripheral blood T cells. T cells were induced to proliferate in the presence of phorbol 12-myristate 13-acetate (PMA) plus ionomycin, anti-CD3 plus anti-CD28, and allogeneic immature or mature dendritic cells. This activity was inhibited by the addition of S1P. Enhanced T-cell proliferation was observed when these cells were stimulated with the same stimuli, but were incubated in serum-free media (SFM). Addition of S1P to SFM inhibited the stimulation of T cells induced by T-cell stimuli, suggesting that S1P is an important inhibitory molecule present in the serum. T-cell proliferation was also inhibited by the addition of dihydrosphingosine 1-phosphate (DHS1P), sphingosine, and ceramide; however, the latter 2 sphingolipids required higher concentrations than S1P. Pretreatment of T cells with pertussis toxin (PTX) blocked the inhibitory effect of S1P on activation with PMA plus ionomycin, but not on activation with anti-CD3 plus anti-CD28. This is corroborated with the down-regulation of S1P1 in T cells stimulated with anti-CD3 plus anti-CD28. Similarly, PTX did not affect the inhibitory effect of S1P on T-cell proliferation when dendritic cells were used as stimuli. Further, S1P or DHS1P but not ceramide or sphingosine enhanced rather than decreased secretion of interleukin 2 and interferon γ by T cells stimulated with anti-CD3 plus anti-CD28. These results show differential effects of S1P on polyclonal T-cell proliferation and cytokine secretion.