Induction of CD69 and inhibition of S1P responses in human T cells in vitro. Platelet-depleted peripheral blood mononuclear cells were treated for 48 hours as noted and S1P-induced bioactivity and CD69 surface expression were assessed (data shown represent means and SD of 3 separate experiments). S1P responses are reported as percentage change relative to nonstimulated conditions. Actin pol., actin polymerization.