Expression of S1P receptors in peripheral blood T cells. (A) mRNA for peripheral blood T cells and for T-cell lines (Jurkat and PEER), an NK-cell line (NK92), B-cell lines (RPMI and .221), and a monocytic cell line (U937) is shown. Shown is RT-PCR analysis of mRNA for S1P₁, S1P₃, S1P₄, and S1P₅, as well as the housekeeping gene for glyceraldehyde-3-phosphate dehydrogenase (G3PDH). (B) Flow cytometric analysis of the expression of S1P receptors in peripheral blood T cells is shown. Background controls in the presence of rabbit IgG (for S1P₁, S1P₄, and S1P₅) or mouse IgG (for S1P₂ and S1P₃) and FITC-conjugated secondary antibodies are shown in black. In the panel designated S1P₂/S1P₃, white and black histograms represent the binding of monoclonal anti-S1P₂ and anti-S1P₃, respectively. Numbers indicate the percentage of positive cells. (C) Anti-S1P₁ and anti-S1P₅ were either left intact or were incubated with S1P₁ or S1P₅ peptide prior to binding the antibodies with T cells. Control is the binding of rabbit IgG plus secondary antibody.