BMMC progenitors were cultured in SCF and IL-3-containing medium, including the indicated concentrations of S1P. After 4–6 wk in these culture conditions, degranulation (A), cytokine production (B), and calcium responses (C, D) were assessed as in Fig. 3. All experiments were conducted in Tyrodes buffer (A, C, D) or medium without serum or cytokines (B) 3 to 5 days after the last change of medium. Results are the average of 3–8 independent cultures. *P < 0.05, **P < 0.01.