Sphingosine-1-phosphate (S1P) is implicated in the regulation of peritoneal B-cell trafficking. Here we show that the effects of S1P on peritoneal B-1 cell migration are mediated by the receptor S1PR4 via direct chemotactic action as well as via upregulation of the expression level of chemokine receptors CXCR4 and CXCR5.
Abstract
B-1 cells are crucially involved in immune defense and regulation of inflammation and autoimmunity. B-1 cells are predominantly located in the peritoneal and pleural cavities, although body cavity B-1 cells recirculate systemically under steady-state conditions. The chemokines CXCL12 and CXCL13 have been identified as the main regulators of peritoneal B-cell trafficking. In mice deficient for sphingosine-1-phosphate receptor 4 (S1PR4), B-1a and B-1b cell numbers are reduced in the peritoneal cavity by an unknown mechanism. In this study, we show that S1PR4-mediated S1P signaling modifies the chemotactic response of peritoneal B cells to CXCL13 and CXCL12 in vitro. In vivo, S1PR4-mediated S1P signaling affects both immigration into and emigration from the peritoneal cavity. Long-term reconstitution experiments of scid mice with wt or
s1pr
4
–/– peritoneal B cells revealed a distinct distributional pattern in secondary lymphoid organs. As a functional consequence, both plasmatic and mucosal IgM levels, the main product of B-1a cells, are reduced in mice reconstituted with
s1pr
4
–/– peritoneal cells. In summary, our data identify S1PR4 as the second S1P receptor (besides S1PR1), which is critically involved in the regulation of peritoneal B-1 cell function.