The chemokine SDF-1alpha triggers a chemotactic response and induces cell polarization in human B lymphocytes

We studied the expression and possible functional role of chemokine receptors CXCR3, CXCR4 and CCR5 in normal human B lymphocytes. B cells from both peripheral blood and tonsils expressed high levels of CXCR4 but not the other chemokine receptors tested. CXCR4 ligand, stromal cell-derived factor (SDF)-1alpha, elicited a potent chemotactic response and induced a polarized motile phenotype in B cells, resulting in redistribution of the adhesion molecule ICAM-3 to a posterior appendage of the cell, termed uropod, and of CXCR4 receptor to the leading edge of migrating B cells. Time-lapse videomicroscopy studies revealed that SDF-1alpha-treated cells recruited additional bystander B cells through the uropod. SDF-1alpha induced levels of cellular recruitment comparable to those elicited by polarization-inducing anti-ICAM-3 monoclonal antibody, in an LFA-1/ICAM-1, -3-dependent fashion. Moreover, this chemokine increased intracellular Ca2+ levels in B lymphocytes, and induced a rapid CXCR4 receptor down-regulation on the cell surface membrane. These results provide new insight into the important biological role of SDF-1alpha in physiological processes in which B cells participate, and suggest a key role for chemokines in normal B cell trafficking and recirculation.