Up-regulation of CXCR3 and CXCR4 expression on activated B cells does not depend on proliferation. Sorted CXCR3^- or CXCR4^- peripheral-blood B cells where labeled with CFDA-SE and stimulated with CpG, IL-2, and IL-10. IFN-γ was added to CXCR3^- B cells to induce the expression of CXCR3. Following 3 days cultures started with CXCR3^- B cells were analyzed for CXCR3 expression, cultures started with CXCR4^- B cells for CXCR4 expression, and compared to the loss of CFDA-SE by FACS. Borders for chemokine receptor staining were set according to isotype controls. One representative result of 3 is shown. Values represent the percentage of CDFA content and CXCR3 or CXCR4 expression, respectively, in each quadrant.