CXCR3 is preferentially expressed on memory B cells coexpressing IgG1. PBMCs were stained for CD19, antibody isotypes, CXCR3, and CXCR4 and analyzed by FACS. To identify IgM memory cells, cells were additionally stained for CD27. Dead cells were excluded by DAPI staining. (A) Representative FACS analysis. Dot plots were gated on living CD19⁺ B cells. IgM⁺ cells were additionally gated for CD27⁺ cells, a marker for memory B cells. (B) Frequencies of CXCR3⁺ and CXCR4⁺ memory B cells expressing the antibody isotypes indicated. Cells were analyzed by FACS as described. Each dot resembles cell frequencies of one individual donor. Differences between CXCR3⁺/IgG1⁺ and CXCR3⁺/IgG2⁺ B cells were significant (P < .05). The horizontal bars show the mean value.