Chemokine receptor expression by B cells. Peripheral blood mononuclear cells (PBMCs) from healthy donors (n = 4 to 7) and rheumatoid arthritis (RA) patients (n = 17 to 18) and synovial cells from RA patients (n = 10 to 11) were stained with CD19, CD27, and CCR5, CCR6, CCR7, CXCR3, CXCR4 or CXCR5, and the expression of the various markers was analyzed by flow cytometry. CD19+ B cells were gated, and the frequency of expression of each chemokine receptor is shown. Data represent mean ± standard error of the mean. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. ST = synovial tissue.