CD27 and rheumatoid arthritis: The frequency of CD27+ by synovial B cells was significantly higher than that of peripheral blood B cells in RA subjects (Figure 2) (peripheral blood, 30.0 ± 5.1% (mean ± SEM); synovial B cells, 62.3 ± 4.7%; P < 0.005, n = 11), as we have previously reported [21], suggesting that a specific subset of B cells might be recruited to the inflammatory site in RA.