CD19 and rheumatoid arthritis: While the frequency of CD19+CD20+/– cells was significantly lower in RA patient SF (P = 0.0005) and synovial tissue (P = 0.02) compared with peripheral blood, the subpopulation distribution was markedly different (Supplemental Figure 1 and Supplemental Figure 2; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.139032DS1).