Among this subset, ACPA/+ patients displayed CD21-/lowCD27-IgG- class significantly increased in peripheral blood and comprising 40% of the CD21-/low cells in SF (95), matching posterior studies in which CD27-IgD- and memory CD27+ IgD- B cells were found in higher ratios in the SF compared to peripheral blood, suggesting these subgroups are key players in RA synovium inflammation (96). Here, PRTN3 is linked to rheumatoid arthritis.