PRTN3 and rheumatoid arthritis: Interestingly, the most striking differences between the three groups were observed in cell clusters representing IgM+IgD+CD27−CD38int CD24int mature-naïve or transitional immature B-cell sub-populations with a decrease in one B-cell sub-population (cluster 23) and an increase in another IgM+ B-cell cluster (cluster 9) in ACPA+ RA (Fig. 2, Supplemental Figs. 4 and 6).