CD27 and rheumatoid arthritis: Interestingly, no significant difference could be seen between RA patients and controls in the frequency or absolute number of the total CD27+ memory B cell pool (median RA 31.3 ± 3.8% vs control 30.3 ± 1.6%, P = 0.6258; median RA 41.0 ± 11.3 cells/μl vs control: 44.6 ± 5.0 cells/μl, P = 0.7022).