BST2 and rheumatoid arthritis: In patient samples from the discovery cohort, memory B cell tetherin showed the strongest associations with diagnosis (SLE:healthy control effect size 0.11 [P = 0.003]; SLE:RA effect size 0.17 [P < 0.001]), plasmablast numbers in rituximab‐treated patients (R = 0.38, P = 0.047), and BILAG 2004.