CR2 and rheumatoid arthritis: Comparable populations associated with other autoimmune diseases include memory CD27−IgD− B cells in juvenile idiopathic arthritis (6), CR2/CD21− B cells in rheumatoid arthritis (RA) (7), and CD21−/low B cells in primary Sjogren's syndrome (8), or CD21lo B cells that emerge after immunization with protein antigen (9).