Research in Brief

An abundance of B cells in the joint synovium correlates with disease severity in patients with early rheumatoid arthritis (RA), according to a cohort study by Felice Rivellese and colleagues. The authors used a semi-quantitative immunohistochemistry approach (verified with digital imaging and RNA sequencing) to assess levels of B cell infiltration in synovial biopsies from 165 patients with treatment-naïve early RA and 164 patients with established RA who had insufficient responses to TNF inhibitors. Synovitis was classified as B-cell-rich in 35% patients with early RA and nearly half (48%) with established disease. In patients with early RA, disease activity (DAS28 and swollen joint count) and seropositivity (anti-citrullinated protein antibodies and rheumatoid factor) were higher in the B-cell-rich group. This was not the case in patients with established disease, suggesting that B-cell-independent pathways might drive inflammation in these patients. Ongoing clinical trials are investigating whether grouping patients according to synovial B cell content might be a useful way to stratify patients who are more or less likely to respond to specific biological disease-modifying antirheumatic drugs, such as the B cell-depleting drug rituximab.