In rituximab‐naive RA patients, the frequency of citrulline‐reactive B cells in the peripheral blood generally correlates with ACPA titers and varies greatly with a median of ~ 1 in 12,500 B cells bearing B cell receptors (BCRs) reactive to citrullinated peptides/proteins.95 Most of these cells are class‐switched postgerminal center memory B cells expressing IgG or IgA BCRs. Here, PRTN3 is linked to rheumatoid arthritis.