BCR and rheumatoid arthritis: Specific autoreactive B cells can make up to 0.2% of the totalB-cell population and are characterized by a B-cell receptor (BCR)that recognizes a specific self-antigen.3 The majority of the patients with established RA recognize and produceanticitrullinated protein antibodies (ACPAs) that can be detectedyears before the onset of the disease and their presence is associatedwith disease onset and severity.2,4