MZB1 and rheumatoid arthritis: It was noteworthy that HLA-DRB5+ Plasma B cells, expressing HLA-DRB5, IGHM, IGHG1, and MZB1, were significantly decreased; however, IGHG4+ Plasma B cells, distinctly expressing IGHG4 from other plasma B subsets, were significantly increased in the peripheral blood of ACPA- RA patients (Fig. 2c, Supplementary Fig. 3a).