As recently reported,39 we observed a high prevalence of IgA+ B cells in the RA joints in line with previous evidence that FDC-like synovial stromal cells directly induce IgA class-switch via a B cell Activating Factor of the TNF Family (BAFF) and A PRoliferation Inducing Ligand (APRIL)-dependent pathway.40, 41. The gene discussed is TNFSF13; the disease is rheumatoid arthritis.