To determine the expression pattern of B1R, CD13, and its primary sheddase MMP-14 on various cell types in RA synovium, we analyzed published single-cell RNA-Seq results generated from 27 RA synovia with a total of 7487 flow cytometry–sorted fibroblasts, MNs, T cells, and B cells. The gene discussed is BDKRB1; the disease is rheumatoid arthritis.