We also confirmed our data by transfecting RA FLSs with B1R siRNA (Supplemental Figure 5) and found that RA FLSs with B1R silencing exhibited decreased sCD13-stimulated Erk1/2 phosphorylation compared with FLSs transfected with scrambled RNA (Figure 4E). This evidence concerns the gene MAPK3 and rheumatoid arthritis.