Finally, to corroborate the role of cathepsin S in the degradation of endostatin in vivo, we measured it in serum samples from RA patients and from the healthy controls and observed a reduction in cathepsin S concentrations and activity after 6 months of tofacitinib treatment relative to the samples before treatment (Figure 9A,B). This evidence concerns the gene COL18A1 and rheumatoid arthritis.