To rule out the possibility that circulatory CTHRC1 protein in RA patients has a different half-life compared to healthy controls and OA patients, for example due to differences in protease content in the blood, we spiked recombinant human CTHRC1 (rhCTHRC1) into samples of plasma or synovial fluid, incubated the samples at 37°C for up to 2 h, and tested protein integrity using SDS-PAGE and immunodetection (Figure 2A). The gene discussed is CTHRC1; the disease is rheumatoid arthritis.