COL1A1, COL5A1/2, COL3A1, and COL12A1 were found to be marginally more abundant in RA compared to OA, whilst COL2A1 and COL6A1/2/3/6 were significantly more abundant in OA compared to RA (Fig. 4C). Here, COL2A1 is linked to rheumatoid arthritis.