COMP and reactive arthritis: Among the 31 other putative ADAMTS4 cleavage sites in COMP (Fig. 2E), we additionally assessed cleavage at the F577-N578 bond in the CTD (Table 1), since COMP peptides resulting from cleavages at this site were previously identified in the synovial fluid of patients with OA, acute trauma, reactive arthritis and rheumatoid arthritis (RA) [56,58] (Table 3).