TNFAIP6 and Arthritis: Given that both HA and IαI are present in synovial fluid of arthritis patients and that the HA concentration in synovial fluid (between 1 and 4 mg/ml (60)) is comparable to our HA films (1 mg/ml (44)), a plausible explanation for the difference could be that the extent of covalent modification correlates with TSG-6 concentration.