Longitudinal IP-10 serum levels are associated with the course of disease activity and remission in rheumatoid arthritis

Although Rheumatoid arthritis (RA) is a chronic, persistent autoimmune disease 10-15% of the RA patients achieve sustained disease modifying anti-rheumatic drugs (DMARD)-free remission over time. Biological mechanisms underlying the resolution of persistent inflammation in RA are yet unidentified and prognostic markers are lacking. It is well established that increased serum levels of IFN-γ-induced protein 10 (IP-10) are associated with (acute) increased inflammatory responses (e.g. in leprosy). In order to assess the potential of IP-10 as a diagnostic tool for inflammatory episodes in RA, we performed a retrospective study and assessed IP-10 levels in longitudinally banked serum samples of patients upon first diagnosis of RA. The selection consisted of 15 persistent RA patients and 19 patients who achieved DMARD-free sustained remission. IP-10 levels, measured with a user-friendly quantitative lateral flow assay (LFA), showed up to 170-fold variation inter-individually and baseline IP-10 levels did not differentiate between the two patient groups. However, a difference in IP-10 level at the first and last visit (ΔIP-10) was observed (p=0.003) between DMARD-free (median ΔIP-10: -662 pg/ml (decrease)) and persistent RA-patients (median ΔIP-10: 468 pg/ml (increase)). Moreover, intra-individual changes in IP-10 during the course of disease corresponded to the disease activity score (p=0.05). These data indicate that IP-10 is associated with disease activity and perseverance of RA. The association of IP-10 with DAS indicates this tool as a practical diagnostic aid to help in monitoring of disease progression in RA patients and may also find application in other chronic diseases with exacerbated inflammatory episodes.