Background/Purpose: Psoriatic arthritis (PsA), an inflammatory musculoskeletal disease, develops in approximately 30% of patients with psoriasis. We previously found that C-X-C motif chemokine 10 (CXCL10) was elevated in psoriasis patients that developed PsA compared to those that did not develop PsA over the same psoriasis duration, thus suggesting CXCL10 is a predictive biomarker of PsA. In this study, we monitored the expression of CXCL10 over time in psoriasis patients that develop PsA.  

Methods: Psoriasis patients were followed prospectively beginning in 2006, and were assessed yearly by a rheumatologist for the presence of PsA. Psoriasis patients who developed PsA were termed ‘converters’, and serum samples were taken at baseline and follow-up visits. The expression of CXCL10 and CRP were measured using Milliplex MAP human magnetic bead panels (EMD Millipore), according to the manufacturer’s instructions.  Data were acquired using the Luminex 200 system and analyzed with the Bio-Plex Manager software (Bio-Rad Laboratories). Statistical differences in protein levels prior to PsA conversion were compared by the Wilcoxon signed rank test and post-conversion by the Friedman test with a Dunn’s Multiple Comparisons post-test (p<0.05 was accepted as significant).

Results: CXCL10 and CRP were measured in 19 psoriasis patients at baseline and at five follow-up time points. CXCL10 levels decreased over time (Figure 1), with a significant reduction at follow-up visit 3 (median 269.4 pg/ml, interquartile range [IQR] 198.6-399.6), visit 4 (median 225.3 pg/ml, IQR 155.1-387.9) and visit 5 (median 226.5 pg/ml, IQR 193.2-450.8) compared to post-conversion visit 2 levels (median 562.16 pg/ml, IQR 338.5-601.8, p<0.001). No significant differences in CRP levels were observed.

Conclusion: We observed a reduction in serum CXCL10 expression in psoriasis patients after they developed PsA which was maintained over time. These results support our previous findings of elevated CXCL10 in synovial fluid compared to serum from PsA patients, reflecting the localized production of CXCL10 over time. This study contributes to our understanding of the role of CXCL10 in the pathogenesis of PsA.

Figure 1: Line graph of CXCL10 and CRP expression in serum from 19 psoriasis converters measured at baseline (0) and follow-up visits (1-5). Dashed line indicates conversion to PsA. A significant difference compared to the post-conversion visit (2) is indicated by # (p<0.001). CRP concentration is expressed per 100 ng/ml.