Serum MRP8/MRP14 as a biomarker for inflammation in autoimmune arthritis

Background

Myeloid related protein (MRP)8 and MRP14 are released by early monocytes upon contact with activated endothelium and correlate with inflammation in rheumatoid arthritis (RA) and juvenile arthritis.

Objective

The aim of the study was to investigate serum MRP8/MRP14 as biomarker for inflammation in chronic arthritis.

Methods

The study included 40 RA patients with active joint involvement (SJC = 14, CRP = 2.4 mg/dl, ESR = 28 mm/hour); 30 SpA patients with peripheral synovitis (SJC = 2, CRP = 2.2 mg/dl, ESR = 21 mm/hour); 10 AS patients with exclusive axial involvement (SJC = 0, CRP = 3.1 mg/dl, ESR = 19 mm/hour); and 20 healthy controls (HC). In 20 RA, 10 peripheral SpA and 10 axial AS patients, sera were also obtained after 6 weeks of infliximab therapy. Serum MRP8/MRP14 was measured by ELISA.

Results

MRP8/MRP14 was increased in RA (1075 ng/ml; P < 0.001), peripheral SpA (815 ng/ml; P < 0.001) and axial AS (710 ng/ml; P < 0.001), as compared with HC (280 ng/ml). In patients with peripheral synovitis, MRP8/MRP14 correlated with CRP (RA, r = 0.77, P < 0.001; peripheral SpA, r = 0.69, P < 0.001) and ESR (RA, r = 0.70, P < 0.001; peripheral SpA, r = 0.62, P = 0.001). MRP8/MRP14 decreased after infliximab in RA (P < 0.001), peripheral SpA (P = 0.009) and axial AS (P = 0.012). Of 9/40 RA, 6/30 peripheral SpA and 1/10 axial AS patients with CRP < 1 mg/dl, only one peripheral SpA patient had increased MRP8/MRP14 (> mean MRP8/MRP14 in HC + 2SD). Of 17/40 RA, 12/30 peripheral SpA and 6 axial AS patients with ESR < 20 mm/hour, 3/17 RA, 6/12 peripheral SpA and 3/6 axial AS patients had raised MRP8/MRP14. Finally, we assessed the sensitivity to change after infliximab. In RA and peripheral SpA, changes in MRP8/MRP14 were not different from changes in CRP and ESR, whereas in axial AS changes in MRP8/MRP14 were less pronounced than changes in ESR (P = 0.005).

Conclusion

Raised MRP8/MRP14 levels, correlations with CRP and ESR, and decrease after infliximab confirm that serum MRP8/MRP14 reflect inflammation. Further research is warranted to assess the added value of MRP8/MRP14 as compared with CRP and ESR.