Serum COMP-C3b complexes in rheumatic diseases and relation to anti-TNF-α treatment

COMP-C3b levels in sera were measured by using an enzyme-linked immunosorbent assay (ELISA) capturing COMP and detecting C3b. Serum COMP was measured by using ELISA.COMP-C3b levels were significantly elevated in patients with RA as well as in systemic lupus erythematosus (SLE), compared with healthy controls. SLE patients with arthritis had significantly higher COMP-C3b levels than did those without. COMP-C3b was furthermore elevated in patients with ankylosing spondylitis (AS), psoriatic arthritis (PsA), reactive arthritis, systemic sclerosis, and OA. COMP-C3b did not correlate with COMP in any of the patient groups. COMP-C3b correlated with disease activity in RA, but not in other diseases. COMP-C3b levels in RA patients decreased on treatment with tumor necrosis factor (TNF)-α inhibitors, whereas the levels increased in patients with AS or PsA. The changes of COMP-C3b did not parallel the changes of C-reactive protein (CRP).COMP-C3b levels are elevated in several rheumatologic diseases and correlate with inflammatory measures in RA. COMP-C3b levels in RA decrease during TNF-α inhibition differently from those of CRP, suggesting that formation of COMP-C3b relates to disease features not reflected by general inflammation measures.Rheumatoid arthritis (RA) is a disabling disease with both a large impact on the quality of life for the patient and a high economic impact on society. It is known that early intervention minimizes tissue damage and disease progression. Therefore specific and sensitive diagnostics are essential for early discovery of disease. Even though rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPAs) are widely used as diagnostics for RA, improvements are needed to enhance the specificity and sensitivity of current molecular markers in RA. Therapy should also improve when new diagnostic assays can differentiate RA patients into groups with different underlying pathologic mechanisms. Several approaches to develop novel serologic ma