COMP-C3b complexes in rheumatoid arthritis with severe extraarticular manifestations.

Objective: To investigate biomarker patterns in rheumatoid arthritis (RA) with extraarticular manifestations.
Methods: Cartilage oligomeric matrix protein (COMP), COMP-C3b, and soluble terminal complement complexes (sTCC) were measured by ELISA.
Results: COMP-C3b levels were higher in patients with RA than in healthy controls and lower in extraarticular RA (ExRA) than in RA controls. In patients with ExRA, sTCC levels were higher than in RA controls, and correlated inversely with serum COMP-C3b levels in the ExRA group.
Conclusion: Patients with ExRA had lower levels of COMP-C3b. This may be a consequence of complement consumption or a lower potential for COMP from these patients to activate complement.