Complement activation in patients with rheumatoid arthritis mediated in part by C-reactive protein.
OBJECTIVE
Complement activation in patients with rheumatoid arthritis (RA) is considered to be triggered by immune complexes. Recently, it was shown that C-reactive protein (CRP) can activate the complement system in vivo. We therefore hypothesized that part of the complement activation in RA is due to CRP. The aim of this study was to investigate CRP-mediated complement activation in RA, and to assess its correlation with disease activity.


METHODS
Complexes between CRP and the activated complement components C3d (C3d-CRP) and C4d (C4d-CRP), which reflect CRP-mediated complement activation, as well as the overall levels of activated C3 and C4 were measured in the plasma of 107 patients with active RA and 177 patients with inactive RA. Inactive RA was defined according to the American College of Rheumatology criteria for clinical remission. Disease activity was assessed by the modified Disease Activity Score (DAS28).


RESULTS
Plasma levels of C3d-CRP and C4d-CRP were increased in the majority of the patients, and were significantly higher in patients with active disease versus those with inactive RA (P < 0.001). In patients with active RA, the plasma concentrations of C3d-CRP and C4d-CRP correlated significantly with the DAS28 (Spearman's rho 0.61 and 0.55, respectively; P < 0.001), whereas these correlations were less pronounced in patients with inactive RA (Spearman's rho 0.28 [P < 0.001] and 0.25 [P = 0.001], respectively). Levels of activated C3 and C4 were also increased in the majority of the patients, particularly in patients with active RA.


CONCLUSIONS
Part of the activation of complement in RA is mediated by CRP and is correlated with disease activity. We suggest that this activation is involved in the pathogenesis of RA.
Molenaar
E T
ET
Vrije Universiteit Medical Center, Amsterdam, The Netherlands.
Voskuyl
A E
AE
Familian
A
A
van Mierlo
G J
GJ
Dijkmans
B A
BA
Hack
C E
CE
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism*; D002097:C-Reactive Protein / Q000276:immunology* / Q000378:metabolism*; D003167:Complement Activation / Q000276:immunology*; D003179:Complement C3b / Q000276:immunology / Q000378:metabolism; D015932:Complement C3c / Q000276:immunology / Q000378:metabolism; D003181:Complement C4 / Q000276:immunology / Q000378:metabolism; D015935:Complement C4b / Q000276:immunology / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments
D003181:Complement C4; D010446:Peptide Fragments; C033860:complement C4c; D003179:Complement C3b; D015932:Complement C3c; D015935:Complement C4b; D002097:C-Reactive Protein