Autoantibodies against C-reactive protein: clinical associations in systemic lupus erythematosus and primary antiphospholipid syndrome

Abstract

Objective: To investigate the prevalence of anti-C-reactive protein (CRP) autoantibodies in patients with systemic lupus erythematosus (SLE) and non-SLE patients with persistent antiphospholipid antibodies (aPL) and their association with clinical manifestations.

Methods: Sera of 137 patients with SLE, 127 with persistent aPL and 30 with idiopathic venous thromboembolic disease, were assayed for the presence of anti-CRP reactivity by ELISA. Associations of anti-CRP reactivity with clinical features, with other autoantibodies, and with serum concentrations of C3 and CRP were assessed.

Results: Antibodies against CRP were seen in 51% (n = 137) of patients with SLE and in 54% (n = 127) of patients with aPL. SLE patients with anti-CRP antibodies showed increased frequencies of anti-dsDNA and aPL antibodies compared to those without anti-CRP (52% vs 26% and 68% vs 31%, respectively). Mean serum C3 levels were lower in the subgroup of patients with SLE positive for anti-CRP antibodies (79 +/- 25 vs 92 +/- 25 mg/dl; p = 0.004 ) and mean serum CRP levels were significantly higher (13 +/- 17 vs 5 +/- 8 mg/l; p = 0.01 ). The frequency of nephritis was higher in SLE patients with anti-CRP antibodies, than in those without (27% vs 13%; p = 0.058). In patients with clinical and serological evidence of antiphospholipid syndrome (APS) the frequency of anti-CRP antibodies was significantly higher than in asymptomatic aPL carriers, in both SLE patients [85% (23 of 27) vs 59% (19 of 32); p = 0.021] and non-SLE patients [76% (38 of 50) vs 19% (9 of 47); p < 0.001]. Among patients with APS with or without SLE, 26 had arterial events, 31 had venous events, 6 had combined arterial and venous events, and 14 had fetal loss. Mean titers of IgG anti-CRP (29 +/- 21, 30 +/- 19, 60 +/- 37, and 26 +/- 12 AU/ml) and frequencies of anti-CRP antibodies (88%, 71%, 50%, and 71%) in these subgroups of patients were comparable.

Conclusion: We confirmed the high prevalence of anti-CRP autoantibodies both in patients with SLE and in non-SLE and aPL-positive patients. We observed that the presence of these antibodies was associated with lupus nephritis and with clinical features of the APS in patients with lupus and non-lupus patients.