Objective: To investigate the relationship between serum anti-C1q antibody levels and renal pathological characteristics in lupus nephritis as well as the prognostic significance of serum anti-C1q antibody.
Methods: Seventy-three patients with biopsy-proven lupus nephritis were enrolled. Anti-C1q antibody was measured in serum samples taken within 7 days before renal biopsy and remeasured at the end of the first and the third month after treatment. All patients were followed at least once a month for 3 months. A cross-sectional study analyzed the relationship between serum anti-C1q antibody levels and renal histopathology and nephritic activity, while a longitudinal study evaluated the prognostic significance of anti-C1q antibody levels in lupus nephritis.
Results: Fifty-eight of 73 patients (79.5%) were reported as having positive baseline serum anti-C1q antibody, with a mean level of 95.3 (+/- 55.2) U/ml. Significant differences were found in serum anti-C1q antibody levels between each World Health Organization (WHO) classification of lupus nephritis. The serum anti-C1q antibody level of WHO class IV was the highest. Serum anti-C1q antibody was positively correlated with the active and chronic indices in renal pathology. Patients with persistent high levels or increased titers of serum anti-C1q antibody tended to develop delayed remission in nephropathy. Serum anti-C1q antibody levels before and after treatment were relevant to renal remission, but serum anti-C1q antibody at the end of the third month after treatment was a stronger predictor for the prognosis after adjustment in the Cox's proportional hazards regression model.
Conclusion: Serum anti-C1q antibody is a valuable noninvasive biological marker for evaluation of renal involvement and lupus prognosis.