Anti-C1q antibodies in systemic lupus erythematosus.
Orbai A-M., Truedsson L., Sturfelt G., Nived O., Fang H., Alarcón GS., Gordon C., Merrill J., Fortin PR., Bruce IN., Isenberg DA., Wallace DJ., Ramsey-Goldman R., Bae S-C., Hanly JG., Sanchez-Guerrero J., Clarke AE., Aranow CB., Manzi S., Urowitz MB., Gladman DD., Kalunian KC., Costner MI., Werth VP., Zoma A., Bernatsky S., Ruiz-Irastorza G., Khamashta MA., Jacobsen S., Buyon JP., Maddison P., Dooley MA., Van Vollenhoven RF., Ginzler E., Stoll T., Peschken C., Jorizzo JL., Callen JP., Lim SS., Fessler BJ., Inanc M., Kamen DL., Rahman A., Steinsson K., Franks AG., Sigler L., Hameed S., Pham N., Brey R., Weisman MH., McGwin G., Magder LS., Petri M.
OBJECTIVE: Anti-C1q has been associated with systemic lupus erythematosus (SLE) and lupus nephritis in previous studies. We studied anti-C1q specificity for SLE (vs rheumatic disease controls) and the association with SLE manifestations in an international multicenter study. METHODS: Information and blood samples were obtained in a cross-sectional study from patients with SLE (n = 308) and other rheumatologic diseases (n = 389) from 25 clinical sites (84% female, 68% Caucasian, 17% African descent, 8% Asian, 7% other). IgG anti-C1q against the collagen-like region was measured by ELISA. RESULTS: Prevalence of anti-C1q was 28% (86/308) in patients with SLE and 13% (49/389) in controls (OR = 2.7, 95% CI: 1.8-4, p < 0.001). Anti-C1q was associated with proteinuria (OR = 3.0, 95% CI: 1.7-5.1, p < 0.001), red cell casts (OR = 2.6, 95% CI: 1.2-5.4, p = 0.015), anti-dsDNA (OR = 3.4, 95% CI: 1.9-6.1, p < 0.001) and anti-Smith (OR = 2.8, 95% CI: 1.5-5.0, p = 0.01). Anti-C1q was independently associated with renal involvement after adjustment for demographics, ANA, anti-dsDNA and low complement (OR = 2.3, 95% CI: 1.3-4.2, p < 0.01). Simultaneously positive anti-C1q, anti-dsDNA and low complement was strongly associated with renal involvement (OR = 14.9, 95% CI: 5.8-38.4, p < 0.01). CONCLUSIONS: Anti-C1q was more common in patients with SLE and those of Asian race/ethnicity. We confirmed a significant association of anti-C1q with renal involvement, independent of demographics and other serologies. Anti-C1q in combination with anti-dsDNA and low complement was the strongest serological association with renal involvement. These data support the usefulness of anti-C1q in SLE, especially in lupus nephritis.