Photo Credit: Md Saiful Islam Khan

The following is a summary of “Anti-C1q antibodies in IgG4-related disease are common and associated with renal involvement and cutaneous small-vessel vasculitis,” published in the January 2025 issue of Rheumatology by Martín-Nares et al. 

Researchers conducted a retrospective study on anti-C1q antibodies in IgG4-related disease (IgG4-RD), focusing on renal involvement and cutaneous small-vessel vasculitis (CSVV). 

They enrolled patients meeting the 2020 Comprehensive Diagnostic Criteria and/or the 2019 ACR/EULAR Classification Criteria for IgG4-RD. Variables included demographics, organ involvement, clinical phenotypes, disease activity, serum biomarkers, follow-up duration, remission, and relapses. Anti-C1q antibodies were measured using a quantitative enzyme-linked immunosorbent assay with a cut-off of <10 U/ml. 

The results showed that 70 patients, with a mean age of 52.1 years, 34 (48.6%) male, had anti-C1q positivity in 74.3%, with a median level of 19.8 U/ml. Active disease correlated with higher anti-C1q levels (P=0.03), and renal involvement was more common in anti-C1q positive patients (P=0.01). About 6 patients (8.6%) with CSVV, all anti-C1q positive, exhibited palpable purpura and multi-organ involvement, with high IgG, IgG1, IgG4, and hypocomplementemia. Skin biopsies in three patients showed leukocytoclastic vasculitis. Anti-C1q levels correlated negatively with C3 and C4 and positively with IgG1, IgG4, and serum-free light chains but did not predict relapse-free survival (RFS). 

Investigators found a high prevalence of anti-C1q antibodies in IgG4-RD, especially with renal involvement and CSVV, supporting immune complex-mediated complement activation in its pathogenesis. 

 Source: academic.oup.com/rheumatology/advance-article-abstract/doi/10.1093/rheumatology/keaf020/7951895