Anti‐C1q antibodies in hepatitis C virus infection

Summary Autoantibodies against C1q have been described in many immune‐complex diseases including hypocomplementaemic urticarial vasculitis and systemic lupus erythematosus (SLE). No study has focused on the role of anti‐C1q antibodies in hepatitis C virus (HCV) infection. The aim of this study was (i) to evaluate the prevalence of anti‐C1q antibodies in HCV infection; and (ii) to analyse the association of anti‐C1q antibodies with clinical and biological features of HCV–mixed cryoglobulinaemia (MC) vasculitis. We searched for anti‐C1q antibodies using an enzyme‐linked immunosorbent assay (ELISA) test in 111 HCV patients (75 had cryoglobulin and 23 systemic vasculitis), 60 SLE patients and 109 blood donors. Anti‐C1q antibodies were detected in 26% of HCV patients compared to 10% of healthy donors ( P  < 0·01), and 38% in patients with SLE. Although there was a higher prevalence of anti‐C1q antibodies among HCV patients with type III cryoglobulin (50%, P  < 0·01), the overall prevalence of anti‐C1q antibodies was similar in HCV patients being cryoglobulin‐positive or cryoglobulin‐negative (26% versus 25%, P  = 0·98). A significant association was found between anti‐C1q antibodies and low C4 fraction of complement ( P  < 0·05). No association was found between anti‐C1q antibodies and HCV genotype, severity of liver disease or with specific clinical signs of HCV–MC vasculitis. This study shows an increased prevalence of anti‐C1q antibodies in HCV‐infected patients. Anti‐C1q antibodies were associated with low C4 levels. No association was found between anti‐C1q antibodies and HCV–MC vasculitis, nor between anti‐C1q antibodies and cryoglobulinaemia.