Conformational epitopes detected by cross-reactive antibodies to envelope 2 glycoprotein of the hepatitis C virus

The prevalence of anti-E2 antibody in persons chronically infected with hepatitis C virus (HCV) is high irrespective of viral genotype, and this cross-reactive antibody is thought to react with a conformational epitope. To investigate the characteristics of this anti-E2 antibody, the immunoreactivity of sera from HCV-1b-infected patients was measured against various modified forms of E2 glycoprotein derived from HCV-H (genotype 1a) by an immunofluorescence technique. Twelve of 18 patients were positive for anti-E2 antibody, and 10 of the 12 required a minimal amino acid (aa) region including aa 406-644 for strong reactivity, suggesting that the major E2 antibody has a conformational epitope in this region. Subsequent analysis using mutant E2 glycoproteins designed to lose N-glycosylation potential at varying sites revealed seven important N-glycosylation sites in this region. Four of these (aa 423,430, 448, and 576) are indispensable for an antibody response.