[Abstract]ObjectiveTo investigate the presence of neutralization antibodies in the sera of hepatitis C patients. MethodsA eukaryotic expression plasmid encoding carboxyl terminal-truncated HCV envelope protein 2 (E2) was transfected into human 293T cells. ELISA method was established to examine the anti-E2 antibodies in the sera of 32 hepatitis C patients. The full-length envelope protein expression plasmid was transfected into 293T cells and the reactivity of transfectant with anti-E2 IgG positive sera was analyzed by immunofluorescence. Five strains of HCV pseudotype particle (HCVpp), including H77 (1a genotype), Con-1 (1b genotype), J4 (1b genotype), J6 (2a genotype), and UNK3a (3a genotype), and two strains of cell cultured HCV (HCVcc) were used to assay the neutralization activity of 12 anti-E2 positive serum samples. MethodsELISA results showed that 26 of 32 serum samples were anti-E2 IgG positive, with the positive rate being 81.3%. The 12 serum samples positive for HCV RNA were all anti-E2 IgG, and the virus load was negatively correlated with the anti-E2 antibody level. The anti-E2 positive sera could neutralize the infections of five strains of HCVpp and two strains of HCVcc to various extents, and the neutralization activity was consistent with the anti-E2 antibody level. MethodsIt is suggested that HCV infection can induce protective humoral immune response, and cross-neutralization antibodies against HCV are present in sera of hepatitis C patients, which indicates a feasibility for developing vaccines that can induce broadly-reactive neutralizing antibodies.