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Background:  We examined the hypothesis that neutralizing antibodies are generated during acute hepatitis C virus (HCV) infection. There is little information on the relevance of neutralizing antibodies to acute hepatitis C because infection is usually asymptomatic and, until recently, convenient models did not exist. Using a recently developed HIV/HCV pseudotype system bearing HCV envelope glycoproteins (gp) E1E2, we examined subject serum for the presence of neutralizing antibodies.

Methods:  We followed 18 injection drug users before, during, and after HCV infection. Seroconversion was defined as incident detection of HCV specific antibodies by Ortho 3.0 ELISA. Anti-E1E2 gp specific antibody responses were detected using H77 genotype 1a antigen from 293T cell lysates in a standard ELISA. HCV pseudotypes were generated by co-transfection of 293T cells with luciferase-expressing HIV plasmid (pNL4-3.Luc.R^-E^-) and an expression plasmid containing the HCV gp (strain H77) or murine leukemia virus (MLV) envelope. For neutralization assays, serum was incubated with HIV/HCV H77 or control HIV/MLV virus and the virus/serum mixture was allowed to infect Hep3B hepatoma cells. Percentage neutralization was determined by comparing pseudotype infectivity in the presence of test serum versus infection in the presence of control HCV-negative plasma.

Results:  HCV RNA and ALT elevations were detected in all subjects during acute infection. HCV specific antibodies were detected (seroconversion) in all subjects, a median of 1.1 months (range 0 to 5.4) after RNA detection. Anti-E1E2 immunoglobulin G (IgG) was substantially delayed, first detected a median of 8.6 months (range 0 to 19) after RNA detection. Neutralizing antibodies were detected in 13 of 18 subjects and were also delayed, first detected a median of 14.2 months (range 0 to 26.6) after RNA detection.  Interestingly, the median time to detection of neutralizing antibodies was less in subjects who cleared HCV infection, 11.5 months (range 9.7 to 14.9), versus those with chronic infection, 14.2 months (range 0 to 26.6).

Conclusions:  IgG responses to HCV glycoproteins, including neutralizing antibodies, can be detected after acute infection. However, these responses occur long after infection, especially in persons with viral persistence. Further research is needed to evaluate the biologic basis for the delayed production of neutralizing antibodies, as well as the role these antibody responses play in the course of disease.

Keywords: HCV; Pseudotype; Neutralization