Background and Aims: The hepatitis C virus (HCV) F protein is a recently described, frameshift product of HCV core encoding sequence. Its function and antigenic properties are unknown. In order to assess the presence of antibodies specific for F protein we characterized specific anti-F antibodies in patients with chronic HCV infection.

Methods: The F protein was cloned from the HCV genome. The recombinant protein was expressed in Escherichia coli and purified by immunoaffinity chromatography. An enzyme-linked immunosorbent assay was developed using the purified recombinant HCV F protein.

Results: Serum samples were collected from 72 patients with chronic HCV infection and from 30 healthy controls. Eighty-two percent of chronic HCV patients had evidence of anti-F antibodies. 59 samples out of the 72 HCV infected patients exhibited a positive anti-F reaction, showing significant difference from the controls with no HCV infection (P < 0.01).

Conclusion: Based on these findings, HCV F protein elicits a specific antibody response, so frameshift could occur in the core-coding sequence in HCV genotype 1a in Iranian patients. As the first report, the prevalence of anti-F antibodies in chronic hepatitis C in Iran is of the order of 82%.