Antigenic relevance of F protein in chronic hepatitis C virus infection

Area of Science:

• Virology
• Immunology
• Hepatology

Background:

• The hepatitis C virus (HCV) F protein is a novel frameshift product derived from the core encoding sequence of genotype 1a.
• The function and antigenic properties of the HCV F protein remain largely unknown.
• Understanding the immune response to novel HCV proteins is crucial for developing diagnostics and therapeutics.

Purpose of the Study:

• To investigate the prevalence and characteristics of antibodies against the HCV F protein in chronically infected individuals.
• To determine if the anti-F antibody response is specific and not due to cross-reactivity with the HCV core protein.
• To explore potential correlations between anti-F antibody prevalence and clinical factors such as HCV RNA level, genotype, and liver disease stage.

Main Methods:

• Enzyme-linked immunosorbent assay (ELISA) was employed to detect anti-F antibodies in serum samples.
• Recombinant HCV F protein (genotype 1a) expressed in Escherichia coli was used as antigen.
• A modified F protein lacking the first 10 amino acids [Delta(1-10)-F] and an F synthetic peptide were used to confirm specificity and exclude cross-reactivity with anti-core antibodies.

Main Results:

• Antibodies against the complete F protein were detected in 62% (96/154) of chronically HCV-infected patients.
• A weaker reactivity against the Delta(1-10)-F protein was observed in 25% (39/154) of samples, while 97% (150/154) had anti-core antibodies.
• No reactivity against F, Delta(1-10)-F, or core proteins was found in healthy controls or patients with other liver diseases, confirming the specificity of the anti-F response.

Conclusions:

• The HCV F protein elicits a specific antibody response in a significant proportion (62%) of individuals with chronic hepatitis C infection.
• The anti-F antibody response appears to be independent of HCV RNA levels, viral genotype, and the stage of liver disease.
• Sequence analysis did not reveal significant differences in F protein sequences that could explain the variability in anti-F antibody responses, suggesting potential F sequence heterogeneity does not impact antibody elicitation.