Characterization of neutralizing antibody responses in HCV infected individuals.

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Hepatitis C virus is a major human pathogen infecting 200 million people world-wide. Currently, there is no vaccine to prevent infection and treatment regimes are only partially effective. IInitial HCV infection is frequently asymptomatic and 30% of people spontaneously clear the virus. The remaining 70% of people develop a life-long chronic infection that causes progressive liver disease, cirrhosis and in some cases liver cancer. The reason why some people are able to clear virus has been attributed to the development of a strong cellular immune response and antibody is belived to play a monir role in achieving viral clearance. However, measurememnt of antibody responses in HCV infected pateints is routinely performed using conventional diagnostic tests that do not measure antibody that can help neutralize and clear virus. We have developed an assay that accurately measures the level of NAb in patient sera. We have found that chronically infected patients have broadly reactive neutralizing antibodies but that patients who clear virus, naturally or through treatment do not have broadly reactive neutralizing antibodies. Possibly explaining this phenomenon is that early during infection, antibody is frequently specific only to the infecting virus therefore to detect neutralizing antibodies, homologous viral sequences must be examined. In addition, we have found evidence that HCV can evade neutralzing antibodies through masking of sites to which antibodies bind. We propose to explore whether acutely infected patients develop NAb to autologous viral sequences, and how do these viral sequences and the antibody titre change throughout the course of infection and treatment. We also plan to determine the mechanism of neutralization resistance through the use of mutagenesis of resistant HCV glycoproteins. These studies are aimed at gaining a thorough understanding of the true role of antibody in HCV infection and its influence on viral evolution.