Quantitative analysis of antibodies to hepatitis C virus during interferon-alpha therapy.

We quantified IgG antibodies to structural (core) and nonstructural (C100-3) hepatitis C virus proteins in 42 patients with chronic hepatitis C treated with a 6-mo course of interferon-alpha. Sera were drawn before and at the end of therapy and also 6 mo after therapy withdrawal; they were stored for later analysis of antibodies and serum hepatitis C virus RNA. Sustained virus clearance was observed at the end of therapy and 6 mo after therapy withdrawal in nine cases; it was accompanied with sustained reductions of antibody to hepatitis C virus core protein and antibody to C100-3 protein. A sustained reduction of antibody to hepatitis C virus core protein was specific to sustained virus clearance, although that of antibody to C100-3 protein was not. None of the patients who did not show reductions of levels of both antibodies at the end of therapy displayed sustained virus clearance. Five patients showed hepatitis C virus RNA negativity and normal aminotransferase levels at the end of therapy without reduction of antibody to hepatitis C virus core protein levels. Of these five patients, relapse of hepatitis occurred in four, and viremia was present 6 mo after therapy withdrawal in all cases. These results demonstrate that testing for antibody titers may add information for evaluating virus clearance after interferon therapy.