DR1 and chronic hepatitis C virus infection: In HLA-DR1 positive patients with chronic hepatitis C a mean of 0.0032%+/− 0.0025 of CD4+ T cells stained tetramer+ (n = 6; range <0.001% to 0.0063%), which is more than 1.5 logs below the mean frequency of tetramer+ CD4+ T cells in patients in the early phase of acute hepatitis C, although still in some cases higher than the control stainings (DR1+HCV- and DR1-HCV+) which were all <0.001% (mean 0.00017%; Figure 6).