Antigenic heterogeneity of the hepatitis C virus NS4 protein as modeled with synthetic peptides

The effect of sequence heterogeneity on the immunologic properties of two s trong antigenic regions of the hepatitis C virus (HCV) NS4 protein was stud ied by using a set of 443 overlapping 20-mer synthetic peptides. One antige nic region comprising the cleavage site between NS4a and NS4b (region 5-1-1 ) was modeled with peptides derived from 73 different known sequences, repr esenting HCV genotypes 1-6. The other antigenic region, designated region 5 9 and located at the C-terminus of the NS4b protein, was modeled with pepti des from 7 known sequences representing genotypes 1-3. All peptides were te sted for antigenic reactivity by enzyme immunoassay with a panel of anti-HC V-positive serum specimens representing genotypes 1-5. The data demonstrate d that immunoreactive peptides fell into two groups. One group, represented by N-terminal peptides, demonstrated genotype-independent immunoreactivity ; the other group, from the central part of region 5-1-1, showed strict gen otype specificity. Nineteen peptides from the genotype-independent group st rongly immunoreacted with a wide range of serum samples containing antibodi es to all 5 HCV genotypes. Twenty-five peptides from the genotype-specific group were found to strongly react with serum containing antibodies only to the genotype from which the peptides were derived. Similar to the N-termin al part of region 5-1-1, peptides derived from region 59 did not show genot ype-specific immunoreactivity. Some peptides derived from the central part of region 59 showed very strong and broad antigenic reactivity. Thus, after examining two antigenic regions of the NS4 protein, we identified short se quences that can be used for the efficient detection of either genotype-ind ependent or genotype-specific HCV antibodies.