Genotype dependence of peptide-based immunoassays for the detection of HCV core antibodies

Detection of hepatitis C virus (HCV) antibodies is partially influenced by the genotype of the infecting isolate. Immunoassays using genotype-1a-derived recombinants or peptides results in diminished reactivity among individuals infected with heterologous genotypes. We examined the magnitude of this effect on detection of core antibodies by using genotype-1a-derived core peptide immunoassays to test 254 HCV anti-core-positive individuals infected with genotypes 1-4 or 6. Peptides corresponding to amino acids 1-18, 10-24, and 11-28 reacted with 60%, 89%, and 85% of all samples, respectively. Peptide 1-18 detected 78% of individuals infected with genotype-1 or 2 but only 43% of those infected with genotypes 3, 4, or 6. Genotype-dependent reactivity was also observed for peptides 10-24 and 11-28. The use of a 34-mer peptide (encompassing amino acids 10-43) within the immunodominant region detected antibodies in 100% of specimens, thereby eliminating the genotype-dependent antibody detection observed with shorter peptides. Sequence differences between peptides and core of the infecting isolate did not entirely account for the genotype-dependent reactivity since some individuals displayed reactivity to peptides containing up to seven amino acid differences relative to the sequence of the infecting isolate, while others with identical core sequences had little or no reactivity. Thus, HCV core sequence divergence accounts for only a portion of the differential core antibody detectability observed when non-type-specific peptides are used. Differences in immune response between individuals infected with identical isolates also plays a significant role in core antibody detection using short peptides.