Patients with chronic non-GT1 infection who have serologic evidence of previous exposure to GT1 show significantly more responses than patients with non-GT1 infection in whom genotype and serotype correspond. Horizontal bars indicate the mean numbers of targeted HCV CD4⁺ T-cell responses against single peptides for each patient as tested by ICS. The number of responses is significantly higher (P < .001) in chronically infected patients with non-GT1 virus that serologically showed evidence for exposure to GT1 than patients chronically infected with a non-GT1 virus in whom genotype and serotype corresponded non-GT1. Serotyping test was performed with the Murex HCV serotyping 1-6 assay (Abbott; “Patients, materials, and methods”).