Figure 1. Functional avidity of HCV-specific CD8+ T cells.

(A) Representative flow cytometry plots showing intracellular IFN-γ staining of a CTL line exposed to target cells pulsed with a range of peptide concentrations. PBMCs from a subject chronically infected with HCV were stimulated for two weeks with the HLA-A*02-restricted NS3₁₀₇₃ epitope. Prior to intracellular IFN-γ staining, the CTL line was cocultured for 5 hours with HLA-A*02+ EBV-immortalized B-cell lines (B-LCLs) pulsed with serially diluted concentrations of the cognate peptide. The background value from the negative control (B-LCLs without peptide loading) was subtracted from all measured response frequencies (IFN-γ+ CD8+/total CD8+). (B) Representative data from intracellular IFN-γ staining of a CTL line specific for the HLA-A*02-restricted NS3₁₀₇₃ epitope (filled circles) and a CTL line specific for the HLA-B*27-restricted NS5B₂₈₄₁ epitope (open circles) across a range of peptide concentrations. The background value from the negative control (B-LCLs without peptide loading) was subtracted from all measured response frequencies (IFN-γ+ CD8+/total CD8+), which were then normalized to the maximum response by defining the smallest value as 0% and the largest value as 100%. (C) The functional avidity of CTL lines, derived from chronically HCV infected subjects, specific for HLA-A*02-restricted epitopes (n = 7, filled circles) and the immunodominant HLA-B*27-restricted epitope NS5B₂₈₄₁ (n = 6, open circles), as well as of CTL lines derived from subjects with resolved infection specific for HLA-A*02-restricted epitopes (n = 3, filled squares) and the immunodominant HLA-B*27-restricted epitope NS5B₂₈₄₁ (n = 4, open squares). Functional avidity was determined as the concentration of peptide required to achieve half-maximal IFN-γ induction (EC₅₀). P-values were calculated using the Mann-Whitney U-test. Horizontal bars represent mean values.