FIGURE 6.

CD4 T cell functional avidity is dependent on the presence of IL-15. WT C57BL/6 mice or IL-15–KO (on B6 background) mice were immunized i.p. with 50 μg per mouse of hep B core 128–140 in CAF09 twice 2 wk apart. Two weeks after the last immunization, splenocytes were stimulated in vitro for immune analyses. (A) Splenocytes were stimulated for 5 d in the presence of increasing concentrations of the hep B core 128–140 helper peptide, and IFN-γ production in the culture supernatant was assessed by IFN-γ ELISA. The curves represent mean and SEM of n = 3 mice per group immunized with hep B core 128–140 in CAF09 (WT and IL-15–KO mice) or WT mice receiving only CAF09 as a control (CAF09). Absolute levels of culture supernatant IFN-γ (pg/ml) (upper panel). IFN-γ production normalized to the maximum production for each mouse (lower panel). (B) From the normalized values in the lower panel in (A), the concentration of peptide needed to induce 50% of the maximum response (EC₅₀) was calculated for each mouse; data points represent avidity shown as log₁₀(EC₅₀) mg/ml hep B 128–140 peptide with SEM. (C) Percentages of PD-1⁺ CD4 T cells (upper panel) and PD-1 expression per cell (MFI; middle panel) for all CD4 T cells. PD-1 MFI for IFN-γ⁺ CD4 T cells after stimulation with hep B 128–140 and ICS (lower panel). Data points represent individual mice; mean and SEM are indicated. The data shown are representative of two experiments with similar results. *p < 0.05, **p < 0.01, one-way ANOVA and Newman–Keul posttest.