The CD4⁺CD25⁺ T cells suppress pathogen-driven responses of CD4⁺ T cells. (A-B) Tetanus toxin (TT:947-967) or haemagglutinin (HA:307-319) peptide-specific CD4⁺ T-cell lines were stimulated by DCs pulsed with the tetanus and the A2 (138-170) peptide or the HA and the A2 peptide in the presence of different numbers of CD4⁺CD25⁺ T cells. After 20 hours of stimulation, IL-2 production in the culture was measured by CTLL-2 cell proliferation. (C) Tetanus-specific CD4⁺ T-cell line was stimulated by the tetanus-loaded DCs in the presence of different numbers of CD4⁺CD25⁺ T cells and the A2 peptide–loaded DCs. After 20 hours of stimulation, IL-2 production in the culture was measured by CTLL-2 cell proliferation. Each bar shows the mean cpm ± SD. Results are representative of at least 2 independent experiments.