CD4+CD25− and CD4+CD25hi splenic T cells were sort purified from (A, B) naïve mice or (B–F) T. gondii infected mice (day 10 of infection). CD25 detection was performed using the PC61 clone anti-CD25 antibody. CD4+CD25− and CD4+CD25hi cells were cultured with (A–D) naïve APC and anti-CD3 antibody or (E–F) T. gondii pulsed APC. (A, C, E) IFN-γ production was assayed in supernatant by ELISA. (B, D, F) Proliferation was determined by 3H Thymidine incorporation. The results shown are the mean ± std. dev. of the group (n = 3) and are representative of 2 independent experiments. # denotes significant difference between CD4+CD25− and CD4+CD25hi cultures (p<0.05). * denotes significant difference between CD4+CD25− and CD4+CD25− and CD4+CD25hi co-cultures (P<0.05).