FIG. 1.

Depletion of CD4⁺ CD25⁺ cells prior to lethal challenge with Tulahuen strain parasites does not lead to increased survival. Mice were given 400 μg anti-CD25 MAb (7D4 clone) or PBS at 7 days and 1 day prior to infection, then infected with either 100 or 1000 Tulahuen strain parasites. (A) Representative flow cytometric analysis of PBLs obtained from one mouse of a PBS-treated group (control) and one mouse of an anti-CD25 MAb-treated group (depleted) immediately prior to infection. Numbers in upper-right corner represent the percentage of CD4⁺ T cells that express CD25. (B) Cumulative data representing the mean frequencies of CD4⁺ CD25⁺ T cells in control and depleted groups prior to depletion, immediately prior to infection, and 6 days after infection with either 100 or 1,000 Tulahuen strain parasites. Each group consisted of 5 mice. Error bars represent standard deviation. (C) On day 15 postinfection, the frequency of TSKb20-specific CD8⁺ T cells was determined by staining PBLs with a FITC-conjugated anti-CD8α antibody and a PE-conjugated class I MHC H2-k^b tetramer loaded with TSKb20. A statistically significant increase was observed in the frequency of TSKb20-specific CD8⁺ T cells in the depleted, compared to the control group, of those mice infected with 1,000 Tulahuen strain parasites (P = 0.013, n = 5 per group). Error bars represent standard deviation. (D) The survival of mice treated with anti-CD25 MAb (filled) or control-treated with PBS (open), prior to infection with 100 (squares) or 1,000 (triangles) Tulahuen strain T. cruzi blood form trypomastigotes, was monitored on a daily basis. Each group was comprised of 5 mice at the start of the experiment.