<i>P</i>. <i>yoelii</i> infection increases PD1 expression on NTS-specific CD4 T cells.

<p>C57BL/6 mice were vaccinated with <i>S</i>. Typhimurium BRD509:2W1S (Vac) and then given <i>P</i>. <i>yoelii</i> (<i>P</i>.<i>y</i>.) as described above. (<b>A</b>) At 14 d post <i>P</i>. <i>yoelii</i> infection, splenic T cells were evaluated by flow cytometry for expression of CTLA-4 and PD1. Bar graphs show percentage of CTLA-4+, and PD1+ among 2W1S-specific CD4 T cells. Data are shown as Mean+SEM (n = 10). (<b>B-D</b>) <i>P</i>. <i>yoelii</i>-infected mice were given either an antibody cocktail consisting of αCTLA-4, αLAG3 and αPDL-1 or isotype control antibodies over 7 days as described in methods. (<b>B</b>) Parasite burden with blocking antibody cocktail (n = 3) or isotype control (n = 2), as determined by blood smears. (<b>C</b>) At 14 days post-<i>P</i>. <i>yoelii</i> infection, all the treated mice were injected i.v. with heat-killed <i>S</i>. Typhimurium lysates for 4 hours. Splenic CD4 T cells were analyzed by flow cytometry for IFN-γ production. Bar graphs show percentage of IFN-γ producing Tbet+ CD44+ 2W1S-specific CD4 T cells with blocking antibody cocktail (n = 3) or isotype control (n = 2). (<b>D</b>) Antibody-treated mice were challenged with 750 CFU of virulent <i>S</i>. Typhimurium via the i.v. route at 14 days after <i>P</i>. <i>yoelii</i> infection. At 3 d post-challenge, bacterial burden was determined in livers and normalized to tissue weight. Data represent Mean+SEM (n = 5 per group). Data are shown as Mean+SEM. Significance of differences between groups was determined using a Student’s <i>t</i> test (*, <i>p</i><0.05; ns, not significant).