Treatment with FTY720 promotes thymic sequestration of CD4⁻CD8⁻ T cells with reduction of the corresponding peripheral pool during <i>T. cruzi</i> infection.

<p>Infected mice had been pretreated with FTY720 or saline every 2 days, starting at day 6 post-infection with <i>T. cruzi</i> parasites. At day 17 post-infection, thymocytes were harvested and (<b>A</b>) absolute cell numbers were determined by direct counting. (<b>B</b>) The cytofluorometric profiles of thymocytes were obtained after staining with anti-CD4 and anti-CD8 mabs. A representative FACS profile is shown and the ratio of each thymocyte population given as means ± SE. (<b>C</b>) The absolute numbers of CD4⁻CD8⁻, CD4⁺CD8⁺, CD4⁺ and CD8⁺ thymocytes were determined. CD4⁻CD8⁻ T cells are increased in FTY720-treated mice by 500%, when compared to infected untreated mice. (<b>D</b>) The accumulation of CD4⁻CD8⁻TCRVβ⁺ T cells in the SCLN during infection was significantly reduced in infected mice treated with FTY720. Data show a means ± SE in two independent experiments using five pooled thymuses. (<b>E</b>) Representative FACS profile of cells from SCLN after staining with anti-CD4 and anti-CD8 mabs (<b>upper panel</b>). Histograms represent TCRVβ expression in both immature CD4⁻CD8⁻ T cells (TCR negative/low) and CD8⁺ mature thymocytes (TCR high). The background staining was defined using the isotype control antibody. Differences between uninfected and infected groups are significant * (<i>p</i><0.05), ** (<i>p</i><0.01) and *** (<i>p</i><0.001). Differences between FTY720-treated and untreated infected groups are significant # (<i>p</i><0.05) and ## (<i>p</i><0.01).