CD4+Foxp3+ regulatory T cells mediate Toxoplasma gondii‐induced T‐cell suppression through an IL‐2‐related mechanism but independently of IL‐10

Acute Toxoplasma gondii infection comprises an immunosuppression stage, characterized by a reduction in T‐cell proliferation in vitro. Treg cells maintain the homeostasis of the immune system, but their role in T. gondii‐induced suppression has not been addressed. We show herein that immunosuppression, affecting both CD4+ and CD8+ T‐cell proliferation, concurs with a reduction in Treg‐cell number. The residual Treg cells, however, are activated and display an increased suppressive capacity. We show that selective elimination of Treg cells using Foxp3EGFP mice leads to a full recovery of CD4+ and CD8+ T‐cell proliferation. After Treg‐cell removal, a reduced production of IL‐10 was observed, but IL‐2 levels were unchanged. The numbers of IL‐10‐producing Treg cells also increased during infection, although the in vitro neutralization of this cytokine did not modify T‐cell proliferation, suggesting that IL‐10 does not mediate the Treg‐mediated suppression. However, addition of rIL‐2 in vitro fully restored T‐cell proliferation from infected animals. Thus, we show that Treg cells mediate the T‐cell suppression observed during acute T. gondii infection through an IL‐2‐dependent mechanism. Our results provide novel insights into the regulation of the immune response against T. gondii.