Depletion with PC61 mAb before Toxoplasma gondii infection eliminates mainly Tregs in BALB/c mice, but activated cells in C57BL/6J mice.

Analysis of regulatory T cells (Tregs) in vivo during infection is crucial for the understanding of immune response modulation. Depletion experiments using anti-CD25 monoclonal antibody (mAb) in order to eliminate Tregs have been widely used for this purpose despite the fact that this approach may also lead to the elimination of activated T cells. We show in this paper that treatment with anti-CD25 mAb before Toxoplasma gondii infection eliminates a different pattern of cell subsets in the resistant BALB/c and the susceptible C57BL/6J mouse strain. Injection with PC61 mAb leads to the elimination of most Tregs in BALB/c mice, while in C57BL/6J animals, treatment depletes other activated subsets [natural killer (NK), B and CD4(+) T cells]. This difference is a consequence of the dramatic cell activation observed in the latter, but not in the former strain. The different effect of the depletion reported here demonstrates that careful analysis in each model is mandatory in order to avoid misleading conclusions.