Induction of Foxp3^hi and Foxp3^int CD4⁺CD25^hi T cells by malaria-infected RBCs is time and concentration-dependent.

<p>PBMC were cultured alone, with uninfected RBCs (nRBC) or iRBCs for 6 days at different iRBC∶PBMC ratios. Cells were analysed by flow cytometry for CD25 and Foxp3 expression in gated CD4⁺CD3⁺ lymphocytes. Dot plots show 1 representative of 12 donors examined (A). Comparative analysis of Foxp3 and isotype control staining on CD4⁺CD25⁻ T cells and CD4⁺CD25⁺ T cells in day 6 cultures revealed specific Foxp3 expression solely in the CD25⁺ population (B). Absolute numbers of different CD4 T cell populations for 4 donors (Mean+/−SEM) were calculated based on light microscopic cell counts and flow cytometry analysis on day 6 of culture of originally 2×10⁷ PBMCs co-cultured in the absence or presence of nRBCs and iRBCs (C). Data from 12 donors demonstrate iRBC concentration-dependent induction of Foxp3^hi and Foxp3^int CD4⁺CD25^hi T cells (D). A representative plot of 1 out of 7 donors shows the induction of these cells over a time course of 6 days (E).