IL-21 is produced by CD4⁺ T cells during <i>P</i>. <i>chabaudi</i> infection.

<p>(A) Flow cytometry plots showing individual examples of IL-21 expression on mononuclear cells from WT C57BL/6 and <i>Il21</i>^<i>-/-</i> mice at day 8 post-infection (top row). For the gating strategy, singlet cells were first selected, followed by live cells and mononuclear cells. In the bottom row, the IL-21-producing mononuclear cells detected in WT C57BL/6 mice, identified by red dots, were overlaid on the plots corresponding to the different combinations of surface biomarkers. (B) Cumulative data showing the differential combination of expression (+) or absence of expression (–) of each surface marker (indicated in the bottom left) on IL-21-producing mononuclear cells. (C) Flow cytometry plots showing individual examples of IL-21 expression on CD3⁺CD4⁺ T cells at day 8 post-infection. (D) Cumulative data showing the percentage (left) and total numbers (right) of IL-21-producing CD4⁺ T cells in the spleen of WT C57BL/6 mice at different days post-infection. Data are representative of at least two independent experiments and were obtained in groups of 4–5 mice per time point. Statistical significance was obtained using the Kruskal-Wallis test comparing each time point with its respective basal level (day 0 post-infection) (*, P<0.05; **, P<0.01; ***, P<0.001); or comparing each surface marker combination with every other surface marker combination within each time point (# #, P<0.01). Bars represent median values.