IL-21 antagonizes virus-induced Treg cell expansion during chronic infection.

<p>(A) Frequencies of splenic Foxp3⁺CD25⁺CD4⁺ T cells from WT and IL-21R^−/− mice at indicated days after infection with indicated doses of LCMV-DOC. (B) Total numbers of Foxp3⁺ cells (2000 PFU LCMV-DOC, 15 dpi). (C) IL-21R expression on GFP⁺CD4⁺Treg cells of naïve and LCMV-DOC infected DEREG mice (2×10⁴ PFU, 15 dpi). The mean fluorescent intensity (MFI) of single mice (left panel) and averages ± SEM of groups (n = 4) (right panel) are shown. (D–G) Analysis of WT (CD45.1⁺):IL-21R^−/−(CD45.2⁺) mixed BM chimeras. (D) Blood frequencies of CD4⁺, CD8⁺ and Foxp3⁺CD25⁺CD4⁺ T cell populations derived from WT and IL-21R^−/− BM 8 weeks after BM transfer prior LCMV infection. Reconstitution efficiency of WT and IL-21R^−/− lymphocytes (lym) were in average 51%:49% and values for the CD4⁺ and CD8⁺ T cell populations were corrected for chimerism. (E) FACS plots show CD25 and Foxp3 expression of CD4⁺ T cells, (F) graphs show frequencies and (G) total numbers of splenic Foxp3⁺CD25⁺ Treg cells 35 dpi with 2000 PFU LCMV-DOC. (H) Suppressive activity of FACS-sorted CD4⁺CD25⁺ Treg cells from infected DEREG or DEREGxIL-21R^−/− mice was assessed as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003362#s4" target="_blank">Materials and Methods</a>. (I) Cell surface expression of putative Treg markers and (J) IL-10 production by Foxp3⁺CD4⁺ T cells isolated from WT or IL-21R^−/− mice infected with 2×10⁴ PFU LCMV-DOC 15 dpi. (J) Dot plots depict IL-10 production of splenic Foxp3⁺ T cells of WT or IL-21R^−/− mice after restimulation with gp61. Shown are representative individuals of groups of mice (n = 4). (K–N) IL-6^−/− and WT mice (n = 5/group) were infected with 2×10⁴ PFU LCMV-DOC and analyzed 30 dpi. Shown are frequencies of Foxp3⁺ cells (K), gp33-specific CD8⁺ T cells (L), IFN-γ-producing CD8⁺ and CD4⁺ T cells (M), and virus titers in organs indicated (N). (A–N) Data represent one of two independent experiments.