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Gut Inflammation in Mice Triggers Proliferation and Function of Mucosal Foxp3+ Regulatory T Cells but Impairs Their Conversion from CD4+ T Cells

Boschetti, G;Kanjarawi, R;Bardel, E;Collardeau-Frachon, S;Duclaux-Loras, R;Moro-Sibilot, L;Almeras, T;Flouri, B;Nancey, S;Kaiserlian, D;

Regulatory Foxp3(+)CD4(+) T cells [Tregs] have been implicated in the control of colitis in T-cell transfer models, yet their ability to regulate colitis induced by innate immunity and the impact of gut inflammation on their fate and function have been poorly documented.,Colitis was induced by dextran sodium sulphate in DEREG transgenic mice. Tregs ablation and transfer experiments showd that Tregs could limit the severity of colitis in B6 mice.,Gut inflammation resulted in increased number of Tregs in mesenteric lymph nodes [MLN] and colon lamina propria [LP], although their frequency decreased due to massive concomitant leukocyte infiltration. This coincided at both sites with a dramatic increase in Ki67(+) Tregs which retained proliferative capacity. Gut inflammation resulted in enhanced suppressive function of Tregs in colon lamina propria and neuropillin-1(-) [NRP1(-)] Treg in MLN. Real-time polymerase chain reaction analysis and flow cytometry [using IL10-egfp-reporter mice] showed that compared with NRP1(+) Treg, NRP1(-) Treg express higher levels of IL-10 transcripts and were enriched in IL10-expressing cells both in the steady state and during colitis. Moreover, Treg conversion in vivo from from nave CD4(+) T cells or Treg precursors was impaired in colitic mice. Finally, gut inflammation caused a decrease in intestinal dendritic cells, affecting both CD103(+)CD11b(+) and CD103(+)CD11b(-) subsets and affected their Treg conversion capacity.,Together, our data indicate that non-specific colon inflammation triggers proliferation and suppressive function of Tregs in the lamina propria and MLN, but impairs their de novo conversion from CD4(+) T cells by intestinal dendritic cells.