CD4+FoxP3+ Tregs are activated by injury

Abstract

Enhanced CD4+CD25+ regulatory T cell (Treg) potency occurs following injury suggesting that Tregs may play a natural role in controlling the host response to injury. This study addresses whether injury can activate Tregs. To accomplish this, we used a FoxP3‐GFP knock‐in mouse as a tool to accurately identify and measure phenotypic changes in FoxP3‐expressing Tregs in sham versus injured mice. FoxP3‐GFP mice were anesthetized and underwent sham or burn injury. At days 1, 3, and 7 after injury, mice were sacrificed and cells were prepared from the injury site, lymph nodes draining the injury site, and spleen. Cells were stained to detect CD4 T cells and counterstained to detect changes in CD25, CD69, CD62L, ICOS, PD‐1, and CTLA‐4 expression levels. We found that injury caused a significant increase in the percentage of FoxP3+ Tregs in the lymph nodes draining the injury site at all time points after injury. In contrast, significant increases in Tregs were not detected until 7 days after injury at the site of injury and in the spleen. The results of experiments testing for phenotypic changes in Tregs after injury showed that injury induced increased expression of CD25, CD62L‐low, ICOS, PD‐1, and CTLA‐4 on lymph node and spleen FoxP3+ Tregs as early as 1 day after injury. At 7 days after injury, FoxP3+ CD4 T cells showed further signs of activation and expressed significantly higher levels of ICOS and CTLA4. We confirmed that injury activates Tregs by performing an adoptive transfer of FoxP3‐GFP+ cells into CD4−/− mice and showing that Tregs from burn mice expressed an activated phenotype. Thus, Tregs are activated by injury and injury can increase the percentage of Tregs at the site of injury, the draining lymph nodes and spleen. Therefore, the enhanced Treg function that occurs after injury might be due to the injury‐induced activation of FoxP3+ Tregs.