Regulatory T Cells Modulate CD4 Proliferation after Severe Trauma via IL-10

Objective: Severely injured patients frequently develop an immunological imbalance following the traumatic insult, which might result in infectious complications evoked by a persisting immunosuppression. Regulatory T cells (Tregs) maintain the immune homeostasis by suppressing proinflammatory responses, however, their functionality after trauma is unclear. Here, we characterized the role of Tregs in regulating the proliferation of CD4(+) lymphocytes in traumatized patients (TP). Methods: Peripheral blood was obtained daily from 29 severely injured TP (Injury Severity Score, ISS ≥16) for ten days following admission to the emergency department (ED). Ten healthy volunteers (HV) served as controls. The frequency and activity of Tregs were assessed by flow cytometry. Proliferation of CD4(+) cells was analyzed either in presence or absence of Tregs, or after blocking of either IL-10 or IL-10R1. Results: The frequencies of CD4(+)CD25(high) and CD4(+)CD25(+)CD127(−) Tregs were significantly decreased immediately upon admission of TP to the ED and during the following 10 post-injury days. Compared with HV CD4(+) T cell proliferation in TP increased significantly upon their admission and on the following days. As expected, CD4(+)CD25(+)CD127(−) Tregs reduced the proliferation of CD4(+) cells in HV, nevertheless, CD4(+) proliferation in TP was increased by Tregs. Neutralization of IL-10 as well as blocking the IL-10R1 increased further CD4(+) T cell proliferation in Tregs-depleted cultures, thereby confirming an IL-10-mediated mechanism of IL-10-regulated CD4(+) T cell proliferation. Neutralization of IL-10 in TP decreased CD4(+) T cell proliferation in Tregs-depleted cultures, whereas blocking of the IL-10R1 receptor had no significant effects. Conclusions: The frequency of Tregs in the CD4(+) T lymphocyte population is reduced after trauma; however, their inductiveness is increased. The mechanisms of deregulated influence of Tregs on CD4(+) T cell proliferation are mediated via IL-10 but not via the IL-10R1.