OBJECTIVE(S): We recently reported increased CD4+CD25+ T regulatory (Treg) activity after burn injury in mice. This study sought to determine if serious injury in humans affects Treg potency and their modulation of Th1 immunity.
METHODS: Peripheral blood was withdrawn from 18 consenting adult patients (37.6±17.2 years) with Injury Severity Scores (ISS) 34.3±13.5 on days 1 and 7 after trauma and from 5 healthy individuals. CD4+ T-cells were purified and sorted into Treg (CD25^high) and Treg-depleted populations. After activation of cells with anti-CD3/CD28 antibody, production of the Th1 cytokine IFNγ and the inhibitory cytokine IL-10 was measured using cytometric bead arrays. Treg activity was measured by in vitro suppression of autologous CD4+ T-cell proliferation. Treg surface expression of TGFβ1 was determined by flow cytometry.
RESULTS: Nine patients (50%) developed infection post-injury. IFNγ production by CD4+ T-cells decreased from day 1 to day 7. However, when Tregs were removed day 7 IFNγ production increased to control levels (Figure 1). Tregs were the chief source of IL-10. Treg suppression of T-cell proliferation increased significantly from day 1 to day 7 (Figure2) as did Treg surface expression of the suppressive cytokine TGFβ1.
CONCLUSIONS: We demonstrate for the first time increased potency of circulating Tregs after serious injury in humans. This appears to be responsible for injury-induced suppression of T-cell activation and reduction in the production of the protective cytokine IFNγ.