Injury Induces Early Activation of T-Cell Receptor Signaling Pathways in CD4+ Regulatory T Cells

Although it is known that injury enhances the regulatory activity of CD4+ regulatory T cells (Tregs), the cellular and molecular mechanisms responsible for injury-induced Treg activation remain unclear. This study was designed to investigate and compare injury-induced T-cell receptor (TCR) signaling in Tregs, non-Tregs, and CD8+ T cells. Specifically, we used phospho-flow cytometry to measure the expression and phosphorylation of ZAP-70, protein kinase C θ, nuclear factor of activated T cells, and glycogen synthase kinase 3β in FoxP3+ Tregs versus FoxP3− non-Tregs versus CD8+ T cells. Groups of male C57BL/6J mice underwent burn or sham injury, and lymph nodes and spleens were harvested at early time points-15, 30, 60, 120, and 240 min-to measure TCR signaling. As early as 15 min after burn injury, we observed a significant upregulation and phosphorylation of ZAP-70, protein kinase C θ, nuclear factor of activated T cells, and glycogen synthase kinase 3β in Tregs prepared from injury-site-draining lymph nodes. Burn injury did not activate TCR signaling in Tregs from the spleen or in CD4+ non-Tregs and CD8+ T cells. In conclusion, the results of this study demonstrate that burn injury activates TCR signaling in Tregs, but not non-Tregs or CD8+ T cells. These findings suggest that injury provides an early TCR-activating signal to Tregs and supply new insights into how injury influences the adaptive immune system. ABBREVIATIONS-GSK-3β-glycogen synthase kinase 3β;MFI-mean fluorescence intensity; NFATc1-nuclear factor of activated T cells; non-Treg CD4+ FoxP3−-nonregulatory T cell; PKC-θ-protein kinase C θ; RFI-relative fluorescence intensity; TCR-T-cell receptor; Treg CD4+ FoxP3+-regulatory T cell; ZAP-70-ζ-associated protein of 70 kd