Pathologic Th1–Treg Cells Exacerbate Acute Lung Injury and Lethality in Sepsis

Sepsis is characterized by dysregulated immune responses induced by damage-associated molecular patterns, such as extracellular cold-inducible RNA-binding protein (eCIRP), that frequently lead to acute lung injury (ALI) and high mortality. Recently, a subset of CD4⁺ T cells possessing both T helper 1 (Th1) and regulatory T cell (Treg) phenotypes, termed Th1-Treg cells, has been identified; however, their function in sepsis remains unknown. In this study, we investigated the dynamics, induction mechanisms, and functional roles of Th1-Treg cells in the development of sepsis-induced ALI. Polymicrobial sepsis was induced in mice using cecal ligation and puncture. In vivo, Th1-Treg cell accumulation in the lungs was analyzed in WT and CIRP^-/- mice following sepsis. In vitro, isolated CD4⁺ T cells from WT and TLR4^-/- mice were treated with eCIRP to evaluate Th1-Treg cell differentiation and downstream signaling pathways. STAT1 and STAT5 activation were evaluated, and pharmacological inhibitors were used to assess their involvement. Adoptive transfer of Th1-Treg cells was conducted to determine their functional impact on ALI and mortality in septic mice. We observed a significant accumulation of Th1-Treg cells in the lungs of WT septic mice compared to sham mice. eCIRP drove the induction of Th1-Treg cells in vitro, and CIRP^-/- mice exhibited decreased Th1-Treg cell accumulation in the lungs compared to WT mice after sepsis. In parallel to Th1-Treg cell induction, eCIRP activated signal transducer and activator of transcription, STAT1 and STAT5. Both the induction of Th1-Treg cells and the activation of STAT1/5 proteins were significantly attenuated in TLR4^-/- mice. Furthermore, pharmacological inhibition of STAT1/5 signaling significantly reduced eCIRP-induced Th1-Treg cell differentiation. Intriguingly, adoptive transfer of Th1-Treg cells significantly exacerbated ALI, resulting in increased mortality in sepsis. Our findings indicate Th1-Treg cells induced by the eCIRP-TLR4-STAT1/5 axis aggravate ALI, worsening mortality in sepsis. Targeting these pathogenic cells potentially alleviates sepsis-induced ALI.