Pneumonia (PNA) is one of the leading causes of death worldwide. PNA can result in devastating acute inflammatory injury in the lung manifesting in acute respiratory distress syndrome (ARDS). Current treatments for PNA have focused on the pathogens, but do not target excessive lung inflammation elicited by the host immune response. Both the emergence of new infections, typified by COVID-19, and the expanding impact of antimicrobial resistant pathogens, highlight the limitations of our current armamentarium and underscore the need to identify additional therapeutic targets in PNA-induced ARDS. With the understanding that resolution of PNA is an actively regulated program to promote return to homeostasis, our work has focused on identifying cellular and molecular mediators of this resolution phase. Others and we have demonstrated that regulatory T cells (Tregs) promote resolution of infectious-ARDS. Our strong preliminary data has identified lung-derived Treg DHX58, which encodes an RNA helicase protein essential for antiviral responses, as a candidate gene upregulated during the resolution phase of ARDS. DHX58- deficient animals fail to resolve lung inflammation after Streptococcus pneumoniae-ARDS with significantly diminished lung Treg numbers during injury resolution, implicating DHX58 in optimal Treg function in vivo. Further, we observed significantly increased 30-day mortality among carriers of a putative loss-of-function variant of DHX58 with infectious ARDS (71% vs. 47%, p=0.01), underscoring the potential clinical impact of DHX58 in ARDS outcomes. Our in-silico analysis of the DHX58 promoter identified numerous estrogen responsive elements (ERE). Indeed, DHX58 expression was induced in Tregs by estradiol (E2). Importantly, our published work showed that therapeutic E2 promotes resolution of preclinical PNA-ARDS in a Treg-dependent manner. Estrogen receptor beta (ER) was necessary for both Treg-dependent rescue of lymphopenic hosts and Treg-mediated suppression of pro-inflammatory cytokine production in macrophages in vitro. Preliminary gene expression analysis and high- dimensional flow cytometry implicate E2 and its downstream-target, DHX58, in the regulation of critical Treg transcription factors (TFs), notably Foxp3 and GATA3. Thus, we hypothesize that E2, in part via ER-dependent upregulation of DHX58, orchestrates critical Treg pro-resolution functions, through regulating expression of key TFs in Tregs. The goals of this proposal are to determine the cellular, molecular and transcriptional determinants of E2-ER-DHX58 in Treg-mediated resolution of PNA-ARDS to provide the mechanistic underpinnings of the regulation and functional role of ER in Tregs.