Murthy, A.; Rodriguez, L. R.; Barboza, W. R.; Tomer, Y.; Bui, S.; Carson, P.; Dimopoulos, T.; Iyer, S.; Chavez, K.; Cooper, C. H.; Katzen, J. B.; Beers, M. F.

Regulatory T (Treg) cells are well recognized for their role in immune regulation; however, their role in tissue regeneration is not fully understood. This study demonstrates such a role of Tregs in a published preclinical murine model of spontaneous pulmonary fibrosis (PF) expressing a human PF related mutation in the Surfactant Protein-C (SP-C) gene (SFTPCI73T). Genetic crosses of SP-CI73T mice with Foxp3GFP and Foxp3DTR lines were utilized to study Treg behavior during PF development. We found that FoxP3+Tregs accumulate during the transition from inflammation to fibrogenesis, peaking at 21-28 days after mutant SftpcI73T induction localizing to both perivascular and distal fibrotic lung regions. Diphtheria toxin mediated ablation of Tregs at 17 days worsened fibrosis and increased levels of TGF{beta} and inflammatory cytokines. Tregs expressed Th2 markers (Gata3+) and elaborated factors including amphiregulin (Areg) and Osteopontin (Spp1). Reductionist experiments showed that lung Tregs enhanced organoid formation when co-cultured with alveolar epithelial cells and adventitial fibroblasts, an effect size mimicked using Areg and Spp1 in combination. Our findings demonstrate that immune-mesenchymal-epithelial signaling crosstalk is present in the distal lung wherein Tregs play a protective role by limiting fibrosis and promoting tissue repair, highlighting their broader function beyond immune modulation in lung injury.