Adoptive transfer of Tregs reduced fibroproliferation in Rag-1−/− mice after LPS injury. (A) Lung sections were stained with Masson’s trichrome to highlight collagen deposition on Day 3 and Day 7 after intratracheal LPS or intratracheal water in WT and Rag-1−/− mice (n ≥ 3 in each group; images are of representative examples, ×200 magnification). (B) Lung sections were stained with Masson’s trichrome on Day 7 after intratracheal LPS or intratracheal water in Rag-1−/− mice, Rag-1−/− mice + Tregs, and Rag-1−/− mice + non-Tregs (images are of representative examples, ×200 magnification, n ≥ 3 in each group). (C) Lung collagen was measured by Sircol assay in all groups on Day 3 and Day 7 after intratracheal LPS (*P = 0.009 and #P = 0.047, n ≥ 4, all groups). (D) BAL collagen was measured by Sircol assay in all groups on Day 3, Day 7, and Day 10 after intratracheal LPS (*P = 0.002, †P = 0.003, ‡P = 0.005, and #P = 0.005, n ≥ 3, all groups). (E) Lung collagen was positively correlated with the natural log of BAL collagen (r = 0.73, P < 0.001, using Pearson product moment correlation).