In this study, to gain a better understanding of the significance of Tregs in pulmonary fibrosis, we perform single-cell RNA-sequencing (scRNA-seq) and Bulk RNA-seq analyses, and reveal the appearance of Tregs uniquely expressing Trefoil factor 1 (Tff1) in the BLM-injured lungs. The gene discussed is TFF1; the disease is pulmonary fibrosis.