CD4 and pulmonary fibrosis: In order to determine whether Tregs accumulate in the lungs of mice subject to TGFβ1-induced lung fibrosis, TGF-β1 transgene positive (Tg+) and transgene negative (Tg−, i.e., wild type) mice were given doxycycline in their drinking water, sacrificed at early (48 h), intermediate (5 days), and late timepoints (14 days) and Tregs were quantified using standard FACS-based assessment of CD4+CD25+FoxP3+ cells on lung digests (Figure 1A).