A prospective cohort study evaluating BAL fluid and plasma from 65 COVID-19 ARDS patients and 63 ventilated controls found elevated levels of TGF-β1 and N-terminal pro-peptide of type III procollagen (NT-PCP-III), alongside increased levels of oxidative stress markers (malondialdehyde [MDA] and oxidized glutathione [GSSG]) and reduced levels of antioxidants (superoxide dismutase [SOD] and reduced glutathione [GSH]). Here, TGFB1 is linked to COVID-19.