TNFSF10 and idiopathic pulmonary fibrosis: TRAIL was present in both IPF plasma and biopsies, and its transcript was elevated in both IPF lung biopsies and explants but lost in IPF BAL cells; however, transcripts for its major receptors were downregulated in both IPF lung biopsies and explants and protein levels for one of its major receptors, DR5, was largely absent from both IPF biopsies and primary IPF fibroblasts.