Notwithstanding the pro-fibrotic, pro-tumorigenic actions of pulmonary fibroblasts, these cells have also been reported to express the co-inhibitory immune checkpoint, PD-L1 (programmed death-ligand 1, CD274), which was identified in biopsy specimens taken from patients with idiopathic pulmonary fibrosis (IPF) [61]. Here, CD274 is linked to pulmonary fibrosis.