PDCD1 and idiopathic pulmonary fibrosis: Moreover, CD8+T cells are sufficient to induce key hallmarks of CD8+T cell exhaustion; aggregated CD8+T cells exhibit elevated PD-1 and PD-L1 mRNA levels in IPF patients and BLM-induced fibrosis mice (65), indicating that the lung in a stage of profibrotic and proinflammatory activation (66).