TNFRSF1A and idiopathic pulmonary fibrosis: Further, a human apoptosis array on both IPF- and control-derived fibroblast CM found a high concentration of secreted pro-apoptotic proteins including, pro-caspase 3, cytochrome C, hypoxia-inducible factor alpha (HIF-1α) and tumor necrosis factor receptor 1 (TNFR1) [61].