SFTPA2 and idiopathic pulmonary fibrosis: Among the stimuli and triggering conditions capable of inducing the UPR and ER stress in AECII are the discovered (heterozygous) mutations in the surfactant protein (SP)-C (SFTPC)- and SP-A2 (SFTPA2) genes in familial IPF, which cause misfolded SP-C and SP-A2 proteins, respectively [22,23,24,25].