TLR9 and idiopathic pulmonary fibrosis: In fact, previously normal lung fibroblasts stimulated with TLR9 agonists develop features of myofibroblasts (Kirillov et al., 2015; Ryu et al., 2017) and excessive concentrations of circulating mtDNA is predictive of poor outcomes in several IPF cohorts (Ryu et al., 2017; Sakamoto et al., 2021).