SPP1 and pulmonary fibrosis: ScRNA-seq has identified three distinct subsets of pulmonary macrophages in both normal and idiopathic pulmonary fibrosis (IPF) lungs: FABP4hi macrophages (characterized by high expression of Fatty Acid Binding Protein 4 (FABP4) and Inhibin Subunit Beta A (INHBA) but low SPP1 and MER Tyrosine Kinase (MERTK)), FCN1hi macrophages (with high Ficolin-1 (FCN1) expression), and SPP1hi macrophages (high expression levels of SPP1 and MERTK, cf. Table 1, Figure 1) [45].