Figure 4.

Macrophage populations in idiopathic pulmonary fibrosis (IPF) lungs. a) SPP1 and FABP4 expression define two discrete populations in IPF and normal lungs. b) (and supplementary figure S18) SPP1^hi macrophages express more SPP1 and make up a higher percentage of cells in lower lobes, while FABP4^hi macrophages are a higher percentage of the cells in healthy and IPF upper lobes. c) Violin plots of combined IPF/control lung data show expression of FABP4, SPP1, LGMN, MERTK, FCN1 and IL1B limited mainly to macrophage populations (clusters 0, FABP4^hi macrophages; cluster 1, SPP1^hi macrophages and cluster 6, FCN1^hi monocyte/macrophages; figure 2). d) (and supplementary figure S19) FABP4 expression is increased in FABP4^hi macrophages, although it is also expressed at lower levels in SPP1^hi macrophages; SPP1, MERTK and LGMN show highly increased expression in SPP1^hi macrophages; FCN1 and IL1B are most highly expressed in FCN1^hi monocyte/macrophages. Immunofluorescent staining for SPP1 shows macrophages embedded in the SPP1/osteopontin matrix; while staining for MERTK and FABP4 reveals these largely two discrete macrophage populations with increased FABP4-staining macrophages in upper lobes and increased MERTK macrophages in lower lobes. Scale bar=100 μm.