Abstract

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease with an elusive aetiology. A common feature of fibrotic areas is the presence of anthracosis localized in cellular structures. Macrophages are professional phagocytes and the key players in the immune and inflammatory response. This study aims to analyze the composition of anthracotic particles in IPF lungs and their effect on different macrophage subtypes in their phagocytic clearance process. Therefore, tissue samples were collected from human lung explants and ashed in a muffle furnace to isolate anthracotic particles using a scanning electron microscope combined with energy-dispersive spectroscopy. IPF lungs contained approximately 3.5 times more anthracosis than controls and a specific metal-containing composition in 25% of IPF lungs. Human monocytes were isolated from healthy blood donors, differentiated into macrophage subtypes (M0, M1, M2a, M2b, M2c, M2d) and incubated with metal particles for phagocytosis experiments. A new real-time cell metabolic analysis showed a significant increase in both, glycolytic as well as mitochondrial ATP production and a shift in bioenergetics towards glycolysis in all macrophage subtypes pronounced in M1 and M0 and RNA-seq analysis an altered gene expression of two IPF marker genes after incubation with metal particles. The results showed that metal particles cause oxidative stress in macrophages and may maintain chronic inflammation, which contributes to the pathogenesis of IPF.