Phagocytosis and Autophagy in THP-1 Cells Exposed to Urban Dust: Possible Role of LC3-Associated Phagocytosis and Canonical Autophagy

Exposure to ambient particulate matter (PM) increases mortality and morbidity due to respiratory and cardiovascular diseases. The aim of this study was to assess the effect of standardized urban dust (UD) on phagocytosis and autophagy in a monocyte-macrophage cell line (THP-1 cells). The cells were grown for 24 h in the medium supplemented with 200 μg·mL−1 coarse carbon black (CB) or UD. In some experiments glutathione (GSH) was depleted in THP-1 cells by buthionine sulfoximine. The cells were double stained with green latex beads (phagocytosis) and with red autophagy marker (LC3) and were evaluated in a flow cytometer. In naive THP-1 cells, about 61% of them were classified as “negative”, while 39% were classified as “double-positive”. Both GSH depletion and UD treatment produced three distinct subpopulations of cells on bivariate scatterplots. A new subpopulation of cells (about 24% of the total number) appeared, with a lower autophagy and phagocytosis, but with a higher autophagy/phagocytosis ratio, when compared to highly positive cells. CB affected, to some extent, phagocytosis without a substantial effect on autophagy. In conclusion, the research on distinct pathways of immune cell activation may be relevant to the diagnostics and therapy of PM-induced pneumotoxicity, inflammation, and tumorigenesis.