FIGURE 5.

Interleukin-6 increases efferocytosis and favors the capacity of human phagocytes to eliminate cholesterol derived from apoptotic cells through stimulation of ABCA1-mediated cholesterol efflux to apoAI. A, human THP-1 macrophages (phagocytes) were treated with or without IL-6 (50 ng/ml) in the presence or in the absence of TO901317 (1 μm) for 24 h. Phagocytes were incubated together with calcein-AM-labeled apoptotic Jurkat cells for 30 min, and positive fluorescent phagocytes that had ingested calcein-AM-labeled apoptotic cells were quantified by flow cytometry. Values are the means ± S.E. of three independent experiments and are expressed as relative to control cells. *, p < 0.05; **, p < 0.001 versus control cells; †, p < 0.01; ††, p < 0.001 versus IL-6-treated cells; ‡, p < 0.01 versus TO901317-stimulated cells. B, phagocytosis of apoptotic cells in Ctrl and ABCA1 KD THP-1 macrophages upon stimulation with TO901317 is shown. Values are the means ± S.E. of three independent experiments and are expressed relative to respective control cells. *, p < 0.05; **, p < 0.005; ***, p < 0.0001 versus control cells. Quantification of c-mer proto-oncogene-tyrosine kinase (MERTK; C), TG2 (D), and THBS1 (E) mRNA levels in THP-1 macrophages upon stimulation with IL-6 is shown. Amounts of mRNA levels were normalized to housekeeping genes (δ-aminolevulinate synthase, α-tubulin, and hypoxanthine phosphoribosyltransferase 1). Values are the means ± S.E. of four independent experiments performed in triplicate. *, p < 0.05 versus None. F, human THP-1 macrophages (Phagocytes) were treated with or without IL-6 (50 ng/ml) in the presence of TO901317 (1 μm) for 24 h. Phagocytes were incubated together with apoptotic [³H]cholesterol-loaded THP-1 macrophages for 30 min, and cholesterol efflux to lipid-free apoAI from phagocytes was assayed for 4 h. Values are the means ± S.E. of two independent experiments. *, p < 0.05; **, p < 0.001 versus non-stimulated cells; ‡, p < 0.01 versus TO901317-stimulated cells.