title: Macrophages use different internalization mechanisms to clear apoptotic and necrotic cells.
abstract: The present study characterized two different internalization mechanisms used by macrophages to engulf apoptotic and necrotic cells. Our in vitro phagocytosis assay used a mouse macrophage cell line, and murine L929sAhFas cells that are induced to die in a necrotic way by TNFR1 and heat shock or in an apoptotic way by Fas stimulation. Scanning electron microscopy (SEM) revealed that apoptotic bodies were taken up by macrophages with formation of tight fitting phagosomes, similar to the 'zipper'-like mechanism of phagocytosis, whereas necrotic cells were internalized by a macropinocytotic mechanism involving formation of multiple ruffles directed towards necrotic debris. Two macropinocytosis markers (Lucifer Yellow (LY) and horseradish peroxidase (HRP)) were excluded from the phagosomes containing apoptotic bodies, but they were present inside the macropinosomes containing necrotic material. Wortmannin (phosphatidylinositol 3'-kinase (PI3K) inhibitor) reduced the uptake of apoptotic cells, but the engulfment of necrotic cells remained unaffected. Our data demonstrate that apoptotic and necrotic cells are internalized differently by macrophages.
authors.affiliation: Department of Human Anatomy, Embryology, Histology and Medical Physics, Ghent University, Ghent 9000, Belgium.
authors.forename: D V
authors.initials: DV
authors.lastname: Krysko
authors.forename: G
authors.initials: G
authors.lastname: Denecker
authors.forename: N
authors.initials: N
authors.lastname: Festjens
authors.forename: S
authors.initials: S
authors.lastname: Gabriels
authors.forename: E
authors.initials: E
authors.lastname: Parthoens
authors.forename: K
authors.initials: K
authors.lastname: D'Herde
authors.forename: P
authors.initials: P
authors.lastname: Vandenabeele
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D004705:Endocytosis / Q000502:physiology*; D005456:Fluorescent Dyes; D006735:Horseradish Peroxidase; D006801:Humans; D007546:Isoquinolines; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008855:Microscopy, Electron, Scanning; D009336:Necrosis / Q000503:physiopathology*; D010587:Phagocytosis / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010873:Pinocytosis / Q000502:physiology*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D005456:Fluorescent Dyes; D007546:Isoquinolines; D000081082:Phosphoinositide-3 Kinase Inhibitors; C017475:lucifer yellow; D006735:Horseradish Peroxidase; D000077191:Wortmannin