A novel real time imaging platform to quantify macrophage phagocytosis

Biochem Pharmacol. 2016 Sep 15;116:107-19. doi: 10.1016/j.bcp.2016.07.011. Epub 2016 Jul 27.

Abstract

Phagocytosis of pathogens, apoptotic cells and debris is a key feature of macrophage function in host defense and tissue homeostasis. Quantification of macrophage phagocytosis in vitro has traditionally been technically challenging. Here we report the optimization and validation of the IncuCyte ZOOM® real time imaging platform for macrophage phagocytosis based on pHrodo® pathogen bioparticles, which only fluoresce when localized in the acidic environment of the phagolysosome. Image analysis and fluorescence quantification were performed with the automated IncuCyte™ Basic Software. Titration of the bioparticle number showed that the system is more sensitive than a spectrofluorometer, as it can detect phagocytosis when using 20× less E. coli bioparticles. We exemplified the power of this real time imaging platform by studying phagocytosis of murine alveolar, bone marrow and peritoneal macrophages. We further demonstrate the ability of this platform to study modulation of the phagocytic process, as pharmacological inhibitors of phagocytosis suppressed bioparticle uptake in a concentration-dependent manner, whereas opsonins augmented phagocytosis. We also investigated the effects of macrophage polarization on E. coli phagocytosis. Bone marrow-derived macrophage (BMDM) priming with M2 stimuli, such as IL-4 and IL-10 resulted in higher engulfment of bioparticles in comparison with M1 polarization. Moreover, we demonstrated that tolerization of BMDMs with lipopolysaccharide (LPS) results in impaired E. coli bioparticle phagocytosis. This novel real time assay will enable researchers to quantify macrophage phagocytosis with a higher degree of accuracy and sensitivity and will allow investigation of limited populations of primary phagocytes in vitro.

Keywords: Bafilomycin A1 (PubChem CID: 6375210); Cytochalasin D (PubChem CID: 5458428); Inflammation; LPS; Macrophage; Nocodazole (PubChem CID: 4122); Phagocytosis.

Publication types

  • Comparative Study
  • Validation Study

MeSH terms

  • Animals
  • Bone Marrow Cells / cytology
  • Bone Marrow Cells / drug effects
  • Bone Marrow Cells / immunology
  • Cell Line
  • Cell-Derived Microparticles / immunology
  • Cell-Derived Microparticles / physiology
  • Cells, Cultured
  • Endotoxins / pharmacology
  • Escherichia coli / immunology
  • Escherichia coli / physiology
  • Humans
  • Image Processing, Computer-Assisted
  • Induced Pluripotent Stem Cells / cytology
  • Induced Pluripotent Stem Cells / drug effects
  • Induced Pluripotent Stem Cells / immunology
  • Interleukins / pharmacology
  • Macrophage Activation / drug effects
  • Macrophages / cytology*
  • Macrophages / drug effects
  • Macrophages / immunology
  • Macrophages / microbiology
  • Macrophages, Alveolar / cytology
  • Macrophages, Alveolar / drug effects
  • Macrophages, Alveolar / immunology
  • Macrophages, Peritoneal / cytology
  • Macrophages, Peritoneal / drug effects
  • Macrophages, Peritoneal / immunology
  • Mice
  • Mice, Inbred C57BL
  • Microscopy, Fluorescence
  • Opsonin Proteins / pharmacology
  • Phagocytosis* / drug effects
  • RAW 264.7 Cells
  • Staphylococcus aureus / immunology
  • Staphylococcus aureus / physiology

Substances

  • Endotoxins
  • Interleukins
  • Opsonin Proteins
  • endotoxin, Escherichia coli