title: Conventional apoptosis assays using propidium iodide generate a significant number of false positives that prevent accurate assessment of cell death.
abstract: The advent of flow cytometry-based applications has significantly impacted the study of cellular apoptosis. Propidium iodide (PI) is a commonly used viability stain in these studies. Unfortunately, we find that conventional Annexin V/PI protocols lead to a significant number of false positive events (up to 40%), which are associated with PI staining of RNA within the cytoplasmic compartment. Both primary cells and cell lines are affected, with large cells (nuclear: cytoplasmic ratios <0.5) showing the highest occurrence. This distribution spans a wide range of animal models including mice, swine, avian, and teleost fish and potentially affects up to 1016 out of 1019 of peer-reviewed papers published in this area since 1995. We show that the primary ramifications from these findings relate to cells experiencing changes in RNA content. Virally infected cells, for example, are qualified as undergoing apoptosis in response to infection based on conventional staining protocols; in fact, these cells are alive and actively producing viral RNA that can serve to produce additional infectious viral particles. Based on our observations we propose a modified protocol, show that it overcomes previous drawbacks for this technique, and that it will allow for more accurate assessment of cell death across various platforms.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Aja M
authors.initials: AM
authors.lastname: Rieger
authors.forename: Brian E
authors.initials: BE
authors.lastname: Hall
authors.forename: Le Thuong
authors.initials: le T
authors.lastname: Luong
authors.forename: Luis M
authors.initials: LM
authors.lastname: Schang
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Barreda
mesh_terms: D000818:Animals; D000880:Anthraquinones / Q000378:metabolism; D017209:Apoptosis; D016923:Cell Death; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D002642:Chick Embryo; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D005189:False Positive Reactions; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000378:metabolism; D005557:Formaldehyde / Q000378:metabolism; D006054:Goldfish; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D011419:Propidium / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D013194:Staining and Labeling / Q000379:methods*; D034421:Sus scrofa; D016707:Tissue Fixation; D014709:Vero Cells; D014779:Virus Replication / Q000235:genetics
chemical_list: C520537:1,5-bis((2-(methylamino)ethyl)amino)-4,8-dihydroxyanthracene-9,10-dione; D000880:Anthraquinones; D005456:Fluorescent Dyes; D012330:RNA, Double-Stranded; D005557:Formaldehyde; D011419:Propidium; D004247:DNA; D012260:Ribonucleases