title: Ultrastructural characterization of endogenous retroviral particles isolated from normal human placentas.
abstract: Human placental endogenous retroviral (ERV) particle isolates were investigated by ultrastructural evaluation. Although retrovirus-like structures in normal human placental tissue sections have been described, the precise nature of these particles has not previously been defined. By direct electron microscopic (EM) observation of placental ERV isolates that display retroviral reverse transcriptase (RTase) activity and a buoyant density consistent with type-C retroviruses (1.17 g/ml on sucrose), we have shown these to contain particles with characteristic retroviral ultrastructural features. Samples were stained with 1.0% phosphotungstic acid (PTA), 0.5% uranyl acetate (UA), and low-angle-shadowed with platinum/palladium. Isolated placental ERV particles have an apparent diameter of approximately 120 nm, are membrane-bound with a short surface fringe, and contain capsid particles (about 90 nm in diameter) within an internal matrix structure. These observations support the view that human placental cells normally express ERV particles.
authors.affiliation: Department of Microbiology/Immunology, Wright State University School of Medicine, Dayton, Ohio 45435.
authors.forename: T W
authors.initials: TW
authors.lastname: Lyden
authors.forename: P M
authors.initials: PM
authors.lastname: Johnson
authors.forename: J M
authors.initials: JM
authors.lastname: Mwenda
authors.forename: N S
authors.initials: NS
authors.lastname: Rote
mesh_terms: D002499:Centrifugation, Density Gradient; D005260:Female; D006801:Humans; D008854:Microscopy, Electron; D009942:Organometallic Compounds; D010165:Palladium; D010772:Phosphotungstic Acid; D010920:Placenta / Q000382:microbiology*; D010984:Platinum; D011136:Polysorbates / Q000494:pharmacology; D011247:Pregnancy; D012194:RNA-Directed DNA Polymerase / Q000378:metabolism; D012190:Retroviridae / Q000201:enzymology / Q000648:ultrastructure*; D013194:Staining and Labeling; D014771:Virion / Q000648:ultrastructure*
chemical_list: D009942:Organometallic Compounds; D011136:Polysorbates; D010772:Phosphotungstic Acid; C005460:uranyl acetate; D010984:Platinum; D010165:Palladium; D012194:RNA-Directed DNA Polymerase