Erythroblast denucleation in the peripheral blood was studied by electron microscopy. Blood was used from dogs anemic either by infection with Babesia canis or from injections of phenylhydrazine hydrochloride. One of the earliest stages of denucleation was the migration of nuclei to the plasmalemma. Mitochondria and coalesced vesicles, derived from the cell membrane of the erythroblast, congregated at the underside of the nuclear envelope unapposed by erythroblastic cell membrane. The coalesced vesicles apparently provided the limiting membrane which surrounded the deep circumference of the extruded nucleus and its associated hemoglobin rim, and also furnished a new plasma membrane for the cell in the area where the nucleus, in denucleation, had utilized the original erythroblastic plasmalemma.It is not known whether loss of nuclei from erythroblasts occurs by extrusion, by karyolysis, or both. Most studies to date have used phase-contrast microscopy to determine the mechanism involved, and the predominant opinion seems to favor nuclear expulsion as the method of denucleationThe present study of erythroblast denucleation was made with the electron microscope, with blood from dogs with either induced or spontaneous anemia. MATERIALS AND METHODSThe blood studied was from dogs anemic as a result of severe parasitism with a hematozoic parasite, Babesia canis, and from dogs made anemic by treating them every other day with three subcutaneous injections of phenylhydrazine hydrochloride at a dosage of 16 mg per kg of body weight. Five to six drops of whole blood were collected in fixative when approximately 10% of the erythrocytic cells were nucleated, as determined by examination of Wright-Giemsa-stained blood smears. 1% OsO4 (12) was employed as a fixative for blood obtained from dogs parasitized with B. canis, while blood from phenylhydrazine-treated dogs was fixed in 2% glutaraldehyde and postfixed in 1% Os04. The fixed blood was embedded in Araldite (13), and cut into thin sections with a dimond knife. Sections on grids were stained with uranyl acetate and lead citrate (14), and were examined with a Philips EM200 electron microscope. RESULTS Light MicroscopyNuclei were located centrally, peripherally, or partially protruded from erythroblasts (Fig. 1). Occasionally nuclei were observed extracellularly. Basophilic, polychromatic, and orthochromatic erythroblasts were present in blood smears. Electron MicroscopyThe mechanism of denucleation was the same in both types of anemia, and thus the results were combined for this study.Erythroblasts with centrally located nuclei contained numerous polyribosomes and a scattering of mitochondria as well as open-spaced vesicles throughout the cytoplasm. Such vesicles ap-
Isolates of Staphylococcus aureus from patients with toxic shock syndrome (TSS) were compared with non-TSS strains of S. aureus with respect to their virulence in rabbits. When the organisms were injected into subcutaneous chambers (perforated polyethylene golf balls) to assess virulence, a rapid mortality was observed with TSS but not with non-TSS strains. Of 16 TSS strains, 11 caused lethal infections in 33 rabbits tested, and none of the 5 control strains caused mortality in 10 rabbits. This evidence of enhanced virulence associated with TSS strains did not appear to be associated with the size of the inoculum. In addition, strains which produced lethal infections appeared to do so despite a reduction in the size of the original inoculum during the first 24 h. All of the TSS strains and none of the non-TSS strains elaborated extracellular protein(s) with a neutral pI when grown in a dialyzed beef heart medium. No other physiological difference was noted between the TSS and non-TSS strains.
Seattle--In the United States, government officials are approving more and more transgenic crops for widespread field testing. But based on new data on the frequency of gene transfer, some ecologists fear that advantageous genes, such as those that confer virus resistance, could escape from the crops into wild plants and create a hardier race of weeds.
The mechanism of mitochondrial extrusion from reticulocytes was studied in whole blood from dogs made anemic by treatment with phenylhydrazine hydrochloride. The initial stage of preparation for mitochondrial extrusion was attraction of vesicles to mitochondria. There was subsequent encirclement of the organelle and other bodies, such as ferritin, by coalesced vesicles forming double membrane-limited vacuoles. Large vacuoles were formed from the union of single vacuoles, and they were usually situated near the periphery of the cell. Fusion of the outer membrane of vacuoles with the plasmalemma of the reticulocyte provided a route for exposure and release of mitochondria and other material to an extracellular location. An extracellular mitochondrion, therefore, was confined by its original double membrane, and a third membrane was derived from the internal boundary of vacuoles.
Artifical infection chambers in rabbits were infected with a toxic shock strain of Staphylococcus aureus in an attempt to determine the nature of the enhanced virulence of toxic shock strains relative to non-toxic shock on August 9, 2020 by guest http://iai.asm.org/ Downloaded from
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