Fusion of erythrocytes by Sendai virus studied by immuno-freeze-etching

Extensive fusion of human erythrocytes agglutinated by Sendai virus was observed after 30 s of incubation at 37 C. Electron microscopy of thin sections failed to reveal the presence of virions, viral fragments, or discrete viral antigens reactive with ferritin-labeled antibody at the sites of fusion. Immuno-freezeetching of membrane surfaces demonstrated the dispersal of viral envelope antigens from what appeared to be original sites of viral attachment. Virus-induced clustering of membrane glycoproteins was interpreted as resulting from interaction of viral antigens with membrane receptor proteins and forming the structural basis for fusion of membranes with one another.

Enhancement of Sendai virus-mediated cell fusion by cupric ions

The effect of divalent cations on cell fusion by concentrated Sendai virus, inactivated by beta-propiolactone, was investigated using Vero and mouse L-929 cells in monolayers. With both cell lines, which are normally resistant to exogenous viral fusion, Cu(2+) in sublethal concentrations was found to promote polykaryon formation to a marked degree. The simultaneous presence of Cu(2+) and virus was required for this effect, which was thought to be related to the cytotoxic action of Cu(2+) on the cell membrane. Accordingly, under standard conditions and in the absence of virus, leakage of isotopically labeled intracellular protein was shown to bear a quantitative relationship to Cu(2+) concentration. Concomitant changes in the membrane were seen electron microscopically to consist of loss of microvilli and the appearance of numerous vesicles on, or adjacent to, the membrane. The relationship of enhanced fusibility to these toxic changes was not further elucidated. The fusion-promoting effect of Cu(2+) far exceeded that of Ca(2+); and other cations tested had no effect.

Virus-erythrocyte interactions

This chapter summarizes the experimental evidence bearing on the nature of virus-erythrocyte reactions characteristic of several taxonomic groups.. Such evidence is culled from (1) the study of conditions necessary for hemagglutination; (2) the examination of specific factors affecting either the cell or the virion to enhance, alter, or abolish the reaction; and (3) the direct physicochemical analysis of cells, viruses, and “receptor analogs.” The hemadsorption phenomenon also provides evidence for virus-erythrocyte interactions, which is based on the attachment of erythrocytes to infected cells in culture having hemagglutinin at their surfaces. This phenomenon reflects the interaction between erythrocytes and viral envelope components. The major virus groups that react with erythrocytes include myxoviruses, paramyxoviruses, pseudomyxoviruses, adenoviruses, arboviruses, reoviruses, enteroviruses, and miscellaneous hemagglutinating viruse (rubella virus, coronaviruses, rhabdoviruses, and oncogenic viruses). The agglutination of erythrocytes by the direct action of viral particles was first described in connection with myxoviruses. This led directly to the discovery of viral neuraminidase—a property unique to myxoviruses and paramyxoviruses. A number of viruses unrelated to myxoviruses have since been shown to agglutinate erythrocytes of various species. The visible result of viral hemagglutination is the “pattern” formed at the bottom of a test tube or well plate by lattices of red cells lightly conjoined by viral hemagglutinin. Hemagglutination serves as a useful direct means of titering intact viral particles or hemagglutinating subunits.

Effect of -propiolactone on Sendai virus

The biological properties (infectivity, hemagglutination, hemolysis, cell fusion, neuraminidase) of Sendai virus were dissociated on the basis of sensitivity to beta-propiolactone, by freeze-thawing, by heating at different temperatures, and by adsorption-elution with formalinized chicken erythrocytes. Possible mechanisms whereby beta-propiolactone selectively destroys viral infectivity are discussed.

Neuraminidase activity in bacterial meningitis

The relation of neuraminidase to morbidity and mortality was examined in patients with Haemophilus influenzae, meningococcal, and pneumococcal meningitis. Ten strains of H. influenzae and eight strains of meningococci from infected cerebrospinal fluid (CSF) did not elaborate neuraminidase. Each of 27 strains of pneumococci from infected CSF elaborated both neuraminidase and N-acetylneuraminic acid (NANA) aldolase. There was no correlation between amount of neuraminidase secreted in vitro and survival of patients. Values for free and total NANA concentrations were derived from admission CSF samples of 63 patients with meningitis; 18 patients infected with Neisseria meningitidis, 10 with H. influenzae and 35 with Diplococcus pneumoniae. Mean values for total NANA were elevated in each type of bacterial meningitis; however, abnormal concentrations of free CSF NANA were detected only in 17 patients with pneumococcal meningitis. 11 of 18 patients with pneumococcal meningitis showing normal free CSF NANA concentrations were cured, whereas only 4 patients with abnormal free NANA levels survived without residua. Both coma and bacteremia occurred significantly more often among patients with elevated concentrations of free CSF NANA. The association of elevated concentrations of free CSF NANA with coma and with an adverse prognosis suggested that neuraminidase may be a factor in the pathogenesis of penumococcal meningitis.

Immunochemical Comparison of Human Erythrocyte Membrane Proteins

Water-soluble glycoprotein (virus receptor substance, VRS) obtained by phenolic extraction of human erythrocyte membranes was compared with a sialic acid-rich protein fraction derived from pyridine-extracted membranes. In double diffusion analysis, electrophoretically pure VRS gave reactions of identity with a major component of the sialoprotein fraction. Quantitative precipitin analyses also showed the close similarity of the two antigens. The amino acid profile of the sialoprotein resembled that of VRS and differed significantly from that of pyridine soluble proteins from which the bulk of the sialoprotein was separable by chromatography on G-200 Sephadex in 33% pyridine. The capacity of the sialoprotein fraction to inhibit influenza virus hemagglutination was significantly less than that of purified VRS.

Electron Microscopic Study of Erythrocyte Receptors with Labeled Antisera to Membrane Components

Hemoglobin-free membranes and erythrocytes of group O, after reaction with ferritin-labeled rabbit antibody to purified virus receptor substance, were examined by electron microscopy. Antibody was found to bind specifically to discrete sites, in thin sections of cells and ghosts, as well as in negative contrast preparations of washed membranes. The distribution of reactive sites was similar to that described by others for ferritin-labeled isoantibody. The same antibody labeled with fluorescein reacted with washed membranes to give a granular type of fluorescence. The relationship of the virus receptor substance-reactive sites to those containing blood group antigens is discussed.

Alpha-L-fucosidase from a soil bacterium

Intracellular glycosidases were measured in cell-free extracts obtained by ultrasonic disruption of a gram-negative soil coccobacillus (Chase, 1938). From these extracts, alpha-l-fucosidase was purified about 120-fold by salting out with (NH(4))(2)SO(4), ion exchange chromatography, and gel filtration. The approximate molecular weight of the enzyme was 50,000; its pH optimum was 5. The enzyme was inhibited by l-fucose and split this sugar from a purified acid mucopolysaccharide from chicken chorioallantoic fluid. The acid mucopolysaccharide is identical with a component (host antigen) of the hemagglutinin of influenza virus. Its antigenic reactivity is altered by cell-free extracts of the bacterium, in which the responsible enzyme is thought to be an alpha-l-fucosidase.

Interactions between Sendai virus and human erythrocytes

Concentrated Sendai virus, when adsorbed to erythrocytes at 4 C, caused invaginations in the plasma membrane. Following elevation of the temperature to 37 C, the plasma membrane became fused with the viral envelope before dissolution of the virions and rupture of the cells. Cell lysis was accompanied by rapid and total loss of hemoglobin to the extracellular space. Following aqueous pyridine extraction, the hemoglobin-free ghosts remaining were found to be devoid of N-acetylneuraminic acid and to have solubility properties different from those of normal erythrocyte ghosts. By the action of viral neuraminidase, bound N-acetylneuraminic acid was also liberated from purified virus receptor substance whose electrophoretic mobility was thereby substantially reduced. Cu(++) selectively inhibited hemolysis and neuraminidase without interfering with hemagglutination and attachment. Neuraminidase appeared to be essential for Sendai virus hemolysis; viral particle size may also be a critical factor in this process.