Quantitative Assessment of Hemadsorption by Myxoviruses: Virus Hemadsorption Assay

The standardization and quantitative evaluation of an assay for myxoviruses, based on the enumeration of individual infected clone 1-5C-4 cells manifesting hemadsorption within 24 h of infection, are described. Hemadsorption was detectable earlier than immunofluorescence in infected cells or hemagglutinins in culture medium. The relationship between virus concentration and cells exhibiting hemadsorption was linear. The assay was highly precise, sensitive, and reproducible.     

Metabolic Requirements for the Development of Hemadsorption Activity and Virus Formation in BHK-21 Cells Infected with Newcastle Disease Virus

Differential effect of various metabolic inhibitors on the development of hemadsorption activity and virus formation in cells infected with Newcastle disease virus (NDV) was investigated. It was found that, in BHK-21 cells infected with NDV, cycloheximide did not prevent the development of hemadsorption activity, whereas protein synthesis and virus formation by the cell were rapidly inhibited by the drug. When the drug was added to the culture at 4.5 h after infection or later, hemadsorption activity of the cell continued to develop normally for about 1 h. Similar increase in hemadsorption activity was found in cells which were treated with anti-NDV serum (to neutralize their hemadsorption activity) and then washed and incubated with cycloheximide. However, when cells were treated with the drug early in the infection (1.5 or 3.0 h), they did not show any detectable hemadsorption reaction throughout the infection. In contrast to cycloheximide, iodoacetate added to the culture together with sodium azide inhibited completely both the development of hemadsorption activity and the formation of progeny virus. These results suggest that the change of cell surface to become hemadsorptive may depend upon the energy generating system but not upon de novo synthesis of protein, whereas production of infectious virus may require continuous synthesis of protein.     

Electron Microscopic Study of Hemadsorption on Vaccinia Virus Infected Cells

Hemadsorption (HAD) induced in HEp-2 cells infected with vaccinia virus was observed. In ultrathin sections, binding of 36 red blood cells (RBCs) was examined in detail and 3 types of HAD were observed: (1) direct and close binding of RBCs to infected HEp-2 cells (cyto-HAD) was observed in cross sections of 27 RBCs, (2) binding of RBCs through microvilli of infected cells was found in 11 RBCs, and (3) five RBCs were distorted to form tentacle-like projections by which they were bound to the HEp-2 cell surface. Scanning electron microscopy revealed that more than 30% of the RBCs were bound to microvilli of vaccinia virus-infected HEp-2 cells, and that the number of microvilli twined round each RBC was over ten. RBCs were attached to certain microvilli through swollen sucker-like tips which were not observable in non-infected HEp-2 cells. RBCs sometimes revealed a polygonal shape at regions of binding to microvilli. Virion-mediated RBC-HEp-2 cell binding could not be observed.     

Morphogenesis of Venezuelan Equine Encephalomyelitis Virus

Morphogenesis of Venezuelan equine encephalomyelitis virus was studied by means of electron microscopy. Virus-specific structures (factories, viroplasts) were found at early stages of infection; these structures were composed of fibrillar and cylindrical formations, aggregates of ribosomes, and viral nucleoids. The latter emerged from fibrillar and cylindrical structures. Aggregates of viral nucleoids were found in the cytoplasm and occasionally in the nuclei of virus-infected cells. Viral envelopes and mature virions were formed on the cell membranes and on the membranes of intracellular vacuoles. Anomalous forms of virions (both polygenomic and oligogenomic) were observed.     

Three-Day Assay for Human Cytomegalovirus Applicable to Serum Neutralization Tests

A fluorescing cell assay (FCA) technique utilizing the indirect fluorescent-antibody method to measure human cytomegalovirus (CMV)-infected cells has been applied to the rapid determination of CMV-neutralizing antibody. Human sera with complement fixation titers to CMV of 1/32 or greater and fluorescein-conjugated rabbit anti-human globulin are the primary and secondary reagents in the fluorescent-antibody test. FCA measured in 3 days the same number of infectious units measured by plaque assay in 2 weeks. FCA and plaque assay yielded identical neutralizing antibody titers to CMV in 20 human sera.     

Neutralization Studies with Marek's Disease Virus and Turkey Herpesvirus

Use of Marek''s disease virus (MDV) in a neutralization test presents several problems, which are described, making this potentially useful test difficult. To obviate these difficulties, a plaque reduction test has been designed based on cross-neutralization of turkey herpesvirus (HVT) by serum-neutralizing MDV. The technique for such a neutralization test is outlined. Kinetics of development of neutralizing antibodies in chickens inoculated with HVT and MDV are described. The neutralization test can be used to evaluate viability of HVT vaccines and the possible role of neutralizing antibodies in the protection afforded by vaccination against MDV-induced tumors.     

Hemagglutination-Inhibition Method and Immunofluorescence Staining with Venezuelan Equine Encephalomyelitis Virus

Hemagglutination and fluorescent antibody (FA) are compared for the direct detection of virus devoid of host cells. A determination was made of the minimal number of tissue plaque-forming units of Venezuelan equine encephalomyelitis virus that could be detected by the hemagglutination technique. Similar concentrations of the virus in bovine albumin borate saline, Brain Heart Infusion broth (Difco), and demineralized water were tested by the FA technique. Somewhat higher concentrations of the virus in bovine albumin borate saline were used in the hemagglutination-inhibition test. The quantitative hemagglutination procedure employed for these studies was carried out at 37 C for 75 min with variations in concentration of goose red cells. As a result of lowering the red cell concentration, smaller concentrations of virus were detected. The direct FA staining procedure applied to slide preparations containing known numbers of tissue culture plaque-forming units of virus was negative. Adsorbed viral antigen on agglutinated goose erythrocytes was visualized by direct and indirect FA techniques.     

Mechanisms of Hemagglutinin Targeted Influenza Virus Neutralization

Human monoclonal antibodies have been identified which neutralize broad spectra of influenza A or B viruses. Here, we dissect the mechanisms by which such antibodies interfere with infectivity. We distinguish four mechanisms that link the conserved hemagglutinin (HA) epitopes of broadly neutralizing antibodies to critical processes in the viral life cycle. HA-stem binding antibodies can act intracellularly by blocking fusion between the viral and endosomal membranes and extracellularly by preventing the proteolytic activation of HA. HA-head binding antibodies prevent viral attachment and release. These insights into newly identified ways by which the human immune system can interfere with influenza virus infection may aid the development of novel universal vaccines and antivirals.     

Virulence of Venezuelan Equine Encephalomyelitis Virus Subtypes for Various Laboratory Hosts

Mice, guinea pigs, and duck embryo cell cultures were inoculated with known subtypes of Venezuelan equine encephalomyelitis (VEE) virus and the attenuated (TC-83) strain of VEE. With the exception of TC-83, all strains were highly pathogenic for suckling mice by either intracranial or intraperitoneal routes of inoculation used. Virulence for older mice and guinea pigs provided a means to distinguish strains. In addition, virulence or lack of virulence for adult mice or guinea pigs provides a rapid method for separating epizootic subtype IB from TC-83 VEE virus isolates.     

Envelope Protein of Influenza Virus I. Hemagglutinating Activity of Reassociated Subunits

The hemagglutinating properties of influenza virus envelope protein, prepared by reassociation of polypeptide subunits, have been defined and compared with those of virus and ether-split hemagglutinin. In general, the characteristics of the intact and ether-split virus were found to be similar, whereas those of the envelope protein were distinctly different. The use of chicken, pigeon, and guinea pig erythrocytes both at 23 and 4 C disclosed that the hemagglutinating titers of envelope protein preparations were particularly dependent on the system employed. Under optimal conditions, with guinea pig cells at 4 C, the titers of envelope protein preparations were equivalent to those of the original virus concentrates. The hemagglutinating activity of envelope protein was particularly sensitive to elevated temperature, concentrated urea, sulfhydryl-reducing reagents, and tryptic digestion at high salt concentrations. In all these respects, the intact virus was more resistant than the envelope protein. Interpretation of the data indicates that the hemagglutinin is stabilized when associated with the lipid micelle at the surface of the virus.     

Inactivation of Venezuelan Equine Encephalomyelitis Virus by gamma-Radiation

Exposure of Venezuelan equine encephalomyelitis (VEE) virus (at -70 C) to 6 × 10⁶ r γ-radiation (⁶⁰Co) resulted in loss of lethality for young adult mice and guinea pigs, and loss of capacity to produce plaques or cytopathic effects in tissue culture. The suckling mouse was more sensitive for detecting live virus in radiated suspensions than was the adult mouse or guinea pig. Live virus was demonstrable in preparations exposed to 6 × 10⁶ r but not in suspensions exposed to 8 × 10⁶ r and more. The rate of inactivation of VEE virus by γ-radiation was an exponential function of the dosage.     

麻疹病毒血凝素基因H的点突变与血凝作用的转变

经Ｂ９５ａ细胞系纯化分离的三株麻疹病毒Ｆｕ、ＩＭＡ、ＳＭＤ的血凝试验（ＨＡＤ）为阴性,但将它们分别感染Ｖｅｒｏ细胞并传代培养后其血凝试验由阴性转变为阳性。实验证明这种血凝表型的转变与血凝素基因Ｈ的表达与吸附无关。以ＰＣＲ扩增血凝素基因Ｈ和融合基因Ｆ,并分别进行序列分析。表明三株病毒在两种培养细胞中传代后其融合基因Ｆ的序列未发现差异。但血凝素基因Ｈ的序列却有显著的点突变并伴随血凝表型的转变。其中Ｆｕ     

Kinetics of the Vaccinia Virus Plaque Neutralization Test

Neutralization of vaccinia virus with immune rabbit serum occurred optimally when incubated at 37 C for 16 to 24 hr in the plaque neutralization test employing the MA-104 embryonic rhesus monkey kidney cell line.     

Studies on the Neutralization of Herpes Simplex Virus

Herpes virus was reacted with an early rabbit antiserum containing predominantly complement-requiring neutralizing (CRN) antibody to produce CRN-antibody-sensitized virus (SV), and the action of complement (C') upon SV was studied. Reduction of infectivity due to C' was about equal with undiluted and 1000-fold diluted SV. Even higher dilutions which contained about 10 to 100 infectious units per 0.05 ml were also completely inactivated by C'. Kinetic experiments revealed that the velocity of titer reduction in the presence of C' of 100-fold diluted SV was not slower than that of undiluted SV. When SV was first treated with C' and then diluted 100-fold, the surviving virus showed but a slightly reduced efficiency of filtration through the 0.45 μ Millipore membrane as compared with SV first diluted 1: 100 and then treated with C'. The titer reduction of SV–C'1 complexes in the presence of C'4 followed a one-hit curve. These results indicated that the reduction of infectivity of SV due to C' was not a result of immunoaggregation of infectious SV. Alternative possible mechanisms of the action of C' are discussed.