Plaque assay and primary isolation of influenza A viruses in an established line of canine kidney cells (MDCK) in the presence of trypsin

A polarized human endometrial cell line that binds and transports polymeric IgA

We have demonstrated that a human endometrial cell line, HEC-1, maintains a transepithelial electrical resistance, directionally transports fluids across the cell monolayer, and releases enveloped viruses at distinct plasma membrane domains: influenza virus is released at the apical surfaces and vesicular stomatitis virus (VSV) at the basolateral surfaces. In addition, we have examined the expression of domain-specific endogenous proteins, including the polyimmunoglobulin receptor. Multiple endogenous polypeptides were found to be secreted into the culture medium at basolateral surfaces, whereas no secretion of specific polypeptides was observed from apical cell surfaces. Distinct patterns of endogenous proteins were also observed on apical and basolateral cell surfaces, with a much more complex polypeptide pattern on the basolateral membranes. Using surface biotinylation and immunofluorescence, the polyimmunoglobulin receptor was found to be expressed on the basolateral surface of HEC-1 monolayers. The specific binding of poly-immunoglobulin A (pIgA) was found to occur on the basolateral surface, and was followed by transcytosis to the apical surface and release into the apical medium. The observed characteristics indicate that the endometrium-derived HEC-1 epithelial cell line can be employed as a model for studies of protein transport in polarized epithelial cells of human endometrial tissues, as well as for studies of the interaction of microorganisms with epithelial cells in the genital tract.

Characteristics of cytotoxic T lymphocytes directed to influenza virus haemagglutinin elicited by immunization with muramyldipeptide-influenza liposome vaccine

We examined the characterization of the antiviral T lymphocytes elicited by immunization with a novel liposome vaccine (MDP-virosome) constructed with synthetic muramyldipeptide; [6-0-(2-tetradecylhexadecanoyl)-N-acetylmuramyl-L-alanyl-D-isoglutamine] , cholesterol, influenza virus haemagglutinin and neuraminidase. The haemagglutinin glycoprotein first appeared to induce a significant subtype-specific cytotoxic activity through its arrangement on the inner and outer surfaces of the MDP-virosome. Splenocytes of BALB/c mice immunized with the virosome vaccine containing H3 haemagglutinin and N2 neuraminidase from human Hong Kong virus markedly lysed H3N2 virus-infected target cells, but not those infected with virus possessing a different subtype such as H1N1 surface antigens. Exposure of these splenic lymphocytes to virus antigen in vitro further enhanced their cytotoxic activity. The cytotoxic lymphocytes generated by the MDP-virosome vaccine expressed Thy 1 and CD4 antigens on their cell surface, and these activities were restricted by class II histocompatibility gene products. The marked reduction of pulmonary virus titres in infected mice caused by transferred immune spleen cells suggested that the MDP-virosome vaccination is able to protect against influenza virus infection through enhanced cellular immune responses.

Receptor specificity of influenza virus influences severity of illness in ferrets

Weanling ferrets were inoculated intranasally with either wild-type or receptor-variant clones of influenza A/Memphis/102/72 to determine if changes in receptor specificity influence virulence of influenza virus infection. Over the 5 days after inoculation, receptor-variant inoculated ferrets had a lower mean elevation in body temperature, greater weight gain and less sneezing than the wild-type group. Influenza virus was recovered from the lungs of fewer receptor-variant infected ferrets (5/12 vs 11/12) and in lower titers than in wild-type infected ferrets at 5 days after inoculation. The viruses recovered from lung homogenates retained the same receptor specificity as the inoculum. Serum hemagglutination inhibition titers for the two groups were similar. These findings suggest that the receptor-variant clone is less virulent but elicits a similar immunogenic response compared with the wild-type clone.

MDCK cell cultures supplemented with high concentrations of trypsin exhibit remarkable susceptibility to influenza C virus

Multiplication of influenza C virus in MDCK cell cultures increased with increasing concentrations of trypsin up to 160 micrograms/ml, whereas maximum growth of influenza A virus in the same culture was observed at a concentration of 10 micrograms/ml. In the presence of 160 micrograms of trypsin per ml MDCK cells showed the same or even higher susceptibility to various strains of influenza C virus compared with HMV-II cells, a human melanoma cell line that has been reported to have high susceptibility to the virus. Complete cleavage of the HE precursor protein of MDCK-grown influenza C virus into HE1 and HE2 subunits was achieved by trypsin at a concentration of 160 micrograms/ml, whereas only partial cleavage was observed at 10 micrograms/ml. The present results thus demonstrate that MDCK cell cultures supplemented with trypsin at a concentration of 160 micrograms/ml become highly susceptible to influenza C virus.

Inhibition of cap (m7GpppXm)-dependent endonuclease of influenza virus by 4-substituted 2,4-dioxobutanoic acid compounds

Synthesis of influenza virus mRNA is primed by capped and methylated (cap 1, m7GpppXm) RNAs which the virus derives by endonucleolytic cleavage from RNA polymerase II transcripts in host cells. The conserved nature of the endonucleolytic processing provides a unique target for the development of antiviral agents for influenza viruses. A series of 4-substituted 2,4-dioxobutanoic acid compounds has been identified as selective inhibitors of this activity in both influenza A and B viruses. These inhibitors exhibited 50% inhibitory concentrations in the range of 0.2 to 29.0 microM for cap-dependent influenza virus transcription and had no effect on the activity of other viral and cellular polymerases when tested at 100- to 500-fold higher concentrations. The compounds did not inhibit the initiation or elongation of influenza virus mRNA synthesis but specifically inhibited the cleavage of capped RNAs by the influenza virus endonuclease and were not inhibitory to the activities of other nucleases. Additionally, the compounds specifically inhibited replication of influenza A and B viruses in cell culture with potencies comparable to the 50% inhibitory concentrations obtained for transcription.

Nasal and otologic effects of experimental influenza A virus infection

Past studies showed that experimental rhinovirus colds in adults resulted in eustachian tube dysfunction and abnormal middle ear pressures. In the present study, the symptoms and pathophysiologic findings accompanying experimental influenza viral infection were documented. A total of 33 healthy adult volunteers were intranasally challenged with an influenza A/Kawasaki/86 (H1N1) virus and cloistered over a 9-day postchallenge period to monitor for evidence of infection, signs and symptoms of illness, and the extent and frequency of pathophysiologic responses of the nose, eustachian tube, and middle ear. Results showed a protective effect of high (> or = 16) prechallenge specific hemagglutination-inhibition antibody titer on the rate of infection and the magnitude and extent of provoked symptoms and pathophysiologic findings. Infected subjects with low (< 16) prechallenge serum antibody titers (n = 21) developed significant respiratory illness. These subjects also had objectively measurable increases in nasal secretion production, and decreased nasal patency and mucociliary clearance rates. More than 80% of the infected subjects developed eustachian tube dysfunction, and approximately 80% had middle ear underpressures of less than -100 mm H2O on study days 4 and 5. Five of 21 infected subjects with low prechallenge antibody titers had otoscopic evidence of otitis media with effusion. These results support a causal role for viral upper respiratory tract infection in the pathogenesis of otitis media, possibly mediated by the early development of eustachian tube dysfunction and abnormal middle ear pressure.

Viruses as model systems in cell biology

This chapter focuses on the contributions that studies with viruses have made to current concepts in cell biology. Among the important advantages that viruses provide in such studies is their structural and genetic simplicity. The chapter describes the methods for growth, assay, and purification of viruses and infection of cells by several viruses that have been widely utilized for studies of cellular processes. Most investigations of virus replication at the cellular level are carried out using animal cells in culture. For the events in individual cells to occur with a high level of synchrony, single cycle growth conditions are used. Cells are infected using a high multiplicity of infectious virus particles in a low volume of medium to enhance the efficiency of virus adsorption to cell surfaces. After the adsorption period, the residual inoculum is removed and replaced with an appropriate culture medium. During further incubation, each individual cell in the culture is at a similar temporal stage in the viral replication process. Therefore, experimental procedures carried out on the entire culture reflect the replicative events occurring within an individual cell. The length of a single cycle of virus growth can range from a few hours to several days, depending on the virus type.

Use of FITC-labeled influenza virus and flow cytometry to assess binding and internalization of virus by monocytes-macrophages and lymphocytes

The binding of influenza virus to the surface of cells and the internalization of virus particles by all or a subset of cells are key points in the pathogenesis of viral infection. The current studies established a method for discrimination of surface-bound from internalized influenza virus. Fluorescein isothiocyanate (FITC) was attached to the viral hemagglutinin and neuroaminidase proteins; the fluorescent virus retained infectivity. A flow cytometric technique was then adapted for study of virus-cell interactions, with addition of ethidium bromide to quench green fluorescence associated with FITC-labeled virus that was cell-bound but remained external. Ethidium bromide was excluded by intact cell membranes, and internalized virions retained green fluorescence. Cells could be examined by fluorescence microscopy or flow cytometry, with flow cytometry allowing rapid, kinetic assessment of large numbers of cells and subsets of virus-exposed cells. The data showed that, whereas a majority of both monocytes-macrophages and lymphocytes bound influenza virus, a large percentage of monocytes-macrophages but only a very small percentage of lymphocytes internalized the virus. This procedure provides a simple and effective method to distinguish surface-bound from internalized influenza virus, and allows precise kinetic analyses on large numbers of cells.

Administration of inactivated and detergent-treated influenza virus to mice before virus challenge reduces mortality

Formalin-inactivated virus (FIV) and the detergent-treated virus (DTV) preparations were tested for their ability to enhance the resistance of mice to experimental influenza infection. FIV (100 micrograms) was administered intravenously to mice. After 24 hr, animals were challenged with 5 LD50 dose intranasally. FIV-treated and non-treated (control) mice had 10% and 100% mortality, respectively. Similar results were obtained with the DTV (40 micrograms) preparation. The pulmonary virus titer of FIV-treated mice was lower when compared with the control. Mechanisms other than acquired immunity may have conferred the early resistance to virus infection in mice.

A study of the advantages and limitations of immunoblotting procedures for the detection of antibodies against influenza virus

An immunoblotting procedure was used to determine the specificity and examine some of the properties of antibodies produced following infection of mice with influenza virus or inoculation with noninfectious material with Alhydrogel or complete Freund's adjuvant. The noninfectious material used was beta-propiolactone-inactivated influenza virus and a preparation (HANA) enriched for the surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA). When influenza viral proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions, each of the anti-viral antisera tested exhibited strong binding. Under reducing conditions, however, much weaker binding was observed especially towards the HA1 subunit of HA. This was particularly apparent with antisera raised to virus or HANA in the absence of adjuvant. A panel of monoclonal antibodies directed to HA also bound well to viral HA separated by SDS-PAGE under nonreducing conditions but failed to recognize epitopes on HA1 separated under reducing conditions. These results suggest that when HA is reduced and immobilized on a solid support, it does not display the conformational features essential for the integrity of all epitopes. The immunoblotting procedure was also used to determine the isotype of anti-viral antibody directed against individual viral proteins and to detect matrix protein 2 (M2) in purified influenza virions and influenza-infected cells using antisera raised to a synthetic peptide representing a sequence within the M2 protein.

Persistence of viral genes in a variant of MDBK cell after productive replication of a mutant of influenza virus A/WSN

The MDBK-R cell line is a variant of the MDBK cell line, which was derived by three consecutive high multiplicity superinfections of MDBK cells with AWBY-140 virus, a mutant of influenza virus A/WSN (H 1N 1). MDBK-R cells are permissive for productive replication of AWBY-140, but resist lysis by the virus and grew normally without producing infectious virus after replication of the mutant occurred there. By polymerase chain reaction (PCR), we demonstrated nucleotide sequences specific to all the 8 genes of AWBY-140 in MDBK-R cells which had been infected with the mutant at a high multiplicity and subsequently received 25 passages. This suggests that the genes of influenza virus mutant persisted in the dividing host cells for a long time after productive infection, when none of the cells was producing virus. We were also able to amplify the M gene related sequence of the mutant from both poly(A)+ and poly(A)- fractions of the RNA extracted from the cells at 27th passage level by PCR, which suggests that the persisting genes were replicated and transcribed, but we failed to demonstrate any viral protein in the cells by Western blotting.

Efficacy of oral administration of live herpes simplex virus type 1 as a vaccine

Mice given herpes simplex virus type 1 (HSV-1) (Miyama +GC strain) intragastrically via a stainless-steel cannula were rendered immune to subsequent lethal intraperitoneal (i.p.) challenge with HSV-1. The orally administered HSV-1 was completely inactivated in the stomach within a few minutes of inoculation. However, systemic immunity was established 14 days after oral inoculation with the virus and retained for up to 6 months. The mechanisms of establishing systemic immunity were investigated by means of adoptive transfer comparisons. When splenic cells from HSV-1-immunized mice were transplanted into nonimmunized mice, all of the recipient mice survived after a lethal i.p. challenge with the virus. Immunity was not established in antithymocyte serum-treated mice or by transfer of serum from immunized to nonimmunized mice. In addition, all HSV-1-immunized mice died after lethal challenge with HSV-2 and influenza virus A. These findings suggest that the immunity was virus specific, with T lymphocytes playing a major role in its establishment. The present study therefore supports the possibility of oral immunization with live HSV-1 as a vaccine.

Heterogeneity of the mutation rates of influenza A viruses: isolation of mutator mutants

The rates of mutation to the mar (monoclonal antibody-resistant) genotype of individual influenza virus plaque isolates, obtained from a stock generated after two successive cloning steps, have been determined by the fluctuation test. When a random sample of 60 clones was analyzed, 7 contained a proportion of mar mutants significantly higher than the average, and among them, 2 showed a mutation rate two to three times higher than the average value obtained for the virus population when the hemagglutinin-specific monoclonal antibody 2G10 was used. In order to look for mutants with higher mutation rates, a systematic search was carried out with a nonmutagenized virus stock, and several clones with increased mutation rates were isolated. One of them (mut43) was characterized further and was shown to have a mutation rate three to four times higher than that of the virus population at the sites defined by two nonoverlapping, hemagglutinin-specific monoclonal antibodies as well as at the site defined by a neuraminidase-specific monoclonal antibody. These results indicate that the mutation rate of an influenza virus is a weighted average of the contributions of a heterogeneous population. The consequences of this fact for the adaptive evolution of influenza viruses are discussed.

Infection enhancement of influenza A NWS virus in primary murine macrophages by anti-hemagglutinin monoclonal antibody

Antibody-dependent enhancement (ADE) of influenza A NWS virus infection was investigated in primary murine macrophages (M phi) using anti-hemagglutinin(HA) monoclonal antibody (mAB). Contrary to previous reports of abortive influenza virus infection in primary M phi, this study demonstrated that the NWS virus replicated productively in both resident peritoneal M phi and thioglycolate-elicited peritoneal M phi providing cleavage of the HA was achieved by trypsin; 5 micrograms/ml of trypsin was the optimum concentration for the induction of infectivity. Under multiple-cycle growth conditions in the presence of mAB at various concentrations in trypsin-containing media, ADE was demonstrated in both M phi in the presence of subneutralizing concentrations of mAB. Flow cytometric analysis showed that the mechanism of virus entry into M phi could be through HA to specific virus receptors, or HA plus antibody to Fc receptors. These results indicate that ADE of the NWS virus infection actually occurs on Fc receptor-bearing primary murine M phi depending on the concentration of antibody in the presence of the appropriate protease for cleavage of viral HA.

Antigenic and genetic variation in influenza A (H1N1) virus isolates recovered from a persistently infected immunodeficient child

Antigenic and genetic variations have been analyzed in eight consecutive isolates recovered from a child with severe combined immunodeficiency syndrome persistently infected with naturally acquired type A (H1N1) influenza virus over a 10-month period. Hemagglutination inhibition reactions and T1 oligonucleotide fingerprinting demonstrated that these viruses were related to strains causing outbreaks in the United States at that time (1983 to 1984) but that antigenic and genetic differences between consecutive isolates could be detected. This variation between isolates was examined further by sequencing the RNAs encoding the HA1 region of the hemagglutinin (HA) and the nucleoprotein (NP) in five of the consecutive isolates. Multiple point mutations were detected in both genes, and a deletion of one amino acid was detected in the HA. Depending on the isolates compared, 5.8 x 10(-3) to 17 x 10(-3) substitutions per nucleotide site per year were detected in the RNAs encoding the HA1, and 3.5 x 10(-3) to 24 x 10(-3) substitutions per nucleotide site per year were detected in the NP gene. Fifty-four percent of the base changes in the HA1 and 73% in the NP led to amino acid substitutions. A progressive accumulation of mutations over time was not observed, suggesting that the genetic diversity of these viruses may best be interpreted as the result of shifts in the population equilibrium (quasi-species) of replicating variant genomes.

Agglutination of human O erythrocytes by influenza A(H1N1) viruses freshly isolated from patients

The hemagglutinin titers of 10 influenza A (H1N1) viruses were examined using the erythrocytes of several species. Human O erythrocytes showed the highest agglutination titer to the viruses, whereas chicken erythrocytes showed a low titer. These findings were noted for at least 10 passages by serial dilutions of the viruses in Madin-Darby canine kidney (MDCK) cells. All influenza A(H1N1) viruses, plaque-cloned directly from throat-washing specimens of patients, also agglutinated human O but not chicken erythrocytes. The results of a hemadsorption test indicated that chicken erythrocytes possess less affinity to MDCK cells infected with the A/Osaka City/2/88(H1N1) stain than to those infected with the A/Yamagata/120/86(H1N1) strain which is used as an inactivated influenza vaccine in Japan. However, there were no significant differences between the A/Osaka City/2/88 and the A/Yamagata/120/86 strains in the hemagglutination inhibition test. Since human O erythrocytes have high agglutination activity to influenza A(H1N1) and also to A(H3N2) and B viruses in MDCK cells, these erythrocytes may be useful for the serological diagnosis of influenza.

Influence of trifluoperazine on the late stage of influenza virus infection in MDCK cells

We investigated the influence of the anticalmodulin drug, trifluoperazine (TFP) on influenza virus growth in MDCK cells. The inhibitory effect of TFP on virus growth was observed even when TFP was added at a late stage of infection. This inhibitory effect was concentration-dependent in the concentration range of 20-35 microM. At 35 microM, TFP caused a complete alteration in the distribution pattern of hemagglutinin (HA), concomitant with a decrease in the appearance of HA on the cell surface. After removal of the drug, the HA gradually began to show a normal distribution pattern and reappeared on the cell surface. The time course of rearrangement of HA was in accord with that of the recovery of cell supernatant infectivity. Scanning electron microscopic study revealed that the drug did not cause accumulation of the progeny viruses on the cell surface. The drug effect on the virus growth was reversed by the simultaneous presence of purified calmodulin (CaM). These data suggest that TFP acts as a reversible inhibitor of influenza virus morphogenesis, but not budding, by disturbing cellular CaM and/or CaM-dependent functions.

Functional role of respiratory tract haemagglutinin-specific IgA antibodies in protection against influenza

Intranasal inoculation of haemagglutinin (HA) purified from influenza virus A/PR/8/34 (PR8, H1N1) together with cholera toxin B subunit, into Balb/c mice resulted in complete protection against PR8 infection in parallel with the induction of high levels of HA-specific IgA and IgG antibodies on the respiratory tract. The respiratory tract IgA and IgG were purified from nasal and lung washings of the immunized mice using affinity columns, and their HA-specific activities were measured by enzyme-linked immunosolvent, plaque neutralization and haemagglutination inhibition assays. The purified IgA and IgG had the following properties: (1) They were able to neutralize virus in vitro. (2) The purified IgA included major antibodies directed against PR8 virus and minor antibodies cross-reactive with A/Yamagata/120/86 (H1N1) or A/Fukuoka/C29/85 (H3N2) virus, while the purified IgG included major antibodies to the homotypic virus, minor antibodies to the H1N1 virus and only a trace amount of antibodies to the H3N2 virus. (3) When separated on a Sephacryl column, most of the IgA anti-HA activities occurred in the polymeric fractions of purified IgA, whereas the IgG anti-HA activities occurred in the monomeric fractions. (4) When passively administered to normal mouse respiratory tract before infection, the purified IgA protected against PR8 infection. These results suggest that HA-specific, polymeric IgA antibodies on the respiratory tract by themselves provide not only protection against the homotypic virus but also higher levels of heterotypic immunity than IgG.

Enhancing effect of centrifugation on isolation of influenza virus from clinical specimens

The use of centrifugation (700 x g, 60 min) in a plaque assay markedly increased (mean, 2.9-fold) the infectivity of all 42 influenza virus strains tested, compared with no centrifugation. Of 13 influenza virus strains isolated from 390 clinical specimens, 9 (69%) were efficiently isolated by the centrifugation assay compared with conventional culture methods. The centrifugation assay may be useful for isolating the influenza virus from clinical specimens.

The synthesis of influenza virus negative-strand RNA takes place in insoluble complexes present in the nuclear matrix fraction

The replication of influenza virus RNA in vitro has been studied by cell fractionation of MDCK-infected cells and characterization of in vitro synthesized RNA. Analysis of the RNA product polarity by liquid hybridization to excess single-stranded DNA probes shows that only the RNP complexes present in the nuclear matrix fraction are able to synthesize negative-polarity RNA. This RNA product has been characterized as authentic vRNA by size analysis, RNase-protection by unlabelled, positive-polarity riboprobes and T1-fingerprinting. Priming the in vitro reaction with ApG stimulates preferentially the synthesis of positive-polarity RNA, while ApGpU stimulates both positive and negative-polarity RNA synthesis.

Rapid focus reduction neutralization test of influenza A and B viruses in microtiter system

A rapid neutralization test for influenza A and B viruses was developed. In this method, a 96-well tissue culture plate was used for the preparation of cell monolayers and the peroxidase-antiperoxidase staining technique was used for the visualization of foci infected with these viruses. In the presence of trypsin and tragacanth gum, clear foci developed 1 day after infection. A linear relationship between virus dilutions and numbers of foci was observed. When neutralizing antibodies in some test sera were assayed, a good correlation was observed between the titers obtained by the focus method and those obtained by the ordinary plaque method. In addition, many serum specimens were investigated by the neutralization test, and it was demonstrated that the test is useful for serological studies of influenza.

Human malignant melanoma cell line (HMV-II) for isolation of influenza C and parainfluenza viruses

HMV-II, a human malignant melanoma cell line, was compared with other cell lines (MDCK, Vero, and LLC-MK2) and primary cultures of monkey kidney (PMK) cells for the isolation and quantification of influenza and parainfluenza viruses. HMV-II cells were superior to MDCK and LLC-MK2 cells in quantification of the influenza C virus and were used successfully in the isolation of the virus from clinical specimens. The HMV-II cell line was also more sensitive for isolating parainfluenza viruses from clinical specimens than were Vero and PMK cells; there was, however, no significant difference in the quantification of the viruses among these cultures. As far as influenza A and B viruses were concerned, the HMV-II cell line was significantly less sensitive than MDCK cells, and no virus was isolated from clinical specimens with HMV-II cells. Thus, HMV-II cells are useful for the isolation of influenza C and parainfluenza viruses as an alternative to embryonated hen's eggs and PMK cells.

Phenotypic hiding: the carryover of mutations in RNA viruses as shown by detection of mar mutants in influenza virus

When influenza virus monoclonal antibody-resistant (mar) mutants are selected by incubation in vitro with excess antibody, 90 to 99% of the mutants are not detectable. This observation may be explained by encapsidation of mar mutant RNAs within phenotypically wild-type envelopes. This phenotypic hiding can be revealed by selection of mar mutants in vivo after virus uncoating. Using experimental procedures appropriate to detect all viable mar mutants in a virus population, we determined precisely the mutation rates to the mar genotype by the fluctuation test for two nonoverlapping monoclonal antibodies.

Molecular mechanism of complex infection by bacteria and virus analyzed by a model using serratial protease and influenza virus in mice

We examined the effect of a serratial exoprotease on the pathogenesis of influenza virus infection in mice as a model of complicated respiratory infection by bacteria and virus in humans. The 56-kilodalton (56-kDa) protease from Serratia marcescens was administrated intranasally to mice at a dose of 10, 20, or 40 micrograms from day 0 to day 3 after inoculation of the influenza virus. Administration of the protease resulted in remarkable enhancement of the lethal effect of the virus and enhancement of pathological changes in the lungs. Influenza virus replication, determined by plaque-forming assay, was accelerated by the protease. Namely, we found a 100-fold increase in virus yield by day 2. The 56-kDa protease caused generation of plasmin activity in the lungs. In vitro experiments showed that plasmin greatly enhanced the yield of influenza virus, although the effect of the 56-kDa protease by itself was much lower than that of plasmin. Furthermore, the 56-kDa protease could induce plasmin production indirectly via activation of plasminogen by the Hageman factor-dependent cascade in the in vitro system. We conclude that this major serratial exoprotease has a deleterious effect on mice infected with influenza virus and that this effect seems to result from enhancement of viral growth by indirect acceleration of plasmin generation induced by the protease.

Efficacy of rimantadine hydrochloride in the treatment of influenza infection of mice

Rimantadine HCl was assessed for its effect on influenza A virus titer in lungs of infected BALB/c mice. Rimantadine administered orally via drinking water, with and without an intraperitoneal prophylactic loading dose, was compared to intraperitoneal administration. Mice were infected with a non-lethal dose of influenza A/Port Chalmers/H3N2 virus and the pulmonary virus titers were determined at intervals over a 21 day period. Prophylactic treatment with rimantadine followed by oral administration resulted in up to a 4 log10 reduction in pulmonary virus titer. The oral doses given to the mice were comparable on a mg/kg/day basis to those recommended for treatment of human infections. Reductions in pulmonary virus titers also occurred after intraperitoneal rimantadine treatment which included a prophylactic dose, but the reductions in pulmonary virus titers were less striking and not consistent over the course of infection. There were no significant reductions in pulmonary virus titers by either route if treatment was started 8 h after exposure to virus.

Plaque quantitation and virus neutralization assays for human astroviruses

Astroviruses, 28 nm-diameter, RNA-containing viruses which have been implicated in gastroenteritis can be cultivated in cell cultures containing trypsin, but do not show distinguishable cytopathic effects. However, with the 5 known astrovirus serotypes which we have been able to cultivate, 3 (types 1, 2, and 5) formed well-defined plaques in LLCMK2 cell cultures under an agar overlay containing trypsin. A virus neutralization assay based on plaque reduction was applied to these 3 serotypes. It was found that rabbit antisera prepared against individual serotypes neutralized virus type-specifically, and no cross-neutralization titers were obtained with any of the antisera to the 5 astrovirus serotypes. The type-specific neutralization observed agreed with the specificities seen by immunofluorescence (IF), whereas ELISA tests with the same antisera show cross-reactivity among all 5 serotypes. There was no virus neutralization detected with astrovirus monoclonal antibodies which were reactive with 5 serotypes by ELISA and IF. The results we have obtained permit quantitative techniques to be applied to epidemiological and biological studies of the human astroviruses.

Enhancement of humoral immune responses against viral vaccines by a non-pyrogenic 6-O-acylmuramyldipeptide and synthetic low toxicity analogues of lipid A

6-O-Acyl derivatives of N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) and synthetic, low toxicity lipid-A analogues were examined for their ability to enhance the potency of current viral vaccines. 6-O-(2-Tetradecylhexadecanoyl)-MDP (B30-MDP) in non-irritative vehicles such as physiological saline, phosphate-buffered saline (PBS), squalene-PBS emulsion, Intralipid or liposomes, significantly stimulated the primary and secondary antibody production of guinea-pigs against influenza split or subunit vaccine and inactivated the hepatitis B virus surface (HBs) antigen. Mice seemed less responsive to the adjuvanticity of B30-MDP than guinea-pigs. Two low toxicity lipid A analogues, acylated beta(1-6)-D-glucosamine disaccharide bisphosphates (which do not have amide-bound or ester-bound 3-acyloxyacyl groups unlike fully toxic Escherichia coli-type lipid A), caused significantly enhanced antibody responses, primary or secondary, when administered to mice by incorporation into liposomes with inactivated HBs antigen.

Biological functions of the NS1 protein of an influenza B virus mutant which has a long carboxyl terminal deletion

To clarify the function of the NS gene of a highly cytolytic mutant of influenza virus B/Yamagata/1/73 which expresses an NS1 protein with a long carboxyl terminal deletion (clone 201), we prepared a single gene reassortant (201 L-77) and a control reassortant (YL-20) in which all the genes were of wild type influenza virus B/Lee/40 origin except NS gene which was derived from either clone 201 or wild type B/Yamagata. Comparative studies have revealed that 201 L-77 destructed infected cells more severely and much earlier after infection than did YL-20, although both produced comparable amount of infectious virus. The highly cytolytic reassortant 201 L-77 produced a small plaque, while the weakly cytolytic reassortant YL-20 produced a large plaque in MDCK cells. There was little difference between the two reassortants in the time course and the amount of synthesis of viral proteins within the infected cells. However, the mode of synthesis of viral RNA (vRNA) by 201 L-77 was greatly altered compared with YL-20.

Difference in growth behavior of human, swine, equine, and avian influenza viruses at a high temperature

Growth characteristics of a wide range of influenza A viruses from different mammals and bird species were examined in an established line of canine kidney (MDCK) cells at an ordinary (37 degrees C) and a high temperature (42 degrees C). Although all viruses employed in the present study possessed a capability of replicating at 37 degrees C, virus growth at 42 degrees C showed considerable variation and reflected differences in the natural hosts of the isolates. All reference strains and isolates from bird species grew well in the MDCK cells maintained at 42 degrees C, but human viruses did not, showing an asymmetrical growth behavior. In contrast to this, growth of swine and equine viruses showed growth characteristics intermediate between human and avian viruses. Of the two swine viruses examined, replication of one strain occurred equally well at both temperatures and another failed to grow at 42 degrees C. Similarly, two of the three equine viruses tested belonging to H3N8 antigenic subtypes grew at 42 degrees C. However, the results obtained from comparison of plaque sizes and growth curves indicated that the replication of the above swine and equine viruses was restricted under a stringent temperature when compared to avian viruses. The detailed analysis of cloned viruses revealed that some of the swine and equine viruses contained two variants which are readily distinguished by growth behavior at 42 degrees C. Genome analysis of parental and virus clones by oligonucleotide mapping and migration profiles of RNA segments did not detect any differences among the above variants exhibiting the asymmetrical growth characteristics at 42 degrees C.

Influenza virus infection of tracheal gland cells in culture

Influenza virus-induced tracheobronchitis causes limited epithelial deciliation but markedly decreased mucociliary transport. This suggests that virus-induced alterations in airway mucus play a role in decreased mucociliary transport. Airway submucosal glands are a primary source of mucus. Therefore, we examined virus-gland cell interactions by exposing primary cultures of isolated feline tracheal gland cells to influenza A/Scotland/840/74 H3N2 virus for 1 h at a multiplicity of infection of 0.1. Virus production and release into the culture medium first occurred between 8 and 12 h postinfection and eventually reached a steady state that continued for at least 8 days. Virus which was produced and released by infected cells infected other monolayers, resulting in viral production similar to that after infection with stock virus. Hemadsorption assays conducted 24 h after infection demonstrated that most of the cells in a monolayer became infected. The infection was nonlytic according to cell morphology, trypan blue dye exclusion, and release of lactate dehydrogenase. Because lysis of a cell subpopulation could have been masked by subsequent cell division, we compared the uptake of [3H]thymidine by infected and control monolayers. There was no increase in uptake by infected monolayers. These results demonstrate that feline tracheal gland cells in primary culture undergo productive and nonlytic infection with influenza A virus. This model provides a unique system for the study of virus-gland interactions isolated from the influence of other tissues.

A microplate method for isolation of viruses from infants and children with acute respiratory infections

Between December 1984 and December 1986, a microplate technique was adopted for isolation of viruses from infants and children with acute respiratory infections. By using two kinds of tissue culture microplates, i.e., the HHVM plate, containing human embryonic fibroblast (HEF), HEp-2, Vero and MDCK cells, and the MK plate which contains secondary monkey kidney cells, 1,080 field viruses were isolated from 1,061 (24.9%) out of 4,254 throat swabs. Of these 1,080 isolates, 1,003 (92.9%) were recovered in the HHVM plates and the remaining 77 (7.1%) in the MK plates. With the HHVM plate, influenza A and B viruses were cultivated in MDCK, RS virus in HEp-2, parainfluenza and mumps viruses in Vero, adenoviruses in both HEF and HEp-2, polioviruses in HEF, HEp-2 and Vero, coxsackie B viruses in both HEp-2 and Vero, rhino and echo viruses in HEF, herpes simplex virus in both HEF and HEp-2, and cytomegalovirus in HEF, although MK were more sensitive than Vero to parainfluenza and coxsackie B viruses. There was no difference in the rate of isolation of viruses between the microplate and ordinary tube methods. Cross contamination in the microplates was negligible for routine work.

Antigenic structure and variation in an influenza virus N9 neuraminidase

We previously determined, by X-ray crystallography, the three-dimensional structure of a complex between influenza virus N9 neuraminidase (NA) and the Fab fragments of monoclonal antibody NC-41 [P. M. Colman, W. G. Laver, J. N. Varghese, A. T. Baker, P. A. Tulloch, G. M. Air, and R. G. Webster, Nature (London) 326:358-363, 1987]. This antibody binds to an epitope on the upper surface of the NA which is made up of four polypeptide loops over an area of approximately 600 A2 (60 nm2). We now describe properties of NC-41 and other monoclonal antibodies to N9 NA and the properties of variants selected with these antibodies (escape mutants). All except one of the escape mutants had single amino acid sequence changes which affected the binding of NC-41 and which therefore are located within the NC-41 epitope. The other one had a change outside the epitope which did not affect the binding of any of the other antibodies. All the antibodies which selected variants inhibited enzyme activity with fetuin (molecular weight, 50,000) as the substrate, but only five, including NC-41, also inhibited enzyme activity with the small substrate N-acetylneuramin-lactose (molecular weight, 600). These five probably inhibited enzyme activity by distorting the catalytic site of the NA. Isolated, intact N9 NA molecules form rosettes in the absence of detergent, and these possess high levels of hemagglutinin activity (W.G. Laver, P.M. Colman, R.G. Webster, V.S. Hinshaw, and G.M. Air, Virology 137:314-323, 1984). The enzyme activity of N9 NA was inhibited efficiently by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, whereas hemagglutinin activity was unaffected. The NAs of several variants with sequence changes in the NC-41 epitope lost hemagglutinin activity without any loss of enzyme activity, suggesting that the two activities are associated with separate sites on the N9 NA head.

Molecular analyses of the hemagglutinin genes of H5 influenza viruses: origin of a virulent turkey strain

Comparative sequence analysis of the hemagglutinin (HA) genes of a highly virulent H5N8 virus isolated from turkeys in Ireland in 1983 and a virus of the same subtype detected simultaneously in healthy ducks showed only four amino acid differences between these strains. Partial sequencing of six of the other genes and antigenic similarity of the neuraminidases established the overall genetic similarity of these two viruses. Comparison of the complete sequence of two H5 gene sequences and partial sequences of other virulent and avirulent H5 viruses provides evidence for at least two different lineages of H5 influenza virus in the world, one in Europe and the other in North America, with virulent and avirulent members in each group. In vivo studies in domestic ducks showed that all of the H5 viruses that are virulent in chickens and turkeys replicate in the internal organs of ducks but did not produce any disease signs. Additionally, both viruses isolated from turkeys and ducks in Ireland were detected in the blood. These studies provide the first conclusive evidence for the possibility that fully virulent influenza viruses in domestic poultry can arise directly from viruses in wild aquatic birds. Studies on the cleavability of the HA of virulent and avirulent H5 viruses showed that the principles established for H7 viruses (F. X. Bosch, M. Orlich, H. D. Klenk, and R. Rott, 1979, Virology 95, 197-207; F. X. Bosch, W. Garten, H. D. Klenk, and R. Rott, 1981, Virology 113, 725-735) also apply to the H5 subtype. These are (1) only the HAs of virulent influenza viruses were cleaved in tissue culture in the absence of trypsin and (2) virulent H5 influenza viruses contain a series of basic amino acids at the cleavage site of the HA, whereas avirulent strains contain only a single arginine with the exception of the avirulent Chicken/Pennsylvania virus. Thus, a series of basic amino acids at the cleavage site probably forms a recognition site for the enzyme(s) responsible for cleavage.

Temperature-sensitive defect of influenza A/Ann Arbor/6/60 cold-adapted variant leads to a blockage of matrix polypeptide incorporation into the plasma membrane of the infected cells

A temperature-sensitive (ts) defect in growth of the A/Ann Arbor/6/60 (A/AA/60) cold-adapted (ca) and ts variant strain has been studied. At the restrictive temperature of 38.5 degrees C, the variant synthesized all the viral polypeptides in normal amounts within the infected cells, but the virions released into the culture fluid contained greatly reduced amounts of the matrix (M1) polypeptide and showed significantly low infectivity per unit hemagglutinin activity. Cell fractionation experiments revealed that incorporation of the M1 polypeptide into plasma membranes of the variant-infected cells was selectively reduced at 38.5 degrees C, whilst it occurred normally at 34 degrees C. The ts reassortants between the A/AA/60 variant and the A/AA/1/80 wild type (wt) strain (non-ts), which had the M gene derived from the wt parent, also showed similar patterns. These results suggest that the ts defect of the variant and its ts reassortants involves the process of incorporation of the M1 polypeptide into the plasma membranes of the infected cells and that this defect is not attributable to the M gene of the variant.

Relative antigenicity in mice of H1N1, H3N2 and B strains present in inactivated influenza virus vaccines

The results of a study on serum HAI and neutralizing antibodies induced in mice by whole influenza virus vaccines containing A/Brazil/11/78 (H1N1), A/Bangkok/1/79 (H3N2) and B/Singapore/222/79 viruses are reported. According to the GMT of HAI, the antigenic potency of the three vaccine strains appear to be different. The A/Brazil/11/78 antigen induced the lowest HAI antibody responses and the A/Bangkok/1/79 antigen the greatest. This behaviour, with a few exceptions, was noted regardless of the HA amount (0.08 microgram 0.4 microgram, 2 micrograms) of each strain present in the vaccine, the number of doses (one or two), or the kind of preparation (monovalent or trivalent). The data obtained with the neutralization test with vaccines with medium HA content are concordant with previous findings. On the basis of the ratios of the GMT of the neutralizing antibodies to the GMT of the HAI antibodies, it was concluded that the HAI antibodies to A/Bangkok/1/79 antigen possess, on the whole, a neutralizing activity that is higher than that found for the HAI antibodies to A/Brazil/11/78 and B/Singapore/222/79 strains. For the latter strains, the neutralizing activity increased after the second dose. The observation of the different degrees of antigenicity of the three vaccine strains suggests that, with currently used inactivated influenza virus vaccines containing equivalent amounts of all three antigens, the dosage should be taken into consideration when the vaccines are used for subjects lacking in previous exposure to vaccine strains.

Isolation of a novel type of interfering influenza B virus defective in the function of M gene

A novel type of interfering influenza B virus which is defective in the function of M gene has been reported. Clone 301, a B type virus clone obtained by successive back-crosses of A/Aichi/2/68 (H 3 N 2) with B/Yamagata/1/73, grew normally in MDCK cells when inoculated at a low multiplicity, but was easily converted to a hemagglutinating but non-infectious form by one cycle of high multiplicity infection. Within MDCK cells infected with infectious clone 301 at a high multiplicity, synthesis of M protein was greatly reduced. The virus particle produced by a high multiplicity infection was devoid of RNA segment 7 (M gene), contained less amount of M protein compared with the standard virus, and interfered with the replication of wild type B/Yamagata, again accompanied by a selective suppression of M protein synthesis within the co-infected cells.

In vitro antiviral activity of the 6-substituted 2-(3',4'-dichlorophenoxy)-2H-pyrano[2,3-b]pyridines MDL 20,610, MDL 20,646, and MDL 20,957

The 6-substituted 2-(3',4'-dichlorophenoxy)-2H-pyrano[2,3-b]pyridines MDL 20,610 (6-SO2CH3), MDL 20,646 (6-Br), and MDL 20,957 (6-Cl) are potent antirhinovirus compounds with median plaque 50% inhibitory concentrations (IC1/2s) of 0.03, 0.006, and 0.006 micrograms/ml, respectively, against the 32 serotypes evaluated. The 6-halogenated analogs produced 99% reductions in progeny virion yields at concentrations as low as 0.004 micrograms/ml. However, these analogs perturbated HeLa cell metabolism at lower concentrations (at or above 5 micrograms/ml) than did the 6-methylsulfonyl analog (at or above 20 micrograms/ml). Compound MDL 20,610 was also active against human, simian, and bovine rotaviruses (cytopathic effect IC1/2s of 0.8 to 1.5 micrograms/ml) and possessed variable enterovirus and paramyxovirus activity.

Evolution of the A/Chicken/Pennsylvania/83 (H5N2) influenza virus

The epidemiological features of the H5N2 outbreak of influenza in poultry were studied by sequencing the HA genes of several viruses isolated during the epidemic. Comparison of the nucleotide sequences of the HA genes indicated there was a single introduction of virulent virus. The variation rate (silent mutations) in the HA gene of the virulent Ck/Penn virus was 9.0 or 14.4% per 10 years depending on the viruses compared and was similar to that in H3 HA gene of human influenza A virus. The virulent and avirulent viruses isolated after October 1983 were derived from a common ancestoral virus and the virulent virus did not supersede the avirulent virus, instead, the virulent and avirulent viruses coexisted and evolved separately during the course of the epidemic. The evolutionary changes in the HA of H5N2 viruses that occurred during the epidemic permitted us to establish that a virus (A/Chick/Washington/84) that was isolated 8 months after the last H5N2 virus had been isolated from poultry in Pennsylvania belonged to the family of potentially dangerous H5N2 viruses and was a direct descendent of the virus that spread to Maryland and Virginia. All of the virulent Ck/Penn viruses retained the amino acid changes at residues 13 and 69 in the HA.

Enzymological heterogeneity of influenza B virus neuraminidase demonstrated by the fluorometric assay method

The neuraminidase activity of 26 strains of influenza B virus isolated from all over the world was investigated colorimetrically, using fetuin as a substrate, and fluorometrically, using 4-methylumbelliferyl(4-MU)-N-Ac-alpha-D-neuraminide as a substrate, with special reference to enzymological heterogeneity. The activity of influenza A viral neuraminidases and of a commercially available pure viral one was strongly inactivated by either ethylenediaminetetraacetic acid or glycoletherdiaminetetraacetic acid, when measured by the fluorometric assay method, whereas that of influenza B ones was not at all. However, the viral neuraminidases of both influenza A and B viruses were found to be calcium ion-dependent by the colorimetric assay method. A difference in the catalytic rate between the two assay methods was observed with influenza B viral neuraminidase to a much greater extent as compared with that of influenza A. A difference in substrate specificity of these enzymes was demonstrated to be due to a difference in the degree of competitive inhibition by N-acetylneuraminic acid. These findings strongly suggest that enzymological heterogeneity in influenza B viral neuraminidase may be attributed to delicate structural differences, between the enzymes of influenza A and B viruses demonstratable only by the fluorometric neuraminidase assay method using 4-MU-N-Ac-alpha-D-neuraminide as a substrate.

Differential infection of receptor-modified host cells by receptor-specific influenza viruses

Influenza viruses of contrasting receptor specificity have been examined for their ability to infect receptor-modified MDCK cells containing sialyloligosaccharide receptor determinants of defined sequence. Cells were treated with sialidase to remove sialic acid and render them resistant to infection and were then incubated with sialyltransferase and CMP-sialic acid to restore sialic acid in the SA alpha 2,6Gal or SA alpha 2,3Gal linkages. The viruses A/RI/5 + /57 and A/duck/Ukraine/1/63, previously shown to exhibit preferential binding of SA alpha 2,6Gal and SA alpha 2,3Gal linkages, respectively, were found to exhibit differential infection of the receptor-modified cells in accord with their receptor specificity. Coinfection of SA alpha 2,3Gal derivatized cells with a mixture of the two viruses resulted in selective propagation of the SA alpha 2,3Gal-specific A/duck/Ukraine/1/63 virus. The results demonstrate the potential for cell surface receptors to mediate selection of receptor-specific variants of influenza virus.

Antigenic analysis of H4 influenza virus isolates using monoclonal antibodies to defined antigenic sites on the hemagglutinin of A/Budgerigar/Hokkaido/1/77 strain

Three non-overlapping antigenic sites were defined on the hemagglutinin of avian influenza virus A/budgerigar/Hokkaido/1/77 (H4N6) by competitive binding assay of monoclonal antibodies to the virus and comparative antigenic analysis of variants selected with monoclonal antibodies. Antigenic relationship among 25 H4 influenza viruses of different bird origin was examined by ELISA with the monoclonal antibodies to each of defined antigenic sites. Two of the three antigenic sites contained epitopes specific to the H4 influenza viruses of budgerigar and mynah origin, and the remaining site contained an epitope which was cross-reactive with almost all of the H4 influenza viruses.

Is bivalent binding of monoclonal antibodies to different antigenic areas on the hemagglutinin of influenza virus required for neutralization of viral infectivity?

Biological activities of Fab fragments of monoclonal IgG antibodies to each of four nonoverlapping antigenic areas on the hemagglutinin molecule of A/seal/Massachusetts/1/80 (H7N7) influenza virus were examined. Fab fragments of the antibodies belonging to groups I and II neutralized viral infectivity. These Fab fragments inhibited hemagglutination of the virus and virus-induced hemolysis at pH 5.9. On the other hand, Fab fragments of groups III and IV antibodies showed neither neutralization nor hemolysis-inhibition activities, while intact IgG molecules of groups III and IV effectively neutralized viral infectivity and inhibited virus-induced hemolysis, as previously found. These IgG molecules scarcely or did not inhibit hemagglutination of the virus. Neutralization of viral infectivity, however, was observed when the virus was coated with Fab fragments of groups III and IV antibodies and then incubated with anti-Fab fragment antibodies. These findings suggest that bivalent binding of the IgG antibodies of groups III and IV is required for neutralization of viral infectivity through a proposed mechanism by which these antibodies interfere with a low pH-induced conformational change resulting in inhibition of the fusion step of the viral replication process.

Characterization of virulent and avirulent A/chicken/Pennsylvania/83 influenza A viruses: potential role of defective interfering RNAs in nature

In April 1983, an influenza virus of low virulence appeared in chickens in Pennsylvania. Subsequently, in October 1983, the virus became virulent and caused high mortality in poultry. The causative agent has been identified as an influenza virus of the H5N2 serotype. The hemagglutinin is antigenically closely related to tern/South Africa/61 (H5N3) and the neuraminidase is similar to that from human H2N2 strains (e.g., A/Japan/305/57) and from some avian influenza virus strains (e.g., A/turkey/Mass/66 [H6N2]). Comparison of the genome RNAs of chicken/Penn with other influenza virus isolates by RNA-RNA hybridization indicated that all of the genes of this virus were closely related to those of various other influenza virus isolates from wild birds. Chickens infected with the virulent strain shed high concentrations of virus in their feces (10(7) 50% egg infective dose per g), and the virus was isolated from the albumin and yolk of eggs layed just before death. Virus was also isolated from house flies in chicken houses. Serological and virological studies showed that humans are not susceptible to infection with the virus, but can serve as short-term mechanical carriers. Analysis of the RNA of the viruses isolated in April and October by gel migration and RNA-RNA hybridization suggested that these strains were very closely related. Oligonucleotide mapping of the individual genes of virulent and avirulent strains showed a limited number of changes in the genome RNAs, but no consistent differences between the virulent and avirulent strains that could be correlated with pathogenicity were found. Polyacrylamide gel analysis of the early (avirulent) isolates demonstrated the presence of low-molecular-weight RNA bands which is indicative of defective-interfering particles. These RNAs were not present in the virulent isolates. Experimental infection of chickens with mixtures of the avirulent and virulent strains demonstrated that the avirulent virus interferes with the pathogenicity of the virulent virus. The results suggest that the original avirulent virus was probably derived from influenza viruses from wild birds and that the virulent strain was derived from the avirulent strain by selective adaptation rather than by recombination or the introduction of a new virus into the population. This adaptation may have involved the loss of defective RNAs, as well as mutations, and thus provides a possible model for a role of defective-interfering particles in nature.

Characterization of a porcine kidney cell line resistant to influenza virus infection

A mutant cell line of porcine kidney cells that resists the cytopathic effect of influenza virus has been obtained and characterized. These cells, designated ESK-R, were originally obtained by prolonged cultivation of cells surviving influenza B/Kanagawa/73 virus infection. No infectious virus was recovered from ESK-R cells, and no evidence for the presence of virus antigens in the cells was demonstrated by immunofluorescent staining. ESK-R cells also showed a distinct resistance to various other strains of both types A and B influenza viruses. The growth of mumps, Sendai, or Newcastle disease virus was considerably restricted, but the cell line normally supported the replication of vesicular stomatitis virus. ESK-R cells were found to lack specific receptors for influenza virus as determined by fluorescence-activated cell sorter analyses. The membrane barrier of ESK-R cells was successfully overcome by nonspecific endocytosis of calcium-coprecipitated virus particles followed by production of an appreciable amount of progeny virus.

Is virulence of H5N2 influenza viruses in chickens associated with loss of carbohydrate from the hemagglutinin?

The A/Chick/Penn/83 (H5N2) influenza virus that appeared in chickens in Pennsylvania in April 1983 and subsequently became virulent in October 1983, was examined for plaque-forming ability and cleavability of the hemagglutinin (HA) molecule. The avirulent virus produced plaques and cleaved the HA only in the presence of trypsin. In contrast, the virulent virus produced plaques and cleaved the HA precursor into HA1 and HA2 in the presence or absence of trypsin. The apparent molecular weight of the HA1 from the avirulent virus was higher than that from the virulent virus, but when the viruses were grown in the presence of tunicamycin, the molecular weights of HA were indistinguishable. Two of nine monoclonal antibodies to the HA of the avirulent virus indicate that there is at least one epitope on the HA that is different between the virulent and avirulent viruses. The amino acid sequences of the HAs from the two viruses were compared by sequencing their respective HA gene. The nucleotide sequence coding for the processed HA polypeptide contained 1641 nucleotides specifying a protein of 547 amino acids. The amino acid sequences of the virulent and avirulent viruses were indistinguishable through the connecting peptide region, indicating that the difference in cleavability of the H5 HA is not directly attributed to the amino acid sequence of the connecting peptide. Four of seven nucleotide changes resulted in amino acid changes at residues 13, 69, and 123 of HA1 and at residue 501 of the HA2 polypeptide. Since there were no deletions or insertions in the amino acid sequence of the virulent or avirulent viruses, the possibility exists that the difference in molecular weight is due to loss of a carbohydrate side chain in the virulent strain. The amino acid change in the virulent strain at residue 13 is the only mutation that could affect a glycosylation site and this is in the vicinity of the connecting peptide. It is postulated that the loss of this carbohydrate may permit access of an enzyme that recognizes the basic amino acid sequences and results in cleavage activation of the HA in the virulent virus.

Adsorption of influenza viruses to nitrocellulose membrane filters by filtration and their quantitative densitometric determination

Influenza viruses concentrated and adsorbed onto nitrocellulose membrane filters by filtration are detected rapidly and sensitively by sequential incubation with the primary antibody and the secondary antibody conjugated with peroxidase. The bound enzyme is detected by incubation with a substrate which is converted to an insoluble colored product. A dual-wavelength TLC scanner is used for densitometric quantitation. The membrane filtration-blotting enzyme immunoassay provides a method for quantitative analysis and rapid typing of influenza isolates. The method may be also applicable for quantitative detection of influenza viruses in throat swab specimens from patients, as well as in tissue culture fluids.

Persistence of Q strain of H2N2 influenza virus in avian species: antigenic, biological and genetic analysis of avian and human H2N2 viruses

The characteristics of an avian influenza virus were compared in detail with those of human Asian (H2N2) influenza viruses. Antigenic analysis by different antisera against H2N2 viruses and monoclonal antibodies to both the hemagglutinin and neuraminidase antigens showed that an avian isolate, A/duck/München/9/79 contained hemagglutinin and neuraminidase subunits closely related to those of the early human H2N2 viruses which had been prevalent in 1957. However, this avian virus gave low HI titers with absorbed and non-absorbed antisera to different human H2N2 viruses isolated in 1957. Like human Q phase variant, such as A/RI/5-/57 (H2N2), hemagglutination of the above avian strain was not inhibited by the purified non-specific gamma-inhibitor from guinea pig serum. Growth behavior at restrictive temperature (42 degrees C) clearly differentiate the avian H2N2 virus from human influenza viruses, showing that the former virus grew well in MDCK cells at 42 degrees C but not the latters. Genomic analysis of these viruses revealed that the oligonucleotide map of H2N2 virus isolated from a duck was quite different from those of human H2N2 viruses from 1957 to 1967. The oligonucleotide mapping also indicated that different H2N2 influenza virus variants had co-circulated in humans in 1957.

Anti-influenza A activity of some N-substituted bicyclo[3.2.1]octane-3-spiro-3'-pyrrolidine hydrochlorides: synthesis and structure

Some N-substituted bicyclo[3.2.1]octane-3-spiro-3'-pyrrolidine hydrochlorides (IX-XII) prepared from bicyclo[3.2.1]octan-3-one (I), were assayed in vitro against influenza A viruses. All materials showed activity similar to 1-adamantanamine hydrochloride. A 1H-NMR study revealed only one isomer at the spiro carbon atom.