Nucleotide sequence and some biological properties of the NS gene of a newly isolated influenza B virus mutant which has a long carboxyl terminal deletion in the NS1 protein

By a heterotypic cross between influenza viruses A/WSN (H1N1) and B/Yamagata/1/73, we obtained a mutant of B/Yamagata (AWBY-234), which expressed a greatly truncated NS1 protein with molecular weight of 13,500. Direct sequencing of the NS gene of the mutant revealed a deletion of a single uridine base at the position 310, 311, or 312 of the plus sense RNA, giving rise to a new stop codon at the position 314-316. The resulting NS1 protein was predicted to be composed of only 90 amino acids, compared with 281 with the NS1 of the wild-type B/Yamagata. AWBY-234 grew normally and induced a typical cytopathic effect in infected MDCK cells much earlier after infection than did the wild-type B/Yamagata. A single gene reassortant in which the NS gene of AWBY-234 was transferred to B/Lee/40 inherited these characteristics from AWBY-234 parent. The single gene reassortant, but not the control reassortant, contained a significant amount of defective particles which can complement each other to produce infectious virus.

Comparison of protective effects of serum antibody on respiratory and systemic infection of Sendai virus in mice

The protective effects of the passive administration of convalescent serum from mice infected with Sendai virus were evaluated in mice challenged intranasally with wild-type and a pantropic variant (F1-R) of Sendai virus. Adoptive transfer of the serum efficiently prevented F1-R from infecting the systemic organs, but it failed to protect the mice from infections of the respiratory tracts by either virus. Virus replication in nasal turbinates was not diminished while infection in the lung was suppressed sufficiently for the infected mice to survive the infection. These findings suggest that serum antibody is less effective for the protection against viral infections on the surface of the respiratory tract, but it is effective for inhibition of spread of the virus into the systemic organs.

Vibrio fluvialis: a new serogroup (19) possessing the Inaba factor antigen of Vibrio cholerae O1

A serogroup of Vibrio fluvialis possessing the C (Inaba) antigen but not the B (Ogawa) nor A antigen of V. cholerae O1 is described. The O-antigen of this serogroup was identical with that of bioserogroup 1875-variant of a marine Vibrio species. As the O-antigen of this serogroup was not agglutinated by any of O-antisera for the 18 serogroups of V. fluvialis already recognized, it was designated O-serogroup 19 of this species.

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.

Infectious influenza A and B virus variants with long carboxyl terminal deletions in the NS1 polypeptides

An influenza A virus, A/turkey/Oregon/71, was shown by protein gel analysis to code for an NS1 protein approximately half the size of those of other influenza A viruses. Sequence analysis of the NS gene of this virus revealed a 10 nucleotide deletion resulting in an NS1 protein of only 124 amino acids. This truncated NS1 polypeptide retained its karyophilic pattern as detected by indirect immunofluorescence analysis of virus infected cells. Also, A/turkey/Oregon/71 virus grew to high titer in embryonated chicken eggs comparable to other influenza A viruses. We also identified a laboratory variant of an influenza B virus, clone 201, which codes for a truncated NS1 protein. Sequence analysis revealed a 13 nucleotide deletion resulting in a shortened NS1 protein of only 127 amino acids as compared to other influenza B virus NS1 proteins possessing a length of 281 amino acids. Again as shown for the NS1 proteins of other influenza B viruses the NS1 polypeptide of B virus clone 201 was found to localize in the nucleus of infected cells. It appears that large deletions in the carboxyl terminus of the NS1 proteins of influenza A and B viruses can be tolerated without affecting the functional integrity of the NS1 polypeptide.

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.

Isolation and preliminary characterization of a highly cytolytic influenza B virus variant with an aberrant NS gene

By repeated backcrosses of influenza virus A/Aichi/2/68 (H3N2) with B/Yamagata/1/73 in MDCK cells, a virus clone with HA of B serotype (clone B/610B5B/201, or clone 201) was obtained, which formed sharp plaques in MDCK cells and induced a severe cell lysis early after infection. Its structural proteins were indistinguishable from those of B/Yamagata. Electrophoresis of the RNA of the clone also showed an identical pattern to that of B/Yamagata except RNA segment 8 (NS gene), which migrated faster than the corresponding segment of B/Yamagata in a 2.8% polyacrylamide gel. Within the clone 201-infected MDCK cells, only one species of nonstructural (NS) polypeptide was demonstrable, which had the same electrophoretic mobility as NS2 of B/Yamagata, and any band which might be taken as the counterpart of NS1 of B/Yamagata was not detectable on the gel. Peptide mapping revealed that NS of clone 201 was structurally different from either NS1 or NS2 of wild-type B/Yamagata. NS gene and its function of clone 201 was successfully transferred to B/Lee/40 by genetic reassortment.

Comparison of nine strains of influenza C virus in growth characteristics and viral polypeptides. Brief report

Nine strains of influenza C virus were compared in their growth characteristics and viral polypeptides using LLCMK2 cells. The results suggested that influenza C virus undergoes genetic changes like influenza A or B virus.

Temperature-sensitive influenza A virus clones originated by a cross between A/Aichi/2/68 (H3N2) and B/Yamagata/1/73

A genetic cross was performed between influenza viruses B/Yamagata/1/73 and clone 6-10, an A type influenza virus derived from a cross between A/Aichi/2/68 (H3N2) and B/Yamagata. Efficiency of plating of B/Yamagata at 39.5 degrees C was less than 10(-3) in MDCK cells, while that of clone 6-10 or A/Aichi was higher than 10(-1). Four of the 15 clones selected for HA of Aichi serotype from the mixed yield, where type B virus was predominant over type A, were temperature-sensitive (ts), with efficiency of plating at 39.5 degrees C less than 10(-2), exceeding the frequency of spontaneous ts mutants among clone 6-10 progeny. Thus, co-existing type B virus not only interfered with the replication of type A, but also rendered it temperature-sensitive. Genetic analysis of the 4ts clones using a set of ts mutants of influenza virus A/WSN (H0N1) revealed that these clones, in contrast with the spontaneous ts mutant of clone 6-10, with ts defect only in NP gene, possessed ts lesions in multiple genes including a common ts defect in M. Polyacrylamide gel electrophoresis of viral RNA and proteins of these clones showed an identical gel pattern to that of clone 6-10, although the rate of synthesis of individual viral polypeptide was variable from clone to clone.

Genetic recombination between temperature-sensitive and wild-type influenza A virus strains

Genetic cross was performed between a temperature-sensitive (ts) mutant of influenza virus A/WSN (H0N1) which carries a ts lesion in M gene, and a wild type A/Aichi/2/68 (H3N2). Twelve clones were isolated randomly from the mixed yield in the absence of any selective procedure and they were individually examined for their ts character. In addition, structural and non-structural polypeptides of an individual clone were analyzed by SDS-polyacrylamide gel electrophoresis (PAGE) to identify from which parent each viral protein was derived. The experiments have shown that at high frequency recombination occurred with respect to every major viral protein; this is compatible with the view that recombination with influenza viruses is actually a mere exchange of RNA segments.

Polypeptide analysis of hepatitis virus type B surface antigen produced by a human hepatoma cell line, PLC/PRF/5

HBs antigen purified from culture fluid of a human hepatoma cell line, PLC/PRF/5, was analyzed by sodium dodecyl-sulfate-polyacrylamide gel electrophoresis. At least 6 polypeptide species were resolved. The polypeptide with a molecular weight of 48,000 was identified as a glycoprotein.

Heterotypic interference between influenza viruses A/Aichi/2/68 and B/Massachusetts/1/71

Virus particles produced by MDCK cells mixedly infected with 3 PFU/cell each of A/Aichi/2/68 (H3N2) (Aichi) and B/Massachusetts/1/71 (Mass) influenza viruses exclusively possessed haemagglutinin (HA) of Mass, although approximately one-fifth of the mixed yield had coding potential for Aichi serotype. Synthesis of major viral proteins of Aichi was markedly suppressed by co-infecting Mass. By increasing the multiplicity of co-infecting Aichi to 30 PFU/cell, interference became reciprocal. Aichi interfered with replication of Mass more severely than Mass did with replication of Aichi. All the major viral proteins of both Aichi and Mass were expressed within the infected cells.

Homologous interference mediated by defective interfering influenza virus derived from a temperature-sensitive mutant of influenza virus

A temperature-sensitive group II mutant of influenza virus, ts-52, with a presumed defect in viral RNA synthesis, readily produced von Magnus-type defective interfering virus (DI virus) when passed serially (four times) at high multiplicity in MDBK cells. The defective virus (ts-52 DI virus) had a high hemagglutinin and a low infectivity titer, and strongly interfered with the replication of standard infectious viruses (both ts-52 and wild-type ts+) in co-infected cells. Progeny virus particles produced by co-infection of DI virus and infectious virus were also defective and also had low infectivity, high hemagglutinating activity, and a strong interfering property. Infectious viruses ts+ and ts-52 were indistinguishable from ts-52 DI viruses by sucrose velocity or density gradient analysis. Additionally, these viruses all possessed similar morphology. However, when the RNA of DI viruses was analyzed by use of polyacrylamide gels containing 6 M urea, there was a reduction in the amount of large RNA species (V1 to V4), and a number of new smaller RNA species (D1 to D6) with molecular weights ranging from 2.9 X 10(5) to 1.05 X 10(5) appeared. Since these smaller RNA species (D1 to D6) were absent in some clones of infectious viruses, but were consistently associated with DI viruses and increased during undiluted passages and during co-infection of ts-52 with DI virus, they appeared to be a characteristic of DI viruses. Additionally, the UV target size of interfering activity and infectivity of DI virus indicated that interfering activity was 40 times more resistant to UV irradiation than was infectivity, further implicating small RNA molecules in interference. Our data suggest that the loss of infectivity observed among DI viruses may be due to nonspecific loss of a viral RNA segment(s), and the interfering property of DI viruses may be due to interfering RNA segments (DIRNA, D1 to D6). ts-52 DI virus interfered with the replication of standard virus (ts+) at both permissive (34 degrees C) and nonpermissive temperatures. The infectivity of the progeny virus was reduced to 0.2% for ts+ and 0.05% for ts-52 virus without a reduction in hemagglutinin titer. Interference was dependent on the concentration of DI virus. A particle ratio of 1 between DI virus (0.001 PFU/cell) and infectious virus (1.0 PFU/cell) produced a maximal amount of interference. Infectious virus yield was reduced 99.9% without any reduction of the yield of DI viruses Interference was also dependent on the time of addition of DI virus. Interference was most effective within the first 3 h of infection by infectious virus, indicating interference with an early function during viral replication.

Identification of hemagglutinin and neuraminidase genes of influenza B virus

The genome of influenza B viruses was shown by electrophoresis to consist of eight RNA segments. The fifth largest segment coded for hemagglutinin and the sixth coded for neuraminidase.

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

A wide variety of influenza A viruses, comprising human, equine, porcine, and avian strains, grew productively in an established line of canine kidney cells (MDCK) under an overlay medium containing trypsin, and formed well-defined plaques regardless of their prior passage history. Plaquing efficiency was comparable to the efficiency of infection in fertile eggs via allantoic route. MDCK cells have also been successfully employed for the primary isolation of influenza A virus from throat washings of patients. Parallel titration of several clinical specimens showed that the inoculation into MDCK cells followed by incubation in the presence of trypsin was an isolation procedure as sensitive as the amniotic inoculation into fertile eggs.

Permanent canine kidney (MDCK) cells for isolation and plaque assay of influenza B viruses

A wide range of influenza B virus strains with various passage histories uniformly formed well-defined clear plaques with high efficiency in cultures of an established line of canine kidney cells (MDCK). PFU titers of the viruses assayed in MDCK exceeded the titers assayed in ovo. With recently isolated strains such as B/Hong Kong/5/72 and Gifu/2/73, the PFU/EID50 ratios were as high as 100 to 400. MDCK cells have been successfully employed for primary isolation of influenza B viruses from throat washings of patients by direct plaquing.

Structural polypeptides of antigenically distinct strains of influenza B virus

Analyses of the polypeptide composition of influenza B viruses by 13 per cent SDS-polyacrylamide gel electrophoresis are reported. The viruses contained polypeptides of eight species ranging in molecular weight from 27,000 to 78,000. Four of them were glocypeptides and were selectively removed from the surface of the virion by Bromelain treatment. One of the blycopeptides was identified as viral neuraminidase. Three antigenically distinct strains of influenza virus, B/Lee/40, B/Massachusetts/1/71 and B/Hong Kong/5/72, showed an essentially identical electrophoretic picture, although strain-to-strain difference was observed in the migration rate of HA1 and HA2 polypeptides.

Isolation and preliminary characterization of temperature-sensitive mutants of influenza virus

Isolation of temperature-sensitive (ts) mutants was attempted from the WSN strain of influenza A virus which was grown and assayed in MDBK cells. After growth of wild-type virus in the presence of 5-fluorouracil, 15 ts mutants were selected for which the ratio of plaquing efficiency at 39.5 C to that at 33 C was 10(-3) or less. In pairwise crosses of ts mutants, recombination and complementation were either very efficient or undetectable. It is suggested, therefore, that the viral genome consists of physically discrete units and recombination occurs as an exchange of these units. All 15 mutants have been assigned with certainty into five recombination groups. Three mutants are suspected to be double mutants. Any two complementing mutants always recombined with each other, and noncomplementing mutants did not recombine. In physiological tests, mutants showed diverse patterns of functional defects at the nonpermissive temperature. However, it was not always possible to correlate these physiological defects with the results of genetic characterization.