Difference in protein patterns of influenza A viruses

Antigenic reactivity and electrophoretic migrational heterogeneity of the three polymerase proteins of type A human and animal influenza viruses

Antigenic reactivity of the three polymerase proteins PB1, PB2, and PA of type A influenza viruses of animal and human origin were analysed by radioimmunoprecipitation using monospecific antisera. Each of the polymerase monospecific antisera made against the polymerase proteins of the human A/WSN/33 (H1N1) influenza virus reacted efficiently with the homologous proteins of all the known thirteen HA subtype viruses of avian influenza virus, three subtypes of human influenza virus, swine and equine influenza viruses. This broad reactivity of each of the antisera indicated that the polymerase proteins are antigenically related among the type A influenza viruses and therefore can be considered as type specific antigens similar to the other viral internal proteins nucleoprotein (NP) and matrix protein (M). No electrophoretic migrational heterogeneity was found among the PB2 proteins of different subtype viruses, whereas PB1 protein exhibited minor variation. However, PA protein from among various viral subtypes showed considerable heterogeneity. Each of the polymerase antisera also immunoprecipitated additional antigenically related polypeptides with distinct electrophoretic mobilities from cells infected with each of the influenza viral subtypes.

Identification of PR8 M1 protein in influenza virus high-yield reassortants by M1-specific monoclonal antibodies

A panel of monoclonal antibodies to the M1 protein of A/PR8/34 (H1N1) (PR8) influenza A virus was found to distinguish in ELISA high-yielding reassortant viruses derived from reassortment of PR8 and X-31 (H3N2) viruses with recently prevalent field strains of H1N1 or H3N2 subtype. These findings are concordant with results of genotyping that demonstrated the presence of PR8 RNA 7 or M1 protein in high-yield reassortants by RNA or protein PAGE. All high-yield vaccine candidate reassortants Application of the M1 monoclonal antibody panel facilitates the isolation of high-yield vaccine candidate reassortants bearing the PR8 M1 gene, and should aid in epidemiologic strain tracking as well.

Growth restriction of influenza A virus by M2 protein antibody is genetically linked to the M1 protein

The M2 protein of influenza A virus is a 97-amino acid integral membrane protein expressed at the surface of infected cells. Recent studies have shown that a monoclonal antibody (14C2) recognizes the N terminus of M2 and restricts the replication of certain influenza A viruses. To investigate the mechanism of M2 antibody growth restriction, 14C2 antibody-resistant variants of strain A/Udorn/72 have been isolated. Most of the variant viruses are not conventional antigenic variants as their M2 protein is still recognized by the 14C2 antibody. A genetic analysis of reassortant influenza viruses prepared from the 14C2 antibody-resistant variants and an antibody-sensitive parent virus indicates that M2 antibody growth restriction is linked to RNA segment 7, which encodes both the membrane protein (M1) and the M2 integral membrane protein. Nucleotide sequence analysis of RNA segment 7 from the variant viruses predicts single amino acid substitutions in the cytoplasmic domain of M2 at positions 71 and 78 or at the N terminus of the M1 protein at residues 31 and 41. To further examine the genetic basis for sensitivity and resistance to the 14C2 antibody, the nucleotide sequences of RNA segment 7 of several natural isolates of influenza virus have been obtained. Differences in the M1 and M2 amino acid sequences for some of the naturally resistant strains correlate with those found for the M2 antibody variant viruses. The possible interaction of M1 and M2 in virion assembly is discussed.

Biochemical and antigenic analysis using monoclonal antibodies of a series of of influenza A (H3N2) and (H1N1) virus reassortants

Reassortant influenza A viruses with high growth capacity in eggs and suitable as candidate vaccine strains or as standard reagents for influenza HA quantification were prepared using the high yielding A/PR/8/34 (H1N1) as one parent and a number of 'wild' strains of influenza A (H1N1) or (H3N2) viruses as the other parent. The genetic and antigenic composition of the reassortants was determined. The parental derivation of genes in the reassortants was established by electrophoretic analysis of virus RNA and virus induced polypeptides. The haemagglutinin (HA) antigens of the three H1N1 viruses (NIB-6, NIB-7 NIB-12) were found to resemble those of the parental viruses when tested against a panel of monoclonal antibodies and using the HI test. A similar correspondence between the antigenic characteristics of the HA of the influenza A (H3N2) reassortants (NIB-1, NIB-4, NIB-5, NIB-8 and NIB-11) and parental viruses was noted. Therefore laboratory manipulations to produce the reassortants did not result in the selection of significant antigenic variants.

The membrane (M1) protein of influenza virus occurs in two forms and is a phosphoprotein

The membrane (M1) protein of influenza virus was found to be heterogenous and to occur in two forms in the virus particle. The two forms of M1 were found in virus which was produced both early and late after infection and in infected cells. The two forms could be separated on polyacrylamide gels under specific conditions. The two components of M1 contained similar tryptic peptides. However, a small proteolytic difference between the two proteins could not be ruled out. Both M1 proteins were present in phosphorylated form in the virus particle. The phosphorylated M1 components were not readily distinguished from phosphorylated nonstructural protein (NS1) when cytoplasm of infected cells was analyzed on polyacrylamide gels. The two phosphorylated M1 components could, however, be detected in infected cells by immunoprecipitation. One M1 component contained only phosphoserine whereas the second contained phosphoserine and a small amount of phosphothreonine as well. In addition to the phosphorylated nucleoprotein and M1, a third phosphorylated protein was routinely detected in virus particles. It was a surface component of the virus, since it could be removed from whole virus with chymotrypsin and contained phosphate at serine residues. The identity of this component was not known.

Anomalous electrophoretic behavior of the membrane (M) protein of influenza virus in polyacrylamide gels

The relative position of M and NS 1 on polyacrylamide gels depends on the concentration of cross-linker in the gel. Inversion in position of M and NS 1 occurs at a cross-linker concentration of 1.2 percent.

Plaquing characteristics of influenza A virus recombinants of defined genetic composition. Brief report

The plaque size and morphology of twenty-two influenza A virus recombinants representing seven distinct families were analyzed on MDCK cells. By examination of the genetic composition of the recombinants no relationship could be established between any gene, including those coding for the surface antigens, and the plaque size and morphology.

Antigenicity in hamsters of inactivated vaccines prepared from recombinant influenza viruses

Inactivated vaccines prepared form influenza virus strains obtained by the recombination of A/PR/8/34 (H1N1) or A/FM/1/47 (H1N1) viruses with A/Victoria/3/75 (H3N2) virus, were tested for their antigenicity in hamsters. The parental origin of the genes of each cloned recombinant virus was determined by polyacrylamide gel electrophoresis, and vaccines prepared from each strain by concentration, purification on sucrose density gradients and inactivation with formalin. All the recombinant strains used in these studies possessed surface haemagglutinin and neuraminidase antigens derived from the A/Victoria/75 parent strain. On inoculation into hamsters, at equivalent concentrations, these vaccines varied in their ability to induce haemagglutination-inhibiting (HI) antibodies in the serum. This variation was not dependent on concentration and was observed using neutralization and single radial haemolysis, as well as HI. The possible reasons for the findings are discussed.

The amantadine-sensitivity of recombinant and parental influenza virus strains

Several wild-type influenza A strains together with recombinants derived from these strains, were tested for sensitivity to amantadine using the in vitro techniques of inhibition in egg-bit culture and plaque reduction in MDCK cells. The results obtained were analysed with reference to the derivation of the recombinants. Susceptibility to amantadine was related to the gene coding for matrix protein, and these data are in agreement with previous reports of studies using other series of influenza viruses.

Electrophoretic migration rate differences of polypeptides of human influenza A viruses: partial analysis of the genome of influenza vaccine recombinant viruses

Electrophoretic migration rate differences were detected in high resolution SDS polyacrylamide gels for nucleoprotein (NP), matrix protein (M), non structural protein (NS1), haemagglutinin (HA) annd, less regularly, for the polymerase polypeptides P1, P2 and P3 induced by different influenza A viruses. The technique allowed parental assignation of the corresponding genes in certain recombinant viruses including A/PR/8/34 (H0N1)--A/HK/117/77 (H1N1), A/Okuda/57 (H2N2)--A/HK/119/77 (H1N1) and A/Leningrad/76 (H3N2)--A/Leningrad/46 (H0N1) recombinants, thus considerably extending the technique which had been applied previously to A/PR/8/34--A/HK/68 (H3N2) only. Agreement in gene assignment between three recombinants of the former group and 11 of 17 recombinants in the A/Okuda/57--A/HK/119/77 group was noted when the data obtained using the polypeptide method was correlated with a direct genetic analysis by others using RNA:RNA hybridisation techniques. The polypeptide method appears to have wide application for the initial rapid analysis of influenza A virus recombinants obtained using parents of different influenza subtypes although complete analysis of the total genome requires the use of RNA hybridisation techniques. Two additional virus induced proteins are described, a phosphorylated form of NS 1 and a non structual polypeptide with a molecular weight of 16K daltons.

Common sequence at the 5' ends of the segmented RNA genomes of influenza A and B viruses

Guanylyl- and methyltransferases, isolated from purified vaccinia virus, were used to specifically label the 5' ends of the genome RNAs of influenza A and B viruses. All eight segments were labeled with [alpha-(32)P]guanosine 5'-triphosphate or S-adenosyl[methyl-(3)H]methionine to form "cap" structures of the type m(7)G(5')pppN(m)-, of which unmethylated (p)ppN- represents the original 5' end. Further analyses indicated that m(7)G(5')pppA(m), m(7)G(5')pppA(m)pGp, and m(7)G(5')pppA(m)pGpUp were released from total and individual labeled RNA segments by digestion with nuclease P1, RNase T1, and RNase A, respectively. Consequently, the 5'-terminal sequences of most or all individual genome RNAs of influenza A and B viruses were deduced to be (p)ppApGpUp. The presence of identical sequences at the ends of RNA segments of both types of influenza viruses indicates that they have been specifically conserved during evolution.

Virulence factors of influenza A viruses: WSN virus neuraminidase required for plaque production in MDBK cells

The genetic basis for the distinctive capacity of influenza A/WSN/33 (H0N1) virus (WSN virus) to produce plaques on bovine kidney (MDBK) cells was found to be related to virus neuraminidase. Recombinant viruses that derived only the neuraminidase of WSN virus were capable of producing plaques, whereas recombinant viruses identical to WSN except for neuraminidase did not produce plaques. With viruses that do not contain WSN neuraminidase, infectivity of virus yields from MDBK cells was increased approximately 1,000-fold after in vitro treatment with trypsin. In contrast, no significant increase in infectivity was observed after trypsin treatment of viruses containing WSN neuraminidase. In addition, polyacrylamide gel analysis of proteins of WSN virus obtained after infection of MDBK cells demonstrated that hemagglutinin was present in the cleaved form (HA1 + HA2), whereas only uncleaved hemagglutinin was obtained with a recombinant virus that derived all of its genes from WSN virus except its neuraminidase. These data are in accord with the hypothesis that neuraminidase may facilitate production of infectious particles by removing sialic acid residues and exposing appropriate cleavage sites on hemagglutinin.

Identification of the defective genes in three mutant groups of influenza virus

Seven complementation-recombination groups of temperature-sensitive (ts) influenza WSN virus mutants have been previously isolated. Recently two of these groups (IV and VI) were shown to possess defects in the neuraminidase and the hemagglutinin gene, respectively, and two groups (I and III) were reported to have defects in the P3 and P1 proteins which are required for complementary RNA synthesis. In this communication we report on the defects in the remaining three mutant groups. Wild-type (ts+) recombinants derived from ts mutants and different non-ts influenza viruses were analyzed on RNA polyacrylamide gels. This technique permitted the identification of the P2 protein, the nucleoprotein, and the M protein as the defective gene products in mutant groups II, V, and VII, respectively. Based on the physiological behavior of mutants in groups II and V, it appears that P2 protein and nucleoprotein are required for virion RNA synthesis during influenza virus replication.

P1 and P3 proteins of influenza virus are required for complementary RNA synthesis

Members of two temperature-sensitive (ts) mutant groups of influenza A/WSN virus defective in complementary RNA synthesis were analyzed with respect to the identity of their defective genes. RNA analysis of recombinants having a ts+ phenotype derived from the mutants and HK virus permitted the identification of RNA 1 and RNA 2 as the single defective gene in mutant groups I and III, respectively. Based on knowledge obtained by mapping the WSN virus genome, it then was possible to determine that biologically functional P3 protein (coded for by RNA 1) and P1 protein (RNA 2) are required for complementary RNA synthesis of influenza virus.