Undisturbed release of influenza virus in the presence of univalent antineuraminidase antibodies

A contributing role for anti-neuraminidase antibodies on immunity to pandemic H1N1 2009 influenza A virus

BACKGROUND

Exposure to contemporary seasonal influenza A viruses affords partial immunity to pandemic H1N1 2009 influenza A virus (pH1N1) infection. The impact of antibodies to the neuraminidase (NA) of seasonal influenza A viruses to cross-immunity against pH1N1 infection is unknown.

METHODS AND RESULTS

Antibodies to the NA of different seasonal H1N1 influenza strains were tested for cross-reactivity against A/California/04/09 (pH1N1). A panel of reverse genetic (rg) recombinant viruses was generated containing 7 genes of the H1N1 influenza strain A/Puerto Rico/08/34 (PR8) and the NA gene of either the pandemic H1N1 2009 strain (pH1N1) or one of the following contemporary seasonal H1N1 strains: A/Solomon/03/06 (rg Solomon) or A/Brisbane/59/07 (rg Brisbane). Convalescent sera collected from mice infected with recombinant viruses were measured for cross-reactive antibodies to pH1N1 via Hemagglutinin Inhibition (HI) or Enzyme-Linked Immunosorbent Assay (ELISA). The ectodomain of a recombinant NA protein from the pH1N1 strain (pNA-ecto) was expressed, purified and used in ELISA to measure cross-reactive antibodies. Analysis of sera from elderly humans immunized with trivalent split-inactivated influenza (TIV) seasonal vaccines prior to 2009 revealed considerable cross-reactivity to pNA-ecto. High titers of cross-reactive antibodies were detected in mice inoculated with either rg Solomon or rg Brisbane. Convalescent sera from mice inoculated with recombinant viruses were used to immunize naïve recipient Balb/c mice by passive transfer prior to challenge with pH1N1. Mice receiving rg California sera were better protected than animals receiving rg Solomon or rg Brisbane sera.

CONCLUSIONS

The NA of contemporary seasonal H1N1 influenza strains induces a cross-reactive antibody response to pH1N1 that correlates with reduced lethality from pH1N1 challenge, albeit less efficiently than anti-pH1N1 NA antibodies. These findings demonstrate that seasonal NA antibodies contribute to but are not sufficient for cross-reactive immunity to pH1N1.

Membrane Glycoproteins of Enveloped Viruses

This chapter focuses on the recent information of the glycoprotein components of enveloped viruses and points out specific findings on viral envelopes. Although enveloped viruses of different major groups vary in size and shape, as well as in the molecular weight of their structural polypeptides, there are general similarities in the types of polypeptide components present in virions. The types of structural components found in viral membranes are summarized briefly in the chapter. All the enveloped viruses studied to date possess one or more glycoprotein species and lipid as a major structural component. The presence of carbohydrate covalently linked to proteins is demonstrated by the incorporation of a radioactive precursor, such as glucosamine or fucose, into viral polypeptides, which is resolved by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Enveloped viruses share many common features in the organization of their structural components, as indicated by several approaches, including electron microscopy, surface-labeling, and proteolytic digestion experiments, and the isolation of subviral components. The chapter summarizes the detailed structure of the glycoproteins of four virus groups: (1) influenza virus glycoproteins, (2) rhabdovirus G protein, (3) togavirus glycoprotein, and (4) paramyxovirus glycoproteins The information obtained includes the size and shape of viral glycoproteins, the number of polypeptide chains in the complete glycoprotein structure, and compositional data on the polypeptide and oligosaccharide portions of the molecules.

A novel monoclonal antibody specific to the C-terminal tail of the gp41 envelope transmembrane protein of human immunodeficiency virus type 1 that preferentially neutralizes virus after it has attached to the target cell and inhibits the production of infectious progeny

SAR1 is a new IgG2a murine monoclonal antibody derived by immunization with a plant virus expressing the sequence GERDRDR from the C-terminal tail of the gp41 transmembrane glycoprotein of human immunodeficiency virus type 1 (HIV-1). SAR1 binds to peptides and proteins carrying the GERDRDR sequence, to some but not all preparations of purified virus, and to cells infected with all viruses tested. In a standard neutralization assay, SAR1 failed to neutralize, or neutralized poorly, a number of T cell line-adapted viruses. However, it was more effective at postattachment neutralization. This was measured by two assays, the inhibition of the syncytium production by input virus, and the inhibition of the production of infectious progeny virus. In general SAR1 was more effective at neutralizing progeny virus than inoculum virus. Fifty percent inhibition of progeny virus production by different HIV-1 strains was obtained with 2-26 microg/ml of SAR1. The SAR1 neutralizing epitope was mapped specifically to the gp41 C-terminal tail. SAR1 is an unusual, if not unique, antibody whose activity supports the view that part of the gp41 C-terminal tail is exposed on the outside of the virion.

A reassortant between influenza A viruses (H7N2) synthesizing an enzymatically inactive neuraminidase at 40 degrees which is not incorporated into infectious particles

Cells infected with a reassortant (113/Ho, H7N2) between A/fowl plague/Rostock/34 (FPV, H7N1) and A/Hong Kong/1/68 (H3N2) carrying RNA segments 1 and 6 of the Hong Kong virus and the residual genes of FPV, synthesized at 40 degrees a neuraminidase (NA) which is enzymatically not active and which is not incorporated into infectious particles. At 40 degrees NA accumulates in the rough endoplasmic reticulum. It contains mainly carbohydrate side chains of the mannose type, and fucose is only scarcely incorporated. At 33 degrees NA of the reassortant is overproduced, and at least some of it is active and is incorporated into viral particles. Under nonreducing conditions during PAGE its NA migrates to the same position as after heating with mercaptoethanol, in contrast to the Hong Kong parent virus. It is speculated that at 40 degrees the tetramerization of the NA in the rough endoplasmic reticulum does not function, and in this way its migration to the cytoplasmic membrane and its incorporation into infectious particles does not occur. Since 113/Ho is as pathogenic for the chicken (body temperature of 41 degrees) as is FPV, the question arises which role the NA plays in virus replication and spread in the infected organism.

The effects of monoclonal antibodies against the hemagglutinin-neuraminidase and fusion protein on the release of Sendai virus from infected cells

Vero cell cultures in Leighton tubes were infected with egg-grown Sendai virus at high multiplicity of infection. Four hours after infection, the cultures were labelled with 35S-methionine, after which various concentrations of fourteen and five mouse monoclonal antibodies directed against different antigenic determinants of the hemagglutinin-neuraminidase (HN) and fusion (F) protein, respectively, were added to the medium. Fourty-eight hours after infection radiolabelled virions released into the medium were collected and purified by discontinuous sucrose gradient centrifugations. The amount of virus-bound radioactivity obtained in the various extracellular materials allowed an estimation of the capacity of the different monoclonal antibodies to inhibit the release of Sendai virus. In addition, the release of virions from infected cells was studied ultrastructurally. Based on their serological reactivity the fourteen anti-HN monoclonal antibodies could be divided into four groups. The first group of clones could not inhibit any biological activity of the virus. These clones were binding proximally, near the base of the HN glycoprotein and could not inhibit the release of the virus. The second group blocked hemolysis, but did not block hemagglutination (HA) or neuraminidase (NA) activity. The third group of clones blocked all biological activities of the HN glycoprotein. The fourth group could only block NA activity. With the exception of one of five monoclonal antibodies belonging to the second group, antibodies of the second, third and fourth group were found to bind more distally on the HN glycoprotein. Except for two monoclonal antibodies of the second group they could all effectively inhibit release of the virus from infected cells. Ultrastructurally, these antibodies caused aggregation of virions in contact with the plasma membrane. The five monoclonal antibodies directed against the F protein reacted with four different antigenic sites. These antibodies could not prevent the release of Sendai virus.

[Influenza]

Influenza is the last great uncontrolled plague of mankind. Pandemics and epidemics occur at regular time intervals. The influenza viruses are divided into the types A, B and C and show unique variability of their surface antigens (hemagglutinin and neuraminidase). Influenza viruses of type A show the largest degree of antigenic variation which, in turn, resulted in the definition of a number of subtypes, each comprising many strains. By comparison, influenza viruses of types B and C exhibit much less variation of their surface antigens. As a consequence, no subtypes but many different strains have been recognized. The degree of antigenic variation correlates with the epidemiologic significance of the virus types, type A being the most and type C the least important. Two different kinds of antigenic variation have been recognized: In the case of minor variation of one or both surface antigens, the term "antigenic drift" is employed. Antigenic drift occurs with all three types of virus, it is caused by point mutations which increase the chance of survival of mutants in the diseased host. In addition, influenza A viruses show sudden and complete changes of their surface antigens in regular time intervals, resulting in the appearance of new subtypes. This event is called "antigenic shift". The mechanisms responsible for antigenic shift are poorly understood, only. In addition to the recycling of preceding subtypes, reassortment resulting from double infection of cells with strains of human and animal origin are considered possible explanations. By use of modern DNA recombinant technology, the base sequences of a series of virus genes and, as a consequence, the amino acid sequence of the corresponding antigens have been determined. By means of monoclonal antibodies, the antigenic structure of many influenza antigens has been further elucidated. It can be expected that further research on the molecular basis of antigenic variation could finally result in an understanding of the causal mechanisms. It is an outstanding feature of the epidemiology of influenza A viruses that a family of related strains prevails for a certain period of time and disappears abruptly as a new subtype emerges.(ABSTRACT TRUNCATED AT 400 WORDS)

Simple and rapid separation of ortho- and paramyxovirus glycoproteins

The hemagglutinin (HA) and neuraminidase (NA) of influenza viruses, as well as the fusion protein (F) and hemagglutinin-neuraminidase (HN) of paramyxoviruses, have been separated in native form using a two-step procedure. The glycoproteins are efficiently extracted from virions using the on-ionic detergent octyl-beta-D-glucoside and are then applied to a column of agarose beads coupled with tyrosine-sulfanilic acid. Pure HA and F are obtained in good yield in the flow-through from this column. NA and HN bind strongly and can be eluted, albeit somewhat contaminated with HA or F, by raising the pH of the column buffer. The separated non-denatured fractions can be used for structural, functional, and antigenic studies.

Further studies of the neuraminidase content of inactivated influenza vaccines and the neuraminidase antibody responses after vaccination of immunologically primed and unprimed populations

Purified concentrates of influenza A/USSR/90/77(H1N1)-like, A/Texas/1/77 (H3N2)-like, and B/Hong Kong/5/72-like viruses used for preparation of investigational and licensed vaccines in 1978 to 1979 were tested for their content of neuraminidase enzyme activity. Concentrates of H1N1 virus used to prepare vaccines for clinical investigations performed in the spring of 1978 had neuraminidase activity at that time which decreased during storage to almost undetectable levels (three lots) or by 50% (one lot) by the winter of 1978. Several other lots of concentrates prepared with H1N1 virus and used for vaccine formulation had no detectable neuraminidase enzyme activity when tested in the winter of 1978, at a time when they would be administered in vaccines. The range of specific activity for different lots of concentrates was about 40-fold for A/Texas/1/77, B/Hong Kong/5/72, and A/USSR/90/77 neuraminidases. Immunogenicity of investigational vaccines prepared with tested concentrates and administered between April and July 1978 was measured in volunteers aged 13 to >50 years. Frequency of neuraminidase antibody rises to two doses of H1N1-containing vaccine was 10% in unprimed subjects aged <26 years and about 18 to 36% in older persons. The frequency of neuraminidase antibody rises to one dose of H3N2-containing vaccine varied from 0 to 32% in different groups (mean, 18%). The frequencies of neuraminidase antibody responses were always much lower than the frequencies of hemagglutinin antibody responses. These observations confirm the existence of practical difficulties in achieving uniformity of the neuraminidase content in influenza vaccines and of ensuring good immunogenicity of vaccine neuraminidase even in primed populations.

Antibody-mediated destruction of virus-infected cells

This chapter describes the effect of antibody on virus-infected cells with special reference to the human system. The destruction by antibody of the infected cells through the mediation of complement is described in detail based in considerable part on the contributions of the authors. Activation of the alternative pathway by the various infected cells is of special interest. The interesting effect of the antibody-dependent cell-mediated cytotoxicity (ADCC) system involving viral antigens in cell killing is also presented. Multiple additional topics are also covered, such as the effect of antibody on the expression of viral proteins both on the surface of the cell and intracellularly. Serum antibody, produced in response to virus infections, is of major importance in preventing the spread of infection by virtue of neutralizing free virus in extracellular fluids. Virus neutralization by antibody is enhanced by complement. Antibody binding to the surface of virus-infected cells can affect virus production and release in the absence of an effector system. Immunoglobulin (IgG) antibody can mediate the destruction of virus-infected cells in conjunction with complement or cytotoxic lymphocytes. In addition, at a conceptual level there is evidence to suggest that antibody may enhance and confer specificity on basic nonspecific humoral and cell-mediated defense mechanisms.

Antigenic relationship between the surface antigens of avian and equine influenze viruses

Influenza virus Equine 1 (A/equine/Prague/56) has a hemagglutinin which is antigenically related to the hemagglutinin of fowl plague virus strain Rostock (FPV) and a neuraminidase which cross-reacts with the enzyme of virus N (A/chick/Germany/49). After a single injection of chickens with Equine 1 virus no hemagglutination inhibiting (HI) and neutralizing antibodies against FPV can be demonstrated, although the birds are fully protected against a lethal dose of FPV. HI and neutralizing antibodies against FPV appear after a second injection of Equine 1 virus several weeks after the first one. Liberation of newly sunthesized FPV from the host cell is ingibited by antibodies cross-reacting with any antigen of virus surface.

Interaction of concanavalin A with the surface of virus-infected cells

Infection of untransformed cells with a wide-range of non-oncogenic enveloped viruses causes a significant increase in their susceptibility to agglutination by concanavalin A (Con A). The increased Con A agglutinability of these cells is not caused by an increase in the number of Con A sites on the cell surface but involves alteration in the surface properties of infected cells to allow redistribution of Con A receptors to form "patches" following binding of Con A to the cell surface. Similarities between Con A-mediated agglutination of normal cells infected with non-oncogenic viruses and the agglutination response to cells transformed by oncogenic viruses will be reviewed. Finally, the use of Con A as an experimental tool to modify the replication and cytopathogenicity of non-oncogenic viruses grown in mammalian cells will be presented.

Inhibition of virus release by antibodies to surface antigens of influenza viruses

When influenza virus was mixed with antisera to its surface subunits before inoculation of cell cultures, anti-hemagglutinin antibodies neutralized infectivity but anti-neuraminidase did not. When the antisera were added after infection of cell cultures, anti-hemagglutinin and anti-neuraminidase antibodies were equally effective in reducing virus titers in culture fluids. Decreased virus titers were not due to interference of antibody with assay and were not accompanied by a reduction in the synthesis of hemagglutinin and neuraminidase subunits. Both antisera also effectively prevented in vitro virus spread. Inhibition of virus release by neuraminidase antibody appeared unrelated to its antienzyme property. Hydrolysis of N-acetyl neuraminic acid residues of infected host cells proceeded unimpaired in the presence of subunit antisera. Anti-hemagglutinin and anti-neuraminidase antibodies may act to prevent virus release by binding newly formed virus subunits to each other and to anti-genically altered cell membranes.