Immune virolysis: effect of antibody and complement on C-type RNA virus

C1q enables influenza hemagglutinin stem binding antibodies to block viral attachment and broadens the antibody escape repertoire

Antigenic drift, the gradual accumulation of amino acid substitutions in the influenza virus hemagglutinin (HA) receptor protein, enables viral immune evasion. Antibodies (Abs) specific for the drift-resistant HA stem region are a promising universal influenza vaccine target. Although anti-stem Abs are not believed to block viral attachment, here we show that complement component 1q (C1q), a 460-kilodalton protein with six Ab Fc-binding domains, confers attachment inhibition to anti-stem Abs and enhances their fusion and neuraminidase inhibition. As a result, virus neutralization activity in vitro is boosted up to 30-fold, and in vivo protection from influenza PR8 infection in mice is enhanced. These effects reflect increased steric hindrance and not increased Ab avidity. C1q greatly expands the anti-stem Ab viral escape repertoire to include residues throughout the HA, some of which cause antigenic alterations in the globular region or modulate HA receptor avidity. We also show that C1q enhances the neutralization activity of non-receptor binding domain anti-SARS-CoV-2 spike Abs, an effect dependent on spike density on the virion surface. These findings demonstrate that C1q can greatly expand Ab function and thereby contribute to viral evolution and immune escape.

Mouse immunoglobulin antibodies require complement for neutralization of mouse retroviruses

The addition of guinea pig complement was found to enhance the neutralizing capacity of mouse antibodies directed against the endogenous ecotropic murine leukemia viruses. The same immune sera, when tested without complement, had low or negligible neutralizing capacities, regardless of whether freshly harvested, unfrozen virus was used to preserve virus infectivity. Antibodies in high titers were found in sera from NFS congenic mice carrying the mouse leukemia virus inducing locus Akv-2. These mouse antibodies were type specific and failed to neutralize either Friend or Moloney leukemia virus. The mouse serum immunoglobulin fraction containing the complement-dependent antibodies was tentatively identified as immunoglobulin M.

Complement, viruses, and virus-infected cells

The attachment of specific antibody to viral glycoproteins and other structures on the surface of a virus or virus-infected cell has a number of potential consequences to the virus or virus-infected cell. Antibody is multivalent and thus able to redistribute or patch surface viral proteins or virus-encoded structures within the lipid bilayer of the viral envelope or the cell membrane. In certain instances, antibody may agglutinate viruses or virus-infected cells. The physical presence of antibody molecules on the virus surface may interfere with the ability of the virus to infect potentially susceptible cells. Antibody on the surface of virus-infected cells may prevent the maturation and release of virus particles; antibody also can alter certain normal cell functions. The Fc portions of antibody molecules bound to virus-infected cells facilitate interactions with effector cells bearing Fc receptors. In the case of lymphocytes and perhaps phagocytic cells, this interaction may lead to antibody-dependent cellular cytotoxicity (ADCC) [51, 58]. The exposed Fc regions may also facilitate attempts at ingestion by monocytes, macrophages, and polymorphonuclear leukocytes.

Irreversible conversion of the physical state of herpes simplex virus preceding inactivation by thermal or antibody treatment

The buoyant density characteristics of infectious particles of herpes simplex virus types 1 and 2 were studied by centrifugation in sucrose and cesium chloride density gradients with a high resolution and satisfactory infectivity recovery. It was shown that two populations of infectious virions differing in buoyant density coexisted, the difference being slight but definite. The ratio of heavy (H) to light (L) viral particles varied depending upon the solute used, the strains of virus, and the cell origin. Circumstances favoring degradation of viral infectivity tended to increase the H portion. Incubation at 37 degrees C largely converted L to H, and heating at 45 degrees C converted all virions to H without infectivity. The L to H conversion was irreversible, and no populations intermediate between L and H were clearly observed. Inactivation by UV light irradiation did not affect the density pattern. That H was not an artefact due to penetration of solutes, osmotic pressure, viral aggregation, or loss of the envelope was shown experimentally. A difference in the outer shape of particles between negatively stained L and H populations was demonstrated by electron microscopy. Both cell-released and cell-bound herpes simplex virus particles gave essentially the same result with respect to the above characteristics. The effect of limiting dilutions of antiserum was similar to that of mild thermal treatment, in that denser virions increased parallel to a decrease in less dense virions. Sensitization with early immunoglobulin G, composed mainly of complement-requiring neutralizing antibody, caused the density transition, and subsequent addition of complement resulted in a further increase in the buoyant density of the sensitized virions. The DNA in virus particles neutralized with immunoglobulin G plus complement remained resistant to DNase treatment. Possible implications of the phenomena are discussed.

Studies on the neutralization of herpes simplex virus. X. Demonstration of complement-requiring neutralizing (CRN) and slow-reacting CRN (s-CRN) antibodies in late IgG

A sample of late IgG from a rabbit hyperimmunized with herpes simplex virus was analyzed for neutralizing (N) and complement-requiring neutralizing (CRN) antibodies. In a usual endpoint test, N and CRN titers were 1: 40 and 1: 160, respectively, but when virus-IgG mixtures were incubated at 0 C overnight before addition of complement (C), an endpoint of 1:1280 was obtained. Virus sensitized at 0 C overnight required more C for inactivation than did sensitized virus formed earlier. Sensitization kinetic curve experiments employing a proper initial virus concentration, which permitted differentiation of sensitized viruses requiring different amounts of C, indicated that formation of sensitized virus detectable only with a relatively large amount of C proceeded slowly at IgG dilutions where the ordinary CRN antibody requiring a smaller amount of C was negligible. The results strongly suggested that the IgG sample contained slow-reacting CRN (s-CRN) antibody in excess of the hitherto known CRN antibody. As to the mechanism of formation of s-CRN complexes, experiments failed to prove the occurrence of complexes initially insensitive to C, and it appears more likely that s-CRN antibody has a comparatively low avidity for virus.

Neutralization of animal viruses

Various aspects of the interaction of bacterial viruses and antibody were studied by Andrewes and Elford in England. Similar studies, as well as studies on animal viruses, were carried out in Australia by Burnet and his colleagues. One result of their extensive studies, which were summarized in great detail, was the conclusion that, with respect to their interaction with antibody, bacterial and animal viruses were basically different. Specifically, the difference resided in the stability of the union of virus and antibody, whereas bacterial viruses formed stable complexes, animal viruses formed complexes that tended to dissociate readily. The introduction of animal cell cultures as host systems greatly aided in the study of animal viruses, with respect to fewer and more readily controlled variables, and by the use of the plaque assay in enhanced quantitative reliability. In 1956, Dulbecco et al. described the interaction of two animal viruses with their respective antibodies. The results of these studies led these investigators to conclude, among other things, that animal viruses, at least the two they studied, reacted with antibodies to form complexes that did not dissociate spontaneously. This interpretation was challenged by Fazekas de St. Groth and Reid. As more animal virus-antibody systems were studied by many investigators, there seemed to be a greater accord for irreversible, rather than reversible, interaction. For this reason, in this chapter it is assumed that there are no differences between bacterial viruses, as one category, and animal viruses, as a separate category, concerning their interaction with antibodies. Rather, differences, when they exist, are considered to be related to the viruses per se. Although this chapter is intended to survey the neutralization of animal viruses, occasional reference is made to the studies on bacterial viruses when these studies are pertinent and illuminating to the topic at hand.

Mechanism of formation of pseudotypes between vesicular stomatitis virus and murine leukemia virus

Pseudotypes of vesicular stomatitis virus (VSV) and Moloney murine leukemia virus (MuLV), defined by their resistance to neutralization by anti-VSV antiserum, are released preferentially at early times after infection of MuLV-producing cells with VSV. At later times, after synthesis of MuLV proteins has been inhibited by the VSV infection, neither MuLV virions nor the VSV (MuLV) pseudotypes are made. Infection of MuLV-producing cells with mutants of VSV having temperature-sensitive lesions in either G or M protein does not generate pseudotypes at nonpermissive temperature, indicating that both proteins are needed for pseudotypes to form. Although the pseudotypes resist neutralization by anti-VSV serum, they are inactivated by anti-VSV serum plus complement, and they can be precipitated by rabbit anti-VSV serum plus goat anti-rabbit IgG. These results, coupled with experiments using a temperature-sensitive mutant of VSV G protein grown at partly restrictive temperature, suggest that small numbers of VSV G protein are obligately incorporated into VSV(MuLV) pseudotypes. There appears to be a stringent requirement for recognition of the viral core by homologous envelope components as the nucleating step in the budding process. Only after such a nucleation can the envelope components of the second virus substitute into the membrane of the budding particle.

Fate of rubella genome ribonucleic acid after immune and nonimmune virolysis in the presence of ribonuclease

To determine whether rubella virion ribonucleic acid (RNA) becomes accessible to nuclease attack after immune lysis of the viral envelope, virions containing radioactively labeled RNA were examined in three ways with the following results. (i) Incubation of purified virus with heat-inactivated rubella convalescent human serum and guinea pig complement resulted in an increase in acid-soluble RNA. Antibody was required; the reaction was temperature dependent and was blocked by ethylenediaminetetraacetic acid. When exogenous nuclease was added prior to lysis, radioactivity in virions was reduced to 15% of that in unlysed control pellets (ii) Sucrose gradient sedimentation profiles of RNA released from lysed and unlysed virions under controlled conditions showed that the nuclease content of serum-virus mixtures was sufficient to eliminate all RNA of genome size, although degradation was not complete. (iii) Virions were also lysed by unheated human immune sera in the absence of guinea pig complement and by some, but not all, unheated antibody-negative sera.

Formation and biologic role of polyoma virus-antibody complexes. A critical role for complement

Interaction of polyoma virus, specific antibody, and complement has been studied. Firm evidence has been gathered that C1 through C3 and not C5 through C9 enhance neutralization of virus-antiviral antibody (V-Ab) complexes. C enhancement of neutralization occurs primarily by agglutination of V-Ab complexes and not by virion lysis or attachment of large protein molecules to the V-Ab complex. In this model, binding of C1, 4, 2, 3 to the V-Ab complex may explain why some viruses concentrate in or infect certain cells bearing C3 receptors such as B lymphocytes, macrophages, and monocytes.

Effect of heat-labile factors on the neutralization of vaccinia virus by human

The effect of unheated guinea pig and human prevaccination serum on the neutralization of vaccinia virus was studied. Enhancement of neutralization was found in all sera containing antibody and was more marked (20- to 150-fold) in sera obtained in the first weeks after primary vaccination than in sera from immune adults or cord sera (4- to 25-fold). The enhancing factor was thought to be complement because it was destroyed by heating and ethylenediaminetetraacetic acid treatment. The fresh serum-enhanced neutralization test represents a highly sensitive and specific test which can be applied to measure low levels of vaccinia antibody not detectable by other means.

Antiviral immune cytolysis at an early stage of paramyxovirus infection

Antiviral antibody and rabbit complement added as early as 5 min after infection, and with relatively low virus/cell multiplicity, lysed mouse ascites lymphoma cells infected with Sendai or Newcastle disease virus. Inactive Sendai virus at much higher input also sensitized ascites cells and mouse fibroblast monolayers to early antiviral immune cytolysis. At 4 C where adsorption but no penetration occurred, antibody removed virus from the cell membrane and little cytolysis was observed. The ascites cells were sensitive to antibody and complement at all times after the start of penetration and uncoating, indicating that viral envelope antigen is constantly present on the cell membrane. Significant cross-reactions by immune cytolysis between Newcastle disease virus- and Sendai virus-infected cells suggested possible participation of host antigens of the viral envelope. No comparable antiviral immune cytolysis was observed with influenza strains PR8 and WSN. Cell viability was estimated by dye exclusion and the ability to form acid from glucose as indicated by colorimetric pH of the medium. The relation of antiviral immune cytolysis to changes in the membrane resulting in cell fusion is considered.