Protection of Mice from Lethal Influenza: Evidence that Defective Interfering Virus Modulates the Immune Response and Not Virus Multiplication

Abstract

SUMMARYIntranasal administration of defective interfering (DI) influenza virus (A/WSN) ensured the survival of 80 ~ of C3H mice otherwise lethally infected with WSN by the intranasal route, whereas a control group which received fl-propiolactone-inactivated DI virus in place of DI virus died at 7.4 days post-infection. DI virus-treated mice developed significantly less lung consolidation than controls although qualitatively the cellular pathology in the two groups was indistinguishable. Surprisingly, in view of the accepted mode of action of DI virus interference, multiplication of infectious virus in the lung, production of viral haemagglutinin (HA) antigen and neuraminidase, and the distribution and amount of viral antigen in cells as shown by immune labelling were unaffected by the presence of active DI virus. Furthermore, assays of lung extracts showed that DI virus was not stimulating significantly greater amounts of interferon than the control inactivated DI virus. An alternative explanation arises from the fact that the pathology of influenza in inbred mice is immune (T lymphocyte)-mediated. Thus, since there is no evidence that DI virus affects virus multiplication we suggest that DI virus is responsible for ameliorating the damaging host responses. Another aspect of the immune response modulated by DI virus was the enhancement of local haemagglutination-inhibiting (HI) antibody in the lung, with peak increases of up to 10-fold over the relevant controls being demonstrated at 5 days after infection. This antibody was presumably complexed to HA antigen in the lung as activity was only demonstrated after elution at low pH. It had no detectable neutralizing activity (< 10 HI : neutralization ratio of convalescent serum) which accounts for the coexistence of local antibody and virus infectivity. Mice infected with virus alone or which received flpropiolactone-inactivated DI virus in addition to a lethal dose of WSN did not develop significant amounts of lung antibody. No differences were seen in serum HI titres. The increased level of antibody could not be attributed to the presence of greater amounts of HA antigen in lungs of mice treated with DI virus, as ELISA showed no significant difference from control preparations. The possibility that the two modulated immune responses are linked through HI antibody blocking access of T cells to cell membraneborne HA antigen is discussed.

One Defective Interfering Particle per Cell Prevents Influenza Virus-mediated Cytopathology: An Efficient Assay System

“…As DI virus-mediated interference in vitro operates at the level of macromolecular synthesis (Perrault, 1981), heterotypic interference in vivo should not be limited by the antigenic variations of influenza virus. However, protection of mice from lethal WSN pneumonia by DI WSN is not accompanied by any demonstrable alteration in virus multiplication and may be mediated by an entirely different mechanism (Dimmock et al, 1986).…”

Protection of Mice from Lethal Influenza by Adoptive Transfer of Non-neutralizing Haemagglutination-inhibiting IgG Obtained from the Lungs of Infected Animals Treated with Defective Interfering Virus

“…After low-speed centrifugation, the supernatant was stored in aliquots at -70 °C until required. Lung extracts were treated at pH 3 to release complexed antibody by dialysis against pH 3 buffer for 6 h at 4 °C and then overnight to restore neutrality (Dimmock et al, 1986). Latterly, extracts were made pH 3 by direct addition of an equal volume of citrate buffer, incubated on ice for 30 min and then returned to pH 7-4 by the addition of 1/10 vol.…”

“…(Dimmock et al, 1986) but was absent from control mice infected with fl-propiolactone (BPL)-inactivated DI virus or only with WSN. The HI activity did not neutralize infectivity.…”

“…However these animals have less lung pathology and, as influenza in the mouse is an immune-mediated disease (Hurd & Heath, 1975;Suzuki et aL, 1974;Sullivan et al, 1976;Wyde et al, 1977;Wyde & Cute, 1978) with a substantial contribution from delayed-type hypersensitivity T lymphocytes (Leung & Ada, 1980;Ada et a/., 1981 ;Liew & Russell, 1980), we have suggested that DI WSN is directly or indirectly capable of modulating the immune responses (Dimmock et al, 1986).…”

“…The HI activity did not neutralize infectivity. Nonetheless because HI activity correlated with protection from lethal infection by DI virus (Dimmock et al, 1986), and promoted antibody-dependent cell cytotoxicity (ADCC) in vitro (L. McLain & N. J. Dimmock, unpublished data) it was necessary to provide proof of its identity. Here we report on the characterization of the haemagglutinin (HA)-specific activity, notably that it comprises immunoglobulins of the IgG1, IgG2a and IgG2b isotypes.…”