Kenneth J. Jakeman

Mechanism of immunity to influenza: maternal and passive neonatal protection following immunization of adult ferrets with a live vaccinia-influenza virus haemagglutinin recombinant but not with recombinants containing other influenza virus proteins.

Neonatal ferrets are protected against infection with influenza virus by milk-derived anti-influenza virus IgG after suckling on an immune mother. Live vaccines protect better than killed vaccines despite their stimulation of lower maternal haemagglutination-inhibiting antibody levels. This suggests that antibody to virus proteins other than the haemagglutinin may also be involved. To investigate this, adult ferrets were immunized intradermally with live vaccinia-influenza virus recombinants each expressing one of the 10 influenza virus polypeptides. Adult ferrets immunized with a recombinant expressing the H3 haemagglutinin were completely protected, and also passively protected their offspring, against a live challenge with clone 7a of the reassortant influenza virus A/Puerto Rico/8/34-A/England/939/69 (H3N2), immunity being mediated by IgG antibody. However, ferrets immunized similarly with recombinants expressing the H1 haemagglutinin, neuraminidase (N1 or N2), polymerases (PB1, PB2 or PAC), matrix protein (M1 or M2), nucleoprotein (NP) or non-structural proteins (NS1 or NS2) were completely susceptible to the influenza virus.

Oral administration of cyclopentane neuraminidase inhibitors protects ferrets against influenza virus infection.

ABSTRACT Several cyclopentane inhibitors of influenza virus neuraminidase that have inhibitory activities in tissue culture similar to those of zanamivir and oseltamivir have recently been described. These new inhibitors have been examined for efficacy against a virulent H3N2 influenza virus when administered orally to infected ferrets. Preliminary studies indicated that oral administration of BCX-1923, BCX-1827, or BCX-1812 (RWJ-270201) at a dose of 5 or 25 mg/kg of body weight was active in ferrets in reducing respiratory and constitutional signs and symptoms, but these antivirals affected virus titers in the upper and lower respiratory tracts only marginally. Of the three compounds, BCX-1812 seemed to be the most efficacious and was examined further at higher doses of 30 and 100 mg/kg. These doses significantly reduced peak virus titers in nasal washes and total virus shedding as measured by areas under the curve. Virus titers in lung homogenates were also reduced compared to those in controls, but the difference was not statistically significant. As was observed with BCX-1812 at lower doses, the nasal inflammatory cellular response, fever, and nasal signs were reduced while ferret activity was not, with activity remaining similar to uninfected animals.

Role of milk-derived IgG in passive maternal protection of neonatal ferrets against influenza.

Neonatal ferrets are protected against infection with influenza virus by colostral and milk-derived anti-influenza virus IgG after suckling on an immune mother. The levels of IgG elicited and then transmitted to neonates were similar when mothers were immunized by either live infection or killed vaccines. Maternal anti-influenza virus IgA and IgM appears not to cross the neonatal gut epithelium although both are present in maternal serum and milk.

Nature of the endogenous pyrogen (EP) induced by influenza viruses: lack of correlation between EP levels and content of the known pyrogenic cytokines, interleukin 1, interleukin 6 and tumour necrosis factor

Fever in influenza results from the release of endogenous pyrogen (EP) following virus-phagocyte interaction and its level correlates with the differing virulence of virus strains. However, the different levels of fever produced in ferrets by intracardial inoculation of EP obtained from the interaction of different virus strains with ferret of human phagocytes did not correlate with the levels of interleukin 1 (IL-1), IL-6 or tumour necrosis factor in the same samples as assayed by conventional in vitro methods. Hence, the EP produced by influenza virus appears to be different to these cytokines.

Role of upper respiratory tract infection in the deaths occurring in neonatal ferrets infected with influenza virus

Passive immunization of ferret neonates by colostrally-derived anti-influenza virus IgG did not entirely prevent infection when mothers were immunized with 1 or 2 doses of formalin inactivated vaccine with adjuvant (alhydrogel). Influenza virus replication was almost completely prevented in the lower respiratory tract but only slightly reduced in the upper respiratory tract leading to deaths in about 50% of the neonates. Such neonates showed at most only minor lesions in the lower respiratory tract but moderate to severe inflammatory changes in the upper respiratory tract of most animals. This supports previous results suggesting that deaths, reminiscent of the human sudden infant death syndrome (SIDS), may arise purely as a result of upper respiratory tract infection, possibly following obstruction of the airways.

INFLUENZA VIRUS ENHANCEMENT OF MEMBRANE LEAKINESS INDUCED BY STAPHYLOCOCCAL ALPHA TOXIN, DIPHTHERIA TOXIN AND STREPTOLYSIN S

Release of alpha-amino[14C]isobutyric acid from ferret Mpf cells was promoted by staphylococcal alpha toxin, diphtheria toxin and streptolysin S. This release was enhanced to a significant extent if the cells had been previously infected with influenza virus strain A/Puerto Rico/8/34 (PR8, H1N1), although infection with virus alone did not increase the release of radiolabel as compared with that from untreated cells; inactivated virus had a similar enhancing action. The mechanism of enhancement is unclear but it occurs between 0.5 and 2h post-inoculation and viral membrane/endosome membrane fusion is essential. Endotoxin had no effect on membrane permeability, either alone or with PR8. The relevance of these in vitro observations to the previously observed enhancement of toxin lethality by influenza virus in vivo is discussed.