Genetic dimorphism in influenza viruses: Characterization of stably associated hemagglutinin mutants differing in antigenicity and biological properties

Abstract

Influenza virus recombinant X-53 produced for use in the 1976 National Immunization Program for swine influenza was found to comprise two types of virions differing in their antigenic, replicative, and plaque-forming characteristics. One type, characteristic of X-53 and designated “L,” was relatively low-yielding in chicken embryos, produced small clear plaques in Madin-Darby dog kidney cells, and was selectively inhibited by heterotypic antibody to the A/sw/Cam/39 strain of swine influenza virus. The other, X-53a or “H,” was high-yielding in chicken embryos, produced large turbid plaques in dog kidney cells, and was not inhibited by concentrations of A/sw/Cam/39 antisera inhibitory to X-53. It was shown that A/NJ/11/76 (HswN1) virus, from which X-53 was derived, and five other swine influenza virus isolates from humans and pigs were dimorphic mixtures of the two types of virus. Segregation of the hemagglutinin genes of L and H variants by further recombination demonstrated that their different properties were pleiotropic phenotypes of mutation in the hemagglutinin gene. Under selective conditions suppressive to the L mutant, mutation of cloned L to H virus was observed. This observation, as well as the apparent ubiquity of the two mutants in nature, suggests that this is another example of viral dimorphism—the stable association of two allelic mutants. Of special significance is the indication that antigenic variants may be selected by selection for properties other than antigenicity, and therefore may represent mutants with pathogenic effects determined by factors other than lesser modulation by host antibody.

Antigenicity in hamsters of inactivated vaccines prepared from recombinant influenza viruses

“…Alternatively, the differences in antigenicity may be due to differences in the surface antigens themselves, and although all the vaccines carried HA and NA antigens derived from A/Victoria/75, differences in various phenotypic properties of the HA of influenza virus strains, indistinguishable by normal serological tests, have been reported (Kilbourne, 1978;Erickson & Kilbourne, 1980). Recent studies have shown that influenza A virus variants can readily emerge on passage (Brand & Palese, 1980), and such variants could differ in their antigenicity.…”

Frequency of naturally occurring antibody to influenza virus antigenic variants selected in vitro with monoclonal antibody

“…The antigenic mutants were repassaged at terminal dilution in the presence of a 1 in 2000 dilution of the monoclonal antibody and the virus harvests used to infect eggs to prepare a working stock of virus. Since passage of influenza A viruses in the absence of antibody pressure can lead on occasion to the selection of antigenic variants (Kilbourne, 1978), control virus clones were obtained from the parental A/Texas/77 virus using normal ascitic fluids and the Sero-epidemiological analysis using antigenic variants The six antigenic variants of A/Texas/77 described above were incorporated into the agarose of SRH plates to determine if they could be distinguished antigenically from the parental virus using human sera (Plate 1). All antigenic variants failed to react with a proportion of children's sera, although the same children's sera reacted with the parent A/Texas/77 virus.…”

Complete structure of the hemagglutinin gene from the human influenza A/Victoria/3/75 (H3N2) strain as determined from cloned DNA

“…Possibly a mutant hemagglutinin gene has been fortuitously cloned during the construction of X47, or else a rare mutation in the population was selectively propagated under the conditions used to maintain and grow the X47 stock. An example of two allelic mutants in a recombinant stock and selective propagation of one type has been described by Kilbourne (1978). The exact difference between the hemagglutinin gene in the natural A/Victoria/3/75 and in X47 remains to be further characterized; for example, by probing with monoclonal antibodies.…”