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HA1 and HA2 polypeptides of influenza A virus haemagglutinin (HA) were separated in purified form using electrophoresis in SDS containing polyacrylamide gels (PAGE) or chloroform-methanol extraction. The populations of HA1 polypeptides were immunogenic but considerably less so than the intact HA molecule and induced antibody which cross-reacted with influenza A and B viruses. After absorption with heterologous influenza B virus, the cross-reacting antibodies were removed and the HA1 antisera then possessed antibodies which reacted only with the cross-reactive (CR) determinants of the HA of the homologous influenza A virus and viruses of the same subtype. Neither strain-specific (SS) nor virus-neutralizing antibodies were detected in these anti-HA1 sera. HA2 polypeptides were less immunogenic and anti-HA2 antisera after absorption with influenza B virus failed to react with influenza A virus in immuno double diffusion tests and only reacted with partially denatured HA in the more sensitive single radial diffusion tests.

An electron microscopic immunogold labelling technique employing monoclonal antibodies has been applied to the antigenic analysis of influenza A and B viruses. Reassortant influenza A H3N2 viruses containing haemagglutinin molecules from viruses isolated between 1968 and 1982 were analysed with a panel of monoclonal antibodies raised against viruses which appeared over the same period. The immunogold labelling technique clearly demonstrated the antigenic drift in the haemagglutinin molecule that occurred between 1968 and 1982. When the technique was applied to the examination of viruses from a more geographically restricted influenza epidemic in a semi-closed community, antigenic variants were found. Furthermore the technique enabled the identification of distinct antigenic variant subpopulations within a single clinical isolate. Analysis of the HA of MDCK cell or egg grown virus by this procedure provided data to support the hypothesis that the host cell exerts selective pressure on subpopulations of virus resulting in the emergence of antigenic variants.

After one passage of influenza A2/Singapore/1/57 virus in mice treated with 150 mg./kg./day of aminoadamantane, a partially drug-resistant strain of virus was detected in 1 of 12 mice. The isolation rate of aminoadamantane-resistant viruses increased to 8 after three passages in drug-treated mice. Some virus strains showed a 500-fold increase in resistance to aminoadamantane and to the structurally related compounds alpha-methyl-1-adamantane methylamine and 2-adamantanamine sulphate. No aminoadamantane-resistant viruses were detected after passage of influenza four times in mice treated with lower (15 or 1.5 mg./kg./day) concentrations of aminoadamantane. Aminoadamantane had no detectable effect on the development of lung lesions in mice infected with the drug-resistant influenza strain, whereas lung lesions were reduced in aminoadamantane treated mice infected with a control strain of influenza A2/Singapore virus. No differences were detected in the buoyant density in caesium chloride, morphology or serology between control and aminoadamantane-resistant strains of virus. These drug-resistant influenza viruses may be useful for detailed studies of the mode of action of aminoadamantane.

Influenza B/LEE/40, B/Rome/1/67, B/Hong Kong/8/73, and B/Victoria/98926/70 viruses have a similar polypeptide composition as analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. These viruses are composed of six or seven polypeptides, depending on whether one or two high-molecular-weight polypeptides are resolved, ranging in molecular weights from 27,000 to 90,400. Three of these polypeptides, namely the heavy and light hemagglutinin chains and the neuraminidase, have attached carbohydrate. Highly purified influenza B/LEE/40 and B/Rome/1/67 virus preparations have RNA-dependent RNA polymerase activity equivalent to the incorporation of 100 and 30 pmol, respectively, of (3)H-UMP per mg of virus protein per h at 37 C, which is demonstrated only in detergent-treated virus suspensions. However, no RNA-dependent DNA polymerase enzyme activity was detected in the two viruses although virus suspensions were "activated" by heat, alpha-chymotrypsin, and detergents. Other enzymatic activities were associated with purified preparations of influenza B virus and were attributed to minor contamination of virus with host cell enzymes. Thus, nucleoside and deoxynucleoside phosphohydrolase enzymes were active in the absence of detergents and catalyzed the release of 1,200 and 1,800 nmol of P(i) per mg of virus protein in 30 min at 37 C from ATP and dATP substrates. Thin-layer chromatography indicated that the products of the phosphohydrolase enzymes of influenza B/LEE/40 were mainly nucleoside diphosphate and monophosphate. The latter enzymes were tightly bound to influenza B/LEE/40 virus and could not be removed completely by repeated centrifugation, including centrifugation of the virus to equilibrium in density gradients of 25 to 40% (wt/vol) cesium chloride. A low degree of RNase (approximately 0.01 mug% contamination) and phosphatase (10-30 nmol of P(i) released per mg of virus protein per 30 min) activity was detected in some, but not all, influenza B/LEE/40 virus preparations.

The haemagglutinin of influenza virus A2/Hong Kong/1/68 was shown to be markedly different from that of previously isolated A2 virus strains. No haemagglutination-inhibiting (HI) antibody to A2/Hong Kong/1/68 virus was detected in serum specimens collected in 1966 from persons aged 60 years or less. In contrast, HI antibody tests with 270 sera collected in 1968 indicated that 9.6% had demonstrable HI antibody at low titres, and 35.2% of 454 postepidemic (1969) sera had demonstrable HI antibody at relatively high titres. Most sera from persons aged 80 years and more collected in 1968 and 1969 had demonstrable HI antibody to influenza virus A2/Hong Kong/1/68. No HI antibody to the Hong Kong virus was detected in pre-epidemic sera from children aged 6 months to 3 years, whereas 32% of postepidemic sera had HI antibody. The acquisition of HI antibody to A2/Hong Kong/1/68 was not accompanied by an increase in the incidence or titres of HI antibody to heterotypic A2 influenza viruses. For sera from children aged 4-11 years, an increase of HI titre to heterotypic A2 influenza was found.

1-Adamantanamine hydrochloride (aminoadamantane) has been shown to inhibit the multiplication of influenza A viruses in cell cultures, organ cultures and experimentally infected mice. An epidemic of influenza in Great Britain in the winter of 1967-68 provided the opportunity to study the prophylactic effect of aminoadamantane in the family environment and this paper reports the results of further observations in January-March 1969 during an influenza epidemic due to A2/Hong Kong/68.In a double-blind, placebo-controlled investigation of aminoadamantane given prophylactically, in doses of 100 mg every 12 hours for 10 days, no protective effect of the drug was demonstrated. In view of the positive effect of the drug in the earlier study during the winter of 1967-68, and the apparent sensitivity of the virus strain, an explanation involving the very high incidence of individuals possessing HI antibody of less than 1:12 is offered.