Analysis of antigenic relationships among influenza virus strains using a taxonomic cluster procedure. Comparison of three kinds of antibody preparations.

Hemagglutination inhibiting (HI) monoclonal antibody preparations (MA) were raised against six influenza A (H3N2) strains from the period 1977-1982. Twenty-three hybridomas were selected and titrated in HI assays against these strains and against 18 influenza A (H3N2) viruses isolated in The Netherlands during the seasons 1981-1982 and 1982-1983. Similar HI tests were performed with conventional post-infection ferret antisera and with ferret antisera adsorbed with heterologous strains of influenza A (H3N2) virus. The resulting serological data were subjected to a computerized taxonomic cluster procedure based on the Euclidean distance between viruses. With respect to the degree of separation between clusters the unadsorbed ferret antisera were inferior to the adsorbed antisera whereas the MA were superior to both. Our results demonstrate that computer programs based on numerical taxonomy can be helpful in processing large numbers of serological data and that MA are indispensable in epidemiological and diagnostic influenza studies

Changes in the morphology of influenza particles induced at low pH

At low pH influenza virus causes membrane fusion. This phenomenon is thought to reflect a part of the infection mechanism of the virus. To obtain more information on the effect of low pH on the virus, the change in morphology of influenza virus particles was studied by electron microscopy. Further, the degradation of haemagglutinin (HA) after trypsin digestion as a function of pH was studied by gel electrophoresis. The results showed that a threshold value existed below which both a change in morphology and an increase in trypsin sensitivity were observed. This threshold pH was found to be strain specific. A number of strains showed a heterogeneity in the particle population with respect to the threshold pH. The various subpopulations appeared to differ genetically. Virus particles with uncleaved precursor HA, HAo, were not effected by the low pH treatment