Comparative electrophoretic study of polypeptides of influenza A/H3N2 viruses isolated in circumscribed geographical areas.

Two distinct groups of influenza A/H3N2 viruses, closely related to A/Bangkok/1/79 and to A/Belgium/2/81, have been chosen from viruses isolated in Italy during 1981 to 1983 with the aim of analysing the biochemical composition of their polypeptides. The strains of each group have shown differences in electrophoretic migration rates in one or more proteins in comparison to the prototype viruses. Polypeptide mobility variations among isolates from circumscribed geographical areas and from single outbreaks have also been observed. In particular, there was a high degree of variability in the NS1 protein. The detection of biochemical differences among identical antigenic variants, probably the result of point mutations in polypeptide sequences or of genetic reassortment among different co-circulating human viruses, is a further expression of the peculiar ability of the influenza A virus to exhibit variation in internal proteins during its circulation.