Antigenicity and evolution amongst recent influenza viruses of HIN1 subtype

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Abstract
The sequence of the HAl subunit region of the haemagglutinin gene of influenza A/USSR/90/77, and A/Brazil/11/78, A/Lackland/3/78, A/England/333/ 80 and A/India/6263/80 was determined by dideoxy-sequencing methods using total virion RHA and specific oligonucleotide primers for reverse trans criptase. These 1977–1980 strains share a minimum of 85% amino acid sequence homology with influenza A/PR/8/34. Most of the surface amino acid substitutions which occurred during the evolution of A/PR/8/34 to A/USSR/90/77 and subsequently in the 1978–1980 strains are located in the 4 antigenic sites previously defined by an analysis of laboratory-eelected mutants of A/PR/8/34. We deduce an evolutionary pathway for the 1977–80 strains and suggest their different epidemic properties may be a consequence of only a few amino acid changes.