pH dependence of influenza A virus-induced haemolysis is determined by the haemagglutinin gene.

The pH-dependent profiles of haemolysis by influenza viruses AHK/8/68 (HK virus) and APR/8/34 (PR8 virus) were found to possess characteristic differences. Both viruses were highly haemolytic at pH 5.0, but while HK virus-induced haemolysis was undetectable above pH 5.5 to 5.6,, PR8 virus-induced haemolysis persisted at higher pH values, becoming undetectable above pH 5.7 to 5.8. In order to determine whether these haemolysis profiles were genetically determined, we studied the pH dependence of haemolysis by eight recombinants of HK and PR8 viruses. The pH profile of each recombinant clearly resembled that of one parent or the other, showing that it is an inherited trait. The pH profile was found to be conferred exclusively by the haemagglutinin (HA) gene.