Recombinant influenza A H3N2 viruses with mutations of HA transmembrane cysteines exhibited altered virological characteristics.

Influenza A H3N2 virus as the cause of 1968 pandemic has since been circulating in human and swine. Our earlier study has shown that mutations of one or two cysteines in the transmembrane domain of H3 hemagglutinin (HA) affected the thermal stability and fusion activity of recombinant HA proteins. Here, we report the successful generation of three recombinant H3N2 mutant viruses (C540S, C544L, and 2C/SL) with mutations of one or two transmembrane cysteines of HA in the background of A/swine/Guangdong/01/98 [H3N2] using reverse genetics, indicating that the mutated cysteines were not essential for virus assembly and growth. Further characterization revealed that recombinant H3N2 mutant viruses exhibited larger plaque sizes, increased growth rate in cells, enhanced fusion activity, reduced thermal and acidic resistances, and increased virulence in embryonated eggs. These results demonstrated that the transmembrane cysteines (C540 and C544) in H3 HA have profound effects on the virological features of H3N2 viruses.