Pleiotropic effects of amino acid substitutions in H5 hemagglutinin of influenza A escape mutants.

We believe that the monitoring of pleiotropic effects of the hemagglutinin (HA) mutations found in H5 escape mutants is essential for accurate prediction of mutants with pandemic potential. In the present study, we assessed multiple characteristics of antibody-selected HA mutations. We examined the pH optimum of fusion, HA heat inactivation, affinity to sialyl receptors, and in vitro and in vivo replication kinetics of various influenza H5 escape mutants. Several amino acid substitutions, including T108I, K152E, R162G, and K218N, reduced the stability of HA as determined by heat inactivation, whereas S128L and T215A substitutions were associated with significant increases in HA thermostability compared to the respective wild-type viruses. HA mutations at positions 108, 113, 115, 121, 123, 128, 162, and 190 and substitutions at positions 123, 199, and 215 affected the replicative ability of H5 escape mutants in vitro and in vivo, respectively. The T108I substitution lowered the pH optimum of fusion and HA temperature stability while increasing viral replicative ability. Taken together, a co-variation between antigenic specificity and different HA phenotypic properties has been demonstrated.