Characterization of host cell binding variants of influenza virus by monoclonal antibodies.

We have previously shown that a plaque-type mutant of influenza virus A/WSN has a growth advantage in MDBK cells because its hemagglutinin (HA) has a greater affinity for host cell receptors than does the HA of the parent virus. We show here that the mutant is also less sensitive than the parent to neutralization by antibodies to epitopes in at least two regions on the HA. WSN-specific monoclonal antibodies which had higher radioimmunoassay (RIA) titers against the parent than the mutant virus also had higher plaque inhibition (PI) and hemagglutination inhibition (HI) titers. In contrast, cross-reacting antibodies bound equally well to the parent and mutant viruses as judged by RIA but those which bound to the Cb region of the HA exhibited higher PI and HI titers against the parent virus. The results suggest that preferential neutralization of the parental virus by antibodies can contribute to the selective advantage of mutants which have increased affinity for cellular receptors.