Antigenic heterogeneity of N2 neuraminidases of avian influenza viruses isolated in Israel

Abstract

Twenty one N2 neuraminidase (NA)-containing viruses isolated in Israel from different avian hosts during 1971–1984 were studied comparatively by means of the panel of 7 monoclonal antibodies (MAB) against A/Guiyang/57(H2N2) virus. Fifteen from the 21 viruses were studied in comprehensive cross reaction NA inhibition (NI) tests with the corresponding polyclonal antisera. The principal result of the studies is that all the isolates can be distributed into two main groups. The 1st group includes the majority of the isolates whose NA shows close relatedness to the “early” (1957 type) N2 NA by NI tests with polyclonal antisera, and demonstrates remarkable stability in the NI tests by reacting with the same 6 from 7 MABs of the panel. The 2nd group does not show any special kinship to either “early” or “late” (1968 type) N2 when analyzed with polyclonal antisera and demonstrates heterogeneity by the analysis with the MABs. A hypothetical explanation of the phenomenon of co-circulation in the local avian reservoir of viral strains displaying either remarkable stability or wide heterogeneity of their NAs is suggested. In accordance with it, the viruses with “stable” (“conservative”) N2 NA did not leave the avian reservoir and, hence, did not drift because of very low antibody “sselection pressure”. Contrary to it, the viruses with heterogeneous N2 NA had been circulating in the human (mammalian) reservoir during various periods before their transfer into the avian reservoir; they drifted accordingly and, being then isolated from birds and designated as “avian” viruses, demonstrate heterogeneity of their NAs which is typical for human viruses.