THE ROLE OF ANTIGENICALLY DIFFERENT VIRUS NEURAMINIDASES AS STRUCTURES IMPLICATED IN RECEPTOR-BINDING PROCESSES

Influenza A viruses exhibit segmented nucleic acid coding for eight di fferent proteins, two of them as glycoproteins exposed on their lipopr otein envelopes, hemagglutinin (HA) and neuraminidase (NA). Hemaggluti nin exhibits receptor-binding activity while neuraminidase develops si alidase cleavage activity which acts on cell receptors. Influenza A st rains responsible for human, avian, equine and porcine respiratory inf ections all over the world present antigenically different hemagglutin in (H-1 to H-14) and neuraminidase (N-1 to N-9) structures on their su rface. The objective of the present investigation was to study the rol e of N-2, N-8, and N-9, antigenically diverse neuraminidase structures of human (N-2) and animal (N-8 and N-9) influenza viruses, in the rec eptor-binding process. Receptor-binding activity of N-2 and N-8 was an alyzed by crossed tests using H3N2 and H3N8 antisera and the hemagglut ination inhibition test as a model. Hemagglutinating activity of antig enically different N-2 and N-8 structures was demonstrable and was inh ibited by homologous antisera (N-2-H3N2, N-8-H3N8) but not by heterolo gous antisera (N-2-H3N8, N-8-H3N2). This previously demonstrated Ns he magglutinating activity was analyzed for receptor-binding specificity using hemagglutination tests and NeuAc alpha2,3Gal and NeuAc alpha2,6G al derivatized erythrocytes. This highly purified N-9 strain was obtai ned from a virus strain isolated from terns by Dr. Peter Colman (CSIRO Division of Biomolecular Engineering, Parkville, Victoria, Australia) . It exhibited receptor-binding specificity for NeuAc alpha2,3Gal sequ ences, a property similar to that observed in hemagglutinins from avia n strains, These results indicate the importance of antigenically diff erent neuraminidase structures as alternative agents for developing re ceptor-binding activity. Further studies are needed to determine the r ole of different neuraminidases as structures responsible for receptor -binding activity influencing the release of progeny virus from host c ells.