ANALYSIS OF VIRAL AND CELLULAR-PARAMETERS WHICH AFFECT THE FUSION PROCESS OF INFLUENZA-VIRUSES

In the present investigation we studied the fusogenic process develope d by influenza A, B and C viruses on cell surfaces and different facto rs associated with virus and cell membrane structures. The biological activity of purified virus strains was evaluated in hemagglutination, nation, sialidase and fusion assays. Hemolysis by influenza A, B and C viruses ranging from 77.4 to 97.2%, from 20.0 to 65.0%, from 0.2 to 9 3.7% and from 9.0 to 76.1% was observed when human, chicken, rabbit an d monkey erythrocytes, respectively, were tested at pH 5.5. At this pH , low hemolysis indexes for influenza A, B and C viruses were observed if horse erythrocytes were used as target cells for the fusion proces s, which could be explained by an inefficient receptor binding activit y of influenza on N-glycolyl sialic acids. Differences in hemagglutini n receptor binding activity due to its specificity to N-acetyl or N-gl ycolyl cell surface oligosaccharides, density of these cellular recept ors and level of negative charges on the cell surface may possibly exp lain these results, showing influence on the sialidase activity and th e fusogenic process. Comparative analysis showed a lack of dependence between the sialidase and fusion activities developed by influenza B v iruses. Influenza A viruses at low sialidase titers (<2) also exhibite d clearly low hemolysis at pH 5.5 (15.8%), while influenza B viruses w ith similarly low sialidase titers showed highly variable hemolysis in dexes (0.2 to 78.0%). These results support the idea that different vi rus and cell-associated factors such as those presented above have a s ignificant effect on the multifactorial fusion process.