HEMAGGLUTINATING AND SIALIDASE ACTIVITIES OF SUBPOPULATIONS OF INFLUENZA-A VIRUSES

The present study was conducted to investigate the characteristics of two samples of influenza A/England/42/72 (H3N2) virus, one of them sel ected by an adsorption-elution technique, to determine the possible ex istence of virus variants or subpopulations. Based on specificity of v irulence-related cell receptor-binding and sialidase activities, this selection technique using human O group erythrocytes revealed the pres ence of variants within a standard virus sample with diversity for the ir hemagglutinating and sialidase activities. The standard-like (E1) s ample exhibited titers of 4 and 32 HAU (hemagglutinating units in 25 m ul) with human O group and chicken erythrocytes, respectively, while t he sample obtained by the adsorption-elution process (E2) exhibited ti ters of 32 and 4 HAU, respectively, with these same types of erythrocy tes. The E2 sample showed higher sialidase activity at pH values betwe en 5.4 and 6.6 with human erythrocytes (128-256 HAU), but the E1 sampl e did not exhibit significant sialidase activity with either human or chicken erythrocytes. The different pH optima for hemolysis (5.2) and sialidase (5.4-6.6) activities and the higher hemolysis indexes presen t in samples with sialidase activity inhibited by heating (at 56-degre es-C for 30 min) or by treatment with EDTA (dilution in buffer contain ing 2 mM EDTA, a chelating agent on calcium-dependent sialidase activi ty) demonstrate the independence of these activities in the selected s ample: native E2 (absorbance = 0.18), EDTA-treated native E2 (absorban ce = 0.28), heated E2 (absorbance = 0.26), EDTA-treated heated E2 (abs orbance = 0.41). The results suggest the presence of different viral s ubpopulations which require further study in order to determine the sp ecific viral variant responsible for disease, or for the development o f immunity and to provide information for the development of vaccines.