Hemagglutinating and sialidase activities of subpopulations of influenza A viruses

Abstract The present study was conducted to investigate the characteristics of two samples of influenza A/England/42/72 (H3N2) virus, one of them selected by an adsorption-elution technique, to determine the possible existence of virus variants or subpopulations. Based on specificity of virulence-related cell receptor-binding and sialidase activities, this selection technique using human O group erythrocytes revealed the presence of variants within a standard virus sample with diversity for their hemagglutinating and sialidase activities. The standard-like (E1) sample exhibited titers of 4 and 32 HAU (hemagglutinating units in 25 microliters) with human O group and chicken erythrocytes, respectively, while the sample obtained by the adsorption-elution process (E2) exhibited titers of 32 and 4 HAU, respectively, with these same types of erythrocytes. The E2 sample showed higher sialidase activity at pH values between 5.4 and 6.6 with human erythrocytes (128-256 HAU), but the E1 sample 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 present in samples with sialidase activity inhibited by heating (at 56 degrees C for 30 min) or by treatment with EDTA (dilution in buffer containing 2 mM EDTA, a chelating agent on calcium-dependent sialidase activity) demonstrate the independence of these activities in the selected sample: native E2 (absorbance = 0.18), EDTA-treated native E2 (absorbance = 0.28), heated E2 (absorbance = 0.26), EDTA-treated heated E2 (absorbance = 0.41).(ABSTRACT TRUNCATED AT 250 WORDS)