Antiviral Action of Methylated β-Lactoglobulin on the Human Influenza Virus A Subtype H3N2

Antiviral activity of methylated β-lactoglobulin (Met-BLG) against H3N2 infected into MDCK cell lines depended on concentration of Met-BLG, viral load, and duration of infection. IC50% of the hemagglutination activity for 1 and 0.2 MOI (multiplicity of infection) after 24 h of incubation at 37 °C in the presence of 5% CO2 were 20 ± 0.8 and 17 ± 0.7 μg mL−1 Met-BLG, respectively. Longer incubation period (4 days) was associated with low IC50% of the hemagglutination activity (7.1 ± 0.3 μg mL−1 Met-BLG) and low IC50% of immuno-fluorescence of viral nucleoproteins (9.7 ± 0.4 μg mL−1 Met-BLG) when using 0.2 and 0.1 MOI, respectively. A concentration of 25 μg mL−1 of Met-BLG reduced the amount of replicating virus by about 2 and 1.3 logs when the viral load was 0.01 and 0.1 MOI, respectively, while higher concentrations reduced it by about 5–6 logs. Antiviral action of Met-BLG was coupled with a cellular protective action, which reached 100% when using 0.01 and 0.1 MOI and 83% when using 1.0 MOI. The time of Met-BLG addition after the viral infection was determinant for its antiviral efficacy and for its protection of the infected MDCK cell lines. Anti-hemagglutination action and cell protective action decreased gradually and in parallel with the delay in the time of Met-BLG addition to disappear totally after 10 h delay.