Comparison of NA activity between cell lysates and supernatants.

(A) NA activity in cell lysates and supernatants at different time points following infection. Cells were infected with NIBRG-14 (H5N1) virus at a multiplicity of infection of 0.001. Each data point represents the mean of three separate experiments. (B) NA activity in cell lysates and supernatants with different viral inocula. MDCK cells were infected with different dilutions of NIBRG-14, with NA activity measured in either the cell culture supernatant or cell lysates 20 h after inoculation. The total NA activity in the supernatants was calculated and compared with the activity in the cell lysates. (C) The neutralizing antibody titers of serum samples measured by the NA-MNT. The neutralizing antibody titer of NIBSC reference sheep antisera (shRef H5N1), high (huHiPos) and moderate (HuMoPos) seropositive samples, and negative (huNeg) human sera were determined by NA-MNT using either cell supernatants or lysates. Each test was repeated five times, with the CVs calculated accordingly. Note: HuHiPos, HuMoPos, and huNeg samples were obtained from a clinical study of the H5N1 candidate vaccine.