Characterization of viruses with different glycosylation patterns on NA. (A) Measurements of NA activity using different glycoconjugates, 4-Muα-Neu5Ac, 6-SLN, and 3-SLN; the NA activity was relative to each WT substrate designated as 100%. (B) Comparison of virus production in chicken hepatocellular carcinoma cells (LMH cells). The virus titers were determined at 48 hpi. (C) TLC of variants of viruses that interact with 6-SL. (D) The 4-MUNANA assay was used to measure the NA activity of 44-72-G virus, deglycosylated 44-72-G virus, and 44-72-219-G virus at 37 and 55 °C. (E) Viral morphology as examined by transmission electron microscopy for WT virus. (F) 44-72-219-G virus. (G) After mice were infected with WT and glycosylation-defective NA virus (44-72-219-G), survival rate and (H) body weight were recorded for 14 d. (A, B, and D) Mean ± SEM for three independent experiments. (G and H) Mean ± SEM for five independent experiments. *P < 0.001. **P < 0.05.