The inhibition of NA enzyme activity by mAbs was measured by
enzyme-linked lectin assay (ELLA) and 20-(4-methylumbelliferyl)-a-D-N-acetylneuraminic acid (Mu-NANA) assay.
ELLA was carried out in a 96-well plate. Briefly, mixtures of
predetermined amount of virus and serial dilutions of antibody
were incubated in duplicate wells of a fetuin-coated plate
overnight at 37 "C. Plates were washed with PBST, followed by
the addition of peanut agglutinin conjugated to horseradish
peroxidase (PNA-HRP) (Sigma, Aldrich, USA). Plates were incubated
at room temperature for 2 h and then washed with PBST,
followed by addition of o-phenylenediamine dihydrochloride
(OPD) substrate. The reaction was stopped, and OD490 values
were read. The Mu-NANA assay was carried out with a
commercially available kit (Applied Biosystems, USA) according
the manufacturer’s instruction. Briefly, mixtures of predetermined
amount of virus and serial dilutions of antibody were incubated in
a 96-well plate for 30 min at 37 "C. Mu-NANA was added and
incubated for 1 h at 37 "C. The reaction was stopped and the plate
was read using an excitation wavelength range of 350 nm to
365 nm and an emission wavelength range of 440 nm to 460 nm.
Median inhibition concentration (IC50) was determined by
quadratic curve fitting (GraphPad Prism).