Figure 2. No sialic acid residue, which is the primary receptor for influenza virus, was detectable on human neutrophils in vitro.

(a–c) The human primary neutrophils were incubated with biotinylated MAA I, MAA II or SNA, subsequently incubated with Dylight 488 labeled Streptavidin (green) and examined with immunofluorescence. No detectable level of sialic acid in α2–3 linkages (a&b) or sialic acid in α2–6 linkages (c) was found on neutrophils. The cells were stained with mouse anti-CD15 antibody (red) to identify the identity of neutrophils. (d) Lectin stain was also performed on MDCK cells as a positive control to ensure the reliability of the technology. Nuclei were stained with DAPI (blue). Scale bar, 20 μm.