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Figure 4: Equine and canine respiratory tissues for the upper respiratory tract (URT) and lower respiratory tract (trachea, lung) stained with lectins specific for sialic acids with α2,6- and α2,3-linkages. Green staining: reaction with fluorescein isothiocyanate (FITC)-labeled Sambucus nigra lectin (Vector Laboratories, Burlingame, CA, USA) indicates the presence of sialic acids linked to galactose by an alpha2,6-linkage (SAα2,6-gal). Red staining: reaction with biotinylated Maackia amurensis lectin (Vector Laboratories) (detected with Alexa Fluor 594-streptavidin complex; Molecular Probes/Invitrogen, Carlsbad, CA, USA), indicates the presence of SAα2,3-gal. Tissues were counterstained with 4,6,-diamidino-2-phenylindole (DAPI).