Schematic representation of the distribution trend of SAα2,6-Gal (SNA), SAα2,3-Galβ(1-4)GlcNAc (MAA I) and SAα2,3-Galβ(1-3)GalNAc (MAA II) receptors along the porcine respiratory tract. Diagram depicts a qualitative, not quantitative, assessment of receptor presence. Along the epithelial tract, SAα2,6-Gal receptor is dominant, with increasing MAA II lectin binding towards the alveolar region. In the sub-epithelial region, MAA II lectin binding is dominant. MAA I lectin binding is localised to the lower tract.