Differential expression of SAα2,6-Gal (SNA lectin) and SAα2,3-Gal (MAA II lectin) receptors in the porcine respiratory tract. Composite confocal images show distribution of SAα2,6-Gal receptors (green) and SAα2,3-Gal receptors (red) with nuclear staining (blue). Representative results that show SAα2,6-Gal receptor as the dominant receptor type on the epithelium of trachea (A), bronchus (B) and bronchiole (C), where epithelial cells and goblet cells are the main contributing cell types. SAα2,3-Gal receptor, on the other hand, is the major receptor in the corresponding sub-epithelial (mucosal) region with sparse concentration of SAα2,6-Gal receptor at blood vessels and mucous/serous glands. Both receptor types are similarly expressed on alveolar lining (D). The specificity of lectin binding is demonstrated on serial tracheal sections stained with haematoxylin and eosin (E), and with both SNA and MAA II lectins on section previously treated with sialidase A, where only faint background binding is detected (F). 1. goblet cell, 2. epithelial lining, 3. gland with occasional blood vessel, 4. submucosal gland, 5. mucosa, 6. smooth muscle, 7. blood vessel. Scale bar = 75 μm.