Providing a selective pressure to select/ evolve the virus with a receptor preference for this receptor. A selective pressure on the receptor specificity of the viral HA to the human host seems to be a prerequisite for the generation of a virus with pandemic potential in accordance with historical data that most infections by swine viruses cause only limited human-tohuman transmission. To become established in a human population, additional factors are likely to be required for optimization of its host-cell tropism. By an integrated biochemical, analytical and data mining approach, it has recently been shown that long a2-6 sialylated glycans with umbrella-like topology n) may be required for sufficient viral transmission between humans: human-adapted HAs bind with high affinity to umbrella-like topology, whereas avian and swine HAs preferentially recognize cone-like topology . The N-glycan profile of human bronchial epithelial cells showed the presence of a2-6 long branches. Previous N-glycans derived from amniotic membrane cells of chicken embryonated eggs used for growing viruses isolated from human hosts consist of short a2-6 trisaccharide branches, NeuAcGalGlcNAc-, but not a long lactosamine structure. Similar to N-glycans isolated from AM cells, N-glycans with a long branch could not be detected in the porcine trachea and porcine lungs; nevertheless, the possibility that long branches may be present on O-linked a2-6 cannot be excluded. However, the recent emergence of S-OIVs with swift human-to-human transmission has confirmed that pigs are the source of the generation of influenza viruses with pandemic potential. Other glycan modifications, such as MK-0683 HDAC inhibitor Fucosylation and sulfation, may be involved in the receptor binding activity of viral HAs. Fucosylation and/or sulfation at Gal or GlcNAc/ GalNAc on position 2 or 3, respectively, of the terminal trisaccharide appear to affect receptor binding activity of some influenza viruses, such as increase in binding affinity of H5N1 and H7N1 chicken viruses to a2-3-linked Sia. Fucose residue detected in N-glycans of the porcine trachea and lungs was found only at the initial GlcNAc of the N-glycan core connected to asparagine. Sulfate residue was not detected in porcine trachea and lung N-glycans. It should be noted that glycoconjugate profiles of the porcine respiratory tract, which are involved in mediation and regulation of many physiological and pathological processes, may vary among different species, ages, sex and lifestyle; however, the finding in this study that Siaa2-6Gals are dominant along the respiratory epithelial tract of a 5-year-old female LWD-pig is in agreement with recently reported lectin-binding profiles of 4-8week-old healthy post-weaned male United Kingdom pigs. All age groups of pigs can be infected by influenza A viruses. During a farrow-to-finish operation, whereas growing-finishing pigs are replaced almost every 6 months for their flesh.