In conclusion, this study shows that a bottom-up, categorization approach combining the IBS method and hierarchical cluster analysis can detect subgroups of subjects based on phenotypes that are associated with b 2 -AR gene polymorphisms. Further research should aim to identify the physiological mechanisms underlying these findings.  The Infection of Chicken Tracheal Epithelial Cells with a H6N1 Avian Influenza Virus Sialic acids (SAs) linked to galactose (Gal) in α2,3- and α2,6-configurations are the receptors for avian and human influenza viruses, respectively. We demonstrate that chicken tracheal ciliated cells express α2,3-linked SA, while goblet cells mainly express α2,6-linked SA. In addition, the plant lectin MAL-II, but not MAA/MAL-I, is bound to the surface of goblet cells, suggesting that SA2,3-linked oligosaccharides with Galβ1–3GalNAc subterminal residues are specifically present on the goblet cells. Moreover, both α2,3- and α2,6-linked SAs are detected on single tracheal basal cells. At a low multiplicity of infection (MOI) avian influenza virus H6N1 is exclusively detected in the ciliated cells, suggesting that the ciliated cell is the major target cell of the H6N1 virus. At a MOI of 1, ciliated, goblet and basal cells are all permissive to the AIV infection. This result clearly elucidates the receptor distribution for the avian influenza virus among chicken tracheal epithelial cells and illustrates a primary cell model for evaluating the cell tropisms of respiratory viruses in poultry. Sialic acids (SAs), consisting of a core of nine-carbon monosaccharide, are usually linked to the outermost capping position of glycans that are conjugated to cell-surface glycoproteins or glycolipids [1] . Sialyltransferase adds SA to the terminal sugar residues, such as galactose (Gal), N-acetylglucosamine (GlcNAc) or N-acetylgalactosamine (GalNAc) [1] . The conjugation between Gal and SA can be either in the form of an a2,3 or an a2,6 glycosidic linkage. In mammals, N-acetylneuraminic acid (Neu5Ac) and Nglycolylneuraminic acid (Neu5Gc) are the two most common types of SA, but Neu5Ac is the major type of SA in birds [2] .