The distribution and relative expression levels of SAa2-3Gal and SAa2-6Gal are summarized in Table 1 . It should be noted that because the relative affinities of the lectins to their targeted glycans may differ, comparing the intensity of staining between the MAA and SNA cannot be used as a quantitative comparison of the relative SAa2-3Gal and SAa2-6Gal expressions. In addition, the H6N1 viral antigens detected in the infected cells at a MOI of 0.1 were mostly restricted to the b-tubulin + cells at 6 h.p.i. (Fig. 5A ). Few H6N1 antigens were detected in the goblet cells or basal cells, possibly due to the low expression of AIV receptors (Figs. 5B and 5C). These results indicate that the ciliated cell, rather than the goblet or the basal cells, is the primary target cell for the AIV. In addition, these data also illustrate that the distribution of SAa2-3Gal expression among cells determines the cell tropism of the AIV H6N1 virus (as summarized in Fig. 6 and Table 1 ).