Alpha2-6-linked Sialic Acid Expression
The alpha2-6 linkage represents one of three common glycosidic linkages (attachments) of the cell surface sugar, sialic acid. The presence of sialic acid in this linkage to glycoproteins on cell surfaces is determined mainly by the activity of the sialyltransferase gene ST6GAL1. There are differences between humans and other hominids with respect to this cell surface structure. Chief among them is the strong presence of the structure on the bronchial epithelial lining of humans, but not in other hominids. A similar difference exists with respect to red blood cells. In contrast, certain tissues of other hominids show higher levels of alpha2-6-linked sialic acids than humans (including cords and vessels of the spleen, lymphoid follicles, and bile ducts in the liver). The human expression of alpha2-6-linked sialic acids on the lining of the human airways can explain the specificity of influenza virus invasion and the relative protection of humans from the "bird flu". The available data predicts that other hominids would be much more susceptible to the "bird flu".