Expression and distribution of sialic acid influenza virus receptors in wild birds

Avian influenza (AI) viruses have been detected in more than 105 wild bird species from 12 different orders but species-related differences in susceptibility to AI viruses exist. Expression of 2,3-linked (avian-type) and 2,6-linked (human-type) sialic acid (SA) influenza virus receptors in tissues is considered one of the determinants of the host range and tissue tropism of influenza viruses. We investigated the expression of these SA receptors in 37 wild bird species from 11 different orders by lectin histochemistry. Two isoforms of Maackia amurensis (MAA) lectin, MAA1 and MAA2, were used to detect 2,3-linked SA, and Sambucus nigra lectin was used to detect 2,6-linked SA. All species evaluated expressed 2,3-linked and 2,6-linked SA receptors in endothelial cells and renal tubular epithelial cells. Both 2,3-linked and -2,6-linked SA receptors were expressed in respiratory and intestinal tract tissues of aquatic and terrestrial wild bird species from different taxa, but differences in SA expression and in the predominant isoform of MAA lectin bound were observed. With a few possible exceptions, these observed differences were not generally predictive of reported species susceptibility to AI viruses based on published experimental and field data.