Actinomyces tissue specificity may depend on differences in receptor specificity for GalNAcβ-containing glycoconjugates

Abstract

Actinomyces naeslundii 12104 and A. viscosus LY7 were compared for receptor specificities and adherence properties because these relate to their oral colonization sites. Both strains bind GalNAcβ-containing glycosphingolipids (GSLs) in a GalNAcβ1-3GalαOethyl-sensitive fashion but differ with respect to the number of cells bound to GSLs and the effect of neighboring sugar groups on the binding. Their hemagglutination and saccharide inhibition profiles confirm the existence of two receptor specificities (for example, when GalNAcβ1-3GalαOethyl is multivalently conjugated to albumin, its inhibitory activity increases fourfold toward strain 12104 but decreases fourfold toward strain LY7). Trypsin or chymotrypsin treatment of human erythrocytes, which possess receptor GSLs, improves their hemagglutination with strain 12104. In contrast, the same treatment of chicken erythrocytes, which lack receptor GSLs, abolishes their hemagglutination. These findings suggest that both GSLs and glycoproteins act as functional receptors on eukaryotic cells. The strains also differ with respect to the following GalNAcβ1-3GalαOethyl-sensitive adherence properties: (i) strain LY7 adheres somewhat better than does strain 12104 to buccal epithelial cells; (ii) in spite of their similar overall coaggregation patterns with streptococci, strain 12104 coaggregates with Streptococcus oralis MPB1 but strain LY7 does not; (iii) strain 12104 alone shows GalNAcβ- sensitive saliva aggregation and adherence to saliva-coated hydroxyapatite. The GSL binding patterns of fresh Actinomyces isolates reveal a high prevalence of LY7-like specificities among buccal isolates, whereas 12104- like specificities are most prevalent among plaque isolates. These findings strongly suggest that fresh Actinomyces isolates use fine specificity for GalNAcβ-containing glycoconjugates in recognition and subsequent colonization of specific oral surfaces.