Role of linkage specific 9-O-acetylated sialoglycoconjugates in activationof the alternate complement pathway in mammalian erythrocytes

Substitution of the -OH group at C-9 of sialic acid by an O-acetyl ester ha s been suggested to modify various biological phenomena that are regulated by sialic acids. Amongst them, enhancement of erythrocyte lysis by 9-O-acet ylated sialic acid determinants through modulation of the alternate pathway of complement has been extensively studied on murine erythrocytes [1]. A v ariable expression of linkage specific 9-O-acetylated sialoglycoconjugates as defined by the lectinogenic epitope of Achatinin-H namely 9-O-acetylated sialic acid alpha2-->6Gal NAc was identified on rabbit, guinea pig, hamste r, rat, mouse and human erythrocytes. This differential expression of linka ge specific 9-O-acetylated sialoglycoconjugates strongly correlated with th e susceptibility of mammalian erythrocytes to lysis by the alternate pathwa y of complement. Additionally, low levels of antibodies directed against O- acetylated sialic acids in these mammalian species suggested that these con stitutively present determinants have low immunogenicity. Taken together, o ur results indicate that complement mediated hemolysis depends not simply u pon the extent of surface 9-O-acetylated sialic acids present but more impo rtantly upon the specific linkage.