The anti-recognition function of sialic acids: studies with erythrocytes and macrophages

Abstract

-Sialic acids have been found to mask antigens, receptors and other recognition sites on molecules and cells. This has been investigated best with hepatocyte and macrophage lectins which recognize 13-galactose and N-acetyl-13-galactosamine residues on molecules and cells exposed by sialidase treatment. The lectin on macrophages leads to the binding and phagocytosis of erythrocytes after the enzymic removal of a critical amount of sialic acids. New techniques (colorimetry, high--performance liquid chromatography, gas-liquid chromatographymass spectrometry) for the determination of the amount and nature of these sialic acids were developed. The interaction of partially desialylated rat erythrocytes with homologous peritoneal macrophages can be inhibited by 13-galactosyl glycosides in a degree depending on the structure of the oligosaccharides and glycoconjugates tested. Although homologous serum stimulates binding and phagocytosis, immunoglobulins and complement factors were found to play no role in this process. The main factor responsible for the masking effect of sialic acids on subterminal 13-galactosyl groups seems to be the carboxyl group of neuraminic acid, as reduction of this group to an alcohol largely abolishes this important function of sialic acids in the macrophage and hepatocyte systems studied. The anti-recognition function of sialic acids illuminates the pathophysiological role of serum sialidases in infectious and other diseases.

Endogenous sialylation of the lipooligosaccharides of Neisseria meningitidis

“…Similarly, it will be important to determine whether meningococcal LOS also are sialylated in vivo and, if so, where the sialylated LOS exist (nasopharynx, blood, cerebrospinal fluid). Other biological functions of sialic acid that are relevant to concepts of meningococcal pathogenesis and host and tissue specificity are lack of recognition by mucosal antibody, complement, phagocytes (48), and terminal galactose-specific lectins (6) and, conversely, recognition by sialic acid-specific lectins (2). Whether the differences observed for in vitro LOS expression accurately reflect any in vivo mechanisms of meningococcal pathogenesis will be an area for future studies.…”

Cellular sialic acid level and phenotypic expression in B16 melanoma cells: Comparison of spontaneous variations and bromodeoxyuridine- and theophylline-induced changes.

“…Sialic acid has been shown to play a role in cell adhesion (6,15,19,20,28). Higher adhesiveness of amelanotic and BrdU-treated melanotic cells could be explained by their lower sialic acid levels, as with the case of lectin-resistant cells (2,25).…”

“…From comparison of spontaneous phenotypic variations, the correlation of sialic acid level with tyrosinase activity was confirmed, while there was only a slight correlation with adhesiveness. It is thus suggested that sialylation/desialylation, being reflected as variations in cellular sialic acid content, is implicated in melanoma cell differentiation in terms of tyrosinase expression.Sialic acid has been shown to play important roles in a variety of biological processes including cell adhesion, cellular recognition and regulation of glycoconjugates' functions (6,15,19,20,28). In melanoma cells, involvement of sialic acid residues has been well documented in determining metastatic potential (13).…”

“…Sialic acid has been shown to play important roles in a variety of biological processes including cell adhesion, cellular recognition and regulation of glycoconjugates' functions (6,15,19,20,28). In melanoma cells, involvement of sialic acid residues has been well documented in determining metastatic potential (13).…”

Synthesis of protein conjugates and analogues of N-acetylneuraminic acid

“…On the other hand, the absence of sialic acids on glycoproteins may have beneficial effects. Thus, the uptake or sequestration of senescent cells by macrophages (14) and liver hepatocyte receptors (15) can trigger the catabolism of useless cells. Perhaps the most interesting 'Author to whom correspondence may be addressed features of the sialic acids are their roles as differentiation (16) and oncodevelopmental (17) antigens.…”