The Masking of Cell-Surface Antigens by Sialic Acid

The role played by sialic acid in masking cell-surface antigens may be ascertained only by the enhanced antigenicity created by its removal from the cell surface. Masking was first noted by Thomsen (1927) in the study of the erythrocyte. In a phenomenon which came to be known as the Thomsen effect, Friedenreich (1930) observed the agglutination of red blood cells under the influence of a substance later shown to be the 

Studying a phenomenon perhaps related to the Thomsen effect, Sanford (1967) reported that incubation with neuraminidase of the mammary carcinoma ascites cell, TA3-Ha, reduced its transplantability in an allogeneic mouse strain (Sanford, 1967). Other examples of the reduced transplantability of neuraminidase-treated tumor cells, both in allogeneic (Currie, 1967 Currie and Bagshawe, 96Sa,b) and syngeneic (Simmons et al., 91 a,b Rios and Simmons, 1973 Sethi and Brandis, 1973 Bekesi et al., 1971) systems were soon reported. 

In an attempt to determine whether this effect of neuraminidase could be applied to the clinical management of human cancer, Simmons and his collaborators (Simmons and Rios, 1971, 1972 Rios and Simmons, 1974) and others (Holland et al., 1972) inoculated tumor-bearing rodents with neuraminidase-treated tumor cells and used this procedure in combination with immunotherapy (Simmons and Rios, 1971 Holland 

Another possible explanation (Simmons and Rios, 1972) is that loss pf sialic acid would lower the negative charge at the cell surface, thus increasing the deformability of the cell (Weiss, 1965) and enhancing its susceptibility to phagocytosis (Lee, 1968). Furthermore, no activity change could be detected, after removal of sialic acid residues with neuraminidase, in the in vitro determination of inhibition of isolated 

Although Currie and Bagshawe (1967) reported that removal of sialic acid from the surface of mouse trophoblasts exposed previously masked histocompatibility antigens, Simmons et aL (1971c) were unable to detect an antigen after treatment of mouse trophoblasts with neuraminidase. 

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