Cell Surface Sialomucin and Resistance to Natural Cell-mediated Cytotoxicity of Rat Mammary Tumor Ascites Cells1

MAT-B1 and M A I -( 1 ascites subîmes of the 13762 rat mammary adenocarcinoma both contain sialomucin as a major cell surface compo nent and are resistant to cytolysis by normal rat spleen lymphocytes |3 ±2% (SD) and O ±1%, respectively). Susceptibility to lysis did not increase following treatment of cells with neuraminidase, fucosidase, or aor 0-galactosidase. Treatment with trypsin significantly increased the susceptibility of MAT-B1 (14 ±3%) but not MAT-CI (5 ±2%). Following 1 month in culture, the sialomucin content of MAT-B1 cells dropped from 30% to 8% (determined by glucosamine labeling) and natural cell-mediated cytolysis increased to 16 ±4%, whereas the sialo mucin content and susceptibility of MAT-CI cells did not change. The results indicate that the relatively minor changes associated with removal of cell surface sialic acid or fucose residues do not result in increased susceptibility of the ascites cells to cytolysis. However, susceptibility of M VI-HI cells to lysis by normal rat spleen lymphocytes was inversely correlated with the amount of major glycoprotein (i = —0.96).