Isolation, purification, and characterization of a mouse plasmacytoma cell surface glycoprotein involved in the resistance of the tumor cells to immune destruction

Cells of a subline of the mouse plasmacytoma LPC-1 are resistant to lysis by cytotoxic T-lymphocytes, probably as a result of the blocking of the major histocompatibility gene complex-encoded cell surface antigens by a trypsin-sensitive glycoprotein of approximately 160 kilodaltons. The glycoprotein (gp160) was extracted from LPC-1 cells with 1.5 M urea and was further purified by ammonium sulfate precipitation with Sephacryl S-300 gel filtration. The gp160 consists of a single peptide chain rich in sialic acid residues (10% of total molecular weight) and has an acidic isoelectric point. The amino acid composition of gp160 is compatible with the linkage of carbohydrates (galactose, glucosamine, and sialic acid) to the protein portion. The apparent weak attachment of gp160 to the cell membrane could explain the finding that LPC-1 cells easily revert from the resistant to the sensitive to the immune lysis phenotype.