Monoclonal antibodies (MAbs) directed to 2 neutral
glycolipids,
isoglobotetraosylceramide and a 6-sugar isogloboneolactoseries hybrid
glycolipid, previously shown to be enriched in rat
colorectal tumor tissue, were produced by immunization with purified
glycolipids. Four MAbs were selected which demonstrate 3 different specificity patterns when tested for binding to purified and crude preparations of neutral
glycolipids, cultured tumor cells and fibroblasts and frozen tissue sections. MAbs 14.2 and 14.10, but not 14.3, stained most epithelial
colorectal carcinomas, rat testis and a subpopulation of cells in the rat gastric mucosa. However, all 3 MAbs showed strong staining and binding to sections and cultured clones of the
cytokeratin-negative
tumor of colorectal origin, which was originally used for preparation of the
glycolipid immunogens. The observed difference between MAbs 14.2/10 and MAb 14.3 could not be explained by differences in binding to the 2 original
glycolipids used for screening. However, MAbs 14.2/10 were demonstrated to bind to high-molecular-weight
glycoprotein(s) (HMW-gp's) previously shown to carry determinants for syngeneic
antibodies and extracted from epithelial
colorectal tumor tissue after extensive
lipid extraction. This suggests that a
protein-bound
carbohydrate determinant, with similarities to the
oligosaccharide part of the isoglobo-series
glycolipids, is responsible for this cross-reactivity. The staining of rat testis could be explained by the strong expression in this tissue of
glycolipids with 8-10
sugar residues bound by the 14.2/10 but not 14.3 MAbs. The cell-surface expression of the 6-sugar hybrid
glycolipid was demonstrated by
complement-dependent cytotoxicity and immunofluorescent staining of viable cells.