A monoclonal antibody (mAb-5G) produced against a tumorigenic rat esophageal cell line, B2T, was shown to react specifically with a unique glycolipid antigen expressed on the cell surface of tumorigenic and certain non-tumorigenic, immortalized rat esophageal cell lines [Cancer Immunol Immunother 36: 94 (1993)]. In enzyme-linked immunosorbent assay experiments, mAb-5G reacted with crude lipid extracts prepared from B2T cells cultured in vitro, but showed very little reactivity with crude lipid extracts prepared from the same cell line passaged once in vivo, unless the antigen was separated from other lipid components by column or thin-layer chromatography (TLC). When a secondary tissue-culture cell line was established from the above B2T tumor tissues and serially subcultured in vitro, the percentage of positively stained cells was increased significantly in immunofluorescence assay. It was also demonstrated that the amount of extractable antigen was increased as the cells were subcultured in vitro up to passage 15, and stabilized thereafter. These results indicate the presence of certain lipid components in crude lipid extracts from B2T cells grown in vivo that are capable of interfering with antigen-antibody binding. On TLC plates, these interfering lipids were identified as phosphatidylcholine, phosphatidylserine, sphingomyelin and gangliosides. The interfering lipids did not bind the antibody, rather they appeared to interfere with antigen accessibility. These lipid substances may modify tumor cell surface antigen(s), thus protecting the tumor cells from host immune destruction.

A monoclonal antibody (mAb-5G) produced against a tumorigenic rat esophageal cell line, B2T, was shown to react specifically with a unique glycolipid antigen expressed on the cell surface of tumorigenic and certain non-tumorigenic, immortalized rat esophageal cell lines [Cancer Immunol Immunother 36: 94 (1993)]. In enzyme-linked immunosorbent assay experiments, mAb-5G reacted with crude lipid extracts prepared from B2T cells cultured in vitro, but showed very little reactivity with crude lipid extracts prepared from the same cell line passaged once in vivo, unless the antigen was separated from other lipid components by column or thin-layer chromatography (TLC). When a secondary tissue-culture cell line was established from the above B2T tumor tissues and serially subcultured in vitro, the percentage of positively stained cells was increased significantly in immunofluorescence assay. It was also demonstrated that the amount of extractable antigen was increased as the cells were subcultured in vitro up to passage 15, and stabilized thereafter. These results indicate the presence of certain lipid components in crude lipid extracts from B2T cells grown in vivo that are capable of interfering with antigen-antibody binding. On TLC plates, these interfering lipids were identified as phosphatidylcholine, phosphatidylserine, sphingomyelin and gangliosides. The interfering lipids did not bind the antibody, rather they appeared to interfere with antigen accessibility. These lipid substances may modify tumor cell surface antigen(s), thus protecting the tumor cells from host immune destruction.

A monoclonal antibody (mAb 5G) was produced against a tumorigenic rat esophageal epithelial cell line, designated B2T. Using an enzyme-linked immunosorbent assay, immunofluorescence assay (IFA), thin-layer chromatography (TLC) and immunoperoxidase staining, it was found that mAb 5G reacted specifically with a glycolipid antigen expressed by three tumorigenic rat esophageal epithelial cell lines, and two out of the three non-tumorigenic, immortalized rat esophageal epithelial cell lines tested; but did not react with primary cultures of normal rat esophageal epithelial cells or fibroblasts. mAb 5G did not bind to rat respiratory tract carcinoma cell lines, to immortalized rat tracheal epithelial cell lines, or to primary cultures of normal rat tracheal epithelial cells. In addition, mAb 5G did not react with any of the human or mouse cell lines tested. In IFA experiments, mAb 5G stained imprints prepared from in vivo propagated B2T tumor tissues, but did not react with normal rat esophageal, tracheal, lung, liver, and kidney tissues. The antigen was identified by TLC as a neutral glycolipid, consisting of two bands, with RF = 0.45 and 0.41, which migrated in proximity to the ceramide trihexoside standard on TLC plates. Densitometric scanning of the antigen bands indicated that the tumorigenic rat esophageal cell lines possessed 50%-90% more mAb-5G-reactive antigen than the non-tumorigenic esophageal cell lines. The results show that mAb 5G reacts specifically with a glycolipid antigen expressed by tumorigenic and certain non-tumorigenic, immortalized rat esophageal epithelial cell lines that might be at the late stages of transformation and early malignancy.