Epitopes immunologically related to glycophorin A on human malignant and non-malignant cells in culture

Molecular and genetic analysis of disseminated neoplastic cells in lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a multisystem disorder of women, characterized by cystic degeneration of the lungs, renal angiomyolipomas (AML), and lymphatic abnormalities. LAM lesions result from the proliferation of benign-appearing, smooth muscle-like LAM cells, which are characterized by loss of heterozygosity (LOH) of one of the tuberous sclerosis complex (TSC) genes. LAM cells are believed to migrate among the involved organs. Because of the apparently metastatic behavior of LAM, we tried to isolate LAM cells from body fluids. A cell fraction separated by density gradient centrifugation from blood had TSC2 LOH in 33 of 60 (55%) LAM patients. Cells with TSC2 LOH were also found in urine from 11 of 14 (79%) patients with AML and in chylous fluid from 1 of 3 (33%) patients. Identification of LAM cells with TSC2 LOH in body fluids was not correlated with severity of lung disease or extrapulmonary involvement and was found in one patient after double lung transplantation. These studies are compatible with a multisite origin for LAM cells. They establish the existence of disseminated, potentially metastatic LAM cells through a relatively simple, noninvasive procedure that should be valuable for molecular and genetic studies of somatic mutations in LAM and perhaps other metastatic diseases.

Glycophorin A interacts with interleukin-2 and inhibits interleukin-2-dependent T-lymphocyte proliferation

Sialoglycolipids shed by tumor cells have been implicated in tumor-induced inhibition of T-lymphocyte responses to interleukin-2 (IL-2). In the present study, we have used glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, to investigate whether shedding of glycoproteins might also contribute to immunosuppression. Glycophorin A inhibited IL-2-stimulated proliferation of the IL-2-dependent cell lines HT-2 and CTLL-2 in a dose-dependent manner. Time course studies on synchronized cell populations indicated that the glycoprotein acted early in the activation process. On the other hand, glycophorin A had essentially no effect on IL-1-mediated stimulation of the IL-1-sensitive thymocyte cell line EL-4 NOB-1. Gel filtration FPLC demonstrated that IL-2 was able to bind to glycophorin aggregates under physiological conditions. Reconstituted vesicles containing glycophorin were also shown to bind IL-2. In addition, both soluble glycophorin aggregates and lipid vesicles containing glycophorin blocked binding of IL-2 to high-affinity cellular IL-2 receptors. Taken together, these results suggest that shedding of tumor sialoglycoproteins with oligosaccharide chains similar to glycophorin A might contribute to negative modulation of IL-2-mediated immune responses.

A major endothelial plasmalemmal sialoglycoprotein, gp60, is immunologically related to glycophorin

Glycophorins, the major sialoglycoproteins of red blood cells in many species, are generally considered to be specific to erythroid cells. Using polyclonal antibodies directed against mouse glycophorin (alpha gp), we have identified a glycoprotein antigenically related to glycophorin on the surface of bovine and rat cultured endothelial cells. Immunoblotting with alpha gp identified a single 60-kDa polypeptide on transfers of SDS/polyacrylamide gels of solubilized confluent endothelial monolayers. In addition, a 60-kDa polypeptide was immunoprecipitated by alpha gp from lysates of 125I-labeled intact endothelial cells. Controls with preimmune serum were negative. This antibody interaction was inhibited by murine erythrocyte ghosts and purified glycophorins. Our past work identified several endothelial surface sialoglycoproteins including a 60-kDa glycoprotein (gp60) that (i) interacts with albumin, (ii) binds Limax flavus, Ricinus communis, and Triticum vulgare agglutinins but not other lectins, (iii) is sequentially precipitated from 125I-labeled cell lysates by using R. communis agglutinin followed by T. vulgare agglutinin, and (iv) is sensitive to sialidase digestion. Immunoblotting of such precipitates with alpha gp demonstrates that lectins recognize the same glycoprotein, namely gp60. These results indicate that gp60, a major endothelial surface sialoglycoprotein, shares antigenic epitope(s) with glycophorin.

Detection of glycophorin A-like glycoproteins on the surface of cultured human cells

1. In previous studies we have isolated and characterized mucin-type glycopeptides from mouse and human melanoma cells. 2. These glycopeptides have clusters of oligosaccharides of the type (NeuNAc)0-2----[Gal----GalNAc] linked to serine and or threonine suggesting an apparent similarity to glycophorin. 3. We now report the interaction of polyclonal anti-glycophorin antibodies with various cultured cells. Antisera to highly purified glycophorin A were raised in rabbits. 4. Human melanoma cells (HM7), human breast cells (HBL-100) and two lines of human breast cancer cells (MCF-7 and MDA-MB-231) showed medium to very strong cell surface fluorescence pattern after staining with rabbit anti-glycophorin F(ab')2 and FITC-conjugated goat anti-rabbit F(ab')2. 5. Immunodiffusion, immunoelectrophoresis and affinity chromatography on anti-glycophorin IgG-Sepharose 4B of detergent extracts of metabolically labeled cultured cells gave further evidence for the presence of glycophorin-like components in these cells. 6. Glycoproteins of MCF-7 cells interacting with anti-glycophorin antibodies were affinity purified and partially characterized.

Monoclonal antibodies to cyanogen bromide fragments of glycophorin A

Eleven mouse monoclonal antibodies directed against epitopes on CNBr peptides of the major sialoglycoconjugate of the human red blood cell, glycophorin A, have been produced by hybridomas derived from P3-X63-Ag8.653 myeloma cells and spleen cells from BALB/c mice immunized with purified glycophorin. The monoclonal antibodies could be divided into four groups according to their reactivities with CNBr peptides in a direct ELISA assay: one antibody (6B5) that binds solely to the aminoterminal octapeptide (CNBr3); two antibodies (8F10 and 9C3) that bind to CNBrl (residues 9-81); two antibodies (3D2 and 4C6) that are reactive with CNBr2, The C-terminal portion of the molecule (residues 82-131); six antibodies (1B4, 4C3, 4E7, 7B10, 7C11 and 9D6) which are cross-reactive with an epitope on both CNBr1 and CNBR3 glycopeptides. This cross-reactive epitope(s) appears to involve both carbohydrate and protein residues.