Distribution of VIM-2 and SSEA-1 glycoconjugate epitopes among human leukocytes and leukemia cells

Abstract

Anti-SSEA-1 which binds to glycoconjugates with a Gal beta 1-4(fuc alpha 1-3)GlcNAc epitope and VIM-2 which binds to gangliosides with a NeuAc alpha 2-3GlcNAc beta-4(FUC alpha 1-3) GlcNAc beta 1-3Gal-epitope were used to determine the expression of their corresponding carbohydrate antigens in human leukocytes and leukemia cells. Expression of these antigens was evaluated by immunohistochemical staining of plastic embedded sections of bone marrow or isolated cells, and by immunostaining of isolated glycosphingolipids separated by thin layer chromatography. The expression of both antigens was restricted to normal and leukemic myeloid cells. A range of positive immunohistochemical staining was found among normal marrow myeloid precursors, with myeloblasts giving weaker staining than more mature cells (promyelocytes, myelocytes, metamyelocytes). A similar trend was observed with leukemia cell lines, in that the myeloblastic cell line KG1 was weakly stained compared to the partially differentiated cell line HL-60. Immunohistochemical staining of marrows from acute leukemia patients showed that the VIM-2 antigen is more strongly expressed than the SSEA-1 antigen. Interestingly, both antibodies stained AMMoL cells more intensely than AML cells. Granulocytes from marrows of chronic myelogenous leukemia (CML) patients were intensely stained by both antibodies, whereas lymphocytic leukemias (acute lymphocytic, chronic lymphocytic and hairy cell marrows) were negative. Thus, although both antigens are restricted to myeloid cells there are differences in the level of expression depending on the level of cell maturity. Immunostaining of glycosphingolipids isolated from myeloid cells demonstrated that the SSEA-1 epitope is carried by several neutral glycosphingolipids and that the VIM-2 epitope is carried by three or more gangliosides. Major SSEA-1 glycosphingolipids, with seven to more than ten monosaccharides, are expressed by all myeloid cells regardless of the level of maturity, although quantitative differences are apparent in different patient samples. Two strongly immunoreactive VIM-2 gangliosides with ten and twelve monosaccharides, respectively were found in myeloid cells. The ratio of these two gangliosides varied dramatically, with greater amounts of the more complex ganglioside being present in most cell samples. Normal neutrophils and CML cells had much greater quantities of the VIM-2 gangliosides than acute leukemia cells. This observation correlates with our earlier findings that: (1) acute leukemia cells have less total ganglioside than granulocytes and (2) acute leukemia cells have a predominance of short chain gangliosides (i.e. less than five monosaccharide units). Finally, both CML cells and normal neutrophils express a shorter chain VIM-2 ganglioside, which was not detected in acute myelogenous leukemia cells.