Human glioma-mesenchymal extracellular matrix antigen defined by monoclonal antibody

The distribution and localization of a glioma-associated antigen defined by monoclonal antibody 81C6 has been examined using human cultured cell lines and tissues. Monoclonal antibody 81C6 was selected from a hybridoma fusion of spleen cells of mice immunized with the glial fibrillary acidic protein-positive human glioma cell line U-251 MG. Results of cell surface radioimmunoassay and absorption analysis demonstrated that 81C6 defined a glioma-mesenchymal extracellular matrix (GMEM) antigen expressed by 14 of 16 gliomas, 1 of 3 neuroblastomas, 1 of 7 melanomas, 2 of 6 sarcoma cell lines, and 8 of 9 cultured fibroblast lines. GMEM was not expressed by carcinoma or by the myeloid-lymphoid cell lines examined. Within the central nervous system, GMEM was expressed in 10 of 11 glioblastomas but was undetected in 5 of 6 astrocytomas and in normal adult and fetal brain by peroxidase-antiperoxidase immunohistology. In glioblastomas, the GMEM antigen was localized to basement membranes of the distinctive glomeruloid endothelial proliferations and hyperplastic blood vessels. The GMEM antigen was also expressed in 3 of 3 glioblastoma cell lines and 6 of 8 glioblastoma biopsy xenografts in athymic nude mice. Among non-central nervous system tissues and tumors, GMEM was found by peroxidase-antiperoxidase immunohistology in normal liver sinusoids, spleen red pulp sinusoids, kidney medullary tubule interstitium, and glomerular mesangium and in association with vascular and stromal elements of several undifferentiated tumors. The GMEM antigen is distinct from previously described forms of fibronectin, laminin, collagen types I to V, hyaluronic acid, chondroitin sulfate, and heparin, as determined by absorption analysis and immunohistological localization in tissues. The expression of GMEM in glioblastoma but not normal brain, association with glioblastoma-proliferative endothelium basement membranes, and expression in glioblastoma cell lines and nude mouse xenografts suggest that GMEM may be a useful marker of gliomas in vivo and in vitro.