A monoclonal antibody termed 'FR77' was obtained from a hybridoma clone established by fusion between P3x63Ag8.653 mouse myeloma cells and spleen cells of a Fischer F344 rat hyperimmune to syngeneic 9L/R3 glioma cells. Immunoperoxidase staining of various cultured cells showed that FR77 was reactive to both rat and human glioma cells, but was not reactive with other nonglioma cells. Immunohistochemical examination of paraffin-embedded or cryostat-frozen sections of various human tissues revealed that FR77 was strongly reactive with glioblastoma, grade III astrocytoma, and craniopharyngioma; partially reactive with intracerebral primitive neuroectodermal tumor, pineoblastoma, and desmoplastic medulloblastoma; and weakly reactive with low-grade astrocytoma. It was not reactive with other types of brain tumors and normal human tissues tested. The FR77-defined antigen was observed to be predominantly localized in the cytoplasm of antigen-bearing cells as suggested by the immunostaining pattern, but part of it was also expressed on the cell surface of glioma cells as demonstrated by a complement-mediated cytotoxic test. Fractionation of the antigenic component and periodic acid treatment of tumor tissue bearing the FR77-defined antigen indicated that the antigen is of a neutral glycolipid nature and that the antigenic determinant to FR77 is present on its sugar portion.
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