Monoclonal antibody At5 was primarily developed against chordin, a notochord-specific antigen of sturgeon fishes. In higher vertebrates the antibody reacted mainly with antigens of neural tissue. In this study the expression of At5 reactive antigens was examined in cultures of dissociated human and rat neural cells. The data presented here show that the antigens recognized by the monoclonal antibody At5 can be expressed by any of main cell types composing the neural tissue: the neurons,

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... es and oligodendrocytes. In situ immunohistochemical studies showed that the majority of human glial tumors investigated were labeled by the monoclonal antibody At5, contrary to meningiomas which did not exhibit the At5 immunoreactivity. In oligodendrogliomas and mixed oligoastrocytomas strong At5 immunoreactivity was observed in oligodendroglial cells whereas in an anaplastic astrocytoma At5 immunoreactivity was characteristic for spindle-like astrocytes with long processes but not for large protoplasmic astrocytes. We conclude here that the specificity of the monoclonal antibody At5 is similar to that of previously generated monoclonal antibody HNK-1 but is more restricted in some cases. Two At5 reactive antigens of very high molecular weight similar to those of human embryonic brain have been identified in an oligodendroglioma. Cells in culture have been always the useful tools for answering questions difficult to approach in the complex environment of normal and malignant tissues. Cultured cells are of particular importance in the case of neural tissue composed of several types of cells some of which are difficult to identify in 5T0 whom correspondence should be addressed at A. N.