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Immunohistochemical analysis of infiltrating lymphocytes in central nervous system tumors.

To investigate cell-mediated immune responses to central nervous system tumors, we immunohistochemically analyzed 32 operative specimens, including 19 primary tumors, 5 recurrent tumors, and 8 metastases, for the presence of infiltrating T lymphocytes. In 1 patient, an additional sample of normal brain was studied. Using monoclonal antibodies against T lymphocyte surface markers with a peroxidase technique on frozen sections, we determined that a mild lymphocytic response was present in 3 of 7 primary glial tumors, 1 of 4 recurrent glial tumors, and in 3 of 9 primary meningiomas. The predominant subset was Leu 2, or suppressor/cytotoxic. In contrast, 5 of 7 intracranial metastatic tumors and 1 extracranial metastasis showed marked infiltration with an overall Leu 3, or helper/inducer, predominance. The remainder of the specimens, including 1 recurrent meningioma, 3 neurinomas, and the normal brain sample, were free of infiltrates. Permanent sections revealed an overall pattern of lymphocytic infiltration similar to that of frozen sections. Although additional studies such as electron microscopy are required to establish definitively the lymphocytic nature of the infiltrates, these results support the concept of the ability of the body to mount a cell-mediated response against central nervous system tumors and imply a differential response to primary and secondary tumors.