An immunohistochemical analysis of T cells in primary B cell malignant lymphoma of the brain.

An immunohistochemical study was performed on small lymphoid cells present in frozen tissue sections of seven cases of primary B cell malignant lymphomas of the brain by using monoclonal antibodies to T cell (Leu-1, OKT-11, Leu-3a, and Leu-2a) and B cell (BA-1 and Leu-12) surface markers. In all the seven cases, positive reaction for Leu-1 and OKT-11 was seen in the majority of the small lymphoid cells which were dispersed among the lymphoma cells or clustered around blood vessels. The large neoplastic cells were unstained by these antibodies. Staining for T cell subsets with antibodies to Leu-3a and Leu-2a showed heterogeneous staining in each case. The ratio of Leu-3a+ to Leu-2a+ cells was less than one in six cases, demonstrating a suppressor/cytotoxic phenotype predominance. Most of these small lymphoid cells were negatively stained by antibodies to BA-1 and Leu-12. From these findings, it was shown that the small lymphoid cells observed in primary B cell lymphomas of the brain were of T cell lineage, distinct from the neoplastic cells, and probably reactive in nature. The implications of these findings are discussed.