Follicular dendritic cells (FDCs) are located in primary and secondary follicles. They play an important role to trap antigen and to retain immune complexes on the surface, and have closely related to differentiation and proliferation of B cells. However, the relationship between FDCs and neoplastic cells still remains unclear. To clarify it, particularly distribution and immunophenotypes of FDCs in neoplastic lesions, we examined immunohistochemically 27 cases of follicular lymphoma (FL) and

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... 9 cases of diffuse lymphoma (111 cases of B cell lymphoma (B-DL) and 48 cases of T cell lymphoma (T-DL)). FDCs in FL-medium were distributed with well-defined and densely nodular network -pattern corresponding to neoplastic follicles . The distribution of FDCs showed more sparsely network-pattern in FL-mixed and FL-large, particularly showing partially follicular growth pattern than in FL-medium. Therefore, FDCs may be closely related to progression of FL into diffuse lymphoma. Eighty-seven cases with diffuse lymphomas showed FDC-network; 64 cases (39 of B-DL and 25 of T-DL) showed small nodular network-pattern corresponding to residual follicles, 23 cases (17 of B-DL and 6 of T-DL) showed well-developed irregular network-pattern in the neoplastic lesions. In the latter cases FDCs may be induced by neoplastic B or T cells, respectively. FDCs in some cases of DL were negative for CD23. This finding suggests that FDCs in these neoplastic condition may differ as to function. -27-