Proliferation of non-Hodgkin-lymphoma lymphocytes in vitro is dependent upon follicular dendritic cell interactions.

Follicular dendritic cells (FDC) are located within the B-cell follicles of non-malignant lymphatic tissues and within non-Hodgkin-lymphomas (NHL) derived from the germinal centre or the mantlezone. The interactions between FDC and non-neoplastic B-cells have been extensively investigated but so far no data on functional studies with FDC isolated from lymphoma tissue are available. Using an enzyme cocktail to digest lymph nodes from patients with NHL followed by density centrifugation, single cell suspensions enriched in FDC and B-lymphocytes were obtained. In these preparations FDC formed small cellular clusters with an average of five neoplastic lymphocytes for every FDC. Immunocytochemistry with Ki67 revealed that after 24 h of culture 23.7% of the cells within the clusters were in late G1 to M phase. In contrast, only 10.2% of the lymphoma cells scattered outside the clusters were in these activated stages. As visualized by autoradiography, after 72 h of incubation the rate of proliferation was 16.8 times higher for the lymphoma cells involved in cluster formation as compared to those lymphocytes not associated with FDC. The data indicate that in vitro FDC from NHL lymph nodes form a microenvironment favourable for the activation and proliferation of lymphoma cells. The search for cytokines secreted by FDC in lymphoma tissue is under way.