T-Cell Clustering in Neoplastic Follicles of Follicular Lymphoma

The nonneoplastic microenvironment is abundant in follicular lymphoma. Its composition has been reported to be associated with the course of the disease. Lack of animal models hampers studies of interaction between lymphoma and bystander cells. We aimed to identify indicators of cellular interaction exemplified by nonrandom distribution of cell types within neoplastic follicles. Physiological germinal centers and follicles in follicular lymphoma were stained to identify macrophages, all T, follicular T-helper, dendritic and B cells. Density of cell types and cell distribution (spatial point pattern) were analyzed by digital image analysis. The density of all T, follicular T-helper and dendritic cells was higher in the dark zone than in the light zone of physiological germinal centers. Densities of cell types in follicular lymphoma were intermediate between the light and the dark zone. All cell types analyzed showed a completely random spatial distribution pattern within the dark and the light zone, respectively. In follicular lymphoma B cells and macrophages displayed complete spatial randomness. In contrast, all T cells, follicular T-helper cells and dendritic cells showed clustering of each individual cell type within a radius of 6-10 μm in the lymphoma. We conclude that the distribution of nonneoplastic cells within follicles of follicular lymphoma is not random. T cells and dendritic cells form clusters within the follicles, suggestive of sites of interaction between microenvironment and lymphoma cells. These clusters might help to understand the interaction of lymphoma cells with the microenvironment and might provide a structure for therapeutic intervention.