Histiocytic and dendritic reticulum cells in follicular structures of follicular lymphoma and reactive hyperplasia. A quantitative electron microscopical analysis.

Histiocytic reticulum cells (HRC) and dendritic reticulum cells (DRC) are integral parts of germinal centres. These cell types are also present in follicles of follicular lymphomas, the neoplastic analogues of physiological germinal centres. In this study the distribution and ultrastructural appearances of HRC and DRC present in normal germinal centres and in neoplastic follicles were established by means of morphometric methods. The number of HRC was significantly lower in malignant follicles than in their reactive counterparts. Quantitative analysis of the cytoplasm and phagolysosomes suggest that HRC are smaller and that their activity is lower in malignant follicles. DRC were present in smaller numbers in these structures, as measured by nuclear counts and their relative volume within the follicles. The ultrastructural features indicate that DRC in follicular lymphoma are functionally less active than in reactive lymph nodes. The possibility that differences between the reticulum cells from reactive and neoplastic follicles may be related to the absence of an immune reaction in malignant follicular lymphoma is discussed. The frequency and appearance of HRC and DRC are suitable as additional parameters to differentiate reactive secondary germinal centres from their malignant analogues.