Cellular composition of follicles of follicle centre cell lymphomas in relation to germinal centres of reactive lymph nodes. A morphometrical electromicroscopical study.

The cell spectrum of neoplastic and benign reactive germinal centres was determined ultrastructurally. The degree in which the cell composition found in reactive germinal centres is maintained in analogous structures of follicular lymphomas was investigated by pattern recognition methods and discriminant analysis based on the frequencies of the various lymphoid and non-lymphoid cell types. The follicular lymphomas included lymphomas with predominantly centrocytes (FCCL, Cb-cc) and lymphomas with predominantly centroblasts (FCCL, Cb). Pattern analysis of FCCL Cb, FCCL Cb-cc and reactive germinal centres indicates that FCCL Cb follicles resemble reactive germinal centres in more aspects than follicles of FCCL Cb-cc. Clear statistical differences were encountered between the frequencies of the lymphoid cell types and of the follicular dendritic and histiocytic reticulum cells in follicles of FCCL Cb-cc and FCCL Cb and reactive germinal centres. Application of a discriminant analysis using a combination of the frequency of centrocytes and follicular dendritic cells demonstrated that both types of neoplastic follicles and reactive germinal centres were correctly classified on the basis of their cell spectrum. For the three groups the most potent discriminator was the centrocyte, whereas the small and large centroblast were of less value. For discrimination between Cb-cc follicles and reactive germinal centres again the centrocyte was the most potent discriminator. Discrimination between FCCL Cb follicles and reactive germinal centres of FCCL Cb-cc follicles can be easily achieved using the frequencies of small centroblasts or centrocytes on their own. These findings indicate that (1) follicles of both FCCL Cb and FCCl Cb-cc differ greatly in the cellular composition and not only with respect to their content of centroblasts but also in their content of follicular dendritic cells and (2) they may be considered as neoplasms representing different developmental phases of germinal centres.