PROLIFERATION CENTERS IN B-CELL MALIGNANT-LYMPHOMA, LYMPHOCYTIC (B-CLL) - AN IMMUNOPHENOTYPIC STUDY

Proliferation centres, also known as pseudofollicles, are present in approximately 90% of lymphocytic lymphomas (B-CLL). They consist of loosely arranged larger cells that often contain prominent nucleoli. In contrast to true B-cell follicles, which may be found entrapped within the small lymphocytic infiltrate in sections of B-CLL, proliferation centres are said not to contain follicular dendritic cells, although their presence has been occasionally recorded. We have carried out an immunohistochemical study of proliferation centres from 30 lymph node specimens of known cases of B-CLL, classified according to the Kiel classification, in six of which fresh frozen in addition to paraffin embedded tissue was available. We have compared proliferation centres with the surrounding small lymphocytic infiltrate and reactive B-cell follicles with respect to the presence of follicular dendritic cells and their associated network of IgM and complement, the cell proliferation fraction, the concentration of T-cells and the expression of bcl-2 protein. Most proliferation centres contained a delicate follicular dendritic cell network which was associated with IgM and complement, and showed a higher proliferation fraction than the surrounding small lymphocytic infiltrate. The proliferation centres contained more T-cells than the surrounding infiltrate and showed decreased expression of bcl-2 protein. Entrapped reactive B-cell follicles contained a much denser network of follicular dendritic cells, associated with much stronger expression of IgM and complement, and exhibited a very high proliferation fraction; they contained many T-cells and expressed very little bcl-2 protein. These results show that proliferation centres share many properties with reactive B-cell follicles and suggest that they may be centres of antigen driven proliferation.