IMMUNOCYTOCHEMICAL DIFFERENTIATION OF REACTIVE HYPERPLASIA FROM FOLLICULAR LYMPHOMA USING MONOCLONAL-ANTIBODIES TO CELL-SURFACE AND PROLIFERATION-RELATED MARKERS

We tested the hypothesis that a panel of antibodies to cell surface, c ytoplasmic, and nuclear antigens could reliably distinguish the cells composing reactive germinal centers from those composing follicular ly mphoma. Immunocytochemistry was performed on deparaffinized sections o f methacarn-fixed lymph node and tonsil (15 cases of reactive hyperpla sia and 14 cases of follicular lymphoma) using antibodies to the nerve growth factor receptor (NGFR5), bcl-2 protein (124), proliferating ce ll nuclear antigen (PCNA; 19A2), and CD45RA (MT2). In 100% of cases of reactive hyperplasia, both MT2 and 124 showed positive immunostaining of mantle zone and scattered interfollicular lymphocytes, but in all cases there was a sharply demarcated absence of immunostaining of germ inal center cells. However, diffuse immunostaining of follicular cente rs with MT2 (64%) and 124 (93%) and scattered intervening cells were s een in follicular lymphoma. The combination of antibodies to CD45RA an d bcl-2 yielded positive immunostaining of follicular center cells in 93% of follicular lymphomas. The germinal center cells of reactive hyp erplasia showed >75% nuclear positivity with antibodies to PCNA, in co ntrast to the follicular lymphoma cells, which showed variable PCNA in dices ranging from 25 to >75%. A minority of follicular lymphoma cases (29%) showed PCNA indices comparable with those seen in cases of reac tive hyperplasia. Antibodies to NGFR were positive in all cases of rea ctive hyperplasia and in 79% of cases of follicular hyperplasia, altho ugh the immunostaining intensity was generally decreased in follicular hyperplasia. In summary, antibodies to bcl-2 appear to be superior to those to CD45RA in distinguishing reactive hyperplasia from follicula r lymphoma. Reactive hyperplasia cannot be discriminated from follicul ar hyperplasia using antibodies to PCNA or to nerve growth factor rece ptor.