A histogenesis of medium-sized B cell lymphoma. Immunohistochemical and genotypic (bcl-1 and bcl-2 gene) study.

Immunohistochemical and genotypic (bcl-1 and bcl-2 gene) studies were performed on 43 cases with B cell lymphoma to clarify the histogenesis of mediumsized B cell lymphoma of follicular lymphoma, medium-sized cell type and of diffuse lymphoma, medium-sized cell type.The cases examined were classified according to LSG classification; 26 cases of diffuse lymphoma, medium-sized cell type (DL-medium), 8 cases of follicular lymphoma, medium-sized cell type (FL-medium), 7 cases of FL, mixed type (FL-mixed), and 2 cases of FL, large cell type (FL-large).Southern blotting analysis revealed that rearranged band of bcl-1 gene were observed in 6 cases (23%) of DL-medium, whereas no rearrangement was found in FL cases. Immunohistochemically, 22 cases (85%) expressed at least one of alkaline phosphatase (ALPase), sIgD and CD5, which are thought to be characteristic of mantle zone lymphocyte (MZL) of secondary follicles. In addition, among 6 cases with bcl-1 gene rearrangement, 5 cases (83%) showed CD5 expression. In contrast, bcl-2 gene rearranged band, using major breakpoint region probe were detected in 6 cases of FL (36%; 3 cases of FL-medium and 3 cases of FL-mixed), whereas all cases of DL-medium were in germline configuration. Five cases (83%) among 6 cases with bcl-2 gene rearrangement expressed CD10, which is characteristic of follicular center cell (FCC). The correlation between CD10 expression and bcl-2 gene rearrangement was statistically significant (p<0.05%) in follicular lymphomas. The genetic data support that DL-medium B cell lymphomas with a phenotype of MZL are of primary follicle or MZL of secondary follicle origin. In addition, there is a close correlation between CD10 expression and bcl-2 gene rearrangement.In conclusion, the histogenesis of DL-medium and FL-medium are not only immunohistochemically but also genotypically distinguishable by their configuration of bcl-1 and bcl-2 gene rearrangement.