Immunohistologic characterization of two malignant lymphomas of germinal center type (centroblastic/centrocytic and centrocytic) with monoclonal antibodies. Follicular and diffuse lymphomas of small-cleaved-cell type are related but distinct entities.

The relationship between follicular lymphomas and diffuse lymphomas of small-cleaved-cell type was investigated with the use of a panel of antibodies against B-cell differentiation antigens. Follicular lymphomas, regardless of histologic subtype, were immunologically homogeneous: Ig+ B1+ B2+ CALLA+ Ia+. Two cases were Ig-negative, and 4 were CALLA-negative. Diffuse small-cleaved-cell (centrocytic) lymphomas were more heterogeneous. The majority were Ig+ B1+ B2+ Ia+ T1+ CALLA-. A minority were B2-negative, T1-negative, or CALLA-positive. An increased frequency of Ig heavy chain class switching and loss of T1 antigen suggest that follicular lymphomas are at a later stage of differentiation than most centrocytic lymphomas. The differences in immunologic phenotype provide further justification for a classification that distinguishes between follicular and diffuse lymphomas of small-cleaved-cell types. The expression of Ig, Ia, B1, and B2 on neoplastic follicular center cells correlates with expression of these antigens on normal B cells. In addition, anti-B2 appears to stain a nonlymphoid dendritic cell present in normal germinal centers and in both follicular and diffuse germinal center cell lymphomas in this study. In follicular lymphomas, the dendritic pattern was similar to that of normal follicles, while in centrocytic lymphomas a more irregular dendritic pattern was seen. Dendritic staining was seen in both nodal and extranodal lymphomas, suggesting that these nonlymphoid cells either migrate with neoplastic B cells or are present in a variety of normal tissues.