Contribution of DRC-1 and Leu-M5 to Differential Diagnosis in B Cell Lymphomas

Dr. Wolfgang Eisterer, Department of Internal Medicine, University of Innsbruck, A-6020 Innsbruck (Austria) An article recently published in this journal [1] discussed the immunohistochemical characteristics of various low-grade non-Hodgkin’s lymphomas. From the investigation of 22 cases, the authors concluded that monocytoid B cell lymphoma, mantle zone lymphoma, small lymphocytic lymphoma and hairy cell leukemia (HCL) can be differentiated by a combination of anti-sIgD, DRC-1, Leu-1 and Leu-M5. We investigated bone marrow biopsies from 260 patients with lymphoproliferative disorders using an immunoperoxidase method on cryostat sections [2, 3]. Our data are in agreement with theirs, especially concerning the fact that the monoclonal antibody (MoAb) Leu-M5 (CDllc) is expressed in HCL in up to 100% of the cases. However, our data (table 1) differ from theirs as we detected Leu-M5 in 16/27 patients with chronic lymphocytic leukemia of the B-cell type (BCLL) and in 7/12 immunocytoma (LP-IC) patients, which confirms previously published data [4]. In addition to the immuno-histological analysis, 42 cases of B-NHL (15 B-CLL, 12 LP-IC, 1 CC, 14 HCL) were also investigated by flow cytometry in order to detect coexpression of LeuM5 with the malignant clone. In 69% (29/42) of these cases, a Leu-M5 coexpression of weak intensity was seen. A network of follicular dendritic cells (DRC-1+) was not only demonstrated in centrocytic NHL [CC (7/8)] and centroblas-tic/centrocytic NHL [CB/CC (4/4)], but also in 32/147 B-CLL and 17/87 LP-IC patients. In B-CLL, DRC-1 positivity was mainly found in association with a nodular pattern of bone marrow infiltration as described by others [5], whereas no such correlation was seen in LP-IC. Furthermore, the authors did not mention MoAb B-Ly7, which has proved exceptionally useful in discriminating HCL from other NHLs [6], also allowing detection of minimal residual disease. We agree with the authors that immuno-histology represents an important diagnostic tool for the classification of low-grade non-Hodgkin’s lymphomas, although MoAbs DRC-1 and Leu-M5 seem to be of minor diagnostic value. Table 1. Immunological phenotype of B-CLL, LP-IC, CC, CB/CC and HCL MoAb B-CLL LP-IC CC CB/CC HCL DRC-1 32/147 17/87 7/8 4/4 0/14 Leu-M5 16/27 7/12 0/1 n.d. 14/14