The surface antigens expressed by the cells of chronic lymphocytic leukemia (CLL) are well known. Most CLL are monoclonal B-cell lymphoproliferative disorders characterized by the coexpression of B-cell antigens and CD5, an antigen present predominantly on T cells. Very little attention, however, has been paid to the quantitative characteristics of the expression of B-cell antigens in CLL. In this study, we used flow cytometry to analyze the expression of CD20, a well-known B-cell-associated antigen, in lymphocytes from 42 cases of CLL and its tissue counterpart, small lymphocytic lymphoma (SLL), and compared the results with results obtained from the analysis of 21 follicular lymphomas, 20 hyperplastic reactive nodes, and 26 samples of normal peripheral blood. The intensity of CD20 expression in the CLL/SLL cells was significantly lower than that of B cells in the other categories. This antigen expression abnormality does not appear to be a universal phenomenon in CLL/SLL, since CD19, another pan-B antigen, was expressed in CLL/SLL at levels higher than those in follicular lymphomas and comparable to those in reactive lymph nodes. These results indicate that the low CD20 expression can be used as a marker for CLL/SLL. The few cases exhibiting intense CD20 expression may represent a biologically different disease. CLL/SLL cells faintly expressing CD20 also show concomitant low CD5 expression in a manner not observed in normal CD5-expressing B cells.

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Detection and accurate classification of lymphoid processes in fine-needle aspirate specimens can be a challenging task for the pathologist. Recognizing the usefulness of flow cytometric methods for the diagnosis of lymphoproliferative disorders (LPDs), the authors applied flow cytometric analysis to 38 tissue samples that had a possible diagnosis of LPD and to fine-needle aspiration-derived cytologic preparations. Four aspirations from each sample provided from .44 x 10(6) to more than 70 x 10(6) cells in total. The highest yields were associated with low-grade B-cell non-Hodgkin's lymphomas (NHLs). Washing cytologic preparation cell suspensions did not enhance diagnostic ability and dramatically reduced cell counts (average decrease, 79.8%), potentially problematic with small samples. Comparison of ploidy, S fraction, and immunophenotypic data from the cytologic preparations and cell suspensions made from the conventionally processed parent tissues indicates that cytologic preparation composition closely parallels the tissue of origin. A multiparametric flow cytometric technique used to enhance detection of B-cell clonal expansions allowed for successful recognition of 17 of 21 (81%) B-cell NHLs in cytologic preparations, with false-negative results primarily reflecting a lack of viable tumor cells in the cytologic preparation cell suspensions. A T-cell NHL and a nonhematopoietic malignancy were also identified in cytologic preparations. None of the benign conditions were interpreted as lymphoma. Flow cytometric techniques applied to fine-needle aspirates of lymphoid processes yield important diagnostic information, which may be maximized by adaptations in processing and flow cytometric analysis.