Expression of the activation antigen, 4F2, by non‐Hodgkin's lymphomas of B‐cell phenotype

The monoclonal antibody, 4F2, which reacts with an antigen expressed by activated and proliferating cells, was applied to frozen sections of nine reactive lymphoid lesions, 146 B‐cell non‐Hodgkin's lymphomas (NHL), and six plasmacytic neoplasms. In reactive cases, the 4F2 antigen was expressed by germinal center cells and interfollicular immunoblasts, the activated or proliferating lymphoid cells, and histiocytes. In the malignant cases, the 4F2 antigen was expressed by 94 (64%) B‐cell NHL and all six plasma cell tumors. The incidence of positivity and intensity of expression loosely correlated with the three morphologic grades of NHL identified in the Working Formulation. Approximately one half of all low‐grade lymphomas, two thirds of intermediate‐grade lymphomas, and all high‐grade lymphomas were 4F2 positive. Similarly, the mean intensity of 4F2 antigen expression increased with higher grade. However, for certain histologic subtypes, 4F2 antigen expression did not correlate with morphologic grade. For example, in the intermediate‐grade category less than one half of diffuse small cleaved cell lymphomas were 4F2 positive, and expression was weak, similar to that of lowgrade lymphomas. In contrast, all other histologic subtypes of lymphoma in the intermediate‐grade category were strongly 4F2 positive. Expression of 4F2 antigen also correlated with plasmacytoid differentiation. Seventy‐three percent of plasmacytoid small lymphocytic lymphomas (compared with 31% of cases of nonplasmacytoid small lymphocytic lymphoma/chronic lymplocytic leukemia) and all plasma cell neoplasms expressed the 4F2 antigen, the latter cases strongly.