Interleukin-4 may contribute to the abundant T-cell reaction and paucity of neoplastic B cells in T-cell-rich B-cell lymphomas.

T-cell-rich B-cell lymphomas (TCRBCLs) are diffuse lymphomas that contain a minority of large neoplastic B cells amidst a majority of non-neoplastic T cells and numerous histiocytes, an unusually pronounced reactive component not seen in most diffuse large B-cell lymphomas (DLBCLs). This reaction may be influenced by various cytokines secreted by lymphoma or reactive cells; therefore, expression of interleukin (IL)-1 beta, IL-2, IL-4, IL-6, and IL-9 was evaluated immunohistochemically on paraffin-embedded sections of 18 TCRBCLs and was compared with that of 15 DLBCLs containing a minority of reactive T cells and to that of seven reactive lymph nodes. Moderate to intense expression of IL-4 was detected in variable numbers of tumor cells and in numerous histiocytes in 16 TCRBCLs. In contrast, intense IL-4 expression in numerous histiocytes was observed in only one of 15 DLBCLs with few T cells. In four other DLBCLs and three reactive nodes, moderate to intense staining for IL-4 was noted only in rare large transformed cells or in occasional histiocytes. Except for one IL-1 beta positive and another IL-9 positive TCRBCL, there was no marking or weak staining only with other cytokine antibodies in the neoplastic and reactive cases studied. The expression of IL-4 in most TCRBCLs, but not in other DLBCLs or in reactive nodes, suggests that this cytokine is one factor involved in the pathobiology of the abundant T-cell reaction and, perhaps, contributes to the paucity of neoplastic B cells in TCRBCLs.