Compelling evidence suggests that survival and proliferation of B-cell chronic lymphocytic leukemia (B-CLL) cells depend on a crosstalk with microenvironmental bystander cells and that the dynamic and interac- tive interplaying between tumor necrosis factor (TNF) superfamily mem- bers and their cognate receptors has a major role in this crosstalk. Death receptor (DR3) 3 is a member of the TNFR superfamily. Its ligand is TNF-like ligand 1A (TL1A), a member of the TNF superfamily. TL1A/DR3 interactions have been reported to modulate the functions of T cells, NK, and NKT cells and play a crucial role in driving inflamma- tory processes in several T-cell-dependent autoimmune diseases. Recent- ly, we showed that the TL1A/DR3 axis reduces B-cell proliferation induced by anti-IgM and IL-2. The objective of this study was to ana- lyze DR3expression and its possible effects on B-CLL proliferation and apoptosis. To this aim, first peripheral blood B cells and lymph node specimens from 35 B-CLL patients were analyzed for the expression of DR3 by flow cytometry, western blotting and immunofluorescence. Flow cytometry analysis showed that, similarly to healthy B cells, B- CLL did not express DR3 in basal conditions, whereas stimulation of B cell receptor (BCR) with anti-IgM antibodies induced significant de novo expression of DR3 in B-CLL (p<0.001). These data were confirmed by western blotting analysis. The relevance of these results were further val- idated by immunofluorescence analysis in lymph node specimens that showed the in situ expression of DR3 in antigen-stimulated B-CLL cells in vivo. Then, we analyzed proliferation and apoptosis in B-CLL cells stimulated with anti-IgM, IL-2, CpG, or CD40L (or a combination of them), in presence or absence of TL1A. Among these stimuli, only the combination of CpG with suboptimal dose of anti-IgM is able to induce proliferation of B-CLL. Remarkably, TL1A reduces B-CLL proliferation induced by anti-IgM antibodies and CpG., whereas no effects of TL1A were detected in the presence of anti-IgM in combination with IL-2, or CD40L. This study describes for the first time the expression of DR3 molecules in B-CLL cells and reveals a novel role of the TL1A/DR3 func- tional axis in modulating leukemic proliferation in vitro. These data sug- gests that TL1A/DR3 may modulate cell crosstalk in the B-CLL microen- vironment in vivo, therefore contributing to B-CLL pathogenesis and pro- gression.
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