| CD40, a 48KD cell membrane molecule, is a type I glycoprotein, encoded by a gene located at 20ql l-2g!3-2, and belongs to the tumor necrosis factor receptor (TNFR) superfamily. CD40 is expressed in many cell types including B cells, dendritic cells, monocytes, endothelial cells, epithelial cells and also many carcinoma cells. CD40 ligand, also named gp39, is expressed mainly in activated CD4+ T helper cells. Interaction by CD40L-CD40 is a main costimulatory signal during antigen- specific immune response and during its regulation. To date, an increasing number of studies indicate that signals mediated by CD40 will lead to B cell proliferation, Ig secreti'on and its class switch; dendritic cell activation and maturation; adhesion molecules expression on endothelial cells, inflammatory factors secretion, and the accumulation of white cells to the inflammatory sites. These indicate CD40 is a very important molecule during immune response.In this study, XG2, a cell line that expresses CD40 strongly, was used to immunize Balb/C mice. The immunized murine splenocyte cells were fused with Sp2/0 or X63 murine myeloma cells; monoclonal antibody screening, immunofluorescence , western blot and competition tests were used and two hybridoma cell lines, 2G11 and 5C11 respectively, which secrete mouse anti-human-CD40 mAbs were obtained.The behavior of human tonsil B cells was observed in a culture system with agonistic anti-CD40 mAb 5C11 and CD32 transfected L (LCD32) cells, containing also IL-4 and other cytokines. The results showed that the combination of 5C11, LCD32 and IL-4permitted resting tonsil B cells to survive and their long-term proliferate in vitro. The CD40 system is an essential tool for the study of B cells.Dendritic cells are the most efficient professional antigen-presenting cells (APC), on which CD40 is expressed throughout DC development, differentiation, maturation and commitment to function. Ligation of CD40 leads DC progenitors to differentiate and mature into DCS, secrecte cytokines and thus enhance stimulation of T cells by DCs. Our study was the first to show that mAb 5C1 1 can trigger the generation, proliferation and maturation of dendritic cells from peripheral blood monocytes, either by itself or in combination with GM-CSF and IL-4.Based on these studies, we further studied the expression of CD40 in malignant B cells particularly focused on B lymphoma cell lines and myeloma cell lines, we also studied the behavior of the malignant B cells after their CD40 activation, and the results are as following:1 ) Sensitization of multiple myeloma and B lymphoma lines to dexamethasone andy-radiation-induced apoptosis by CD40 activationB-cell malignancies, such as chronic lymphocytic leukemia (CLL), malignant Blymphoma and multiple myeloma (MM), commonly present with advanced disease and multiple sites of organ involvement. With the significant advances in chemotherapy and radiotherapy, about 60-70% of patients suffering from these diseases achieve complete remission (CR). However, in many cases residual tumor cells showing drug and/or radiation resistance causes a recrudescence of the disease. Development of novel therapies is required therefore, to block the proliferation of the residual tumor cells.In this study, we examined the effects of dexamethasone(Dex), 60Co-y-irradiation and of CD40 activation on the growth of malignant B cells in vitro, using the human multiple myeloma cell line, XG2, and the B lymphoma Daudi cell line as models. Both lines are resistant to Dex and irradiation; 10"7M dexamethasone or 10 Gy of y- irradiation induced only minimal growth arrest and apoptosis of the cells. Treatment of the cells with the agonistic anti-CD40 monoclonal antibody 5C1 1 partially inhibited the proliferation of the Daudi cells; XG2 underwent apoptosis. XG2 is an IL-6-dependent myeloma cell line andCD40 activation blocked XG2 in the Gl phase of the cell cycle, in a manner similar to the effect of IL-6 deprivation. Daudi was blocked in the G2/M phase after treatment wit...
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