| CD40, a 45-50kD membrane molecule, belongs to TNFR super-family. It is mainly expressed on mature B cells and can be involved in a variety of biological effects, such as cell proliferation, differentiation, germinal center development, Ig secretion and isotype switch , the up-regulation of cell molecules like CD80, CD86, CD95, ICAM-1 and the secretion of cytokines like IL-6, TNFα, LT and several chemokines. In addition, in the aspect of signal transduction, CD40 is similar to LMP1, one of the virus proteins expressed on B cells transformed by EBV. Furthermore, in the case of CD40 ligation, CD40 and LMP1 on the transformed cells can be recruited to lipid rafts to constitute a signalsome transducing signals. The ligand of CD40, CD40L, or CD154, a 39kD membrance molecule, belongs to TNF super family. CD40L is transiently expressed on antigen-activated CD4~+ T cells in the form of trimer. It can also be normally expressed on germinal center (GC) B cells or abnormally expressed on B cell-originated malignant cells. It is known to all that the maturation of B cells is dependent on the binding to CD40L transiently expressed on CD4~+ T cells within the GC, which promotes the ligation of CD40 on B cells and results in the survival, proliferation and differentiation of high-affinity, non-autorecreative B cells. CD40-CD40L interaction between B-T cells within the GC is able to refrain B cells from apoptosis. But, the number of T cells within the GC is limited and the expression of CD40L on GC B cells is transient. So, such a strict mechanism of selection leads to the survival of only a fraction of functional B cells, while the malignant or autoreactive B cells failing to bind to T cells are cleared out. However, many malignant cells can escape the selective mechanism within the GC and survive finally with a further proliferation, which draws great interests from people. In recentyears, more and more articles reported the fact that receptors and ligands could be co-expressed on the same cells, especially on malignant cells. In this way, the malignant cells can self-form autonomous signaling without external supports. It is possible that some carcinogenic factors like virus infection may result in the ectopic expressions or the up-regulation of such expressions, which can be involved in the mechanism of malignant cells escaping from apoptosis or the attack of immune cells. Furthermore, the exact effects of co-expression of receptors and ligands on malignant cells deserve us to explore.1. Effects of Epstein-Barr "Virus (EBV) infection on phenotype changes and biological characteristics of Multiple Myeloma (MM) cells Flow cytometry detection was carried out to analyze 10 cases of freshly isolated MM cells. The result showed the co-expression of CD40 and CD40L on No.2, 5, 9, 10 MM specimen cells, especially, the high co-expression on No.5, 10 specimens. Using EBV to infect MM cell line RPMI 8226 in vitro, we found that EBV could infect MM cells in vitro for the first time through the detection of LMP1 and EBNA-2 expression. EBV infection of RPMI8226 cells can up-regulate CD40 ligand on the level of both mRNA and protein, which could be involved in the anti-apoptosis function of the infected cells. In addition, the Confocal image showed two of CD40, CD40L and LMP1 molecules co-localized on infected cells. Furthermore, the chemokine receptor CXCR4 on RPMI8226 cells was up-regulated after EBV infection. And, in the presence of chemokine SDF-la, the ability of infected cells to migrate was improved. It is known to all, the ability to undergo anti-apoptosis and the ability to migrate are two important biological characteristics of malignant cells. In sum, it is possible that EBV, as one of the highly risky factors for MM, get involved in the origin and development of MM by transforming GC B cells to achieve anti-apoptosis function and by improving their ability to migrate from the GC to peripheral blood.2. The biological effects of co-expression of CD40 and CD40L on B lymphoma cells Two B lymphoma cell lines, Daudi and Raji, were chosen to make a further study. Flow cytometry detection revealed that CD40 and CD40 ligand were highly co-expressed on the two cell lines. Confocal microscope detection showed the co-localization of CD40 andCD40L on the membrane of Daudi or Raji cells. Antagnist antibody CD40mAb(3G3) or CD40LmAb(4Fl) established by our own institute was used to interdict CD40-CD40L signalling. Results showed that the antagonist antibody inhibited the growth, proliferation of lymphoma cells and induced their apoptosis in a dose-dependent manner with different cell lines. The conclusion was reached that the co-expression of CD40 and CD40L on Daudi or Raji cells contributed to the survival, growth, proliferation and the anti-apoptosis characteristics of malignant cells, providing a new target for the clinical application of immunotherapy to malignancies.
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