The islet primary nonfunction (PNF) is a serious problem in islet transplantation. In this study, we investigated whether DcR3-secreting transgenic (Tg) islets could reduce PNF. We generated Tg mice expressing human DcR3. The transgenically expressed DcR3 protected islets from IFN-gamma plus IL-1beta- or TNF-alpha plus IL-1beta-induced dysfunction and apoptosis in vitro. The Tg islets presented significantly reduced PNF after transplantation. Mechanistically, in addition to the known FasL apoptotic pathway, components of two other apoptosis pathways, that is, HVEM/LTbetaR for the LIGHT pathway and DR3 for the TL1A pathway, were found to be expressed in islets. Recombinant LIGHT- and TL1A-induced islet apoptosis in the absence of the FasL/Fas pathway, as well as DcR3, could block such induction. These results for the first time demonstrated that LIGHT and TL1A were capable of inducing islet apoptosis in addition to FasL, while DcR3 protected the islets by blocking all three apoptosis pathways. By DNA microarray analysis, we discovered that Adcyap was up-regulated >700-fold and Bank1 was down-regulated 50-fold in the cytokine-assaulted Tg islets, compared with WT islets. Forced overexpression of Adcyap1 by plasmid transfection or knockdown of Bank1 expression by small interfering RNA in insulinoma NIT-1 cells protected them from cytokine-triggered apoptosis, indicating that indeed DcR3 protects beta cells via the action of these two downstream molecules. This study has revealed novel mechanisms by which DcR3 protects islet survival, and it has identified new therapeutic targets of diabetes.