Abstract： Objective To determine the roles of MyD88 and Trif,critical adaptor proteins for TLR signaling,in production of donor-specific antibodies (DSA) and memory T cells in a presensitized mouse cardiac transplant model.Methods Skin grafts from Balb/c mice were transplanted into either wild type B6 mice or B6 Myd88 and Trif double knockout mice (Myd88/Trif DKO).The recipients were subsequently transplanted heterotopically with cardiac grafts from the same donors two weeks after skin transplantation.Plasma DSA levels and spleen phenotypical analysis were performed prior to heart transplant or at time of cardiac rejection by using flow cytometry.Results Recipients presensitized with skin grafts developed accelerated cardiac allograft rejection in the absence of Myd88 and Trif.However,plasma DSA,especially IgG2,was significantly decreased (P＜0.05) in Myd88/Trif DKO mice,compared to that in Wild Type mice at 2nd week after skin transplantation.The production of DSAs including all IgG subtypes was further reduced 3 days following heart transplantation in the Myd88/Trif DKO.In addition,MyD88/Trif DKO mice had impaired ability to generate memory T cells,as percentages of both CD44hi CD4+ and CD44hi CD8+ were significantly lower in the DKO than in Wild Type mice (P＜0.01,P＜0.05).Conclusion Simultaneous ablation of MyD88 and Trif in recipients significantly decreases the production of serum DSAs and spleen memory T cells following allogeneic skin and heart transplantation,supporting a crucial role of TLR signaling in adaptive immune responses in organ transplantation.