Immunological inhibition of transplanted liver allografts by adeno-associated virus vector encoding CTLA4Ig in rats

BACKGROUND: Blockade interaction between CD28 and B7 with CTLA4Ig has been shown to induce experimental transplantation tolerance. In order to prolong the inhibitory effect of CTLA4Ig, a recombinant adeno-associated virus vector pSNAV expressing CTLA4Ig was constructed, and its effects on transplanted liver allografts were investigated. METHODS: The pSNAV-CTLA4Ig construct was infused into partial liver allografts of rats via the portal vein during transplantation. CTLA4Ig expression in the transplanted livers was detected with reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and immunohistochemistry. Furthermore, real-time quantitative PCR was used to measure the expression of IL-2, IFN-gamma, IL-4 and IL-10 in the allografts. RESULTS: The expression of CTLA4Ig in the partial allograft was detected successfully and pSNAV-CTLA4Ig improved the survival rate of rats after liver transplantation. Agarose gel analysis of RT-PCR products indicated the presence of CTLA4Ig in the pSNAV-CTLA4Ig treatment group. Cytokines expressed in allografts on day 7 after orthotopic liver transplantation showed that IL-2, IFN-gamma, IL-4 and IL-10 mRNA levels decreased in transplant recipients treated with pSNAV-CTLA4Ig compared with those treated with pSNAV-LacZ (1.62 +/- 0.09,1.52 +/- 0.11,1.50 +/- 0.07 and 1.43 +/- 0.07 versus 1.29 +/- 0.09, 1.32 +/- 0.07, 1.34 +/- 0.06 and 1.35 +/- 0.04, respectively). CONCLUSIONS: pSNAV-CTLA4Ig effectively expressed CTLA4Ig in liver allografts. CTLA4Ig improved the pathological findings after liver transplantation. CTLA4Ig induced immune tolerance of liver transplantation, and the mechanism involved induced alteration of Th1 and Th2 cytokine transcripts. The adeno-associated virus vector encoding CTLA4Ig may be useful in the clinical study of transplantation tolerance.

Expression of iNOS in early injury in a rat model of small-for-size liver transplantation

BACKGROUND: Living donor liver transplantation has been widely accepted as the treatment of choice for end-stage liver disease. Large amounts of nitric oxide generated by inducible nitric oxide synthase (iNOS) have been shown to play an important role in many inflammatory and immune reactions, but expression of iNOS in small-for-size liver transplantation is unknown. The aims of this study were to determine the time course of iNOS mRNA and protein as well as the redox state of liver biopsies in a rat model of small-for-size liver transplantation. METHODS: Male Sprague-Dawley rats were divided into a control group, a warm ischemia-reperfusion (IR) group, and a small-for-size liver graft group. Real-time RT-PCR and Western blotting were used to characterize the time course of the expression of iNOS mRNA and protein, respectively. Malondialdehyde (MDA) and superoxide dismutase (SOD) were used as markers to characterize the redox state of liver tissues, and the time courses of MDA and SOD levels were also measured. RESULTS: The expression of iNOS mRNA and protein levels in the warm IR and small-for-size graft groups both significantly increased after reperfusion, and peaked at 3 hours. Moreover, the increase in MDA was accompanied by increased iNOS in the period of 1-24 hours after reperfusion. The MDA levels in the warm IR and small-for-size graft groups significantly increased after reperfusion, peaked at 3 hours, and decreased thereafter. The direction of change in SOD was opposite that of the change in MDA. CONCLUSIONS: The expression of iNOS mRNA and protein is activated after reperfusion both in hepatic warm IR injury and small-for-size liver graft. Furthermore, the results of this study suggest that iNOS contributes to the damage in warm IR injury and small-for-size grafts via free oxygen radicals.

Methylprednisolone inhibits activated CD4^+ T cell survival promoted by toll-like receptor ligands

BACKGROUND: Methylprednisolone (MP) can affect the survival of CD4(+) T lymphocytes and plays an important role in adaptive immune responses; however, its mechanism of action is not clear. Recent studies have shown that toll-like receptors (TLRs) on CD4(+) T cells can directly modulate adaptive immune responses by affecting the survival and proliferation of activated CD4(+) T cells. This study aimed to investigate the relationship between MP, TLRs and activated CD4(+) T cells. METHODS: We separated and purified CD4(+) T cells from mice, activated them in vitro, and co-cultured them with TLR ligands, MP or inhibitors of nuclear factor-kappa B (NF-kappa B) and activator protein 1 (AP-1). We then assessed CD4(+) T cell survival and proliferation and the expression of NF-kappa B and AP-1. RESULTS: Activated CD4(+) T cells showed increased TLR-3 and TLR-9 mRNA expression, but polyinosinic-polycytidylic acid (poly I:C) and MP had no effect on the expression of these mRNAs. Still, poly I:C and CpG oligodeoxynucleotides (CpG DNA) increased the survival of activated CD4(+) T cells, whereas MP reduced the survival of activated CD4(+) T cells and could inhibit the survival effects of poly I:C and CpG DNA. The NF-kappa B essential modifier-binding domain (NBD) inhibited the survival of activated CD4(+) T cells induced by poly I:C and CpG DNA, but the AP-1 inhibitor crucumin did not have the same effect. The increased expression of NF-kappa B induced by poly I:C and CpG DNA in activated CD4(+) T cells could be inhibited by MP, but the same was not true for the increased expression of AP-1 induced by poly I:C and CpG DNA. Finally, the proliferation of activated CD4(+) T cells was not affected by poly I:C or MP. CONCLUSION: The survival of activated CD4(+) T cells is promoted by TLR ligands, but this effect is inhibited by MP.