Intraportal donor bone marrow transplantation improves intestinal allograft survival in rats under FK506-based immunosuppression

Involvement of prostaglandin receptors (EPR2–4) in in vivo immunosuppression of PGE2 in rat skin transplant model

BACKGROUND

Prostaglandin E2 (PGE2) is known to modulate immune responses and is widely viewed as a general immunosuppressant. There have been recognized four receptors for PGE2 (EP1-EP4 receptor) so far, and EP2 and EP4 receptors are mainly involved in the immunosuppressive effect of PGE2 in vitro. In the present study we examined the in vivo immunosuppressive effects of selective EP receptor agonists using a high-responder rat skin transplantation model.

MATERIALS AND METHODS

Skin allografts from ACI donors were transplanted onto LEW recipients. Agents were injected everyday between day 0 and day 5 after skin transplantation at the dose of 300 microg/kg subcutaneously. Survival of the skin allograft, histological changes and changes of the intragraft cytokine expressions were analyzed using the reverse transcription polymerase chain reaction (RT-PCR). We also assessed the mixed lymphocyte reaction (MLR) assay using splenocytes.

RESULTS

PGE2 significantly prolonged allograft survival (18.8+/-1.5 days) compared with untreated control (14.8+/-0.8 days). EP2R+EP3R+EP4R agonists also prolonged allograft survival (18.0+/-1.0 days) although EP3R agonist or EP2R+EP4R agonists alone failed (15.5+/-0.7, 15.4+/-1.3 days, respectively). RT-PCR analysis in the skin grafts demonstrated IL-10 up-regulation and IFN-gamma down-regulation in all groups except untreated control and EP2R agonist-treated groups. MLR was significantly reduced in groups of EP2R+EP4R agonists, EP2R+EP3R+EP4R agonists and PGE2, compared with untreated control.

CONCLUSIONS

The effect of PGE2 to prolong the survival of skin transplant requires the action of a combination of three receptors, i.e., EP2+EP3+EP4.

Prolonged survival of donor-specific rat intestinal allograft by administration of bone-marrow-derived immature dendritic cells

It has been reported that intraportal administration of donor antigens induced donor-specific hyporesponsiveness. We studied here the effects of transplantation of BM-derived immature dendritic cells (imDCs) and mature DCs (mDCs) via portal vein on rat small intestinal allograft survival. This study comprised four treatment groups: 1) untreated controls; 2) FK506 alone; 3) intraportal donor-specific BM-derived imDCs transplantation+FK506; 4) mDCs/Tx+FK506. Allograft survival was minimal in control group (5.2+/-0.8 days) and maximal in imDC+FK506 group (28.4+/-3.0 days). The rats in mDC+FK506 group showed systemic inflammatory reaction due to GVHR, and died within 10 days after transplantation. The in vitro MLR reaction using imDCs was also strongly inhibited both in direct and indirect recognition pathways. The impact of imDCs for the specific induction of transplant tolerance may suggest that immunization with donor-specific imDCs has therapeutic potential in organ transplantation.