Predominant expression of T helper 2 cytokines and altered expression of Thelper 1 cytokines in long-term allograft survival induced by intrathymic immune modulation with donor class I major histocompatibility complex peptides

Background. We have recently demonstrated that three synthetic peptides cor responding to the cu-helices of the alpha 1 and alpha 2 domains of the dono r class I RT1.A(a) molecule served as efficient CD4(+) T-cell epitopes for indirect recognition of this molecule during cardiac allograft rejection in the PVG.R8-to-PVG.1U rat strain combination. These peptides induce long-te rm graft survival when injected into the thymus 7 days before transplantati on under the cover of transient immunosuppression with anti-rat lymphocyte serum. In this study, we analyzed intragraft cytokine gene expression to te st whether immune deviation to the T helper(Th) 2 response is associated wi th long-term allograft survival in this model. Methods. Intragraft; cytokine gene expression was analyzed using a competit ive reverse transcription polymerase chain reaction method we developed for this study. Cytokine gene expression was quantified in control allografts (n=5) with acute rejection and allografts from intrathymically manipulated recipients with acute rejection (n=5), delayed rejection (n=7), or no rejec tion (n=8). Results. Long-surviving allografts expressed high levels of interleukin (IL )-4, IL-10, transforming growth factor (TGF)-beta, interferon (IFN)-gamma, and undetectable levels of IL-2, Allografts that were rejected in a delayed fashion expressed mostly IL-2, IFN-gamma, and TGF-beta with low or undetec table levels of IL-4 and IL-10. Acutely rejected allografts from unmanipula ted controls or peptide-manipulated recipients expressed high levels of IL- 2, IFN-gamma, TGF-beta and undetectable levels of IL-4 or IL-10. All allogr afts also expressed T-cell receptor C beta gene, providing evidence for the presence of T-cell infiltrates in the grafts. Conclusions. These observations demonstrate that acute graft rejection in t his model is associated with the expression of Th1 cytokines, IL-2, and IFN -gamma, whereas long-term survival is associated with predominant expressio n of Th2 cytokines, IL-4, and IL-10. The expression of IFN-gamma in long-su rviving allografts in the absence of IL-2 provides evidence for altered act ivation of the Th1 response in this intrathymic immune modulation model.