Polymerase chain reaction detection of chimerism in rats based on an allelic polymorphism for T cell antigen receptor C beta genes

Prolongation of skin allograft survival is associated with reduced Th1 cytokine responses in the WKY-->F344 rat model

BACKGROUND

We have reported previously that F344 rats develop a spontaneous tolerance to WKY lung allografts and show long-term retention of donor-specific skin grafts placed 35 days after lung transplantation. In this study, we investigated the immunologic mechanisms that may be responsible for the prolonged skin graft survival in animals tolerized with lung allografts.

METHODS

In the rejection group, WKY skin grafts were placed on normal F344 rats, whereas, in the tolerance group, the skin grafts were placed on F344 rats that had received a WKY lung transplant 35 days before skin grafting. Th1 (interleukin [IL]-2 and interferon-gamma [IFN-gamma]) and Th2 (IL-4 and IL-10) cytokine as well as transforming growth factor-beta1 mRNA expression in skin grafts and in draining lymph nodes were determined by reverse transcription-polymerase chain reaction. Macrophage and lymphocyte infiltration in skin grafts and the number of Langerhans cells in epidermal sheets of the grafts were examined by immunohistochemistry.

RESULTS

IL-2 and IFN-gamma mRNA expression was significantly decreased in both the skin grafts and the draining lymph nodes of the tolerance group, compared to the rejection group, whereas IL-10 and transforming growth factor-beta1 mRNA expression was similar in both groups and IL-4 mRNA was rarely detected. Decreased and delayed CD8+, macrophage, and natural killer cell infiltration in the skin grafts from the tolerance group was also detected. Similar reduction in the number of Langerhans cells in the epidermis of the grafts from both groups was seen on day 1 after skin grafting, and thereafter the number remained stable in both groups.

CONCLUSIONS

Reduced expression of Th1 cytokines and decreased infiltration of CD8+ cells, macrophages, and natural killer cells in the skin grafts may be responsible for prolongation of skin graft survival in the tolerance group.

Predominant expression of T helper 2 cytokines and altered expression of T helper 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 corresponding to the alpha-helices of the alpha1 and alpha2 domains of the donor class I RT1.Aa molecule served as efficient CD4+ T-cell epitopes for indirect recognition of this molecule during cardiac allograft rejection in the PVG.R8-toPVG.1U rat strain combination. These peptides induce long-term graft survival when injected into the thymus 7 days before transplantation under the cover of transient immunosuppression with anti-rat lymphocyte serum. In this study, we analyzed intragraft cytokine gene expression to test whether immune deviation to the T helper (Th) 2 response is associated with long-term allograft survival in this model.

METHODS

Intragraft cytokine gene expression was analyzed using a competitive 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 rejection (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 undetectable levels of IL-4 and IL-10. Acutely rejected allografts from unmanipulated 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 allografts also expressed T-cell receptor Cbeta gene, providing evidence for the presence of T-cell infiltrates in the grafts.

CONCLUSIONS

These observations demonstrate that acute graft rejection in this model is associated with the expression of Th1 cytokines, IL-2, and IFN-gamma, whereas long-term survival is associated with predominant expression of Th2 cytokines, IL-4, and IL-10. The expression of IFN-gamma in long-surviving allografts in the absence of IL-2 provides evidence for altered activation of the Th1 response in this intrathymic immune modulation model.

Induction of allograft nonresponsiveness after intrathymic inoculation with donor class I allopeptides. II. Evidence for persistent chronic rejection despite high levels of donor microchimerism

We have recently demonstrated that three synthetic peptides corresponding to the donor class I RT1.Aa molecule induce long-term survival of cardiac allografts in the PVG.R8-to-PVG.1U rat strain combination (disparate for one isolated class I, RT1.A, molecule) when presented to the recipient immune system in the thymus. Long-term graft survivors had measurable levels of donor-reactive alloantibodies in their serum. In this study, we examined long-term allografts for the presence of chronic rejection and donor microchimerism to assess whether this regimen of immune modulation establishes true tolerance and whether this tolerance is dependent upon the presence of donor-recipient microchimerism. Histological examination of long-term heart grafts (>100 days) demonstrated chronic rejection, including a mild degree of myocardial infiltration by mononuclear cells, mild to moderate myocardial fibrosis, and various vascular changes ranging from focal intimal thickening to total vascular lumen blockade due to smooth muscle cell proliferation. In contrast, long-term syngeneic hearts transplanted under similar experimental conditions lacked these pathological manifestations. Donor microchimerism was analyzed using the polymerase chain reaction with a pair of oligonucleotides specific for the donor class I RT1.Aa gene and genomic DNA harvested from various tissues from graft recipients. We detected high levels of donor microchimerism in the heart, kidney, liver, skin, bone marrow, thymus, and lymph nodes of long-term graft recipients. Donor microchimerism was also detected in unmanipulated control graft recipients at rejection (7 days) and in intrathymically manipulated recipients that rejected allografts in a delayed fashion (12-82 days). These data clearly demonstrate that intrathymic inoculation of donor class I allopeptides induces long-term graft survival but does not prevent chronic rejection. Allograft rejection occurred despite high levels of donor microchimerism, providing direct evidence that donor-recipient microchimerism is not sufficient for the prevention of acute or chronic rejection in this model.

Induction of specific tolerance through mixed hematopoietic chimerism prevents chronic renal allograft rejection in a rat model

BACKGROUND

Chronic rejection is the leading cause of late graft loss in kidney transplantation. We tested the ability of mixed hematopoietic chimerism to prevent chronic renal allograft rejection in an established rat model and described possible mechanisms responsible for this tolerance.

METHODS

Mixed hematopoietic chimerism was established in lethally irradiated F-344 rats by reconstitution with Lewis bone marrow. Four groups (n = 5 each) received orthotopic kidney transplants: (1) allograft controls, (2) isograft controls, (3) experimental chimeras, and (4) specificity control. After 120 days kidney grafts were examined histologically, immunohistochemically, and for cytokine interferon-gamma, interleukin-2 (IL-2), IL-4, and IL-10 gene transcripts by means of reverse transcriptase polymerase chain reaction techniques.

RESULTS

Allograft control group exhibited severe parenchymal fibrosis; isograft control and chimera groups failed to develop this lesion. Immunohistochemical analysis revealed increased CD8+ lymphocytes and ED-1+ monocyte-macrophages infiltrating the tubulointerstitium of control allografts. Interferon-gamma and IL-2 were absent in isografts. IL-4 was absent and IL-10 was positive in all grafts. Chimeras promptly rejected third-party allografts.

CONCLUSIONS

Induction of specific tolerance through mixed hematopoietic chimerism prevents chronic renal allograft rejection. These results support the hypothesis of an immunologic basis of chronic rejection and advance previous observations that the induction of specific tolerance enables long-term solid organ transplantation without the use of immunosuppression.

Pretransplant injection of allograft recipients with donor blood or lymphocytes permits allograft tolerance without the presence of persistent donor microchimerism

Donor-recipient microchimerism has recently been suggested to play a critical role in the induction and maintenance of allograft tolerance. In this study we sought evidence for this hypothesis using the LEW-to-ACI cardiac allograft as a model system. Donor-specific tolerance to cardiac allografts was induced by intravenous or intraportal injection of graft recipients with donor peripheral blood, T cells, or B cells 7 days before transplantation. All the graft recipients injected with donor antigens accepted donor heart grafts indefinitely when compared with control recipients that rejected donor allografts in 12 days. Long-term graft survivors rejected third-party BN heart allografts in 14 days without an adverse effect on the survival of the first LEW heart allografts, demonstrating the specificity of the tolerance. Tissue lysates prepared from heart, kidney, liver, bone marrow, thymus, lymph nodes, and spleen of tolerant (>120 days) graft recipients were analyzed for the presence of donor DNA using LEW T cell receptor C beta gene-specific primers for polymerase chain reaction that detects donor DNA at > or = 1:10,000 dilution. Donor DNA was detected in 77% of tolerant graft recipients. Chimeric recipients showed variations in the levels and presence of donor DNA in different tissues. The status of donor microchimerism, with respect to its presence and tissue distribution, was dependent upon the donor cell type and route of injection used for the induction of tolerance. Intraportal injection of the graft recipients with donor peripheral blood resulted in the highest degree of chimerism, whereas intravenous injection with donor B cells did not induce detectable microchimerism in this group of recipients. These data clearly demonstrate that the presence of microchimerism is common following administration of donor cells, but that its presence is not an absolute requirement for the long-term survival of allografts.