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Clinical and laboratory findings of acute rejection (AR) are often late and misleading. Core needle biopsy, the most reliable diagnostic method, is usually performed late in the course of AR and is associated with several complications. Therefore noninvasive approaches to monitor the immune system for detection of early AR is one of the major aims in transplant medicine. In a fully MHC-mismatched renal allograft model in the rat, we quantified donor-derived DNA (ddDNA) in the recipient serum using real-time RT-PCR as an alternative screening procedure for the early diagnosis of acute rejection. We also investigated the influence of different immunosuppressive protocols on the levels of ddDNA. Our results show that donor-derived DNA is present in the serum of kidney allograft recipients prior to acute rejection. Animals that received a syngeneic graft and animals that received a mismatched allograft but were treated with immunosuppressive drugs did not show significant elevations of ddDNA. When steroid therapy failed to avoid acute rejection, the animals showed a delayed peak of ddDNA. In summary, the detection of ddDNA in recipient serum offers a noninvasive diagnostic approach to uncover ongoing rejection processes in the graft.

Chronic allograft dysfunction remains the major obstacle for long-term successful transplantation. To date there is no effective treatment. Overexpression of protective genes has provided increased graft function and survival. This mechanism has been implicated in the process of graft accommodation. One of these genes that has been shown to mediate protective effects decodes the enzyme heme oxygenase-1 (HO-1), and an HO-1 downstream product, carbon monoxide (CO). Using an established model of kidney chronic allograft rejection in the rat, we investigated the impact of methylene chloride (MC), a CO donor, as a therapeutic tool to reduce chronic graft deterioration. We showed that donor and long-term recipient treatment with MC improved graft function and reduced histological signs of chronic rejection. Carbon monoxide may be a promising agent to improve graft quality and long-term graft function.

There is increasing evidence that the induction of the enzyme heme oxygenase-1 (HO-1) improves both graft function and survival. Although it has been shown that HO-1 promotes graft protection, it remains unknown whether it reduces graft immunogenicity by modulating dendritic cells. In the current experiment, we investigated the impact of HO-1 induction on frequencies and trafficking of donor-derived dendritic cells (DCs). Kidneys from DA rats were transplanted into untreated Lewis recipients. Donor animals were treated with cobalt protoporphyrin (CoPP; 5 mg/kg IP) 24 hours prior to organ harvesting to induce HO-1. Controls remained untreated or received zinc protoporphyrin (ZnPP; 20 mg/kg, IP) to block HO-1 induction. Analyses of grafts, spleens, lymph nodes and blood of Lewis recipients were performed at days 1 and 3 posttransplantation. Donor-specific DCs were determined by flow cytometry using haplotype-specific mAb against RT1(ab) and mAb against OX62(+) antigens. Cell markers (CD4/CD8(+) T cells, ED1(+) monocytes, MHC class II(+) CD86(+) DC) were measured by immunohistochemical staining. T-cell alloreactivity of recipient splenocytes was measured by ELISPOT. Induction of HO-1 reduced frequencies of donor-derived DCs in the graft and recipient compartments, which was associated with reduced frequencies of CD4(+) T cells and CD8(+) T cells and alloreactivity. Expression of costimulatory molecule CD86 and MHC class II antigens were also reduced, although not significantly. Thus, induction of HO-1 reduced graft immunogenicity. These mechanisms may explain the protective effects of HO-1 induction.

With a growing demand for transplants, grafts from older donors are increasingly used. However, altered immune responses associated with increasing donor age may influence graft survival. We dissected the effects of donor age on the immune response in an experimental model. Kidneys from young and old F-344 donors (3 and 18 months) transplanted into young Lewis recipients (3 months) were followed for 6 months. Renal function, structural changes, and immune activation were tested at serial time intervals. Splenocytes and peripheral blood mononuclear cells were examined by flow cytometry; alloantigen-specific intracellular IFN-gamma secretion was evaluated by ELISPOT. Grafts from both young and old donors survived the observation period. The ratio of structural changes (6/1 months) increased twofold in old vs young grafts. In parallel, the ratio of renal function declined by fivefold in recipients of old donor kidneys. Most interestingly, elderly grafts produced a modified immune response: the numbers of T/B cells and alloreactive T cells increased early following the transplantation of old grafts (P < .05). However, by 6 months, the amounts of T and B cells as well as alloantigen-specific immune responses were comparable in recipients of old versus young grafts. Older grafts elicit a stronger immune response during the early period posttransplantation. This process is associated with an increased immunogenicity in older grafts. Clinical immunosuppressive protocols need to consider these effects.