BLOCKING NF-KAPPAB ACTIVATION IN RECIPIENT T CELLS PROLONGS SMALL BOWEL ALLOGRAFT SURVIVAL IN A MOUSE MODEL OF ORTHOTOPIC SB TRANSPLANTATION

Abstract

P1027 Background: Previous studies reveal that blocking T-cell specific NF-kappaB activation permits long term survival of cardiac allografts but does not prevents skin allograft rejection, suggesting a differential mechanism for T-cell priming in response to different organs or tissues. It has also been known that NF-kappaB activation is critical in inflammatory bowel diseases. However, its role in small bowel allograft rejection has not been evaluated. Methods: To study the potential role of NF-kappaB activation in SB allograft rejection, nuclear extracts were isolated from mucosal scrapings of C57BL/6 (H-2b) isografts or C57BL/6 to BALB/c (H-2d) SB allografts on POD 7. Activation of NF-kappaB complex (p65) was quantified with an ELISA-based kit. To further determine if NF-kappaB activation in recipient T cells is required for SB allograft rejection, we have developed a mouse model of orthotopic small bowel transplantation in which host survival is entirely dependent upon graft function. IkappaBalpha transgenic mice (B6 background) with defective NF-kappaB translocation in T cells due to the presence of a NF-kappaB super repressor (a mutant IkappaBalpha transgene) were transplanted with BALB/c SB allografts with no additional immunosupression. Wild type B6 recipients of BALB/c SB allograft served as controls. Graft tissues were procured at POD 5 or when the recipient was moribund due to rejection (endpoint of rejection) for histology, immunopathology, as well as for function using an assay for sucrase activity. Results: We found that nuclear levels of NF-kappaB p65 subunit in SB isografts is 9.8+/− 1.6 ng/ml (mean+/− SD), while it was significantly increased in SB allografts (28.4+/−7.7 ng/ml, p<0.01). These results suggest that SB allograft rejection is associated with a significant upregulation of NF-kappaB. Our data on the survival of the orthotopic small bowel transplants showed that all B6 isografts (n=3) survival more than 100 days, while allografts (n=4) developed dehydration, diarrhea, weight loss and eventually died of graft failure by POD 9 with typical histologic features of SB allograft rejection. In addition, there was 50% decrease in epithelial sucrase activity as measured in SB allografts on POD 5 relative to the isografts. In contrast, BALB/c SB allografts transplanted into IkappaBalpha transgenic mice survived and continued to demonstrate weight gain at 4 weeks posttransplant. These grafts examined on POD 9 had no histologic evidence of rejection and demonstrated normal sucrase activity. Immunofluorescent staining showed significantly less CD4+ T cells and macrophages in the SB allografts transplanted into transgenic recipients compared to the WT SB allografts. Interestingly, CD8+ T cell infiltrates appeared similar in both SB allografts. Conclusions: Inhibition of NF-kappaB activation in recipient T cells prevents SB allograft rejection and preserves graft function, thereby prolonging survival in SB allografts and allograft recipients. These data suggest T-cell specific NF-kappaB activation is essential for SB allograft rejection and targeting this pathway may prove to be an effective strategy to prevent SB allograft rejection.