EARLY SMALL BOWEL (SB) ALLOGRAFT REJECTION CAUSES A FUNCTIONAL DEFECT IN INTESTINAL EPITHELIAL SUCRASE ACTIVITY.

Abstract

P1216 Introduction: Intestinal sucrase is a major epithelial brush border membrane hydrolase expressed by the SB epithelium. Sucrase activity has been used as a marker to differentiate mature villus cells from less mature crypt cells. A loss of sucrase activity has been associated with SB inflammation and reflects compromised epithelial function and/or a decrease in the ratio of villus to crypt cells, both features of early SB allograft rejection. Sucrase may therefore be useful as an early marker of acute SB allograft rejection and as a marker of graft dysfunction associated with chronic rejection. This study is to determine if changes in sucrase activity correlate with SB allograft rejection and to evaluate possible mechanisms underlying these changes. Methods: SB transplants using BALB/c donors and BALB/c recipients (isografts), or BALB/c donors and C57BL/6 recipients (allograft) were performed. Sucrase activity in graft epithelial proteins isolates on PODs 3, 5 and 7 were measured using standard methods. Sections of SB grafts were examined to establish the typical progression of histopathologic and morphometric changes. To evaluate the role of TNF/TNFR signaling pathway and Nuclear factor (NF)-kappaB activation in regulating sucrase activity during SB allograft rejection, SB grafts from B6 TNF receptor (R)-1 and R2 double knock out (TNFR−/−) mice or B6 mIkappaBalpha transgenic mice (with a SB epithelial specific defect in NF-kappaB activation) were transplanted to BALB/c recipients. Results: Our results revealed that posttransplant histopathologic changes including villus shortening, goblet cell loss and crypt hyperplasia progressed consistently in SB allograft between POD3 and POD7. Morphometric analysis showed a 40 percent decrease in the villus to crypt ratio by POD 5 in SB allograft, compared to isografts (P<0.01). Consistently, epithelial sucrase activity was significantly decreased in the SB allograft with 55% reduction on POD 5 (p<0.05,) and 85% on POD7 (p<0.01), compared to isografts. Interestingly, sucrase activity in both TNFR−/− SB allograft and mIkappaBalpha SB allografts were comparable to isografts. Conclusions: Small bowel (SB) allograft rejection is associated with an epithelial functional defect in intestinal epithelial sucrase activity, which suggests there is a defect of epithelial cell maturation or regeneration. Blocking TNF/TNFR signaling pathways or inhibiting epithelial NF-kappaB activation prevents this loss of sucrase activity, indicating an important connection between TNF and NF-kappaB in epithelial cell function during SB allograft rejection.