CONICET | Buscador de Institutos y Recursos Humanos

Introduction: Intestinal transplantation (IT) faces many challenges, amongthem, the necessity to understand and detect rejection processes. Rodentmodels of IT are used to provide evidence for intervention strategies as wellas improve knowledge of IT biology. Our aim was to determine the kineticsof small bowel rejection with emphasis in the characterization of acute cellularrejection (ACR) in the different layers of the graft since most of the informationcoming from the clinics is on mucosal layer, the only one that is accessible byendoscopic biopsies.Methods: Allogeneic (ALLO) heterotopic IT in rats was performed followingstandard procedure. ACR was diagnosed by H-E staining analysis. Also,real-time PCR from microdissected samples (epithelial, muscular and serosalayer) and whole graft to determine gene expression was performed at 5 and10-12 postoperative days (POD). An Isogenic IT group was performed as acontrol.Results: ACR was observed since 5 POD in ALLO group with mild rejectionas the most characteristic grade. Severe ACR was diagnosed in all ALLOsamples at 10-12 POD. Descriptive analysis showed a well-preserved archi-tecture at 5 POD; confluent and loose apoptotic cells in the intestinal epithe-lium and perivascular infiltrate in all layers were evident. At 10-12 POD,significant cellular infiltrate, epithelial damage, ulcers and an increase of apo-ptotic cells were observed. Muscular and serosa layers showed inflammatorycell infiltrate and intercellular edema.At 5 POD, some markers were consistently increased in ALLO groupssuch as CXCL10 that showed a 120 ± 80-fold increase compared withnontransplanted tissue. Furthermore, IFNg and IDO showed a trend to be in-creased at these time points. Remarkably, other inflammation-related genes,such as CXCL1 and IL6 showed consistent increase in ALLO groups at 10-12POD, when severe ACR was established. When a principal component anal-ysis of the overall gene expression markers was performed, ALLO group at10-12 POD clearly separated from the other conditions. The analysis of geneexpression at different layers of the graft was coincident with whole tissue bi-opsies: higher levels of IL6 and CXCL1 were observed in ALLO groups at10-12 POD with important activation of this response in serosa and muscularlayer. Interestingly, IL22 expression was only measurable in epithelial layer inALLO groups at 10-12 POD, indicating ACR-induced expression in this com-partment. Serosa layer showed some of the highest relative increases in pro-inflammatory gene expression also in ALLO groups at 10-12 POD.Conclusion: Although in the clinic mucosal rejection has been extensivelycharacterized, in our animal model we could document that all graft layersare affected by ACR since the initial stages. Serosa and muscular layer showhigh expression of proinflammatory markers, with differential expression ofIL22 in the epithelial compartment. This information could be useful in thesearch for early biomarkers of ACR.