Apoptosis in Gut-Associated Lymphoid Tissue (GALT): A Response to Injury or a Physiologic Mechanism?

MONGINI CLAUDIA; RUYBAL PAULA; GARCÍA RIVELLO HERNÁN; MOCETTI ESTEBAN; ESCALADA ANA; CHRISTIANSEN SILVIA; ARGIAY PABLO

Cambridge, Inglaterra

Simposio; 5th International Symposium on Intestinal Transplantation; 1997

Intestinal injury causes intestinal permeability, bacterial translocation and activation of the macrophages of the lamina propria, thus releasing mediators that perpetuate tissue injury. Our working hypothesis states that the local release of cytokines and others mediators can induce apoptosis in GALT, generating local immunosuppression and lack of response against antigenic overexposure, thus perpetuating systemic damage. Objective: the aim of this study is to investigate the presence of apoptosis in GALT in a model of mesenteric ischemia and reperfusion in rats. Materials And Methods: twentyseven female adults Wistar rats anesthetized with intraperitoneal chloral hydrate were divided into four groups: A) basal control (n=8): anesthesia; laparotomy; removal of bowel, mesenteric lymph nodes (MLN), thymus, and spleen. B) anesthesia control (n=7): anesthesia, and removal of all forementioned tissues 45 minutes later. C) sham (n=6): anesthesia, laparotomy, bowel mobilization, and removal of the tissues 45 minutes later. D) ischemia and reperfusion (n=6): anesthesia, laparotomy, clamping of the mesenteric artery for 30 minutes and reperfusion for 15 minutes, followed by removal of the tissue. The presence of apoptosis in the mononuclear lymphoid cells was studied through: 1) detection of fragmented internucleosomal DNA through electrophoresis in agarose gels, 2) fluorescence microscopy, 3) flow cytometry, and 4) "in situ" detection fragmented DNA (TUNEL assay). Results: the preliminary results (fragmented DNA), show the following percentages of apoptosis:     Groups “Z” Test Tissue A B C D (p) MLN 50 24,85 100 100 < 0,05 Thymus 0 14,28 80 80 < 0,01 Spleen 0 14,28 83,33 80 < 0,01   Conclusions: these results show a significant local and systemic influence of ischemia and reperfusion, as well as surgical stress, over the incidence of apoptosis in mononuclear lymphoid cells, thus suggesting a mechanism of postinjury immune depression. However, the presence of apoptosis in the MLN of control groups A and B would indicate a physiologic mechanism or one mediated by minimal stimuli (anesthesia?). The nature of this mechanism and its qualitative and quantitative differences with the one mediated by mesenteric injury remain to be studied.