Apoptosis as an instrument for immune regulation: study on a liver/small bowel tolerant rat model

[Apoptosis participation in the acute rejection of intestinal transplantation in rats]

BACKGROUND

Intestinal transplantation is a possible treatment for patients with short bowel syndrome, aiming the reintroduction of oral diet. However, the major obstacle in this procedure is the strong rejection. Delay in rejection diagnosis may be irreversible and lethal.

AIM

To define method for early diagnosis of rejection based on the apoptosis from intestinal allograft.

MATERIAL AND METHODS

Isogenic rats Brown-Norway (BN) and Lewis (LEW) were submitted to intestinal heterotopic allotransplantation and divided in two groups: LEW donor to LEW recipient isograft group C and BN donor to LEW recipient allograft group (Tx). According to the day of sacrifice, Tx group were subdivided in three subgroups with eight animals each as follow: Tx3-- sacrificed at third postoperative day (POD), Tx5 -- sacrificed at fifth POD and Tx7 -- sacrificed at seventh POD. Eight animals from control group were subdivided in three moments according to the time of biopsy from the graft as follow: C3 -- biopsy at third POD; C5 -- biopsy at fifth POD and C7 -- biopsy at seventh POD. All animals from control group were sacrificed at seventh POD. Rejection parameters were compared between the control groups (C3 vs C5, C3 vs C7 and C5 vs C7, and allograft group (Tx3 vs Tx5, Tx3 vs Tx7 and Tx5 vs Tx7). The same parameters were analyzed between the control group and allograft groups ( C3 vs Tx3, C5 vs Tx5 and C7 vs Tx7). In C group no statistical significant difference regarding the expression of the apoptotic cells were detected, while in Tx group, the presence of apoptotic cells were remarkable since the third postoperative day.

Orthotopic liver/small bowel transplantation in rats: a microsurgical model inducing tolerance

Liver cirrhosis in patients with short bowel syndrome is successfully treated in humans by simultaneous liver/small bowel transplantation. However, until now, a clinically relevant experimental rat model for this procedure has not existed. We therefore established a protocol that, for the first time in rats, allows the simultaneous transplantation of arterialized liver and small bowel into an orthotopic position. Short-term immunosuppression induced not only allograft acceptance but tolerance (as demonstrated by indicator heart/skin transplantation). The immunosuppressive dose required to achieve this result was dramatically less than that of protocols for successful small bowel transplantation alone. Immunohistochemistry detected a transient rejection crisis before tolerance. During this crisis, apoptotic recipient-type T lymphocytes, mainly CD8+ cells, accumulated in the liver but not in the small bowel allograft. The initiation of T-cell apoptosis is one possible explanation for the specific immunosuppressive effect of the liver allograft, which also supports the simultaneously transplanted small bowel allograft in our model.