Rat-to-mouse small bowel xenotransplantation:: A novel model for studying acute vascular and hyperacute xenograft rejection and xenogenic cell migration

The present study was undertaken to establish a rat-to-mouse vascularized small bowel xenotransplantation model to study acute vascular and hyperacute xenograft rejection, and xenogenic cell migration. Lewis rat small bowel grafts were transplanted heterotopically to group 1, Balb/c mice, and group 2, Balb/c mice pre-sensitized with a donor spleen cell injection. The grafts were examined by serial pathology and flow cytometry. In group 1, acute vascular rejection was present by the 5th post-operative day (POD). Immunohistology showed a strong endothelial deposition of IgG, IgM and C3, associated with a minimal lymphocytic infiltrate. There was a vigorous cell migration from the recipient to the graft, in which recipient origin cells comprised 80.1 +/- 6.9% of the graft mesenteric lymph node by POD 3. However, there was almost no cell migration from the graft to the recipient. The intestinal xenografts in the group 2 showed massive hemorrhage, fibrin deposition, vascular congestion and thrombosis 60 min after transplantation. IgG and C3 were present on the endothelium as early as 1 min after reperfusion. The vigorous humorally-mediated vascular damage and rapid elimination of donor cells seen with intestinal xenograft rejection are distinct from the usual picture of allograft rejection. Hyperacute rejection can be induced by recipient pre-sensitization with donor spleen cells. The potential advantages of studying xenotransplantation in this model include: (1) the wide range of immunologic reagents available for mice; (2) the opportunity to study the progression of vascular damage easily by performing serial biopsies in the same animal; and (3) the opportunity to study, in vivo, two-way cellular response by examining cell trafficking in the mesenteric lymph nodes.