[Immune reactions after allogeneic small bowel transplantation. Graft rejection and graft versus host reaction in the rat model].

Small bowel transplantation is characterized by the specific immunological problem of graft versus host reaction (GVHR) which appears in addition to rejection reaction. GVHR is induced and maintained by the immunocompetent cells of the graft. In order to clarify the basic mechanisms of these interfering reactions heterotopic accessory small bowel transplantations in the rat were carried out. Immunological reactions were estimated by assessment of mortality rates of recipients, histological examinations, and measurement of cytotoxic T-cell reactivity within the graft and recipient. The strength of the rejection reaction depends on the degree of histoincompatibility between donor and recipient, and the length of the graft. The expression of GVHR is also dependent on the histoincompatibility of the donor and the amount of lymphatic tissue grafted within the small intestine. The GVHR shows a characteristic time course, peaking 20 days after transplantation. GVH-T-cell-reactivity can be found in different lymphatic compartments of the graft and recipient. GVHR causes autoimmune reactivity within the recipients. These results clarify basic immunological mechanisms of rejection and GVHR thus providing an indispensable condition for clinical small bowel transplantation.