Rejection of ileal versus jejunal allografts.

Small-bowel allografts are replete with lymphocytes, which may be the main stimulus for the recipient's immune system, thereby inducing rejection. Since most of the lymphoid tissue is located in the ileum, one would expect ileal grafts to be rejected more rapidly than are jejunal grafts. To test this theory, we transplanted a jejunal (n = 13) or an ileal segment (n = 9) or the entire small bowel (n = 6) orthotopically in the BN----LEW rat strain combination. Jejunal grafts included a short segment of the mesentery, whereas ileal and whole small-bowel grafts included the entire mesentery with its lymph nodes. Segmental as well as entire-bowel grafts induced peak anti-BN titers on the 6th to 7th postoperative day. In rats with entire-bowel grafts, rejection culminated in the recipient's death after an average of 9.5 +/- 1 days from graft necrosis and peritonitis; the rejection of jejunal (13.1 +/- 2.1 days) and ileal grafts (12.9 +/- 1.3 days) was less rapid. Segmental grafts were often encapsulated, and the causes of death were inanition and intestinal obstruction. Thus, despite their high lymphocyte content, ileal grafts were not rejected more quickly than were jejunal grafts; they should, therefore, be preferred because of their greater specialized absorptive capacity. Histologically, entire-bowel grafts were found to be rejected as rapidly as were segmental grafts; however, the toxic effects of the larger grafts that are undergoing rejection lead to earlier death of the recipient.