Small bowel allograft rejection detected by serum intestinal fatty acid-binding protein is reversible.

We hypothesized that, following experimental small bowel transplantation, immunosuppressive therapy initiated on the day of the initial rise in serum intestinal fatty acid-binding protein (I-FABP) would result in graft salvage. In previously published work, we showed that I-FABP was not detectable in the serum of isografted Lewis rats, but could be measured in the peripheral circulation during small bowel allograft rejection. A clinically useful method to monitor trans- planted allografts for rejection should detect the problem early in its evolution so that treatment to reverse the process would salvage a functional organ. Lewis rats served as recipients of LBNF1 out-of-continuity small bowel allografts and were studied in two groups: group I (control) received no immunosuppression and group II received cyclosporine (CsA, 15 mg/kg/d, p.o.) when I-FABP rose to > or = 80 ng/ml. Serum I-FABP was measured daily until the time of sacrifice. Full-thickness graft biopsies were obtained on postoperative days 3 (baseline), 6 or 7 (elevated I-FABP), 10, and 14 (sacrifice). Following transplantation baseline serum I-FABP (day 2 or 3) averaged < or = 10.0 ng/ml. I-FABP remained at baseline through day 5 (range 0-50 ng/ml) in all animals and then rose abruptly on either day 6 or 7 (range 86-150 ng/ml; P < 0.001 vs. baseline). Histology on day 6 or 7 revealed a mild-to-moderate cellular rejection. Cyclosporine therapy reversed the rejection reaction and restored the bowel to normal histology. Serum I-FABP returned to baseline. In untreated animals, serum I-FABP remained elevated for several days and then returned to baseline levels coincident with fulminant rejection and mucosal sloughing. I-FABP was released into the peripheral circulation early in the evolution of acute rejection in this model of small bowel transplantation. Immunosuppressive therapy initiated when elevated levels of I-FABP were detected in the serum resulted in graft salvage. Cyclosporine immunotherapy consistently reversed rejection in this model. This article represents the first report of salvage of small bowel allografts when immunosuppressive therapy was instituted prospectively on the basis of a serum marker. Immunoreactive I-FABP appears to hold significant potential as a biochemical screening tool for acute rejection occurring In small bowell allografts.