Biochemical detection of small intestinal allograft rejection by elevated circulating levels of serum intestinal fatty acid binding protein

Background. Intestinal fatty acid binding protein (I-FABP) was investigated as a serum marker for acute intestinal allograft rejection. Its behavior was compared with that of another putative marker of intestinal damage, hexosaminidase. Methods. Transplants were performed in three groups of rats: group 1, Lewis to Lewis; group 2, ACI to Lewis, no immunosuppression; and group 3, ACI to Lewis with cyclosporine given on posttransplant days 0 through 5. Daily serum I-FABP and hexosamidase levels were quantitated and serial graft biopsy specimens were obtained. Results. Serum I-FABP levels fell to 20 ng/ml or less in all animals between posttransplant days 3 and 4. In group 1, I-FABP levels remained at baseline throughout the experiment. In group 2, I-FABP levels rose dramatically on either day 6 or 7 and declined to baseline within 4 days of the peak. On the day that I-FABP levels increased, findings of biopsy specimens were consistent with early rejection. In group 3 the rise in serum I-FABP levels was delayed 2 to 10 days. Hexosaminidase did not correlate with rejection. Conclusions. Serum I-FABP content correlated with early histologic manifestations of rejection. Hexosaminidase was insensitive as a marker in this model. I-FABP, which has a human analog, has potential as a biochemical marker for early intestinal allograft rejection.