Background
There is to date no reliable biomarker of intestinal acute cellular rejection (ACR). As small intestine is the primary organ responsible for terminal digestion of proteins and absorption of amino acids, our objective was to determine whether plasma amino acids may be used as markers of ACR using a model of allogenic small bowel transplantation (SBT) in pigs.

Methods
Pigs were divided into group 1 (n=8; controls; segmental autotransplantation), group 2 (n=8; allotransplantation; non-immunosuppressed recipients), and group 3 (n=8; allotransplantation; immunosuppressed recipients). Intestinal specimens for histological studies were obtained at the end of cold flushing (T0), and on postoperative day 8 (T1). Plasma amino acids levels were measured on samples harvested at T0 and T1.

Results
In groups 1 and 3, intestinal histology revealed no significant changes between T0 and T1 specimens. In group 2, graft histology revealed moderate to severe rejection on T1 specimens. Seven plasma amino acids were significantly correlated with the occurrence of acute intestinal rejection: phenylalanine, aspartate, citrulline, taurine, glycine, isoleucine, and tyrosine. For each marker, a cut-off level which would be felpful for clinical use to decide between rejection or not was determined and a score was built. An ACR was found in 100% of cases when the score was equal to 4 (Se=Sp=100%; AUC=1).

Conclusion
Our study suggests for the first time that seven plasma amino acid levels may be used in combination as markers of intestinal rejection.