Serum citrulline and rejection in small bowel transplantation: A preliminary report

Background. There is no known serum marker for intestinal rejection. Serum concentrations of the amino acid citrulline arise almost exclusively from t he intestinal mucosa. We examined the impact of acute cellular rejection (A CR) of intestinal allografts on serum citrulline levels. Methods. Citrulline concentrations were assayed in serum samples of healthy volunteers (n=6) and seven patients who underwent small bowel transplants (SBTx). Trends in mean citrulline concentrations versus degree of ACR were assessed by matching posttransplantation citrulline concentrations with pat ients' grade of ACR at time of serum collection. Rejection was confirmed by biopsy and graded by following standardized criteria. An additional patien t had citrulline concentrations determined for 31 sequential specimens 3-60 days posttransplant. Results. Mean citrulline concentrations in controls were significantly high er than posttransplantation samples at any rejection grade. Mean concentrat ions declined significantly as rejection severity increased. The overall do wnward trend was statistically significant (P<0.05). In sequential measurem ents, citrulline levels increased significantly over time with declining se verity of rejection. The increase in mean citrulline concentration between posttransplant days 3-16 and 52-60 was significant (P<0.01). Conclusions. Serum citrulline levels decline with increasing grade of ACR a nd may be a useful serum marker for intestinal rejection.