Immune monitoring in organ transplantation using neopterin.

Transplantation has become an established and successful therapy. Rejections and infections are the principal immune-related complications in the post-transplant course. A reliable and early diagnosis is necessary to prevent graft failure and patient morbidity. Despite the immunologic nature of these complications the diagnostic procedures still rely on functional tests and organ biopsies. Non-invasive monitoring remains to be one of the major goals in transplant medicine. Neopterin is a sensitive marker of the cellular immune response. It reflects the activation of macrophages and can be easily measured in serum, plasma, urine or other body fluids. This review summarises studies on the diagnostic value of neopterin in transplant medicine. Based on these results key factors for immune monitoring in regard to neopterin are evaluated. In particular the unspecificity of diagnostic immune markers, the kinetics of the immune response, the importance of adjustment of neopterin to kidney function, and quantitative differences in immune pathways against viruses and allografts are discussed. Reflecting these points a concept to use neopterin for non-invasive immune monitoring in the clinical routine is presented. This approach calculates probabilities for specific post-transplant complications based on daily measurements of neopterin, a combination with the acute phase reactant amyloid A, and a modification of the likelihood ratio concept.