High serum tryptophan concentration in pollinosis patients is associated with unresponsiveness to pollen extract therapy

Background/Aims: The immunologic background of allergic asthma and rhinitis includes a preponderance of Th2-type immunity. In parallel, Th1-type immune response is suppressed by Th2-type cytokines. As a consequence, biochemical pathways triggered by Th1-type cytokine interferon-gamma, such as tryptophan degradation by indoleamine 2,3-dioxygenase and neopterin production, might be altered. We examined whether they are related to the outcome of hyposensitization therapy in atopic patients. Methods: In serum specimens of 44 atopic patients (18 women, 26 men) before any specific immunotherapy, tryptophan and kynurenine concentrations were measured by HPLC, and the kynurenine to tryptophan ratio (kyn/trp) was calculated. Neopterin concentrations were measured by ELISA. Results were compared with concentrations in 38 serum specimens from healthy blood donors and with the outcome of specific subcutaneous immunotherapy in atopics: on clinical grounds, 27 patients were classified as responders, and 17 patients as non-responders. Results: Serum tryptophan concentrations were higher in atopics (84.3 +/- 24.4 mu M) than in blood donors (57.9 +/- 7.46 mu M; p < 0.001), kynurenine and kyn/trp were not different between the 2 groups. All of the neopterin concentrations measured in patients were < 8.7 nM, the upper limit of the normal. Non-responders to subcutaneous immunotherapy had significantly higher tryptophan concentrations (95.7 +/- 27.0 mu M) than responders (77.1 +/- 19.9 mu M; p = 0.01). No other marker concentrations differed between the groups. Conclusions: The measurement of serum tryptophan may present an option to predict the outcome of pollen extract therapy. Higher tryptophan levels may result from lower indoleamine 2,3-dioxygenase activity in atopics. However, this possible relationship needs to be confirmed in further studies. Copyright (C) 2008 S. Karger AG, Basel.