This study evaluates serum tryptophan, kynurenine, kynurenine-to-tryptophan ratio, and neopterin levels in patients with pollen-induced allergic rhinitis (AR) during and outside of the pollen season, along with these values in healthy subjects. A total of 102 patients (56 female and 46 male, median age 28.7 years) were included in this study: 56 with seasonal AR evaluated outside of the pollen season and thus without allergic inflammation and symptoms, and 46 with seasonal AR evaluated during the pollen season with symptoms. A skin prick test and blood sampling for assessing serum concentrations of tryptophan and kynurenine and of immune activation marker neopterin were performed in all subjects. Tryptophan and kynurenine serum concentrations were higher in AR patients than in controls and were also higher out of pollen season than during this season. In conclusion, this preliminary study demonstrates that serum tryptophan metabolism could serve as a biomarker in patients with AR.
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