Tryptophan metabolism and its mechanism in allergic rhinitis

Allergic rhinitis is a common upper respiratory tract disease in immune diseases and one of the common chronic diseases. General symptoms for nasal congestion, runny, sneezing. The disease is caused by many factors. It has been reported that tryptophan metabolism is associated with allergic rhinitis. Tryptophan metabolism pathway is bacterial metabolism (exogenous metabolism) and endogenous metabolism. The main rate-limiting enzyme of endogenous metabolism is indoleamine 2, 3-dioxygenase (IDO), acts on the (AHR), of aryl hydrocarbon receptor through kynurenine pathway metabolite to induce the proliferation of tregs, promote the secretion of IL-10, inhibit the immunity and decrease the allergic reaction. Bacterial metabolism of tryptophan produces a large number of metabolites, of which indole is a major tryptophan metabolite in bacteria. Indole could increase the expression of foxp3 and induce the proliferation of tregs. It can also inhibit delayed hypersensitivity by regulating microrna-induced transformation from pro-inflammatory Th17 cells to anti-inflammatory tregs. Key words: Rhinitis, Allergic, Seasonal; Tryptophan; Kynurenine