Antigens linked to dendritic cells in allergen-specific immunotherapy for asthma boost tryptophan metabolism and change the Th17/Treg balance in the airways. Tryptophan metabolism has long been thought to play a role in the pathogenesis of allergic illnesses such as asthma. The purpose of this investigation was to examine if tryptophan metabolites are responsible for the changes in Th17/Treg balance as well as the reduction in airway hyperreactivity and inflammation found during allergen-specific immunotherapy in an asthma model.

To create an asthma model, mice were given intraperitoneal injections of ovalbumin, followed by allergen-specific immunotherapy at high doses to promote immunological tolerance. To determine whether the animal model was successful, airway hyperreactivity and serum ovalbumin-specific immunoglobulin E levels were examined. The researchers then looked at how tryptophan metabolism inhibition and the addition of tryptophan metabolites affected allergen-specific immunotherapy-induced changes in the Th17/Treg balance as well as reduction in airway inflammation and inflammatory cytokines. The production of tryptophan metabolites was partly responsible for the rise in Tregs, decrease in airway inflammation, and decrease in inflammatory cytokines caused by allergen-specific immunotherapy. An increase in tryptophan metabolites is one of the ways through which allergen-specific immunotherapy produces immunological tolerance in the context of asthma.