In a recent study, higher 5-hydroxytryptamine (5-HT) levels were seen in the serum of allergic rhinitis patients. Regulatory T cells (Tregs) can be converted to Th17 cells by 5-HT-primed dendritic cells. Investigators aimed to clarify the function of 5-HT in the regulation of Treg activities. Blood samples were taken from people suffering from perennial allergic rhinitis. Magnetic cell sorting was used to separate Tregs from blood samples. Using enzyme-linked immunosorbent assay (ELISA), the level of other cytokines and 5-HT was estimated.

The findings revealed that serum 5-HT levels in allergic rhinitis people were greater than in healthy control individuals. There was a positive association between 5-HT concentrations and allergic rhinitis-associated concentration of cytokine in serum. A negative connection was discovered between serum 5-HT levels and Treg peripheral frequency. In dendritic cells, 5-HT increased the expression of interleukin (IL)-21 and IL-6. Co-culture of 5-HT-primed dendritic cells with Tregs resulted in Th17 cell conversion.

Signal transducer and activator of transcription 3 (STAT3) inhibition effectively prevented the 5-HT-related conversion of Th17 cells from Tregs. Hence, the dysfunction of Treg is associated with  the pathogenesis of allergic rhinitis.