The SP-TLR axis, which locally primes the nasal mucosa, is impeded in patients with allergic rhinitis

Background Substance P (SP) and toll-like receptors (TLRs) contribute to airway disease, particularly during viral infection. We recently demonstrated that SP can act as an initial response to viral stimuli in the upper airway by upregulating TLRs in the nasal epithelia (the SP-TLR axis). Patients with allergic rhinitis (AR) suffer from prolonged airway infections. The aim of the present study was to examine if patients with AR exhibit a disturbance in the SP-TLR axis. Method Human nasal biopsies and human nasal epithelial cells (HNEC) from healthy volunteers and patients with AR were cultured in the presence of SP. Epithelial expression of TLR4, neutral endopeptidase (NEP) and neurokinin 1 (NK1) were evaluated with flow cytometry and/or quantitative polymerase chain reaction after 30 min to 24 h. The effect of SP on nasal lipopolysaccharide-induced interleukin-8 (IL-8) release was investigated. Results SP stimulation of tissue from healthy volunteers resulted in a transient increase of the TLR4 expression, whereas stimulation of AR patient-derived material led to a delayed and prolonged upregulation of TLR4. NEP expression in HNEC was lower in AR than healthy controls whereas NK1 receptor expression was increased. SP pretreatment increased TLR4-dependent IL-8 expression in healthy controls, but not in AR. Conclusions SP-induced regulation of TLR4 in the human nasal mucosa is disturbed in AR. An altered SP-mediated innate immune response may contribute to the dysfunctional and often prolonged responses to infection in AR.

Automated summary

This study examined the disturbance in the SP-TLR axis in patients with allergic rhinitis. It was found that TLR4 expression was delayed and prolonged, NEP expression was lower, and NK1 receptor expression was increased in AR patients compared to healthy controls. SP-induced regulation of TLR4 was disrupted in AR, suggesting an altered innate immune response that may contribute to prolonged responses to infection in AR.