Methods: Wild-type (WT), MC-deficient (Mcpt5/DTA), FcRγ-chain-deficient (Fcer1γ‒/‒), LTC4-synthase-deficient (Ltc4s−⁄−), Cysltr1−⁄−, Cysltr2−⁄−, and Gpr99−⁄− mice received a single intranasal (i.n.) dose of 0 or 30 µg A.alternata, and nasal goblet cell (GC) mucin content was assessed by Periodic acid-Schiff (PAS+) staining after 1 hour. GPR99 expression in the nasal mucosa was assessed by RT-PCR in WT mice and by X-gal staining of tissue sections in Gpr99−⁄− mice.
Results: A.alternata elicited GC mucin release in WT mice, as detected by a reduction in PAS+ GCs. There was no detectable mucin release in A.alternata-treated Mcpt5/DTA, Ltc4s−⁄−, Gpr99−⁄− mice and a reduction in Cysltr1−⁄− mice. By contrast, mucin release was intact in Fcer1γ‒/‒ and Cysltr2−⁄− mice. GPR99 transcript was detected in the nasal mucosa of WT mice and transcript for E.coli β-galactosidase, inserted in the targeted deletion of Gpr99, was detected in Gpr99‒/‒ mice. X-gal staining confirmed GPR99 expression in nasal epithelial cells. Finally, i.n. LTE4 elicited GC mucin release in WT mice that was absent in Gpr99−⁄− mice.
Conclusions: These results demonstrate that GPR99 is expressed on murine respiratory epithelial cells and controls their secretory function. Moreover our results suggest that the innate immune response of respiratory epithelial cells to A.alternata is controlled, in part, through a MC-cysLT-GPR99 axis.