Activin-A Is a Pro-Inflammatory Regulator in Type-2-Driven Upper Airway Disease.

BACKGROUND: Allergic upper airway disease involves pro-inflammatory type-2 cytokines such as IL-5 and regulatory tissue repair mediators, in particular transforming growth factor (TGF)-β1. The TGF-β-superfamily member activin-A displays multiple biological functions and shares certain signalling pathways with TGF-β1. We aimed to examine the coregulation of mucosal activin-A and TGF-β1 in acute allergic and chronic Th2-driven upper airway disease.

METHODS: We investigated mucosal cytokine expression profiles and kinetics using RT-PCR after nasal allergen challenges in patients with seasonal allergic rhinitis. Furthermore, we analysed mucosal specimens from patients with chronic upper airway disease with nasal polyps using ELISPOTs and confocal microscopy. In addition, we stimulated nasal mucosa ex vivo from patients with nasal polyps as well as primary nasal cell cultures from healthy donors.

RESULTS: Mucosal activin-A expression revealed increasing correlation with IL-5 and TGF-β1 at 0.25, 6, and 24 h, respectively, and was significantly upregulated at 6 h after allergen challenge. The correlated expression was found to be more pronounced in chronic disease with nasal polyps, showing substantially (48-fold) increased activin-A-producing cells in nasal polyps by ELISPOT, while submucosal downstream signalling as determined by confocal microscopy was decreased. Ex vivo stimulations of nasal tissue suggested that activin-A and TGF-β1 mutually regulate each other's expression at the mRNA level and, when combined, enhance IL-5 expression.

CONCLUSION: Activin-A in allergic upper airway disease acts as a pro-inflammatory mediator and TGF-β1 modifier. Our data in the upper airways oppose the view of potentially anti-inflammatory properties in contrast to lymphatic compartments.