S. mansoni -derived omega-1 prevents OVA-specific allergic airway inflammation via hampering of cDC2 migration

Abstract

Chronic infection with Schistosoma mansoni parasites is associated with reduced allergic sensitization in humans, while schistosome eggs protects against allergic airway inflammation (AAI) in mice. One of the main secretory/excretory molecules from schistosome eggs is the glycosylated T2-RNAse Omega-1 (ω1). We hypothesized that ω1 induces protection against AAI during infection. Peritoneal administration of ω1 prior to sensitization with Ovalbumin (OVA) reduced airway eosinophilia and pathology, and OVA-specific Th2 responses upon challenge, independent from changes in regulatory T cells. ω1 was taken up by monocyte-derived dendritic cells, mannose receptor (CD206)-positive conventional type 2 dendritic cells (CD206 ⁺ cDC2), and by recruited peritoneal macrophages. Additionally, ω1 impaired CCR7, F-actin, and costimulatory molecule expression on myeloid cells and cDC2 migration in and ex vivo, as evidenced by reduced OVA ⁺ CD206 ⁺ cDC2 in the draining mediastinal lymph nodes (medLn) and retainment in the peritoneal cavity, while antigen processing and presentation in cDC2 were not affected by ω1 treatment. Importantly, RNAse mutant ω1 was unable to reduce AAI or affect DC migration, indicating that ω1 effects are dependent on its RNAse activity. Altogether, ω1 hampers migration of OVA ⁺ cDC2 to the draining medLn in mice, elucidating how ω1 prevents allergic airway inflammation in the OVA/alum mouse model.

Author summary

Asthma is a chronic inflammatory disease, leading to cough, wheeze, and shortness of breath. The prevalence has increased drastically in Westernized societies and is now increasing in low- and middle-income countries. Chronic infection with the parasitic helminth, Schistosoma ( S.) mansoni protects against allergic airway inflammation (AAI) in mice, and is associated with reduced skin prick test positivity to inhaled allergens in humans. Here we show that peritoneal administration of ω1, a single glycoprotein secreted by S. mansoni eggs, reduced OVA/alum-induced AAI. ω1 is taken up in the peritoneal cavity by dendritic cells (DCs) expressing the mannose receptor, reducing their expression of CCR7 and migratory capacity to the draining mediastinal lymph nodes. This results in accumulation of DCs in the peritoneal cavity of allergic mice and reduced numbers of DCs reaching the draining lymph nodes. The effects observed for ω1 is dependent on its RNAse activity, since the RNAse mutant form of ω1 was unable to reduce AAI nor affect DC migration. Our findings provide insights into how ω1 can modulated the immune response during allergic inflammation, and this may open new avenues for the development of novel therapeutic strategies for allergic asthma.