In allergic asthma, inhalation of airborne allergens such as house dust mite (HDM) effectively activates both innate and adaptive immunity in the lung mucosa. To determine the role of the eicosanoid PGI2 and its receptor IP during allergic airway sensitization, HDM responses in mice lacking a functional IP receptor (IP−/−) were compared to wild type (WT) mice. Surprisingly, IP−/− mice had increased numbers of pulmonary CD3−NK1.1+Ly49b+ NK cells producing IFN-γ that was inversely associated with the number of type 2 innate lymphoid cells (ILC2s) expressing IL-33Rα and IL-13 compared to WT animals. This phenomenon was associated with elevated CX3CL1 levels in the airways of IP−/− mice and treatment with a neutralizing antibody to CX3CL1 reduced IFN-γ production by the lung NK cells. Remarkably, IP−/− mice were less responsive to HDM challenge than WT counterparts since intranasal instillation of the allergen induced markedly reduced levels of airway eosinophils, CD4+ lymphocyte infiltration and mucus production, as well as depressed levels of CCL2 chemokine and Th2 cytokines. NK cells were responsible for such attenuated responses since depletion of NK1.1+ cells in IP−/− mice restored both the HDM-induced lung inflammation and ILC2 numbers, while transfer of CD3−NK1.1+ NK cells into the airways of WT hosts suppressed the inflammatory response. Collectively, these data demonstrate a hitherto unknown role for PGI2 in regulating the number and properties of NK cells resident in lung tissue and reveal a role for NK cells in limiting lung tissue ILC2s and preventing allergic inflammatory responses to inhaled HDM allergen.

BackgroundEpidemiological studies suggest that prenatal and early life environmental exposures have adverse effects on pulmonary function and are important contributors in the development of childhood asthma and allergic disease. The mechanism by which environmental tobacco smoke (ETS) exposure in utero promotes the development of allergic asthma remains unclear. In this study, we investigated the immunological consequences of prenatal exposure to ETS in order to understand events responsible for the development or exacerbation of allergic asthma.MethodsPregnant C57BL/6 mice were exposed to either ETS or filtered air throughout gestation and the effect on pulmonary inflammation in the offspring were examined and compared. Specifically, the effects on eosinophilic inflammation, airway hyperreactivity, goblet cell hyperplasia, properties of pulmonary natural killer (NK) cells and type 2 cytokines elicited in response to inhaled house dust mite (HDM) allergen were investigated in the progeny.ResultsExposure to ETS prenatally significantly exacerbated HDM-induced airway eosinophilic inflammation, hyperreactivity, mucus secretion, cysteinyl leukotriene biosynthesis and type 2 cytokine production in the offspring. Consistently, lung mononuclear cells from ETS-exposed offspring secreted higher levels of IL-13 when stimulated in vitro with anti-αβ TCR antibody or HDM allergen. Moreover, offspring from ETS-exposed dams exhibited a higher frequency of CD11b+ dendritic cells and CD3+CD4+ T lymphocytes in the lungs following allergen inhalation compared to air-exposed mice. Unexpectedly, the exacerbated allergic inflammation in the ETS-exposed offspring was associated with a reduction in CD3−CD19−NK1.1+CD94+ NK cell numbers and their IFN-γ production, highlighting a role for altered innate immunity in the enhanced allergic response.ConclusionOur results reveal that prenatal exposure to ETS predisposes offspring to an exacerbated allergic airway inflammation that is associated with a reduction in pulmonary NK cell function, suggesting that NK cells play a key role in controlling asthma severity.

Multi-walled carbon nanotubes (MWCNT) have been reported to promote lung inflammation and fibrosis. The commercial demand for nanoparticle-based materials has expanded rapidly and as demand for nanomaterials grows, so does the urgency of establishing an appreciation of the degree of health risk associated with their increased production and exposure. In this study, we examined whether MWCNT inhalation elicited pulmonary eosinophilic inflammation and influenced the development of allergic airway inflammatory responses. Our data revealed that instillation of FA21 MWCNT into the airways of mice resulted in a rapid increase, within 24 h, in the number of eosinophils present in the lungs. The inflammatory response elicited was also associated with an increase in the level of cysteinyl leukotrienes (cysLTs) present in the bronchoalveolar lavage fluid. CysLTs were implicated in the airway inflammatory response since pharmacological inhibition of their biosynthesis using the 5-lipoxygenase inhibitor Zileuton resulted in a marked reduction in the severity of inflammation observed. Moreover, FA21 MWCNT entering the airways of mice suffering from house dust mite (HDM)-elicited allergic lung inflammation markedly exacerbated the intensity of the airway inflammation. This response was characterized by a pulmonary eosinophilia, lymphocyte infiltration, and raised cysLT levels. The severity of pulmonary inflammation caused by either inhalation of MWCNT alone or in conjunction with HDM allergen correlated with the level of nickel present in the material, since preparations that contained higher levels of nickel (FA21, 5.54% Ni by weight) were extremely effective at eliciting or exacerbating inflammatory or allergic responses while preparations containing lower amounts of nickel (FA04, 2.54% Ni by weight) failed to initiate or exacerbate pulmonary inflammation. In summary, instillation of high nickel MWCNT into the lungs promoted eosinophilic inflammation and caused an intense exacerbation of pre-existing allergic airway inflammation by facilitating cysLT biosynthesis. These findings suggest that exposure to airborne MWCNT is likely to have adverse inflammatory effects in individuals suffering from atopic asthma and, in this context, further investigation of the therapeutic effects of pharmacological agents that block leukotriene synthesis is warranted.