Mechanistic studies on the allergy protective effect of Acinetobacter lwoffii in the mouse
BACKGROUND: Early childhood or even prenatal exposures to farm bacteria such as Acinetobacter lwoffii have been demonstrated an association with a decreased incidence of allergy and asthma later in life. Studies in mouse models demonstrated that intranasal application of A. lwoffii stimulates local...
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|Summary:||BACKGROUND: Early childhood or even prenatal exposures to farm bacteria such as Acinetobacter lwoffii have been demonstrated an association with a decreased incidence of allergy and asthma later in life. Studies in mouse models demonstrated that intranasal application of A. lwoffii stimulates local and systemic innate immunity as reflected by increased levels of the pro-inflammatory cytokines, especially interleukin-6 (IL-6) levels in lungs and serum.
AIMS AND HYPOTHESIS: The key concept of this study was to understand different mechanistic pathways of the A. lwoffii protective effect against asthma. We hypothesized that interleukin-6 (IL-6) might contributes to the protective effect of A. lwoffii against asthma/allergy development. We further supposed that treatment with A. lwoffii stimulates the innate immune system in which it can skew the function of the adaptive immune system towards mechanisms know to favor lower asthma and/or allergy susceptibility. Furthermore, we expand our hypothesis to highlight the role of the cecum microbiota changes in mediating the protective effects of the A. lwoffii against asthma in the WT and IL-6 KO mice.
METHOD AND RESULTS: We first investigate the innate immune response upon contact with A. lwoffii, the mouse was chronically treated with A. lwoffii and then the blood and bronchial lavage were collected for pro-inflammatory cytokines measurement, TNFa and IL-1b developed tolerance after the 5th application but the IL-6 exhibit unusual response with no tolerance during the repeated treatment. Further assessments in Wild-type and IL-6 knockout mice pre-exposed to A. lwoffii and subjected to the OVA model of airway inflammation demonstrate a pivotal role of IL-6 in mediating the protective effects of A. lwoffii. This data was supported with the in vitro data where the mouse primary macrophages (PM), plasmacytoid dendritic cells (pDCs), and myeloid dendritic cells (mDCs) exposed to A. lwoffii secreted huge amounts of IL-6, as measured in the culture supernatants. Culturing of naïve murine T cells with supernatant from A. lwoffii-exposed macrophages or recombinant IL-6 induce the secretion of high levels of IL-10 and less extend of IL-17. The subsequent animal experiment revealed that IL-10 but not IL-17 deficient mice pretreated with A. lwoffii failed to develop protection against airway inflammation, suggesting that IL-10 but not IL-17 plays an important role in mediating the effects of A. lwoffii downstream of
IL-6. On top of that, the microbial DNA from the cecum content of the IL-6 KO and WT littermate mice were isolated and sequenced to investigate the changes in the relative abundance of taxa in the cecum microbiome. The genotype effect, the A. lwoffii effect, the OVA sensitization effect, and the A. lwoffii effect in OVA-sensitized mice were studied in IL-6 KO and WT littermate animal. The data demonstrated an important role of the Ruminococcaceae family which is indicating their susceptibility to immune control which is maybe underlying the immunological/anti-allergic phenotypes in the IL-6 KO mice, the A. lwoffii is having its immunological effects through the inhibition of the Ruminococcaceae family.
CONCLUSION: Protective effects of A. lwoffii against asthma development seem to be at least partly mediated by IL-6. Thus IL-6 might be an important modulator of the adaptive immune system towards the non-/anti-allergic direction. The in vitro macrophages exposed to A. lwoffii secrete huge amounts of IL-6, which in turn stimulates the synthesis of IL-10 and IL-17 by T cells after culturing the naïve T cells with supernatant from A. lwoffii-exposed macrophages. A subsequent experiment in mouse model demonstrates that IL-10 but not IL-17 play an important role in downstream the protective effects of A. lwoffii on adaptive immunity. Furthermore, the microbiome analysis in the IL-6 KO and WT littermate indicates a possible immune regulation via the Ruminococcaceae family which is maybe underlying the immunological/anti-allergic phenotypes in the IL-6 KO mice, the A. lwoffii is having its immunological effects through the inhibition of the Ruminococcaceae family. Further investigations in germ-free mice are required to address the role Ruminococcaceae, and additional in-depth investigations, including those on the possible interaction with IL-10, are ongoing.|
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