Type 2 innate lymphoid cells (ILC2s) and their adaptive counterpart type 2 T helper (T_H2) cells respond to interleukin-33 (IL-33) by producing IL-5, which is a crucial cytokine for eosinophil development in the bone marrow. The aim of this study was to determine if bone marrow ILC2s, T_H cells, and eosinophils are locally regulated by IL-33 in terms of number and activation upon exposure to the common aeroallergen house dust mite (HDM). Mice that were sensitized and challenged with HDM by intranasal exposures induced eosinophil development in the bone marrow with an initial increase of IL5Rα⁺ eosinophil progenitors, following elevated numbers of mature eosinophils and the induction of airway eosinophilia. Bone marrow ILC2s, T_H2, and eosinophils all responded to HDM challenge by increased IL-33 receptor (ST2) expression. However, only ILC2s, but not T_H cells, revealed increased ST2 expression at the onset of eosinophil development, which significantly correlated with the number of eosinophil progenitors. In summary, our findings suggest that airway allergen challenges with HDM activates IL-33-responsive ILC2s, T_H cells, and eosinophils locally in the bone marrow. Targeting the IL-33/ST2 axis in allergic diseases including asthma may be beneficial by decreasing eosinophil production in the bone marrow.

The polarization of CD4+ T cells into different T helper subsets is an important process in many diseases, including asthma. Part of the adaptive immune system, T cells are responsible for propagating signals to alert and prime the immune system. MicroRNAs (miRNAs) are small non-coding RNAs that act on numerous targets in the cell to regulate a variety of cellular processes, including roles in T cell polarization. In this study, we aimed to identify genes dysregulated in peripheral blood mononuclear cells from individuals with asthma. Moreover, we sought to examine miRNAs that may regulate the candidate genes and explore their functional relationship. Utilizing a focused gene array, we identified the serum/glucocorticoid-regulated kinase 1 (SGK1) gene to be upregulated in circulating peripheral blood mononuclear cells, which included T cells, from individuals with asthma. Several miRNAs were bioinformatically identified to target SGK1, but miR-19a was the only screened candidate that negatively correlated to SGK1 expression. Further analysis of the miR-19a-SGK1 relationship showed a negative correlation in CD4+ T cells in situ and direct binding in vitro during T cell activation. Moreover, we observed a negative correlation of miR-19a and SGK1 during early type 2 polarization of CD4+ naïve human T cells. Thus, we suggest that miR-19a has a role in binding and regulating SGK1 transcript levels during T cell development.

Background: Type 2 innate lymphoid cells (ILC2s) are regulators of type 2 inflammation in asthma. The mechanistic target of rapamycin (mTOR) inhibitor, rapamycin, has previously been reported to suppress inflammatory properties of lung ILC2s in an interleukin (IL)33-induced asthma mouse model. IL-33 induces bone marrow eosinophilia and we aimed to determine the anti-inflammatory properties of rapamycin with a focus on bone marrow eosinophils and ILC2s. Methods: Mice were pre-treated intraperitoneally with rapamycin one hour before receiving intranasal doses of recombinant IL-33 and were compared to control mice. IL-33-stimulated bone marrow cultures were treated with or without rapamycin and type 2 inflammation was determined by measuring IL-5⁺ ILC2s. Flow cytometry was used to characterize eosinophils and to measure the activity of the mTOR complex in ILC2s. Results: A significant reduction in eosinophil numbers with a lower mean fluorescence intensity of the IL-33 receptor ST2 was observed in the rapamycin+IL-33 group compared to IL-33 only. The total number of ILC2s was unchanged. Phosphorylation of Rps6, indicative of mTOR activity, was increased in ILC2s from the IL-33 only group and a reduced activity was observed in the rapamycin+IL-33 group. Furthermore, IL-5⁺ ILC2s decreased in bone marrow cultures with rapamycin+IL-33 compared to IL-33 only. Conclusion: Our data indicate that the mTOR pathway is essential for type 2 inflammation caused by bone marrow IL-5⁺ ILC2s in IL-33-induced eosinophilic inflammation. This mechanism can influence eosinophilopoiesis and the recruitment of eosinophils to sites of inflammation that might have implications for asthma pathogenesis.

Background: There is an unmet need to understand the underlying mechanisms contributing to the pathogenesis in asthma subgroups. Thus, in the current study we aimed to determine protein profiles in bronchial lavage (BL) fluid obtained from non-allergic (NAA) and allergic (AA) asthma groups and healthy controls. Methods: BL was collected from 20 well-characterized subjects (6-7/group) from the cohort West Sweden Asthma Study (WSAS). Proteins were quantified by LC-MS/MS. The protein expression profiles were examined using the software Qlucore Omics Explorer. Results: In total 3467 proteins were quantified and 2962 were quantified in all samples. The majority of the significantly altered proteins (p<0.01) were downregulated in the two asthma groups compared to healthy controls. However, comparing NAA subjects with AA subjects, distinct unique proteins were identified distinguishing the two asthma groups. Fifty proteins were significantly downregulated in NAA compared to AA. These proteins were associated with GO term connected to ciliogenesis, mRNA splicing and lung epithelial cell differentiation. Eight proteins were significantly upregulated in NAA compared to AA and two of these were connected to the classical complement pathway. Conclusion: The two asthma groups display a unique proteomic profile compared to healthy controls. Interestingly, distinct protein profiles were identified, separating the two asthma groups. These findings need to be validated and further explored in order to identify new disease mechanisms that distinguish different asthma groups.