Inception of early-life allergen–induced airway hyperresponsiveness is reliant on IL-13+CD4+ T cells

Airway hyperresponsiveness (AHR) is a critical feature of wheezing and asthma in children, but the initiating immune mechanisms remain unconfirmed. We demonstrate that both recombinant interleukin-33 (rIL-33) and allergen [house dust mite (HDM) or Alternaria alternata] exposure from day 3 of life resulted in significantly increased pulmonary IL-13+CD4+ T cells, which were indispensable for the development of AHR. In contrast, adult mice had a predominance of pulmonary LinnegCD45+CD90+IL-13+ type 2 innate lymphoid cells (ILC2s) after administration of rIL-33. HDM exposure of neonatal IL-33 knockout (KO) mice still resulted in AHR. However, neonatal CD4creIL-13 KO mice (lacking IL-13+CD4+ T cells) exposed to allergen from day 3 of life were protected from AHR despite persistent pulmonary eosinophilia, elevated IL-33 levels, and IL-13+ ILCs. Moreover, neonatal mice were protected from AHR when inhaled Acinetobacter lwoffii (an environmental bacterial isolate found in cattle farms, which is known to protect from childhood asthma) was administered concurrent with HDM. A. lwoffii blocked the expansion of pulmonary IL-13+CD4+ T cells, whereas IL-13+ ILCs and IL-33 remained elevated. Administration of A. lwoffii mirrored the findings from the CD4creIL-13 KO mice, providing a translational approach for disease protection in early life. These data demonstrate that IL-13+CD4+ T cells, rather than IL-13+ ILCs or IL-33, are critical for inception of allergic AHR in early life

Transcriptomic analysis reveals diverse gene expression changes in airway macrophages during experimental allergic airway disease.

Background: Airway macrophages (AMs) are the most abundant leukocytes in the healthy airway lumen and have a highly specialised but plastic phenotype that is governed by signals in the local microenvironment. AMs are thought to maintain immunological homeostasis in the steady state, but have also been implicated in the pathogenesis of allergic airway disease (AAD). In this study, we aimed to better understand these potentially contrasting AM functions using transcriptomic analysis. Methods: Bulk RNA sequencing was performed on AMs (CD11c + Siglec F + CD64 + CD45 + SSC hi) flow cytometry sorted from C57BL/6 mice during experimental AAD driven by repeated house dust mite inhalation (AMs HDM), compared to control AMs from non-allergic mice. Differentially expressed genes were further analysed by hierarchical clustering and biological pathway analysis. Results: AMs HDM showed increased expression of genes associated with antigen presentation, inflammatory cell recruitment and tissue repair, including several chemokine and matrix metalloproteinase genes. This was accompanied by increased expression of mitochondrial electron transport chain subunit genes and the retinoic acid biosynthetic enzyme gene Raldh2. Conversely, AMs HDM displayed decreased expression of a number of cell cycle genes, genes related to cytoskeletal functions and a subset of genes implicated in antimicrobial innate immunity, such as Tlr5, Il18 and Tnf. Differential gene expression in AMs HDM was consistent with upstream effects of the cytokines IL-4 and IFN-γ, both of which were present at increased concentrations in lung tissue after HDM treatment. Conclusions: These data highlight diverse gene expression changes in the total AM population in a clinically relevant mouse model of AAD, collectively suggestive of contributions to inflammation and tissue repair/remodelling, but with decreases in certain steady state cellular and immunological functions

Airway macrophage-intrinsic TGF-β1 regulates pulmonary immunity during early life allergen exposure

Background Early life represents a major risk window for asthma development. However, the mechanisms controlling the threshold for establishment of allergic airway inflammation in early life are incompletely understood. Airway macrophages (AMs) regulate pulmonary allergic responses and undergo TGF-β–dependent postnatal development, but the role of AM maturation factors such as TGF-β in controlling the threshold for pathogenic immune responses to inhaled allergens remains unclear. Objective Our aim was to test the hypothesis that AM-derived TGF-β1 regulates pathogenic immunity to inhaled allergen in early life. Methods Conditional knockout (Tgfb1ΔCD11c) mice, with TGF-β1 deficiency in AMs and other CD11c+ cells, were analyzed throughout early life and following neonatal house dust mite (HDM) inhalation. The roles of specific chemokine receptors were determined by using in vivo blocking antibodies. Results AM-intrinsic TGF-β1 was redundant for initial population of the neonatal lung with AMs, but AMs from Tgfb1ΔCD11c mice failed to adopt a mature homeostatic AM phenotype in the first weeks of life. Evidence of constitutive TGF-β1 signaling was also observed in pediatric human AMs. TGF-β1–deficient AMs expressed enhanced levels of monocyte-attractant chemokines, and accordingly, Tgfb1ΔCD11c mice exposed to HDM throughout early life accumulated CCR2-dependent inflammatory CD11c+ mononuclear phagocytes into the airway niche that expressed the proallergic chemokine CCL8. Tgfb1ΔCD11c mice displayed augmented TH2, group 2 innate lymphoid cell, and airway remodeling responses to HDM, which were ameliorated by blockade of the CCL8 receptor CCR8. Conclusion Our results highlight a causal relationship between AM maturity, chemokines, and pathogenic immunity to environmental stimuli in early life and identify TGF-β1 as a key regulator of this