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Background: Early microbial exposure is associate with protective allergic asthma. We have previously demonstrated that Streptococcus pneumoniae aminopeptidase N (PepN), one of the pneumococcal components, inhibits ovalbumin (OVA) -induced airway inflammation in murine models of allergic asthma, but the underlying mechanism was incompletely determined. Methods: BALB/c mice were pretreated with the PepN protein and exposed intranasally to HDM allergen. The anti-inflammatory mechanisms were investigated using depletion and adoptive transfer experiments as well as transcriptome analysis and isolated lung CD11chigh macrophages. Results: We found pretreatment of mice with PepN promoted the proliferation of lung-resident F4/80+CD11chigh macrophages in situ but also mobilized bone marrow monocytes to infiltrate lung tissue that were then transformed into CD11high macrophages. PepN pre-programmed the macrophages during maturation to an anti-inflammatory phenotype by shaping the metabolic preference for oxidative phosphorylation (OXPHOS) and also inhibited the inflammatory response of macrophages by activating AMP-activated protein kinase. Furthermore, PepN treated macrophages also exhibited high-level costimulatory signaling molecules which directed the differentiation into Treg. Conclusion: Our results demonstrated that the expansion of CD11chigh macrophages in lungs and the OXPHOS metabolic bias of macrophages are associated with reduced allergic airway inflammation after PepN exposure, which paves the way for its application in preventing allergic asthma. [ABSTRACT FROM AUTHOR]

Efferocytosis can resolve airway inflammation and enhance airway tolerance in allergic asthma. While previous work has reported that progranulin (PGRN) regulated macrophage efferocytosis, but it is unclear whether PGRN‐mediated efferocytosis is associated with asthma. Here, we found that in an ovalbumin (OVA)‐induced allergic asthma model, the airway inflammation was suppressed and the apoptosis in lung tissues was ameliorated in PGRN‐deficient mice. In contrast, PGRN knockdown in human bronchial epithelial cells increased apoptosis in vitro. Furthermore, PGRN‐deficient macrophages had significantly stronger efferocytosis ability than wild type (WT) macrophages both in vitro and in vivo. PGRN‐deficient peritoneal macrophages (PMs) exhibited increased expression of genes associated with efferocytosis including milk fat globule‐epidermal growth factor 8 (MFG‐E8), peroxisome proliferator‐activated receptor gamma (PPAR‐γ) and sirtuin1 (SIRT1) and increased capacity to produce the anti‐inflammatory mediator interleukin (IL)‐10 during efferocytosis. GW9662, the inhibitor of PPAR‐γ, abolished increased efferocytosis and MFG‐E8 expression in PGRN‐deficient PMs suggesting that PGRN deficiency enhanced MFG‐E8‐mediated efferocytosis through PPAR‐γ. Correspondingly, efferocytosis genes were increased in the lungs of OVA‐induced PGRN‐deficient mice. GW9662 treatment reduced MFG‐E8 expression but did not significantly affect airway inflammation. Our results demonstrated that PGRN deficiency enhanced efferocytosis via the PPAR‐γ/MFG‐E8 pathway and this may be one of the reasons PGRN deficiency results in inhibition of airway inflammation in allergic asthma. [ABSTRACT FROM AUTHOR]