The preprogrammed anti-inflammatory phenotypes of CD11c^high macrophages by Streptococcus pneumoniae aminopeptidase N safeguard from allergic asthma

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 CD11c^high macrophages.

Results: We found pretreatment of mice with PepN promoted the proliferation of lung-resident F4/80⁺CD11c^high macrophages in situ but also mobilized bone marrow monocytes to infiltrate lung tissue that were then transformed into CD11^high 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 CD11c^high 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.