Single-cell proteomics and transcriptomics capture eosinophil development and identify the role of IL-5 in their lineage transit amplification.

The activities, ontogeny, and mechanisms of lineage expansion of eosinophils are less well resolved than those of other immune cells, despite the use of biological therapies targeting the eosinophilia-promoting cytokine interleukin (IL)-5 or its receptor, IL-5Rα. We combined single-cell proteomics and transcriptomics and generated transgenic IL-5Rα reporter mice to revisit eosinophilopoiesis. We reconciled human and murine eosinophilopoiesis and provided extensive cell-surface immunophenotyping and transcriptomes at different stages along the continuum of eosinophil maturation. We used these resources to show that IL-5 promoted eosinophil-lineage expansion via transit amplification, while its deletion or neutralization did not compromise eosinophil maturation. Informed from our resources, we also showed that interferon response factor-8, considered an essential promoter of myelopoiesis, was not intrinsically required for eosinophilopoiesis. This work hence provides resources, methods, and insights for understanding eosinophil ontogeny, the effects of current precision therapeutics, and the regulation of eosinophil development and numbers in health and disease.

Lung Interstitial Macrophages Can Present Soluble Antigens and Induce Foxp3+ Regulatory T Cells.

Lung macrophages constitute a sophisticated surveillance and defense system that contributes to tissue homeostasis and host defense and allows the host to cope with the myriad of insults and antigens to which the lung mucosa is exposed. As opposed to alveolar macrophages, lung interstitial macrophages (IMs) express high levels of Type 2 major histocompatibility complex (MHC-II), a hallmark of antigen-presenting cells. Here, we showed that lung IMs, like dendritic cells, possess the machinery to present soluble antigens in an MHC-II-restricted way. Using ex vivo ovalbumin (OVA)-specific T cell proliferation assays, we found that OVA-pulsed IMs could trigger OVA-specific CD4+ T cell proliferation and Foxp3 expression through MHC-II-, IL-10-, and transforming growth factor ß-dependent mechanisms. Moreover, we showed that IMs efficiently captured locally instilled antigens in vivo, did not migrate to the draining lymph nodes, and enhanced local interactions with CD4+ T cells in a model of OVA-induced allergic asthma. These results support that IMs can present antigens to CD4+ T cells and trigger regulatory T cells, which might attenuate lung immune responses and have functional consequences for lung immunity and T cell-mediated disorders.