Apolipoprotein E controls the development of monocyte-derived alveolar macrophages upon pulmonary inflammatory adaptation

The lung is constantly exposed to the outside world and optimal adaptation of immune responses is crucial for efficient pathogen clearance. However, mechanisms that lead to lung-associated macrophages' functional and developmental adaptation remain elusive. To reveal such mechanisms, we developed a reductionist model of environmental intranasal β-glucan exposure, allowing for the detailed interrogation of molecular mechanisms of pulmonary macrophage adaptation. Employing single-cell transcriptomics, high dimensional imaging, and flow cytometric characterization paired with in vivo and ex vivo challenge models, we reveal that pulmonary low-grade inflammation results in the development of Apolipoprotein E (ApoE) -dependent monocyte-derived alveolar macrophages (ApoE+CD11b+ AM). ApoE+CD11b+ AMs expressed high levels of CD11b, ApoE, Gpnmb, and Ccl6, were glycolytic, highly phagocytic, and produced large amounts of interleukin 6 upon restimulation. Functional differences were cell intrinsic and myeloid cell-specific ApoE ablation inhibited Ly6c+ monocyte to ApoE+CD11b+ AM differentiation dependent on M-CSF secretion, promoting ApoE+CD11b+ AM cell death and thus impeding ApoE+CD11b+ AM maintenance. In vivo, β-glucan-elicited ApoE+CD11b+ AMs limited the bacterial burden of Legionella pneumophilia post-infection and improved the disease outcome in vivo and ex vivo in a murine lung fibrosis model. Collectively these data identify ApoE+CD11b+ AMs generated uponenvironmental cues, under the control of ApoE signaling, as an essential determinant for lung adaptation enhancing tissue resilience

Transmission of trained immunity and heterologous resistance to infections across generations.

Intergenerational inheritance of immune traits linked to epigenetic modifications has been demonstrated in plants and invertebrates. Here we provide evidence for transmission of trained immunity across generations to murine progeny that survived a sublethal systemic infection with Candida albicans or a zymosan challenge. The progeny of trained mice exhibited cellular, developmental, transcriptional and epigenetic changes associated with the bone marrow-resident myeloid effector and progenitor cell compartment. Moreover, the progeny of trained mice showed enhanced responsiveness to endotoxin challenge, alongside improved protection against systemic heterologous Escherichia coli and Listeria monocytogenes infections. Sperm DNA of parental male mice intravenously infected with the fungus C. albicans showed DNA methylation differences linked to immune gene loci. These results provide evidence for inheritance of trained immunity in mammals, enhancing protection against infections

Transmission of trained immunity and heterologous resistance to infections across generations

Intergenerational inheritance of immune traits linked to epigenetic modifications has been demonstrated in plants and invertebrates. Here we provide evidence for transmission of trained immunity across generations to murine progeny that survived a sublethal systemic infection with Candida albicans or a zymosan challenge. The progeny of trained mice exhibited cellular, developmental, transcriptional and epigenetic changes associated with the bone marrow-resident myeloid effector and progenitor cell compartment. Moreover, the progeny of trained mice showed enhanced responsiveness to endotoxin challenge, alongside improved protection against systemic heterologous Escherichia coli and Listeria monocytogenes infections. Sperm DNA of parental male mice intravenously infected with the fungus C. albicans showed DNA methylation differences linked to immune gene loci. These results provide evidence for inheritance of trained immunity in mammals, enhancing protection against infections. © 2021, The Author(s), under exclusive licence to Springer Nature America, Inc