CD103+ pulmonary dendritic cells preferentially acquire and present apoptotic cell–associated antigen

CD103-expressing dendritic cells in the lungs preferentially take up and cross-present antigen from apoptotic cells

Biology of lung macrophages in health and disease

Tissue-resident alveolar and interstitial macrophages and recruited macrophages are critical players in innate immunity and maintenance of lung homeostasis. Until recently, assessing the differential functional contributions of tissue-resident versus recruited macrophages has been challenging because they share overlapping cell surface markers, making it difficult to separate them using conventional methods. This review describes how scRNA-seq and spatial transcriptomics can separate these subpopulations and help unravel the complexity of macrophage biology in homeostasis and disease. First, we provide a guide to identifying and distinguishing lung macrophages from other mononuclear phagocytes in humans and mice. Second, we outline emerging concepts related to the development and function of the various lung macrophages in the alveolar, perivascular, and interstitial niches. Finally, we describe how different tissue states profoundly alter their functions, including acute and chronic lung disease, cancer, and aging

Promoter Specificity and Efficacy in Conditional and Inducible Transgenic Targeting of Lung Macrophages

Conditional and inducible Cre-loxP systems are used to target gene deletion to specific cell lineages and tissues through promoter-restricted expression of the bacterial DNA recombinase, Cre. Although Cre-loxP systems are widely used to target gene deletion in lung macrophages, limited data are published on the specificity and efficiency of “macrophage targeting” Cre lines. Using R26-stopfl/fl-TdTomato and tetOn-GFP reporter lines, we assessed the specificity and efficiency of four commercially available Cre driver lines that are often considered “macrophage specific.” We evaluated two conditional (Csf1r-Cre and LysM-Cre) and two inducible [CX3CR1-estrogen receptor-Cre (ERCre) and CD68-rtTA] lines. We assessed Cre activation in six resident lung myeloid populations, as well as activation in lung leukocytes, lung epithelial and endothelial cells, peripheral blood leukocytes, and tissue macrophages of the spleen, bone marrow, and peritoneal cavity. Although Csf1r-Cre and LysM-Cre target resident alveolar macrophages (ResAM) and interstitial macrophages (IM) with high efficiency, neither line is specific for macrophages. Csf1r-Cre targets all leukocyte populations, while LysM-Cre targets dendritic cell, neutrophils, monocytes, and a quarter of lung epithelial cells. CX3CR1-ERCre and CD68-rtTA both target IM, but do not target ResAM. Further, although neither line is specific for macrophages, a pulse-wait administration of tamoxifen or doxycycline can be used to significantly improve IM specificity in these inducible lines. In summary, while Cre-loxP remains a powerful tool to study macrophage function, numerous pitfalls exist. Herein, we document strengths and weaknesses of Csf1r-Cre, LysM-Cre, CX3CR1-ERCre, and CD68-rtTA systems for targeting specific macrophage populations in the lungs and provide data that will aid investigators in selecting the proper strain

CCL5-producing migratory dendritic cells guide CCR5+ monocytes into the draining lymph nodes

Dendritic cells (DCs) and monocytes capture, transport, and present antigen to cognate T cells in the draining lymph nodes (LNs) in a CCR7-dependent manner. Since only migratory DCs express this chemokine receptor, it is unclear how monocytes reach the LN. In steady-state and following inhalation of several PAMPs, scRNA-seq identified LN mononuclear phagocytes as monocytes, resident, or migratory type 1 and type 2 conventional (c)DCs, despite the downregulation of Xcr1, Clec9a, H2-Ab1, Sirpa, and Clec10a transcripts on migratory cDCs. Migratory cDCs, however, upregulated Ccr7, Ccl17, Ccl22, and Ccl5. Migratory monocytes expressed Ccr5, a high-affinity receptor for Ccl5. Using two tracking methods, we observed that both CD88hiCD26lomonocytes and CD88-CD26hi cDCs captured inhaled antigens in the lung and migrated to LNs. Antigen exposure in mixed-chimeric Ccl5-, Ccr2-, Ccr5-, Ccr7-, and Batf3-deficient mice demonstrated that while antigen-bearing DCs use CCR7 to reach the LN, monocytes use CCR5 to follow CCL5-secreting migratory cDCs into the LN, where they regulate DC-mediated immunity

Antigen-Specific Regulation of IgE Antibodies by Non-Antigen–Specific γδ T Cells

We re-examined the observation that γδ T cells, when transferred from mice tolerized to an inhaled conventional Ag, suppress the allergic IgE response to this Ag specifically. Using OVA and hen egg lysozyme in crisscross fashion, we confirmed the Ag-specific IgE-regulatory effect of the γδ T cells. Although only Vγ4+ γδ T cells are regulators, the Ag specificity does not stem from specificity of their γδ TCRs. Instead, the Vγ4+ γδ T cells failed to respond to either Ag, but rapidly acquired Ag-specific regulatory function in vivo following i.v. injection of non-T cells derived from the spleen of Ag-tolerized mice. This correlated with their in vivo Ag acquisition from i.v. injected Ag-loaded splenic non-T cells, and in vivo transfer of membrane label provided evidence for direct contact between the injected splenic non-T cells and the Vγ4+ γδ T cells. Together, our data suggest that Ag itself, when acquired by γδ T cells, directs the specificity of their IgE suppression

Advancing lung immunology research : an official American Thoracic Society workshop report

The mammalian airways and lungs are exposed to a myriad of inhaled particulate matter, allergens, and pathogens. The immune system plays an essential role in protecting the host from respiratory pathogens, but a dysregulated immune response during respiratory infection can impair pathogen clearance and lead to immunopathology. Furthermore, inappropriate immunity to inhaled antigens can lead to pulmonary diseases. A complex network of epithelial, neural, stromal, and immune cells has evolved to sense and respond to inhaled antigens, including the decision to promote tolerance versus a rapid, robust, and targeted immune response. Although there has been great progress in understanding the mechanisms governing immunity to respiratory pathogens and aeroantigens, we are only beginning to develop an integrated understanding of the cellular networks governing tissue immunity within the lungs and how it changes after inflammation and over the human life course. An integrated model of airway and lung immunity will be necessary to improve mucosal vaccine design as well as prevent and treat acute and chronic inflammatory pulmonary diseases. Given the importance of immunology in pulmonary research, the American Thoracic Society convened a working group to highlight central areas of investigation to advance the science of lung immunology and improve human health