CD116+ fetal precursors migrate to the perinatal lung and give rise to human alveolar macrophages

Despite their importance in lung health and disease, it remains unknown how human alveolar macrophages develop early in life. Here we define the ontogeny of human alveolar macrophages from embryonic progenitors in vivo, using a humanized mouse model expressing human cytokines (MISTRG mice). We identified alveolar macrophage progenitors in human fetal liver that expressed the GM-CSF receptor CD116 and the transcription factor MYB. Transplantation experiments in MISTRG mice established a precursor–product relationship between CD34−CD116+ fetal liver cells and human alveolar macrophages in vivo. Moreover, we discovered circulating CD116+CD64−CD115+ macrophage precursors that migrated from the liver to the lung. Similar precursors were present in human fetal lung and expressed the chemokine receptor CX3CR1. Fetal CD116+CD64− macrophage precursors had a proliferative gene signature, outcompeted adult precursors in occupying the perinatal alveolar niche, and developed into functional alveolar macrophages. The discovery of the fetal alveolar macrophage progenitor advances our understanding of human macrophage origin and ontogeny.

CD23 Mediates Innate Immunity Against Aspergillus Fumigatus Infection in Human Alveolar Macrophages Through Activation by PU.1

Aspergillosis is a common cause of morbidity and mortality in immunocompromised populations. CD23 is a novel C-type lectin receptors (CLR) recognizing α-mannan and β-glucan in the cell wall of Aspergillus fumigatus (AF) that exerts a host innate immune response. However, the molecular mechanism underlying CD23 mediating immunity against AF infection in human alveolar macrophages is still unclear. In this study, we detected the expression of CD23 and PU.1 and the inflammatory markers IL-1β, IL-6, TNF-α and IL-10 by qRT–PCR, Western blotting and enzyme linked immunosorbent assay (ELISA) analysis in human alveolar macrophages (AMs) with AF infection. Phagocytosis of macrophages with altered CD23 expression and histological changes in lung tissues transfected with CD23-expressing adenoviruses in AF infection were investigated. Dual luciferase, chromatin immunoprecipitation assay (ChIP) and electrophoretic mobility shift assay (EMSA) was performed to detect the interaction of PU.1 and CD23. The results showed that the expression of CD23, PU.1 and these inflammatory markers increased significantly with the time of AF infection. Increasing CD23 expression strengthened the phagocytosis of AMs, and exogenous CD23 attenuated pathological defects in immunodeficient mouse lung tissues with AF infection. Moreover, CD23 was directly activated by PU.1. PU.1 siRNA resulted in downregulation of inflammatory marker expression, but overexpression of CD23 significantly increased the expression of these markers. Our study concluded that CD23 mediates innate immunity against AF in human AMs through activation of PU.1. Therefore, PU.1/CD23 may be a new anti-aspergillosis therapeutic for the treatment of invasive aspergillosis with the deepening of gene therapy and its wide application in the clinic.

Small Noncoding RNAs MTS0997 and MTS1338 Affect the Adaptation and Virulence of Mycobacterium tuberculosis

Tuberculosis (TB) is currently the leading cause of death among bacterial infectious diseases. The spectrum of disease manifestations depends on both host immune responses and the ability of Mycobacterium tuberculosis to resist it. Small non-coding RNAs are known to regulate gene expression; however, their functional role in the relationship of M. tuberculosis with the host is poorly understood. Here, we investigated the effect of small non-coding sRNAs MTS1338 and MTS0997 on M. tuberculosis properties by creating knockout strains. We also assessed the effect of small non-coding RNAs on the survival of wild type and mutant mycobacteria in primary cultures of human alveolar macrophages and the virulence of these strains in a mouse infection model. Wild-type and mutants survived differentially in human alveolar macrophages. Infection of I/St mice with KO M. tuberculosis H37RV strains provided beneficial effects onto major TB phenotypes. We observed attenuated tuberculosis-specific inflammatory responses, including reduced cellular infiltration and decreased granuloma formation in the lungs. Infections caused by KO strains were characterized by significantly lower inflammation of mouse lung tissue and increased survival time of infected animals. Thus, the deletion of MTS0997 and MTS1338 lead to a significant decrease in the virulence of M. tuberculosis.

BordetellaAdenylate Cyclase Toxin Inhibits Monocyte-to-Macrophage Transition and Dedifferentiates Human Alveolar Macrophages into Monocyte-like Cells

ABSTRACTMonocytes arriving at the site of infection differentiate into functional effector macrophages to replenish the resident sentinel cells.Bordetella pertussis, the pertussis agent, secretes an adenylate cyclase toxin-hemolysin (CyaA) that binds myeloid phagocytes through complement receptor 3 (CD11b/CD18) and swiftly delivers its adenylyl cyclase enzyme domain into phagocytes. This ablates the bactericidal capacities of phagocytes through massive and unregulated conversion of cytosolic ATP into the key signaling molecule cAMP. We show that exposure of primary human monocytes to as low a concentration as 22.5 pM CyaA, or a low (2:1) multiplicity of infection by CyaA-producingB. pertussisbacteria, blocks macrophage colony-stimulating factor (M-CSF)-driven differentiation of monocytes. CyaA-induced cAMP signaling mediated through the activity of protein kinase A (PKA) efficiently blocked expression of macrophage markers, and the monocytes exposed to 22.5 pM CyaA failed to acquire the characteristic intracellular complexity of mature macrophage cells. Neither M-CSF-induced endoplasmic reticulum (ER) expansion nor accumulation of Golgi bodies, mitochondria, or lysosomes was observed in toxin-exposed monocytes, which remained small and poorly phagocytic and lacked pseudopodia. Exposure to 22.5 pM CyaA toxin provoked loss of macrophage marker expression onin vitrodifferentiated macrophages, as well as on primary human alveolar macrophages, which appeared to dedifferentiate into monocyte-like cells with upregulated CD14 levels. This is the first report that terminally differentiated tissue-resident macrophage cells can be dedifferentiatedin vitro. The results suggest that blocking of monocyte-to-macrophage transition and/or dedifferentiation of the sentinel cells of innate immunity through cAMP-elevating toxin action may represent a novel immune evasion strategy of bacterial pathogens.IMPORTANCEMacrophages are key sentinel cells of the immune system, and, as such, they are targeted by the toxins produced by the pertussis agentBordetella pertussis. The adenylate cyclase toxin (CyaA) mediates immune evasion ofB. pertussisby suspending the bactericidal activities of myeloid phagocytes. We reveal a novel mechanism of potential subversion of host immunity, where CyaA at very low (22 pM) concentrations could inhibit maturation of human monocyte precursors into the more phagocytic macrophage cells. Furthermore, exposure to low CyaA amounts has been shown to trigger dedifferentiation of mature primary human alveolar macrophages back into monocyte-like cells. This unprecedented capacity is likely to promote survival of the pathogen in the airways, both by preventing maturation of monocytes attracted to the site of infection into phagocytic macrophages and by dedifferentiation of the already airway-resident sentinel cells.