human-lung-dendritic-cells-spatial-distribution-phenotypic

Human Lung Dendritic Cells: Spatial Distribution and Phenotypic Identification in Endobronchial Biopsies Using Immunohistochemistry and Flow Cytometry

The lungs are constantly exposed to the external environment, which in addition to harmless particles, also contains pathogens, allergens, and toxins. In ...

Karolinska Institutet

The proinflammatory microenvironment in the respiratory airway induces maturation of both resident and infiltrating dendritic cells (DCs) upon influenza A virus (IAV) infection. This results in upregulation of antiviral pathways as well as modulation of endocytic processes, which affect the susceptibility of DCs to IAV infection. Therefore, it is highly relevant to understand how IAV interacts with and infects mature DCs. To investigate how different subsets of human myeloid DCs (MDCs) involved in tissue inflammation are affected by inflammatory stimulation during IAV infection, we stimulated primary blood MDCs and inflammatory monocyte-derived DCs (MDDCs) with TLR ligands, resulting in maturation. Interestingly, MDDCs but not MDCs were protected against IAV infection after LPS (TLR4) stimulation. In contrast, stimulation with TLR7/8 ligand protected MDCs but not MDDCs from IAV infection. The reduced susceptibility to IAV infection correlated with induction of type I IFNs. We found that differential expression of TLR4, TRIF, and MyD88 in the two MDC subsets regulated the ability of the cells to enter an antiviral state upon maturation. This difference was functionally confirmed using small interfering RNA and inhibitors. Our data show that different human MDC subsets may play distinct roles during IAV infection, as their capacity to induce type I IFNs is dependent on TLR-specific maturation, resulting in differential susceptibility to IAV infection.

Protection of human myeloid dendritic cell subsets against influenza A virus infection is differentially regulated upon TLR stimulation.

Every breath we take contains potentially harmful pathogens or allergens. Dendritic cells (DCs), monocytes, and macrophages are essential in maintaining a delicate balance of initiating immunity without causing collateral damage to the lungs because of an exaggerated inflammatory response. To document the diversity of lung mononuclear phagocytes at steady-state, we performed bronchoscopies on 20 healthy subjects, sampling the proximal and distal airways (bronchial wash and bronchoalveolar lavage, respectively), as well as mucosal tissue (endobronchial biopsies). In addition to a substantial population of alveolar macrophages, we identified subpopulations of monocytes, myeloid DCs (MDCs), and plasmacytoid DCs in the lung mucosa. Intermediate monocytes and MDCs were highly frequent in the airways compared with peripheral blood. Strikingly, the density of mononuclear phagocytes increased upon descending the airways. Monocytes from blood and airways produced 10-fold more proinflammatory cytokines than MDCs upon ex vivo stimulation. However, airway monocytes were less inflammatory than blood monocytes, suggesting a more tolerant nature. The findings of this study establish how to identify human lung mononuclear phagocytes and how they function in normal conditions, so that dysregulations in patients with respiratory diseases can be detected to elucidate their contribution to immunity or pathogenesis.

Dendritic Cells and Monocytes with Distinct Inflammatory Responses Reside in Lung Mucosa of Healthy Humans.

Epidermal Langerhans cells (LCs) are spatially separated from dermal dendritic cells (DCs) in healthy human skin. In active psoriasis, maintained by local production of IL-23 and IL-17, DCs infiltrate both skin compartments. Here we show that CCR2(+) epidermal DCs (eDCs), phenotypically distinct from dermal DCs, were strictly confined to lesional psoriasis. The eDCs exceeded the number of LCs and displayed high expression of genes involved in neutrophil recruitment and the activation of keratinocytes and T cells. In active lesions, resident LCs responded to Toll Like Receptor (TLR) 4 and TLR 7/8 activation with increased IL-23 production whereas eDCs produced IL-1β in addition to IL-23 and TNF. eDCs were absent from resolved psoriasis. Instead, LCs from anti-TNF treated lesions retained high IL23A expression and responded to TLR stimulation by producing IL-23. Our results reveal phenotypic and functional properties of eDCs and resident LCs in different clinical phases of psoriasis, and the capacity of these cells to amplify the epidermal microenvironment through the secretion of IL-17 polarizing cytokines.

Article	Year
Protection of human myeloid dendritic cell subsets against influenza A virus infection is differentially regulated upon TLR stimulation. Journal of immunology (Baltimore, Md. : 1950)\| PubMed ID: 25801434	2015
Dendritic Cells and Monocytes with Distinct Inflammatory Responses Reside in Lung Mucosa of Healthy Humans. Journal of immunology (Baltimore, Md. : 1950)\| PubMed ID: 27183618	2016
Dynamic changes in resident and infiltrating epidermal dendritic cells in active and resolved psoriasis. The Journal of investigative dermatology\| PubMed ID: 28011143	2016

Faezzah Baharom

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