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Axl expression is induced by TGF-β1 during Langerhans cell differentiation and enhances apoptotic cell uptake and blocks proinflammatory cytokine production.

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The transcription factor aryl hydrocarbon receptor (AhR) represents a promising therapeutic target in allergy and autoimmunity. AhR signaling induced by the newly described ligand VAF347 inhibits allergic lung inflammation as well as suppresses pancreatic islet allograft rejection. These effects are likely mediated via alterations in dendritic cell (DC) function. Moreover, VAF347 induces tolerogenic DCs. Langerhans cells (LCs) are immediate targets of exogenous AhR ligands at epithelial surfaces; how they respond to AhR ligands remained undefined. We studied AhR expression and function in human LCs and myelopoietic cell subsets using a lineage differentiation and gene transduction model of human CD34+ hematopoietic progenitors. We found that AhR is highly regulated during myeloid subset differentiation. LCs expressed highest AhR levels followed by monocytes. Conversely, neutrophil granulocytes lacked AhR expression. AhR ligands including VAF347 arrested the differentiation of monocytes and LCs at an early precursor cell stage, whereas progenitor cell expansion or granulopoiesis remained unimpaired. AhR expression was coregulated with the transcription factor PU.1 during myeloid subset differentiation. VAF347 inhibited PU.1 induction during initial monocytic differentiation, and ectopic PU.1 restored monocyte and LC generation in the presence of this compound. AhR ligands failed to interfere with cytokine receptor signaling during LC differentiation and failed to impair LC activation/maturation. VAF347-mediated antiproliferative effect on precursors undergoing LC lineage differentiation occurred in a clinically applicable serum-free culture model and was not accompanied by apoptosis induction. In conclusion, AhR agonist signaling interferes with transcriptional processes leading to monocyte/DC lineage commitment of human myeloid progenitor cells.

Stemflow production is affected by a suite of biotic and abiotic factors. It has proven difficult to determine the importance of individual canopy structure metrics on stemflow production. The disentanglement of the role and importance of individual canopy structure metrics would advance our understanding of the dynamics of stemflow production. This work employed ten isolated (i.e. no overlapping crowns) experimental European beech (Fagus sylvatica L.) saplings to examine the effects of various canopy structural metrics on stemflow production in east‐central Germany. The following canopy structural metrics were utilized in a hierarchical cluster analysis using Ward's method to separate the saplings into groups: primary branch count per unit projected crown area, secondary branch count per unit projected crown area, total branch count per unit projected crown area, mean branch inclination angle, minimum branch inclination angle, maximum branch inclination angle, total dry woody biomass per unit projected crown area, total foliar dry biomass per unit projected crown area and total dry biomass per unit projected crown area. Cluster group means revealed that saplings, which generate the largest stemflow yields, once controlled for sapling size, have straighter boles (but some trunk lean), more steeply inclined branches, a larger number of branches, more woody surface area and fewer numbers of leaves. Our results may prove valuable as a guide to researchers wishing to couple LiDAR and fine‐scale architectural models with the canopy metrics that govern stemflow to provide a better understanding of the canopy on the hydrology and biogeochemistry of forests. Copyright © 2013 John Wiley & Sons, Ltd.