Our results suggest that TLR2-mediated sensing of S. aureus-derived signals is strongly impaired in LC from AD skin. This phenomenon may partly contribute to the immune deviation in AD and the lack of S. aureus clearance.

The traditional view of how intracellular effector proteins are recruited to the B cell antigen receptor (BCR) complex at the plasma membrane is based on the occurrence of direct protein-protein interactions, as exemplified by the recruitment of the tyrosine kinase Syk (spleen tyrosine kinase) to phosphorylated motifs in BCR signaling subunits. By contrast, the subcellular targeting of the cytosolic adaptor protein SLP-65 (Src homology 2 domain-containing leukocyte adaptor protein of 65 kD), which serves as a proximal Syk substrate, is unclear. We showed that SLP-65 activation required its association at vesicular compartments in resting B cells. A module of ∼50 amino acid residues located at the amino terminus of SLP-65 anchored SLP-65 to the vesicles. Nuclear magnetic resonance spectroscopy showed that the SLP-65 amino terminus was structurally disordered in solution, but could bind in a structured manner to noncharged lipid components of cellular membranes. Our finding that preformed vesicular signaling scaffolds are required for B cell activation indicates that vesicles may deliver preassembled signaling cargo to sites of BCR activation.

Our study shows that AhR activation by FICZ reduces FcεRI and upregulates IDO expression in LC. This AhR-mediated anti-inflammatory feedback mechanism may dampen the allergen-induced inflammation in AD.

The SH2 domain-containing leukocyte adaptor proteins, SLP-65 (1) (BLNK (2), BASH (3)), and SLP-76 (4), are instrumental to integrate and collect signals from antigen receptors on B and T lymphocytes, respectively. In their N-terminal half, the two effector proteins encompass a variety of similar consensus motifs for either inducible tyrosine phosphorylation by Syk/ ZAP-70 family kinases or constitutive association to proteins with Src homology (SH) 3 3 domains. Both SLP adaptors possess a C-terminal SH2 domain with a very high degree of sequence similarity and reported binding specificity for phosphorylated tyrosine residues in the consensus motif YXDV (in single letter code for amino acids, with X being any amino acid). The similar overall structure of the two SLP family members matches their closely related signaling roles. Most prominently, their scaffolding functions are mandatory for the correct subcellular localization and activation of phospholipase C-␥ (PLC-␥) isoforms to induce mobilization of the second messenger Ca 2ϩ . Surprisingly and despite the common protein architecture, the molecular mechanisms through which SLP-65 and SLP-76 assemble and target the Ca 2ϩ initiation complexes in B and T cells, respectively, appear to be different (5).Downstream of the B cell antigen receptor (BCR), phosphorylated SLP-65 provides docking sites for the SH2 domains of Bruton's tyrosine kinase (Btk) and PLC-␥2 (2, 6 -9). Simultaneous recruitment of both enzymes must occur in cis, i.e. to a given SLP-65 molecule because only tri-molecular complex formation enables Btk to phosphorylate and thereby activate its target PLC-␥2 (9). To provide PLC-␥2 with access to its lipid substrate phosphatidylinositol 4,5-bisphosphate, the assembled Ca 2ϩ initiation complex needs to be tethered at the plasma membrane. As shown more recently, membrane anchoring requires an N-terminal leucine zipper motif in SLP-65, but the exact mechanism remains elusive (10). However, the N terminus of SLP-76 does not contain such a leucine zipper. In fact, nucleation of the Ca 2ϩ initiation complex upon engagement of the T cell antigen receptor (TCR) involves not only the intracellular adaptor SLP-76 but also (the transmembraneous linker of activated T cells) LAT (5,11,12). Tyrosine-phosphorylated LAT binds PLC-␥1 directly and associates simultaneously with a SLP-76/Itk complex through the Grb2 family member Gads. Itk is the T cell paralogue of Btk. LAT-and Gads-related molecules in B cells are NTAL (13) (alternatively named Lab (14)) and Grb2 itself. We recently showed that the NTAL/Grb2 module is indeed critically involved in BCR-triggered Ca 2ϩ elevation but through a SLP-65-independent mechanism (15, 16).One mode of stimulation-dependent membrane recruitment of SLP-65 involves its SH2 domain, which directly binds the *

IMPORTANCE Atopic dermatitis (AD) is the most common chronic inflammatory skin disease and is driven by a complex pathophysiology underlying highly heterogeneous phenotypes. Current advances in precision medicine emphasize the need for stratification. OBJECTIVE To perform deep phenotyping and identification of severity-associated factors in adolescent and adult patients with AD. DESIGN, SETTING, AND PARTICIPANTS Cross-sectional data from the baseline visit of a prospective longitudinal study investigating the phenotype among inpatients and outpatients with AD from the Department of Dermatology and Allergy of the University Hospital Bonn enrolled between November 2016 and February 2020.MAIN OUTCOMES AND MEASURES Patients were stratified by severity groups using the Eczema Area and Severity Index (EASI). The associations of 130 factors with AD severity were analyzed applying a machine learning-gradient boosting approach with cross-validationbased tuning as well as multinomial logistic regression.RESULTS A total of 367 patients (157 male [42.8%]; mean [SD] age, 39 [17] years; 94% adults) were analyzed. Among the participants, 177 (48.2%) had mild disease (EASI Յ7), 120 (32.7%) had moderate disease (EASI >7 and Յ 21), and 70 (19.1%) had severe disease (EASI >21).

Dendritic cells (DCs) have been recognized as key players bridging innate and adaptive immune systems. They control the balance of the adaptive immune response, and the functional behavior of DCs is mainly dictated by their microenvironment. Atopic dermatitis (AD) is a paradigmatic disease where the inflammatory microenvironment has a deep impact on DCs. The emergence of IgE-mediated sensitization is tightly related to the impact of locally released cytokines by either keratinocytes, T cells, or other cells involved in the inflammatory reaction. This review will focus on the recent and relevant findings in the field of immunobiology of DCs and their role in AD.

Taken together, our findings show that in human, LC ligation of TLR2 by S.a.-derived products down-regulates FcεRI and its transcription factor PU.1, thus suggesting that FcεRI is controlled by PU.1 in these cells.

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