No abstract

Atopic dermatitis (AD) is a common chronic inflammatory skin disease that has increased in prevalence over the last half century. A growing body of evidence suggests that there are a variety of defects in the innate immune system that collectively affect the development and severity of AD. The reduction in antimicrobial peptides, diminished recruitment of innate immune cells (PMNs, pDC, and NK cells) to the skin, epithelial barrier disruption, and TLR2 defects are just some of the credible explanations for AD patients' susceptibility to pathogens such as Staphylococcus aureus, herpes simplex virus, and vaccinia virus. Although the focus for several years has been to identify defects in the innate immune system that might explain AD patients' susceptibility to cutaneous pathogens, it has become clear that some innate immune defects might promote inflammation and thereby aggravate or even induce the development of AD. Here we review the innate immune system, and highlight many of the potential innate networks that may be important in AD patients susceptible to cutaneous pathogens.

Respiratory epithelial cells (EpCs) orchestrate airway mucosal inflammation in response to diverse environmental stimuli, but how distinct EpC programs are regulated remains poorly understood. Here, we report that inhalation of aeroallergens leads to expansion of airway brush cells (BrCs), specialized chemosensory EpCs and the dominant epithelial source of interleukin-25 (IL-25). BrC expansion was attenuated in mice lacking either LTC4 synthase, the biosynthetic enzyme required for cysteinyl leukotriene (CysLT) generation, or the EpC receptor for leukotriene E4 (LTE4), CysLT3R. LTE4 inhalation was sufficient to elicit CysLT3R-dependent BrC expansion in the murine airway through an IL-25–dependent but STAT6-independent signaling pathway. Last, blockade of IL-25 attenuated both aeroallergen and LTE4-elicited CysLT3R-dependent type 2 lung inflammation. These results demonstrate that CysLT3R senses the endogenously generated lipid ligand LTE4 and regulates airway BrC number and function.

Chemosensory epithelial cells (EpCs) are specialized cells that promote innate type 2 immunity and protective neurally mediated reflexes in the airway. Their effector programs and modes of activation are not fully understood. Here, we define the transcriptional signature of two choline acetyltransferase–expressing nasal EpC populations. They are found in the respiratory and olfactory mucosa and express key chemosensory cell genes including the transcription factor Pou2f3, the cation channel Trpm5, and the cytokine Il25. Moreover, these cells share a core transcriptional signature with chemosensory cells from intestine, trachea and thymus, and cluster with tracheal brush cells (BrCs) independently from other respiratory EpCs, indicating that they are part of the brush/tuft cell family. Both nasal BrC subsets express high levels of transcripts encoding cysteinyl leukotriene (CysLT) biosynthetic enzymes. In response to ionophore, unfractionated nasal BrCs generate CysLTs at levels exceeding that of the adjacent hematopoietic cells isolated from naïve mucosa. Among activating receptors, BrCs express the purinergic receptor P2Y2. Accordingly, the epithelial stress signal ATP and aeroallergens that elicit ATP release trigger BrC CysLT generation, which is mediated by the P2Y2 receptor. ATP- and aeroallergen-elicited CysLT generation in the nasal lavage is reduced in mice lacking Pou2f3, a requisite transcription factor for BrC development. Last, aeroallergen-induced airway eosinophilia is reduced in BrC-deficient mice. These results identify a previously undescribed BrC sensor and effector pathway leading to generation of lipid mediators in response to luminal signals. Further, they suggest that BrC sensing of local damage may provide an important sentinel immune function.

Cysteinyl leukotrienes (cysLTs), leukotriene C 4 (LTC 4 ), LTD 4 , and LTE 4 are proinflammatory lipid mediators with pathobiologic function in asthma. LTE 4 , the stable cysLT, is a weak agonist for the type 1 and type 2 cysLT receptors (CysLTRs), which constrict airway smooth muscle, but elicits airflow obstruction and pulmonary inflammation in patients with asthma. We recently identified GPR99 as a high-affinity receptor for LTE 4 that mediates cutaneous vascular permeability. Here we demonstrate that a single intranasal exposure to extract from the respiratory pathogen Alternaria alternata elicits profound epithelial cell (EpC) mucin release and submucosal swelling in the nasal mucosa of mice that depends on cysLTs, as it is absent in mice deficient in the terminal enzyme for cysLT biosynthesis, LTC 4 synthase (LTC 4 S). These mucosal changes are associated with mast cell (MC) activation and absent in MC-deficient mice, suggesting a role for MCs in control of EpC function. Of the three CysLTRs, only GPR99-deficient mice are fully protected from EpC mucin release and swelling elicited by Alternaria or by intranasal LTE 4 . GPR99 expression is detected on lung and nasal EpCs, which release mucin to doses of LTE 4 one log lower than that required to elicit submucosal swelling. Finally, mice deficient in MCs, LTC 4 S, or GPR99 have reduced baseline numbers of goblet cells, indicating an additional function in regulating EpC homeostasis. These results demonstrate a novel role for GPR99 among CysLTRs in control of respiratory EpC function and suggest that inhibition of LTE 4 and of GPR99 may have therapeutic benefits in asthma.C ysteinyl leukotrienes (cysLTs), leukotriene C 4 (LTC 4 ), LTD 4 , and LTE 4 are lipid mediators detected during asthma exacerbations triggered by allergen (1), aspirin (2, 3), and respiratory viruses (4). The cysLTs elicit vascular permeability, inflammation, and bronchoconstriction through three G-protein-coupled receptors. The type 1 cysLT receptor (CysLTR), CysLT 1 R, is the highaffinity receptor for LTD 4 and the dominant CysLTR mediating airway smooth muscle constriction (5-8). The type 2 CysLTR, CysLT 2 R, has prominent effects on the vascular endothelium (9-12) and also elicits bronchial constriction (13,14). LTE 4 , the stable cysLT (15-18), is a weak agonist for CysLT 1 R and CysLT 2 R in transfected cells (5, 19), but elicits airflow obstruction in patients with asthma (20-22). Moreover, LTE 4 has comparable activity to LTC 4 and LTD 4 in eliciting a wheal and flare response in human skin (23), and LTE 4 elicits cutaneous vascular permeability in mice lacking both CysLT 1 R and CysLT 2 R, suggesting the existence of a high-affinity receptor for LTE 4 , which was recently identified as GPR99 (24,25). However, the mechanism by which LTE 4 induces lung pathobiology and the role of GPR99 remain poorly understood.The cysLTs are derived from arachidonate through the serial enzymatic actions of 5-lipoxygenase and leukotriene C 4 synthase (LTC 4 S). LTC 4 , the terminal product of intrac...

Background: The cause of severe nasal polyposis in aspirinexacerbated respiratory disease (AERD) is unknown. Elevated antibody levels have been associated with disease severity in nasal polyps, but upstream drivers of local antibody production in nasal polyps are undetermined. Objective: We sought to identify upstream drivers and phenotypic properties of local antibody-expressing cells in nasal polyps from subjects with AERD. Methods: Sinus tissue was obtained from subjects with AERD, chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP), CRS without nasal polyps, and controls without CRS. Tissue antibody levels were quantified via ELISA and immunohistochemistry and were correlated with disease severity. Antibody-expressing cells were profiled with single-cell RNA sequencing, flow cytometry, and immunofluorescence, with IL-5Ra function determined through IL-5 stimulation and subsequent RNA sequencing and quantitative PCR. Results: Tissue IgE and IgG4 levels were elevated in AERD compared with in controls (P < .01 for IgE and P < .001 for IgG4 vs CRSwNP). Subjects with AERD whose nasal polyps recurred rapidly had higher IgE levels than did subjects with AERD, with slower regrowth (P 5 .005). Single-cell RNA sequencing revealed increased IL5RA, IGHG4, and IGHE in antibodyexpressing cells from patients with AERD compared with antibody-expressing cells from patients with CRSwNP. There were more IL-5Ra 1 plasma cells in the polyp tissue from those with AERD than in polyp tissue from those with CRSwNP (P 5 .026). IL-5 stimulation of plasma cells in vitro induced changes in a distinct set of transcripts. Conclusions: Our study identifies an increase in antibodyexpressing cells in AERD defined by transcript enrichment of IL5RA and IGHG4 or IGHE, with confirmed surface expression of IL-5Ra and functional IL-5 signaling. Tissue IgE and IgG4 levels are elevated in AERD, and higher IgE levels are associated with faster nasal polyp regrowth. Our findings suggest a role for IL-5Ra 1 antibody-expressing cells in facilitating local antibody production and severe nasal polyps in AERD.

In contrast to resident constitutive mast cells (CMCs), mucosal MCs (MMCs) appear in lung and trachea of sensitized mice only following inhalation challenge. We monitored the influx and maturation of MCs by their expression of Kit, FcεRI, β7 integrin and side scatter (SSC) by flow cytometry. Influx of MC progenitors (MCps) (FcεRIlo, Kitint, β7hi, SSClo) peaks 1 day after challenges and subsides to baseline by day 7 post-challenge. The mature MMCs appear as a distinct population on day 7 and peak at day 14 with higher SSC and FcεRI expression, but lower β7 and Kit expression. A distinct transitional population is present between 1 and 7 days post-challenge. Maturation occurs more rapidly in the trachea. The resident tracheal CMC had higher SSC, FcεRI, and Kit and lower β7 integrin expression than the MMC. By histology, the MMCs follow similar kinetics to the flow cytometry-identified mature MMCs and are notably persistent for >42 days. Steroid treatment reduced inflammation and MCp influx but had no effect on established MMC. Thus changes in SSC, FcεRI, and Kit together with expression of αE/α4:β7 integrins characterizes the development of induced MMCs from MCps and distinguishes them from resident CMC in the trachea and large airways.

No abstract