Dendritic cells revisited in human allergic rhinitis and asthma

CD169+ Macrophages Mediate the Immune Response of Allergic Rhinitis Through the Keap1/Nrf2/HO-1 Axis

CD169+ macrophages are a newly defined macrophage subpopulation that can recognize and bind with other cells through related ligands, playing an essential role in antigen presentation and immune tolerance. However, its role in Allergic Rhinitis (AR) is still unclear. To investigate the characteristics of CD169+ macrophages in AR, this work first detects their expression patterns in the nasal mucosa of clinical patients. These results show a significant increase in CD169+ macrophages in the nasal mucosa of patients with AR. Subsequently, this work establishes an animal AR model using CD169 transgenic mice and compared the advantages of the two models. Moreover, this work also demonstrates the effects of CD169 knockout on eosinophils, Th cells, Treg cells, and the migration of dendritic cells (DCs). In addition, this metabolomic data shows that CD169+ macrophages can upregulate alanine production and increase reactive oxygen species (ROS) levels. This process may be mediated through the Keap1/Nrf2/HO-1 signaling pathway. In addition, this work also finds that SLC38A2 plays an essential role in the process of CD169+ macrophages promoting alanine uptake by DCs. This study confirms that CD169+ macrophages can upregulate their internal alanine production and increase ROS levels through the Keap1/Nrf2/HO-1 axis, playing an irreplaceable role in AR.

Mannose and Lactobionic Acid in Nasal Vaccination: Enhancing Antigen Delivery via C-Type Lectin Receptors

BACKGROUND/OBJECTIVES

Nasal vaccines are a promising strategy for enhancing mucosal immune responses and preventing diseases at mucosal sites by stimulating the secretion of secretory IgA, which is crucial for early pathogen neutralization. However, designing effective nasal vaccines is challenging due to the complex immunological mechanisms in the nasal mucosa, which must balance protection and tolerance against constant exposure to inhaled pathogens. The nasal route also presents unique formulation and delivery hurdles, such as the mucous layer hindering antigen penetration and immune cell access.

METHODS

This review focuses on cutting-edge approaches to enhance nasal vaccine delivery, particularly those targeting C-type lectin receptors (CLRs) like the mannose receptor and macrophage galactose-type lectin (MGL) receptor. It elucidates the roles of these receptors in antigen recognition and uptake by antigen-presenting cells (APCs), providing insights into optimizing vaccine delivery.

RESULTS

While a comprehensive examination of targeted glycoconjugate vaccine development is outside the scope of this study, we provide key examples of glycan-based ligands, such as lactobionic acid and mannose, which can selectively target CLRs in the nasal mucosa.

CONCLUSIONS

With the rise of new viral infections, this review aims to facilitate the design of innovative vaccines and equip researchers, clinicians, and vaccine developers with the knowledge to enhance immune defenses against respiratory pathogens, ultimately protecting public health.

Effects of Panax species and their bioactive components on allergic airway diseases

Panax species include Panax ginseng Meyer, Panax quinquefolium L., Panax notoginseng, Panax japonicum, Panax trifolium, and Panax pseudoginseng, which contain bioactive components (BCs) such as ginsenosides and polysaccharides. Recently, growing evidence has revealed the pharmacological effects of Panax species and their BCs on allergic airway diseases (AADs), including allergic asthma (AA) and allergic rhinitis (AR). AADs are characterized by damaged epithelium, sustained acquired immune responses with enforced Th2 responses, allergen-specific IgE production, and enhanced production of histamine and leukotrienes by activated mast cells and basophils. In this review, we summarize how Panax species and their BCs modulate acquired immune responses involving interactions between dendritic cells and T cells, reduce the pro-inflammatory responses of epithelial cells, and reduce allergenic responses from basophils and mast cells in vitro. In addition, we highlight the current understanding of the alleviative effects of Panax species and their BCs against AA and AR in vivo. Moreover, we discuss the unmet needs of research and considerations for the treatment of patients to provide basic scientific knowledge for the treatment of AADs using Panax species and their BCs.

Immunosuppressive Ability of Trichinella spiralis Adults Can Ameliorate Type 2 Inflammation in a Murine Allergy Model

BACKGROUND

There is an increase in the global incidence of allergies. The hygiene hypothesis and the old friend hypothesis reveal that helminths are associated with the prevalence of allergic diseases. The therapeutic potential of Trichinella spiralis is recognized; however, the stage at which it exerts its immunomodulatory effect is unclear.

METHODS

We evaluated the differentiation of bone marrow-derived macrophages stimulated with T spiralis excretory-secretory products. Based on an ovalbumin-induced murine model, T spiralis was introduced during 3 allergy phases. Cytokine levels and immune cell subsets in the lung, spleen, and peritoneal cavity were assessed.

RESULTS

We found that T spiralis infection reduced lung inflammation, increased anti-inflammatory cytokines, and decreased Th2 cytokines and alarms. Recruitment of eosinophils, CD11b+ dendritic cells, and interstitial macrophages to the lung was significantly suppressed, whereas Treg cells and alternatively activated macrophages increased in T spiralis infection groups vs the ovalbumin group. Notably, when T spiralis was infected prior to ovalbumin challenge, intestinal adults promoted proportions of CD103+ dendritic cells and alveolar macrophages.

CONCLUSIONS

T spiralis strongly suppressed type 2 inflammation, and adults maintained lung immune homeostasis.

Long-term hypoxic hUCMSCs-derived extracellular vesicles alleviates allergic rhinitis through triggering immunotolerance of their VEGF-mediated inhibition of dendritic cells maturation

BACKGROUND

Extensions of mesenchymal stem cells (MSCs) in vitro may lead to the loss of their biological functions. However, hypoxic culturation has been shown to enhance the proliferation, survival, and immunomodulatory capacity of MSCs.

OBJECTIVE

We aimed to investigate the effects of long-term hypoxic cultivation on the properties of human umbilical cord-derived MSCs (hUCMSCs) and the therapeutic effects of their extracellular vesicles (EVs) in allergic rhinitis (AR).

METHODS

Proliferation, senescence, telomerase activity and multipotent properties of hUCMSCs were analyzed under long-term culturation of hypoxia (1%) or normoxia (21%), and the therapeutic effects of their conditional medium (CM) and EVs were evaluated in OVA-induced AR mice. Effects of hypoxia-EVs (Hy-EVs) or normoxia-EVs (No-EVs) on human monocyte-derived dendritic cells (DCs) were investigated, and the possible mechanisms of Hy-EVs in induction of immunotolerance were further explored.

RESULTS

Long-term hypoxia significantly promoted the proliferation, inhibited cell senescence, maintained the multipotent status of hUCMSCs. Hy-CM and Hy-EVs showed better therapeutic effects in AR mice compared to No-EVs, seen as improvement of AR-related behaviors such as rubbing and sneezing, and attenuation of inflammation in nasal tissues. In addition, Hy-EVs significantly reduced the expressions of HLA-DR, CD80, CD40, and CD83 induced by OVA plus LPS in DCs, inhibiting the maturation of DCs. Furthermore, we observed that VEGF was remarkably enriched in Hy-EVs, but not in No-EVs, and the inhibition of DCs maturation was markedly neutralized by VEGF antibodies, suggesting that VEGF derived from Hy-EVs was responsible for the inhibition of DCs maturation.

CONCLUSION

Our results demonstrated that long-term hypoxia significantly promoted the proliferation, inhibited cell senescence, maintained the multipotent status of hUCMSCs, and hypoxia treated hUCMSCs-derived EVs enhanced their therapeutic effects in AR mice through VEGF-mediated inhibition of DCs maturation.

Gene Signatures and Associated Transcription Factors of Allergic Rhinitis: KLF4 Expression Is Associated with Immune Response

This study is aimed at investigating the potential molecular features of allergic rhinitis (AR) and identifying gene signatures and related transcription factors using transcriptome analysis and in silico datasets. Transcriptome profiles were obtained using three independent cohorts (GSE101720, GSE19190, and GSE46171) comprising healthy controls (HC) and patients with AR. The pooled dataset (n = 82) was used to identify the critical signatures of AR compared with HC. Subsequently, key transcription factors were identified by a combined analysis using transcriptome and in silico datasets. Gene ontology: bioprocess (GO: BP) analysis using differentially expressed genes (DEGs) revealed that immune response-related genes were significantly enriched in AR compared with HC. Among them, IL1RL1, CD274, and CD44 were significantly higher in AR patients. We also identified key transcription factors between HC and AR using the in silico dataset and found that AR samples frequently express KLF transcription factor 4 (KLF4), which regulates immune response-related genes including IL1RL1, CD274, and CD44 in human nasal epithelial cells. Our integrative analysis of transcriptomic regulation provides new insights into AR, which may help in developing precision management for patients with AR.

Effect of early postnatal supplementation of newborns with probiotic strain E. coli O83:K24:H31 on allergy incidence, dendritic cells, and microbiota

Introduction

Probiotic administration seems to be a rational approach to promote maturation of the neonatal immune system. Mutual interaction of the microbiota with the host immune system is critical for the setting of appropriate immune responses including a tolerogenic one and thevmaintenance of homeostasis. On the other hand, our knowledge on the modes of actions of probiotics is still scarce.

Methods

In our study, probiotic strain Escherichia coli O83:K24:H31 (EcO83) was administered to neonates of allergic mothers (AMs; neonates with increased risk for allergy development) within 48 h after the delivery, and the impact of this early postnatal supplementation on allergy incidence and selected immune markers has been analyzed 10 years after the primary EcO83 administration.

Results

We have observed decreased allergy incidence in 10-year-old children supplemented with EcO83 (13 of 52 children were allergic) in comparison with non-supplemented children of AMs (16 of 42 children were allergic). The early postnatal EcO83 supplementation appeared to limit the allergy in the high-risk group (children of AMs) compared to that in the low-risk group (children of healthy mothers). Dendritic cells (DCs) in the peripheral blood of EcO83-supplemented children do not differ significantly in cell surface presence of CD83. The immunomodulatory capacity of EcO83 on DCs was tested in vitro as well. Both directly isolated myeloid and in vitro monocyte-derived DCs from cord blood increased CD83 expression together with interleukin (IL)-10 secretion after EcO83 stimulation. The effect of early postnatal EcO83 supplementation on the microbiota composition of 10-year-old children was characterized by next-generation sequencing, and we have not observed significant changes in the microbiota composition of EcO83-supplemented and non-supplemented children at the age of 10 years.

Conclusions

Early postnatal EcO83 supplementation appears to lower allergy incidence in children of AMs. It seems that the beneficial effect of EcO83 is mediated via modulation of DC functional capacities without impacting the microbiota composition. Larger-scale studies will be necessary to confirm these preliminary findings.

Ameliorative Effect of Imperatorin on Dermatophagoides pteronyssinus-Induced Allergic Asthma by Suppressing the Th2 Response in Mice

Imperatorin is a furanocoumarin derivative and an effective ingredient in several Chinese medicinal herbs. It has favorable expectorant, analgesic, and anti-inflammatory effects. In this study, we investigated whether imperatorin has protective effects against Dermatophagoides pteronyssinus (Der p)-induced asthma in mice. Lung and bronchial tissues were histopathologically examined through hematoxylin–eosin staining. The concentrations of immunoglobin E (IgE), IgG1, IgG2a in serum and those of T helper 1 (Th1) and two cytokines and eosinophil-activated chemokines in bronchoalveolar lavage fluid (BALF) were detected using an enzyme immunoassay. Histological examination revealed that imperatorin reduced inflammatory cell infiltration, mucus hypersecretion, and endothelial cell hyperplasia. The examination also indicated that imperatorin could reduce the inflammatory cell count in BALF as well as IgE and IgG1 expression in serum, but IgG2a expression was significantly increased. Imperatorin reduced the production of interleukin (IL)-4, IL-5, and IL-13 by Th2, promoted the production of interferon-γ and IL-12 by Th1, and increased the production of IL-10 in bronchoalveolar lavage fluid. These findings suggest that imperatorin has a considerable anti-inflammatory effect on Der p-induced allergic asthma in mice.

Emerging Insights into the Impact of Air Pollution on Immune-Mediated Asthma Pathogenesis

PURPOSE OF REVIEW

Increases in ambient levels of air pollutants have been linked to lung inflammation and remodeling, processes that lead to the development and exacerbation of allergic asthma. Conventional research has focused on the role of CD4+ T helper 2 (TH2) cells in the pathogenesis of air pollution-induced asthma. However, much work in the past decade has uncovered an array of air pollution-induced non-TH2 immune mechanisms that contribute to allergic airway inflammation and disease.

RECENT FINDINGS

In this article, we review current research demonstrating the connection between common air pollutants and their downstream effects on non-TH2 immune responses emerging as key players in asthma, including PRRs, ILCs, and non-TH2 T cell subsets. We also discuss the proposed mechanisms by which air pollution increases immune-mediated asthma risk, including pre-existing genetic risk, epigenetic alterations in immune cells, and perturbation of the composition and function of the lung and gut microbiomes. Together, these studies reveal the multifaceted impacts of various air pollutants on innate and adaptive immune functions via genetic, epigenetic, and microbiome-based mechanisms that facilitate the induction and worsening of asthma.

Role of Respiratory Epithelial Cells in Allergic Diseases

The airway epithelium provides the first line of defense to the surrounding environment. However, dysfunctions of this physical barrier are frequently observed in allergic diseases, which are tightly connected with pro- or anti-inflammatory processes. When the epithelial cells are confronted with allergens or pathogens, specific response mechanisms are set in motion, which in homeostasis, lead to the elimination of the invaders and leave permanent traces on the respiratory epithelium. However, allergens can also cause damage in the sensitized organism, which can be ascribed to the excessive immune reactions. The tight interaction of epithelial cells of the upper and lower airways with local and systemic immune cells can leave an imprint that may mirror the pathophysiology. The interaction with effector T cells, along with the macrophages, play an important role in this response, as reflected in the gene expression profiles (transcriptomes) of the epithelial cells, as well as in the secretory pattern (secretomes). Further, the storage of information from past exposures as memories within discrete cell types may allow a tissue to inform and fundamentally alter its future responses. Recently, several lines of evidence have highlighted the contributions from myeloid cells, lymphoid cells, stromal cells, mast cells, and epithelial cells to the emerging concepts of inflammatory memory and trained immunity.

Association of childhood rhinitis with phthalate acid esters in household dust in Shanghai residences

OBJECTIVE

Phthalate acid esters (PAEs) have been identified to be associated with children's health. Present study was conducted to assess associations between PAEs in household dust and childhood rhinitis.

METHODS

Based on phase II of CCHH study (China, Children, Home, Health) conducted in Shanghai, China, 266 indoor dust samples were collected from participants' families. Concentrations of PAEs in dust samples were measured by chemical treatment and gas chromatograph-mass spectrometer. Information about individuals and residences was surveyed by questionnaires. Logistic regression models were applied to obtain the associations between PAEs and childhood rhinitis.

RESULTS

Higher concentrations of benzyl butyl phthalate (BBP) were found in those families with children who had diagnosed rhinitis. Significantly higher concentrations of bis(2-ethylhexyl) phthalate (DEHP) and PAEs with high molecular weight (HMW-PAEs) were found in the positive group of lifetime rhinitis. Using the multiple and ordinal logistic regression models adjusted by covariates, dibutyl phthalate (DBP), DEHP, and HMW-PAEs were found to be significantly associated with diagnosed rhinitis. Boys who exposure to higher concentrations of DBP, DEHP, HMW-PAEs, and total PAEs have significant associations with diagnosed rhinitis compared with girls who exposure to lower concentration of PAEs.

CONCLUSIONS

Present observational study indicated that exposure to high concentrations of DBP, DEHP, and HMW-PAEs in house settled dust was a risk factor for rhinitis for children, especially for boys.

The Role of CD40 in Allergic Rhinitis and Airway Remodelling

Background

Allergic rhinitis (AR) affects millions of people and is lack of effective treatment. CD40 is an important costimulatory molecule in immunity. However, few studies have focused on the role of CD40 in AR.

Methods

In this study, we built mouse model of chronic AR. The mice were divided into the AR, control, intravenous CD40 siRNA, and nasal CD40 siRNA groups (n = 6 each). We detected OVA-sIgE, IL-4, IL-5, IL-13, IL-10, IFN-γ, and TGF-β levels in serum and supernatant by ELISA, CD40⁺ splenic DCs, and Foxp3⁺ Tregs by flow cytometry and CD40 mRNA by RT²-PCR. We also used PAS and MT stains to assess tissue remodelling.

Results

(1) The OVA-sIgE, IL-4, IL-5, and IL-13 levels in the serum or supernatant of nasal septal membrane of AR mice were significantly higher than control. After treated with CD40 siRNA, those indicators were significantly decreased. The IFN-γ, IL-10, and TGF-β levels in AR mice were significantly lower than that in control and were increased by administration of CD40 siRNA. (2) AR mice had significantly fewer Foxp3⁺ Tregs in the spleen than control mice. After treated with CD40 siRNA, AR mice had significantly more Foxp3⁺ Tregs. (3) AR mice exhibited a significantly higher CD40 mRNA levels than control. Administration of CD40 siRNA significantly reduced the CD40 mRNA level. (4) The AR mice showed significantly greater collagen deposition than the control in MT staining. Applications of CD40 siRNA significantly reduced the collagen deposition in AR mice.

Conclusion

CD40 siRNA therapy shows promise for chronic AR as it significantly attenuated allergic symptoms and Th2-related inflammation and upregulated Foxp3⁺ Tregs. CD40 plays a role in tissue remodelling in AR, which can be inhibited by CD40 siRNA application.

A novel therapeutic modality using CRISPR-engineered dendritic cells to treat allergies

Despite the important roles of dendritic cells (DCs) in airway allergies, current therapeutic strategies such as drugs, allergen immunotherapy and biologics haven't been targeted at them. In this study, we established a promising DC-based therapeutic approach for the alleviation of allergic rhinitis (AR)-associated allergic reactions, using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated targeted gene disruption. RNA sequencing analysis revealed upregulation of vacuolar protein sorting 37 B (VPS37B) in AR-derived DCs, indicating a novel molecular target. Following antigen presentation, VPS37A and VPS37B enabled endocytosis of the mannose receptor, which recognizes the house dust mite (HDM) allergen Der p 1. DCs with targeted disruption of VPS37A/B alleviated Th2 cytokine production when co-cultured in vitro with allogeneic naïve CD4⁺ T cell from patients with AR. Furthermore, nasal administration of Vps37a/b-disrupted bone marrow DCs to a mouse model of AR resulted in strongly reduced AR-related symptoms. Thus, this novel modality using genetically engineered DCs can provide an effective therapeutic and preventative strategy for allergic diseases.

Long Non-coding RNAs and mRNAs Expression Profiles of Monocyte-Derived Dendritic Cells From PBMCs in AR

Objective

The objective of this study is to explore the long non-coding RNAs (lncRNAs) and messenger RNAs (mRNAs) expression profiles of monocyte-derived dendritic cells (DCs) obtained from peripheral blood mononuclear cells (PBMCs). DCs are known to play a major role in the regulating function of allergic rhinitis (AR).

Methods

PBMCs were separately isolated from the human peripheral blood of patients with AR and normal person (NP). The mixed lymphocyte reaction (MLR) assay was used to evaluate the function of DCs. Flow cytometry was used to determine the immune regulatory function of immature DCs (imDCs) and mature DCs (mDCs). lncRNAs and mRNAs in the NP group (DCs isolated from NP) and the test group (DCs isolated from patients with AR) were identified via chip technology and bioinformatic analyses. Moreover, bioinformatic analyses were employed to identify the related biological functions of monocyte-derived DCs and construct the functional networks of lncRNAs and mRNAs that are differentially expressed (DE) in imDCs and mDCs.

Results

MLR was significantly higher in the mDCs group than that in the imDCs group. CD14 was highly expressed in imDCs, whereas HLA-DR, CD80, and CD86 were highly expressed in mDCs (p < 0.001). We identified 962 DE lncRNAs and 308 DE mRNAs in the imDCs of NP and patients with AR. Additionally, there were 601 DE lncRNAs and 168 DE mRNAs in the mDCs in the NP and test groups. Quantitative RT-qPCR was used to study the significant fold changes of lncRNAs and mRNAs. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis found 16 significant regulated pathways in imDCs and 10 significant regulated pathways in mDCs, including the phagosome, cell adhesion signaling pathway, and inflammatory mediator regulation of TRP channels pathway.

Conclusion

Our research studied the lncRNA and mRNA expression profiles of monocyte-derived DCs and demonstrated the functional networks that are involved in monocyte-derived DCs-mediated regulation in AR. These results provided possible molecular mechanisms of monocyte-derived DCs in the immunoregulating function and laid the foundation for the molecular therapeutic targets of AR.

Fms-Like Tyrosine Kinase 3-Independent Dendritic Cells Are Major Mediators of Th2 Immune Responses in Allergen-Induced Asthmatic Mice

Dendritic cells (DCs) are the main mediators of Th2 immune responses in allergic asthma, and Fms-like tyrosine kinase 3 ligand (Flt3L) is an important growth factor for the development and homeostasis of DCs. This study identified the DC populations that primarily cause the initiation and development of allergic lung inflammation using Fms-like tyrosine kinase 3 (Flt3) knockout (KO) mice with allergen-induced allergic asthma. We observed type 2 allergic lung inflammation with goblet cell hyperplasia in Flt3 KO mice, despite a significant reduction in total DCs, particularly CD103⁺ DCs, which was barely detected. In addition, bone marrow-derived dendritic cells (BMDCs) from Flt3 KO mice directed Th2 immune responses in vitro, and the adoptive transfer of these BMDCs exacerbated allergic asthma with more marked Th2 responses than that of BMDCs from wild-type (WT) mice. Furthermore, we found that Flt3L regulated the in vitro expression of OX40 ligand (OX40L) in DCs, which is correlated with DC phenotype in in vivo models. In conclusion, we revealed that Flt3-independent CD11b⁺ DCs direct Th2 responses with the elevated OX40L and are the primary cause of allergic asthma. Our findings suggest that Flt3 is required to control type 2 allergic inflammation.

Whole Transcriptome Analysis of Myeloid Dendritic Cells Reveals Distinct Genetic Regulation in Patients with Allergies

Dendritic cells (DCs) play critical roles in atopic diseases, orchestrating both innate and adaptive immune systems. Nevertheless, limited information is available regarding the mechanism through which DCs induce hyperresponsiveness in patients with allergies. This study aims to reveal novel genetic alterations and future therapeutic target molecules in the DCs from patients with allergies using whole transcriptome sequencing. Transcriptome sequencing of human BDCA-3+/CD11c+ DCs sorted from peripheral blood monocytes obtained from six patients with allergies and four healthy controls was conducted. Gene expression profile data were analyzed, and an ingenuity pathway analysis was performed. A total of 1638 differentially expressed genes were identified at p-values < 0.05, with 11 genes showing a log2-fold change ≥1.5. The top gene network was associated with cell death/survival and organismal injury/abnormality. In validation experiments, amphiregulin (AREG) showed consistent results with transcriptome sequencing data, with increased mRNA expression in THP-1-derived DCs after Der p 1 stimulation and higher protein expression in myeloid DCs obtained from patients with allergies. This study suggests an alteration in the expression of DCs in patients with allergies, proposing related altered functions and intracellular mechanisms. Notably, AREG might play a crucial role in DCs by inducing the Th2 immune response.

The roles of B cell activation factor (BAFF) and a proliferation-inducing ligand (APRIL) in allergic asthma

Allergic asthma, which is the most common type of asthma, is mediated by the IgE response, and B cells are key drivers of allergic inflammation in the lungs. B cell activation factor (BAFF) and proliferation inducing ligand (APRIL) are members of the TNF superfamily. BAFF and APRIL interact with three receptors, namely the B cell activation factor receptor (BAFF-r), B cell maturation antigen (BCMA), and transmembrane activator; calcium modulator; and cyclophilin ligand interactor (TACI). The interaction of BAFF and APRIL with their receptors induces B cell activation, differentiation, and antibody production. BAFF and APRIL are produced by airway epithelial cells during the response to allergens or infectious agents, and have shown to induce local IgE production, thus establishing allergic inflammation in the airways. BAFF can maintain in inflamed airways during infection and can inhibit regulatory T cells (Tregs), thereby promoting allergic inflammation in the airways. This review aims to outline current knowledge about BAFF/APRIL systems in humans as well as in murine models of allergic asthma. The precise role of BAFF and APRIL and their receptors in allergic asthma remains unclear. Therefore, further studies are required to identify and elucidate their roles in enhancing IgE production and activating immune cells that drive the Th2 effector response and initiate allergic inflammation in asthma. Targeting BAFF/APRIL or their cognate receptors may offer a novel therapeutic approach in asthma treatment.

What have recent advances in therapy taught us about severe asthma disease mechanisms?

Introduction: Severe asthma still represents a worldwide challenge. The need for further treatment options has stimulated basic and pharmacological research to focus on the immune and inflammatory background of asthma. The new biologic drugs express the considerable advances in the field and besides providing a revolutionary treatment option for severe asthma, contribute themselves to better understand the pathophysiologic mechanisms they address, paving the way to new potential targets.Areas covered: A selective search on PubMed and Medline was performed, including the evidence on immunology of severe asthma published up to May 2019 by focusing on the immunological effects of biologic drugs underlying their clinical outcomes.Expert opinion: The recent pharmacological research in the field of biologics has represented an exceptional opportunity for exploring severe asthma mechanisms. However, some points deserve to be addressed by further investigation. Although in the absence of safety warnings so far, interfering with the immune system may raise some safety concerns, especially in the long-term use. Particularly when interacting with epithelial and innate immunity the selection of candidates probably deserves special caution. Also, whether biologics exert a true disease-modifying effect is not completely clear. As a direct practical implication, the optimal treatment duration is still controversial.

PARP-1 Is Critical for Recruitment of Dendritic Cells to the Lung in a Mouse Model of Asthma but Dispensable for Their Differentiation and Function

Dendritic cells (DCs) are critical in asthma and many other immune diseases. We previously demonstrated a role for PARP-1 in asthma. Evidence on PARP-1 playing a role in Th2-associated DC function is not clear. In this study, we examined whether PARP-1 is critical for DC differentiation and function using bone marrow progenitors and their migration to the lung in an ovalbumin-based mouse model of asthma. Results show that changes in PARP-1 levels during GM-CSF-induced DC differentiation from bone marrow progenitors were cyclic and appear to be part of an array of changes that included STAT3/STAT5/STAT6/GRAIL/RAD51. Interestingly, PARP-1 gene deletion affected primarily STAT6 and γH2AX. PARP-1 inhibition significantly reduced the migration of DCs to the lungs of ovalbumin-challenged mice, which was associated with a concomitant reduction in lung levels of the adhesion molecule VCAM-1. The requirement of PARP-1 for VCAM-1 expression was confirmed using endothelial and lung smooth muscle cells. PARP-1 expression and activity were also required for VCAM-1 in differentiated DCs. An assessment of CD11b⁺/CD11c⁺/MHCII^high DCs in spleens and lymph nodes of OVA-sensitized mice revealed that PARP-1 inhibition genetically or by olaparib exerted little to no effect on DC differentiation, percentage of CD80⁺/CD86⁺/CD40⁺-expressing cells, or their capacity to promote proliferation of ovalbumin-primed (OTII) CD4⁺ T cells. These findings were corroborated using GM-CSF-induced differentiation of DCs from the bone marrow. Surprisingly, the PARP-1^−/− DCs exhibited a higher intrinsic capacity to induce OTII CD4⁺ T cell proliferation in the absence of ovalbumin. Overall, our results show that PARP-1 plays little to no role in DC differentiation and function and that the protective effect of PARP-1 inhibition against asthma is associated with a prevention of DC migration to the lung through a reduction in VCAM-1 expression. Given the current use of PARP inhibitors (e.g., olaparib) in the clinic, the present results may be of interest for the relevant therapies.

Dendritic cells modified with Der p1 antigen as a therapeutic potential for allergic rhinitis in a murine model via regulatory effects on IL-4, IL-10 and IL-13

OBJECTIVES

House dust mites, including Der p1, are common allergens. The current study was designed to explore the allergen-specific immune tolerance effects of Der p1-modified dendritic cells (DCs) through IL-4, IL-10 and IL-13 on an allergic rhinitis (AR) mouse model.

METHODS

A lentivirus was modified to express Derp1. Then, immature DCs from mice were infected with this modified lentivirus to generate a lenti-Derp1-GFP DCs. 24 mice were random divided into four groups (n = 6 each), AR mouse were sensitized by Derp1 allergens and treated with lenti-GFP DCs (GFP-DC/AR group), or lenti-Derp1-GFP DCs (Der p1-DC/AR group) and dexamethasone (Dex/AR group), mice in the control group were treated with PBS instead of Der p1 then also intraperitoneally injected with 5 × 10⁶ lenti-GFP DCs/mouse. AR symptoms expressed by each mouse were recorded. The proportions of CD4⁺CD25⁺Foxp3⁺ regulatory T cells among CD4⁺ T cells in the peripheral blood, and mRNA and protein expression levels of IL-4, IL-10, and IL-13 were measured.

RESULTS

DCs infected with lenti-Derp1-GFP stimulated the maturation of DCs. Compared with the GFP-DC/AR group, mice in the Der p1-DC/AR group showed an ameliorated allergic response, a significant decrease in the levels of serum IgE, IgG1, and histamine, and a decrease in the expression of IL-4 and IL-13 mRNA and protein in the nasal mucosa. The expression of IL-10 increased in the Der p1-DC/AR group to a level similar to that observed in the Dex/AR group.

CONCLUSIONS

These results indicate that Der p1-modified DCs have therapeutic potential for AR via downregulation of IL-4 and IL-13, and upregulation of IL-10.

Jagged1-expressing adenovirus-infected dendritic cells induce expansion of Foxp3+ regulatory T cells and alleviate T helper type 2-mediated allergic asthma in mice

Dendritic cells (DCs) are professional antigen-presenting cells that play a key role in directing T-cell responses. Regulatory T (Treg) cells possess an immunosuppressive ability to inhibit effector T-cell responses, and Notch ligand Jagged1 (Jag1) is implicated in Treg cell differentiation. In this study, we evaluated whether bone marrow-derived DCs genetically engineered to express Jag1 (Jag1-DCs) would affect the maturation and function of DCs in vitro and further investigated the immunoregulatory ability of Jag1-DCs to manipulate T helper type 2 (Th2) -mediated allergic asthma in mice. We produced Jag1-DCs by adenoviral transduction. Overexpression of Jag1 by ovalbumin (OVA) -stimulated Jag1-DCs exhibited increased expression of programmed cell death ligand 1 (PD-L1) and OX40L molecules. Subsequently, co-culture of these OVA-pulsed Jag1-DCs with allogeneic or syngeneic CD4⁺ T cells promoted the generation of Foxp3⁺ Treg cells, and blocking PD-L1 using specific antibodies partially reduced Treg cell expansion. Furthermore, adoptive transfer of OVA-pulsed Jag1-DCs to mice with OVA-induced asthma reduced allergen-specific immunoglobulin E production, airway hyperresponsiveness, airway inflammation, and secretion of Th2-type cytokines (interleukin-4, interleukin-5, and interleukin-13). Notably, an increased number of Foxp3⁺ Treg cells associated with enhanced levels of transforming growth factor-β production was observed in Jag1-DC-treated mice. These data indicate that transgenic expression of Jag1 by DCs promotes induction of Foxp3⁺ Treg cells, which ameliorated Th2-mediated allergic asthma in mice. Our study supports an attractive strategy to artificially generate immunoregulatory DCs and provides a novel approach for manipulating Th2 cell-driven deleterious immune diseases.

Recent Advances in Experimental Allergy

Atopic disorders are on the rise and pose a great burden on society. A better understanding of the underlying mechanisms is required for the development of improved or novel therapeutic strategies. Here we aim to highlight recent advances in experimental allergy, with a particular focus on proposed treatment alternatives for airway disorders, atopic dermatitis, and food allergy. Furthermore, we discuss recent work focusing on molecular and cellular mechanisms that might offer candidates for future preventive or therapeutic intervention.

Chronic rhinosinusitis: pathogenesis, therapy options, and more

INTRODUCTION

When rhinosinusitis - the inflammation of the nasal cavity and paranasal sinuses - persists for over 12 weeks, it is termed 'chronic rhinosinusitis' (CRS). Both innate and adaptive immunity contribute to the heterogeneous inflammatory pathogenesis of CRS, which is driven by genetic and environmental factors and the microbiome. CRS is classified by the presence of polyps. Molecular mechanisms in CRS with nasal polyps are similar to those in atopic diseases.

AREAS COVERED

This review focuses on the immune pathogenesis of CRS, differences between the two CRS subtypes, and latest treatments that may aid in the provision of personalized medicine.

EXPERT OPINION

Basic research in the last decade has helped significantly in enhancing our knowledge of the pathophysiologic processes of CRS, due to which there is now a better understanding of the associated natural history, physiopathology, novel treatments, and prevention strategies. Treatment success depends on the clarification of the underlying pathogenesis and disease-contributing factors. The exploration of disease endotypes and introduction of novel agents are important advancements. Prior studies performed without disease-endotyping resulted in the inefficiency of certain drugs and insignificant results. The identification of biomarkers, development of personalized approaches, and utilization of disease algorithms are required for CRS therapy success.

Is IgE or eosinophils the key player in allergic asthma pathogenesis? Are we asking the right question?

Bronchial asthma (BA) is a chronic inflammatory disease with a marked heterogeneity in pathophysiology and etiology. The heterogeneity of BA may be related to the inducing mechanism(s) (allergic vs non-allergic), the histopathological background (eosinophilic vs non-eosinophilic), and the clinical manifestations, particularly in terms of severity and frequency of exacerbations. Asthma can be divided into at least two different endotypes based on the degree of Th2 inflammation (T2 'high' and T2 'low'). For patients with severe uncontrolled asthma, monoclonal antibodies (mAbs) against immunoglobulin E (IgE) or interleukin (IL)-5 are now available as add-on treatments. Treatment decisions for individual patients should consider the biological background in terms of the "driving mechanisms" of inflammation as this should predict the patients' likely responses to treatment. The question is not whether an anti-IgE or an anti-eosinophilic strategy is more effective, but rather what the mechanism is at the origin of the airway. While IgE is involved early in the inflammatory cascade and can be considered as a cause of allergic asthma, eosinophilia can be considered a consequence of the whole process. This article discusses the different roles of the IgE and IL-5/eosinophil pathways in the pathogenic mechanisms of airway inflammation occurring in allergic asthma, and the possible reasons to choose an anti-IgE mAb or anti-IL-5 treatment.

HMGB1 regulates T helper 2 and T helper17 cell differentiation both directly and indirectly in asthmatic mice

The Th (T helper) 2 response is characteristic of allergic asthma, and Th17 cells are involved in more severe asthma. Recent studies demonstrated that HMGB1 (High mobility group box 1 protein) regulates airway inflammation and the Th2, Th17 inflammatory response in asthma. HMGB1 can interact with Toll-like receptors (TLR) 2 and 4, and the receptor for advanced glycation end products (RAGE), activating the NF-κB (nuclear factor kappa B) signaling pathway and inducing the release of downstream inflammatory mediators. Both Th cells and dendritic cells express TLR2, TLR4, and RAGE receptors. Therefore, we speculate that HMGB1 could regulate the differentiation of Th2, Th17 cells in asthma through direct and indirect mechanisms. An ovalbumin (OVA)-induced mouse asthmatic model was established. Anti-HMGB1 antibody or rHMGB1 was administered to OVA-sensitized mice 30 min prior to each challenge. For in vitro studies, magnetically separated CD4⁺ naive T cells were stimulated with or without rHMGB1 and/or anti-HMGB1 antibody. BMDCs (bone marrow-derived dendritic cells)-stimulated with or without rHMGB1 and/or anti-HMGB1 antibody were cocultured with CD4⁺ naive T cells. Our study showed that administration of rHMGB1 aggravated airway inflammation and mucus production, and induced Th2, Th17 polarization in asthmatic mice, and that anti-HMGB1 antibody weakened characteristic features of asthma and blocked the Th2, Th17 inflammatory responses. HMGB1 could directly act on naive T cells to induce differentiation of Th2, Th17 cells in vitro through activating the TLR2, TLR4, RAGE-NF-κB signal pathway in CD4⁺ naive T cells. HMGB1 could also indirectly promote Th2, Th17 differentiation via activating the TLR2, TLR4, RAGE-NF-κB signal pathway in DCs to mediate their maturation and antigen-presenting ability in vitro.

Sex-based differences in CD103+ dendritic cells promote female-predominant Th2 cytokine production during allergic asthma

BACKGROUND

Gender disparities in adult patients with asthma regarding its prevalence and severity are mainly due to enhanced type 2 T-helper (Th2) cytokine production in female patients compared to that in male patients. However, the pathways mediating this effect remain unclear.

OBJECTIVE

We aimed to determine the roles of two major subsets of dendritic cells (DCs) in females, specifically those displaying CD11b or CD103, during enhanced Th2 priming after allergen exposure, using an ovalbumin-induced asthma mouse model.

METHODS

Sex-based differences in the number of DCs at inflamed sites, costimulatory molecule expression on DCs, and the ability of DCs to differentiate naïve CD4⁺ T cells into Th2 population were evaluated after allergen exposure in asthmatic mice. In addition, we assessed the role of 17β-oestradiol in CD103⁺ DC function during Th2 priming in vitro.

RESULTS

The number of CD11b^high DCs and CD103⁺ DCs in the lung and bronchial lymph node (BLN) was increased to a greater extent in female mice than in male mice at 16 to 20 hours after ovalbumin (OVA) inhalation. In BLNs, CD86 and I-A/I-E expression levels and antigen uptake ability in CD103⁺ DCs, but not in CD11b^high DCs, were greater in female mice than in male mice. Furthermore, CD4⁺ T cells cultured with CD103⁺ DCs from female mice produced higher levels of interleukin (IL)-4, IL-5, and IL-13, compared with CD4⁺ T cells cultured with CD103⁺ DCs from male mice. The 17β-oestradiol-oriented enhancement of CD86 expression on CD103⁺ DCs after allergen exposure induced the enhanced IL-5 production from CD4⁺ T cells.

CONCLUSIONS AND CLINICAL RELEVANCE

These findings suggest that with regard to asthma, enhanced Th2 cytokine production in females might be attributed to 17β-oestradiol-mediated Th2-oriented CD103⁺ DCs in the BLN.

New approaches for identifying and testing potential new anti-asthma agents

INTRODUCTION

Asthma is a chronic disease with significant heterogeneity in clinical features, disease severity, pattern of underlying disease mechanisms, and responsiveness to specific treatments. While the majority of asthmatic patients are controlled by standard pharmacological strategies, a significant subgroup has limited therapeutic options representing a major unmet need. Ongoing asthma research aims to better characterize distinct clinical phenotypes, molecular endotypes, associated reliable biomarkers, and also to develop a series of new effective targeted treatment modalities. Areas covered: The expanding knowledge on the pathogenetic mechanisms of asthma has allowed researchers to investigate a range of new treatment options matched to patient profiles. The aim of this review is to provide a comprehensive and updated overview of the currently available, new and developing approaches for identifying and testing potential treatment options for asthma management. Expert opinion: Future therapeutic strategies for asthma require the identification of reliable biomarkers that can help with diagnosis and endotyping, in order to determine the most effective drug for the right patient phenotype. Furthermore, in addition to the identification of clinical and inflammatory phenotypes, it is expected that a better understanding of the mechanisms of airway remodeling will likely optimize asthma targeted treatment.

Derp1-modified dendritic cells attenuate allergic inflammation by regulating the development of T helper type1(Th1)/Th2 cells and regulatory T cells in a murine model of allergic rhinitis

The CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) are known to regulate Th2-induced allergic rhinitis (AR). In this study, we evaluated the efficacy of Derp1-modified dendritic cells (DCs) in AR immunotherapy. Derp1 was synthesized and transfected into DCs to generate Derp1-modified DCs. Phenotypes of Derp1-modified DCs were analyzed with flow cytometry using antibodies against DC markers CD11c, CD11b, CD59, CD103 and Toll-like receptor 1(TLR1). Four groups of subject mice were formed; the controls were treated with immature DCs, while the AR mice models were sensitized with Derp1(AR) and treated with DCs(DC-AR) or Derp1-modified DCs (Derp1DC-AR). The frequency of sneezing and scratching, eosinophil cell count, and Th1/Th2 ratio in the spleen were measured for all groups. The percentage of CD4⁺CD25⁺Foxp3⁺ Tregs in peripheral blood mononuclear cells was measured using flow cytometry; serum IgE, IgG1, and histamine were measured using enzyme-linked immunosorbent assay; expression levels of transcription factors T-bet, GATA3, Foxp3+ and IL-10 were analyzed using reverse transcription-polymerase chain reaction, and Western blot used in analyzed expression of Foxp3+ and IL-10 in nasal mucosa. Treatment with Derp1-modified DCs ameliorated the allergic response. The Derp1DC-AR group had significantly lower eosinophil cell count and the IgE, IgG1, and histamine levels than the AR and DC-AR groups, and higher mRNA levels of Th1 transcription factors T-bet, IL-10 and Foxp3 in nasal mucosa than DC-AR mice, but Th2 transcription factors GATA3 mRNA expression level has the opposite results. Furthermore, the Th1/Th2 ratio and percentage of CD4⁺CD25⁺Foxp3⁺ Tregs was significantly lower in the AR group (p<0.05), but higher in the Derp1DC-AR group than in the control group (p<0.01). Thus, the Derp1-modified DCs increased the percentage of CD4⁺CD25⁺Foxp3⁺Tregs and influenced the balance of Th1/Th2, showing an immunotherapeutic effect against AR.

Bone Marrow Mesenchymal Stem Cells Inhibit the Function of Dendritic Cells by Secreting Galectin-1

This study aimed to investigate whether bone marrow-derived mesenchymal stem cells (BM-MSCs) can inhibit function of dendritic cells (DCs) by secreting Galectin-1 (Gal-1). BM-MSCs have been shown to inhibit the maturation and function of DCs, further inhibiting the activation and proliferation of T cells. However, the detailed mechanism remains unknown. In this current study, MSCs and DCs derived from mouse bone marrow were cocultured using Transwell culture plates under different in vitro conditions. The results showed that as the ratio of MSC to DC of the coculture system increased and the coculture time of the two cells prolonged, the concentrations of Gal-1, interleukin- (IL-) 10, and IL-12 in the supernatants were increased and the protein expression of Gal-1 on and within DCs was also enhanced. The phosphorylation of extracellular signal-regulated kinase (ERK) pathway in DCs was boosted, whereas p38 mitogen-activated protein kinase (MAPK) pathway phosphorylation was weakened. Meanwhile, the expression of costimulatory molecules on the surface of DCs was decreased, and the proliferative effect of DCs on allogeneic T cells was also decreased. Therefore, this present study indicated that Gal-1 secreted from MSCs upregulated expression of Gal-1 and stimulated formation of tolerance immunophenotype on DCs, where the underlying mechanism was the regulation of the MAPK signaling pathway in DCs, thereby inhibiting the function of DCs.

Human Lung Mononuclear Phagocytes in Health and Disease

The lungs are vulnerable to attack by respiratory insults such as toxins, allergens, and pathogens, given their continuous exposure to the air we breathe. Our immune system has evolved to provide protection against an array of potential threats without causing collateral damage to the lung tissue. In order to swiftly detect invading pathogens, monocytes, macrophages, and dendritic cells (DCs)-together termed mononuclear phagocytes (MNPs)-line the respiratory tract with the key task of surveying the lung microenvironment in order to discriminate between harmless and harmful antigens and initiate immune responses when necessary. Each cell type excels at specific tasks: monocytes produce large amounts of cytokines, macrophages are highly phagocytic, whereas DCs excel at activating naïve T cells. Extensive studies in murine models have established a division of labor between the different populations of MNPs at steady state and during infection or inflammation. However, a translation of important findings in mice is only beginning to be explored in humans, given the challenge of working with rare cells in inaccessible human tissues. Important progress has been made in recent years on the phenotype and function of human lung MNPs. In addition to a substantial population of alveolar macrophages, three subsets of DCs have been identified in the human airways at steady state. More recently, monocyte-derived cells have also been described in healthy human lungs. Depending on the source of samples, such as lung tissue resections or bronchoalveolar lavage, the specific subsets of MNPs recovered may differ. This review provides an update on existing studies investigating human respiratory MNP populations during health and disease. Often, inflammatory MNPs are found to accumulate in the lungs of patients with pulmonary conditions. In respiratory infections or inflammatory diseases, this may contribute to disease severity, but in cancer patients this may improve clinical outcomes. By expanding on this knowledge, specific lung MNPs may be targeted or modulated in order to attain favorable responses that can improve preventive or treatment strategies against respiratory infections, lung cancer, or lung inflammatory diseases.

Toll-like receptor-mediated involvement of innate immune cells in asthma disease

BACKGROUND

Innate immune cells as the first line of defense are adept at recognizing and triggering appropriate response against various pathogens. Apart from the protective functions, the innate immunity plays an essential role in mediation of allergic responses. Dendritic cells (DCs) and airway epithelial cells (AECs) along with other innate cells such as granulocytes, natural killer cells (NKs), natural killer T cells (NKTs), and alternatively activated macrophages (AAMs) are able to orchestrate allergic responses, especially asthma. Chronic stimulation of TLRs by airway stimuli induces local inflammation which gradually results in the recruitment and settling of innate cells around airways.

SCOPE OF REVIEW

This review discusses how recruitment and accumulation of the inflammatory cells in the site of insult facilitate hypersensitivity reactions and initiate airway inflammation. We indicate that these cells are well equipped to highly sensitive receptors known as toll-like receptors (TLRs) making them fit to prime adaptive immune response. Based on emerging findings, we highlight the pivotal role of TLRs in regulation of innate cells function in the context of asthma disease.

MAJOR CONCLUSIONS

Stimulation of the TLRs of innate cells by allergens has been found to accelerate and regulate allergic airway inflammation. In fact, the sophisticated interaction between environmental allergens and TLRs leads to release of various pro-inflammatory mediators from innate cells supporting asthma development.

GENERAL SIGNIFICANCE

This review highlights that TLRs have a substantial role in priming innate cells and cytokine release, suggesting that the involvement of TLRs of innate immune cells can modulate the function of these cells in asthma disease.

Indoor pollutant hexabromocyclododecane enhances house dust mite-induced activation of human monocyte-derived dendritic cells

The indoor pollutant hexabromocyclododecane (HBCD) has been added as flame retardant to many consumer products but detaches and accumulates in house dust. Inhalation of house dust leads to exposure to house dust mite (HDM) allergens in the presence of HBCD. Activation of dendritic cells is crucial in the sensitization to HDM allergens. The current study examined whether exposure to HBCD affected activation/maturation of HDM-exposed human dendritic cells (DC). Human monocyte-derived DC (moDC) were exposed simultaneously to HDM and a concentration range of HBCD (0.1-20 μM) in vitro. HDM exposure of moDC induced expression of co-stimulatory molecule CD80 and production of pro-inflammatory cytokines interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α. However, simultaneous exposure of moDC to HBCD and HDM enhanced the expression of antigen presenting molecule HLA-DR, co-stimulatory molecule CD86 and pro-inflammatory cytokine IL-8 depending on the dose of HBCD. Our results indicate that simultaneous exposure of HDM and HBCD can enhance the antigen presentation and maturation/activation of DC.

Dendritic cells in inflammatory sinonasal diseases

Dendritic cells (DCs) are critical in linking the innate and adaptive immune responses, which have been implicated in the pathogenesis of many immune and inflammatory diseases as well as the development of tumours. The role of DCs in the pathophysiology of lung diseases has been widely studied. However, the phenotype, subset and function of DCs in upper airways under physiological or pathological conditions remain largely undefined. Allergic rhinitis (AR) and chronic rhinosinusitis (CRS) are two important upper airway diseases with a high worldwide prevalence. Aberrant innate and adaptive immune responses have been considered to play an important role in the pathogenesis of AR and CRS. To this end, understanding the function of DCs in shaping the immune responses in sinonasal mucosa is critical in exploring the pathogenic mechanisms underlying AR and CRS as well as in developing novel therapeutic strategies. This review summarizes the phenotype, subset, function and regulation of DCs in sinonasal mucosa, particularly in the setting of AR and CRS. Furthermore, this review discusses the perspectives for future research and potential clinical utility focusing on DC pathways in the context of AR and CRS.

Origin, Localization, and Immunoregulatory Properties of Pulmonary Phagocytes in Allergic Asthma

Allergic asthma is a chronic inflammatory disease of the airways that is driven by maladaptive T helper 2 (Th2) and Th17 immune responses against harmless, airborne substances. Pulmonary phagocytes represent the first line of defense in the lung where they constantly sense the local environment for potential threats. They comprise two distinct cell types, i.e., macrophages and dendritic cells (DC) that differ in their origins and functions. Alveolar macrophages quickly take up most of the inhaled allergens, yet do not deliver their cargo to naive T cells sampling in draining lymph nodes. In contrast, pulmonary DCs instruct CD4(+) T cells develop into Th2 and Th17 effectors, initiating the maladaptive immune responses toward harmless environmental substances observed in allergic individuals. Unraveling the mechanisms underlying this mistaken identity of harmless, airborne substances by innate immune cells is one of the great challenges in asthma research. The identification of different pulmonary DC subsets, their role in antigen uptake, migration to the draining lymph nodes, and their potential to instruct distinct T cell responses has set the stage to unravel this mystery. However, at this point, a detailed understanding of the spatiotemporal resolution of DC subset localization, allergen uptake, processing, autocrine and paracrine cellular crosstalk, and the humoral factors that define the activation status of DCs is still lacking. In addition to DCs, at least two distinct macrophage populations have been identified in the lung that are either located in the airway/alveolar lumen or in the interstitium. Recent data suggest that such populations can exert either pro- or anti-inflammatory functions. Similar to the DC subsets, detailed insights into the individual roles of alveolar and interstitial macrophages during the different phases of asthma development are still missing. Here, we will provide an update on the current understanding of the origin, localization, and function of the diverse pulmonary antigen-presenting cell subsets, in particular with regard to the development and regulation of allergic asthma. While most data are from mouse models of experimental asthma, we have also included available human data to judge the translational value of the findings obtained in experimental asthma models.