Pollen-derived adenosine is a necessary cofactor for ragweed allergy

Modulation of Bronchial Epithelial Barrier Integrity by Low Molecular Weight Components from Birch Pollen

Pollen, in addition to allergens, comprise low molecular weight components (LMC) smaller than 3 kDa. Emerging evidence indicates the relevance of LMC in allergic immune responses. However, the interaction of birch pollen (BP)-derived LMC and epithelial cells has not been extensively studied. We investigated epithelial barrier modifications induced by exposure to BP LMC, using the human bronchial epithelial cell line 16HBE14o-. Epithelial cell monolayers were apically exposed to the major BP allergen Bet v 1, aqueous BP extract or BP-derived LMC. Barrier integrity after the treatments was monitored by measuring transepithelial electrical resistance at regular intervals and by using the xCELLigence Real-Time Cell Analysis system. The polarized release of cytokines 24 h following treatment was measured using a multiplex immunoassay. Epithelial barrier integrity was significantly enhanced upon exposure to BP LMC. Moreover, BP LMC induced the repair of papain-mediated epithelial barrier damage. The apical release of CCL5 and TNF-α was significantly reduced after exposure to BP LMC, while the basolateral release of IL-6 significantly increased. In conclusion, the results of our study demonstrate that BP-derived LMC modify the physical and immunological properties of bronchial epithelial cells and thus regulate airway epithelial barrier responses.

When the allergy alarm bells toll: The role of Toll-like receptors in allergic diseases and treatment

Toll-like receptors of the human immune system are specialized pathogen detectors able to link innate and adaptive immune responses. TLR ligands include among others bacteria-, mycoplasma- or virus-derived compounds such as lipids, lipo- and glycoproteins and nucleic acids. Not only are genetic variations in TLR-related genes associated with the pathogenesis of allergic diseases, including asthma and allergic rhinitis, their expression also differs between allergic and non-allergic individuals. Due to a complex interplay of genes, environmental factors, and allergen sources the interpretation of TLRs involved in immunoglobulin E-mediated diseases remains challenging. Therefore, it is imperative to dissect the role of TLRs in allergies. In this review, we discuss i) the expression of TLRs in organs and cell types involved in the allergic immune response, ii) their involvement in modulating allergy-associated or -protective immune responses, and iii) how differential activation of TLRs by environmental factors, such as microbial, viral or air pollutant exposure, results in allergy development. However, we focus on iv) allergen sources interacting with TLRs, and v) how targeting TLRs could be employed in novel therapeutic strategies. Understanding the contributions of TLRs to allergy development allow the identification of knowledge gaps, provide guidance for ongoing research efforts, and built the foundation for future exploitation of TLRs in vaccine design.

Asthma: The Use of Animal Models and Their Translational Utility

Asthma is characterized by chronic lower airway inflammation that results in airway remodeling, which can lead to a permanent decrease in lung function. The pathophysiology driving the development of asthma is complex and heterogenous. Animal models have been and continue to be essential for the discovery of molecular pathways driving the pathophysiology of asthma and novel therapeutic approaches. Animal models of asthma may be induced or naturally occurring. Species used to study asthma include mouse, rat, guinea pig, cat, dog, sheep, horse, and nonhuman primate. Some of the aspects to consider when evaluating any of these asthma models are cost, labor, reagent availability, regulatory burden, relevance to natural disease in humans, type of lower airway inflammation, biological samples available for testing, and ultimately whether the model can answer the research question(s). This review aims to discuss the animal models most available for asthma investigation, with an emphasis on describing the inciting antigen/allergen, inflammatory response induced, and its translation to human asthma.

Allergen-free extracts from birch, ragweed, and hazel pollen activate human and guinea-pig submucous and spinal sensory neurons

BACKGROUND

Non-allergenic, low molecular weight components of pollen grains are suspected to trigger changes in gut functions, sometimes leading to inflammatory conditions. Based on extensive neuroimmune communication in the gut wall, we investigated the effects of aqueous pollen extracts (APE) on enteric and spinal sensory neurons.

METHODS

Using Ca²⁺ and fast potentiometric imaging, we recorded the responses of guinea-pig and human submucous and guinea-pig dorsal root ganglion (DRG) neurons to microejection of low (<3 kDa) and high (≥3 kDa) molecular weight APEs of birch, ragweed, and hazel. Histamine was determined pharmacologically and by mass spectrometry (LC-MS/MS).

KEY RESULTS

Birch APE_<3kDa evoked strong [Ca⁺² ]_i signals in the vast majority of guinea-pig DRG neurons, and in guinea-pig and human enteric neurons. The effect of birch APE_≥3kDa was much weaker. Fast neuroimaging in human enteric neurons revealed an instantaneous spike discharge after microejection of birch, ragweed, and hazel APE_<3kDa [median (interquartile range) at 7.0 Hz (6.2/9.8), 5.7 Hz (4.4/7.1), and 8.4 Hz (4.3/12.5), respectively]. The percentage of responding neurons per ganglion were similar [birch 40.0% (33.3/100.0), ragweed 50.8% (34.4/85.6), and hazel 83.3% (57.1/100.0)]. A mixture of histamine receptor (H1-H3) blockers significantly reduced nerve activation evoked by birch and ragweed APEs_<3kDa , but was ineffective on hazel. Histamine concentrations in ragweed, birch and hazel APE's < 3 kDa were 0.764, 0.047, and 0.013 μM, respectively.

CONCLUSIONS

Allergen-free APEs from birch, ragweed, and hazel evoked strong nerve activation. Altered nerve-immune signaling as a result of severe pollen exposure could be a pathophysiological feature of allergic and non-allergic gut inflammation.

Pericytes: The lung-forgotten cell type

Pericytes are a heterogeneous population of mesenchymal cells located on the abluminal surface of microvessels, where they provide structural and biochemical support. Pericytes have been implicated in numerous lung diseases including pulmonary arterial hypertension (PAH) and allergic asthma due to their ability to differentiate into scar-forming myofibroblasts, leading to collagen deposition and matrix remodelling and thus driving tissue fibrosis. Pericyte-extracellular matrix interactions as well as other biochemical cues play crucial roles in these processes. In this review, we give an overview of lung pericytes, the key pro-fibrotic mediators they interact with, and detail recent advances in preclinical studies on how pericytes are disrupted and contribute to lung diseases including PAH, allergic asthma, and chronic obstructive pulmonary disease (COPD). Several recent studies using mouse models of PAH have demonstrated that pericytes contribute to these pathological events; efforts are currently underway to mitigate pericyte dysfunction in PAH by targeting the TGF-β, CXCR7, and CXCR4 signalling pathways. In allergic asthma, the dissociation of pericytes from the endothelium of blood vessels and their migration towards inflamed areas of the airway contribute to the characteristic airway remodelling observed in allergic asthma. Although several factors have been suggested to influence this migration such as TGF-β, IL-4, IL-13, and periostin, recent evidence points to the CXCL12/CXCR4 pathway as a potential therapeutic target. Pericytes might also play an essential role in lung dysfunction in response to ageing, as they are responsive to environmental risk factors such as cigarette smoke and air pollutants, which are the main drivers of COPD. However, there is currently no direct evidence delineating the contribution of pericytes to COPD pathology. Although there is a lack of human clinical data, the recent available evidence derived from in vitro and animal-based models shows that pericytes play important roles in the initiation and maintenance of chronic lung diseases and are amenable to pharmacological interventions. Therefore, further studies in this field are required to elucidate if targeting pericytes can treat lung diseases.

Dietary digestible carbohydrates are associated with higher prevalence of asthma in humans and with aggravated lung allergic inflammation in mice

BACKGROUND

Dietary carbohydrates and fats are intrinsically correlated within the habitual diet. We aimed to disentangle the associations of starch and sucrose from those of fat, in relation to allergic sensitization, asthma and rhinoconjuctivitis prevalence in humans, and to investigate underlying mechanisms using murine models.

METHODS

Epidemiological data from participants of two German birth cohorts (age 15) were used in logistic regression analyses testing cross-sectional associations of starch and sucrose (and their main dietary sources) with aeroallergen sensitization, asthma and rhinoconjunctivitis, adjusting for correlated fats (saturated, monounsaturated, omega-6 and omega-3 polyunsaturated) and other covariates. For mechanistic insights, murine models of aeroallergen-induced allergic airway inflammation (AAI) fed with a low-fat-high-sucrose or -high-starch versus a high-fat diet were used to characterize and quantify disease development. Metabolic and physiologic parameters were used to track outcomes of dietary interventions and cellular and molecular responses to monitor the development of AAI. Oxidative stress biomarkers were measured in murine sera or lung homogenates.

RESULTS

We demonstrate a direct association of dietary sucrose with asthma prevalence in males, while starch was associated with higher asthma prevalence in females. In mice, high-carbohydrate feeding, despite scant metabolic effects, aggravated AAI compared to high-fat in both sexes, as displayed by humoral response, mucus hypersecretion, lung inflammatory cell infiltration and T_H 2-T_H 17 profiles. Compared to high-fat, high-carbohydrate intake was associated with increased pulmonary oxidative stress, signals of metabolic switch to glycolysis and decreased systemic anti-oxidative capacity.

CONCLUSION

High consumption of digestible carbohydrates is associated with an increased prevalence of asthma in humans and aggravated lung allergic inflammation in mice, involving oxidative stress-related mechanisms.

Influence of the environment on ragweed pollen and their sensitizing capacity in a mouse model of allergic lung inflammation

Common ragweed (Ambrosia artemisiifolia) is an invasive plant with allergenic pollen. Due to environmental changes, ragweed pollen (RWP) airborne concentrations are predicted to quadruple in Europe by 2050 and more than double allergic sensitization of Europeans by 2060. We developed an experimental RWP model of allergy in BALB/c mice to evaluate how the number of RWP and how RWP collected from different geographical environments influence disease. We administered RWP six times over 3 weeks intranasally to the mice and then evaluated disease parameters 72 h later or allowed the mice to recover for at least 90 days before rechallenging them with RWP to elicit a disease relapse. Doses over 300 pollen grains induced lung eosinophilia. Higher doses of 3,000 and 30,000 pollen grains increased both eosinophils and neutrophils and induced disease relapses. RWP harvested from diverse geographical regions induced a spectrum of allergic lung disease from mild inflammation to moderate eosinophilic and severe mixed eosinophilic-neutrophilic lung infiltrates. After a recovery period, mice rechallenged with pollen developed a robust disease relapse. We found no correlation between Amb a 1 content, the major immunodominant allergen, endotoxin content, or RWP structure with disease severity. These results demonstrate that there is an environmental impact on RWP with clinical consequences that may underlie the increasing sensitization rates and the severity of pollen-induced disease exacerbation in patients. The multitude of diverse environmental factors governing distinctive patterns of disease induced by RWP remains unclear. Further studies are necessary to elucidate how the environment influences the complex interaction between RWP and human health.

Lung Epithelial CYP1 Activity Regulates Aryl Hydrocarbon Receptor Dependent Allergic Airway Inflammation

The lung epithelial barrier serves as a guardian towards environmental insults and responds to allergen encounter with a cascade of immune reactions that can possibly lead to inflammation. Whether the environmental sensor aryl hydrocarbon receptor (AhR) together with its downstream targets cytochrome P450 (CYP1) family members contribute to the regulation of allergic airway inflammation remains unexplored. By employing knockout mice for AhR and for single CYP1 family members, we found that AhR^-/- and CYP1B1^-/- but not CYP1A1^-/- or CYP1A2^-/- animals display enhanced allergic airway inflammation compared to WT. Expression analysis, immunofluorescence staining of murine and human lung sections and bone marrow chimeras suggest an important role of CYP1B1 in non-hematopoietic lung epithelial cells to prevent exacerbation of allergic airway inflammation. Transcriptional analysis of murine and human lung epithelial cells indicates a functional link of AhR to barrier protection/inflammatory mediator signaling upon allergen challenge. In contrast, CYP1B1 deficiency leads to enhanced expression and activity of CYP1A1 in lung epithelial cells and to an increased availability of the AhR ligand kynurenic acid following allergen challenge. Thus, differential CYP1 family member expression and signaling via the AhR in epithelial cells represents an immunoregulatory layer protecting the lung from exacerbation of allergic airway inflammation.

Evaluation of a Novel Adjuvanted Vaccine for Ultrashort Regimen Therapy of Artemisia Pollen-Induced Allergic Bronchial Asthma in a Mouse Model

Wormwood (Artemisia) pollen is among the top 10 aeroallergens globally that cause allergic rhinitis and bronchial asthma. Allergen-specific immunotherapy (ASIT) is the gold standard for treating patients with allergic rhinitis, conjunctivitis, and asthma. A significant disadvantage of today's ASIT methods is the long duration of therapy and multiplicity of allergen administrations. The goal of this study was to undertake a pilot study in mice of a novel ultrashort vaccine immunotherapy regimen incorporating various adjuvants to assess its ability to treat allergic bronchial asthma caused by wormwood pollen. We evaluated in a mouse model of wormwood pollen allergy candidates comprising recombinant Art v 1 wormwood pollen protein formulated with either newer (Advax, Advax-CpG, ISA-51) or more traditional [aluminum hydroxide, squalene water emulsion (SWE)] adjuvants administered by the intramuscular or subcutaneous route vs. intranasal administration of a mucosal vaccine formulation using chitosan-mannose nanoparticle entrapped with Art v 1 protein. The vaccine formulations were administered to previously wormwood pollen-sensitized animals, four times at weekly intervals. Desensitization was determined by measuring decreases in immunoglobulin E (IgE), cellular immunity, ear swelling test, and pathological changes in the lungs of animals after aeroallergen challenge. Art v 1 protein formulation with Advax, Advax-CpG, SWE, or ISA-51 adjuvants induced a significant decrease in both total and Art v 1-specific IgE with a concurrent increase in Art v 1-specific IgG compared to the positive control group. There was a shift in T-cell cytokine secretion toward a Th1 (Advax-CpG, ISA-51, and Advax) or a balanced Th1/Th2 (SWE) pattern. Protection against lung inflammatory reaction after challenge was seen with ISA-51, Advax, and SWE Art v 1 formulations. Overall, the ISA-51-adjuvanted vaccine group induced the largest reduction of allergic ear swelling and protection against type 2 and non-type 2 lung inflammation in challenged animals. This pilot study shows the potential to develop an ultrashort ASIT regimen for wormwood pollen-induced bronchial asthma using appropriately adjuvanted recombinant Art v 1 protein. The data support further preclinical studies with the ultimate goal of advancing this therapy to human clinical trials.

TGF-β1 Drives Inflammatory Th Cell But Not Treg Cell Compartment Upon Allergen Exposure

TGF-β1 is known to have a pro-inflammatory impact by inducing Th9 and Th17 cells, while it also induces anti-inflammatory Treg cells (Tregs). In the context of allergic airway inflammation (AAI) its dual role can be of critical importance in influencing the outcome of the disease. Here we demonstrate that TGF-β is a major player in AAI by driving effector T cells, while Tregs differentiate independently. Induction of experimental AAI and airway hyperreactivity in a mouse model with inducible genetic ablation of the gene encoding for TGFβ-receptor 2 (Tgfbr2) on CD4⁺T cells significantly reduced the disease phenotype. Further, it blocked the induction of pro-inflammatory T cell frequencies (Th2, Th9, Th17), but increased Treg cells. To translate these findings into a human clinically relevant context, Th2, Th9 and Treg cells were quantified both locally in induced sputum and systemically in blood of allergic rhinitis and asthma patients with or without allergen-specific immunotherapy (AIT). Natural allergen exposure induced local and systemic Th2, Th9, and reduced Tregs cells, while therapeutic allergen exposure by AIT suppressed Th2 and Th9 cell frequencies along with TGF-β and IL-9 secretion. Altogether, these findings support that neutralization of TGF-β represents a viable therapeutic option in allergy and asthma, not posing the risk of immune dysregulation by impacting Tregs cells.

Ragweed plants grown under elevated CO2 levels produce pollen which elicit stronger allergic lung inflammation

BACKGROUND

Common ragweed has been spreading as a neophyte in Europe. Elevated CO₂ levels, a hallmark of global climate change, have been shown to increase ragweed pollen production, but their effects on pollen allergenicity remain to be elucidated.

METHODS

Ragweed was grown in climate-controlled chambers under normal (380 ppm, control) or elevated (700 ppm, based on RCP4.5 scenario) CO₂ levels. Aqueous pollen extracts (RWE) from control- or CO₂ -pollen were administered in vivo in a mouse model for allergic disease (daily for 3-11 days, n = 5) and employed in human in vitro systems of nasal epithelial cells (HNECs), monocyte-derived dendritic cells (DCs), and HNEC-DC co-cultures. Additionally, adjuvant factors and metabolites in control- and CO₂ -RWE were investigated using ELISA and untargeted metabolomics.

RESULTS

In vivo, CO₂ -RWE induced stronger allergic lung inflammation compared to control-RWE, as indicated by lung inflammatory cell infiltrate and mediators, mucus hypersecretion, and serum total IgE. In vitro, HNECs stimulated with RWE increased indistinctively the production of pro-inflammatory cytokines (IL-8, IL-1β, and IL-6). In contrast, supernatants from CO₂ -RWE-stimulated HNECs, compared to control-RWE-stimulated HNECS, significantly increased TNF and decreased IL-10 production in DCs. Comparable results were obtained by stimulating DCs directly with RWEs. The metabolome analysis revealed differential expression of secondary plant metabolites in control- vs CO₂ -RWE. Mixes of these metabolites elicited similar responses in DCs as compared to respective RWEs.

CONCLUSION

Our results indicate that elevated ambient CO₂ levels elicit a stronger RWE-induced allergic response in vivo and in vitro and that RWE increased allergenicity depends on the interplay of multiple metabolites.

Mimicking Antigen-Driven Asthma in Rodent Models-How Close Can We Get?

Asthma is a heterogeneous disease with increasing prevalence worldwide characterized by chronic airway inflammation, increased mucus secretion and bronchial hyperresponsiveness. The phenotypic heterogeneity among asthmatic patients is accompanied by different endotypes, mainly Type 2 or non-Type 2. To investigate the pathomechanism of this complex disease many animal models have been developed, each trying to mimic specific aspects of the human disease. Rodents have classically been employed in animal models of asthma. The present review provides an overview of currently used Type 2 vs. non-Type 2 rodent asthma models, both acute and chronic. It further assesses the methods used to simulate disease development and exacerbations as well as to quantify allergic airway inflammation, including lung physiologic, cellular and molecular immunologic responses. Furthermore, the employment of genetically modified animals, which provide an in-depth understanding of the role of a variety of molecules, signaling pathways and receptors implicated in the development of this disease as well as humanized models of allergic inflammation, which have been recently developed to overcome differences between the rodent and human immune systems, are discussed. Nevertheless, differences between mice and humans should be carefully considered and limits of extrapolation should be wisely taken into account when translating experimental results into clinical use.

Initiating pollen sensitization - complex source, complex mechanisms

The mechanisms involved in the induction of allergic sensitization by pollen are not fully understood. Within the last few decades, findings from epidemiological and experimental studies support the notion that allergic sensitization is not only dependent on the genetics of the host and environmental factors, but also on intrinsic features of the allergenic source itself. In this review, we summarize the current concepts and newest advances in research focusing on the initial mechanisms inducing pollen sensitization. Pollen allergens are embedded in a complex and heterogeneous matrix composed of a myriad of bioactive molecules that are co-delivered during the allergic sensitization. Surprisingly, several purified allergens were shown to lack inherent sensitizing potential. Thus, growing evidence supports an essential role of pollen-derived components co-delivered with the allergens in the initiation of allergic sensitization. The pollen matrix, which is composed by intrinsic molecules (e.g. proteins, metabolites, lipids, carbohydrates) and extrinsic compounds (e.g. viruses, particles from air pollutants, pollen-linked microbiome), provide a specific context for the allergen and has been proposed as a determinant of Th2 polarization. In addition, the involvement of various pattern recognition receptors (PRRs), secreted alarmins, innate immune cells, and the dependency of DCs in driving pollen-induced Th2 inflammatory processes suggest that allergic sensitization to pollen most likely results from particular combinations of pollen-specific signals rather than from a common determinant of allergenicity. The exact identification and characterization of such pollen-derived Th2-polarizing molecules should provide mechanistic insights into Th2 polarization and pave the way for novel preventive and therapeutic strategies against pollen allergies.

Pollen exposure weakens innate defense against respiratory viruses

BACKGROUND

Hundreds of plant species release their pollen into the air every year during early spring. During that period, pollen allergic as well as non-allergic patients frequently present to doctors with severe respiratory tract infections. Our objective was therefore to assess whether pollen may interfere with antiviral immunity.

METHODS

We combined data from real-life human exposure cohorts, a mouse model and human cell culture to test our hypothesis.

RESULTS

Pollen significantly diminished interferon-λ and pro-inflammatory chemokine responses of airway epithelia to rhinovirus and viral mimics and decreased nuclear translocation of interferon regulatory factors. In mice infected with respiratory syncytial virus, co-exposure to pollen caused attenuated antiviral gene expression and increased pulmonary viral titers. In non-allergic human volunteers, nasal symptoms were positively correlated with airborne birch pollen abundance, and nasal birch pollen challenge led to downregulation of type I and -III interferons in nasal mucosa. In a large patient cohort, numbers of rhinoviruspositive cases were correlated with airborne birch pollen concentrations.

CONCLUSION

The ability of pollen to suppress innate antiviral immunity, independent of allergy, suggests that high-risk population groups should avoid extensive outdoor activities when pollen and respiratory virus seasons coincide.

The role of environmental factors in allergy: A critical reappraisal

Allergies are usually referred to as type I hypersensitivity reactions against innocuous environmental antigens, characterized by a Th2/IgE-dominated inflammation. They can manifest themselves in various organs, such as skin, gastrointestinal and respiratory tract, and comprise diseases as diverse as allergic rhinitis and conjunctivitis, bronchial asthma, oral allergy syndrome, food allergy, urticaria and atopic eczema, but also anaphylactic shock. Within the last decades, there was a significant global increase in allergy prevalence, which has been mostly attributed to changes in environment and lifestyle. But which, among all factors discussed, are the most relevant, and what are the mechanisms by which these factors promote or prevent the development of allergic diseases? To answer this, it is necessary to go back to the two key questions that have occupied allergy researchers for the last decades: Firstly, what makes an allergen an allergen? Secondly, why are more and more individuals affected? Within the last decade, we have made considerable progress in answering these questions. This review gives an overview over scientific progress in the field, summarizes latest findings and points out future prospective and research needs.

Artemisia pollen is the main vector for airborne endotoxin

BACKGROUND

Endotoxin (LPS) released from gram-negative bacteria causes strong immunologic and inflammatory effects and, when airborne, can contribute to respiratory conditions, such as allergic asthma.

OBJECTIVES

We sought to identify the source of airborne endotoxin and the effect of this endotoxin on allergic sensitization.

METHODS

We determined LPS levels in outdoor air on a daily basis for 4 consecutive years in Munich (Germany) and Davos (Switzerland). Air was sampled as particulate matter (PM) greater than 10 μm (PM > 10) and PM between 2.5 and 10 μm. LPS levels were determined by using the recombinant Factor C assay.

RESULTS

More than 60% of the annual endotoxin exposure was detected in the PM > 10 fraction, showing that bacteria do not aerosolize as independent units or aggregates but adhered to large particles. In Munich 70% of annual exposure was detected between June 12th and August 28th. Multivariate modeling showed that endotoxin levels could be explained by phenological parameters (ie, plant growth). Indeed, days with high airborne endotoxin levels correlated well with the amount of Artemisia pollen in the air. Pollen collected from plants across Europe (100 locations) showed that the highest levels of endotoxin were detected on Artemisia vulgaris (mugwort) pollen, with little on other pollen. Microbiome analysis showed that LPS concentrations on mugwort pollen were related to the presence of Pseudomonas species and Pantoea species communities. In a mouse model of allergic disease, the presence of LPS on mugwort pollen was needed for allergic sensitization.

CONCLUSIONS

The majority of airborne endotoxin stems from bacteria dispersed with pollen of only one plant: mugwort. This LPS was essential for inducing inflammation of the lung and allergic sensitization.

[Allergy - an environmental disease]

The increase in allergies is a phenomenon that is being observed in all fast-developing countries. For a long time, science has taken as a starting point that solely a genetic predisposition is a precondition for the development of an allergy. Today, knowledge of environmental factors that can alter genes or the transcription of genes in the cells, has improved. Epidemiological studies have meanwhile identified several environmental factors that have a protective or supporting effect on allergy development. The environmental microbiome has recently gained central interest. A common theme in most of the studies is diversity: reduced diversity is correlated with enhanced risk for chronic inflammatory diseases and allergy.It is now of great interest for research to further analyze such environment-gene and/or environment-human interactions on all levels - from organs to cells to small and microstructures such as genes. For immunologists, it is specifically about understanding the influencing factors and effector pathways of allergens, and to apply thereby obtained insights in the follow-up for the ultimate goal of allergy research - prevention.

Air Pollution and Climate Change Effects on Allergies in the Anthropocene: Abundance, Interaction, and Modification of Allergens and Adjuvants

Air pollution and climate change are potential drivers for the increasing burden of allergic diseases. The molecular mechanisms by which air pollutants and climate parameters may influence allergic diseases, however, are complex and elusive. This article provides an overview of physical, chemical and biological interactions between air pollution, climate change, allergens, adjuvants and the immune system, addressing how these interactions may promote the development of allergies. We reviewed and synthesized key findings from atmospheric, climate, and biomedical research. The current state of knowledge, open questions, and future research perspectives are outlined and discussed. The Anthropocene, as the present era of globally pervasive anthropogenic influence on planet Earth and, thus, on the human environment, is characterized by a strong increase of carbon dioxide, ozone, nitrogen oxides, and combustion- or traffic-related particulate matter in the atmosphere. These environmental factors can enhance the abundance and induce chemical modifications of allergens, increase oxidative stress in the human body, and skew the immune system toward allergic reactions. In particular, air pollutants can act as adjuvants and alter the immunogenicity of allergenic proteins, while climate change affects the atmospheric abundance and human exposure to bioaerosols and aeroallergens. To fully understand and effectively mitigate the adverse effects of air pollution and climate change on allergic diseases, several challenges remain to be resolved. Among these are the identification and quantification of immunochemical reaction pathways involving allergens and adjuvants under relevant environmental and physiological conditions.

A metabolomic, geographic, and seasonal analysis of the contribution of pollen-derived adenosine to allergic sensitization

BACKGROUND

Studies on ragweed and birch pollen extracts suggested that the adenosine content is an important factor in allergic sensitization. However, exposure levels from other pollens and considerations of geographic and seasonal factors have not been evaluated.

OBJECTIVE

This study compared the metabolite profile of pollen species important for allergic disease, specifically measured the adenosine content, and evaluated exposure to pollen-derived adenosine.

METHODS

An NMR metabolomics approach was used to measure metabolite concentrations in twenty-six pollen extracts. Pollen count data was analyzed from five cities to model exposure.

RESULTS

A principal component analysis of the various metabolites identified by NMR showed that pollen extracts could be differentiated primarily by sugar content: glucose, fructose, sucrose, and myo-inositol. In extracts of 10 mg of pollen/ml, the adenosine was highest for grasses (45 μM) followed by trees (23 μM) and weeds (19 μM). Pollen count data showed that tree pollen was typically 5-10 times the amount of other pollens. At the daily peaks of tree, grass, and weed season the pollen-derived adenosine exposure per day is likely to only be 1.1, 0.11, and 0.12 μg, respectively. Seasonal models of pollen exposure and respiration suggest that it would be a rare event limited to tree pollen season for concentrations of pollen-derived adenosine to approach physiological levels.

CONCLUSIONS

Sugar content and other metabolites may be useful in classifying pollens. Unless other factors create localized exposures that are very different from these models, pollen-derived adenosine is unlikely to be a major factor in allergic sensitization.

Pollen derived low molecular compounds enhance the human allergen specific immune response in vivo

BACKGROUND

Besides allergens, pollen release bioactive, low molecular weight compounds that modulate and stimulate allergic reactions. Clinical relevance of these substances has not been investigated to date.

OBJECTIVE

To elucidate the effect of a non-allergenic, low molecular weight factors from aqueous birch pollen extracts (Bet-APE < 3 kDa) on the human allergic immune response in vivo.

METHODS

Birch and grass pollen allergic individuals underwent skin prick testing with allergen alone, allergen plus Bet-APE < 3 kDa, or allergen plus pre-identified candidate substances from low molecular pollen fraction. Nasal allergen challenges were performed in non-atopic and pollen allergic individuals using a 3 day repeated threshold challenge battery. Subjects were either exposed to allergen alone or to allergen plus Bet-APE< 3 kDa. Local cytokine levels, nasal secretion weights, nasal congestion and symptom scores were determined.

RESULTS

Skin prick test reactions to pollen elicited larger weals when allergens were tested together with the low molecular weight compounds from pollen. Similar results were obtained with candidate pollen-associated lipid mediators. In nasal lining fluids of allergic patients challenged with allergen plus Bet-APE < 3 kDa, IL-8 and IgE was significantly increased as compared to allergen-only challenged patients. These patients also produced increased amounts of total nasal secretion and reported more severe rhinorrhea than the allergen-only challenged group.

CONCLUSIONS

Low molecular compounds from pollen enhance the allergen specific immune response in the skin and nose. They are therefore of potential clinical relevance in allergic patients.

Pollen Allergens for Molecular Diagnosis

Pollen allergens are one of the main causes of type I allergies affecting up to 30% of the population in industrialized countries. Climatic changes affect the duration and intensity of pollen seasons and may together with pollution contribute to increased incidences of respiratory allergy and asthma. Allergenic grasses, trees, and weeds often present similar habitats and flowering periods compromising clinical anamnesis. Molecule-based approaches enable distinction between genuine sensitization and clinically mostly irrelevant IgE cross-reactivity due to, e. g., panallergens or carbohydrate determinants. In addition, sensitivity as well as specificity can be improved and lead to identification of the primary sensitizing source which is particularly beneficial regarding polysensitized patients. This review gives an overview on relevant pollen allergens and their usefulness in daily practice. Appropriate allergy diagnosis is directly influencing decisions for therapeutic interventions, and thus, reliable biomarkers are pivotal when considering allergen immunotherapy in the context of precision medicine.

Pollen-Associated Microbiome Correlates with Pollution Parameters and the Allergenicity of Pollen

Pollen allergies have been rapidly increasing over the last decades. Many allergenic proteins and non-allergenic adjuvant compounds of pollen are involved in the plant defense against environmental or microbial stress. The first aim of this study was to analyze and compare the colonizing microbes on allergenic pollen. The second aim was to investigate detectable correlations between pollen microbiota and parameters of air pollution or pollen allergenicity. To reach these aims, bacterial and fungal DNA was isolated from pollen samples of timothy grass (Phleum pratense, n = 20) and birch trees (Betula pendula, n = 55). With this isolated DNA, a terminal restriction fragment length polymorphism analysis was performed. One result was that the microbial diversity on birch tree and timothy grass pollen samples (Shannon/Simpson diversity indices) was partly significantly correlated to allergenicity parameters (Bet v 1/Phl p 5, pollen-associated lipid mediators). Furthermore, the microbial diversity on birch pollen samples was correlated to on-site air pollution (nitrogen dioxide (NO2), ammonia (NH3), and ozone (O3)). What is more, a significant negative correlation was observed between the microbial diversity on birch pollen and the measured NO2 concentrations on the corresponding trees. Our results showed that the microbial composition of pollen was correlated to environmental exposure parameters alongside with a differential expression of allergen and pollen-associated lipid mediators. This might translate into altered allergenicity of pollen due to environmental and microbial stress.

Latest developments in allergic rhinitis in Allergy for clinicians and researchers

Research efforts in allergic rhinitis have always been intense. Over the past 3 years, numerous breakthroughs in basic science and clinical research have been made, augmenting our understanding of this condition that afflicts a significant proportion of the global population. New epidemiological findings, novel insights into the molecular and cellular mechanisms of allergy, enhancement of current developmental theories, new concepts of the goals and endpoints of management, and latest therapeutic modalities that includes the harnessing of information technology and big data are some areas where important advances were made. We attempt to bring you a summary of the key research advances made in the field of allergic rhinitis from 2013 to 2015.