Multi-Approach Analysis for the Identification of Proteases within Birch Pollen

Spatiotemporal proteolytic susceptibility of allergens: positive or negative effects on the allergic sensitization?

From their expression in their respective allergenic source to their processing by antigen presenting cells, allergens continuously encounter proteases. The ability of allergens to resist to proteolysis by digestive enzymes or host-cell/microbial proteases is considered as an important property that influences their allergenic potential. However, the relationship between proteolytic stability and allergenicity is much more complex and depends on various factors, such as the protein structure dynamics, the exposure level, the route of sensitization, and their respective protease susceptibility. In this review, we summarize and discuss the current knowledge on several aspects of allergen proteolytic stability in different environments including the allergenic sources, routes of sensitization (skin, respiratory tract, gastrointestinal tract) and endolysosomal compartment of antigen-presenting cells. Proteolytic stability alone cannot represent a definitive criterion to allergenicity. The proteolytic susceptibility of allergens in processed extracts can affect allergy diagnosis and immunotherapy. Furthermore, the fine tuning of allergen stability during antigen processing can be exploited for the development of novel immunotherapeutic strategies.

Improved Classification Performance of Bacteria in Interference Using Raman and Fourier-Transform Infrared Spectroscopy Combined with Machine Learning

The rapid and sensitive detection of pathogenic and suspicious bioaerosols are essential for public health protection. The impact of pollen on the identification of bacterial species by Raman and Fourier-Transform Infrared (FTIR) spectra cannot be overlooked. The spectral features of the fourteen class samples were preprocessed and extracted by machine learning algorithms to serve as input data for training purposes. The two types of spectral data were classified using classification models. The partial least squares discriminant analysis (PLS-DA) model achieved classification accuracies of 78.57% and 92.85%, respectively. The Raman spectral data were accurately classified by the support vector machine (SVM) algorithm, with a 100% accuracy rate. The two spectra and their fusion data were correctly classified with 100% accuracy by the random forest (RF) algorithm. The spectral processed algorithms investigated provide an efficient method for eliminating the impact of pollen interference.

NLRP3 promotes allergic responses to birch pollen extract in a model of intranasal sensitization

Introduction & Objective

Allergic sensitization is an essential step in the development of allergic airway inflammation to birch pollen (BP); however, this process remains to be fully elucidated. Recent scientific advances have highlighted the importance of the allergen context. In this regard, microbial patterns (PAMPs) present on BP have attracted increasing interest. As these PAMPs are recognized by specialized pattern recognition receptors (PRRs), this study aims at investigating the roles of intracellular PRRs and the inflammasome regulator NLRP3.

Methods

We established a physiologically relevant intranasal and adjuvant-free sensitization procedure to study BP-induced systemic and local lung inflammation.

Results

Strikingly, BP-sensitized Nlrp3-deficient mice showed significantly lower IgE levels, Th2-associated cytokines, cell infiltration into the lung, mucin production and epithelial thickening than their wild-type counterparts, which appears to be independent of inflammasome formation. Intriguingly, bone-marrow chimera revealed that expression of NLRP3 in the hematopoietic system is required to trigger an allergic response.

Conclusion

Overall, this study identifies NLRP3 as an important driver of BP-induced allergic immune 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.

Birch pollen-The unpleasant herald of spring

Type I respiratory allergies to birch pollen and pollen from related trees of the order Fagales are increasing in industrialized countries, especially in the temperate zone of the Northern hemisphere, but the reasons for this increase are still debated and seem to be multifaceted. While the most important allergenic molecules of birch pollen have been identified and characterized, the contribution of other pollen components, such as lipids, non-allergenic immunomodulatory proteins, or the pollen microbiome, to the development of allergic reactions are sparsely known. Furthermore, what also needs to be considered is that pollen is exposed to external influences which can alter its allergenicity. These external influences include environmental factors such as gaseous pollutants like ozone or nitrogen oxides or particulate air pollutants, but also meteorological events like changes in temperature, humidity, or precipitation. In this review, we look at the birch pollen from different angles and summarize current knowledge on internal and external influences that have an impact on the allergenicity of birch pollen and its interactions with the epithelial barrier. We focus on epithelial cells since these cells are the first line of defense in respiratory disease and are increasingly considered to be a regulatory tissue for the protection against the development of respiratory allergies.

Detection and pH-Thermal Characterization of Proteinases Exclusive of Honeybee Worker-Fate Larvae (Apis mellifera L.)

The occurrence of the honeybee caste polyphenism arises when a change in diet is transduced into cellular metabolic responses, resulting in a developmental shift mediated by gene expression. The aim of this investigation was to detect and describe the expression profile of water-soluble proteases during the ontogenesis of honeybee worker-fate larvae. The extraction of insect homogenates was followed by the electrophoretic separation of the protein extract in polyacrylamide gels under semi-denaturing condition, precast with gelatin, pollen, or royal jelly protein extracts. The worker-fate honeybee larva showed a proteolytic pattern that varied with aging, and a protease with the highest activity at 72 h after hatching was named PS4. PS4 has a molecular weight of 45 kDa, it remained active until cell sealing, and its enzymatic properties suggest a serine-proteinase nature. To define the process that originates a queen-fate larvae, royal jelly and pollen were analysed, but PS4 was not detected in either of them. The effect of food on the PS4 was investigated by mixing crude extracts of queen and worker-fate larvae with pollen and royal jelly, respectively. Only royal jelly inhibited PS4 in worker-fate larvae. Taken together, our data suggest that PS4 could be involved in caste differentiation.

Eosinophilic esophagitis auxiliary diagnosis based on a peptide ligand to eosinophil cationic protein in esophageal mucus of pediatric patients

Eosinophilic esophagitis (EoE) is a chronic inflammatory condition of the esophagus characterized by increased number of eosinophils. Currently, EoE diagnosis is based on endoscopic procedures for histopathological examination, eosinophils' counting and, often, in clinical practice, the challenge is the differentiation between EoE and gastroesophageal reflux disease (GERD). Our aim was to develop novel peptide ligand to Eosinophil cationic protein (ECP) present in EoE biopsies of patients with potential to be used for detection. We performed a comparative proteomic analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) of esophageal biopsies from pediatric patients with eosinophilic esophagitis, gastroesophageal reflux disease and control individuals. Then, phage display technology was used to select peptides against specific up-regulated protein from EoE patients. Twelve phage clones were selected after three biopanning rounds, and the best phage clone reactivity was evaluated by phage-ELISA assay using esophageal mucus samples from 94 pediatric patients. Mass spectrometry showed that eosinophil cationic protein (ECP) was one of the most up-regulated proteins in EoE patients, which is an eosinophil granule protein usually deposited on tissues to mediate remodeling, but in excess may cause fibrosis and hypertrophy, especially in allergic responses. A highly reactive ECP-ligand peptide (E5) was able to distinguish reactive mucus of EoE patients from GERD and the control individuals by Phage-ELISA, achieving a sensitivity of 84.62%, and a specificity of 82.72%. This is the first study that successfully demonstrated an antibody-like peptide targeting ECP at the esophagus mucus as a useful auxilliary tool for EoE diagnosis with a significant association with atopic disorders and dysphagia.ClinicalTrials.gov no.: NCT03069573.

How Do Pollen Allergens Sensitize?

Plant pollen is one of the main sources of allergens causing allergic diseases such as allergic rhinitis and asthma. Several allergens in plant pollen are panallergens which are also present in other allergen sources. As a result, sensitized individuals may also experience food allergies. The mechanism of sensitization and development of allergic inflammation is a consequence of the interaction of allergens with a large number of molecular factors that often are acting in a complex with other compounds, for example low-molecular-mass ligands, which contribute to the induction a type 2-driven response of immune system. In this review, special attention is paid not only to properties of allergens but also to an important role of their interaction with lipids and other hydrophobic molecules in pollen sensitization. The reactions of epithelial cells lining the nasal and bronchial mucosa and of other immunocompetent cells will also be considered, in particular the mechanisms of the activation of B and T lymphocytes and the formation of allergen-specific antibody responses.

Analysis of allergen components and identification of bioactivity of HSP70 in pollen of Populus deltoides

Background

Allergies caused by pollen from Populus deltoides are common, but the allergic components are still unclear.

Methods

The total proteins in pollen of P. deltoides were analyzed by proteomics, and the potential allergens were identified via the WHO/IUIS database and the allergenOnline database retrieval. One target protein was screened by bioinformatics and expressed in Escherichia coli. The biological activity of the expressed product was verified by animal experiments.

Results

The total of 3929 proteins in pollen of P. deltoides were identified, and 46 potential allergens belonging to 10 protein families were recognized by database retrieval. B9N9W6 protein of Hsp70 family was screened by bioinformatics analysis and expressed successfully. ELISA showed that B9N9W6 can stimulate the immune system to produce specific IgE and promote the generation of IL-4. Flow cytometry showed that B9N9W6 can significantly stimulate the proliferation of CD4⁺ T cells and promote the polarization of Th2 cells. The pathological sections of mice lung tissues indicated that alveolar destruction was more severe in the B9N9W6 group than that of extract group, and there were more inflammatory cells infiltration, mucus exudation and bleeding.

Conclusion

B9N9W6 is an important antigenic substance in the pollen of P. deltoides. Due to the conserved structure of Hsp70 family, more attention should be paid to the possibility of sensitization when Hsp70 from any pathogenic species is administered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12953-021-00178-8.

Birch Pollen Induces Toll-Like Receptor 4-Dependent Dendritic Cell Activation Favoring T Cell Responses

Seasonal exposure to birch pollen (BP) is a major cause of pollinosis. The specific role of Toll-like receptor 4 (TLR4) in BP-induced allergic inflammation and the identification of key factors in birch pollen extracts (BPE) initiating this process remain to be explored. This study aimed to examine (i) the importance of TLR4 for dendritic cell (DC) activation by BPE, (ii) the extent of the contribution of BPE-derived lipopolysaccharide (LPS) and other potential TLR4 adjuvant(s) in BPE, and (iii) the relevance of the TLR4-dependent activation of BPE-stimulated DCs in the initiation of an adaptive immune response. In vitro, activation of murine bone marrow-derived DCs (BMDCs) and human monocyte-derived DCs by BPE or the equivalent LPS (nLPS) was analyzed by flow cytometry. Polymyxin B (PMB), a TLR4 antagonist and TLR4-deficient BMDCs were used to investigate the TLR4 signaling in DC activation. The immunostimulatory activity of BPE was compared to protein-/lipid-depleted BPE-fractions. In co-cultures of BPE-pulsed BMDCs and Bet v 1-specific hybridoma T cells, the influence of the TLR4-dependent DC activation on T cell activation was analyzed. In vivo immunization of IL-4 reporter mice was conducted to study BPE-induced Th2 polarization upon PMB pre-treatment. Murine and human DC activation induced by either BPE or nLPS was inhibited by the TLR4 antagonist or by PMB, and abrogated in TLR4-deficient BMDCs compared to wild-type BMDCs. The lipid-free but not the protein-free fraction showed a reduced capacity to activate the TLR4 signaling and murine DCs. In human DCs, nLPS only partially reproduced the BPE-induced activation intensity. BPE-primed BMDCs efficiently stimulated T cell activation, which was repressed by the TLR4 antagonist or PMB, and the addition of nLPS to Bet v 1 did not reproduce the effect of BPE. In vivo, immunization with BPE induced a significant Th2 polarization, whereas administration of BPE pre-incubated with PMB showed a decreased tendency. These findings suggest that TLR4 is a major pathway by which BPE triggers DC activation that is involved in the initiation of adaptive immune responses. Further characterization of these BP-derived TLR4 adjuvants could provide new candidates for therapeutic strategies targeting specific mechanisms in BP-induced allergic inflammation.

Comparative proteomics of common allergenic tree pollens of birch, alder, and hazel

BACKGROUND

In addition to known allergens, other proteins in pollen can aid the development of an immune response in allergic individuals. The contribution of the "unknown" protein allergens is apparent in phylogenetically related species where, despite of high homology of the lead allergens, the degree of allergenic potential can vary greatly. The aim of this study was to identify other potentially allergenic proteins in pollen of three common and highly related allergenic tree species: birch (Betula pendula), hazel (Corylus avellana) and alder (Alnus glutinosa).

METHODS

For that purpose, we carried out a comprehensive, comparative proteomic screening of the pollen from the three species. In order to maximize protein recovery and coverage, different protein extraction and isolation strategies during sample preparation were employed.

RESULTS

As a result, we report 2500-3000 identified proteins per each of the pollen species. Identified proteins were further used for a number of annotation steps, providing insight into differential distribution of peptidases, peptidase inhibitors and other potential allergenic proteins across the three species. Moreover, we carried out functional enrichment analyses that, interestingly, corroborated high species similarity in spite of their relatively distinct protein profiles.

CONCLUSION

We provide to our knowledge first insight into proteomes of two very important allergenic pollen types, hazel and alder, where not even transcriptomics data are available, and compared them to birch. Datasets from this study can be readily used as protein databases and as such serve as basis for further functional studies.

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.

Unravelling the virome in birch: RNA-Seq reveals a complex of known and novel viruses

To unravel the virome in birch trees of German and Finnish origin exhibiting symptoms of birch leaf-roll disease (BRLD), high-throughput sequencing (HTS) was employed. In total five viruses, among which three were so far unknown, were detected by RNAseq. One to five virus variants were identified in the transcriptome of individual trees. The novel viruses were genetically—fully or partially—characterized, belonging to the genera Carlavirus, Idaeovirus and Capillovirus and are tentatively named birch carlavirus, birch idaeovirus, and birch capillovirus, respectively. The recently discovered birch leafroll-associated virus was systematically detected by HTS in symptomatic seedlings but not in symptomless ones. The new carlavirus was detected only in one of the three symptomatic seedlings. The novel putative Capillovirus was detected in all seedlings—irrespective of their BLRD status—while the Idaeovirus was identified in a plant without leaf symptoms at the time of sampling. Further efforts are needed to complete Koch’s postulates and to clarify the possible association of the detected viruses with the BLR disease. Our study elucidates the viral population in single birch seedlings and provides a comprehensive overview for the diversities of the viral communities they harbor, to date.

Multiple roles of Bet v 1 ligands in allergen stabilization and modulation of endosomal protease activity

Background

Over 100 million people worldwide suffer from birch pollen allergy. Bet v 1 has been identified as the major birch pollen allergen. However, the molecular mechanisms of birch allergic sensitization, including the roles of Bet v 1 and other components of the birch pollen extract, remain incompletely understood. Here, we examined how known birch pollen–derived molecules influence the endolysosomal processing of Bet v 1, thereby shaping its allergenicity.

Methods

We analyzed the biochemical and immunological interaction of ligands with Bet v 1. We then investigated the proteolytic processing of Bet v 1 by endosomal extracts in the presence and absence of ligands, followed by a detailed kinetic analysis of Bet v 1 processing by individual endolysosomal proteases as well as the T‐cell epitope presentation in BMDCs.

Results

We identified E₁ phytoprostanes as novel Bet v 1 ligands. Pollen‐derived ligands enhanced the proteolytic resistance of Bet v 1, affecting degradation kinetics and preferential cleavage sites of the endolysosomal proteases cathepsin S and legumain. E₁ phytoprostanes exhibited a dual role by stabilizing Bet v 1 and inhibiting cathepsin protease activity.

Conclusion

Bet v 1 can serve as a transporter of pollen‐derived, bioactive compounds. When carried to the endolysosome, such compounds can modulate the proteolytic activity, including its processing by cysteine cathepsins. We unveil a paradigm shift from an allergen‐centered view to a more systemic view that includes the host endolysosomal enzymes.

Allergen-specific IgE levels and the ability of IgE-allergen complexes to cross-link determine the extent of CD23-mediated T-cell activation

Background

CD23 mediates IgE-facilitated allergen presentation and subsequent allergen-specific T-cell activation in allergic patients.

Objective

We sought to investigate key factors regulating IgE-facilitated allergen presentation through CD23 and subsequent T-cell activation.

Methods

To study T-cell activation by free allergens and different types of IgE–Bet v 1 complexes, we used a molecular model based on monoclonal human Bet v 1–specific IgE, monomeric and oligomeric Bet v 1 allergen, an MHC-matched CD23-expressing B-cell line, and a T-cell line expressing a human Bet v 1–specific T-cell receptor. The ability to cross-link Fcε receptors of complexes consisting of either IgE and monomeric Bet v 1 or IgE and oligomeric Bet v 1 was studied in human FcεRI-expressing basophils. T-cell proliferation by monomeric or oligomeric Bet v 1, which cross-links Fcε receptors to a different extent, was studied in allergic patients’ PBMCs with and without CD23-expressing B cells.

Results

In our model non–cross-linking IgE–Bet v 1 monomer complexes, as well as cross-linking IgE–Bet v 1 oligomer complexes, induced T-cell activation, which was dependent on the concentration of specific IgE. However, T-cell activation by cross-linking IgE–Bet v 1 oligomer complexes was approximately 125-fold more efficient. Relevant T-cell proliferation occurred in allergic patients’ PBMCs only in the presence of B cells, and its magnitude depended on the ability of IgE–Bet v 1 complexes to cross-link CD23.

Conclusion

The extent of CD23-mediated T-cell activation depends on the concentration of allergen-specific IgE and the cross-linking ability of IgE-allergen complexes.

Proteomics, Holm Oak (Quercus ilex L.) and Other Recalcitrant and Orphan Forest Tree Species: How do They See Each Other?

Proteomics has had a big impact on plant biology, considered as a valuable tool for several forest species, such as Quercus, Pines, Poplars, and Eucalyptus. This review assesses the potential and limitations of the proteomics approaches and is focused on Quercus ilex as a model species and other forest tree species. Proteomics has been used with Q. ilex since 2003 with the main aim of examining natural variability, developmental processes, and responses to biotic and abiotic stresses as in other species of the genus Quercus or Pinus. As with the progress in techniques in proteomics in other plant species, the research in Q. ilex moved from 2-DE based strategy to the latest gel-free shotgun workflows. Experimental design, protein extraction, mass spectrometric analysis, confidence levels of qualitative and quantitative proteomics data, and their interpretation are a true challenge with relation to forest tree species due to their extreme orphan and recalcitrant (non-orthodox) nature. Implementing a systems biology approach, it is time to validate proteomics data using complementary techniques and integrate it with the -omics and classical approaches. The full potential of the protein field in plant research is quite far from being entirely exploited. However, despite the methodological limitations present in proteomics, there is no doubt that this discipline has contributed to deeper knowledge of plant biology and, currently, is increasingly employed for translational purposes.