Dectin-2 recognition of house dust mite triggers cysteinyl leukotriene generation by dendritic cells

Escherichia coli heat-labile detoxified enterotoxin modulates dendritic cell function and attenuates allergic airway inflammation

Various mutant forms of Escherichia coli heat-labile enterotoxin (LT) have been used as a mucosal adjuvant for vaccines, as it enhances immune responses to specific antigens including antigen-specific IgA antibodies when administrated intranasally or orally. We hypothesized that a detoxified mutant form of LT, LTS61K, could modulate dendritic cell (DC) function and alleviate allergen-induced airway inflammation. Two protocols, preventative and therapeutic, were used to evaluate the effects of LTS61K in a Dermatophagoides pteronyssinus (Der p)-sensitized and challenged murine model of asthma. LTS61K or Der p-primed bone marrow-derived dendritic cells (BMDCs) were also adoptively transferred into Der p-sensitized and challenged mice. Intranasal inoculations with LTS61K or LTS61K/Der p decreased allergen-induced airway inflammation and alleviated systemic T_H2-type immune responses. Bronchoalveolar lavage fluid (BALF) and sera from LTS61K/Der p-treated mice also had higher concentrations of Der p-specific immunoglobulin (Ig) A than those of other groups. In vitro, BMDCs stimulated with Der p underwent cellular maturation and secreted proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)α In contrast, Der p-stimulated BMDCs that were pretreated with LTS61K showed decreased IL-6 and TNFα production and were less mature. Intratracheal adoptive transfer of LTS61K- or LTS61K/Der p-primed BMDCs into Der p-sensitized mice reduced inflammatory cell infiltration and T_H2-type chemokines in BALF and alleviated airway inflammation in treated mice. LTS61K influenced DC maturation and decreased inflammatory cytokine production. Moreover, LTS61K/Der p induced increased Der p-specific IgA production to decrease allergic T_H2 cytokine responses and alleviated airway inflammation in Der p-sensitized mice. These results suggest that the immunomodulatory effects of LTS61K may have clinical applications for allergy and asthma treatment.

Airway epithelial regulation of pulmonary immune homeostasis and inflammation

Recent genetic, structural and functional studies have identified the airway and lung epithelium as a key orchestrator of the immune response. Further, there is now strong evidence that epithelium dysfunction is involved in the development of inflammatory disorders of the lung. Here we review the characteristic immune responses that are orchestrated by the epithelium in response to diverse triggers such as pollutants, cigarette smoke, bacterial peptides, and viruses. We focus in part on the role of epithelium-derived interleukin (IL)-25, IL-33 and thymic stromal lymphopoietin (TSLP), as well as CC family chemokines as critical regulators of the immune response. We cite examples of the function of the epithelium in host defense and the role of epithelium dysfunction in the development of inflammatory diseases.

Dectin-2 regulates the effector phase of house dust mite-elicited pulmonary inflammation independently from its role in sensitization

The myeloid C-type lectin receptor Dectin-2 directs the generation of Th2 and Th17 immune responses to the house dust mite Dermatophagoides farinae through the generation of cysteinyl leukotrienes and proinflammatory cytokines, respectively, but a role for Dectin-2 in effector phase responses has not been described. In this study, we demonstrate that administration of the Dectin-2 mAb solely at the time of D. farinae challenge abrogated eosinophilic and neutrophilic inflammation in the bronchoalveolar lavage fluid and Th1, Th2, and Th17 inflammation in the lung of previously sensitized mice. Furthermore, Dectin-2 null mice (Clec4n(-/-)) sensitized with the adoptive transfer of D. farinae-pulsed wild-type (WT) bone marrow-derived dendritic cells (DCs) also had less D. farinae-elicited pulmonary inflammation, supporting an effector function for Dectin-2. The protection from pulmonary inflammation seen with the Dectin-2 mAb or in Clec4n(-/-) mice was associated with little or no reduction in lung-draining lymph node cells or their cytokine production and with no reduction in serum IgE. WT and Clec4n(-/-) mice recipients, sensitized with D. farinae-pulsed WT bone marrow-derived DCs, had comparable levels of D. farinae-elicited IL-6, IL-23, TNF-α, and cysteinyl leukotrienes in the lung. By contrast, D. farinae-elicited CCL4 and CCL8 production from pulmonary CD11c(+)CD11b(+)Ly6C(+) and CD11c(+)CD11b(+)Ly6C(-)CD64(+) monocyte-derived DCs was reduced in Clec4n(-/-) recipients. Addition of CCL8 at the time of D. farinae challenge abrogated the protection from eosinophilic, neutrophilic, and Th2 pulmonary inflammation seen in Clec4n(-/-) recipients. Taken together, these results reveal that Dectin-2 regulates monocyte-derived DC function in the pulmonary microenvironment at D. farinae challenge to promote the local inflammatory response.

Signalling C-type lectin receptors, microbial recognition and immunity

Signalling C‐type lectin receptors (CLRs) are crucial in shaping the immune response to fungal pathogens, but comparably little is known about the role of these receptors in bacterial, viral and parasitic infections. CLRs have many diverse functions depending on the signalling motifs in their cytoplasmic domains, and can induce endocytic, phagocytic, antimicrobial, pro‐inflammatory or anti‐inflammatory responses which are either protective or not during an infection. Understanding the role of CLRs in shaping anti‐microbial immunity offers great potential for the future development of therapeutics for disease intervention. In this review we will focus on the recognition of bacterial, viral and parasitic pathogens by CLRs, and how these receptors influence the outcome of infection. We will also provide a brief update on the role of CLRs in antifungal immunity.

Role of Dectin-2 for host defense against systemic infection with Candida glabrata

Although Candida glabrata is an important pathogenic Candida species, relatively little is known about its innate immune recognition. Here, we explore the potential role of Dectin-2 for host defense against C. glabrata. Dectin-2-deficient (Dectin-2^−/−) mice were found to be more susceptible to C. glabrata infections, showing a defective fungal clearance in kidneys but not in the liver. The increased susceptibility to infection was accompanied by lower production of T helper 1 (Th1) and Th17-derived cytokines by splenocytes of Dectin-2^−/− mice, while macrophage-derived cytokines were less affected. These defects were associated with a moderate yet significant decrease in phagocytosis of the fungus by the Dectin-2^−/− macrophages and neutrophils. Neutrophils of Dectin-2^−/− mice also displayed lower production of reactive oxygen species (ROS) upon challenge with opsonized C. glabrata or C. albicans. This study suggests that Dectin-2 is important in host defense against C. glabrata and provides new insights into the host defense mechanisms against this important fungal pathogen.

Systems biology of host-mycobiota interactions: dissecting Dectin-1 and Dectin-2 signalling in immune cells with DC-ATLAS

Modelling the networks sustaining the fruitful coexistence between fungi and their mammalian hosts is becoming increasingly important to control emerging fungal pathogens. The C-type lectins Dectin-1 and Dectin-2 are involved in host defense mechanisms against fungal infection driving inflammatory and adaptive immune responses and complement in containing fungal burdens. Recognizing carbohydrate structures in pathogens, their engagement induces maturation of dendritic cells (DCs) into potent immuno-stimulatory cells endowed with the capacity to efficiently prime T cells. Owing to these properties, Dectin-1 and Dectin-2 agonists are currently under investigation as promising adjuvants in vaccination procedures for the treatment of fungal infection. Thus, a detailed understanding of events' cascade specifically triggered in DCs upon engagement is of great interest in translational research. Here, we summarize the current knowledge on Dectin-1 and Dectin-2 signalling in DCs highlighting similarities and differences. Detailed maps are annotated, using the Biological Connection Markup Language (BCML) data model, and stored in DC-ATLAS, a versatile resource for the interpretation of high-throughput data generated perturbing the signalling network of DCs.

C-type lectin receptors orchestrate antifungal immunity

Fungal infections are an emerging threat for human health. A coordinated host immune response is fundamental for successful elimination of an invading fungal microbe. A panel of C-type lectin receptors expressed on antigen-presenting dendritic cells enable innate recognition of fungal cell wall carbohydrates and tailors adaptive responses via the instruction of CD4+ T helper cell fates. Well-balanced T helper cell type 1 and IL-17-producing T helper cell responses are crucial in antifungal immunity and facilitate phagocytic clearance of fungal encounters. Strikingly, different classes of fungi trigger distinct sets of C-type lectin receptors to evoke a pathogen-specific T helper response. In this review, we outline the key roles of several C-type lectin receptors during the generation of protective antifungal immunity, with particular emphasis on the distinct signaling pathways and transcriptional programs triggered by these receptors, which collaborate to orchestrate polarization of the T helper response.

A distinct sensitization pattern associated with asthma and the thymic stromal lymphopoietin (TSLP) genotype

BACKGROUND

Atopy is a phenotypically heterogeneous condition, and the extent to which atopy accounts for asthma is controversial. In this study, we aimed to identify the presence of distinct sensitization patterns to common inhaled allergens and their association with asthma, allergic rhinitis and TSLP genotypes.

METHODS

We studied 1683 adults from Tsukuba, a city in central Japan and 297 adults from Kamishihoro, a cedar-free, birch-dominant town in northern Japan. Levels of total serum IgE and specific IgE antibodies towards 14 major inhaled allergens were measured. With the use of these measures, cluster analysis was applied to classify the subjects' sensitization patterns. We also examined the genetic effects of 2 TSLP functional SNPs on the development of each sensitization pattern.

RESULTS

In the Tsukuba study, cluster analysis identified four clusters, including "Dust mite dominant", "Multiple pollen", "Cedar dominant", and "Low reactivity". In the Kamishihoro study, "Dust mite dominant", "Multiple pollen" and "Low reactivity" clusters were also identified, but a "Cedar dominant" cluster was not formed. The association with asthma was strongest for the "Dust mite dominant" cluster in both the Tsukuba and the Kamishihoro studies. In never smokers, both SNPs were associated with the "Dust mite dominant" cluster (OR > 1.2). In contrast, in current or past smokers, these alleles were inversely associated with the "Multiple pollen" cluster (OR < 0.5).

CONCLUSIONS

Cluster analysis identified the presence of distinct sensitization patterns to common inhaled allergens. TSLP may cause asthma by promoting innate allergic responses to indoor allergens and this contribution is significantly modified by smoking.

Innate immune responses in house dust mite allergy

Sensitizations to house dust mites (HDM) trigger strong exacerbated allergen-induced inflammation of the skin and airways mucosa from atopic subjects resulting in atopic dermatitis as well as allergic rhinitis and asthma. Initially, the Th2-biased HDM allergic response was considered to be mediated only by allergen B- and T-cell epitopes to promote allergen-specific IgE production as well as IL-4, IL-5, and IL-13 to recruit inflammatory cells. But this general molecular model of HDM allergenicity must be revisited as a growing literature suggests that stimulations of innate immune activation pathways by HDM allergens offer new answers to the following question: what makes an HDM allergen an allergen? Indeed, HDM is a carrier not only for allergenic proteins but also microbial adjuvant compounds, both of which are able to stimulate innate signaling pathways leading to allergy. This paper will describe the multiple ways used by HDM allergens together with microbial compounds to control the initiation of the allergic response through engagement of innate immunity.

Rat macrophage C-type lectin is an activating receptor expressed by phagocytic cells

Macrophage C-type lectin (MCL) is a membrane surface receptor encoded by the Antigen Presenting Lectin-like gene Complex (APLEC). We generated a mouse monoclonal antibody for the study of this receptor in the rat. We demonstrate that rat MCL is expressed on blood monocytes and neutrophils, as well as on several tissue macrophage populations, including alveolar and peritoneal cavity macrophages. We also demonstrate MCL expression on a subset of resident spleen macrophages. Immunohistochemistry analysis of the spleen showed staining specifically in the marginal zone and red pulp. Exposure to pro-inflammatory mediators or to yeast cell wall extract (zymosan) increased surface MCL expression on peritoneal macrophages. We characterized a rat myeloid cell line, RMW, which expresses high levels of MCL. We found that MCL co-immunoprecipitated with the activating adaptor protein FcεRIγ in these cells. Moreover, beads coated with anti-MCL antibody increased phagocytosis in the RMW cells. Together, these observations indicate that rat MCL is a receptor that activates phagocytosis in myeloid cells under inflammatory conditions.

Targeting the SYK-BTK axis for the treatment of immunological and hematological disorders: recent progress and therapeutic perspectives

Spleen Tyrosine Kinase (SYK) and Bruton's Tyrosine Kinase (BTK) are non-receptor cytoplasmic tyrosine kinases that are primarily expressed in cells of hematopoietic lineage. Both are key mediators in coupling activated immunoreceptors to downstream signaling events that affect diverse biological functions, from cellular proliferation, differentiation and adhesion to innate and adaptive immune responses. As such, pharmacological inhibitors of SYK or BTK are being actively pursued as potential immunomodulatory agents for the treatment of autoimmune and inflammatory disorders. Deregulation of SYK or BTK activity has also been implicated in certain hematological malignancies. To date, from a clinical perspective, pharmacological inhibition of SYK activity has demonstrated encouraging efficacy in patients with rheumatoid arthritis (RA), while patients with relapsed or refractory chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) have benefited from covalent inhibitors of BTK in early clinical studies. Here, we review and discuss recent insights into the emerging role of the SYK-BTK axis in innate immune cell function as well as in the maintenance of survival and homing signals for tumor cell progression. The current progress on the clinical development of SYK and BTK inhibitors is also highlighted.

Pattern recognition receptors and their role in invasive aspergillosis

Pattern recognition receptors (PRRs) are germline receptors that recognize conserved structures on microorganisms. Several PRRs have been identified in the recent years that are involved in the immune response against Aspergillus fumigatus. The role of PRRs in invasive pulmonary aspergillosis becomes especially apparent in the setting of an immunocompromised status of the host because of the redundancy of many PRRs in the host defense against A. fumigatus. Studies that investigated the PRRs and their effector pathways in invasive aspergillosis have led to a better understanding of the pathogenesis of invasive aspergillosis in immunocompromised patients. This knowledge may pave the way for novel diagnostic and immunomodulatory treatment strategies that are needed to overcome the high mortality associated with invasive A. fumigatus infection in immunocompromised patients.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.

Cysteinyl leukotriene receptors, old and new; implications for asthma

The cysteinyl leukotrienes (cys-LTs) are three structurally similar, but functionally distinct lipid mediators of inflammation. The parent cys-LT, LTC(4) , is synthesized by and released from mast cells, eosinophils, basophils, and macrophages, and is converted to the potent constrictor LTD(4) and the stable metabolite, LTE(4) . While only two cys-LT-selective receptors (CysLTRs) have been identified, cloned, and characterized, studies dating back three decades predicted the existence of at least three functional CysLTRs, each with a characteristic physiological function in airways and other tissues. The recent demonstration that mice lacking both known CysLTRs exhibit full (and in some instances, augmented) physiological responses to cys-LTs verifies the existence of unidentified CysLTRs. Moreover, the ability to manipulate receptor expression in both whole animal and cellular systems reveals that the functions of CysLTRs are controlled at multiple levels, including receptor-receptor interactions. Finally, studies in transgenic mice have uncovered a potentially major role for cys-LTs in controlling the induction of Th(2) responses to common allergens. This review focuses on these recent findings and their potential clinical implications.

In search of a tolerance-induction strategy for cow's milk allergies: significant reduction of beta-lactoglobulin allergenicity via transglutaminase/cysteine polymerization

OBJECTIVE

To explore the use of β-lactoglobulin polymerized using microbial transglutaminase and heating to identify whether protein polymerization could reduce in vivo allergenicity and maintain in vitro and ex vivo immunoreactivity for use in tolerance-induction protocols.

METHODS

Based on previous protocols applied in mice and children, we performed in vivo challenges (using a skin prick test) with native and polymerized β-lactoglobulin in adult patients with an IgE-mediated allergy to plactoglobulin. In vitro humoral immunoreactivity was analyzed using immunoblotting. Cell-mediated immunoreactivity was analyzed using ex vivo challenges with native and polymerized β-lactoglobulin and monitored by leukocyte adherence inhibition tests.

RESULTS

The skin tests demonstrated that there was a significant reduction in immediate cutaneous reactivity after polymerization. Polymerization did not decrease the immunoblotting detection of s-IgE specific to β-lactoglobulin. Cell-mediated immunoreactivity, as assessed by ex vivo challenges and leukocyte adherence inhibition tests, did not exhibit significant differences between leukocytes challenged with native versus polymerized β-lactoglobulin.

CONCLUSIONS

The polymerization of β-lactoglobulin decreased in vivo allergenicity and did not decrease in vitro humoral or ex vivo cell-mediated immunoreactivity. Therefore, we conclude that inducing polymerization using transglutaminase represents a promising technique to produce suitable molecules for the purpose of designing oral/ sublingual tolerance induction protocols for the treatment of allergies.

Differential dependencies of monocytes and neutrophils on dectin-1, dectin-2 and complement for the recognition of fungal particles in inflammation

We have re-investigated the role of the complement system and the non-opsonic pattern recognition receptors dectin-1 and dectin-2 in the recognition of fungal particles by inflammatory neutrophils, monocytes and macrophages. We have used in vivo and ex vivo models to study the recognition and response of these cells: i) We confirm previous observations regarding the importance of complement to neutrophil but not monocytic responses; ii) We show that dectin-1 is important for driving inflammatory cell recruitment to fungal stimuli and that it biases the immediate inflammatory response to one that favors neutrophil over monocyte recruitment; iii) We show that dectin-2 contributes to the physical recognition of fungal particles by inflammatory monocytes/macrophages, but is also expressed on neutrophils, where we show it has the potential to contribute to cellular activation; iv) Additionally, we show that serum-opsonization has the potential to interfere with non-opsonic recognition of fungal particles by dectin-1 and dectin-2, presumably through masking of ligands. Collectively these roles are consistent with previously described roles of dectin-1 and dectin-2 in driving inflammatory and adaptive immune responses and complement in containing fungal burdens. This study emphasizes the importance of heterogeneity of receptor expression across myeloid cell subsets in protective immune responses.

The mannose receptor

The MR is a highly effective endocytic receptor with a broad binding specificity encompassing ligands of microbial and endogenous origin and a poorly characterized ability to modulate cellular activation. This review provides an update of the latest developments in the field. It discusses how MR biology might be affected by glycosylation and proteolytic processing, MR involvement in antigen delivery, and the potential contribution of MR to T cell differentiation and cellular activation. Further understanding of these areas will, no doubt, inform the design of novel, therapeutic tools for improved vaccination, control of inflammation, and tumor chemotherapy, which will benefit from exploiting MR-efficient internalization properties and unique pattern of expression.

Interleukin-1α controls allergic sensitization to inhaled house dust mite via the epithelial release of GM-CSF and IL-33

IL-1α promotes a cascade of cytokine production from epithelial cells culminating in Th2 immunity to house dust mite allergens.

House dust mite (HDM) is one of the most common allergens worldwide. In this study, we have addressed the involvement of IL-1 in the interaction between HDM and the innate immune response driven by lung epithelial cells (ECs) and dendritic cells (DCs) that leads to asthma. Mice lacking IL-1R on radioresistant cells, but not hematopoietic cells, failed to mount a Th2 immune response and did not develop asthma to HDM. Experiments performed in vivo and in isolated air–liquid interface cultures of bronchial ECs showed that TLR4 signals induced the release of IL-1α, which then acted in an autocrine manner to trigger the release of DC-attracting chemokines, GM-CSF, and IL-33. Consequently, allergic sensitization to HDM was abolished in vivo when IL-1α, GM-CSF, or IL-33 was neutralized. Thymic stromal lymphopoietin (TSLP) became important only when high doses of allergen were administered. These findings put IL-1α upstream in the cytokine cascade leading to epithelial and DC activation in response to inhaled HDM allergen.

The role of dendritic cells in asthma

Dendritic cells (DCs) are known to play a central role in sensing the presence of foreign antigens and infectious agents and in initiating appropriate immune responses. More recently, an additional role has been discovered for DCs in determining whether the response to potential environmental allergens will be one of tolerance or whether a vigorous response along allergic pathways will be initiated. This review discusses ways in which DCs participate specifically in initiating allergic responses, particularly those associated with allergic asthma, and how interventions focused on DCs might lead to new therapeutic approaches to asthma.

Role and relevance of mast cells in fungal infections

In addition to their detrimental role in allergic diseases, mast cells (MCs) are well known to be important cells of the innate immune system. In the last decade, they have been shown to contribute significantly to optimal host defense against numerous pathogens including parasites, bacteria, and viruses. The contribution of MCs to the immune responses in fungal infections, however, is largely unknown. In this review, we first discuss key features of mast cell responses to pathogens in general and then summarize the current knowledge on the function of MCs in the defense against fungal pathogens. We especially focus on the potential and proven mechanisms by which MCs can detect fungal infections and on possible MC effector mechanisms in protecting from fungal infections.

Gene-by-environment effect of house dust mite on purinergic receptor P2Y12 (P2RY12) and lung function in children with asthma

BACKGROUND

Distinct receptors likely exist for leukotriene (LT)E(4), a potent mediator of airway inflammation. Purinergic receptor P2Y12 is needed for LTE(4)-induced airways inflammation, and P2Y12 antagonism attenuates house dust mite-induced pulmonary eosinophilia in mice. Although experimental data support a role for P2Y12 in airway inflammation, its role in human asthma has never been studied.

OBJECTIVE

To test for association between variants in the P2Y12 gene (P2RY12) and lung function in human subjects with asthma, and to examine for gene-by-environment interaction with house dust mite exposure.

METHODS

Nineteen single nucleotide polymorphisms (SNPs) in P2RY12 were genotyped in 422 children with asthma and their parents (n = 1266). Using family based methods, we tested for associations between these SNPs and five lung function measures. We performed haplotype association analyses and tested for gene-by-environment interactions using house dust mite exposure. We used the false discovery rate to account for multiple comparisons.

RESULTS

Five SNPs in P2RY12 were associated with multiple lung function measures (P-values 0.006–0.025). Haplotypes in P2RY12 were also associated with lung function (P-values 0.0055–0.046). House dust mite exposure modulated associations between P2RY12 and lung function, with minor allele homozygotes exposed to house dust mite demonstrating worse lung function than those unexposed (significant interaction P-values 0.0028–0.040).

CONCLUSIONS AND CLINICAL RELEVANCE

The P2RY12 variants were associated with lung function in a large family-based asthma cohort. House dust mite exposure caused significant gene-by-environment effects. Our findings add the first human evidence to experimental data supporting a role for P2Y12 in lung function. P2Y12 could represent a novel target for asthma treatment.

Mite-induced inflammation: More than allergy

Clinical observations have suggested that there is an association of atopic conditions with hypersensitivity reactions to nonsteroidal anti-inflammatory drugs (NSAIDs). This relationship has been especially present in patients allergic to mites. This study was designed to review clinical and experimental evidence linking atopy, mite allergy, and hypersensitivity to aspirin and NSAIDs and discuss the possible mechanisms explaining this association. A review of the medical literature concerning the association of atopic diseases, mite hypersensitivity, and intolerance to NSAIDs using PubMed and other relevant articles is presented. NSAID-sensitive patients are frequently atopic and allergic to mites, and patients who develop oral mite anaphylaxis (OMA) show an increased prevalence of NSAID hypersensitivity. The study of atopic, mite-sensitive patients, who experience urticaria and angioedema when exposed to NSAIDs and patients with OMA suggests an interesting interaction between atopic allergy and disorders of leukotriene synthesis or metabolism. Various mechanisms that could be involved in this interaction are presented, including genetic factors, inhibition of cyclooxygenase-1, and other effects (not related to IgE sensitization) of mite constituents on the immune system. The association of mite hypersensitivity with aspirin/NSAIDs intolerance has been confirmed and provides additional clues to various nonallergic pathways that may contribute to the acute and chronic inflammatory process observed in atopic, mite-allergic, individuals. The clinical relevance of these observations is presently under investigation.

Innate Immunity and the Role of Epithelial Barrier During Aspergillus fumigatus Infection

Fungi are the most important eukaryotic infective agents in Europe which largely overpass parasite infections. Total number of people dying of fungal infection is increasing and this trend is likely to continue due to the increase in immunosuppressive treatments. The opportunistic pathogen Aspergillus fumigatus (Af) is a saprophytic filamentous fungus that can cause invasive pulmonary diseases in immuno-compromised hosts. In veterinary medicine aspergillosis is also a recurrent problem since it infects various species, birds are particularly susceptible. It propagates through airborne conidia (spores), which are inhaled into the small airways where they may germinate and initiate an infection. The host epithelium has permanent contact with the environment and a multitude of diverse microorganisms, resulting in a network of the host’s defense mechanisms. Pathogens use various strategies to invade epithelial barriers, to exploit eukaryotic host function to their own benefit and disseminate throughout the host using the epithelium as a reservoir. The current revue will discuss the ways how epithelial and innate immunity cells can contlol Af infection. We will focus on Af strategies for the host’s invasion, antifungal innate immune response and antimicrobial activities of the respiratory epithelial cells.

The translational repressor T-cell intracellular antigen-1 (TIA-1) is a key modulator of Th2 and Th17 responses driving pulmonary inflammation induced by exposure to house dust mite

T-cell intracellular antigen-1 (TIA-1) is a translational repressor that dampens the production of proinflammatory cytokines and enzymes. In this study we investigated the role of TIA-1 in a mouse model of pulmonary inflammation induced by exposure to the allergenic extract (Df) of the house dust mite Dermatophagoides farinae. When intranasally challenged with a low dose of Df, mice lacking TIA-1 protein (Tia-1(-/-)) showed more severe airway and tissue eosinophilia, infiltration of lung bronchovascular bundles, and goblet cell metaplasia than wild-type littermates. Tia-1(-/-) mice also had higher levels of Df-specific IgE and IgG(1) in serum and ex vivo restimulated Tia-1(-/-) lymph node cells and splenocytes transcribed and released more Th2/Th17 cytokines. To evaluate the site of action of TIA-1, we studied the response to Df in bone marrow chimeras. These experiments revealed that TIA-1 acts on both hematopoietic and non-hematopoietic cells to dampen pulmonary inflammation. Our results identify TIA-1 as a negative regulator of allergen-mediated pulmonary inflammation in vivo. Thus, TIA-1 might be an important player in the pathogenesis of bronchial asthma.

Signaling by myeloid C-type lectin receptors in immunity and homeostasis

Myeloid cells are key drivers of physiological responses to pathogen invasion or tissue damage. Members of the C-type lectin receptor (CLR) family stand out among the specialized receptors utilized by myeloid cells to orchestrate these responses. CLR ligands include carbohydrate, protein, and lipid components of both pathogens and self, which variably trigger endocytic, phagocytic, proinflammatory, or anti-inflammatory reactions. These varied outcomes rely on a versatile system for CLR signaling that includes tyrosine-based motifs that recruit kinases, phosphatases, or endocytic adaptors as well as nontyrosine-based signals that modulate the activation of other pathways or couple to the uptake machinery. Here, we review the signaling properties of myeloid CLRs and how they impact the role of myeloid cells in innate and adaptive immunity.

Lung dendritic cells in respiratory viral infection and asthma: from protection to immunopathology

Lung dendritic cells (DCs) bridge innate and adaptive immunity, and depending on context, they also induce a Th1, Th2, or Th17 response to optimally clear infectious threats. Conversely, lung DCs can also mount maladaptive Th2 immune responses to harmless allergens and, in this way, contribute to immunopathology. It is now clear that the various aspects of DC biology can be understood only if we take into account the functional specializations of different DC subsets that are present in the lung in homeostasis or are attracted to the lung as part of the inflammatory response to inhaled noxious stimuli. Lung DCs are heavily influenced by the nearby epithelial cells, and a model is emerging whereby direct communication between DCs and epithelial cells determines the outcome of the pulmonary immune response. Here, we have approached DC biology from the perspective of viral infection and allergy to illustrate these emerging concepts.

Shifting of immune responsiveness to house dust mite by influenza A infection: genomic insights

Respiratory viral infections have been associated with an increased incidence of allergic asthma. However, the mechanisms by which respiratory infections facilitate allergic airway disease are incompletely understood. We previously showed that exposure to a low dose of house dust mite (HDM) resulted in enhanced HDM-mediated allergic airway inflammation, and, importantly, marked airway hyperreactivity only when allergen exposure occurred during an acute influenza A infection. In this study, we evaluated the impact of concurrent influenza infection and allergen exposure at the genomic level, using whole-genome microarray. Our data showed that, in contrast to exposure to a low dose of HDM, influenza A infection led to a dramatic increase in gene expression, particularly of TLRs, C-type lectin receptors, several complement components, as well as FcεR1. Additionally, we observed increased expression of a number of genes encoding chemokines and cytokines associated with the recruitment of proinflammatory cells. Moreover, HDM exposure in the context of an influenza A infection resulted in the induction of unique genes, including calgranulin A (S100a8), an endogenous damage-associated molecular pattern and TLR4 agonist. In addition, we observed significantly increased expression of serum amyloid A (Saa3) and serine protease inhibitor 3n (Serpina3n). This study showed that influenza infection markedly increased the expression of multiple gene classes capable of sensing allergens and amplifying the ensuing immune-inflammatory response. We propose that influenza A infection primes the lung environment in such a way as to lower the threshold of allergen responsiveness, thus facilitating the emergence of a clinically significant allergic phenotype.

Cytokines and the regulation of fungus-specific CD4 T cell differentiation

CD4 T cells play important and non-redundant roles in protection against infection with diverse fungi. Distinct CD4 T cell subsets can mediate protection against fungal disease where Th1 and Th17 CD4 T cell subsets have been found to promote fungal clearance and protective immunity against diverse fungal pathogens. The differentiation of naïve CD4 T cells into Th1 or Th17 cells is crucially controlled by their interaction with dendritic cells and instructed by cytokines. IL-12 and IFN-γ promote Th1 differentiation while TGF-β, IL-6, IL-1, IL-21 and IL-23 promote Th17 differentiation and maintenance. The production of these cytokines by DCs is in turn regulated by innate receptors triggered in response to fungal infection. In this review we will discuss the contributions of cytokines found to influence fungus-specific CD4 T cell differentiation and their role in defense against fungal disease. We will also highlight the contributions of innate receptors involved in recognition of fungi and how they shape cytokine secretion and CD4 T cell differentiation.

Lung dendritic cell-epithelial cell crosstalk in Th2 responses to allergens

Dendritic cells (DC) have been shown to be responsible for the initiation and maintenance of adaptive Th2 responses in asthma. It is increasingly clear that DC functions are strongly influenced by crosstalk with neighboring cells like epithelial cells, which can release a number of innate cytokines promoting Th2 responses. Clinically relevant allergens often interfere directly or indirectly with the innate immune functions of airway epithelial cells and DC. A better understanding of these interactions might lead to a better prevention and ultimately to new treatments for asthma.

Immune responses against Aspergillus fumigatus: what have we learned?

PURPOSE OF REVIEW

Aspergillus fumigatus causes invasive and allergenic disease. Host defense relies on the ability of the respiratory immune system to restrict spore germination into invasive hyphae and to limit fungus-induced or inflammation-induced damage in infected tissues. This review covers the molecular and cellular events that mediate innate and CD4 T-cell responses to A. fumigatus and fungal attributes that counter hostile microenvironments and, in turn, affect host responses.

RECENT FINDINGS

Host recognition of fungal cell wall components is critical for fungal uptake, killing, and the formation of protective innate and CD4 T-cell effector populations. Beyond the known role of neutrophils and macrophages, circulating monocytes, dendritic cells, and natural killer cells contribute to optimal defense against A. fumigatus. Genetic and pharmacologic manipulation of A. fumigatus reveals that hypoxia adaptation, cell wall assembly, and secondary metabolite production in mammalian tissues contribute to fungal pathogenesis and the outcome of infection.

SUMMARY

Greater understanding of the immune mechanisms that underlie protective responses and fungal pathways that promote microbial adaptation and growth in mammalian tissue provide a conceptual framework for improving current antifungal therapies.

Mite allergen decreases DC-SIGN expression and modulates human dendritic cell differentiation and function in allergic asthma

House dust mites (HDMs) induce allergic asthma in sensitized individuals, although how HDMs activate immature mucosal dendritic cells (DCs) to render the T helper cell type 2 (Th2)-mediated immune response is unclear. In this study, our results showed a significant calcium-dependent lectin binding of Dermatophagoides pteronyssinus (Der p) extracts to DC-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), the C-type lectin receptors (CLRs) of DCs. Moreover, monocyte-derived DCs (MDDCs) of Der p-sensitized asthmatics (AS) exhibited decreased expression of DC-SIGN, increased endocytosis, and impaired differentiation of DC precursors. The Der p-induced downregulation of DC-SIGN expression in the differentiation of immature MDDCs may be because of the internalization of Der p-DC-SIGN complex. MDDCs of AS produced more interleukin (IL)-6 and less IL-12p70 cytokines when stimulated with lipopolysaccharide (LPS) or Der p than those of nonallergic controls (NC). In the co-culture experiments, MDDCs pretreated with Der p induced GATA-3 expression and IL-4 cytokine productions in naive CD4(+) T cells. These effects of Der p on the differentiation and function of MDDCs could be partially blocked by anti-DC-SIGN antibodies. In conclusion, our results suggest a critical step of allergen sensitization that involves CLRs in the innate immune response of DCs, which may provide a therapeutic or preventive potential for allergic asthma.

Myeloid C-type lectin receptors in pathogen recognition and host defense

C-type lectin receptors (CLRs) comprise a heterogeneous group of transmembrane proteins. Many of them are expressed in myeloid cells and signal in response to pathogen-derived or self ligands to initiate or regulate cell activation. Here, we review the properties of myeloid CLRs, highlighting how their signaling function is coordinated with that of other innate receptor families to control immunity to infection.

Orchestrating house dust mite-associated allergy in the lung

House dust mites (HDM; Dermatophagoides sp.) are one of the commonest aeroallergens worldwide and up to 85% of asthmatics are typically HDM allergic. Allergenicity is associated both with the mites themselves and with ligands derived from mite-associated bacterial and fungal products. Murine models of allergic airways disease for asthma research have recently switched from the use of surrogate allergen ovalbumin together with adjuvant to use of the HDM extract. This has accelerated understanding of how adaptive and innate immunity generate downstream pathology. We review the myriad ways in which HDM allergic responses are orchestrated. Understanding the molecular pathways that elicit HDM-associated pathology is likely to reveal novel targets for therapeutic intervention.

The role of innate immunity activation in house dust mite allergy

House dust mite (HDM) allergy is a frequent inflammatory disease found worldwide. Although allergen-specific CD4(+) Th2 cells orchestrate the HDM allergic response, notably through induction of IgE directed towards mite allergens, recent studies have demonstrated that innate immunity activation also plays a critical role in HDM-induced allergy pathogenesis. HDM allergens can not only be considered proteins that induce adaptive Th2-biased responses in susceptible subjects but also as strong activators of innate immune cells, including skin keratinocytes and airway epithelial cells. The contribution of microbial adjuvant factors, derived from HDM carriers or the environment, is also essential in such cell stimulation. This review highlights how HDM allergens, together with microbial compounds, promote allergic responses through pattern recognition receptor-dependent pathways.

The purinergic G protein-coupled receptor 6 inhibits effector T cell activation in allergic pulmonary inflammation

We show that the P2Y(6) receptor, a purinergic G protein-coupled receptor with a high affinity for the nucleotide uridine diphosphate, is an important endogenous inhibitor of T cell function in allergic pulmonary inflammation. Mice conditionally deficient in P2Y(6) receptors [p2ry6 (flox/flox);cre/+ mice] exhibited severe airway and tissue pathology relative to P2Y(6)-sufficient [p2ry6 (flox/flox)] littermates (+/+ mice) when treated intranasally with an extract of the dust mite Dermatophagoides farinae (Df). P2Y(6) receptors were inducibly expressed by lung, lymph node, and splenic CD4(+) and CD8(+) T cells of Df-treated +/+ mice. Df-restimulated P2Y(6)-deficient lymph node cells produced higher levels of Th1 and Th2 cytokines, and polyclonally stimulated P2Y(6)-deficient CD4(+) T cells proliferated faster than comparably stimulated P2Y(6)-sufficient cells. The absence of P2Y(6) receptors on CD4(+) cells, but not APCs, was sufficient to amplify cytokine generation. Thus, P2Y(6) receptors protect the lung against exuberant allergen-induced pulmonary inflammation by inhibiting the activation of effector T cells.

Innate antifungal immunity: the key role of phagocytes

Fungal diseases have emerged as significant causes of morbidity and mortality, particularly in immune-compromised individuals, prompting greater interest in understanding the mechanisms of host resistance to these pathogens. Consequently, the past few decades have seen a tremendous increase in our knowledge of the innate and adaptive components underlying the protective (and nonprotective) mechanisms of antifungal immunity. What has emerged from these studies is that phagocytic cells are essential for protection and that defects in these cells compromise the host's ability to resist fungal infection. This review covers the functions of phagocytes in innate antifungal immunity, along with selected examples of the strategies that are used by fungal pathogens to subvert these defenses.

Microarrayed recombinant allergens for diagnostic testing

The development of protein microarray-based immunoassays and the availability of recombinant allergens have, to a significant extent, emerged together over the past decade. Their long-anticipated wider application to allergy diagnosis has recently begun to accelerate. This review discusses some of the strengths and weaknesses of molecularly defined allergy testing and the microarray platform. Several recent applications of microarray assays to allergy testing are also summarized. Promising findings, particularly in the context of food and latex allergy, point to the potential for greater resolution between clinical reactivity and asymptomatic sensitization with this platform.

Small animals models for drug discovery

There has been an explosion of studies of animal models of asthma in the past 20 years. The elucidation of fundamental immunological mechanisms underlying the development of allergy and the complex cytokine and chemokines networks underlying the responses have been substantially unraveled. Translation of findings to human asthma have been slow and hindered by the varied phenotypes that human asthma represents. New areas for expansion of modeling include virally mediated airway inflammation, oxidant stress, and the interactions of stimuli triggering innate immune and adaptive immune responses.

The catalytic architecture of leukotriene C4 synthase with two arginine residues

Leukotriene (LT) C(4) and its metabolites, LTD(4) and LTE(4), are involved in the pathobiology of bronchial asthma. LTC(4) synthase is the nuclear membrane-embedded enzyme responsible for LTC(4) biosynthesis, catalyzing the conjugation of two substrates that have considerably different water solubility; that amphipathic LTA(4) as a derivative of arachidonic acid and a water-soluble glutathione (GSH). A previous crystal structure revealed important details of GSH binding and implied a GSH activating function for Arg-104. In addition, Arg-31 was also proposed to participate in the catalysis based on the putative LTA(4) binding model. In this study enzymatic assay with mutant enzymes demonstrates that Arg-104 is required for the binding and activation of GSH and that Arg-31 is needed for catalysis probably by activating the epoxide group of LTA(4).

Dendritic cells and airway epithelial cells at the interface between innate and adaptive immune responses

Because they can recognize and sample inhaled allergens, dendritic cells (DC) have been shown to be responsible for the initiation and maintenance of adaptive Th2 responses in asthma. It is increasingly clear that DC functions are strongly influenced by a crosstalk with neighboring cells like epithelial cells. Whereas the epithelium was initially considered only as a barrier, it is now seen as a central player in controlling the function of lung DCs through release of innate cytokines-promoting Th2 responses. Clinically relevant allergens, as well as known environmental and genetic risk factors for allergy and asthma, often interfere directly or indirectly with the innate immune functions of airway epithelial cells and DC. A better understanding of these interactions might lead to a better prevention and ultimately to new treatments for asthma.

Skin test reactivity of allergic subjects to basidiomycetes' crude extracts in a tropical environment

Fungal allergies can be detected by the skin prick test with extracts of the organisms, but not all fungi, including the basidiomycetes, are being examined. We determined the level of sensitization to basidiomycetes in allergic subjects and compared their reactivity to commercial extracts commonly used to detect allergies. Crude spore extracts of the basidiomycetes Ganoderma applanatum, Chlorophyllum molybdites, and Pleurotus ostreatus, which are known to release numerous spores, were examined along with commercial extracts on 33 subjects with asthma, allergic or non-allergic rhinitis. Overall, affected subjects showed the highest reactivity to mites (36%), followed by Ganoderma applanatum (30%), grass (27%) Chlorophyllum molybdites (12%) and Pleurotus ostreatus (12%). Allergic rhinitis patients were most reactive to mites (58%), grass (42%), Ganoderma applanatum (25%), Penicillium spp. (25%), and cat (17%). Those with asthma primarily responded to mites (44%), Ganoderma applanatum (44%), grass (33%), and Pleurotus ostreatus (22%). IgE levels correlated with positive basidiomycetes extracts. This finding, coupled with higher reactivity to basidiospores as compared to mitospores, and the similar sensitivities of patients to G. applanatum and mites, suggest that basidiomycetes are important allergen sources in the tropics.