Human blood dendritic cells from allergic subjects have impaired capacity to produce interferon-alpha via Toll-like receptor 9

Peptidoglycan recognition protein 1 enhances experimental asthma by promoting Th2 and Th17 and limiting regulatory T cell and plasmacytoid dendritic cell responses

Asthma is a common inflammatory disease involving cross-talk between innate and adaptive immunity. We reveal that antibacterial innate immunity protein, peptidoglycan recognition protein (Pglyrp)1, is involved in the development of allergic asthma. Pglyrp1(-/-) mice developed less severe asthma than wild-type (WT) mice following sensitization with house dust mite (allergen) (HDM). HDM-sensitized Pglyrp1(-/-) mice, compared with WT mice, had diminished bronchial hyperresponsiveness (lung airway resistance); numbers of eosinophils, neutrophils, lymphocytes, and macrophages in bronchoalveolar lavage fluid and lungs; inflammatory cell infiltrates in the lungs around bronchi, bronchioles, and pulmonary arteries and veins; lung remodeling (mucin-producing goblet cell hyperplasia and metaplasia and smooth muscle hypertrophy and fibrosis); levels of IgE, eotaxins, IL-4, IL-5, and IL-17 in the lungs; and numbers of Th2 and Th17 cells and expression of their marker genes in the lungs. The mechanism underlying this decreased sensitivity of Pglyrp1(-/-) mice to asthma was increased generation and activation of CD8α(+)β(+) and CD8α(+)β(-) plasmacytoid dendritic cells (pDC) and increased recruitment and activity of regulatory T (Treg) cells in the lungs. In vivo depletion of pDC in HDM-sensitized Pglyrp1(-/-) mice reversed the low responsive asthma phenotype of Pglyrp1(-/-) mice to resemble the more severe WT phenotype. Thus, Pglyrp1(-/-) mice efficiently control allergic asthma by upregulating pDC and Treg cells in the lungs, whereas in WT mice, Pglyrp1 is proinflammatory and decreases pDC and Treg cells and increases proasthmatic Th2 and Th17 responses. Blocking Pglyrp1 or enhancing pDC in the lungs may be beneficial for prevention and treatment of asthma.

CpG-Induced IFN-α production of plasmacytoid dendritic cells: time and dosage dependence and the effect of structural modifications to the CpG backbone

Plasmacytoid dendritic cells (pDCs) represent a highly specialized immune cell subset and are considered to be the main sentinels against viral infections and play an important role in the development of immune tolerance. pDCs are able to recognize cytosine-phosphate-guanosine (CpG) motifs within microbial DNA, which are unmethylated CG dinucleotides in a certain sequence context and trigger the secretion of interferon (IFN)-α and other proinflammatory cytokines. Here we used the typical class A CpG oligodeoxynucleotide (ODN) 2216, the B-class ODN 2006, and the newly synthesized CpG ODN TM64 to explore the potency and kinetics of IFN-α stimulation of pDC. TM64 CpG ODN has a hexanucleotide sequence TCGTGT that leads to an increased cellular uptake and features a CpG nucleotide within the sequence that leads to a potent specific B-cell stimulation, thus characteristics similar to a class B CpG. Our data reveals that all CpGs act as both dosage- and time-dependent stimuli of IFN-α secretion. The relationship between concentration of the stimulant and the secreted amount of IFN-α is not linear and results in a plateau formation, with saturation kinetics. Alteration to the backbone can change duration and quantity of overall IFN-α secretion.

Dendritic cells, viruses, and the development of atopic disease

Dendritic cells are important residents of the lung environment. They have been associated with asthma and other inflammatory diseases of the airways. In addition to their antigen-presenting functions, dendritic cells have the ability to modulate the lung environment to promote atopic disease. While it has long been known that respiratory viral infections associate with the development and exacerbation of atopic diseases, the exact mechanisms have been unclear. Recent studies have begun to show the critical importance of the dendritic cell in this process. This paper focuses on these data demonstrating how different populations of dendritic cells are capable of bridging the adaptive and innate immune systems, ultimately leading to the translation of viral illness into atopic disease.

Innate immune responses to rhinovirus are reduced by the high-affinity IgE receptor in allergic asthmatic children

BACKGROUND

Children with allergic asthma have more frequent and severe human rhinovirus (HRV)-induced wheezing and asthma exacerbations through unclear mechanisms.

OBJECTIVE

We sought to determine whether increased high-affinity IgE receptor (FcεRI) expression and cross-linking impairs innate immune responses to HRV, particularly in allergic asthmatic children.

METHODS

PBMCs were obtained from 44 children, and surface expression of FcεRI on plasmacytoid dendritic cells (pDCs), myeloid dendritic cells, monocytes, and basophils was assessed by using flow cytometry. Cells were also incubated with rabbit anti-human IgE to cross-link FcεRI, followed by stimulation with HRV-16, and IFN-α and IFN-λ1 production was measured by Luminex. The relationships among FcεRI expression and cross-linking, HRV-induced IFN-α and IFN-λ1 production, and childhood allergy and asthma were subsequently analyzed.

RESULTS

FcεRIα expression on pDCs was inversely associated with HRV-induced IFN-α and IFN-λ1 production. Cross-linking FcεRI before HRV stimulation further reduced PBMC IFN-α (47% relative reduction; 95% CI, 32% to 62%; P< .0001) and IFN-λ1 (81% relative reduction; 95% CI, 69% to 93%; P< .0001) secretion. Allergic asthmatic children had higher surface expression of FcεRIα on pDCs and myeloid dendritic cells when compared with that seen in nonallergic nonasthmatic children. Furthermore, after FcεRI cross-linking, allergic asthmatic children had significantly lower HRV-induced IFN responses than allergic nonasthmatic children (IFN-α, P= .004; IFN-λ1, P= .02) and nonallergic nonasthmatic children (IFN-α, P= .002; IFN-λ1, P= .01).

CONCLUSIONS

Allergic asthmatic children have impaired innate immune responses to HRV that correlate with increased FcεRI expression on pDCs and are reduced by FcεRI cross-linking. These effects likely increase susceptibility to HRV-induced wheezing and asthma exacerbations.

Developments in the field of allergy in 2010 through the eyes of Clinical and Experimental Allergy

In 2010 over 200 articles were published in Clinical and Experimental Allergy including editorials, reviews, opinion articles, letters, book reviews and of course at the heart of the journal, papers containing original data which have moved the field of allergy forward on a number of fronts. For the third year running the editors felt it would be of value to summarize the key messages contained in these papers as a snapshot of where the cutting edge of research into allergic disease is leading. We have broadly followed the sections of the journal, although this year the mechanistic articles are grouped together and the studies involving experimental models of disease are discussed throughout the paper. In the field of asthma and rhinitis phenotypes and biomarkers continue to a major pre-occupation of our authors. There is continued interest in mechanisms of inflammation and disordered lung function with the mouse model of asthma continuing to offer new insights. There is also a steady flow of papers investigating new therapies, including those derived from plants and herbs, although many are mechanistic with too few high quality clinical trials. The mechanisms involved in allergic disease are well covered with many strong papers using clinical material to ask relevant questions. Pro-pre and snybiotics continue to be of major interest to our authors and this remains a controversial and complicated field. The discipline of epidemiology has retained its interest in risk factors for the development of allergic disease with a view to refining and debating the reasons for the allergy epidemic. There is continued interest in the relationship between helminthic disease and allergy with a new twist in 2010 involving studies using infection with helminths as a potential treatment. The genetics of allergic disease continues to be very productive, although the field has moved on from only investigating single nucleotide polymorphisms of candidate genes to Genome Wide Association Studies and an increasing and welcome emphasis on gene-environment interactions. In the field of clinical allergy there is steady flow of papers describing patterns of drug allergy with renewed interest in reactions to contrast media, but food allergy is the major area of interest in this section of the journal. Lastly in the field of allergens there is a growing interest in the role of component resolved diagnosis in improving the diagnosis and management of allergic disease. Another excellent year, full of fascinating and high quality work, which the journal has been proud to bring to the allergy community.

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.

Innate IFNs and plasmacytoid dendritic cells constrain Th2 cytokine responses to rhinovirus: a regulatory mechanism with relevance to asthma

Human rhinoviruses (RV) cause only minor illness in healthy individuals, but can have deleterious consequences in people with asthma. This study sought to examine normal homeostatic mechanisms regulating adaptive immunity to RV in healthy humans, focusing on effects of IFN-αβ and plasmacytoid dendritic cells (pDC) on Th2 immune responses. PBMC were isolated from 27 healthy individuals and cultured with RV16 for up to 5 d. In some experiments, IFN-αβ was neutralized using a decoy receptor that blocks IFN signaling, whereas specific dendritic cell subsets were depleted from cultures with immune-magnetic beads. RV16 induced robust expression of IFN-α, IFN-β, multiple IFN-stimulated genes, and T cell-polarizing factors within the first 24 h. At 5 d, the production of memory T cell-derived IFN-γ, IL-10, and IL-13, but not IL-17A, was significantly elevated. Neutralizing the effects of type-I IFN with the decoy receptor B18R led to a significant increase in IL-13 synthesis, but had no effect on IFN-γ synthesis. Depletion of pDC from RV-stimulated cultures markedly inhibited IFN-α secretion, and led to a significant increase in expression and production of the Th2 cytokines IL-5 (p = 0.02), IL-9 (p < 0.01), and IL-13 (p < 0.01), but had no effect on IFN-γ synthesis. Depletion of CD1c(+) dendritic cells did not alter cytokine synthesis. In healthy humans, pDC and the IFN-αβ they secrete selectively constrain Th2 cytokine synthesis following RV exposure in vitro. This important regulatory mechanism may be lost in asthma; deficient IFN-αβ synthesis and/or pDC dysfunction have the potential to contribute to asthma exacerbations during RV infections.

Allergic rhinitis

Allergic rhinitis is a costly disease associated with significant morbidity. It impacts the quality of life of millions of individuals, particularly in industrialized nations, and it is on the rise. Lost productivity and total healthcare expenditure exceeds several billion dollars annually in the United States, with an estimate of >$6 billion spent on prescription medications alone. It is also associated with asthma and other atopic conditions, sinusitis, otitis media, and sleep apnea. Primary care physicians should be well adept at recognizing and initiating empiric first-line therapy for chronic rhinitis. Allergen avoidance, topical nasal steroids, and antihistamines may be sufficient for some patients. In most cases, referral to a board-certified allergy specialist for skin testing and targeted management is indicated. It is essential to make sure that patients abstain from using antihistamines at least 1 week prior to reporting to the allergist for skin testing in order to avoid false-negative results. Traditional subcutaneous allergen immunotherapy, when performed by an experienced allergist, affords relief in >75% of cases. The growing armament of treatment options for refractory allergic rhinitis includes oral and sublingual immunotherapy, recombinant allergens, conjugated DNA vaccines, and anti-immunoglobulin E monoclonal antibody.

Cellular immune response parameters that influence IgE sensitization

In vitro basophil responses have long been used in mechanistic studies to help assess the human allergic diathesis, particularly during therapeutic intervention. Recent evidence points to the use of dendritic cells (DCs) in also being valuable in evaluating therapies aimed at lessening disease through immunomodulation. This review article therefore takes a look at some of the recent advances in old and new assays employing both basophils and DCs, with the added perception that the responses mediated by two cell types are insightful towards understanding immune cell mechanisms underlying allergic disease.

Basophils: emerging roles in the pathogenesis of allergic disease

After approximately 130 years since their discovery as rare granulocytes that circulate in blood, basophils are just now gaining respect as significant contributors in the pathogenesis underlying allergic inflammation and disease. While long known for secreting preformed and newly synthesized mediators and for selectively infiltrating tissue during immunoglobulin E (IgE)-mediated inflammation, their role has largely been viewed as redundant to that of tissue mast cells in functioning as effector cells. This line of thought has persisted even though it has been known in humans for approximately 20 years that basophils additionally produce relatively large quantities of cytokines, e.g. interleukin-4 (IL-4)/IL-13, that are central for the manifestations of allergic disease. Studies using novel IL-4 reporter mice have significantly added to the in vivo importance of basophils as IL-4 producing cells, with recent findings indicating that these cells also function as antigen-presenting cells essential in initiating T-helper 2 responses. If confirmed and translated to humans, these provocative findings will give new meaning to the role basophils have in allergic disease, and in immunology overall.

Rhinoviruses, allergic inflammation, and asthma

Viral infections affect wheezing and asthma in children and adults of all ages. In infancy, wheezing illnesses are usually viral in origin, and children with more severe wheezing episodes are more likely to develop recurrent episodes of asthma and to develop asthma later in childhood. Children who develop allergen-specific immunoglobulin E (allergic sensitization) and those who wheeze with human rhinoviruses (HRV) are at especially high risk for asthma. In older children and adults, HRV infections generally cause relatively mild respiratory illnesses and yet contribute to acute and potentially severe exacerbations in patients with asthma. These findings underline the importance of understanding the synergistic nature of allergic sensitization and infections with HRV in infants relative to the onset of asthma and in children and adults with respect to exacerbations of asthma. This review discusses clinical and experimental evidence of virus-allergen interactions and evaluates theories which relate immunologic responses to respiratory viruses and allergens to the pathogenesis and disease activity of asthma. Greater understanding of the relationship between viral respiratory infections, allergic inflammation, and asthma is likely to suggest new strategies for the prevention and treatment of asthma.

Impaired IFN-α secretion by plasmacytoid dendritic cells induced by TLR9 activation in chronic idiopathic urticaria

BACKGROUND

Understanding the early events of the immune response, through the activation of plasmacytoid dendritic cells (pDC) by Toll-like receptor (TLR)9-sensing, could contribute to the evaluation of immune dysregulation in chronic idiopathic urticaria (CIU).

OBJECTIVES

We decided to investigate innate immunity in CIU and the mechanisms implicated in the modulation of interferon (IFN)-α production by pDC upon TLR9 activation.

METHODS

Patients with CIU (n = 31) and healthy control subjects (HC, n = 36) were enrolled in the study. Leucocytes cultured with the TLR9 ligand, CpG type A, or with inhibitory-oligodeoxynucleotide (ODN) were used to determine IFN-α secretion by enzyme-linked immunosorbent assay. Enumeration of pDC, intracellular IFN-α and signal transducers and activators of transcription protein (STAT) (1 and 4) phosphorylation were assessed by flow cytometry. TLR9 and regulatory factor-7 mRNA transcripts were evaluated by real-time polymerase chain reaction. Evidence of pDC in the skin lesions of patients was analysed with immunohistochemistry staining.

RESULTS

The findings show a decreased IFN-α secretion induced by CpG A by leucocytes, due to the diminished IFN-α expression on pDC in CIU. It was mediated by TLR9-activation since inhibitory-ODN further suppressed TLR9-induced IFN-α secretion. A normal pDC percentage and degree of activation by the expression of costimulatory molecules was observed in CIU, with the rare presence of pDC in the skin lesion. In addition, an increased constitutive STAT1 phosphorylation on nonstimulated lymphocytes and a downregulation of TLR9 mRNA transcripts after CpG A activation were verified in patients with CIU.

CONCLUSIONS

The findings showed an innate immune response in CIU disturbed by impairment of the pDC response to TLR9 activation.

Regulation of effector and memory T-cell functions by type I interferon

Type I interferon (IFN-α/β) is comprised of a family of highly related molecules that exert potent antiviral activity by interfering with virus replication and spread. IFN-α/β secretion is tightly regulated through pathogen sensing pathways that are operative in most somatic cells. However, specialized antigen-presenting plasmacytoid dendritic cells are uniquely equipped with the capacity to secrete extremely high levels of IFN-α/β, suggesting a key role for this cytokine in priming adaptive T-cell responses. Recent studies in both mice and humans have demonstrated a role for IFN-α/β in directly influencing the fate of both CD4(+) and CD8(+) T cells during the initial phases of antigen recognition. As such, IFN-α/β, among other innate cytokines, is considered an important 'third signal' that shapes the effector and memory T-cell pool. Moreover, IFN-α/β also serves as a counter-regulator of T helper type 2 and type 17 responses, which may be important in the treatment of atopy and autoimmunity, and in the development of novel vaccine adjuvants.

The crucial role of dendritic cells in rhinitis

PURPOSE OF REVIEW

Dendritic cells generally play an important role as sentinels in the immune system. They are also very important in protecting the airways from invading pathogens and harmful particles and antigens. This review discusses current knowledge about dendritic cell function and the interaction between dendritic cells and their surroundings, the epithelium, during their presence in the nasal mucosa.

RECENT FINDINGS

There are some phenotypical differences between myeloid dendritic cells and plasmacytoid dendritic cells in different types of rhinitis. Since it has become possible to perform functional studies on purified dendritic cell populations obtained from the upper airway mucosa, a number of studies have appeared. Some confirm that thymic stromal lymphopoietin is present in the nasal mucosa and that it may influence dendritic cell-T-cell interaction in a pro-Th2 way. Epithelial cells share several characteristics with dendritic cells, but they cannot migrate and move antigens to draining lymph nodes.

SUMMARY

Several functional dendritic cell studies have been published indicating that there are disease-dependent dendritic cell differences in rhinitis. In addition to these differences, factors like epithelial cells and T cells influence dendritic cells. Several new therapeutic options are available targeting direct or indirect dendritic cell functions.

Differential development of plasmacytoid dendritic cells in Th1- and Th2-like cytokine milieus

BACKGROUND

Plasmacytoid dendritic cells (pDCs) infiltrate sites of Th1- and Th2-dominant inflammation and many studies have been performed to analyse their role in these immune responses. In contrast, much less is known about the effects of a Th1 or Th2 cytokine milieu on pDC function. Therefore, we investigated the impact of Th1- and Th2-like conditions during the development of pDCs on their antigen expression and function.

METHODS

PDCs were matured in vitro by the addition of IL-3 under Th1- or Th2-like conditions. Antigen expression and TLR7-ligand-induced cytokine secretion was analysed by flow cytometry and ELISA. Furthermore, the CD4(+) T-cell polarizing capacity of pDCs was determined as well as their potential to induce CD4(+) T-cell proliferation.

RESULTS

PDCs matured under Th1-like conditions showed a higher expression of antigens involved in T-cell co-stimulation and antigen presentation like CD40, CD80, CD83 and HLA-DR as well as a higher secretion of IL-6 and IFN-α in response to TLR7-ligation compared to Th2-pDCs. Furthermore, Th1-pDCs induced a significantly higher CD4(+) T-cell proliferation and primed a higher percentage of CD4(+) T cells to express IFN-γ and IL-2 after TLR7-ligation compared to Th2-pDCs. In contrast, Th2-pDCs were characterized by a significant upregulation of BDCA-3 and IL-4 expression following TLR7-ligation.

CONCLUSION

This study is the first to demonstrate the crucial impact of a surrounding cytokine environment on the development of pDC function including antigen expression. Based on these findings, it can be speculated that antiviral/bacterial pDC functions could be impaired during acute allergic conditions.

Virus/allergen interactions and exacerbations of asthma

Clinical research findings indicate that there are synergistic interactions between allergy and viral infection that cause increased severity of asthma exacerbations. This article summarizes the current literature linking these 2 risk factors for asthma exacerbation, and reviews experimental data suggesting potential mechanisms for interactions between viral infection and allergy that cause asthma exacerbations. In addition, the authors discuss clinical evidence that treatment of allergic inflammation could help to reduce the frequency and severity of virus-induced exacerbations of asthma.

Altered cytokine production by dendritic cells from infants with atopic dermatitis

Dendritic cells (DC) are potent initiators of immune responses, compared to other professional antigen-presenting cells, based on their ability to capture antigen, express high amounts of MHC and co-stimulatory molecules, and to secrete immunostimulatory cytokines. Altered functions of DC in atopic individuals have been observed, though it is not clear if this is a cause or a result of the development of allergic disease. In this report we demonstrate altered cytokine production by DC isolated from infants with atopic dermatitis but without a diagnosis of asthma, compared to infants with non-atopic dermatitis. Increased production of IL-6, IL-10 and IFNα from DC isolated from atopic infants is less apparent when DC from infants were examined 1 year later. An increase in the same cytokines was observed in neonatal mice that are genetically predisposed towards allergic inflammation. These results suggest that an atopic environment promotes altered cytokine production by DC from infants.

Role of viral respiratory infections in asthma and asthma exacerbations

Viral respiratory tract infections are common and usually selflimited illnesses. For patients at risk of asthma, or with existing asthma, viral respiratory tract infections can have a profound effect on the expression of disease or loss of control. New evidence has shown that wheezing episodes early in life due to human rhinoviruses are a major risk factor for the later diagnosis of asthma at age 6 years. For those with existing asthma, exacerbations are a major cause of morbidity, can need acute care, and can, albeit rarely, result in death. Viral respiratory tract infections, predominantly those caused by human rhinoviruses, are associated with asthma exacerbations. There is also evidence that deficiencies in antiviral activity and the integrity of the airway epithelial barrier could make individuals with asthma more likely to have severe viral respiratory infections of the lower airway, and thus increase the risk of exacerbation. In view of the effect of respiratory viruses on many aspects of asthma, efforts to understand the mechanisms and risk factors by which these airway infections cause changes in airway pathophysiology are a first step towards improved treatment.

The ABCs of rhinoviruses, wheezing, and asthma

Human rhinoviruses (HRVs) were discovered as common cold pathogens over 50 years ago. Recent advances in molecular viral diagnostics have led to an appreciation of their role in more-significant respiratory illnesses, including bronchiolitis in infancy, childhood pneumonia, and acute exacerbations of chronic respiratory diseases such as asthma, chronic obstructive lung disease, and cystic fibrosis. Until a few years ago, only two groups of HRVs (A and B) had been recognized. However, full and partial sequencing of HRVs led to the discovery of a third species of HRV (HRV-C) that has distinct structural and biologic features. Risk factors and pathogenic mechanisms for more-severe HRV infections are being defined, and yet fundamental questions persist about mechanisms relating this common pathogen to allergic diseases and asthma. The close relationship between HRV infections and asthma suggests that antiviral treatments could have a major impact on the morbidity associated with this chronic respiratory disease.

Dangerous allergens: innate immunity, dendritic cells and allergic asthma

Immune responses can be compartmentalized into innate versus adaptive components. This relatively recent dichotomy positioned the innate immune system at the interface between the host and the external environment, and provided a new conceptual framework with which to view allergic diseases, including asthma. Among the cells of the innate immune system, antigen-presenting dendritic cells are now thought to be intimately involved in allergen recognition, as well as modulating allergic immune responses. This review summarizes current thinking regarding the role of dendritic cells in allergic asthma and concludes with a summary of emerging concepts in the field.

Subcutaneous allergen immunotherapy restores human dendritic cell innate immune function

BACKGROUND

We recently reported that human blood dendritic cells from allergic subjects have impaired IFN-alpha production following toll-like receptor 9 (TLR9)-dependent innate immune stimulation. It is not known how subcutaneous allergen immunotherapy (SCIT) affects dendritic cell immune responses.

OBJECTIVE

The aim of this study is to determine how SCIT affects human dendritic cell function.

METHODS

Peripheral blood mononuclear cell (PBMC) and plasmacytoid dendritic cells (pDCs) were isolated from the blood of seven dust mite allergic subjects at baseline and upon reaching a standard SCIT maintenance dose that included dust mite and other aeroallergens. Cells were stimulated with various adaptive and innate immune receptor stimuli, or media alone for 20 h with secreted cytokine levels determined by ELISA. A portion of the cells were used to measure intracellular signalling proteins by flow cytometry. Humoral immune responses were measured from plasma.

RESULTS

SCIT resulted in a threefold increase in PBMC production of IFN-alpha in response to CpG at 100 nM (P=0.015) and at 500 nM (P=0.015), n=7. The predominant cell type known to produce IFN-alpha in response to CpG (CpG ODN-2216) and other TLR9 agonists is the pDC. As expected, a robust innate immune response from isolated pDCs was re-established among allergic subjects undergoing SCIT resulting in a fivefold increase in IFN-alpha production in response to CpG at 500 nM (P=0.046), n=7. In contrast, IL-6 production was unaffected by SCIT (P=0.468). Consistent with published reports, IgG4 blocking antibody increased 10-fold with SCIT (P=0.031), n=7. There was no significant increase in the frequency of pDCs or the expression of TLR9 that would account for the rise in IFN-alpha production.

CONCLUSIONS

Allergen immunotherapy increases dendritic cell TLR9-mediated innate immune function, which has previously been shown to be impaired at baseline in allergic subjects.

Systematic cytokine receptor profiling reveals GM-CSF as a novel TLR-independent activator of human plasmacytoid predendritic cells

Human plasmacytoid predendritic cells (pDCs) can be activated during microbial infection through Toll-like receptor engagement. They are also involved in nonmicrobial inflammatory diseases, but their activation pathways in this context remain elusive. To identify Toll-like receptor-independent pDC activators, we performed a systematic analysis of cytokine receptors on primary human pDCs. Six receptors were expressed both at mRNA and protein levels: interleukin-3 receptor (IL-3R), IL-6R, IL-10R, IL-18R, interferon-gamma receptor, and granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor. Only GM-CSF and IL-3 were able to efficiently promote pDC survival and induce their differentiation into dendritic cells. Allogeneic naive CD4 T cells primed with GM-CSF-activated pDCs produced more interferon-gamma and less IL-4 and IL-10 compared with IL-3-activated pDCs, indicating a shift in the Th1/Th2 balance. Our data point at a novel function of GM-CSF, which may serve as a link between a pathologic inflammatory environment, pDC activation, and the modulation of CD4 T-cell responses.

Counterregulation between the FcepsilonRI pathway and antiviral responses in human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play essential roles in directing immune responses. These cells may be particularly important in determining the nature of immune responses to viral infections in patients with allergic asthma as well those with other atopic diseases. The purposes of this study were 1) to compare the functional capacity of pDCs in patients with one type of allergic disorder, allergic asthma, and controls; 2) to determine whether IgE cross-linking affects antiviral responses of influenza-exposed pDCs; and 3) to determine whether evidence of counterregulation of FcepsilonRIalpha and IFN-alpha pathways exists in these cells. pDC function was assessed in a subset of asthma patients and in controls by measuring IFN-alpha production after exposure of purified pDCs to influenza viruses. FcepsilonRIalpha expression on pDCs was determined by flow cytometry in blood samples from patients with allergic asthma and controls. pDCs from patients with asthma secreted significantly less IFN-alpha upon exposure to influenza A (572 versus 2815; p = 0.03), and secretion was inversely correlated with serum IgE levels. Moreover, IgE cross-linking prior to viral challenge resulted in 1) abrogation of the influenza-induced pDC IFN-alpha response; 2) diminished influenza and gardiquimod-induced TLR-7 upregulation in pDCs; and 3) interruption of influenza-induced upregulation of pDC maturation/costimulatory molecules. In addition, exposure to influenza and gardiquimod resulted in upregulation of TLR-7, with concomitant downregulation of FcepsilonRIalpha expression in pDCs. These data suggest that counterregulation of FcepsilonRI and TLR-7 pathways exists in pDCs, and that IgE cross-linking impairs pDC antiviral responses.

Human skin and oral mucosal dendritic cells as 'good guys' and 'bad guys' in allergic immune responses

Recent progress achieved by an impressive number of studies focusing upon the ontogenesis and immunobiology of epidermal Langerhans cells (LCs) and other cutaneous dendritic cell (DC) populations as well as DCs at oral mucosal tissue has profoundly revised our understanding of the role of DCs in different tissues and microenvironments. By sensing their environment for microbial signals or allergens and bridging innate and adaptive immunity in a sophisticated manner, subtypes of DCs play a critical role in the maintenance of the immunological homeostasis in the periphery. Thereby, DCs, located directly at the interface to the environment, fulfil opposing tasks as they are key players in both the control and the generation of allergic inflammation. Furthermore, it is under ongoing debate whether DCs attenuate or aggravate allergic inflammation. As a consequence, accumulated knowledge gained in this field within the last few years has provided an excellent basis for innovative therapeutic opportunities which tend to target specifically the multi-faceted properties of DCs at distinct anatomical sites.

Dendritic cells: bridging innate and adaptive immunity in atopic dermatitis

Much knowledge has been gained about the multifaceted functions of dendritic cells (DCs). The central role of various DC subtypes as bridges between innate and adaptive immunity has become more and more evident. However, a high number of differences exist in the expression of pattern-recognition receptors, the first sensors of the innate immune system, in particular Toll-like receptors (TLRs) by distinct DC subtypes (including myeloid and plasmacytoid DCs), their maturation stage, and tissue distribution, as well as state of health or disease. Furthermore, a plethora of variations in human and murine model systems have to be considered. This review sheds some light on this complex and rapidly growing field. It summarizes the most recent findings and deals with the role of TLR-expressing DCs as promoters of chronic inflammatory immune responses in patients with atopic dermatitis, as well as tolerogenic pathways. Therefore TLR-bearing DCs represent promising targets, which might help to improve tolerance induction during immunotherapeutic approaches in the future.

Pulmonary allergic responses augment interleukin-13 secretion by circulating basophils yet suppress interferon-alpha from plasmacytoid dendritic cells

BACKGROUND

Allergic inflammatory processes may have the capacity to propagate systemically through the actions of circulating leucocytes. Consequently, basophils from allergic individuals are often 'primed', as evidenced by their hyperresponsiveness in vitro. IFN-alpha secreted predominantly by plasmacytoid dendritic cells (pDCs), suppresses basophil priming for IL-13 production in vitro.

OBJECTIVE

This study sought in vivo correlates arising during experimental allergen challenge that support an 'axis-interplay' between basophils and pDCs.

METHODS

Using segmental allergen challenge (SAC) in the lung, the immune responses of both cell types from the blood were investigated in volunteers (n=10) before and 24 h after allergen exposure. These responses were then correlated with inflammatory parameters measured in bronchoalveolar lavage fluids (BALF).

RESULTS

In the blood, SAC significantly augmented IL-13 secretion by basophils induced by IL-3 (P=0.009), yet reduced IFN-alpha secreted by pDCs stimulated with CpG (P=0.018). Both parameters were negatively correlated (P=0.0015), at least among those subjects that secreted the latter. Circulating basophil IL-13 responses further correlated with post-SAC bronchoalveolar lavage (BAL) parameters including IL-13 protein (P=0.04), basophil (P=0.051), eosinophil (P=0.0018), and total cell counts (P<0.003). Basophil and IL-13 levels in BAL correlated likewise (P=0.0002).

CONCLUSIONS

These results support a mechanism of immune regulation whereby an allergen reduces innate immune responses and IFN-alpha production by pDCs, resulting in an enhanced inflammation and basophil cytokine production at sites of allergen exposure.

Decreases in human dendritic cell-dependent T(H)2-like responses after acute in vivo IgE neutralization

BACKGROUND

Dendritic cells (DCs) and other professional antigen-presenting cells express a variant of the high-affinity IgE receptor known as alphagamma(2), which, on the basis of in vitro findings, has long been implicated to function in facilitating allergen uptake and presentation to T(H) cells.

OBJECTIVES

To use omalizumab as an in vivo tool to neutralize IgE binding to circulating dendritic cells and to assess whether this results in altered DC-dependent T-cell responsiveness to allergen ex vivo.

METHODS

Subjects with cat allergy were enrolled in a 3.5-month, double blind, randomized (3.5:1), placebo-controlled trial of omalizumab using standard dosing for allergic asthma. Blood plasmacytoid and myeloid DCs were assessed at baseline and posttreatment for expression of surface IgE, FcepsilonRIalpha, and induction of CD4(+)T-cell proliferation and cytokine responses to cat allergen.

RESULTS

IgE expression on plasmacytoid and myeloid DCs from omalizumab-treated subjects (n = 12) decreased by > or =95% posttreatment (P = .0005), whereas FcepsilonRIalpha expression decreased by 66% and 48%, respectively (P = .0005). Cat allergen-induced proliferation in DC/T-cell cocultures observed at baseline was suppressed approximately 20% to 40% postomalizumab treatment (P = .001). Multiplexing for cytokines in plasmacytoid DC/T-cell cocultures also showed decreases in IL-5, IL-13, and IL-10 (P < .05), whereas IL-2 and IFN-gamma were unaltered or slightly increased. These changes were not evident in placebo-control subjects (n = 4).

CONCLUSION

IgE likely facilitates allergen presentation by dendritic cells in vivo and is also important in regulating DC-dependent T-cell cytokines during effector phases of allergic disease.

Antigen aggregation decides the fate of the allergic immune response

Previously, defined naturally occurring isoforms of allergenic proteins were classified as hypoallergens and therefore suggested as an agent for immunotherapy in the future. In this paper, we report for the first time the molecular background of hypoallergenicity by comparing the immunological behavior of hyperallergenic Betula verrucosa major Ag 1a (Bet v 1a) and hypoallergenic Bet v 1d, two isoforms of the major birch pollen allergen Betula verrucosa 1. Despite their cross-reactivity, Bet v 1a and Bet v 1d differ in their capacity to induce protective Ab responses in BALB/c mice. Both isoforms induced similar specific IgE levels, but only Bet v 1d expressed relevant titers of serum IgGs and IgAs. Interestingly, hypoallergenic Bet v 1d activated dendritic cells more efficiently, followed by the production of increased amounts of Th1- as well as Th2-type cytokines. Surprisingly, compared with Bet v 1a, Bet v 1d-immunized mice showed a decreased proliferation of regulatory T cells. Crystallographic studies and dynamic light scattering revealed that Bet v 1d demonstrated a high tendency to form disulfide-linked aggregates due to a serine to cysteine exchange at residue 113. We conclude that aggregation of Bet v 1d triggers the establishment of a protective Ab titer and supports a rationale for Bet v 1d being a promising candidate for specific immunotherapy of birch pollen allergy.

Allergic skin diseases

The skin is one of the largest immunologic organs and is affected by both external and internal factors, as well as innate and adaptive immune responses. Many skin disorders, such as atopic dermatitis, contact dermatitis, urticaria, angioedema, psoriasis, and autoimmune blistering disorders, are immune mediated. Most of these diseases are chronic, inflammatory, and proliferative, in which both genetic and environmental factors play important roles. These immunologic mechanisms might have implications for potential targets of future therapeutic interventions.

Early-life environment, developmental immunotoxicology, and the risk of pediatric allergic disease including asthma

Incidence of childhood allergic disease including asthma (AD-A) has risen since the mid-20th century with much of the increase linked to changes in environment affecting the immune system. Childhood allergy is an early life disease where predisposing environmental exposures, sensitization, and onset of symptoms all occur before adulthood. Predisposition toward allergic disease (AD) is among the constellation of adverse outcomes following developmental immunotoxicity (DIT; problematic exposure of the developing immune system to xenobiotics and physical environmental factors). Because novel immune maturation events occur in early life, and the pregnancy state itself imposes certain restrictions on immune functional development, the period from mid-gestation until 2 years after birth is one of particular concern relative to DIT and AD-A. Several prenatal-perinatal risk factors have been identified as contributing to a DIT-mediated immune dysfunction and increased risk of AD. These include maternal smoking, environmental tobacco smoke, diesel exhaust and traffic-related particles, heavy metals, antibiotics, environmental estrogens and other endocrine disruptors, and alcohol. Diet and microbial exposure also significantly influence immune maturation and risk of allergy. This review considers (1) the critical developmental windows of vulnerability for the immune system that appear to be targets for risk of AD, (2) a model in which the immune system of the DIT-affected infant exhibits immune dysfunction skewed toward AD, and (3) the lack of allergy-relevant safety testing of drugs and chemicals that could identify DIT hazards and minimize problematic exposure of pregnant women and children.

Aberrant function of peripheral blood myeloid and plasmacytoid dendritic cells in atopic dermatitis patients

BACKGROUND

Dendritic cells (DCs) can act both as innate cells in host defense and as antigen-presenting cells for naive T cells in adaptive immunity. These functions, among others, are determined by the level of production of particular cytokines. Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by an initial phase predominated by T(H)2 cytokines that switches into a second, more chronic T(H)1-dominated eczematous phase.

OBJECTIVE

To assess to what extent the AD phenotype is associated with an aberrant phenotype and function of DCs.

METHODS

Classic CD1c(+)/blood DC antigen (BDCA)-1(+) myeloid (m) DCs and CD304(+)/BDCA4(+) plasmacytoid (p) DCs, the natural IFN-producing cells, were isolated from peripheral blood of patients with AD and healthy controls and analyzed for their phenotype and function.

RESULTS

Purified CD1c(+)/BDCA1(+) mDCs from patients with AD showed a selective and dramatic reduction of IL-12p70 and TNF-alpha release. IL-12p70 reduction was attributed to a defective expression of both IL-12p35 and IL-12p40 subunits. Accordingly, mature CD1c(+)/BDCA1(+) mDCs from patients with AD induced considerably less IFN-gamma-producing and more IL-4-producing T(H) cells compared with mDCs from healthy controls. In addition, CD304(+)/BDCA4(+) pDCs from patients with AD produced significantly lower levels of IFN-alpha compared with healthy controls.

CONCLUSION

Myeloid DCs and pDCs from patients with AD show defective IL-12, TNF-alpha, and IFN-alpha production, which may contribute to increased susceptibility to infection and to the maintenance of the T(H)2 cell-mediated allergic state in patients with AD.

Interferons modulate Fc epsilon RI-dependent production of autoregulatory IL-10 by circulating human monocytoid dendritic cells

BACKGROUND

Immature human blood monocytoid dendritic cells (mDCs) express high-affinity receptors for IgE (Fc epsilon RI), yet their exact function and regulation remain poorly understood.

OBJECTIVE

We sought to characterize Fc epsilon RI-dependent cytokine responses and their regulation in circulating human blood mDCs.

METHODS

Fc epsilon RI-dependent cytokine responses of circulating mDCs were studied by using anti-Fc epsilon RI alpha stimulation. Plasmacytoid dendritic cell (pDC) cross-regulation through Toll-like receptor 9 on these responses was investigated by examining the effects of exogenous IFN-alpha pretreatment and by coculturing pDCs and mDCs stimulated with CpG. Culture supernatants were analyzed by means of ELISA to determine cytokine levels. Cell markers were determined by means of flow cytometry.

RESULTS

mDCs express marked levels of Fc epsilon RI (net mean fluorescence intensity, 196 +/- 49; n = 4). After Fc epsilon RI-dependent activation in mDCs, TNF-alpha (2189 +/- 864 pg/10(6) mDCs, n = 3) levels were upregulated within 4 hours, whereas IL-10 (112 +/- 47 pg/10(6) mDCs, n = 3) levels were detectable only after 24 hours of incubation. After adding IL-10-neutralizing antibody, TNF-alpha Fc epsilon RI-dependent responses were significantly augmented (3903 +/- 197 pg/10(6) mDCs, P < .01, n = 3). Conversely, recombinant IL-10 dose-dependently inhibited Fc epsilon RI-mediated TNF-alpha responses up to 86% +/- 3% (n = 3, P < .001). Pretreatment of mDCs with IFN-alpha (100 U/mL) enhanced Fc epsilon RI-dependent secretion of IL-10 by 3.2-fold (183 +/- 11 pg/10(6) mDCs, n = 4) compared with that seen in untreated cells (57 +/- 33 pg/10(6) mDCs, P < .001, n = 4). In pDC/mDC cocultures pretreated with CpG, Fc epsilon RI-dependent IL-10 secretion by mDCs was similarly augmented by 3-fold.

CONCLUSIONS

Autocrine secretion of IL-10, a critical autoregulator of Fc epsilon RI-dependent proinflammatory responses in mDCs, is cross-regulated by IFN-alpha, a major product of Toll-like receptor 9 responses in pDCs that normally promotes T(H)1 immunity.