A complex role for complement in allergic asthma

Dysregulation of complement system and CD4+ T cell activation pathways implicated in allergic response

Allergy is a complex disease that is likely to involve dysregulated CD4+ T cell activation. Here we propose a novel methodology to gain insight into how coordinated behaviour emerges between disease-dysregulated pathways in response to pathophysiological stimuli. Using peripheral blood mononuclear cells of allergic rhinitis patients and controls cultured with and without pollen allergens, we integrate CD4+ T cell gene expression from microarray data and genetic markers of allergic sensitisation from GWAS data at the pathway level using enrichment analysis; implicating the complement system in both cellular and systemic response to pollen allergens. We delineate a novel disease network linking T cell activation to the complement system that is significantly enriched for genes exhibiting correlated gene expression and protein-protein interactions, suggesting a tight biological coordination that is dysregulated in the disease state in response to pollen allergen but not to diluent. This novel disease network has high predictive power for the gene and protein expression of the Th2 cytokine profile (IL-4, IL-5, IL-10, IL-13) and of the Th2 master regulator (GATA3), suggesting its involvement in the early stages of CD4+ T cell differentiation. Dissection of the complement system gene expression identifies 7 genes specifically associated with atopic response to pollen, including C1QR1, CFD, CFP, ITGB2, ITGAX and confirms the role of C3AR1 and C5AR1. Two of these genes (ITGB2 and C3AR1) are also implicated in the network linking complement system to T cell activation, which comprises 6 differentially expressed genes. C3AR1 is also significantly associated with allergic sensitisation in GWAS data.

Breathing exercises for adults with asthma

BACKGROUND

Breathing exercises have been widely used worldwide as a complementary therapy to the pharmacological treatment of people with asthma.

OBJECTIVES

To evaluate the evidence for the efficacy of breathing exercises in the management of patients with asthma.

SEARCH METHODS

The search for trials led review authors to review the literature available in The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL and AMED and to perform handsearching of respiratory journals and meeting abstracts. Trial registers and reference lists of included articles were also consulted.The literature search has been updated to January 2013.

SELECTION CRITERIA

We included randomised controlled trials of breathing exercises in adults with asthma compared with a control group receiving asthma education or, alternatively, with no active control group.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. RevMan software was used for data analysis based on the fixed-effect model. Continuous outcomes were expressed as mean differences (MDs) with confidence intervals (CIs) of 95%. Heterogeneity was assessed by inspecting the forest plots. The Chi(2) test was applied, with a P value of 0.10 indicating statistical significance. The I(2) statistic was implemented, with a value greater than 50% representing a substantial level of heterogeneity.

MAIN RESULTS

A total of 13 studies involving 906 participants are included in the review. The trials were different from one another in terms of type of breathing exercise performed, number of participants enrolled, number and duration of sessions completed, outcomes reported and statistical presentation of data. Asthma severity in participants from the included studies ranged from mild to moderate, and the samples consisted solely of outpatients. The following outcomes were measured: quality of life, asthma symptoms, number of acute exacerbations and lung function. Eleven studies compared breathing exercise with inactive control, and two with asthma education control groups. All eight studies that assessed quality of life reported an improvement in this outcome. An improvement in the number of acute exacerbations was observed by the only study that assessed this outcome. Six of seven included studies showed significant differences favouring breathing exercises for asthma symptoms. Effects on lung function were more variable, with no difference reported in five of the eleven studies that assessed this outcome, while the other six showed a significant difference for this outcome, which favoured breathing exercises. As a result of substantial heterogeneity among the studies, meta-analysis was possible only for asthma symptoms and changes in the Asthma Quality of Life Questionnaire (AQLQ). Each meta-analysis included only two studies and showed a significant difference favouring breathing exercises (MD -3.22, 95% CI -6.31 to -0.13 for asthma symptoms; MD 0.79, 95% CI 0.50 to 1.08 for change in AQLQ). Assessment of risk of bias was impaired by incomplete reporting of methodological aspects of most of the included trials.

AUTHORS' CONCLUSIONS

Even though individual trials reported positive effects of breathing exercises, no reliable conclusions could be drawn concerning the use of breathing exercises for asthma in clinical practice. This was a result of methodological differences among the included studies and poor reporting of methodological aspects in most of the included studies. However, trends for improvement are encouraging, and further studies including full descriptions of treatment methods and outcome measurements are required.

Inspiratory muscle training for asthma

BACKGROUND

In some people with asthma, expiratory airflow limitation, premature closure of small airways, activity of inspiratory muscles at the end of expiration and reduced pulmonary compliance may lead to lung hyperinflation. With the increase in lung volume, chest wall geometry is modified, shortening the inspiratory muscles and leaving them at a sub-optimal position in their length-tension relationship. Thus, the capacity of these muscles to generate tension is reduced. An increase in cross-sectional area of the inspiratory muscles caused by hypertrophy could offset the functional weakening induced by hyperinflation. Previous studies have shown that inspiratory muscle training promotes diaphragm hypertrophy in healthy people and patients with chronic heart failure, and increases the proportion of type I fibres and the size of type II fibres of the external intercostal muscles in patients with chronic obstructive pulmonary disease. However, its effects on clinical outcomes in patients with asthma are unclear.

OBJECTIVES

To evaluate the efficacy of inspiratory muscle training with either an external resistive device or threshold loading in people with asthma.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register of trials, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov and reference lists of included studies. The latest search was performed in November 2012.

SELECTION CRITERIA

We included randomised controlled trials that involved the use of an external inspiratory muscle training device versus a control (sham or no inspiratory training device) in people with stable asthma.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We included five studies involving 113 adults. Participants in four studies had mild to moderate asthma and the fifth study included participants independent of their asthma severity. There were substantial differences between the studies, including the training protocol, duration of training sessions (10 to 30 minutes) and duration of the intervention (3 to 25 weeks). Three clinical trials were produced by the same research group. Risk of bias in the included studies was difficult to ascertain accurately due to poor reporting of methods.The included studies showed a statistically significant increase in inspiratory muscle strength, measured by maximal inspiratory pressure (PImax) (mean difference (MD) 13.34 cmH2O, 95% CI 4.70 to 21.98, 4 studies, 84 participants, low quality evidence). Our other primary outcome, exacerbations requiring a course of oral or inhaled corticosteroids or emergency department visits, was not reported. For the secondary outcomes, results from one trial showed no statistically significant difference between the inspiratory muscle training group and the control group for maximal expiratory pressure, peak expiratory flow rate, forced expiratory volume in one second, forced vital capacity, sensation of dyspnoea and use of beta2-agonist. There were no studies describing inspiratory muscle endurance, hospital admissions or days off work or school.

AUTHORS' CONCLUSIONS

There is no conclusive evidence in this review to support or refute inspiratory muscle training for asthma. The evidence was limited by the small number of trials with few participants together with the risk of bias. More well conducted randomised controlled trials are needed. Future trials should investigate the following outcomes: lung function, exacerbation rate, asthma symptoms, hospital admissions, use of medications and days off work or school. Inspiratory muscle training should also be assessed in people with more severe asthma and conducted in children with asthma.

Clinical presentation, pathogenesis, diagnosis, and treatment of epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease. The pathogenic relevance of autoantibodies targeting type VII collagen (COL7) has been well-documented. Therefore, EBA is a prototypical autoimmune disease with a well-characterized pathogenic relevance of autoantibody binding to the target antigen. EBA is a rare disease with an incidence of 0.2 new cases per million and per year. The current treatment of EBA relies on general immunosuppressive therapy, which does not lead to remission in all cases. Therefore, there is a high, so far unmet medical need for the development of novel therapeutic options. During the last 10 years, several novel in vitro and in vivo models of EBA have been established. These models demonstrated a critical role of the genetic background, T cells, and cytokines for mediating the loss of tolerance towards COL7. Neutrophils, complement activation, Fc gamma receptor engagement, cytokines, several molecules involved in cell signaling, release of reactive oxygen species, and matrix metalloproteinases are crucial for autoantibody-induced tissue injury in EBA. Based on this growing understanding of the diseases' pathogenesis, several potential novel therapeutic targets have emerged. In this review, the clinical presentation, pathogenesis, diagnosis, and current treatment options for EBA are discussed in detail.

C5a receptor signalling in dendritic cells controls the development of maladaptive Th2 and Th17 immunity in experimental allergic asthma

The pathways underlying dendritic cell (DC) activation in allergic asthma are incompletely understood. Here we demonstrate that adoptive transfer of ovalbumin-pulsed wild-type (wt) but not of C5a receptor-deficient (C5aR⁻/⁻) bone marrow (BM)-derived DCs (BMDCs) induced mixed T helper type 2 (Th2)/Th17 maladaptive immunity, associated with severe airway hyperresponsiveness, mucus production, and mixed eosinophilic/neutrophilic inflammation. Mechanistically, antigen uptake, processing, and CD11b expression were reduced in C5aR⁻/⁻ BMDCs. Further, interleukin (IL)-1β, -6, and -23 production were impaired resulting in reduced Th17 cell differentiation, associated with accelerated activated T-cell death in vitro and in vivo. Surprisingly, we found an increased frequency of CD11b(hi)CD11c(int)Gr1⁺F4/80⁺ cells, expressing arginase and nitric oxide synthase in C5aR⁻/⁻ BM preparations. Intratracheal administration of ovalbumin-pulsed wt DCs and sorted CD11b(hi)CD11c(int)Gr1⁺F4/80⁺ C5aR⁻/⁻ cells reduced Th2 immune responses in vivo. Together, we uncover novel roles for C5aR in Th17 differentiation, T-cell survival, and differentiation of a DC-suppressor population controlling Th2 immunity in experimental allergic asthma.

Complement in immune and inflammatory disorders: pathophysiological mechanisms

Although acute or chronic inflammation is a common component of many clinical disorders, the underlying processes can be highly distinct. In recent years, the complement system has been associated with a growing number of immunological and inflammatory conditions that include degenerative diseases, cancer, and transplant rejection. It becomes evident that excessive activation or insufficient control of complement activation on host cells can cause an immune imbalance that may fuel a vicious cycle between complement, inflammatory cells, and tissue damage that exacerbates clinical complications. Although the exact involvement of complement needs to be carefully investigated for each disease, therapeutic modulation of complement activity emerges as an attractive target for upstream inhibition of inflammatory processes. This review provides an update about the functional and collaborative capabilities of complement, highlights major disease areas with known complement contribution, and indicates the potential for complement as a focal point in immunomodulatory strategies for treating inflammatory diseases.

Complement component 3C3 and C3a receptor are required in chitin-dependent allergic sensitization to Aspergillus fumigatus but dispensable in chitin-induced innate allergic inflammation

Levels of the anaphylatoxin C3a are increased in patients with asthma compared with those in nonasthmatics and increase further still during asthma exacerbations. However, the role of C3a during sensitization to allergen is poorly understood. Sensitization to fungal allergens, such as Aspergillus fumigatus, is a strong risk factor for the development of asthma. Exposure to chitin, a structural polysaccharide of the fungal cell wall, induces innate allergic inflammation and may promote sensitization to fungal allergens. Here, we found that coincubation of chitin with serum or intratracheal administration of chitin in mice resulted in the generation of C3a. We established a model of chitin-dependent sensitization to soluble Aspergillus antigens to test the contribution of complement to these events. C3^−/− and C3aR^−/− mice were protected from chitin-dependent sensitization to Aspergillus and had reduced lung eosinophilia and type 2 cytokines and serum IgE. In contrast, complement-deficient mice were not protected against chitin-induced innate allergic inflammation. In sensitized mice, plasmacytoid dendritic cells from complement-deficient animals acquired a tolerogenic profile associated with enhanced regulatory T cell responses and suppressed Th2 and Th17 responses specific for Aspergillus. Thus, chitin induces the generation of C3a in the lung, and chitin-dependent allergic sensitization to Aspergillus requires C3aR signaling, which suppresses regulatory dendritic cells and T cells and induces allergy-promoting T cells.

Asthma is one of the fastest growing chronic illnesses worldwide. Chitin, a ubiquitous polymer in our environment and a key component in the cell wall of fungal spores and the exoskeletons of insects, parasites, and crustaceans, triggers innate allergic inflammation. However, there is little understanding of how chitin is initially recognized by mammals and how early recognition of chitin affects sensitization to environmental allergens and development of allergic asthma. The complement system is evolutionarily one of the oldest facets of the early or innate warning systems in mammals. We studied whether and how complement components influence the recognition of chitin and shape the downstream sensitization toward fungal allergens. We show here that complement recognition of chitin plays a critical role in shaping the behavior of dendritic cells, which in turn regulate the function of T cells that mediate allergic responses to fungi.

impact of aluminum exposure on the immune system: a mini review

Aluminum (Al) is widely used in daily life and will lead to environmental release and exposure. The toxicity of Al had been documented, and which attracted a growing concern on human and animal health. The immune system appears to be sensitive to Al exposure. But few studies focused on the potential immunological responses induced by Al. It is imperative to study the effects of Al on the immune function and this review discusses the effects of Al on autoimmunity, oral tolerance, expression of the immune cells, hypersensitivity and erythrocyte immune function. It will provide evidence to study the association between Al and immune function.

Lipopolysaccharide inhibits Th2 lung inflammation induced by house dust mite allergens in mice

The complex biology of asthma compels the use of more relevant human allergens, such as house dust mite (HDM), to improve the translation of animal models into human asthma. LPS exposure is associated with aggravations of asthma, but the mechanisms remain unclear. Here, we studied the effects of increasing LPS doses on HDM-evoked allergic lung inflammation. To this end, mice were intranasally sensitized and challenged with HDM with or without increasing doses of LPS (0.001-10 μg). LPS dose-dependently inhibited HDM-induced eosinophil recruitment into the lungs and mucus production in the airways. LPS attenuated the production of Th2 cytokines (IL-4, IL-5, IL-10, and IL-13) in HDM-challenged lungs, while enhancing the HDM-induced release of IL-17, IL-33, IFN-γ, and TNF-α. The shift toward a Th1 inflammatory response was further illustrated by predominant neutrophilic lung inflammation after LPS administration at higher doses. LPS did not influence HDM-induced plasma IgE concentrations. Although LPS did not significantly affect the activation of coagulation or complement in HDM-challenged lungs, it reduced HDM-initiated endothelial cell activation. This study is the first to provide insights into the effects of LPS in an allergic lung inflammation model making use of a clinically relevant allergen without a systemic adjuvant, revealing that LPS dose-dependently inhibits HDM-induced pulmonary Th2 responses.

A new role of the complement system: C3 provides protection in a mouse model of lung infection with intracellular Chlamydia psittaci

The complement system modulates the intensity of innate and specific immunity. While it protects against infections by extracellular bacteria its role in infection with obligate intracellular bacteria, such as the avian and human pathogen Chlamydia (C.) psittaci, is still unknown. In the present study, knockout mice lacking C3 and thus all main complement effector functions were intranasally infected with C. psittaci strain DC15. Clinical parameters, lung histology, and cytokine levels were determined. A subset of infections was additionally performed with mice lacking C5 or C5a receptors. Complement activation occurred before symptoms of pneumonia appeared. Mice lacking C3 were ∼100 times more susceptible to the intracellular bacteria compared to wild-type mice, with all C3^−/− mice succumbing to infection after day 9. At a low infective dose, C3^−/− mice became severely ill after an even longer delay, the kinetics suggesting a so far unknown link of complement to the adaptive, protective immune response against chlamydiae. The lethal phenotype of C3^−/− mice is not based on differences in the anti-chlamydial IgG response (which is slightly delayed) as demonstrated by serum transfer experiments. In addition, during the first week of infection, the absence of C3 was associated with partial protection characterized by reduced weight loss, better clinical score and lower bacterial burden, which might be explained by a different mechanism. Lack of complement functions downstream of C5 had little effect. This study demonstrates for the first time a strong and complex influence of complement effector functions, downstream of C3 and upstream of C5, on the outcome of an infection with intracellular bacteria, such as C. psittaci.

Functional defects of CD46-induced regulatory T cells to suppress airway inflammation in mite allergic asthma

Defective recruitment of regulatory T cells (Treg) function to the airway is important in the pathogenesis of allergic asthma. Complement regulatory protein (CD46) is a newly defined costimulatory molecule for Treg activation, which together with IL-10/granzyme B production may aid in suppressing asthmatic inflammation. This study examines chemotaxis and adhesion molecule expression on CD3/CD46-activated CD4(+) T cells (Tregs) from patients with and without asthma to suppress mite allergen-induced respiratory epithelial cells inflammation and to elucidate the mechanism of CD46-mediated Treg activation. Diminished IL-10/granzyme B and CCR4 expression from CD3/CD46-activated Tregs appeared in asthmatic subjects. CD3/CD46-activated Tregs from asthma patients co-cultured with BEAS-2B cells suppressed Dermatophagoides pteronyssinus 2 induced nuclear factor-κB/p65 by cell contact inhibition. Decreased interaction of CD3/CD46-mediated Tregs and BEAS-2B cells from asthmatics was associated with downregulated phosphorylation of protein kinase B (AKT) expression. Results provide the first evidence that decreased interaction between CD46-mediated Tregs and lung epithelial cells with less IL-10/granzyme B production may cause airway inflammation in allergic asthma.

Eculizumab for treatment of asthma

INTRODUCTION

Asthma is an inflammatory disease, which can be exacerbated by stimuli such as viral infections and exposure to allergens. Asthma continues to be a profound public health problem due to asthma exacerbation in a low proportion of patients in need of more effective medications.

AREAS COVERED

The C5 complement pathway has been proposed as a new target for the treatment of asthma, supported by clinical observations of increased C5a levels in asthmatic airways, constitutive expression of C5 receptors on bronchial epithelium and smooth muscle cells, and preclinical studies in mice demonstrating inhibition of C5 cleavage reduced established airway inflammation and improves lung function. Eculizumab is a monoclonal antibody, which binds to the complement protein C5, thereby preventing the formation of C5a and C5b-9. The research discussed in this review describes development of eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria and the efficacy of eculizumab on allergen-induced asthmatic responses in a placebo-controlled study.

EXPERT OPINION

In an allergen-challenge model of asthma, there was a significant period effect with eculizumab, with inhibition of the late asthmatic response in subjects who received placebo treatment first. Although this study provides some evidence that eculizumab may be effective to attenuate allergen-induced responses, the role of C5 in asthma remains to be clarified.

Sasa quelpaertensis phenylpropanoid derivative suppresses lipopolysaccharide-induced nitric oxide synthase and cyclo-oxygenase-2 expressions in RAW 264.7 cells

3-O-p-Coumaroyl-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-O-β-D-gulcopyranosylpropanol (ESQ10) is a naturally occurring phenylpropanoid derivative isolated from Sasa quelpaertensis (Gramineae). In the present study, we discovered that ESQ10 inhibits nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. ESQ10 attenuated LPS-induced synthesis of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in parallel and inhibited LPS-induced interleukin-6 production, as determined by an enzyme-linked immunosorbent assay in the macrophages. The mechanism of the antiinflammatory action of ESQ10, i.e., suppression of nuclear factor (NF)-κB and mitogen-activated protein kinase activation, has been documented. However, ESQ10 could not influence LPS-mediated IκB-α degradation and extracellular signal-regulated kinase/c-Jun amino-terminal kinase phosphorylation at concentrations of up to 373 µM. To test the potential application of ESQ10 as a topical material, we also conducted a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay on human HaCaT keratinocytes as well as human dermal fibroblast cells. In this assay, ESQ10 did not induce cytotoxicity. Taken together, the results suggest that ESQ10 may be considered an antiinflammatory candidate for treating inflammatory and skin diseases.

Induced sputum proteome in healthy subjects and asthmatic patients

BACKGROUND

Asthma is a heterogeneous disease characterized by abnormal airway pathophysiology and susceptibility to different stimuli, as exemplified by a subset of patients with exercise-induced bronchoconstriction. Induced sputum provides a noninvasive method to sample airway biofluids that are enriched in proteins.

OBJECTIVE

We hypothesized that novel mechanisms in the pathogenesis of asthma might be revealed by studying the patterns of protein expression in induced sputum.

METHODS

We used shotgun proteomics to analyze induced sputum from 5 healthy subjects and 10 asthmatic patients, including 5 with exercise-induced bronchoconstriction. Differential protein expression among asthmatic patients, asthma subphenotypes, and control subjects was determined by using spectral counting and computational methods.

RESULTS

Using Gene Ontology analysis, we defined the functional landscape of the induced sputum proteome and applied network analysis to construct a protein interaction map for this airway compartment. Shotgun proteomics analysis identified a number of proteins the differential enrichment or depletion of which robustly distinguished asthmatic patients from healthy control subjects and captured the effects of exercise on induced sputum proteome. Functional and network analysis identified key processes, including proteolytic activity, that are known contributors to airway remodeling. Importantly, this approach highlighted previously unrecognized roles for differentially expressed proteins in pathways implicated in asthma, such as modulation of phospholipase A(2) by secretoglobin, a putative role for S100A8/9 in human asthma, and selective upregulation of complement component 3a in response to exercise in asthmatic patients.

CONCLUSION

Computationally intensive analysis of induced sputum proteome is a powerful approach to understanding the pathophysiology of asthma and a promising methodology to investigating other diseases of the airways.

The role of complement in the diagnosis and management of allergic rhinitis and allergic asthma

Allergic rhinitis and asthma are common chronic inflammatory diseases of the nasal mucus membranes and the upper airways with a high prevalence in Western countries. In addition to maladaptive T-helper type 2 (Th2) immunity, Th17 cells can drive the inflammatory responses in both diseases. Several reports have shown that the complement system is activated locally and systemically in allergic rhinitis and/or allergic asthma patients. Importantly, recent findings in experimental models of allergic rhinitis and allergic asthma suggest that the complement cleavage products complement 3a and complement 5a and the activation of their corresponding receptors in antigen-presenting cells regulate the development of maladaptive Th2 and Th17 immunity. These findings in experimental asthma are corroborated by genome-wide searches and candidate gene studies in humans. We discuss recent findings in experimental and human allergic airway diseases suggesting that complement may serve as a new diagnostic and therapeutic target for both disorders.

Effects of aluminum exposure on the allergic responses and humoral immune function in rats

This study was conducted to assess effects of aluminum (Al) exposure on allergic responsive reactions and humoral immune function in rats. Forty male Wistar rats (5 weeks old) weighed 110-120 g were randomly allocated into four groups and were orally exposed to 0, 64.18, 128.36, and 256.72 mg/kg body weight aluminum trichloride in drinking water for 120 days. The levels of immunoglobulin (Ig) G, IgA, IgM, IgE, Complement factor (C)3, and C4 in serum were determined by ELISA and nephelometric assays at the end of experiment. The results showed that the levels of IgM, C3, and C4 were lowered, and the levels of IgG, IgA, and IgE were increased in an Al-dose dependent manner. The increased in IgE level and the decreased in C3 and C4 levels indicate that Al induces allergic responses in rats; while the increased levels in IgG and IgA and the decreased level in IgM suggest that Al disorders the humoral immune function in rats.

Complement: a key system for immune surveillance and homeostasis

Nearly a century after the significance of the human complement system was recognized, we have come to realize that its functions extend far beyond the elimination of microbes. Complement acts as a rapid and efficient immune surveillance system that has distinct effects on healthy and altered host cells and foreign intruders. By eliminating cellular debris and infectious microbes, orchestrating immune responses and sending 'danger' signals, complement contributes substantially to homeostasis, but it can also take action against healthy cells if not properly controlled. This review describes our updated view of the function, structure and dynamics of the complement network, highlights its interconnection with immunity at large and with other endogenous pathways, and illustrates its multiple roles in homeostasis and disease.