Regulation of immunologic homeostasis in peripheral tissues by dendritic cells: the respiratory tract as a paradigm

The Common Mucosal System Fifty Years on: From Cell Traffic in the Rabbit to Immune Resilience to SARS-CoV-2 Infection by Shifting Risk within Normal and Disease Populations

The idea of a common mucosal immune system (CMS) is 50 years old. Its relevance to immune protection at mucosal sites and its potential to modulate the impact of vaccination-induced protection against infection of the airway has been poorly understood. The consequent failure of the current SARS-CoV-2 vaccination to satisfy expectations with respect to prevention of infection, viral transmission, duration of protection, and pattern of clinical protection, led to public health and medical decisions now under review. This review summarises knowledge of the CMS in man, including the powerful role it plays in immune protection and lessons with respect to what can and cannot be achieved by systemic and mucosal vaccination for the prevention of airway infection. The powerful impact in both health and disease of optimising delivery of immune protection using selected isolates from the respiratory microbiome is demonstrated through a review of randomised controlled trials (RCTs) in subjects with chronic airway disease, and in otherwise healthy individuals with risk factors, in whom the idea of mucosal immune resilience is introduced. This review is dedicated to two giants of mucosal immunology: Professors John Bienenstock and Allan Cripps. Their recent deaths are keenly felt by their colleagues and students.

Th2A cells: The pathogenic players in allergic diseases

Proallergic type 2 helper T (Th2A) cells are a subset of memory Th2 cells confined to atopic individuals, and they include all the allergen-specific Th2 cells. Recently, many studies have shown that Th2A cells characterized by CD3+ CD4+ HPGDS+ CRTH2+ CD161high ST2high CD49dhigh CD27low play a crucial role in allergic diseases, such as atopic dermatitis (AD), food allergy (FA), allergic rhinitis (AR), asthma, and eosinophilic esophagitis (EoE). In this review, we summarize the discovery, biomarkers, and biological properties of Th2A cells to gain new insights into the pathogenesis of allergic diseases.

Involvement of the Innate Immune System in the Pathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common, socially significant disease characterized by progressive airflow limitation due to chronic inflammation in the bronchi. Although the causes of COPD are considered to be known, the pathogenesis of the disease continues to be a relevant topic of study. Mechanisms of the innate immune system are involved in various links in the pathogenesis of COPD, leading to persistence of chronic inflammation in the bronchi, their bacterial colonization and disruption of lung structure and function. Bronchial epithelial cells, neutrophils, macrophages and other cells are involved in the development and progression of the disease, demonstrating multiple compromised immune mechanisms.

Murine Intraepithelial Dendritic Cells Interact With Phagocytic Cells During Aspergillus fumigatus-Induced Inflammation

People are constantly exposed to airborne fungal spores, including Aspergillus fumigatus conidia that can cause life-threatening conditions in immunocompromised patients or acute exacerbations in allergics. However, immunocompetent hosts do not exhibit mycoses or systemic inflammation, due to the sufficient but not excessive antifungal immune response that prevent fungal invasion. Intraepithelial dendritic cells (IE-DCs) of the conducting airway mucosa are located in the primary site of the inhalant pathogen entry; these cells can sense A. fumigatus conidia and maintain homeostasis. The mechanisms by which IE-DCs contribute to regulating the antifungal immune response and controlling conidia dissemination are not understood. To clarify the role of IE-DCs in the balance between pathogen sensing and immune tolerance we investigated the A. fumigatus conidia distribution in optically cleared mouse lungs and estimated the kinetics of the local phagocytic response during the course of inflammation. MHCII⁺ antigen-presenting cells, including IE-DCs, and CD11b⁺ phagocytes were identified by immunohistochemistry and three-dimensional fluorescence confocal laser-scanning microscopy of conducting airway whole-mounts. Application of A. fumigatus conidia increased the number of CD11b⁺ phagocytes in the conducting airway mucosa and induced the trafficking of these cells through the conducting airway wall to the luminal side of the epithelium. Some CD11b⁺ phagocytes internalized conidia in the conducting airway lumen. During the migration through the airway wall, CD11b⁺ phagocytes formed clusters. Permanently located in the airway wall IE-DCs contacted both single CD11b⁺ phagocytes and clusters. Based on the spatiotemporal characteristics of the interactions between IE-DCs and CD11b⁺ phagocytes, we provide a novel anatomical rationale for the contribution of IE-DCs to controlling the excessive phagocyte-mediated immune response rather than participating in pathogen uptake.

Expression of Langerin/CD207 in airways, lung and associated lymph nodes of a stranded striped dolphin (Stenella coeruleoalba)

The airways and lungs of vertebrates are an entrance way for several microbial pathogens. Cetaceans present an upper and lower respiratory anatomy that allows the rapid flow of large air volumes, which may lead to high susceptibility to respiratory infections. Mortality and stranding rate of Cetaceans increased dramatically, so wide the knowledge about the immune system and specific antibodies identifying immune cells populations, is of fundamental importance to monitor and document cetacean health. The aim of this study was to identify the localization of dendritic cells marked by Langerin/CD207 in airways, lungs and associated lymph nodes, of the striped dolphin Stenella coeruleoalba. Samples of trachea, bronchi, lungs and lung-associated lymph nodes were obtained from a stranded adult male of Stenella coeruleoalba. Our results showed abundant lymphoid aggregates (LAs) in the lung of S. ceruleoalba. Langerhans-like dendritic cells were well distributed along the epithelium and interstitium of respiratory tract and in associated lymph nodes. The present study deepens the knowledge about the cetacean's immune system and report about the exploitability of a commercial antibody (Langerin/CD207) for cetacean species.

Morphological characteristic and functional dependencies of dendritic cell in developing rabbit lung during fetal and neonatal life

Recently, pulmonary DC deserved the attention of researchers and clinicians as it was implicated in many diseases afflicting human lungs. However, there are no available data about the morphological or functional features of pulmonary dendritic cells in fetal or early neonatal life. The present study aimed to demonstrate the morphological development of DCs using light-, electron-microscopy, and immunohistochemistry. DCs showed strong immunoreactivity for both CD8 and CD56. Moreover, DCs strongly expressed CD34, VEGF, NSE, and connexin-43 within the developing pulmonary tissue. By SEM, DCs were polyhedral in shape with short cell processes in fetal life. By the advancement of the age, DCs became more numerous and exhibited rounded to oval cell bodies with many fine dendrites. TEM revealed that at early fetal life, DCs were characterized by their heterochromatic indented nuclei, few cell processes and few organelles. With the advancement of age, DCs showed dendrite-like processes and displayed signs of high endocytic activities with releasing of secretory materials. At late fetal life, DCs showed an obvious increase in the nuclear/cytoplasmic ratio and they exhibited a unique connection with type II pneumocytes and pulmonary endothelium by gap junction. In the early neonate, the DCs cells were seen in association with T-lymphocytes, neutrophils, telocytes (TCs), and air-blood barrier. They possessed many fine dendrites, the characteristic Birbeck granules and many vesicles. DCs may contribute to apoptosis, endocytosis, and angiogenesis. The difference in the maturation status may reflect different roles for DCs in the lung. The immature DCs may have an antigen-uptake role through endocytosis, while mature DCs may involve in antigen presentation to T-cells.

Immunological Processes Driving IgE Sensitisation and Disease Development in Males and Females

IgE sensitisation has increased significantly over the last decades and is a crucial factor in the development of allergic diseases. IgE antibodies are produced by B cells through the process of antigen presentation by dendritic cells, subsequent differentiation of CD4⁺ Th2 cells, and class switching in B cells. However, many of the factors regulating these processes remain unclear. These processes affect males and females differently, resulting in a significantly higher prevalence of IgE sensitisation in males compared to females from an early age. Before the onset of puberty, this increased prevalence of IgE sensitisation is also associated with a higher prevalence of clinical symptoms in males; however, after puberty, females experience a surge in the incidence of allergic symptoms. This is particularly apparent in allergic asthma, but also in other allergic diseases such as food and contact allergies. This has been partly attributed to the pro- versus anti-allergic effects of female versus male sex hormones; however, it remains unclear how the expression of sex hormones translates IgE sensitisation into clinical symptoms. In this review, we describe the recent epidemiological findings on IgE sensitisation in male and females and discuss recent mechanistic studies casting further light on how the expression of sex hormones may influence the innate and adaptive immune system at mucosal surfaces and how sex hormones may be involved in translating IgE sensitisation into clinical manifestations.

Functional differences in airway dendritic cells determine susceptibility to IgE-sensitization

Respiratory IgE-sensitization to innocuous antigens increases the risk for developing diseases such as allergic asthma. Dendritic cells (DC) residing in the airways orchestrate the immune response following antigen exposure and their ability to sample and present antigens to naïve T cells in airway draining lymph nodes contributes to allergen-specific IgE-sensitization. In order to characterize inhaled antigen capture and presentation by DC subtypes in vivo, we used an adjuvant-free respiratory sensitization model using two genetically distinct rat strains, one of which is naturally resistant and the other naturally susceptible to allergic sensitization. Upon multiple exposures to ovalbumin (OVA), the susceptible strain developed OVA-specific IgE and airway inflammation, whereas the resistant strain did not. Using fluorescently tagged OVA and flow cytometry, we demonstrated significant differences in antigen uptake efficiency and presentation associated with either IgE-sensitization or resistance to allergen exposures in respective strains. We further identified CD4⁺ conventional DC (cDC) as the subset involved in airway antigen sampling in both strains, however, CD4⁺ cDC in the susceptible strain were less efficient in OVA sampling and displayed increased MHC-II expression compared with the resistant strain. This was associated with generation of an exaggerated Th2 response and a deficiency of airway regulatory T cells in the susceptible strain. These data suggest that subsets of cDC are able to induce either sensitization or resistance to inhaled antigens as determined by genetic background, which may provide an underlying basis for genetically determined susceptibility to respiratory allergic sensitization and IgE production in susceptible individuals.

Dendritic Cells and Monocytes with Distinct Inflammatory Responses Reside in Lung Mucosa of Healthy Humans

Every breath we take contains potentially harmful pathogens or allergens. Dendritic cells (DCs), monocytes, and macrophages are essential in maintaining a delicate balance of initiating immunity without causing collateral damage to the lungs because of an exaggerated inflammatory response. To document the diversity of lung mononuclear phagocytes at steady-state, we performed bronchoscopies on 20 healthy subjects, sampling the proximal and distal airways (bronchial wash and bronchoalveolar lavage, respectively), as well as mucosal tissue (endobronchial biopsies). In addition to a substantial population of alveolar macrophages, we identified subpopulations of monocytes, myeloid DCs (MDCs), and plasmacytoid DCs in the lung mucosa. Intermediate monocytes and MDCs were highly frequent in the airways compared with peripheral blood. Strikingly, the density of mononuclear phagocytes increased upon descending the airways. Monocytes from blood and airways produced 10-fold more proinflammatory cytokines than MDCs upon ex vivo stimulation. However, airway monocytes were less inflammatory than blood monocytes, suggesting a more tolerant nature. The findings of this study establish how to identify human lung mononuclear phagocytes and how they function in normal conditions, so that dysregulations in patients with respiratory diseases can be detected to elucidate their contribution to immunity or pathogenesis.

Comparison of gene expression of Toll-like receptors and antimicrobial peptides in immune organs and tissues between Yorkshire and Tibetan pigs

Toll-like receptors (TLRs), an important family of pattern-recognition receptors, and antimicrobial peptides (AMPs) contribute to the first line of innate protection of mammals against microbes. To compare characteristics of innate immunity between Tibetan and Yorkshire pigs, we investigated the mRNA abundance of TLR genes (TLR1-TLR9) and two AMP-encoding genes (PBD-1 and PR-39) in thymus, spleen, blood, palatine tonsils, and mesenteric and pulmonary hilar lymph nodes of the two breeds at ages of 6, 12 and 24 weeks using quantitative real-time PCR. Results showed that all mRNAs were detected in all tissues. Transcript levels of the major TLR genes of Tibetan pigs were significantly higher than those of Yorkshires in most tissues of the immune system, with a higher abundance of porcine (PBD-1) (beta-defensin-1) and PR-39 mRNA in lymphoid organs and tissues, especially blood, palatine tonsils, and mesenteric and pulmonary hilar lymph nodes. Our data suggest that Tibetan pigs have stronger innate immunity for triggering local and/or systemic immune responses to eliminate infections with pathogenic microorganisms.

Airway inflammation in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is an inflammatory airway disease whose incidence and mortality increases every year. It is associated with an abnormal inflammatory response of the lung to toxic particles or gases (usually cigarette smoke). A central role in the pathophysiology has been shown to play a chronic inflammation of the airways that is expressed primarily by hypersecretion of mucus, stenosis of the smaller airways and the establishment of pulmonary emphysema. There is an increasing trend for assessing the inflammatory pattern of inflammatory airway diseases through mediators measured by noninvasive techniques. Markers in biological fluids and exhaled air have been the subject of intense evaluation over the past few years, with some of them reaching their introduction into clinical practice, while others remain as research tools. Of particular interest for the scientific community is the discovery of clinically exploitable biomarkers associated with specific phenotypes of the disease. Studying the effects of therapeutic interventions in these biomarkers may lead to targeted therapy based on phenotype and this is perhaps the future of therapeutics in COPD.

Intranasal inoculation of white-tailed deer (Odocoileus virginianus) with lyophilized chronic wasting disease prion particulate complexed to montmorillonite clay

Chronic wasting disease (CWD), the only known prion disease endemic in wildlife, is a persistent problem in both wild and captive North American cervid populations. This disease continues to spread and cases are found in new areas each year. Indirect transmission can occur via the environment and is thought to occur by the oral and/or intranasal route. Oral transmission has been experimentally demonstrated and although intranasal transmission has been postulated, it has not been tested in a natural host until recently. Prions have been shown to adsorb strongly to clay particles and upon oral inoculation the prion/clay combination exhibits increased infectivity in rodent models. Deer and elk undoubtedly and chronically inhale dust particles routinely while living in the landscape while foraging and rutting. We therefore hypothesized that dust represents a viable vehicle for intranasal CWD prion exposure. To test this hypothesis, CWD-positive brain homogenate was mixed with montmorillonite clay (Mte), lyophilized, pulverized and inoculated intranasally into white-tailed deer once a week for 6 weeks. Deer were euthanized at 95, 105, 120 and 175 days post final inoculation and tissues examined for CWD-associated prion proteins by immunohistochemistry. Our results demonstrate that CWD can be efficiently transmitted utilizing Mte particles as a prion carrier and intranasal exposure.

Aeroallergen challenge promotes dendritic cell proliferation in the airways

Aeroallergen provocation induces the rapid accumulation of CD11c(+)MHC class II (MHC II)(+) dendritic cells (DCs) in the lungs, which is driven by an increased recruitment of blood-derived DC precursors. Recent data show, however, that well-differentiated DCs proliferate in situ in various tissues. This may also contribute to their allergen-induced expansion; therefore, we studied DC proliferation in the airways of mice in the steady state and after local aeroallergen provocation. Confocal whole-mount microscopy was used to visualize proliferating DCs in different microanatomical compartments of the lung. We demonstrate that in the steady state, CD11c(+)MHC II(+) DCs proliferate in both the epithelial and subepithelial layers of the airway mucosa as well as in the lung parenchyma. A 1-h pulse of the nucleotide 5-ethynyl-2'-deoxyuridine was sufficient to label 5% of DCs in both layers of the airway mucosa. On the level of whole-lung tissue, 3-5% of both CD11b(+) and CD11b(-) DC populations and 0.3% of CD11c(+)MHC II(low) lung macrophages incorporated 5-ethynyl-2'-deoxyuridine. Aeroallergen provocation caused a 3-fold increase in the frequency of locally proliferating DCs in the airway mucosa. This increase in mucosal DC proliferation was later followed by an elevation in the number of DCs. The recruitment of monocyte-derived inflammatory DCs contributed to the increasing number of DCs in the lung parenchyma, but not in the airway mucosa. We conclude that local proliferation significantly contributes to airway DC homeostasis in the steady state and that it is the major mechanism underlying the expansion of the mucosal epithelial/subepithelial DC network in allergic inflammation.

Pathogenesis of indirect (secondary) acute lung injury

At present, therapeutic interventions to treat acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) remain largely limited to lung-protective strategies, as no real molecular-pathophysiologic-driven therapeutic intervention has yet become available. This is in part the result of the heterogeneous nature of the etiological processes that contribute to the state of ALI/ARDS. This article sets out to understand the development of ALI resulting from indirect pulmonary insults, such as extrapulmonary sepsis and trauma, shock, burn injury or mass transfusion, as opposed to direct pulmonary challenges, such as pneumonia, aspiration or lung contusion. Here, we consider not only the experimental and clinical data concerning the roles of various immune (neutrophil, macrophage, lymphocyte and dendritic) as well as nonimmune (epithelial and endothelial) cells in orchestrating the development of ALI resulting from indirect pulmonary stimuli, but also how these cell populations might be targeted therapeutically.

Pulmonary dendritic cells in lungs of preterm infants: neglected participants in bronchopulmonary dysplasia?

Preterm infants are at risk for bronchopulmonary dysplasia (BPD), a chronic lung disease characterized by disrupted alveolar remodeling and microvascular dysangiogenesis. The pathogenesis of BPD is multifactorial, with contributions from antenatal and/or postnatal infection and inflammation. The potential role of dendritic cells, critical immune regulatory cells with potent angiogenic activities, remains undetermined. We studied the prevalence and topography of dendritic cells in postmortem lungs of short- and long-term ventilated preterm infants born between 23 and 29 weeks in gestation. Controls were age-matched infants who had lived less than 12 hours. Dendritic cells were identified by anti-DC-SIGN immunohistochemistry and were co-localized with endothelial and smooth muscle cells by double immunofluorescence. Lungs of early and late control infants without evidence of antenatal infection contained scattered DC-SIGN-positive dendritic cells in the peripheral lung parenchyma. Lungs of early control infants with a history of chorioamnionitis/antenatal infection and lungs of short- or long-term ventilated preterm infants showed a dramatic (more than 3-fold) increase in dendritic cells. Double labeling highlighted a close association between dendritic cells and small- or medium-sized pulmonary vessels. In conclusion, we demonstrated that dendritic cells are an integral component of normal postcanalicular lung development. Antenatal infection and ventilation/BPD are associated with significant pulmonary recruitment of dendritic cells. The recently described angiogenic effects of dendritic cells and their intimate association with the pulmonary microvasculature indicate that dendritic cells may participate in BPD-associated dysangiogenesis. Elucidation of the role of this immunovascular axis may lead to novel therapeutic approaches to BPD.

Expression of C-type lectin, SIGNR3, on subsets of dendritic cells, macrophages, and monocytes

The C-type lectin SIGNR3 is a mouse homologue of human DC-SIGN, which shares carbohydrate-binding specificity with human DC-SIGN. However, the expression profile of SIGNR3 is largely unknown. To examine the expression of SIGNR3 in immune cells, we generated SIGNR3-specific mAb and investigated SIGNR3 expression in vivo. SIGNR3 was expressed on a fraction of MHC II(+) DCs and Mϕs in the dermis and CD115(+)Ly6C(int-low) monocytes in the blood and BM. In the LNs, SIGNR3(+) cells localized adjacent to PNAd(+) HEV-like vessels. They were also found in interfollicular regions in sLNs but not mLNs. Those SIGNR3(+) cells expressed CD11b and variable levels of CD11c and MHC II. As in LNs, SIGNR3 was expressed on a large proportion of the CD11b(+)CD11c(int-high) cells in the spleen. In the lung, SIGNR3(+) cells belonged to the CD11b(+)CD11c(int) population, and Mϕs in the airway and lung faintly expressed SIGNR3. When PKH67-labeled CD115(+)Ly6C(high) BM monocytes were transferred into normal recipients, they up-regulated SIGNR3 expression along with the decrease in Ly6C expression during the circulation and upon arrival at the peripheral LNs through HEV. In addition, CD11b(high)Ly6C(high) monocytes that entered sLNs differentiated into CD11b(+) DCs in a couple of days, whereas those in the spleen, mLNs, and lung differentiated into CD11c(int) monocytic cells. These results suggest that SIGNR3 is a new differentiation marker for myeloid mononuclear cells and indicate that some DCs, especially in the sLNs, are possibly replenished by Ly6C(high) monocytes.

Type-I IFN signaling suppresses an excessive IFN-gamma response and thus prevents lung damage and chronic inflammation during Pneumocystis (PC) clearance in CD4 T cell-competent mice

Immune-reconstitution after highly active antiretroviral therapy (HAART) is often incomplete, and some HIV-infected individuals fail to regenerate type-I interferon (IFN)-producing pDCs. We recently demonstrated that during Pneumocystis (PC) infection in CD4 T cell-competent mice the absence of type-I IFN signaling results in chronic pulmonary inflammation and fibrosis despite clearance. Because the mechanisms involved are poorly understood, we further characterized the role of type-I IFN signaling in immune responses to PC. We show that type-I IFN signaling around day 7 postinfection is critical to the outcome of inflammation. Microarray analysis of pulmonary CD11c(+) cells revealed that at day 7 post infection, wild-type cells up-regulated type-I IFN-responsive genes as well as SOCS1, which is a critical negative-regulator of type-I IFN and IFN-gamma signaling. This was associated with an eosinophilic lung inflammation, PC clearance, and complete restitution. However, pulmonary CD11c(+) cells from IFNAR(-/-) mice demonstrated increased tumor necrosis factor (TNF)-alpha production and lacked SOCS1-induction at day 7. This was followed by a transient lymphocytic and IFN-gamma response before switching to a chronic eosinophilic inflammation of the lung. Early neutralization of TNF-alpha did not prevent chronic inflammation in IFNAR(-/-) mice, but treatment with an anti-IFN-gamma antibody did. We propose that during PC lung infection type-I IFNs induce SOCS1-associated regulatory mechanisms, which prevent excessive IFN-gamma-mediated responses that cause chronic lung damage. Therefore, partial immune-reconstitution in AIDS, attributable to reduced type-I IFN actions, might disrupt regulatory aspects of inflammation, causing unexplained chronic pulmonary complications as seen in some patients during HAART.

Identification and isolation of rodent respiratory tract dendritic cells

This chapter describes the preparation of respiratory tract tissue from both mice and rats for the isolation of respiratory tract dendritic cells (RTDC). The methods describe in detail the preparation of cells from the respiratory tract tissue of the main conducting airways (representing mucosal populations) and peripheral lung (representing predominantly interstitial populations) in both rodent species. Our research in this area has found that these anatomical sites differ in their composition of antigen-presenting cell (APC) types including RTDC, and that phenotypic and functional differences exist in RTDC isolated from these sites. We predominantly use a flow cytometry-based approach to identify and sort RTDC as this is the most accurate way of isolating RTDC subsets in an environment where many typical dendritic cell surface markers are shared by other APC populations.

Plasmacytoid dendritic cells control lung inflammation and monocyte recruitment in indirect acute lung injury in mice

Indirect acute lung injury (ALI, not caused by a direct insult to the lung) represents the first organ dysfunction in trauma patients, with nonpulmonary sepsis being the most common cause of indirect ALI. Dendritic cells (DCs) are thought to participate in a number of inflammatory lung diseases; however, their role in indirect ALI is currently not established. Using a clinically relevant model of indirect ALI induced in mice by hemorrhagic shock followed 24 hours later by polymicrobial septic challenge, we report that mature DC numbers were markedly increased in the lung during indirect ALI. DC depletion induced a significant increase in indirect ALI severity, which was associated with enhanced lung and plasma proinflammatory cytokine concentration and recruitment of proinflammatory CD115(+) monocytes in response to increased lung monocyte chemotactic protein-1 production. Among the different DC subpopulations, plasmacytoid DCs, which were induced and activated in the lung during indirect ALI, were responsible for this effect because their specific depletion reproduced the observations made in DC-depleted mice. As the recruitment of monocytes to the lung plays a central deleterious role in the pathophysiology of indirect ALI, our data therefore position plasmacytoid DCs as important regulators of acute lung inflammation.

[Dendritic cells in hypertrophied adenoid at children with otitis media with effusion]

INTRODUCTION

The adenoids are organized as lymphoepithelial structures that play an important role in protecting both the upper respiratory and alimentary tract regions. This functions requires dendritic cells (DC) which are one of the major populations of immune cells. Due to the presence of specific receptors (DC) are able to respond to both intra- and extracellular antigens. Dendritic cells activating immunological response in tonsil contribute formation immunologic competent cells on necessity of rolling inflammatory process in middle ear.

AIM OF STUDY

An investigation was executed in hypertrophied adenoids with or without otitis media with effusion.

METHODS

By flow cytometry percentage of CD11c+ myeloid DC and 123+ plasmacytoid DC in hypertrophied adenoid and hypertrophied adenoid and otitis media with effusion was analyzed.

RESULTS

The percentage of CD11c+ myeloid DC and 123+ plasmacytoid DC was similar in hypertrophied adenoid and otitis media with effusion compored to the control group.

CONCLUSIONS

Our data show that part of dendritic cells has not on course of inflammatory process influence rolling in middle ear.

The role of dendritic cells and regulatory T cells in the regulation of allergic asthma

Airways hyperresponsiveness (AHR) is one of the major clinical features of allergic airways disease including allergic asthma, however the immunological mechanisms leading to the induction and regulation of this disorder are not fully understood. In this review we will summarise the evidence of a number of studies, principally in murine models of AHR, suggesting a central role for respiratory tract dendritic cells (RTDC) in the induction of AHR through the generation of lung-homing, allergen-specific effector T cells. We will also summarise the evidence supporting a role for regulatory T cells in the attenuation of AHR and will propose that, as a counterpoint to their capacity to induce AHR, RTDC may also play a role in the attenuation of AHR through the generation of regulatory T cells (T(reg)). A better understanding of the relationship between the physiological and immunological responses to allergen-induced AHR attenuation, and particularly the role of RTDC and T(reg) in this process, will be essential for the development of new treatments and therapies.

Innate immune control and regulation of influenza virus infections

Adaptive immune responses are critical for the control and clearance of influenza A virus (IAV) infection. However, in recent years, it has become increasingly apparent that innate immune cells, including natural killer cells, alveolar macrophages (aMphi), and dendritic cells (DC) are essential following IAV infection in the direct control of viral replication or in the induction and regulation of virus-specific adaptive immune responses. This review will discuss the role of these innate immune cells following IAV infection, with a particular focus on DC and their ability to induce and regulate the adaptive IAV-specific immune response.

Between a cough and a wheeze: dendritic cells at the nexus of tobacco smoke-induced allergic airway sensitization

Exposure to cigarette smoke represents a major risk factor for the development of asthma. Enhanced sensitization toward allergens has been observed in humans and laboratory animals exposed to cigarette smoke. Pulmonary dendritic cells (DCs) are crucially involved in sensitization toward allergens and play an important role in the development of T helper (Th)2-mediated allergic airway inflammation. We propose the concept that aberrant DC activation forms the basis for the deviation of the lung's default tolerogenic response toward allergic inflammation when harmless antigens are concomittantly inhaled with tobacco smoke. This review will summarize evidence suggesting that tobacco smoke can achieve this effect by providing numerous triggers of innate immunity, which can profoundly modulate airway DC biology. Tobacco smoke can affect the airway DC network either directly or indirectly by causing the release of DC-targeted mediators from the pulmonary tissue environment, resulting in the induction of a Th2-oriented pathological immune response. A thorough knowledge of the molecular pathways involved may open the door to novel approaches in the treatment of asthma.

Specific Lactobacillus species differentially activate Toll-like receptors and downstream signals in dendritic cells

BACKGROUND

Dendritic cells (DCs) regulate mucosal T-cell immunity and encounter several distinct bacteria of the gut flora, including lactobacilli. Gram-positive lactobacilli have been suggested to play an important role in exerting adjuvanticity effects on innate immune cells at mucosal sites.

AIMS & METHODS

In the present report, we studied the effects of specific Lactobacillus species on human monocyte derived DCs.

RESULTS

We show that lactobacilli activate DCs by differentially inducing the expression of Toll-like receptors and bioactive IL-12 in Lactobacillus-treated DCs. Further, these specific Lactobacillus spp. did not activate the phosphorylation of p38 MAPK, which might be a downstream effect of the remarkable capacity of lactobacilli to induce IL-12 in DCs that skew T cells significantly toward an IFN-gamma-secreting Th1 response.

CONCLUSION

These results highlight an important role of specific Lactobacillus spp. as adjuvants in triggering DC function, which in turn may determine the immunological outcome in an environment wherein innate cells reside.

Respiratory dendritic cells: mediators of tolerance and immunity

The respiratory tract is under constant bombardment from both innocuous and pathogenic material. The decision of how to respond to these challenges is mediated by a specialized set of antigen presenting cells within the lungs called dendritic cells (DC). Proper respiratory homeostasis requires that these respiratory DC (rDC) utilize both the local lung inflammatory environment as well as recognition of pathogen-specific patterns to determine whether to maintain homeostasis by either driving tolerance or immunity to the inhaled material. This review will focus on rDC and highlight how rDC regulate tolerance and immunity.

Allergic airways disease develops after an increase in allergen capture and processing in the airway mucosa

Airway mucosal dendritic cells (AMDC) and other airway APCs continuously sample inhaled Ags and regulate the nature of any resulting T cell-mediated immune response. Although immunity develops to harmful pathogens, tolerance arises to nonpathogenic Ags in healthy individuals. This homeostasis is thought to be disrupted in allergic respiratory disorders such as allergic asthma, such that a potentially damaging Th2-biased, CD4(+) T cell-mediated inflammatory response develops against intrinsically nonpathogenic allergens. Using a mouse model of experimental allergic airways disease (EAAD), we have investigated the functional changes occurring in AMDC and other airway APC populations during disease onset. Onset of EAAD was characterized by early and transient activation of airway CD4(+) T cells coinciding with up-regulation of CD40 expression exclusively on CD11b(-) AMDC. Concurrent enhanced allergen uptake and processing occurred within all airway APC populations, including B cells, macrophages, and both CD11b(+) and CD11b(-) AMDC subsets. Immune serum transfer into naive animals recapitulated the enhanced allergen uptake observed in airway APC populations and mediated activation of naive allergen-specific, airway CD4(+) T cells following inhaled allergen challenge. These data suggest that the onset of EAAD is initiated by enhanced allergen capture and processing by a number of airway APC populations and that allergen-specific Igs play a role in the conversion of normally quiescent AMDC subsets into those capable of inducing airway CD4(+) T cell activation.

Controls for lung dendritic cell maturation and migration during respiratory viral infection

Dendritic cells are ideally suited to orchestrate the innate and adaptive immune responses to infection, but we know little about how these cells respond to infection with common respiratory viruses. Paramyxoviral infections are the most frequent cause of serious respiratory illness in childhood and are associated with an increased risk of asthma. We therefore used a high-fidelity mouse model of paramyxoviral respiratory infection triggered by Sendai virus to examine the response of conventional and plasmacytoid dendritic cells (cDCs and pDCs, respectively) in the lung. We found that pDCs are scarce at baseline but become the predominant population of lung dendritic cells during infection. This recruitment allows for a source of IFN-alpha locally at the site of infection. In contrast, cDCs rapidly differentiate into myeloid cDCs and begin to migrate from the lung to draining lymph nodes within 2 h after viral inoculation. These events cause the number of lung cDCs to decrease rapidly and remain decreased at the site of viral infection. Maturation and migration of lung cDCs depends on Ccl5 and Ccr5 signals because these events are significantly impaired in Ccl5(-/-) and Ccr5(-/-) mice. cDCs failure to migrate to draining lymph nodes in Ccl5(-/-) or Ccr5(-/-) mice is associated with impaired up-regulation of CCR7 that would normally direct this process. Our results indicate that pDCs and cDCs respond distinctly to respiratory paramyxoviral infection with patterns of movement that should serve to coordinate the innate and adaptive immune responses, respectively.

Spatial interactions between dendritic cells and sensory nerves in allergic airway inflammation

Neuroimmune interactions play a critical role in the pathogenesis of asthma. Symptoms like wheezing and cough have been attributed to neural dysregulation, whereas sensitization and the induction of allergic inflammation have been linked with the activity of dendritic cells. Neuropeptides were previously shown to control dendritic cell function in vitro, suggesting interactions between dendritic cells and sensory nerves. Here we characterized the anatomical basis of the interactions between dendritic cells and nerves in the airways of mice and monitored the changes during allergic inflammation. Airway microdissection, whole-mount immunohistology, and confocal microscopy were used for the three-dimensional quantitative mapping of airway nerves and dendritic cells along the main axial pathway of nonsensitized versus ovalbumin-sensitized and -challenged CD11c-enhanced yellow fluorescent protein (CD11c-EYFP) transgenic mice. CD11c-EYFP-positive airway mucosal dendritic cells were contacted by calcitonin gene-related peptide-immunoreactive sensory fibers and their co-localization increased in allergic inflammation. Moreover, protein gene product 9.5-positive neuroepithelial bodies and airway ganglia were associated with dendritic cells. In human airways, human leukocyte antigen DR-positive mucosal dendritic cells were found in the close proximity of sensory nerves and neuroepithelial cells. These results provide morphologic evidence of the interactions between dendritic cells and the neural network of the airways at multiple anatomical sites.

Mouse respiratory tract dendritic cell subsets and the immunological fate of inhaled antigens

It is widely accepted that tissue dendritic cells (DC) function as immune sentinels by alerting T cells to foreign antigen after delivering and presenting it in the draining lymph nodes. Over the last two decades, studies in animal models, particularly rodents, have demonstrated that respiratory tract DC are crucial for the adaptive immune response to inhaled antigen. Indeed, the fate of inhaled antigen is inextricably linked to the function of respiratory tract DC. In this review, we will discuss the characteristics of respiratory tract DC from mice and recent data that may help to explain their role in the fate of inhaled antigen.

Influence of mucosal adjuvants on antigen passage and CD4+ T cell activation during the primary response to airborne allergen

Ag delivery via the nasal route typically induces tolerance or fails to polarize CD4+ T cell responses unless an adjuvant is provided. To better understand this process, we assessed the effects of two mucosal adjuvants, Escherichia coli LPS and cholera toxin (CT), on Ag passage and T cell activation in the draining lymph nodes (DLN) of BALB/c mice following per nasal administration of the model protein allergen, OVA. We found a range of cell types acquired small amounts of fluorescent OVA in the DLN 4 h after per nasal administration. However, this early uptake was eclipsed by a wave of OVA+CD8alpha(low) dendritic cells that accumulated in the DLN over the next 20 h to become the dominant OVA-processing and -presenting population. Both LPS and CT stimulated increases in CD80 and CD86 expression on OVA+CD8alpha(low) DC. LPS also increased the number of OVA+CD8alpha(low) dendritic cells accumulating in the DLN. When the primary T cell response was examined after adoptive transfer of CD4+ T cells from DO11.10 mice, CT and LPS stimulated surprisingly similar effects on T cell activation and proliferation, IL-4 and IFN-gamma priming, and memory T cell production. Despite these similarities, T cell recipients immunized with CT, but not LPS, developed lung eosinophilia upon secondary OVA challenge. Thus, we found no bias within the DLN in Ag handling or the primary T cell response associated with the eventual Th2 polarization induced by CT, and suggest that additional tissue-specific factors influence the development of allergic disease in the airways.

Lung dendritic cells and the inflammatory response

OBJECTIVE

To discuss the role of conventional and plasmacytoid dendritic cells in inducing and modulating immune responses in the lung.

DATA SOURCES

The primary literature and selected review articles studying the role of dendritic cells in both rodent and human lungs as identified via a PubMed/MEDLINE search using the keywords dendritic cell, antigen-presenting cell, viral airway disease, asthma, allergy, and atopy.

STUDY SELECTION

The author's knowledge of the field was used to identify studies that were relevant to the stated objective.

RESULTS

Dendritic cells are well positioned in the respiratory tract and other mucosal surfaces to respond to any foreign protein. These cells are crucial to the initiation of the adaptive immune response through induction of antigen specific T-cell responses. These cells also play an important role in the regulation of developing and ongoing immune responses, an area that is currently under intense investigation. This review discusses the various subsets of human and rodent dendritic cells and the pathways involved in antigen processing and subsequent immune regulation by dendritic cells in the lung using both viral and nonviral allergenic protein exposure as examples.

CONCLUSIONS

Conventional and plasmacytoid dendritic cells are uniquely situated in the immune cascade to not only initiate but also modulate immune responses. Therapeutic interventions in allergic and asthmatic diseases will likely be developed to take advantage of this exclusive position of the dendritic cell.

CD8 alpha+, but not CD8 alpha-, dendritic cells tolerize Th2 responses via contact-dependent and -independent mechanisms, and reverse airway hyperresponsiveness, Th2, and eosinophil responses in a mouse model of asthma

Splenic CD8alpha+ dendritic cells reportedly tolerize T cell responses by inducing Fas ligand-mediated apoptosis, suppressing IL-2 expression, or catabolizing T cell tryptophan reserves through expression of IDO. We report in this study that CD8alpha+, but not CD8alpha-, dendritic cells purified from the spleens of normal mice can tolerize the Th2 responses of cells from asthma phenotype mice through more than one mechanism. This tolerance could largely be reversed in vitro by anti-IL-10 or anti-TGFbeta Ab treatment. However, loss of direct dendritic cell-T cell contact also reduced tolerance, although to a lesser extent, as did adding the IDO inhibitor 1-methyltryptophan or an excess of free tryptophan to the cultures. Within 3 wk of reconstituting asthma phenotype mice with 1 x 10(5) OVA-pulsed CD8alpha+, but not CD8alpha-, dendritic cells, the mice experienced a reversal of airway hyperresponsiveness, eosinophilic airway responses, and pulmonary Th2 cytokine expression. This data indicates that CD8alpha+ dendritic cells can simultaneously use multiple mechanisms for tolerization of T cells and that, in vivo, they are capable of tolerizing a well-established disease complex such as allergic lung disease/asthma.

Anatomical location determines the distribution and function of dendritic cells and other APCs in the respiratory tract

APCs, including dendritic cells (DC), are central to Ag surveillance in the respiratory tract (RT). Research in this area is dominated by mouse studies on purportedly representative RT-APC populations derived from whole-lung digests, comprising mainly parenchymal tissue. Our recent rat studies identified major functional differences between DC populations from airway mucosal vs parenchymal tissue, thus seriously questioning the validity of this approach. We addressed this issue for the first time in the mouse by separately characterizing RT-APC populations from these two different RT compartments. CD11c(high) myeloid DC (mDC) and B cells were common to both locations, whereas a short-lived CD11c(neg) mDC was unique to airway mucosa and long-lived CD11c(high) macrophage and rapid-turnover multipotential precursor populations were predominantly confined to the lung parenchyma. Airway mucosal mDC were more endocytic and presented peptide to naive CD4+ T cells more efficiently than their lung counterparts. However, mDC from neither site could present whole protein without further maturation in vitro, or following trafficking to lymph nodes in vivo, indicating a novel mechanism whereby RT-DC function is regulated at the level of protein processing but not peptide loading for naive T cell activation.

Functional plasticity of human respiratory tract dendritic cells: GM-CSF enhances T(H)2 development

BACKGROUND

Dendritic cells within the human respiratory mucosa (RTDCs) are proposed to initiate immune responses to foreign antigens. Their capacity to polarize T-cell responses, however, has not been investigated.

OBJECTIVE

To compare RTDCs with peripheral blood dendritic cells (PBDCs) with regard to phenotype, cytokine production, capacity to polarize T-cell responses, and effects of exposure to the pleiotropic cytokine, GM-CSF.

METHODS

CD1a(+) RTDCs and CD1c(+) PBDCs were purified from nasal turbinates of patients with nonatopic rhinitis and peripheral blood of healthy individuals, respectively. In some experiments, matched CD1c(+) RTDCs and PBDCs from patients with rhinitis were compared. The phenotype of DC was examined by flow cytometry and cytokine production by cytometric bead array. DCs were cocultured with allogeneic naive CD4(+) T cells, and cytokine production was determined by immunophenotyping, cytometric bead array, and ELISA.

RESULTS

Both RTDCs and PBDCs exhibited an immature phenotype, but RTDCs expressed lower levels of MHC class II antigen. Cross-linking of CD40 on PBDCs, but not RTDCs, induced production of IL-12p70. In mixed lymphocyte cultures, RTDCs induced a T(H)1/T(H)2 profile, whereas PBDCs induced a T(H)1 profile. Exposure of RTDCs to GM-CSF induced a T(H)2 pattern of response in the mixed lymphocyte cultures. In contrast, exposure of PBDCs to GM-CSF promoted a T(H)1 response.

CONCLUSION

This report emphasizes the importance of studying tissue-derived primary DCs, demonstrates functional plasticity of RTDCs, and implicates GM-CSF in amplifying the potential of RTDCs to initiate T(H)2 responses in the airways.

Asthmatic bronchial epithelium activated by the proteolytic allergen Der p 1 increases selective dendritic cell recruitment

BACKGROUND

Airway dendritic cells (DCs) are crucial for allergen-induced sensitization and inflammation in allergic asthma. After allergen challenge, an increased number of DCs is observed in airway epithelium from patients with allergy.

OBJECTIVE

Because Der p 1, a cysteine protease allergen from Dermatophagoides pteronyssinus , induces chemokine production by bronchial epithelial cells (BECs), the purpose of this investigation was to evaluate the capacity of BEC exposed to Der p 1 to recruit DCs.

METHODS

Chemotactic activity of BEAS-2B, a bronchial epithelial cell line, and BECs from nonatopic controls and patients with allergic asthma was evaluated on the migration of precursors, immature and mature monocyte-derived DCs (MDDCs), and CD34 + -derived Langerhans cells (LCs).

RESULTS

C-C chemokine ligand (CCL)-2, CCL5, and C-X-C chemokine ligand 10 production by BEAS-2B and BEC was increased after Der p 1 exposure, whereas the proenzyme proDer p 1 devoid of enzymatic activity had no effect. Der p 1 stimulation of BEAS-2B and BEC from both groups increased significantly the recruitment of MDDC precursors, depending on CCL2, CCL5, and C-X-C chemokine ligand 10 production. In a reconstituted polarized epithelium, apical application of Der p 1 enhanced MDDC precursor migration into the epithelial layer. Moreover, Der p 1 stimulation of BEC from patients with asthma but not from controls increased the migration of LC precursors, mainly dependent on CCL20 secretion. No migration of immature and mature DCs was observed.

CONCLUSION

These data confirmed that BECs participate in the homeostasis of the DC network present within the bronchial epithelium through the secretion of chemokines. In allergic asthma, upregulation of CCL20 production induced LC recruitment, the role of which remains to be determined.

Differential capacity of CD8+ alpha or CD8- alpha dendritic cell subsets to prime for eosinophilic airway inflammation in the T-helper type 2-prone milieu of the lung

BACKGROUND

Different subsets of dendritic cells (DCs), identified in mouse spleen by their differential expression of CD8 alpha, can induce different T-helper (Th) responses after systemic administration. CD8 alpha(-) DCs have been shown to preferentially induce Th type 2 (Th2) responses whereas CD8 alpha(+) DCs induce Th1 responses.

OBJECTIVE

To study if these DC subsets can still induce different Th responses in the Th2-prone milieu of the lung and differentially prime for eosinophilic airway inflammation, typical of asthma.

METHODS

Donor mice first received daily Flt3L injections to expand DC numbers. Purified CD8 alpha(+) or CD8 alpha(-) splenic DCs were pulsed with ovalbumin (OVA) or phosphate-buffered saline and injected intratracheally into recipient mice in which carboxyfluorescein diacetate succinimidyl ester-labelled OVA-specific T cell receptor transgenic T cells had been injected intravenously 2 days earlier. T cell proliferation and cytokine production of Ag-specific T cells were evaluated in the mediastinal lymph nodes (MLNs) 4 days later. The capacity of both subsets of DCs, to prime for eosinophilic airway inflammation was determined by challenging the mice with OVA aerosol 10 days later.

RESULTS

CD8 alpha(-) DCs migrated to the MLN and induced a vigorous proliferative T cell response accompanied by high-level production of IL-4, IL-5, IL-10 and also IFN-gamma during the primary response and during challenge with aerosol, leading to eosinophilic airway inflammation. In the absence of migration to the MLN, CD8 alpha(+) DCs still induced a proliferative response with identical levels of IFN-gamma but reduced Th2 cytokines compared with CD8 alpha(-) DCs, which led to weak eosinophilic airway inflammation upon OVA aerosol challenge. Unpulsed DCs did not induce proliferation or cytokine production in Ag-specific T cells.

CONCLUSION

CD8 alpha(-) DCs are superior compared with CD8 alpha(+) DCs in inducing Th2 responses and eosinophilic airway inflammation in the Th2-prone environment of the lung.

Dendritic cells and the regulation of the allergic immune response

Studies in mouse models of asthma have revealed a critical role for airway dendritic cells in the induction of Th2 sensitization to inhaled allergens. Under some conditions, subsets of dendritic cells can also induce tolerance or Th1 responses to the same allergens, depending on the context in which the antigen is seen. This article discusses various aspects of DC biology as it relates to allergic sensitization and also provides a summary of the recent evidence that dendritic cells function beyond sensitization.

Mediators of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem that is now a leading cause of death. COPD is associated with a chronic inflammatory response, predominantly in small airways and lung parenchyma, which is characterized by increased numbers of macrophages, neutrophils, and T lymphocytes. The inflammatory mediators involved in COPD have not been clearly defined, in contrast to asthma, but it is now apparent that many lipid mediators, inflammatory peptides, reactive oxygen and nitrogen species, chemokines, cytokines, and growth factors are involved in orchestrating the complex inflammatory process that results in small airway fibrosis and alveolar destruction. Many proteases are also involved in the inflammatory process and are responsible for the destruction of elastin fibers in the lung parenchyma, which is the hallmark of emphysema. The identification of inflammatory mediators and understanding their interactions is important for the development of anti-inflammatory treatments for this important disease.

The role of dendritic cells in asthma

PURPOSE OF REVIEW

The central importance of respiratory tract dendritic cells in the regulation of adaptive immune responses to inhaled antigens is now well established. Dendritic cells are not merely a conduit for the transfer of antigen to regional lymph nodes, but rather function as a sophisticated information transfer system linking the airway micro-environment to the adaptive immune system. Evidence from both animal models and clinical studies points to a critical role for dendritic cells in both allergic sensitization and the pathogenesis of chronic airway inflammation.

RECENT FINDINGS

This article reviews recent information on the distribution and function of dendritic cells in healthy individuals, the responsiveness of these cells to external stimuli, and the factors regulating their activation and turnover within the lung. Animal models of allergic airway inflammation continue to shed new light on the role of lung dendritic cells in T helper 1/T helper 2 switching, and the ability of these cells to direct regulatory T-cell development and immune tolerance. Recent studies have further characterized circulating dendritic cell populations, highlighting important functional differences between dendritic cells from atopic and nonatopic individuals, and have delineated the involvement of these cells in the late phase response to inhaled allergen.

SUMMARY

Because of the immunoregulatory properties of dendritic cells, the future is likely to see a concerted effort to further define the role that these cells play in allergic sensitization, as a basis for the development of new treatments for asthma and other atopic disorders.

Role for cysteinyl leukotrienes in allergen-induced change in circulating dendritic cell number in asthma

BACKGROUND

Dendritic cells are important antigen-presenting cells. After an allergen inhalation, their numbers rapidly decrease in circulation and increase in the airway mucosa.

OBJECTIVE

To investigate whether allergen-induced changes in the number of circulating dendritic cells are mediated by cysteinyl leukotrienes.

METHODS

In a randomized, double-blind, crossover study, we examined the effects of 2 weeks of treatment with pranlukast (a cysteinyl leukotriene 1 [CysLT1] receptor antagonist) 300 mg twice daily and placebo on allergen-induced changes in airway responses and circulating dendritic cells in 15 subjects with mild asthma. We examined by flow cytometry, before and at 3 hours and 24 hours after allergen inhalation, the proportion of myeloid (CD33+) and plasmacytoid (CD123+) dendritic cells (HLA-DR+, CD14-, CD16-) among all peripheral blood mononuclear cells. The fraction of dendritic cells expressing CysLT1 receptor was also determined.

RESULTS

Compared with placebo, pranlukast significantly attenuated both the maximum early (by 55%) and the late (by 39%) asthma responses, the allergen-induced methacholine airway hyperresponsiveness, and the increase in macrophage inflammatory protein 1alpha and 3alpha in induced sputum. A significantly greater proportion of CD33+ cells (55%) expressed CysLT1 receptor compared with CD123+ cells (11%). Consistent with this, pranlukast prevented the allergen-induced decrease in CD33+ dendritic cells at 3 hours postallergen (mean Delta from baseline, +4.4%) compared with placebo (mean Delta, -8.4; P <.05), but not CD123+ cells.

CONCLUSION

Pretreatment with pranlukast attenuated allergen-induced airway responses and the decrease in circulating myeloid dendritic cells, demonstrating a novel role of cysteinyl leukotrienes in dendritic cell trafficking.

Pathophysiology of airflow limitation in chronic obstructive pulmonary disease

The airflow limitation that defines chronic obstructive pulmonary disease (COPD) is the result of a prolonged time constant for lung emptying, caused by increased resistance of the small conducting airways and increased compliance of the lung as a result of emphysematous destruction. These lesions are associated with a chronic innate and adaptive inflammatory immune response of the host to a lifetime exposure to inhaled toxic gases and particles. Processes contributing to obstruction in the small conducting airways include disruption of the epithelial barrier, interference with mucociliary clearance apparatus that results in accumulation of inflammatory mucous exudates in the small airway lumen, infiltration of the airway walls by inflammatory cells, and deposition of connective tissue in the airway wall. This remodelling and repair thickens the airway walls, reduces lumen calibre, and restricts the normal increase in calibre produced by lung inflation. Emphysematous lung destruction is associated with an infiltration of the same type of inflammatory cells found in the airways. The centrilobular pattern of emphysematous destruction is most closely associated with cigarette smoking, and although it is initially focused on respiratory bronchioles, separate lesions coalesce to destroy large volumes of lung tissue. The panacinar pattern of emphysema is characterised by a more even involvement of the acinus and is associated with alpha1 antitrypsin deficiency. The technology needed to diagnose and quantitate the individual small airway and emphysema phenotypes present in people with COPD is being developed, and should prove helpful in the assessment of therapeutic interventions designed to modify the progress of either phenotype.

The human immune response to Mycobacterium tuberculosis in lung and lymph node

A key issue for the study of tuberculosis is to understand why individuals infected with Mycobacterium tuberculosis (Mtb) experience different clinical outcomes. To better understand the dynamics of Mtb infection and immunity, we have previously developed a temporal mathematical model that qualitatively and quantitatively characterizes the cellular and cytokine control network during infection. In this work we extend that model to a two compartmental model to capture the important processes of cellular activation and priming that occur between the lung and the nearest draining lymph node. We are able to reproduce typical disease progression scenarios including primary infection, latency or clearance. Then we use the model to predict key processes determining these different disease trajectories (i.e. identify bifurcation parameters), suggesting directions for further basic science study and potential new treatment strategies.

Intranasal immunization with a colloid-formulated bacterial extract induces an acute inflammatory response in the lungs and elicits specific immune responses

Nonspecific stimulation of lung defenses by repeated oral administration of immunomodulators, such as bacterial extracts, has shown potential for the prevention of respiratory tract infections. Here, we show that intranasal (i.n.) immunization with a bacterial extract formulated as a colloid induces an acute inflammatory response in the lungs characterized by increased production of CCL and CXCL chemokines and a major influx of dendritic cells (DCs) and neutrophils, with a higher proportion of DCs showing an activated phenotype (high CD80/CD86 expression). Cytokine levels measured in bronchoalveolar-lavage samples showed a small increase in the production of tumor necrosis factor alpha and similar levels of the other cytokines measured (interleukin 10 [IL-10], IL-12, and gamma interferon [IFN-gamma]) in immunized mice compared with control mice. However, the recall response of primed animals after antigenic challenge induced increased expression of IL-12 and IFN-gamma mRNAs in lung homogenates. Overall, all these effects were not due to the lipopolysaccharide content in the bacterial extract. Furthermore, we found that three i.n. doses administered 2 to 3 weeks apart were enough to elicit long-lasting specific serum immunoglobulin G (IgG) and secretory IgA antibody responses. Assessment of IgG subclasses showed a balanced pattern of IgG1-IgG2a responses. The serum total IgE concentrations were also elevated in immunized mice 2 weeks after the third dose, but they significantly decreased soon afterwards. Our results suggest that simple formulations of bacterial extracts administered i.n. are highly immunogenic, eliciting local and systemic immune responses, and may serve as the basis for cost-effective immunotherapies for the prevention and treatment of respiratory infections.

Alveolar Macrophages as Orchestrators of COPD

Alveolar macrophages play a critical role in the pathophysiology of COPD and are a major target for future anti-inflammatory therapy. Macrophage numbers are markedly increased in the lung and alveolar space of patients with COPD and are localized to sites of alveolar destruction. The increased numbers of macrophages may result from increased recruitment of blood monocytes, prolonged survival in the lung and to a lesser extent to increased proliferation in the lung. Alveolar macrophages from COPD patients have an increased baseline and stimulated secretion of inflammatory proteins, including certain cytokines, chemokines, reactive oxygen species and elastolytic enzymes, which together could account for all of the pathophysiological features of COPD. Alveolar macrophages form COPD appear to be resistant to the anti-inflammatory effects of corticosteriods and this is linked to reduced activity and expression of histone deacetylase 2, a nuclear enzyme that switches off inflammatory genes activated through the transcription factor nuclear factor-KB. Alternative anti-inflammatory therapies that inhibit macrophages are therefore needed in the future to deal with the chronic inflammation of COPD. These drugs may include resveratrol, theophylline derivatives, MAP kinase inhibitors and phosphodiesterase-4 inhibitors.

Reduced levels of soluble CD14 in atopic children

BACKGROUND

A reduced microbial stimulation has been reported as a reason for the increasing prevalence of atopic diseases in industrialized countries. Antigen-presenting cells (APC), responding to microbial signals by pattern recognition receptors such as CD14, have an important role in the development of the Th1/Th2 balance.

OBJECTIVE

We hypothesized that atopic children have a lower expression of CD14 on monocytes and lower soluble CD14 levels (sCD14).

METHODS

Seventy-six children were followed prospectively from birth and signs of atopic disease were evaluated. The expression of CD14 on monocytes was analysed with flow cytometry at 0, 3, 6, 12 and 18 months. Circulating levels of sCD14 were analysed by ELISA and total IgE was analysed by fluoroenzymo immunoassay at these ages, and in a subgroup, followed up at 7 years.

RESULTS

Levels of sCD14 were reduced at 7 years both in children with a current or a cumulative history of atopy compared to non-atopic children with P=0.002 and 0.001, respectively. Sensitized children with atopic symptoms had lower sCD14 at 3 and 18 months and at 7 years of age than non-atopic non-sensitized children with P=0.023, 0.039 and 0.008, respectively.

CONCLUSION

The lower levels of sCD14 observed in atopic children may be a consequence of an atopic family heredity and/or atopic disease, but it may also reflect a reduced capacity to respond to microbial signals.

Why are dendritic cells important in allergic diseases of the respiratory tract?

Increasing evidence points to the role of antigen-presenting dendritic cells (DC) in regulating adaptive immune responses. DC are especially sensitive to signals derived from microbes, allergens, and the airway tissue microenvironment, can polarize naïve T-cells into either Th1 or Th2 effector cells, and are increasingly recognized as having a central role in the establishment of T-cell memory and tolerance to inhaled antigens. DC form a closely meshed network within the respiratory mucosa and are rapidly recruited from the circulation in response to a variety of proinflammatory stimuli. Studies using animal models have highlighted the role of DC in both initiation and maintenance of allergic airway inflammation. Increased numbers of airway mucosal DC are found in both allergic rhinitis and asthma, and an increasing number of investigators have highlighted important functional differences between DC from atopic and normal individuals. This article reviews recent information on the involvement of DC in the pathogenesis of allergic airway disease and the means by which DC could be exploited as targets for therapy in asthma and allergic rhinitis.