Search

IL-27 is a heterodimeric cytokine composed of the subunits p28 and Epstein-Barr virus induced gene (EBI)-3 and is known for its effects on T-cell function and differentiation. IL-27 signals through the widely expressed IL-27 receptor (IL-27R), composed of the ligand-specific IL-27Rα chain and gp130. Engagement of the IL-27R activates STAT1 signaling, induces the expression of the type 1 helper T-cell (Th1) cytokine, interferon γ, and suppresses the differentiation of Th2 and Th17 cells. This study investigates the role of IL-27 signaling in respiratory syncytial virus (RSV) infection using IL-27Rα–deficient mice (IL-27rKO). Analysis of lungs from RSV-infected IL-27rKO mice showed exacerbation of mucus secretion compared with wild type, as well as enhanced expression of Muc5ac and Gob5 mRNA, markers of goblet cell metaplasia/hyperplasia. When compared with wild-type mice, RSV-challenged IL-27rKO mice had enhanced expression of Th17-associated cytokine IL-17a and an imbalance between Th1 and Th2 cytokine levels. Neutralization of IL-17 in RSV-infected IL-27rKO mice resulted in a significant decrease in the pulmonary mucus response and inhibition of the Th2-associated cytokines. Interestingly, IL-17 blockage led to an increase in the expression of IL-27 subunits p28 and EBI-3 in the lungs and lymph nodes of RSV-infected mice. Thus, IL-27 functions as a regulatory cytokine during RSV pathogenesis by suppressing the development of Th17 cells, but it also appears to be regulated by IL-17 induced by the virus.

During the past decade, extensive research has undeniably improved the formulation and delivery of oral vaccines. Nevertheless, several factors, such as the harsh gastrointestinal environment together with tolerance induction to exogenous antigens, have thus far impeded the optimal effectiveness and clinical application of oral delivery systems. The current study encompasses an initial evaluation of the stability, biocompatibility, and cellular uptake of two promising candidate systems for oral antigen delivery, that is, calcium carbonate- (CP) and mannitol-templated (MP) porous microspheres. Both spray-dried formulations were efficiently internalized by human intestinal epithelial cells (Caco-2 and HT-29) and degraded into phagolysosomal intracellular compartments. In addition, cellular particle uptake and processing significantly up-regulated the expression of (HLA) class-II and costimulatory molecules on intestinal epithelial cells. Even though the high surface-area-to-volume ratio of the microspheres was expected to favor protease access, antigen release was remarkably limited in simulated intestinal fluid and was even absent under gastric conditions. Finally, neither CP nor MP exerted cytotoxicity upon prolonged in vitro incubation with high antigen concentration. Altogether, these data support the potential of CP and MP for oral antigen delivery and motivate the further development of these promising carrier systems in in vivo studies.

Continuously improving the developmental process and the efficacy of oral vaccines is essential in the fight against intestinal pathogens. A promising strategy for vaccination applying safe, biodegradable and non-replicating antigen delivery systems has gained increased interest for eliciting cellular and humoral immune responses. The current study evaluates the potential of β-glucan particles (GP) as an oral antigen delivery system and their adjuvant characteristics. GP are efficiently internalized by human intestinal epithelial cell lines (Caco-2 and HT-29 cells), without exerting negative effects on cell viability. GP triggered the expression of pro-inflammatory cytokines IL-23p19, IL-8 and the β-glucan receptors dectin-1 and TLR2 by activated Caco-2 cells, and CCL20 in HT-29 cells. In contrast, the expression level of TGF-β, an important mediator of oral tolerance, was significantly downregulated in HT-29 cells. Additionally, adoptive transfer experiments showed proliferating ovalbumin (OVA)-specific CD4(+) T cells mainly in the spleens of GP-OVA-fed mice. Furthermore, we detected a significantly increased IL-17 and a trend towards increased IFN-γ production in the spleen of GP-OVA-fed mice upon antigen restimulation. Oral administration of GP-OVA induced increased OVA-specific IgA, secretory-IgA (S-IgA) and secretory component (SC) production in intestinal fluids. Our data show that GP vehicles are able to deliver OVA via an oral route allowing efficient antigen presentation alongside adaptive immune activation, resulting in a Th17-biased response and the production of OVA-specific IgA, secretory-IgA and secretory component antibodies.

Inflammation is a main pathogenetic factor in the development and progression of chronic obstructive pulmonary disease (COPD). Recently, it has become clear that not only the innate, but also the specific immune response plays a role. A striking finding, in particular in lungs of patients with severe COPD, often with a predominant emphysema phenotype, is the presence of B-cell follicles. As seen in other tissues, these follicles are the result of lymphoid neogenesis. The finding of oligoclonality in B-cell follicles in COPD suggests that they play a role in local antigen specific immune responses. To date, it is not known which antigens may be involved; microbial antigens, cigarette smoke-derived antigens and antigens from extracellular matrix breakdown products have been suggested. Consequently, the pathogenetic role of this follicular B-cell response is not yet clear. It might be protective against microbial colonisation and infection of the lower respiratory tract and, therefore, beneficial, or it could be of a more harmful (autoimmune) nature, directed against lung tissue components. It is necessary to determine the specific antigen(s) and to explore the exact role of the COPD related B-cell response in order to include modulation of this response and develop therapeutic options.

Exposure to dogs in early infancy has been shown to reduce the risk of childhood allergic disease development, and dog ownership is associated with a distinct house dust microbial exposure. Here, we demonstrate, using murine models, that exposure of mice to dog-associated house dust protects against ovalbumin or cockroach allergen-mediated airway pathology. Protected animals exhibited significant reduction in the total number of airway T cells, down-regulation of Th2-related airway responses, as well as mucin secretion. Following dog-associated dust exposure, the cecal microbiome of protected animals was extensively restructured with significant enrichment of, amongst others, Lactobacillus johnsonii. Supplementation of wild-type animals with L. johnsonii protected them against both airway allergen challenge or infection with respiratory syncytial virus. L. johnsonii-mediated protection was associated with significant reductions in the total number and proportion of activated CD11c(+)/CD11b(+) and CD11c(+)/CD8(+) cells, as well as significantly reduced airway Th2 cytokine expression. Our results reveal that exposure to dog-associated household dust results in protection against airway allergen challenge and a distinct gastrointestinal microbiome composition. Moreover, the study identifies L. johnsonii as a pivotal species within the gastrointestinal tract capable of influencing adaptive immunity at remote mucosal surfaces in a manner that is protective against a variety of respiratory insults.

Gastro-intestinal infections are still a main cause of enteric diseases and mortality among humans and animals. Oral vaccination is crucial in generating an adequate local mucosal immune response, however the hostile environment of the intestinal tract and oral tolerance remain huge obstacles that inhibit the ability to successfully develop new mucosal vaccines. A promising strategy for vaccination with safe, biodegradable non-replicating antigen delivery systems has gained increased interest for eliciting cellular and humoral immune responses. The current study evaluates the potential of β-glucan (BGP) and calcium carbonate (CaCO3)- and mannitol-templated polyelectrolyte particles as mucosal antigen delivery systems and their adjuvant characteristics. All microparticle types are efficiently internalized by Caco-2 and HT-29 cell lines and in particular the BGP triggered the expression of pro-inflammatory cytokines IL-23p19, IL-8 and beta-glucan receptors in activated Caco-2 cells and CCL20 in HT-29 cells. In contrast, the expression level of TGF-b, an important mediator of the active component of oral tolerance, was significantly downregulated in HT-29 cells. Oral administration of BGP induced intestinal adaptive immune responses characterized by an increased sIgA and secretory component production. Interestingly, adoptive transfer experiments pointed out the proliferation of naive OVA-specific CD4+ OT-II cells and increased IL-17 production in spleens of BGP-fed mice upon antigen restimulation. These results demonstrate that BGP enhances MHC-II-presentation and promotes mucosal immune responses preferably skewed towards an Th17 response and represents a promising strategy for oral vaccination.

The cytosolic RNA helicases melanoma differentiation–associated gene 5 and retinoic acid–inducible gene-I and their adaptor IFN-β promoter stimulator (IPS-1) have been implicated in the recognition of viral RNA and the production of type I IFN. Complementing the endosomal TLR, melanoma differentiation–associated gene 5, and retinoic acid–inducible gene-I provides alternative mechanisms for viral detection in cells with reduced phagocytosis or autophagy. The infection route of respiratory syncytial virus (RSV)—via fusion of virus particles with the cell membrane—points to IPS-1 signaling as the pathway of choice for downstream antiviral responses. In the current study, viral clearance and inflammation resolution were indeed strongly affected by the absence of an initial IPS-1–mediated IFN-β response. Despite the blunted inflammatory response in IPS-1–deficient alveolar epithelial cells, pulmonary macrophages, and CD11b+ dendritic cells (DC), the lungs of RSV-infected IPS-1–knockout mice showed augmented recruitment of inflammatory neutrophils, monocytes, and DC. Interestingly, pulmonary CD103+ DC could functionally compensate for IPS-1 deficiency with the upregulation of certain inflammatory cytokines and chemokines, possibly via TLR3 and TLR7 signaling. The increased inflammation and reduced viral clearance in IPS-1–knockout mice was accompanied by increased T cell activation and IFN-γ production. Experiments with bone marrow chimeras indicated that RSV-induced lung pathology was most severe when IPS-1 expression was lacking in both immune and nonimmune cell populations. Similarly, viral clearance was rescued upon restored IPS-1 signaling in either the nonimmune or the immune compartment. These data support a nonredundant function for IPS-1 in controlling RSV-induced inflammation and viral replication.

Smokers have a twofold increased risk to develop Crohn's disease (CD). However, little is known about the mechanisms through which smoking affects CD pathogenesis. Especially Crohn's ileitis is negatively influenced by smoking. Interestingly, the ileum and, more in particular, the Peyer's patches in the terminal ileum are also the sites where the first CD lesions are found. Several chemokines are implicated in the pathogenesis, among which is the CCL20-CCR6 pathway. Here, we studied the gut-associated lymphoid tissue in C57BL/6 wild-type mice and in CCR6-deficient mice after exposure to air or cigarette smoke for 24 weeks. Apoptotic index of the follicle-associated epithelium overlying the Peyer's patches was evaluated. We found that chronic smoke exposure induced apoptosis in the follicle-associated epithelium. Furthermore, immune cell numbers and differentiation along with chemokine expression were determined in Peyer's patches. Important changes in immune cell composition were observed: total dendritic cells, CD4+ T cells (including regulatory T cells) and CD8+ T cells increased significantly after smoke exposure. The CD11b+ dendritic cell subset almost doubled. Interestingly, these changes were accompanied by an upregulated mRNA expression of the chemokines CCL9 and CCL20. However, no differences in the increase of dendritic cells were observed between wild-type and CCR6-deficient mice. Our results show that cigarette smoke exposure increases apoptosis in the follicle-associated epithelium and is associated with immune cell accumulation in Peyer's patches.

Hyaluronan (HA) is a component of the extracellular matrix and low molecular weight (LMW) HA fragments have pro-inflammatory capacities. Exposing mice to cigarette smoke (CS) for 1 or 6 months results in enhanced deposition of LMW HA in lung parenchyma and airway walls and in altered expression of HA synthases and hyaluronidases (Bracke et al ., Am J Respir Cell Mol Biol. 2010;42(6):753-61). To pinpoint a source of HA, we studied HA-production and expression of HA modulating enzymes in primary murine pulmonary fibroblasts stimulated with cigarette smoke extract (CSE) or TGF-β1. Fibroblasts were isolated from lungs of C57BL/6 mice and cultured in vitro . At passage 6, cells were stimulated for 24h or 48h with control medium, 5% CSE or 2ng/ml TGF-β1. mRNA expression of HA synthases (Has1, Has2, Has3) and hyaluronidases (Hyal1, Hyal2) was evaluated by RT-PCR. HA production was measured in supernatant by ELISA. In vitro stimulation of pulmonary fibroblasts with CSE significantly decreased the mRNA expression of Has1 (synthesizing high molecular weight (HMW) HA) and significantly increased the expression of Hyal2 (degrading HMW HA to LMW HA fragments). Stimulation with TGF-β1 resulted in significantly increased mRNA expression of Has2 (synthesizing HMW HA). Accordingly, HA-levels in the fibroblast supernatant decreased significantly upon 48h stimulation with CSE, while they were significantly increased upon 24h or 48h stimulation with TGF-β1. Decreased Has1 and increased Hyal2 in CSE-stimulated fibroblasts suggests reduced synthesis and enhanced breakdown of HMW HA. This may contribute to the accumulation of LMW HA fragments, observed in CS-exposed mice.

Background: Cigarette smoke (CS) is a major risk factor for the development of COPD. CS exposure is associated with an increased risk of bacterial colonization and respiratory tract infection, because of suppressed antibacterial activities of the immune system and delayed clearance of microbial agents from the lungs. Colonization with Staphylococcus aureus results in release of virulent enterotoxins, with superantigen activity which causes T cell activation. Objective: To study the effect of Staphylococcus aureus enterotoxin B (SEB) on CS-induced inflammation, in a mouse model of COPD. Methods: C57/Bl6 mice were exposed to CS or air for 4 weeks (5 cigarettes/exposure, 4x/day, 5 days/week). Endonasal SEB (10 μg/ml) or saline was concomitantly applied starting from week 3, on alternate days. 24 h after the last CS and SEB exposure, mice were sacrificed and bronchoalveolar lavage (BAL) fluid and lung tissue were collected. Results: Combined exposure to CS and SEB resulted in a raised number of lymphocytes and neutrophils in BAL, as well as increased numbers of CD8 + T lymphocytes and granulocytes in lung tissue, compared to sole CS or SEB exposure. Moreover, concomitant CS/SEB exposure induced both IL-13 mRNA expression in lungs and goblet cell hyperplasia in the airway wall. In addition, combined CS/SEB exposure stimulated the formation of dense, organized aggregates of B- and T- lymphocytes in lungs, as well as significant higher CXCL-13 (protein, mRNA) and CCL19 (mRNA) levels in lungs. Conclusions: Combined CS and SEB exposure aggravates CS-induced inflammation in mice, suggesting that Staphylococcus aureus could influence the pathogenesis of COPD. Background Cigarette smoking is associated with an increased risk of bacterial colonization and respiratory tract infection, because of suppressed antibacterial activities of the immune system and delayed clearance of microbial agents from the lungs [1]. This is particularly relevant in COPD patients, where bacterial colonization in the lower respiratory tract has been shown [2]. These bacteria are implicated both in stable COPD and during exacerbations, where most commonly pneumococci, Haemophilus influenza, Moraxella catarrhalis and Staphylococcus aureus (S. aureus)are found [3]. Interestingly, colonization with S. aureus may embody a major source of superantigens as a set of toxins are being produced including S. aureus enterotoxins (SAEs) [4]. These toxins activate up to 20% of all T cells in the body by binding the human leukocyte antigen (HLA) class II molecules on antigen-presenting cells (APCs) and specific V beta regions of the T cell receptor [5]. Between 50 and 80% of S. aureus isolates are positive for at least one superantigen gene, and close to 50% of

Chronic obstructive pulmonary disease is mainly triggered by cigarette smoke (CS) and progresses even after smoking cessation. CS induces an exaggerated influx of inflammatory cells to the bronchoalveolar space and lung parenchyma, likely resulting from a complex interplay between chemoattractants and their respective receptors. In a murine CS model of chronic obstructive pulmonary disease, we studied the importance of chemokine-like receptor ChemR23 for the induction and resolution of inflammation in CS-exposed lungs. Subacute and chronic CS exposure increased protein levels of the ChemR23 ligand and chemoattractant, chemerin, in bronchoalveolar lavage (BAL) fluid of wild-type (WT) mice. Moreover, the proinflammatory chemokines CXCL1, CCL2, and CCL20 were increased in the airways of CS-exposed WT mice, accompanied by a massive accumulation of inflammatory neutrophils and monocytes, CD11bhiCD103− and CD11bloCD103+ dendritic cells (DCs), and CD4+ and CD8+ T cells. The lung parenchyma of WT mice was infiltrated with inflammatory neutrophils, CD11bhiCD103− DCs, and activated CD4+ T cells after CS exposure. CS-induced inflammation was severely attenuated in BAL fluid and lungs of ChemR23 knockout mice with regard to the induction of inflammatory chemokines and the recruitment of inflammatory cells. Neutrophils and CD8+ T cells persisted in the airways of WT mice, as did the airway-derived conventional DCs in the mediastinal lymph nodes, for at least 14 d after smoking cessation. In the BAL fluid of CS-exposed ChemR23 knockout mice, there was a remarkable delayed accumulation of T cells 14 d after the final exposure. Our data support a role for ChemR23 in directing innate and adaptive immune cells to CS-exposed lungs.

Chronic obstructive pulmonary disease (COPD) is characterized by infiltration of inflammatory cells, destruction of lung parenchyma, and airway wall remodeling. Hyaluronan (HA) is a component of the extracellular matrix, and low-molecular-weight (LMW) HA fragments have proinflammatory capacities. We evaluated the presence of HA in alveolar and airway walls of C57BL/6 mice that were exposed to air or cigarette smoke (CS) for 4 weeks (subacute) or 24 weeks (chronic). We measured deposition of the extracellular matrix proteins collagen and fibronectin in airway walls and determined the molecular weight of HA purified from lung tissue. In addition, we studied the expression of HA-modulating genes by RT-PCR. HA staining in alveolar walls was significantly enhanced upon chronic CS exposure, whereas HA levels in the airway walls were already significantly higher upon subacute CS exposure and remained elevated upon chronic CS exposure. This differed from the deposition of collagen and fibronectin, which are only elevated at the chronic time point. In lungs of CS-exposed mice, the molecular weight of HA clearly shifted toward more LMW HA fragments. CS exposure significantly increased the mRNA expression of the HA synthase gene Has3 in total lung tissue, whereas the expression of Has1 was decreased. These in vivo studies in an experimental model of COPD show that CS exposure leads to enhanced deposition of (mostly LMW) HA in alveolar and bronchial walls by altering the expression of HA-modulating enzymes. This may contribute to airway wall remodeling and pulmonary inflammation in COPD.

Peribronchial lymphoid follicles have recently been identified as one of the hallmark features of (severe) chronic obstructive pulmonary disease (COPD). However, little is known about the relative contribution of peribronchial lymphoid follicles vs mediastinal lymph nodes in inflammatory responses in COPD patients and animal models. In a murine model of COPD, we studied inflammatory responses in airways, lungs, and mediastinal lymph nodes of wild-type (WT) vs CCR7 knockout (CCR7−/−) mice upon subacute or chronic exposure to cigarette smoke (CS). Although crucial for the organization of the secondary lymphoid organs, CCR7 was not required for the development of chronic CS-induced pulmonary lymphoid follicles. Moreover, T cell numbers were significantly increased in airways and lungs of air-exposed CCR7−/− mice, and they continued to increase upon chronic CS exposure. Unexpectedly, subacute CS-induced inflammation in airways and lungs, including airway neutrophilia and the recruitment of inflammatory-type CD11b+ dendritic cells, depended greatly on CCR7. In the draining lymph nodes, chronic CS exposure induced CCR7-dependent recruitment of airway-derived dendritic cells, accompanied by increases in CD4+ and CD8+ T cells. Correspondingly, CS exposure up-regulated mRNA expression of CCR7 ligands CCL19 and CCL21-Ser in lymph nodes of WT mice, but not CCR7−/− mice. In the lungs of WT mice, chronic CS exposure significantly increased CCL19 mRNA and protein. Furthermore, double staining for CCL19 and pro-surfactant protein C showed that alveolar type II cells express high levels of CCL19. These data unveil a so far unappreciated role for CCR7 in modulating inflammatory responses in airways and lungs.

BackgroundThe tachykinins, substance P and neurokinin A, present in sensory nerves and inflammatory cells such as macrophages and dendritic cells, are considered as pro-inflammatory agents. Inflammation of the airways and lung parenchyma plays a major role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and increased tachykinin levels are recovered from the airways of COPD patients. The aim of our study was to clarify the involvement of the tachykinin NK1receptor, the preferential receptor for substance P, in cigarette smoke (CS)-induced pulmonary inflammation and emphysema in a mouse model of COPD.MethodsTachykinin NK1receptor knockout (NK1-R-/-) mice and their wild type controls (all in a mixed 129/sv-C57BL/6 background) were subjected to sub acute (4 weeks) or chronic (24 weeks) exposure to air or CS. 24 hours after the last exposure, pulmonary inflammation and development of emphysema were evaluated.ResultsSub acute and chronic exposure to CS resulted in a substantial accumulation of inflammatory cells in the airways of both WT and NK1-R-/-mice. However, the CS-induced increase in macrophages and dendritic cells was significantly impaired in NK1-R-/-mice, compared to WT controls, and correlated with an attenuated release of MIP-3α/CCL20 and TGF-β1. Chronic exposure to CS resulted in development of pulmonary emphysema in WT mice. NK1-R-/-mice showed already enlarged airspaces upon air-exposure. Upon CS-exposure, the NK1-R-/-mice did not develop additional destruction of the lung parenchyma. Moreover, an impaired production of MMP-12 by alveolar macrophages upon CS-exposure was observed in these KO mice. In a pharmacological validation experiment using the NK1receptor antagonist RP 67580, we confirmed the protective effect of absence of the NK1receptor on CS-induced pulmonary inflammation.ConclusionThese data suggest that the tachykinin NK1receptor is involved in the accumulation of macrophages and dendritic cells in the airways upon CS-exposure and in the development of smoking-induced emphysema. As both inflammation of the airways and parenchymal destruction are important characteristics of COPD, these findings may have implications in the future treatment of this devastating disease.

In chronic obstructive pulmonary disease (COPD), chronic inflammation is accompanied by peribronchial lymphoid aggregates. Lymphotoxin (LT)-alpha, crucial in secondary lymphoid organogenesis, may be involved in lymphoid neogenesis. We examined cigarette smoke (CS)-induced pulmonary lymphoid neogenesis and inflammation in vivo in LT alpha knockout (LT alpha(-/-)) and wild-type (WT) mice and studied the expression of lymphoid chemokines by lung fibroblasts in vitro. T-cell numbers (in bronchoalveolar lavage fluid (BALF) and lungs) and lymphoid aggregate numbers were significantly higher in air-exposed LT alpha(-/-) mice than in WT animals, and increased upon chronic CS exposure in both genotypes. In contrast, local immunoglobulin A responses upon chronic CS exposure were attenuated in LT alpha(-/-) mice. CXC chemokine ligand (CXCL) 13 and CC chemokine ligand (CCL) 19 mRNA in total lung and CXCL13 protein level in BALF increased upon CS exposure in WT, but not in LT alpha(-/-) mice. In vitro lymphotoxin-beta receptor (LT beta R) stimulation induced CXCL13 and CCL19 mRNA in WT lung fibroblasts. Furthermore, in vitro exposure to CS extract upregulated CXCL13 mRNA expression in WT, but not in LT beta R-/-, lung fibroblasts. In this murine model of COPD, CS induces pulmonary expression of lymphoid chemokines CXCL13 and CCL19 in a LT alpha beta-LT beta R-dependent fashion. However, LT alpha is not required for CS-induced pulmonary lymphocyte accumulation and neogenesis of lymphoid aggregates.

Upon replication of Respiratory Syncytial Virus (RSV), double-stranded viral RNA can be detected in the endosomes via Toll-like receptor 3 (TLR3) signaling or by the cytoplasmic helicases retinoic acid inducible gene I (RIG-I) and melanoma differentiation-associated gene (Mda5). The latter interact downstream with IFNβ promoter stimulator (IPS-1). We previously demonstrated that TLR3 deficiency worsens RSV-induced lung pathology, yet leaves viral clearance intact. The present study examined the importance of IPS-1 signaling for anti-viral responses in primary cultures of alveolar epithelial cells (AECs), in dendritic cells (DCs), and macrophages (mΦ), as well as in vivo using IPS-1 knockout (KO) mice. In AECs, RSV induced IFNβ, IL6, CXCL1, CCL2 and CCL5 in an IPS-1 dependent manner. In DCs, the expression of IFNβ and CCL2 also required IPS-1. Conversely, RSV-induced cytokine and chemokine expression was enhanced in IPS-1 KO mΦ, while T-cells of infected IPS-1 KO mice showed a predominant Th1 profile with increased IFNγ. Plaque assays revealed higher RSV titers in IPS-1 deficient mice, accompanied by more severe granulocytic infiltration. Our data suggest a significant contribution of the IPS-1 pathway to the RSV-induced type I interferon response and inflammatory cytokine/chemokine production. Future experiments, using bone marrow chimeras, will help to elucidate the role of IPS-1 in both the structural and hematopoietic mediated response to viral infection.

Chronic obstructive pulmonary disease (COPD) is characterised by chronic inflammation of the airways and progressive destruction of lung parenchyma, a process that in most cases is initiated by cigarette smoking. Several mechanisms are involved in the development of the disease: influx of inflammatory cells into the lung (leading to chronic inflammation of the airways), imbalance between proteolytic and anti-proteolytic activity (resulting in the destruction of healthy lung tissue) and oxidative stress. Recently, an increasing number of data suggest a fourth important mechanism involved in the development of COPD: apoptosis of structural cells in the lung might possibly be an important upstream event in the pathogenesis of COPD. There is an increase in apoptotic alveolar epithelial and endothelial cells in the lungs of COPD patients. Since this is not counterbalanced by an increase in proliferation of these structural cells, the net result is destruction of lung tissue and the development of emphysema. Data from animal models suggest a role for Vascular Endothelial Growth Factor (VEGF) in the induction of apoptosis of structural cells in the lung. Other mediators of apoptosis, such as caspase-3 and ceramide, could be interesting targets to prevent apoptosis and the development of emphysema. In this review, recent data on the role of apoptosis in COPD from both animal models as well as from studies on human subjects will be discussed. The aim is to provide an up to date summary on the increasing knowledge on the role of apoptosis in COPD and pulmonary emphysema.

To the Editors: The characterisation of regulatory T (Treg) cells in chronic obstructive pulmonary disease (COPD) has become of particular interest considering the recent reports on adaptive immune responses in COPD. More specifically, peribronchial and parenchymal lymphoid follicles ( i.e. tertiary lymphoid organs) correlate in number with disease severity in COPD patients 1 and murine models of COPD 2, but their developing mechanisms and function have yet to be revealed 3. In COPD patients, pulmonary lymphoid follicles mainly appear as a B-cell core surrounded by a predominant cluster of differentiation (CD)4+ T-cell population 3. Treg cells situated within these structures are ideally located to exert cell contact-dependent immunosuppression. The observation on increased Treg cells in lymphoid follicles of moderate COPD patients by Plumb et al. 4, is therefore particularly intriguing. The different reports on Treg cells in COPD vary greatly, depending on the pulmonary anatomical compartment of interest and the phenotype used to define …