Innate immune receptors on neutrophils and their role in chronic lung disease

Neutrophil-Dependent Immunity During Pulmonary Infections and Inflammations

Rapid recruitment of neutrophils to an inflamed site is one of the hallmarks of an effective host defense mechanism. The main pathway through which this happens is by the innate immune response. Neutrophils, which play an important part in innate immune defense, migrate into lungs through the modulation actions of chemokines to execute a variety of pro-inflammatory functions. Despite the importance of chemokines in host immunity, little has been discussed on their roles in host immunity. A holistic understanding of neutrophil recruitment, pattern recognition pathways, the roles of chemokines and the pathophysiological roles of neutrophils in host immunity may allow for new approaches in the treatment of infectious and inflammatory disease of the lung. Herein, this review aims at highlighting some of the developments in lung neutrophil-immunity by focusing on the functions and roles of CXC/CC chemokines and pattern recognition receptors in neutrophil immunity during pulmonary inflammations. The pathophysiological roles of neutrophils in COVID-19 and thromboembolism have also been summarized. We finally summarized various neutrophil biomarkers that can be utilized as prognostic molecules in pulmonary inflammations and discussed various neutrophil-targeted therapies for neutrophil-driven pulmonary inflammatory diseases.

Probiotics and Trained Immunity

The characteristics of innate immunity have recently been investigated in depth in several research articles, and original findings suggest that innate immunity also has a memory capacity, which has been named “trained immunity”. This notion has revolutionized our knowledge of the innate immune response. Thus, stimulation of trained immunity represents a therapeutic alternative that is worth exploring. In this context, probiotics, live microorganisms which when administered in adequate amounts confer a health benefit on the host, represent attractive candidates for the stimulation of trained immunity; however, although numerous studies have documented the beneficial proprieties of these microorganisms, their mechanisms of action are not yet fully understood. In this review, we propose to explore the putative connection between probiotics and stimulation of trained immunity.

The role of inflammation in cystic fibrosis pulmonary exacerbations

INTRODUCTION

Cystic Fibrosis pulmonary exacerbations are critical events in the lives of people with CF that have deleterious effects on lung function, quality of life, and life expectancy. There are significant unmet needs in the management of exacerbations. We review here the associated inflammatory changes that underlie these events and are of interest for the development of biomarkers of exacerbation.

AREAS COVERED

Inflammatory responses in CF are abnormal and contribute to a sustained proinflammatory lung microenvironment, abundant in proinflammatory mediators and deficient in counter-regulatory mediators that terminate and resolve inflammation. There is increasing interest in these inflammatory pathways to discover novel biomarkers for pulmonary exacerbation management. In this review, we explore the inflammatory changes occurring during intravenous antibiotic therapy for exacerbation and how they may be applied as biomarkers to guide exacerbation therapy. A literature search was conducted using the PubMed database in February 2020.

EXPERT OPINION

Heterogeneity in inflammatory responses to treatment of a pulmonary exacerbation, a disease process with complex pathophysiology, limits the clinical utility of individual biomarkers. Biomarker panels may be a more successful strategy to capture informative changes within the CF population to improve pulmonary exacerbation management and outcomes.

Inhibition of metalloproteinases in therapy for severe lung injury due to COVID-19

Since its first appearance in December 2019 in the Chinese province of Wuhan, COVID-19 has spread rapidly throughout the world and poses a serious threat to public health. Acute respiratory failure due to widespread lung inflammation progress to acute respiratory distress syndrome (ARDS) with an altered pulmonary and alveolar function that can lead to disability, prolong hospitalizations, and adverse outcomes.

While there is no specific treatment for severe acute lung injury (ALI) and ARDS due to the COVID-19 and the management is mostly supportive, it is very important to better understand the pathophysiological processes activated by the inflammatory mediators such as cytokines and metalloproteinases with the aim of their subsequent inhibition in the course of the complex treatment.

Herein, we will discuss the pathophysiological mechanisms of ALI/ARDS, with a focus on the pivotal role played by matrix metalloproteinases (MMP) and the kinin-kallikrein system (KKS), and the effects of the possible pharmacological interventions.

Aprotinin is a nonspecific protease inhibitor especially of trypsin, chymotrypsin, plasmin, and kallikrein, and it is many years in clinical use. Aprotinin inhibits the release of pro-inflammatory cytokines and involved in the process of glycoprotein homeostasis. Experimental data support that the use of aprotinin to inhibit MMPs and KKS may be a new potential approach to the treatment of ALI / ARDS.

Basic fibroblast growth factor protects against influenza A virus-induced acute lung injury by recruiting neutrophils

Influenza virus (IAV) infection is a major cause of severe respiratory illness that affects almost every country in the world. IAV infections result in respiratory illness and even acute lung injury and death, but the underlying mechanisms responsible for IAV pathogenesis have not yet been fully elucidated. In this study, the basic fibroblast growth factor 2 (FGF2) level was markedly increased in H1N1 virus-infected humans and mice. FGF2, which is predominately derived from epithelial cells, recruits and activates neutrophils via the FGFR2-PI3K-AKT-NFκB signaling pathway. FGF2 depletion or knockout exacerbated influenza-associated disease by impairing neutrophil recruitment and activation. More importantly, administration of the recombinant FGF2 protein significantly alleviated the severity of IAV-induced lung injury and promoted the survival of IAV-infected mice. Based on the results from experiments in which neutrophils were depleted and adoptively transferred, FGF2 protected mice against IAV infection by recruiting neutrophils. Thus, FGF2 plays a critical role in preventing IAV-induced lung injury, and FGF2 is a promising potential therapeutic target during IAV infection.

Sequence-based structural analysis and evaluation of polymorphism in buffalo Nod-like receptor-1 gene

In this study, we have sequence characterized and analyzed the polymorphism in buffalo NOD1 (nucleotide-binding oligomerization domain 1) gene as well as its expression analysis. Full-length sequence analysis of NOD1 revealed this gene in buffalo being conserved with respect to the domain structures, similar to other species. Alternate splice variants having exon3 skipping also identified for the first time in the gene expressed in buffalo-purified peripheral blood mononuclear cells (PBMCs). Phylogenetically ruminant species were found to be clustering together and buffalo displaying maximum similarity with cattle. Sequencing of NOD1 across 12 Indian buffalo breeds identified 23 polymorphic sites within coding region, among which 16 were synonymous and 7 changes found to be non-synonymous. Four SNPs (single nucleotide polymorphisms) of them were genotyped in 393 animals belonging to 12 riverine, swamp and hybrid (riverine × swamp) buffalo populations of diverse phenotypes and utilities, showing variable allelic frequencies. Principal component analysis revealed, riverine and swamp buffaloes being distinctly placed with the distribution of breeds within the group based on the geographical isolation. Further, quantitative real-time PCR detected NOD1 expression in multiple tissues with PBMCs and lungs showing highest expression among the tissues examined. Structural analysis based on the translated amino acid sequence of buffalo NOD1 identified four protein interaction motifs LxxLL important for ligand binding. Molecular interaction analysis of iE-DAP and NOD1-LRR and their complex stability and binding-free energy studies indicated variable binding energies in buffalo and cattle NOD1. Overall, the study reveals unique structural features in buffalo NOD1, important for species-specific ligand interaction.

Innate Immunity of the Lung: From Basic Mechanisms to Translational Medicine

The respiratory tract is faced daily with 10,000 L of inhaled air. While the majority of air contains harmless environmental components, the pulmonary immune system also has to cope with harmful microbial or sterile threats and react rapidly to protect the host at this intimate barrier zone. The airways are endowed with a broad armamentarium of cellular and humoral host defense mechanisms, most of which belong to the innate arm of the immune system. The complex interplay between resident and infiltrating immune cells and secreted innate immune proteins shapes the outcome of host-pathogen, host-allergen, and host-particle interactions within the mucosal airway compartment. Here, we summarize and discuss recent findings on pulmonary innate immunity and highlight key pathways relevant for biomarker and therapeutic targeting strategies for acute and chronic diseases of the respiratory tract.

Toll-like receptor-mediated involvement of innate immune cells in asthma disease

BACKGROUND

Innate immune cells as the first line of defense are adept at recognizing and triggering appropriate response against various pathogens. Apart from the protective functions, the innate immunity plays an essential role in mediation of allergic responses. Dendritic cells (DCs) and airway epithelial cells (AECs) along with other innate cells such as granulocytes, natural killer cells (NKs), natural killer T cells (NKTs), and alternatively activated macrophages (AAMs) are able to orchestrate allergic responses, especially asthma. Chronic stimulation of TLRs by airway stimuli induces local inflammation which gradually results in the recruitment and settling of innate cells around airways.

SCOPE OF REVIEW

This review discusses how recruitment and accumulation of the inflammatory cells in the site of insult facilitate hypersensitivity reactions and initiate airway inflammation. We indicate that these cells are well equipped to highly sensitive receptors known as toll-like receptors (TLRs) making them fit to prime adaptive immune response. Based on emerging findings, we highlight the pivotal role of TLRs in regulation of innate cells function in the context of asthma disease.

MAJOR CONCLUSIONS

Stimulation of the TLRs of innate cells by allergens has been found to accelerate and regulate allergic airway inflammation. In fact, the sophisticated interaction between environmental allergens and TLRs leads to release of various pro-inflammatory mediators from innate cells supporting asthma development.

GENERAL SIGNIFICANCE

This review highlights that TLRs have a substantial role in priming innate cells and cytokine release, suggesting that the involvement of TLRs of innate immune cells can modulate the function of these cells in asthma disease.

Current Concepts and Controversies in Innate Immunity of Cystic Fibrosis Lung Disease

Cystic fibrosis (CF) lung disease is characterized by chronic infection and inflammation. The inflammatory response in CF is dominated by the activation of the innate immune system. Bacteria and fungi represent the key pathogens chronically colonizing the CF airways. In response, innate immune pattern recognition receptors, expressed by airway epithelial and myeloid cells, sense the microbial threat and release chemoattractants to recruit large numbers of neutrophils into CF airways. However, neutrophils fail to efficiently clear the invading pathogens, but instead release harmful proteases and oxidants and finally cause tissue injury. Here, we summarize and discuss current concepts and controversies in the field of innate immunity in CF lung disease, facing the ongoing questions of whether inflammation is good or bad in CF and how innate immune mechanisms could be harnessed therapeutically.

Neutrophils in cystic fibrosis

Cystic fibrosis (CF) lung disease is characterized by chronic infection and inflammation. Among inflammatory cells, neutrophils represent the major cell population accumulating in the airways of CF patients. While neutrophils provide the first defensive cellular shield against bacterial and fungal pathogens, in chronic disease conditions such as CF these short-lived immune cells release their toxic granule contents that cause tissue remodeling and irreversible structural damage to the host. A variety of human and murine studies have analyzed neutrophils and their products in the context of CF, yet their precise functional role and therapeutic potential remain controversial and incompletely understood. Here, we summarize the current evidence in this field to shed light on the complex and multi-faceted role of neutrophils in CF lung disease.

Advances in the treatment of virus-induced asthma

Viral exacerbations continue to represent the major burden in terms of morbidity, mortality and health care costs associated with asthma. Those at greatest risk for acute asthma are those with more severe airways disease and poor asthma control. It is this group with established asthma in whom acute exacerbations triggered by virus infections remain a serious cause of increased morbidity. A range of novel therapies are emerging to treat asthma and in particular target this group with poor disease control, and in most cases their efficacy is now being judged by their ability to reduce the frequency of acute exacerbations. Critical for the development of new treatment approaches is an improved understanding of virus-host interaction in the context of the asthmatic airway. This requires research into the virology of the disease in physiological models in conjunction with detailed phenotypic characterisation of asthma patients to identify targets amenable to therapeutic intervention.

Unfolding the Role of Large Heat Shock Proteins: New Insights and Therapeutic Implications

Heat shock proteins (HSPs) of eukaryotes are evolutionarily conserved molecules present in all the major intracellular organelles. They mainly function as molecular chaperones and participate in maintenance of protein homeostasis in physiological state and under stressful conditions. Despite their relative abundance, the large HSPs, i.e., Hsp110 and glucose-regulated protein 170 (Grp170), have received less attention compared to other conventional HSPs. These proteins are distantly related to the Hsp70 and belong to Hsp70 superfamily. Increased sizes of Hsp110 and Grp170, due to the presence of a loop structure, result in their exceptional capability in binding to polypeptide substrates or non-protein ligands, such as pathogen-associated molecules. These interactions that occur in the extracellular environment during tissue injury or microbial infection may lead to amplification of an immune response engaging both innate and adaptive immune components. Here, we review the current advances in understanding these large HSPs as molecular chaperones in proteostasis control and immune modulation as well as their therapeutic implications in treatment of cancer and neurodegeneration. Given their unique immunoregulatory activities, we also discuss the emerging evidence of their potential involvement in inflammatory and immune-related diseases.

Identification and characterization of a novel Toll-like receptor 2 homologue in the large yellow croaker Larimichthys crocea

Toll-like receptors (TLRs) are key components of innate immunity that play significant roles in immune defence against pathogen invasion. In the present study, we identified a novel TLR2 homologue (LycTLR2b) in large yellow croaker (Larimichthys crocea) that shared low sequence identity with the previously reported large yellow croaker TLR2 (tentatively named LycTLR2a). The full-length cDNA of LycTLR2b was 2926 nucleotides (nt) long and encoded a protein consisting of 797 amino acids (aa). The deduced LycTLR2b protein exhibited a typical TLR domain architecture including a signal peptide, seven leucine-rich repeats (LRRs) in the extracellular region, a transmembrane domain, and a Toll-Interleukin 1 receptor (TIR) domain in the cytoplasmic region. Phylogenetic analysis showed that both LycTLR2a and LycTLR2b fall into a major clade formed by all TLR2 sequences, and are divided into two distinct branches. Genomic organization revealed that the LycTLR2b gene lacks intron, which is similar to zebrafish and human TLR2 genes, whereas the LycTLR2a gene contains multiple introns, as found in damselfish TLR2a and Fugu TLR2 genes. Syntenic analysis suggested that the occurrence of LycTLR2a and LycTLR2b may result from a relatively recent genome duplication event. LycTLR2b mRNA was constitutively expressed in all tissues examined although at different levels. Following bacterial vaccine challenge, LycTLR2b expression levels were significantly up-regulated in both spleen and head kidney tissues. Taken together, these results indicated that two different TLR2 homologues, which may play roles in antibacterial immunity, exist in large yellow croaker.

Esophageal cancer-related gene-4 (ECRG4) interactions with the innate immunity receptor complex

OBJECTIVE AND DESIGN

The human c2orf40 gene encodes a tumor suppressor gene called esophageal cancer-related gene-4 (ECRG4) with pro- and anti-inflammatory activities that depend on cell surface processing. Here, we investigated its physical and functional association with the innate immunity receptor complex.

METHODS

Interactions between ECRG4 and the innate immunity receptor complex were assessed by flow cytometry, immunohistochemistry, confocal microscopy, and co-immunoprecipitation. Phage display was used for ligand targeting to cells that overexpress the TLR4-MD2-CD14.

RESULTS

Immunoprecipitation and immunohistochemical studies demonstrate a physical interaction between ECRG4 and TLR4-MD2-CD14 on human granulocytes. Flow cytometry shows ECRG4 on the cell surface of a subset of CD14(+) and CD16(+) leukocytes. In a cohort of trauma patients, the C-terminal 16 amino acid domain of ECRG4 (ECRG4(133-148)) appears to be processed and shed, presumably at a thrombin-like consensus sequence. Phage targeting this putative ligand shows that this peptide sequence internalizes into cells through the TLR4/CD14/MD2 complex, but modulates inflammation through non-canonical, NFκB signal transduction.

CONCLUSIONS

ECRG4 is present on the surface of human monocytes and granulocytes. Its interaction with the human innate immunity receptor complex supports a role for cell surface activation of ECRG4 during inflammation and implicates this receptor in its mechanism of action.

Reprint of Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca(2+) signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

Impaired functions of macrophage from cystic fibrosis patients: CD11b, TLR-5 decrease and sCD14, inflammatory cytokines increase

BACKGROUND

Early in life, cystic fibrosis (CF) patients are infected with microorganisms. The role of macrophages has largely been underestimated in literature, whereas the focus being mostly on neutrophils and epithelial cells. Macrophages may however play a significant role in the initiating stages of this disease, via an inability to act as a suppressor cell. Yet macrophage dysfunction may be the first step in cascade of events leading to chronic inflammation/infection in CF. Moreover, reports have suggested that CFTR contribute to altered inflammatory response in CF by modification of normal macrophage functions.

OBJECTIVES

In order to highlight possible intrinsic macrophage defects due to impaired CFTR, we have studied inflammatory cytokines secretions, recognition of pathogens and phagocytosis in peripheral blood monocyte-derived macrophages from stable adult CF patients and healthy subjects (non-CF).

RESULTS

In CF macrophage supernatants, concentrations of sCD14, IL-1β, IL-6, TNF-α and IL-10 were strongly raised. Furthermore expression of CD11b and TLR-5 were sorely decreased on CF macrophages. Beside, no difference was observed for mCD14, CD16, CD64, TLR-4 and TLR1/TLR-2 expressions. Moreover, a strong inhibition of phagocytosis was observed for CF macrophages. Elsewhere CFTR inhibition in non-CF macrophages also led to alterations of phagocytosis function as well as CD11b expression.

CONCLUSIONS

Altogether, these findings demonstrate excessive inflammation in CF macrophages, characterized by overproduction of sCD14 and inflammatory cytokines, with decreased expression of CD11b and TLR-5, and impaired phagocytosis. This leads to altered clearance of pathogens and non-resolution of infection by CF macrophages, thereby inducing an exaggerated pro-inflammatory response.

Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca^2 + signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

•

Neutrophils are crucial players in innate and adaptive immunity.

•

Neutrophils also participate in autoimmune and inflammatory diseases.

•

Various neutrophil receptors recognize pathogens and the inflammatory environment.

•

The various cell surface receptors trigger diverse intracellular signaling.

•

Neutrophil receptors and signaling are potential targets in inflammatory diseases.

Genetic variations in toll-like receptor pathway and lung function decline in Cystic fibrosis patients

The toll-like receptor (TLR) family maintains pulmonary homeostasis by pathogen recognition, clearance and regulation of inflammation. Genes affecting inflammation response play a key role in modifying Cystic fibrosis (CF) lung disease severity. We assessed the impact of single nucleotide polymorphisms (SNPs) of TLR genes (TLR1 to TLR10, CD14, lipopolyssacharide-binding protein (LBP)) on lung function in CF patients. Each SNP was tested for time-dependent effect on FEV1, using six genetic models. In addition, we investigated associations between SNP genotypes and extreme subject specific slopes of FEV1 decline. Variant alleles of polymorphisms of TLR2 rs1898830, rs5743708, and rs3804100 demonstrated a consistent association with lung disease severity (p = 0.008, p = 0.006 and p = 0.029 respectively). Patients homozygous for variant C allele of TLR5 polymorphism rs5744174 are more frequently associated with extreme fast FEV1 decline (OR: 20 (95% Confidence Interval:1.85-216.18)). Patients homozygous AA for TLR1 polymorphism rs5743551 are more frequently associated with faster decline of FEV1 compared to heterozygous genotype (OR:7.33 (95% CI:1.63-33.11). Our findings indicate that variations in TLR1, TLR2 and TLR5 genes may influence CF lung function decline. Further functional analysis is required to provide new insights into the pathogenesis of TLRs in CF lung disease severity.

Toll-like receptor-2/6 and Toll-like receptor-9 agonists suppress viral replication but not airway hyperreactivity in guinea pigs

Respiratory virus infections cause airway hyperreactivity (AHR). Preventative strategies for virus-induced AHR remain limited. Toll-like receptors (TLRs) have been suggested as a therapeutic target because of their central role in triggering antiviral immune responses. Previous studies showed that concurrent treatment with TLR2/6 and TLR9 agonists reduced lethality and the microbial burden in murine models of bacterial and viral pneumonia. This study investigated the effects of TLR2/6 and TLR9 agonist pretreatment on parainfluenza virus pneumonia and virus-induced AHR in guinea pigs in vivo. Synthetic TLR2/6 lipopeptide agonist Pam₂CSK₄ and Class C oligodeoxynucleotide TLR9 agonist ODN2395, administered in combination 24 hours before virus infection, significantly reduced viral replication in the lung. Despite a fivefold reduction in viral titers, concurrent TLR2/6 and TLR9 agonist pretreatment did not prevent virus-induced AHR or virus-induced inhibitory M2 muscarinic receptor dysfunction. Interestingly, the TLR agonists independently caused non-M2-dependent AHR. These data confirm the therapeutic antiviral potential of TLR agonists, while suggesting that virus inhibition may be insufficient to prevent virus-induced airway pathophysiology. Furthermore, TLR agonists independently cause AHR, albeit through a distinctly different mechanism from that of parainfluenza virus.

Impact of cagPAI and T4SS on the inflammatory response of human neutrophils to Helicobacter pylori infection

Helicobacter pylori contains a pathogenicity island, cagPAI, with genes homologous to components of the type IV secretion system (T4SS) of Agrobacterium tumefaciens. The T4SS components assemble a structure that transfers CagA protein and peptidoglycan into host epithelial cells, causing the increased release of interleukin 8 (IL8) from the cells. The Toll-like receptors on neutrophils recognize H. pylori, initiating signaling pathways that enhance the activation of NF-κB. However, the roles of cagPAI and T4SS in the inflammatory response of neutrophils are unknown. We evaluated the participation of cagPAI and T4SS in the response of human neutrophils to H. pylori infection. Neutrophils were isolated from the blood of healthy donors and infected with H. pylori cagPAI(+), cagPAI(-), and cagPAI mutant strains virB4 (-) and virD4 (-). Whereas cagPAI(+) strain 26695 induced the greatest IL8 production, a proinflammatory response, cagPAI(-) strain 8822 induced the greatest IL10 production, an anti-inflammatory response. In contrast, the virB4 (-) and virD4 (-) mutant strains produced significantly more of the two proinflammatory cytokines IL1β and tumor necrosis factor αthan the cagPAI(+) strain 26695. We observed that H. pylori downregulated the expression of TLRs 2 and 5 but upregulated TLR9 expression in a cagPAI and T4SS-independent manner. These results show for the first time that the response of human neutrophils to H. pylori may vary from a pro-inflammatory to an anti-inflammatory response, depending on cagPAI and the integrity of T4SS.

Activation of an immune-regulatory macrophage response and inhibition of lung inflammation in a mouse model of COPD using heat-shock protein alpha B-crystallin-loaded PLGA microparticles

As an extracellular protein, the small heat-shock protein alpha B-crystallin (HSPB5) has anti-inflammatory effects in several mouse models of inflammation. Here, we show that these effects are associated with the ability of HSPB5 to activate an immune-regulatory response in macrophages via endosomal/phagosomal CD14 and Toll-like receptors 1 and 2. Humans, however, possess natural antibodies against HSPB5 that block receptor binding. To protect it from these antibodies, we encapsulated HSPB5 in porous PLGA microparticles. We document here size, morphology, protein loading and release characteristics of such microparticles. Apart from effectively protecting HSPB5 from neutralization, PLGA microparticles also strongly promoted macrophage targeting of HSPB via phagocytosis. As a result, HSPB5 in porous PLGA microparticles was more than 100-fold more effective in activating macrophages than free soluble protein. Yet, the immune-regulatory nature of the macrophage response, as documented here by microarray transcript profiling, remained the same. In mice developing cigarette smoke-induced COPD, HSPB5-loaded PLGA microparticles were selectively taken up by alveolar macrophages upon intratracheal administration, and significantly suppressed lung infiltration by lymphocytes and neutrophils. In contrast, 30-fold higher doses of free soluble HSPB5 remained ineffective. Our data indicate that porous HSPB5-PLGA microparticles hold considerable promise as an anti-inflammatory biomaterial for humans.

Down-regulation of NOD1 in neutrophils of periparturient dairy cows

Increased susceptibility of periparturient dairy cows to infectious diseases has been linked to neutrophil dysfunction. Cytoplasmic nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) mediate numerous aspects of innate immunity in humans and experimental animals. The authors hypothesized that neutrophils in periparturient cows have reduced NLR expression, resulting in declined immune responses to NLR activation. In this study, blood neutrophils from periparturient and mid-lactating cows were isolated and assessed for mRNA and protein expression of NOD1 and NOD2. Neutrophil phagocytosis and oxidative burst activity following NLR agonist-induced activation were also investigated. Periparturient cows demonstrated weak-to-absent NOD1 mRNA expression along with a significant reduction in NOD1 protein in their neutrophils. However, no difference in NOD2 protein expression was observed between groups although NOD2 mRNA abundance in periparturient cows was significantly reduced. Phagocytosis and oxidative burst activity measured by production of reactive oxygen species (ROS) were diminished in periparturient cows. NOD1 activation enhanced phagocytosis and ROS production in both isolated cell populations, regardless of the lactation stage. Nevertheless, NOD1-activated neutrophils showed reduced phagocytosis and ROS generation in periparturient cows with respect to mid-lactating subjects. Collectively, our findings suggest that NOD1 down-regulation in neutrophils may be a mechanism involved in periparturient neutrophil dysregulation.

Innate immunity in cystic fibrosis lung disease

Chronic lung disease determines the morbidity and mortality of cystic fibrosis (CF) patients. The pulmonary immune response in CF is characterized by an early and non-resolving activation of the innate immune system, which is dysregulated at several levels. Here we provide a comprehensive overview of innate immunity in CF lung disease, involving (i) epithelial dysfunction, (ii) pathogen sensing, (iii) leukocyte recruitment, (iv) phagocyte impairment, (v) mechanisms linking innate and adaptive immunity and (iv) the potential clinical relevance. Dissecting the complex network of innate immune regulation and associated pro-inflammatory cascades in CF lung disease may pave the way for novel immune-targeted therapies in CF and other chronic infective lung diseases.

Neutrophils augment LPS-mediated pro-inflammatory signaling in human lung epithelial cells

BACKGROUND

The role of polymorphonuclear neutrophils in pulmonary host defense is well recognized. The influence of a pre-existing inflammation driven by neutrophils (neutrophilic inflammation) on the airway epithelial response toward pro-inflammatory exogenous triggers, however, is still poorly addressed. Therefore, the aim of the present study is to investigate the effect of neutrophils on lipopolysaccharide (LPS)-induced pro-inflammatory signaling in lung epithelial cells. Additionally, underlying signaling pathways are examined.

METHODS

Human bronchial epithelial cells (BEAS-2B) were co-incubated with human peripheral blood neutrophils or bone-marrow derived neutrophils from either C57BL/6J wild type or nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase deficient (p47(phox-/-)) mice. Upon stimulation with LPS, interleukin (IL)-8 production and reactive oxygen species (ROS) generation were measured. Additionally, activation of the extracellular signal-regulated kinases (ERK) 1/2 and nuclear factor (NF)-κB signaling pathways was analyzed.

RESULTS

Our studies show that the presence of neutrophils synergistically increases LPS-induced IL-8 and ROS production by BEAS-2B cells without inducing cytotoxicity. The observed IL-8 response to endotoxin increases in proportion to time, LPS-concentration and the number of neutrophils present. Moreover, this synergistic IL-8 production strongly correlated with the chemotactic properties of the co-incubations and significantly depended on a functional neutrophilic NADPH oxidase. The presence of neutrophils also augments LPS-induced phosphorylation of ERK1/2 and IκBα as well as NF-κB RelA DNA binding activity in BEAS-2B cells.

CONCLUSIONS

Our results indicate that the pro-inflammatory effects of LPS toward lung epithelial cells are amplified during a pre-existing neutrophilic inflammation. These findings support the concept that patients suffering from pulmonary neutrophilic inflammation are more susceptible toward exogenous pro-inflammatory triggers.

Dual role of Toll-like receptors in asthma and chronic obstructive pulmonary disease

During the last decade, significant research has been focused on Toll-like receptors (TLRs) in the pathogenesis of airway diseases. TLRs are pattern recognition receptors that play pivotal roles in the detection of and response to pathogens. Because of the involvement of TLRs in innate and adaptive immunity, these receptors are currently being exploited as possible targets for drug development. Asthma and chronic obstructive pulmonary disease (COPD) are chronic inflammatory airway diseases in which innate and adaptive immunity play an important role. To date, asthma is the most common chronic disease in children aged 5 years and older. COPD is prevalent amongst the elderly and is currently the fifth-leading cause of death worldwide with still-growing prevalence. Both of these inflammatory diseases result in shortness of breath, which is treated, often ineffectively, with bronchodilators and glucocorticosteroids. Symptomatic treatment approaches are similar for both diseases; however, the underlying immunological mechanisms differ greatly. There is a clear need for improved treatment specific for asthma and for COPD. This review provides an update on the role of TLRs in asthma and in COPD and discusses the merits and difficulties of targeting these proteins as novel treatment strategies for airway diseases. TLR agonist, TLR adjuvant, and TLR antagonist therapies could all be argued to be effective in airway disease management. Because of a possible dual role of TLRs in airway diseases with shared symptoms and risk factors but different immunological mechanisms, caution should be taken while designing pulmonary TLR-based therapies.

CXCL8 attenuates chemoattractant-induced equine neutrophil migration

The chemokine, CXCL8, is a potent chemoattractant but it has also been shown to attenuate the migratory response of human neutrophils to the bacterial peptide, FMLP; this could lead to retention of cells in infected tissue and, potentially, to enhanced clearance of bacteria. This study has examined the effect of CXCL8 on equine neutrophil migration and adherence in response to PAF and LTB(4), chemoattractants that may play a role in non-infectious inflammatory conditions of the horse associated with neutrophil recruitment to the target tissue. The effects of CXCL8 on PAF- and LTB(4)-induced responses were determined using a ChemoTx plate migration assay and by measuring adhesion to protein-coated plastic. The CXCR1/2 antagonist, SB225002, was used to investigate whether the observed effects were receptor mediated and the role of cAMP was examined by measuring intracellular cAMP following exposure to agonists alone and in combination and by establishing the effect of dibutyryl cAMP on neutrophil migration. CXCL8, LTB(4) and PAF each induced migration and adhesion. Exposure of neutrophils to a combination of CXCL8 and PAF reduced the magnitude of the responses to that of unstimulated cells. In contrast, although the effect was less than additive, the response to co-stimulation with CXCL8 and LTB(4) were not nearly as pronounced. CXCL8 acted in a receptor mediated manner, the attenuation of PAF-induced responses being reversed by SB225002 at a concentration that blocks CXCR2. CXCL8, PAF and LTB(4) alone increased intracellular cAMP. In co-incubation studies, combination of CXCL8 with PAF led to an additive increase in cAMP whereas no increase above that obtained in response to LTB(4) alone was seen. Dibutyryl cAMP significantly reduced neutrophil migration in response to either CXCL8 or PAF alone. These results demonstrate that CXCL8, in addition to being a potent chemoattractant and pro-adhesive molecule for equine neutrophils, is able to attenuate responses to PAF and, to a much lesser extent, LTB(4). This effect, which appears to be CXCR2-mediated and cAMP dependent, could lead in vivo to trapping of cells at sites of inflammation resulting potentially in either enhanced clearance of injurious stimuli or increased local tissue damage by activated cells.

CFTR inhibition provokes an inflammatory response associated with an imbalance of the annexin A1 pathway

Cystic fibrosis (CF), a disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, is characterized by chronic bacterial infections and inflammation in the lung. Having previously shown that deletion of CFTR is associated with lower expression of the endogenous anti-inflammatory protein Annexin A1 (AnxA1), we investigated further this possible functional connection using a validated CFTR inhibitor. Treatment of mice with the CFTR inhibitor-172 (CFTR(172)) augmented the acute peritonitis promoted by zymosan, an effect associated with lower AnxA1 levels in peritoneal cells. Similar results were obtained with another, chemically distinct, CFTR inhibitor. The pro-inflammatory effect of CFTR(172) was lost in AnxA1(-/-), as well as CFTR(-/-) mice. Importantly, administration of hrAnxA1 and its peptido-mimetic to CFTR(-/-) animals or to animals treated with CFTR(172) corrected the exaggerated leukocyte migration seen in these animals. In vitro assays with human Polymorphonuclear leukocyte (PMN) demonstrated that CFTR(172) reduced cell-associated AnxA1 by promoting release of the protein in microparticles. We propose that the reduced impact of the counterregulatory properties of AnxA1 in CF cells contributes to the inflammatory phenotype characteristic of this disease. Thus, these findings provide an important insight into the mechanism underlying the inflammatory disease associated with CFTR inhibition while, at the same time, providing a novel pharmacological target for controlling the inflammatory phenotype of CF.

Why is Pseudomonas aeruginosa a pathogen?

Despite the expression of a myriad of virulence factors, healthy individuals are generally able to resist infections with Pseudomonas aeruginosa. Polymorphonuclear leukocyte-dependent killing is the major mechanism responsible for resistance; dysregulation of host defense mechanisms in addition to expression of specific bacterial factors can result in life-threatening infections with this bacterium.