Secretory component is cleaved by neutrophil serine proteinases but its epithelial production is increased by neutrophils through NF-kappa B- and p38 mitogen-activated protein kinase-dependent mechanisms

The memory of airway epithelium damage in smokers and COPD patients

Chronic obstructive pulmonary disease (COPD), a devastating and irreversible lung disease, causes structural and functional defects in the bronchial epithelium, the (ir)reversibility of which remains unexplored in vitro. This study aimed to investigate the persistence of COPD-related epithelial defects in long-term airway epithelial cultures derived from non-smokers, smokers, and COPD patients. Barrier function, polarity, cell commitment, epithelial-to-mesenchymal transition, and inflammation were evaluated and compared with native epithelium characteristics. The role of inflammation was explored using cytokines. We show that barrier dysfunction, compromised polarity, and lineage abnormalities observed in smokers and COPD persisted for up to 10 wk. Goblet cell hyperplasia was associated with recent cigarette smoke exposure. Conversely, increased IL-8/CXCL-8 release and abnormal epithelial-to-mesenchymal transition diminished over time. These ex vivo observations matched surgical samples' abnormalities. Cytokine treatment induced COPD-like changes in control cultures and reactivated epithelial-to-mesenchymal transition in COPD cells. In conclusion, these findings suggest that the airway epithelium of smokers and COPD patients retains a multidimensional memory of its original state and previous cigarette smoke-induced injuries, maintaining these abnormalities for extended periods.

A new hope? Possibilities of therapeutic IgA antibodies in the treatment of inflammatory lung diseases

Inflammatory lung diseases represent a persistent burden for patients and the global healthcare system. The combination of high morbidity, (partially) high mortality and limited innovations in the last decades, have resulted in a great demand for new therapeutics. Are therapeutic IgA antibodies possibly a new hope in the treatment of inflammatory lung diseases? Current research increasingly unravels the elementary functions of IgA as protector against infections and as modulator of overwhelming inflammation. With a focus on IgA, this review describes the pathological alterations in mucosal immunity and how they contribute to chronic inflammation in the most common inflammatory lung diseases. The current knowledge of IgA functions in the circulation, and particularly in the respiratory mucosa, are summarized. The interplay between neutrophils and IgA seems to be key in control of inflammation. In addition, the hurdles and benefits of therapeutic IgA antibodies, as well as the currently known clinically used IgA preparations are described. The data highlighted here, together with upcoming research strategies aiming at circumventing the current pitfalls in IgA research may pave the way for this promising antibody class in the application of inflammatory lung diseases.

Molecular cloning and characteristic analysis of polymeric immunoglobulin receptor-like (plgRL) in large yellow croaker (Larimichthys crocea)

In the present study, the polyimmunoglobulin receptor-like (pIgRL) of large yellow croaker (Larimichthys crocea) was first cloned and characterized. LcpIgRL's full-length cDNA was 1610 bp, encoding 377 amino acids, and the protein's predicted molecular weight was 41.9 kDa, containing two immunoglobulin-like structural domains. The transcript levels of LcpIgRL in different tissues of healthy large yellow croaker were examined by real-time fluorescence quantitative PCR, and the results showed that the gills and head kidney had the highest levels. Within 36 h of the large yellow croaker being infected with Vibrio harveyi, pIgRL mRNA first increased and then decreased in all determined tissues, with the highest expression in the skin and hindgut. Furthermore, a recombinant protein of the extracellular region of LcpIgRL was expressed in E. coli BL21, and a murine rLcpIgRL polyclonal antibody was prepared, which could react specifically with the natural LcpIgRL in skin mucus, but no natural LcpIgRL was detected in serum. Meanwhile, it was found that the rLcpIgRL could bind to the recombinant IgM and the natural IgM, indicating that LcpIgRL could mediate the transport of IgM in mucus. In addition, rLcpIgRL binds to Aeromonas hydrophila and V. harveyi, as well as lipopolysaccharide (LPS) and various saccharides, and reduced binding to bacteria was observed under LPS treatment, suggesting that LcpIgRL can bind to bacteria to prevent infection and that saccharide binding is an important mechanism of interaction between pIgRL and bacteria.

Investigating the Link between Alpha-1 Antitrypsin and Human Neutrophil Elastase in Bronchoalveolar Lavage Fluid of COVID-19 Patients

Neutrophils play a pathogenic role in COVID-19 by releasing Neutrophils Extracellular Traps (NETs) or human neutrophil elastase (HNE). Given that HNE is inhibited by α1-antitrypsin (AAT), we aimed to assess the content of HNE, α1-antitrypsin (AAT) and HNE-AAT complexes (the AAT/HNE balance) in 33 bronchoalveolar lavage fluid (BALf) samples from COVID-19 patients. These samples were submitted for Gel-Electrophoresis, Western Blot and ELISA, and proteins (bound to AAT or HNE) were identified by Liquid Chromatography-Mass Spectrometry. NETs' release was analyzed by confocal microscopy. Both HNE and AAT were clearly detectable in BALf at high levels. Contrary to what was previously observed in other settings, the formation of HNE-AAT complex was not detected in COVID-19. Rather, HNE was found to be bound to acute phase proteins, histones and C3. Due to the relevant role of NETs, we assessed the ability of free AAT to bind to histones. While confirming this binding, AAT was not able to inhibit NET formation. In conclusion, despite the finding of a high burden of free and bound HNE, the lack of the HNE-AAT inhibitory complex in COVID-19 BALf demonstrates that AAT is not able to block HNE activity. Furthermore, while binding to histones, AAT does not prevent NET formation nor their noxious activity.

Secretory Immunoglobulin A Immunity in Chronic Obstructive Respiratory Diseases

Chronic obstructive pulmonary disease (COPD), asthma and cystic fibrosis (CF) are distinct respiratory diseases that share features such as the obstruction of small airways and disease flare-ups that are called exacerbations and are often caused by infections. Along the airway epithelium, immunoglobulin (Ig) A contributes to first line mucosal protection against inhaled particles and pathogens. Dimeric IgA produced by mucosal plasma cells is transported towards the apical pole of airway epithelial cells by the polymeric Ig receptor (pIgR), where it is released as secretory IgA. Secretory IgA mediates immune exclusion and promotes the clearance of pathogens from the airway surface by inhibiting their adherence to the epithelium. In this review, we summarize the current knowledge regarding alterations of the IgA/pIgR system observed in those major obstructive airway diseases and discuss their implication for disease pathogenesis.

The Role of IgA in Chronic Upper Airway Disease: Friend or Foe?

Chronic upper airway inflammation is amongst the most prevalent chronic disease entities in the Western world with prevalence around 30% (rhinitis) and 11% (rhinosinusitis). Chronic rhinitis and rhinosinusitis may severely impair the quality of life, leading to a significant socio-economic burden. It becomes more and more clear that the respiratory mucosa which forms a physiological as well as chemical barrier for inhaled particles, plays a key role in maintaining homeostasis and driving disease. In a healthy state, the mucosal immune system provides protection against pathogens as well as maintains a tolerance toward non-harmful commensal microbes and benign environmental substances such as allergens. One of the most important players of the mucosal immune system is immunoglobulin (Ig) A, which is well-studied in gut research where it has emerged as a key factor in creating tolerance to potential food allergens and maintaining a healthy microbiome. Although, it is very likely that IgA plays a similar role at the level of the respiratory epithelium, very little research has been performed on the role of this protein in the airways, especially in chronic upper airway diseases. This review summarizes what is known about IgA in upper airway homeostasis, as well as in rhinitis and rhinosinusitis, including current and possible new treatments that may interfere with the IgA system. By doing so, we identify unmet needs in exploring the different roles of IgA in the upper airways required to find new biomarkers or therapeutic options for treating chronic rhinitis and rhinosinusitis.

Immunoglobulin A Mucosal Immunity and Altered Respiratory Epithelium in Cystic Fibrosis

The respiratory epithelium represents the first chemical, immune, and physical barrier against inhaled noxious materials, particularly pathogens in cystic fibrosis. Local mucus thickening, altered mucociliary clearance, and reduced pH due to CFTR protein dysfunction favor bacterial overgrowth and excessive inflammation. We aimed in this review to summarize respiratory mucosal alterations within the epithelium and current knowledge on local immunity linked to immunoglobulin A in patients with cystic fibrosis.

Activation of the JNK/MAPK Signaling Pathway by TGF-β1 Enhances Neonatal Fc Receptor Expression and IgG Transcytosis

The neonatal Fc receptor (FcRn) transports maternal immunoglobulin G (IgG) to the foetus or newborn and protects the IgG from degradation. FcRn is expressed in several porcine tissues and cell types and its expression levels are regulated by immune and inflammatory events. IPEC-J2 cells are porcine intestinal columnar epithelial cells that were isolated from neonatal piglet mid-jejunum. We hypothesized that transforming growth factor β1 (TGF-β1) upregulated pFcRn expression in IPEC-J2 cells. To test this hypothesis, we treated IPEC-J2 cells with TGF-β1 and demonstrated that porcine FcRn (pFcRn) expression was significantly increased. SP600125, a specific mitogen-activated protein kinase (MAPK) inhibitor, reduced TGF-β1-induced pFcRn expression in IPEC-J2 cells. We performed luciferase reporter assays and showed that the c-JUN sensitive region of the pFcRn promoter gene was located between positions -1215 and -140. The c-JUN sequence, in combination with the pFcRn promoter, regulated luciferase reporter activity in response to TGF-β1 stimulation. Chromatin immunoprecipitation confirmed that there were three c-JUN binding sites in the pFcRn promoter. Furthermore, in addition to increased pFcRn expression, TGF-β1 also enhanced IgG transcytosis in IPEC-J2 cells. In summary, our data showed that the modulation of JNK/MAPK signaling by TGF-β1 was sufficient to upregulate pFcRn expression.

Traffic generated emissions alter the lung microbiota by promoting the expansion of Proteobacteria in C57Bl/6 mice placed on a high-fat diet

Air pollution has been documented to contribute to severe respiratory diseases like asthma and chronic obstructive pulmonary disorder (COPD). Although these diseases demonstrate a shift in the lung microbiota towards Proteobacteria, the effects of traffic generated emissions on lung microbiota profiles have not been well-characterized. Thus, we investigated the hypothesis that exposure to traffic-generated emissions can alter lung microbiota and immune defenses. Since a large population of the Western world consumes a diet rich in fats, we sought to investigate the synergistic effects of mixed vehicle emissions and high-fat diet consumption. We exposed 3-month-old male C57Bl/6 mice placed either on regular chow (LF) or a high-fat (HF: 45% kcal fat) diet to mixed emissions (ME: 30 µg PM/m³ gasoline engine emissions+70 µg PM/m³ diesel engine emissions) or filtered air (FA) for 6 h/d, 7 d/wk for 30 days. Levels of pulmonary immunoglobulins IgA, IgG, and IgM were analyzed by ELISA, and lung microbial profiling was done using qPCR and Illumina 16 S sequencing. We observed a significant decrease in lung IgA in the ME-exposed animals, compared to the FA-exposed animals, both fed a HF diet. Our results also revealed a significant decrease in lung IgG in the ME-exposed animals both on the LF diet and HF diet, in comparison to the FA-exposed animals. We also observed an expansion of Enterobacteriaceae belonging to the Proteobacteria phylum in the ME-exposed groups on the HF diet. Collectively, we show that the combined effects of ME and HF diet result in decreased immune surveillance and lung bacterial dysbiosis, which is of significance in lung diseases.

Canonical WNT pathway is activated in the airway epithelium in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a devastating lung disease, mainly due to cigarette smoking, which represents the third cause of mortality worldwide. The mechanisms driving its epithelial salient features remain largely elusive. We aimed to evaluate the activation and the role of the canonical, β-catenin-dependant WNT pathway in the airway epithelium from COPD patients.

METHODS

The WNT/β-catenin pathway was first assessed by WNT-targeted RNA sequencing of the air/liquid interface-reconstituted bronchial epithelium from COPD and control patients. Airway expression of total and active β-catenin was assessed in lung sections, as well as WNT components in laser-microdissected airway epithelium. Finally, we evaluated the role of WNT at the bronchial epithelial level by modulating the pathway in the reconstituted COPD epithelium.

FINDINGS

We show that the WNT/β-catenin pathway is upregulated in the COPD airway epithelium as compared with that of non-smokers and control smokers, in targeted RNA-sequencing of in vitro reconstituted airway epithelium, and in situ in lung tissue and laser-microdissected epithelium. Extrinsic activation of this pathway in COPD-derived airway epithelium inhibited epithelial differentiation, polarity and barrier function, and induced TGF-β-related epithelial-to-mesenchymal transition (EMT). Conversely, canonical WNT inhibition increased ciliated cell numbers, epithelial polarity and barrier function, whilst inhibiting EMT, thus reversing COPD features.

INTERPRETATION

In conclusion, the aberrant reactivation of the canonical WNT pathway in the adult airway epithelium recapitulates the diseased phenotype observed in COPD patients, suggesting that this pathway or its downstream effectors could represent a future therapeutic target.

FUNDING

This study was supported by the Fondation Mont-Godinne, the FNRS and the WELBIO.

Lung immunoglobulin A immunity dysregulation in cystic fibrosis

BACKGROUND

In cystic fibrosis (CF), recurrent infections suggest impaired mucosal immunity but whether production of secretory immunoglobulin A (S-IgA) is impaired remains elusive. S-IgA is generated following polymeric immunoglobulin receptor (pIgR)-mediated transepithelial transport of dimeric (d-)IgA and represents a major defence through neutralisation of inhaled pathogens like Pseudomonas aeruginosa (Pa).

METHODS

Human lung tissue (n = 74), human sputum (n = 118), primary human bronchial epithelial cells (HBEC) (cultured in air-liquid interface) (n = 19) and mouse lung tissue and bronchoalveolar lavage were studied for pIgR expression, IgA secretion and regulation.

FINDINGS

Increased epithelial pIgR immunostaining was observed in CF lung explants, associated with more IgA-producing plasma cells, sputum and serum IgA, especially Pa-specific IgA. In contrast, pIgR and IgA transport were downregulated in F508del mice, CFTR-inhibited HBEC, and CF HBEC. Moreover, the unfolded protein response (UPR) due to F508del mutation, inhibited IgA transport in Calu-3 cells. Conversely, pIgR expression and IgA secretion were strongly upregulated following Pa lung infection in control and F508del mice, through an inflammatory host response involving interleukin-17.

INTERPRETATION

A complex regulation of IgA secretion occurs in the CF lung, UPR induced by CFTR mutation/dysfunction inhibiting d-IgA transcytosis, and Pa infection unexpectedly unleashing this secretory defence mechanism.

FUNDING

This work was supported by the Forton's grant of the King Baudouin's Foundation, Belgium, the Fondazione Ricerca Fibrosi Cistica, Italy, and the Fonds National de la Recherche Scientifique, Belgium.

Low serum IgA and airway injury in World Trade Center-exposed firefighters: a 17-year longitudinal study

Serum IgA ≤70 mg/dL (low IgA) is associated with exacerbations of chronic obstructive pulmonary disease. The association of low IgA with longitudinal lung function is poorly defined. This study included 917 World Trade Center (WTC)-exposed firefighters with longitudinal spirometry measured between September 2001 and September 2018 and IgA measured between October 2001 and March 2002. Low IgA, compared with IgA >70 mg/dL, was associated with lower forced expiratory volume in 1 s (FEV1) % predicted in the year following 11 September 2001 (94.1% vs 98.6%, p<0.001), increased risk of FEV1/FVC <0.70 (HR 3.8, 95% CI 1.6 to 8.8) and increased antibiotic treatment (22.5/100 vs 11.6/100 person-years, p=0.002). Following WTC exposure, early IgA ≤70 mg/dL was associated with worse lung function and increased antibiotic treatment.

Bronchial Epithelial IgA Secretion Is Impaired in Asthma. Role of IL-4/IL-13

RATIONALE

Asthma is associated with increased lung IgE production, but whether the secretory IgA system is affected in this disease remains unknown.

OBJECTIVES

We explored mucosal IgA transport in human asthma and its potential regulation by T-helper cell type 2 inflammation.

METHODS

Bronchial biopsies from asthma and control subjects were assayed for bronchial epithelial polymeric immunoglobulin receptor (pIgR) expression and correlated to T-helper cell type 2 biomarkers. Bronchial epithelium reconstituted in vitro from these subjects, on culture in air-liquid interface, was assayed for pIgR expression and regulation by IL-4/IL-13.

MEASUREMENTS AND MAIN RESULTS

Downregulation of pIgR protein was observed in the bronchial epithelium from patients with asthma (P = 0.0002 vs. control subjects). This epithelial defect was not observed ex vivo in the cultured epithelium from patients with asthma. Exogenous IL-13 and IL-4 could inhibit pIgR expression and IgA transcytosis. Mechanistic experiments showed that autocrine transforming growth factor-β mediates the IL-4/IL-13 effect on the pIgR, with a partial contribution of upregulated transforming growth factor-α/epidermal growth factor receptor.

CONCLUSIONS

This study shows impaired bronchial epithelial pIgR expression in asthma, presumably affecting secretory IgA-mediated frontline defense as a result of type 2 immune activation of the transforming growth factor pathway.

The Role of the Polymeric Immunoglobulin Receptor and Secretory Immunoglobulins during Mucosal Infection and Immunity

The gastrointestinal tract houses millions of microbes, and thus has evolved several host defense mechanisms to keep them at bay, and prevent their entry into the host. One such mucosal surface defense is the secretion of secretory immunoglobulins (SIg). Secretion of SIg depends on the polymeric immunoglobulin receptor (pIgR), which transports polymeric Ig (IgA or IgM) from the basolateral surface of the epithelium to the apical side. Upon reaching the luminal side, a portion of pIgR, called secretory component (SC) is cleaved off to release Ig, forming SIg. Through antigen-specific and non-specific binding, SIg can modulate microbial communities and pathogenic microbes via several mechanisms: agglutination and exclusion from the epithelial surface, neutralization, or via host immunity and complement activation. Given the crucial role of SIg as a microbial scavenger, some pathogens also evolved ways to modulate and utilize pIgR and SIg to facilitate infection. This review will cover the regulation of the pIgR/SIg cycle, mechanisms of SIg-mediated mucosal protection as well as pathogen utilization of SIg.

Secretory IgA Deficiency in Individual Small Airways Is Associated with Persistent Inflammation and Remodeling

RATIONALE

Maintenance of a surface immune barrier is important for homeostasis in organs with mucosal surfaces that interface with the external environment; however, the role of the mucosal immune system in chronic lung diseases is incompletely understood.

OBJECTIVES

We examined the relationship between secretory IgA (SIgA) on the mucosal surface of small airways and parameters of inflammation and airway wall remodeling in chronic obstructive pulmonary disease (COPD).

METHODS

We studied 1,104 small airways (<2 mm in diameter) from 50 former smokers with COPD and 39 control subjects. Small airways were identified on serial tissue sections and examined for epithelial morphology, SIgA, bacterial DNA, nuclear factor-κB activation, neutrophil and macrophage infiltration, and airway wall thickness.

MEASUREMENTS AND MAIN RESULTS

Morphometric evaluation of small airways revealed increased mean airway wall thickness and inflammatory cell counts in lungs from patients with COPD compared with control subjects, whereas SIgA level on the mucosal surface was decreased. However, when small airways were classified as SIgA intact or SIgA deficient, we found that pathologic changes were localized almost exclusively to SIgA-deficient airways, regardless of study group. SIgA-deficient airways were characterized by (1) abnormal epithelial morphology, (2) invasion of bacteria across the apical epithelial barrier, (3) nuclear factor-κB activation, (4) accumulation of macrophages and neutrophils, and (5) fibrotic remodeling of the airway wall.

CONCLUSIONS

Our findings support the concept that localized, acquired SIgA deficiency in individual small airways of patients with COPD allows colonizing bacteria to cross the epithelial barrier and drive persistent inflammation and airway wall remodeling, even after smoking cessation.

Increased IgA production by B-cells in COPD via lung epithelial interleukin-6 and TACI pathways

Despite their relevance to mucosal defense, production of IgA and the function of lung B-cells remain unknown in chronic obstructive pulmonary disease (COPD). We assessed IgA synthesis in the lungs of COPD (n=28) and control (n=21) patients, and regulation of B-cells co-cultured with in vitro-reconstituted airway epithelium. In COPD lung tissue, synthesis of IgA1 was increased, which led to its accumulation in subepithelial areas. In vitro, the COPD bronchial epithelium imprinted normal human B-cells for increased production of IgA (mainly IgA1) and maturation into CD38(+) plasma cells. These effects were associated with upregulation of TACI (transmembrane activator and CAML interactor) and were observed under resting conditions, while being partly inhibited upon stimulation with cigarette smoke extract. Interleukin (IL)-6 and BAFF (B-cell activating factor)/APRIL (a proliferation-inducing ligand) were upregulated in the COPD epithelium and lung tissue, respectively; the IgA-promoting effect of the COPD bronchial epithelium was inhibited by targeting IL-6 and, to a lower extent, by blocking TACI. These data show that in COPD, the bronchial epithelium imprints B-cells with signals promoting maturation into IgA-producing plasma cells through the action of two epithelial/B-cell axes, namely the IL-6/IL-6 receptor and BAFF-APRIL/TACI pathways, while cigarette smoke partly counteracts this IgA-promoting effect.

Expression and prognostic significance of the polymeric immunoglobulin receptor in esophageal and gastric adenocarcinoma

INTRODUCTION

The polymeric immunoglobulin receptor (PIGR) has been proposed to be a candidate prognostic biomarker in a few cancer forms, and one previous study reported that reduced PIGR expression signifies more aggressive tumours of the distal esophagus and gastroesophageal junction (GEJ). In the present study, we examined the expression, clinicopathological correlates and prognostic significance of PIGR expression in an extended cohort of adenocarcinoma of the upper gastrointestinal tract.

MATERIALS AND METHODS

Immunohistochemical PIGR expression was examined in a consecutive cohort of patients with surgically resected, radio-chemonaive adenocarcinoma of the esophagus, GE-junction and stomach (n = 173), including paired samples of benign-appearing squamous epithelium (n = 51), gastric mucosa (n = 114), Barrett's esophagus (BE) or intestinal metaplasia (IM) (n = 57) and lymph node metastases (n = 75). Non-parametric tests were applied to explore associations between PIGR expression in primary tumours and clinicopathological characteristics. Classification and regression tree analysis was applied for selection of prognostic cut-off. The impact of PIGR expression on overall survival (OS) and recurrence-free survival (RFS) was assessed by Kaplan-Meier analysis and hazard ratios (HR) calculated by adjusted and unadjusted Cox proportional hazards modelling.

RESULTS

PIGR expression was significantly higher in intestinal metaplasia (BE or gastric IM) compared to normal tissues and cancer (p < 0.001). Reduced PIGR expression in primary tumours was significantly associated with more advanced tumour stage (p = 0.002) and inversely associated with involved margins (p = 0.034). PIGR expression did not differ between primary tumours and lymph node metastases. There was no significant difference in PIGR expression between tumours with and without a background of intestinal metaplasia. High PIGR expression was an independent predictor of a prolonged OS (HR = 0.60, 95% CI 0.36-0.99) and RFS (HR = 0.49, 95% CI 0.27-0.90) in patients with radically resected (R0) primary tumours and of an improved RFS (HR = 0.32, 95% CI 0.15-0.69) in curatively treated patients with R0 resection/distant metastasis-free disease.

CONCLUSION

High PIGR expression independently predicts a decreased risk of recurrence and an improved survival in patients with adenocarcinoma of the upper gastrointestinal tract. These findings are of potential clinical relevance and merit further validation.

Bronchial secretory immunoglobulin a deficiency correlates with airway inflammation and progression of chronic obstructive pulmonary disease

RATIONALE

Although airway inflammation can persist for years after smoking cessation in patients with chronic obstructive pulmonary disease (COPD), the mechanisms of persistent inflammation are largely unknown.

OBJECTIVES

We investigated relationships between bronchial epithelial remodeling, polymeric immunoglobulin receptor (pIgR) expression, secretory IgA (SIgA), airway inflammation, and mural remodeling in COPD.

METHODS

Lung tissue specimens and bronchoalveolar lavage were obtained from lifetime nonsmokers and former smokers with or without COPD. Epithelial structural changes were quantified by morphometric analysis. Expression of pIgR was determined by immunostaining and real-time polymerase chain reaction. Immunohistochemistry was performed for IgA, CD4 and CD8 lymphocytes, and cytomegalovirus and Epstein-Barr virus antigens. Total IgA and SIgA were measured by ELISA and IgA transcytosis was studied using cultured human bronchial epithelial cells.

MEASUREMENTS AND MAIN RESULTS

Areas of bronchial mucosa covered by normal pseudostratified ciliated epithelium were characterized by pIgR expression with SIgA present on the mucosal surface. In contrast, areas of bronchial epithelial remodeling had reduced pIgR expression, localized SIgA deficiency, and increased CD4(+) and CD8(+) lymphocyte infiltration. In small airways (<2 mm), these changes were associated with presence of herpesvirus antigens, airway wall remodeling, and airflow limitation in patients with COPD. Patients with COPD had reduced SIgA in bronchoalveolar lavage. Air-liquid interface epithelial cell cultures revealed that complete epithelial differentiation was required for normal pIgR expression and IgA transcytosis.

CONCLUSIONS

Our findings indicate that epithelial structural abnormalities lead to localized SIgA deficiency in COPD airways. Impaired mucosal immunity may contribute to persistent airway inflammation and progressive airway remodeling in COPD.

Mechanisms of action and clinical application of macrolides as immunomodulatory medications

Macrolides have diverse biological activities and an ability to modulate inflammation and immunity in eukaryotes without affecting homeostatic immunity. These properties have led to their long-term use in treating neutrophil-dominated inflammation in diffuse panbronchiolitis, bronchiectasis, rhinosinusitis, and cystic fibrosis. These immunomodulatory activities appear to be polymodal, but evidence suggests that many of these effects are due to inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and nuclear factor kappa B (NF-kappaB) activation. Macrolides accumulate within cells, suggesting that they may associate with receptors or carriers responsible for the regulation of cell cycle and immunity. A concern is that long-term use of macrolides increases the emergence of antimicrobial resistance. Nonantimicrobial macrolides are now in development as potential immunomodulatory therapies.

Dual effect of neutrophils on pIgR/secretory component in human bronchial epithelial cells: role of TGF-beta

Neutrophils have a dual affect on epithelial pIgR/SC, the critical receptor for transcellular routing of mucosal IgA, but mechanisms of pIgR/SC upregulation remain elusive. Requirements of cytokine, redox, and signalling pathways for pIgR/SC production were assessed in human bronchial epithelial (Calu-3) cells cocultured with increasing numbers of blood neutrophils. Increased SC production was observed after incubation for 48 hrs with intermediate neutrophil numbers (1.25 to 2.5 × 10⁶), was favoured by the elastase inhibitor SLPI, and correlated with increased TGF-β production. Exogenous TGF-β stimulated SC production with a maximal effect at 48 hrs and both TGF-β- and neutrophil-driven SC upregulation were dependent on redox balance and p38 MAP-kinase activation. This paper shows that activated neutrophils could upregulate epithelial pIgR/SC production through TGF-β-mediated activation of a redox-sensitive and p38 MAPK-dependent pathway. An imbalance between the two neutrophil-driven opposite mechanisms (SC upregulation and SC degradation) could lead to downregulation of pIgR/SC, as observed in severe COPD.

LL-37 complexation with glycosaminoglycans in cystic fibrosis lungs inhibits antimicrobial activity, which can be restored by hypertonic saline

There is an abundance of antimicrobial peptides in cystic fibrosis (CF) lungs. Despite this, individuals with CF are susceptible to microbial colonization and infection. In this study, we investigated the antimicrobial response within the CF lung, focusing on the human cathelicidin LL-37. We demonstrate the presence of the LL-37 precursor, human cathelicidin precursor protein designated 18-kDa cationic antimicrobial protein, in the CF lung along with evidence that it is processed to active LL-37 by proteinase-3. We demonstrate that despite supranormal levels of LL-37, the lung fluid from CF patients exhibits no demonstrable antimicrobial activity. Furthermore Pseudomonas killing by physiological concentrations of exogenous LL-37 is inhibited by CF bronchoalveolar lavage (BAL) fluid due to proteolytic degradation of LL-37 by neutrophil elastase and cathepsin D. The endogenous LL-37 in CF BAL fluid is protected from this proteolysis by interactions with glycosaminoglycans, but while this protects LL-37 from proteolysis it results in inactivation of LL-37 antimicrobial activity. By digesting glycosaminoglycans in CF BAL fluid, endogenous LL-37 is liberated and the antimicrobial properties of CF BAL fluid restored. High sodium concentrations also liberate LL-37 in CF BAL fluid in vitro. This is also seen in vivo in CF sputum where LL-37 is complexed to glycosaminoglycans but is liberated following nebulized hypertonic saline resulting in increased antimicrobial effect. These data suggest glycosaminoglycan-LL-37 complexes to be potential therapeutic targets. Factors that disrupt glycosaminoglycan-LL-37 aggregates promote the antimicrobial effects of LL-37 with the caveat that concomitant administration of antiproteases may be needed to protect the now liberated LL-37 from proteolytic cleavage.

Clinical research progress in secretory component structure and function

SIgA, which consists of 2 monomer IgA, 1 molecular chain J and a molecular secretory component (SC), plays a critical role and is considered as the first-line defense in the mucosal immunity. As an important part of SIgA, SC is the extracellular cleaved ectodomain of polymeric immunoglobulin receptor (pIgR). SC plays an important role in the formation and transportation of SIgA and SC could also protect the hinge area of SIgA and enhance its anti-infective activity. Therefore, the SC has attracted increasing attention from researchers and great progress has been recently made in its structure and function.

Immune response to allergens in sheep sensitized to house dust mite

Background

House dust mite (HDM) allergens are a major cause of allergic asthma. Most studies using animal models of allergic asthma have used rodents sensitized with the 'un-natural' allergen ovalbumin. It has only recently been recognized that the use of animal models based on HDM provide a more relevant insight into the allergen-induced mechanisms that underpin human allergic disease. We have previously described a sheep model of human allergic asthma that uses Dermatophagoides pteronyssinus HDM. The present study extends our understanding of the immune effects of HDM and the allergens Der p 1 and Der p 2 in the sheep model of asthma.

Methods

Peripheral blood sera from non-sensitized (control) sheep and sheep sensitized to HDM was collected to determine immunoglobulin (Ig) reactivities to HDM, Der p 1 and Der p 2 by ELISA. Bronchoalveolar lavage (BAL) fluid collected following allergen challenge was also assessed for the presence of HDM-specific antibodies. To examine the cellular immune response to HDM allergens, T cell proliferation and cutaneous responses were assessed in sensitized and control sheep.

Results

Strong HDM- and Der p 1-specific IgE, IgG₁, IgG₂ and IgA serum responses were observed in sensitized sheep, while detectable levels of HDM-specific IgG₁ and IgA were seen in BAL fluid of allergen-challenged lungs. In contrast, minimal antibody reactivity was observed to Der p 2. Marked T cell proliferation and late phase cutaneous responses, accompanied by the recruitment of eosinophils, indicates the induction of a cellular and delayed-type hypersensitivity (DTH) type II response by HDM and Der p 1 allergen, but not Der p 2.

Conclusion

This work characterizes the humoral and cellular immune effects of HDM extract and its major constituent allergens in sheep sensitized to HDM. The effects of allergen in HDM-sensitized sheep were detectable both locally and systemically, and probably mediated via enzymatic and immune actions of the major HDM allergen Der p 1. This study extends our understanding of the actions of this important allergen relevant to human allergic asthma and its effects in sheep experimentally sensitized to HDM allergens.

Macrolide antibiotics as immunomodulatory medications: proposed mechanisms of action

Macrolide antibiotics administered in sub-antimicrobial doses improve pulmonary function and decrease exacerbation frequency for persons with diffuse panbronchiolitis or cystic fibrosis. Data also suggest a beneficial effect of macrolide antibiotics in the treatment of steroid dependent asthma. Many potential immunomodulatory effects of macrolide antibiotics have been reported including the ability to down-regulate prolonged inflammation, decreasing airway mucus secretion, inhibiting bacterial biofilm, decreasing the production of reactive oxygen species, inhibiting neutrophil activation and mobilization, accelerating neutrophil apoptosis, and blocking the activation of nuclear transcription factors. Macrolides initially decrease, then increase, and have finally a sustained suppression of cytokine secretions from normal human bronchial epithelial cells through inhibition and activation of extracellular signal-regulated kinases (ERK) and then reversibly retard cell proliferation probably through ERK. Consistent with this, macrolide antibiotics possibly reduce mucin production as well as neutrophil migration by interfering with ERK signal transduction.

Tumour necrosis factor-alpha-mediated human polymeric immunoglobulin receptor expression is regulated by both mitogen-activated protein kinase and phosphatidylinositol-3-kinase in HT-29 cell line

Human polymeric immunoglobulin receptor (pIgR) is present on the surface of glandular epithelium, and it plays a crucial role in the mucosal immune defence. pIgR expression in HT-29 cells is up-regulated by one of the proinflammatory cytokines, tumour necrosis factor (TNF)-alpha. However, the mechanism used by the TNF-alpha-mediated signalling pathway has not been examined exclusively. To elucidate this mechanism in detail, HT-29 cells were cotreated with TNF-alpha and mitogen-activated protein kinase kinase (MAPKK, also called MEK1) inhibitor, PD98059, and the amount of free secretory component (SC) secreted into the culture medium was measured. The amount of free SC stimulated by TNF-alpha was increased by addition of PD98059. This up-regulation occurred at the transcriptional level. The amount of SC was also up-regulated by addition of TNF-alpha with U0126, an inhibitor of MEK1 and MEK2. Nuclear factor (NF)-kappaB activity and NF-kappaB binding to the kappaB2 site localized upstream of the pIgR gene did not change after coincubation of HT-29 cells with TNF-alpha and PD98059. The expression level of pIgR by TNF-alpha was decreased by LY294002, an inhibitor of phosphatidylinositol-3-kinase (PI3K), at the transcriptional level. Extracellular signal-regulated kinase (ERK)1/2 phosphorylation and NF-kappaB binding to the kappaB2 site were not affected by LY294002 treatment. These data suggest that TNF-alpha-mediated pIgR expression is negatively regulated by ERK pathway, which is independent of NF-kappaB. In addition, decrease of SC production by Ly294002 suggests that the presence of PI3K mediated regulation of SC production.

Grass pollen immunotherapy induces an allergen-specific IgA2 antibody response associated with mucosal TGF-beta expression

Allergen immunotherapy (IT) has long-term efficacy in IgE-mediated allergic rhinitis and asthma. IT has been shown to modify lymphocyte responses to allergen, inducing IL-10 production and IgG Abs. In contrast, a putative role for IgA and local TGF-beta-producing cells remains to be determined. In 44 patients with seasonal rhinitis/asthma, serum IgA1, IgA2, and polymeric (J chain-containing) Abs to the major allergen Phl p 5 were determined by ELISA before and after a 2-year double-blind trial of grass pollen (Phleum pratense) injection IT. Nasal TGF-beta expression was assessed by in situ hybridization. Sera from five IT patients were fractionated for functional analysis of the effects of IgA and IgG Abs on IL-10 production by blood monocytes and allergen-IgE binding to B cells. Serum Phl p 5-specific IgA2 Abs increased after a 2-year treatment (approximately 8-fold increase, p = 0.002) in contrast to IgA1. Increases in polymeric Abs to Phl p 5 (approximately 2-fold increase, p = 0.02) and in nasal TGF-beta mRNA (p = 0.05) were also observed, and TGF-beta mRNA correlated with serum Phl p 5 IgA2 (r = 0.61, p = 0.009). Post-IT IgA fractions triggered IL-10 secretion by monocytes while not inhibiting allergen-IgE binding to B cells as observed with IgG fractions. This study shows for the first time that the IgA response to IT is selective for IgA2, correlates with increased local TGF-beta expression, and induces monocyte IL-10 expression, suggesting that IgA Abs could thereby contribute to the tolerance developed in IT-treated allergic patients.

Impact of the molecular form of immunoglobulin A on functional activity in defense against Streptococcus pneumoniae

Antibodies of the immunoglobulin A (IgA) class react with capsular polysaccharides of Streptococcus pneumoniae and support complement-dependent opsonophagocytosis (OPC) of the organism by phagocytes. We characterized the biologic impact of the molecular forms of human monoclonal capsule-specific IgA (monomeric IgA [mIgA], polymeric IgA [pIgA], and secretory IgA [SIgA]) on OPC and susceptibility to cleavage by IgA1 protease. The efficiency of SIgA in support of OPC of S. pneumoniae was comparable to that of pIgA, and both forms exceeded that of mIgA by a fivefold margin. This structure-function relationship was associated with three factors. First, the avidities, or functional affinities, of both pIgA and SIgA for pneumococcal capsules exceeded those of mIgA. Second, both pIgA and SIgA required less complement to achieve similar levels of bacterial OPC than did mIgA, indicating that secretory component does not hinder the effect of complement. Third, both pIgA and SIgA mediated agglutination of the organism, whereas mIgA did not. All three forms of capsule-specific IgA showed comparable susceptibilities to cleavage and functional inhibition by bacterial IgA1 protease, demonstrating that secretory component does not prevent the proteolytic degradation of IgA1 by IgA1 protease. IgA1 cleavage results in formation of identical Fab fragments for each of the molecular forms, thereby abolishing the contribution of multivalence of pIgA and SIgA. In summary, the polymeric forms of IgA (both pIgA and SIgA) provide a substantial advantage in binding, agglutination, and OPC of the organism.

Endometrial carcinoma biomarker discovery and verification using differentially tagged clinical samples with multidimensional liquid chromatography and tandem mass spectrometry

The utility of differentially expressed proteins discovered and identified in an earlier study (DeSouza, L., Diehl, G., Rodrigues, M. J., Guo, J., Romaschin, A. D., Colgan, T. J., and Siu, K. W. M. (2005) Search for cancer markers from endometrial tissues using differentially labeled tags iTRAQ and cleavable ICAT with multidimensional liquid chromatography and tandem mass spectrometry. J. Proteome Res. 4, 377-386) to discriminate malignant and benign endometrial tissue samples was verified in a 40-sample iTRAQ (isobaric tags for relative and absolute quantitation) labeling study involving normal proliferative and secretory samples and Types I and II endometrial cancer samples. None of these proteins had the sensitivity and specificity to be used individually to discriminate between normal and cancer samples. However, a panel of pyruvate kinase, chaperonin 10, and alpha1-antitrypsin achieved the best results with a sensitivity, specificity, predictive value, and positive predictive value of 0.95 each in a logistic regression analysis. In addition, three new potential markers were discovered, whereas two other proteins showed promising trends but were not detected in sufficient numbers of samples to permit statistical validation. Differential expressions of some of these candidate biomarkers were independently verified using immunohistochemistry.

Macrolide antibiotics modulate ERK phosphorylation and IL-8 and GM-CSF production by human bronchial epithelial cells

Macrolide antibiotics decrease proinflammatory cytokine production in airway cells from subjects with chronic airway inflammation. However, in subjects with chronic obstructive pulmonary disease, short-term azithromycin (AZM) therapy causes a transient early increase in the blood neutrophil oxidative burst followed by a decrease in inflammatory markers with longer administration. We studied the effects of clarithromycin (CAM) and AZM on proinflammatory cytokine production from normal human bronchial epithelial (NHBE) cells. CAM decreased IL-8 over the first 6 h and then significantly increased interleukin (IL)-8 at 12–72 h after exposure ( P < 0.0001). AZM also increased IL-8 at 24 and 48 h, and CAM increased granulocyte-macrophage colony-stimulating factor at 48 h. In the presence of LPS, both CAM and AZM dose-dependently increased IL-8 secretion over 24 h, but after 5 days of exposure to 10 μg/ml CAM there is suppression of IL-8 ( P < 0.001). PD-98059, an inhibitor of MAP kinase/ERK kinase, inhibited CAM-induced IL-8 ( P < 0.0001) and GM-CSF ( P < 0.01) release. The p38 MAP kinase inhibitor SB-203580 increased CAM-induced IL-8 release ( P < 0.001), and the c-jun NH2-terminal kinase inhibitor SP-600125 had no effect on IL-8. At 120 min and 6 h, CAM increased phospho-ERK1/2 (pERK) but not phospho-p38 or phospho-JNK. Over the first 90 min, CAM at 10 μg/ml inhibited pERK and then increased pERK in parallel with measured IL-8 secretion. After daily CAM exposure for 5 days, both IL-8 and pERK returned to baseline. The p38 MAP kinase inhibitor, SB-203580 increased ERK phosphorylation and IL-8 secretion. These results suggest that macrolide antibiotics can differentially modulate proinflammatory cytokine secretion in NHBE cells, in part through ERK.

The polymeric immunoglobulin receptor: bridging innate and adaptive immune responses at mucosal surfaces

Secretory antibodies of the immunoglobulin A (IgA) class form the first line of antigen-specific immune protection against inhaled, ingested, and sexually transmitted pathogens and antigens at mucosal surfaces. Epithelial transcytosis of polymeric IgA (pIgA) is mediated by the polymeric immunoglobulin receptor (pIgR). At the apical surface, the extracellular ligand-binding region of pIgR, known as secretory component (SC), is cleaved and released in free form or as a component of secretory IgA (SIgA). SC has innate anti-microbial properties, and it protects SIgA from proteolytic degradation. Expression of pIgR is regulated by microbial products through Toll-like receptor signaling and by host factors such as cytokines and hormones. Recent studies of the structure of the extracellular ligand-binding domain of pIgR have revealed mechanisms by which it binds pIgA and other ligands. During transcytosis, pIgA has been shown to neutralize pathogens and antigens within intracellular vesicular compartments. The recent identification of disease-associated polymorphisms in human pIgR near the cleavage site may help to unravel the mystery of how pIgR is cleaved to SC. The identification of novel functions for SC and SIgA has expanded our view of the immunobiology of pIgR, a key component of the mucosal immune system that bridges innate and adaptive immune defense.

Low levels of tissue inhibitors of metalloproteinases with a high matrix metalloproteinase-9/tissue inhibitor of metalloproteinase-1 ratio are present in tracheal aspirate fluids of infants who develop chronic lung disease

OBJECTIVE

The pathogenesis of chronic lung disease (CLD) involves inflammation with proteolytic damage to lung extracellular matrix. Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that, acting in concert with their tissue inhibitors, tightly orchestrate extracellular matrix morphogenesis and repair after injury. Imbalances in their levels relative to that of their inhibitors have been implicated in diseases characterized by matrix disruption and remodeling. We investigated the possibility that imbalances in MMP-9 and MMP-2 relative to their tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2, respectively, in tracheal aspirates of preterm infants may be involved in the development of CLD.

METHODS

Serial tracheal aspirates collected from birth until extubation in 49 ventilated preterm infants (24-32 weeks' gestations) were analyzed for MMP-2, MMP-9, TIMP-1, and TIMP-2. Data normalized by TA values of free secretory component of immunoglobulin A were compared for CLD (n = 22) versus no CLD (n = 27). Also, known clinical predictors of CLD (gestational age, birth weight, and sex) were assessed for both groups. Association of predictors with the outcome CLD was assessed by logistic regression.

RESULTS

Mean gestational age was lower in CLD infants, but birth weight and gender were comparable for both groups. CLD infants had significantly lower TIMP-1 level with higher MMP-9/TIMP-1 ratio during the first 2 weeks of life and low TIMP-2 and MMP-2 levels during the first 3 days of life compared with no-CLD infants. Logistic regression analysis indicated that the findings are predictive of CLD.

CONCLUSIONS

We conclude that low tracheal aspirate levels of TIMPs, with a high MMP-9/TIMP-1 ratio early in life, are associated with subsequent development of CLD.

Free secretory component from cystic fibrosis sputa displays the cystic fibrosis glycosylation phenotype

Secretory IgA contributes to humoral defense mechanisms against pathogens targeting mucosal surfaces, and secretory component (SC) fulfills multiple roles in this defense. The aims of this study were to quantify total SC and to analyze the form of free SC in sputa from normal subjects, subjects with asthma, and subjects with cystic fibrosis (CF). Significantly higher levels of SC were detected in CF compared with both other groups. Gel filtration chromatography revealed that SC in CF was relatively degraded. Free SC normally binds interleukin (IL)-8 and inhibits its function. However, in CF sputa, IL-8 binding to intact SC was reduced. Analysis of the total carbohydrate content of free SC signified overglycosylation in CF compared with normal subjects and subjects with asthma. Monosaccharide composition analysis of free SC from CF subjects revealed overfucosylation and undersialylation, in agreement with the reported CF glycosylation phenotype. SC binding to IL-8 did not interfere with the binding of IL-8 to heparin, indicating distinct binding sites on IL-8 for negative regulation of function by SC and heparin. We suggest that defective structure and function of SC contribute to the characteristic sustained inflammatory response in the CF airways.