Immunocytochemical localization of surfactant protein D (SP-D) in type II cells, Clara cells, and alveolar macrophages of rat lung

The Immune Modulatory Role of Surfactants in Mycoplasma pneumoniae Infection

Mycoplasma pneumoniae is a prevalent respiratory microbe that causes acute inflammation in the respiratory system. Surfactant proteins (SP), particularly SP-A and SP-D, are essential for the immunological protection against M. pneumoniae infection. Variant SP-A2 may lead to immune reactions, which could account for the variability in clinical manifestations among individuals. Mechanistically, these surfactant proteins may act as candidate receptors, facilitating both the adhesion of M. pneumoniae and internalization of community-acquired respiratory distress syndrome toxin. They also exhibit a high affinity for lipid ligands on the surface of M. pneumoniae membranes via their carbohydrate recognition domains, which aid in the direct clearing of the bacteria. In addition, SP-A and SP-D demonstrated synergistic effects in augmenting the intake and elimination of M. pneumoniae by alveolar macrophages. Furthermore, these surfactant proteins negatively regulate pulmonary inflammation by influencing lymphocyte and dendritic cell activities, reducing airway eosinophilic infiltration, and managing asthma-related inflammatory responses. A thorough understanding of the immunomodulatory roles of surfactant proteins in M. pneumoniae infection will shed light on how homeostasis is preserved during mycoplasma pneumonia and may guide the development of novel therapeutic strategies against this organism.

The expression of the surfactant proteins SP-A and SP-B during postnatal alveolarization of the rat lung

OBJECTIVE

Surfactant-specific proteins (SP) are responsible for the functional and structural integrity as well as for the stabilization of the intra-alveolar surfactant. Morphological lung maturation starts in rat lungs after birth. The aim of this study was to investigate whether the expression of the hydrophilic SP-A and the hydrophobic SP-B is associated with characteristic postnatal changes characterizing morphological lung maturation.

METHODS

Stereological methods were performed on the light microscope. Using immunohistochemical and molecular biological methods (Western Blot, RT-qPCR), the SP-A and SP-B of adult rat lungs and of those with different postnatal developmental stages (3, 7, 14 and 21 days after birth) were characterized.

RESULTS

As signs of alveolarization the total septal surface and volume increased and the septal thickness decreased. The significantly highest relative surface fraction of SP-A labeled alveolar epithelial cells type II (AEII) was found together with the highest relative SP-A gene expression before the alveolarization (3th postnatal day). With the downregulation of SP-A gene expression during and after alveolarization (between postnatal days 7 and 14), the surface fraction of the SP-A labeled AEII also decreased, so they are lowest in adult animals. The surface fraction of SP-B labeled AEII and the SP-B gene expression showed the significantly highest levels in adults, the protein expression increased also significantly at the end of morphological lung maturation. There were no alterations in the SP-B expression before and during alveolarization until postnatal day 14. The protein expression as well as the gene expression of SP-A and SP-B correlated very well with the total surface of alveolar septa independent of the postnatal age.

CONCLUSION

The expression of SP-A and SP-B is differentially associated with morphological lung maturation and correlates with increased septation of alveoli as indirect clue for alveolarization.

Malondialdehyde acetaldehyde adduction of surfactant protein D attenuates SARS-CoV-2 spike protein binding and virus neutralization

BACKGROUND

Over 43% of the world's population regularly consumes alcohol. Although not commonly known, alcohol can have a significant impact on the respiratory environment. Living in the time of the COVID-19 pandemic, alcohol misuse can have a particularly deleterious effect on SARS-CoV-2-infected individuals and, in turn, the overall healthcare system. Patients with alcohol use disorders have higher odds of COVID-19-associated hospitalization and mortality. Even though the detrimental role of alcohol on COVID-19 outcomes has been established, the underlying mechanisms are yet to be fully understood. Alcohol misuse has been shown to induce oxidative damage in the lungs through the production of reactive aldehydes such as malondialdehyde and acetaldehyde (MAA). MAA can then form adducts with proteins, altering their structure and function. One such protein is surfactant protein D (SPD), which plays an important role in innate immunity against pathogens.

METHODS AND RESULTS

In this study, we examined whether MAA adduction of SPD (SPD-MAA) attenuates the ability of SPD to bind SARS-CoV-2 spike protein, reversing SPD-mediated virus neutralization. Using ELISA, we show that SPD-MAA is unable to competitively bind spike protein and prevent ACE2 receptor binding. Similarly, SPD-MAA fails to inhibit entry of wild-type SARS-CoV-2 virus into Calu-3 cells, a lung epithelial cell line, as well as ciliated primary human bronchial epithelial cells isolated from healthy individuals.

CONCLUSIONS

Overall, MAA adduction of SPD, a consequence of alcohol overconsumption, represents one mechanism of compromised lung innate defense against SARS-CoV-2, highlighting a possible mechanism underlying COVID-19 severity and related mortality in patients who misuse alcohol.

Models using native tracheobronchial mucus in the context of pulmonary drug delivery research: Composition, structure and barrier properties

Mucus covers all wet epithelia and acts as a protective barrier. In the airways of the lungs, the viscoelastic mucus meshwork entraps and clears inhaled materials and efficiently removes them by mucociliary escalation. In addition to physical and chemical interaction mechanisms, the role of macromolecular glycoproteins (mucins) and antimicrobial constituents in innate immune defense are receiving increasing attention. Collectively, mucus displays a major barrier for inhaled aerosols, also including therapeutics. This review discusses the origin and composition of tracheobronchial mucus in relation to its (barrier) function, as well as some pathophysiological changes in the context of pulmonary diseases. Mucus models that contemplate key features such as elastic-dominant rheology, composition, filtering mechanisms and microbial interactions are critically reviewed in the context of health and disease considering different collection methods of native human pulmonary mucus. Finally, the prerequisites towards a standardization of mucus models in a regulatory context and their role in drug delivery research are addressed.

Resolution of multifocal micronodular pneumocyte hyperplasia with everolimus in a patient with tuberous sclerosis complex

A woman with a diagnosis of tuberous sclerosis complex (TSC) presented with TSC2 gene mutation and various manifestations, including epilepsy, renal angiomyolipomas (AML), and pathologically confirmed multifocal micronodular pneumocyte hyperplasia (MMPH). With oral administration of everolimus, a mammalian target of rapamycin (mTOR) inhibitor, MMPH and AML were markedly reduced. Further, after starting treatment with everolimus, serum levels of surfactant protein (SP)-A and SP-D, which reflect type II pneumocyte hyperplasia, decreased to the normal range. At the time of writing of this manuscript, 6 years after starting everolimus, MMPH lesions did not relapse and SP-A/D remained the low levels. This is the first case of everolimus efficacy shown for histologically confirmed MMPH in genetically determined TSC patient, with time course of serum SP-A and SP-D.

Human Surfactant Protein D Binds Spike Protein and Acts as an Entry Inhibitor of SARS-CoV-2 Pseudotyped Viral Particles

Human SP-D is a potent innate immune molecule whose presence at pulmonary mucosal surfaces allows its role in immune surveillance against pathogens. Higher levels of serum SP-D have been reported in the patients with severe acute respiratory syndrome coronavirus (SARS-CoV). Studies have suggested the ability of human SP-D to recognise spike glycoprotein of SARS-CoV; its interaction with HCoV-229E strain leads to viral inhibition in human bronchial epithelial (16HBE) cells. Previous studies have reported that a recombinant fragment of human SP-D (rfhSP-D) composed of 8 Gly-X-Y repeats, neck and CRD region, can act against a range of viral pathogens including influenza A Virus and Respiratory Syncytial Virus in vitro, in vivo and ex vivo. In this context, this study was aimed at examining the likely protective role of rfhSP-D against SARS-CoV-2 infection. rfhSP-D showed a dose-responsive binding to S1 spike protein of SARS-CoV-2 and its receptor binding domain. Importantly, rfhSP-D inhibited interaction of S1 protein with the HEK293T cells overexpressing human angiotensin converting enzyme 2 (hACE2). The protective role of rfhSP-D against SARS-CoV-2 infection as an entry inhibitor was further validated by the use of pseudotyped lentiviral particles expressing SARS-CoV-2 S1 protein; ~0.5 RLU fold reduction in viral entry was seen following treatment with rfhSP-D (10 µg/ml). These results highlight the therapeutic potential of rfhSP-D in SARS-CoV-2 infection and merit pre-clinical studies in animal models.

Genetic disorders of the surfactant system: focus on adult disease

Genes involved in the production of pulmonary surfactant are crucial for the development and maintenance of healthy lungs. Germline mutations in surfactant-related genes cause a spectrum of severe monogenic pulmonary diseases in patients of all ages. The majority of affected patients present at a very young age, however, a considerable portion of patients have adult-onset disease. Mutations in surfactant-related genes are present in up to 8% of adult patients with familial interstitial lung disease (ILD) and associate with the development of pulmonary fibrosis and lung cancer.High disease penetrance and variable expressivity underscore the potential value of genetic analysis for diagnostic purposes. However, scarce genotype-phenotype correlations and insufficient knowledge of mutation-specific pathogenic processes hamper the development of mutation-specific treatment options.This article describes the genetic origin of surfactant-related lung disease and presents spectra for gene, age, sex and pulmonary phenotype of adult carriers of germline mutations in surfactant-related genes.

Serum surfactant protein D as a predictive biomarker for the efficacy of pirfenidone in patients with idiopathic pulmonary fibrosis: a post-hoc analysis of the phase 3 trial in Japan

Background

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal disorder with a variable disease course. The recent advancement of antifibrotic therapy has increased the need for reliable and specific biomarkers. This study aimed to assess alveolar epithelial biomarkers as predictors for the efficacy of the antifibrotic drug pirfenidone.

Methods

We conducted a post-hoc analysis of the prospective, multicenter, randomized, placebo-controlled, phase 3 trial of pirfenidone in Japan (total, n = 267; pirfenidone, n = 163; placebo, n = 104). Logistic regression analysis was performed to extract parameters that predicted disease progression, defined by a ≥ 10% relative decline in vital capacity (VC) from baseline and/or death, at week 52. For assessment of serum surfactant protein (SP)-D, SP-A and Krebs von den Lungen (KL)-6, all patients were dichotomized by the median concentration of each biomarker at baseline to the high and low biomarker subgroups. Associations of these concentrations were examined with changes in VC at each time point from baseline up to week 52, along with progression-free survival (PFS). Additionally, the effect of pirfenidone treatment on serial longitudinal concentrations of these biomarkers were evaluated.

Results

In the multivariate logistic regression analysis, body mass index (BMI), %VC and SP-D in the pirfenidone group, and BMI and %VC in the placebo group were indicated as predictors of disease progression. Pirfenidone treatment reduced the decline in VC with statistical significance in the low SP-D and low SP-A subgroups over most of the treatment period, and also prolonged PFS in the low SP-D and low KL-6 subgroups. Furthermore, SP-D levels over time course were reduced in the pirfenidone group from as early as week 8 until the 52-week treatment period compared with the placebo group.

Conclusions

Serum SP-D was the most consistent biomarker for the efficacy of pirfenidone in the cohort trial of IPF. Serial measurements of SP-D might have a potential for application as a pharmacodynamic biomarker.

Trial registration The clinical trial was registered with the Japan Pharmaceutical Information Center (JAPIC) on September 13, 2005 (registration No. JapicCTI-050121; http://Clinicaltrials.jp)

Soluble pattern recognition molecules: Guardians and regulators of homeostasis at airway mucosal surfaces

Maintenance of homeostasis at body barriers that are constantly challenged by microbes, toxins and potentially bioactive (macro)molecules requires complex, highly orchestrated mechanisms of protection. Recent discoveries in respiratory research have shed light on the unprecedented role of airway epithelial cells (AEC), which, besides immune cells homing to the lung, also significantly contribute to host defence by expressing membrane‐bound and soluble pattern recognition receptors (sPRR). Recent evidence suggests that distinct, evolutionary ancient, sPRR secreted by AEC might become activated by usually innocuous proteins, commonly referred to as allergens. We here provide a systematic overview on sPRR detectable in the mucus lining of AEC. Some of them become actively produced and secreted by AECs (like the pentraxins C‐reactive protein and pentraxin 3; the collectins mannose binding protein and surfactant proteins A and D; H‐ficolin; serum amyloid A; and the complement components C3 and C5). Others are elaborated by innate and adaptive immune cells such as monocytes/macrophages and T cells (like the pentraxins C‐reactive protein and pentraxin 3; L‐ficolin; serum amyloid A; and the complement components C3 and C5). Herein we discuss how sPRRs may contribute to homeostasis but sometimes also to overt disease (e.g. airway hyperreactivity and asthma) at the alveolar–air interface.

Serum Amyloid A in Stable COPD Patients is Associated with the Frequent Exacerbator Phenotype

Background

We sought to determine whether circulating inflammatory biomarkers were associated with the frequent exacerbator phenotype in stable COPD patients ie, those with two or more exacerbations in the previous year.

Methods

Eighty-eight stable, severe, COPD patients (4 females) were assessed for exacerbation frequency, pulmonary function, fraction of expired nitric oxide (F_ENO); inflammatory variables were measured in venous blood. Logistic regression assessed associations between the frequent exacerbator phenotype and systemic inflammation.

Results

Compared with infrequent exacerbators, frequent exacerbators (n=10; 11.4%) had greater serum concentration (median (25th-75th quartile)) of serum amyloid A (SAA; 134 (84–178) vs 71 (38–116) ng/mL; P=0.024), surfactant protein D (SP-D; 15.6 (9.0–19.3) vs 8.5 (3.6–14.9) ng/mL; P=0.049) and interleukin-4 (IL-4; 0.12 (0.08–1.44) vs 0.03 (0.01–0.10) pg/mL; P=0.001). SAA, SP-D and IL-4 were not significantly correlated with FEV₁%predicted or FVC %predicted. After adjusting for sex, age, BMI, FEV₁/FVC and smoking pack-years, only SAA remained independently associated with the frequent exacerbator phenotype (OR 1.49[1.09–2.04]; P=0.012). The odds of being a frequent exacerbator was 18-times greater in the highest SAA quartile (≥124.1 ng/mL) than the lowest SAA quartile (≤44.1 ng/mL) (OR 18.34[1.30–258.81]; P=0.031), and there was a significant positive trend of increasing OR with increasing SAA quartile (P=0.008). For SAA, the area under the receiver operating characteristic curve was 0.721 for identification of frequent exacerbators; an SAA cut-off of 87.0 ng/mL yielded an 80% sensitivity and 61.5% specificity.

Conclusion

In stable COPD patients, SAA was independently associated with the frequent exacerbator phenotype, suggesting that SAA may be a useful serum biomarker to inform progression or management in COPD.

Neonatal endotoxin stimulation is associated with a long-term bronchiolar epithelial expression of innate immune and anti-allergic markers that attenuates the allergic response

Allergic asthma is the most common phenotype of the pathology, having an early-onset in childhood and producing a Th2-driven airways remodeling process that leads to symptoms and pathophysiological changes. The avoidance of aeroallergen exposure in early life has been shown to prevent asthma, but without repeated success and with the underlying preventive mechanisms at the beginning of asthma far to be fully recognized. In the present study, we aimed to evaluate if neonatal LPS-induced boost in epithelial host defenses contribute to prevent OVA-induced asthma in adult mice. To this, we focused on the response of bronchiolar club cells (CC), which are highly specialized in maintaining the epithelial homeostasis in the lung. In these cells, neonatal LPS administration increased the expression of TLR4 and TNFα, as well as the immunodulatory/antiallergic proteins: club cell secretory protein (CCSP) and surfactant protein D (SP-D). LPS also prevented mucous metaplasia of club cells and reduced the epidermal growth factor receptor (EGFR)-dependent mucin overproduction, with mice displaying normal breathing patterns after OVA challenge. Furthermore, the overexpression of the epithelial Th2-related molecule TSLP was blunted, and normal TSLP and IL-4 levels were found in the bronchoalveolar lavage. A lower eosinophilia was detected in LPS-pretreated mice, along with an increase in phagocytes and regulatory cells (CD4+CD25+FOXP3+ and CD4+IL-10+), together with higher levels of IL-12 and TNFα. In conclusion, our study demonstrates stable asthma-preventive epithelial effects promoted by neonatal LPS stimulation, leading to the presence of regulatory cells in the lung. These anti-allergic dynamic mechanisms would be overlaid in the epithelium, favored by an adequate epidemiological environment, during the development of asthma.

Collectins: Innate Immune Pattern Recognition Molecules

Collectins are collagen-containing C-type (calcium-dependent) lectins which are important pathogen pattern recognising innate immune molecules. Their primary structure is characterised by an N-terminal, triple-helical collagenous region made up of Gly-X-Y repeats, an a-helical coiled-coil trimerising neck region, and a C-terminal C-type lectin or carbohydrate recognition domain (CRD). Further oligomerisation of this primary structure can give rise to more complex and multimeric structures that can be seen under electron microscope. Collectins can be found in serum as well as in a range of tissues at the mucosal surfaces. Mannanbinding lectin can activate the complement system while other members of the collectin family are extremely versatile in recognising a diverse range of pathogens via their CRDs and bring about effector functions designed at the clearance of invading pathogens. These mechanisms include opsonisation, enhancement of phagocytosis, triggering superoxidative burst and nitric oxide production. Collectins can also potentiate the adaptive immune response via antigen presenting cells such as macrophages and dendritic cells through modulation of cytokines and chemokines, thus they can act as a link between innate and adaptive immunity. This chapter describes the structure-function relationships of collectins, their diverse functions, and their interaction with viruses, bacteria, fungi and parasites.

Frequent appearance of club cell (Clara cell)-like cells as a histological marker for ALK-positive lung adenocarcinoma

Anaplastic lymphoma kinase-rearranged (ALK⁺ ) lung cancers show characteristic histological features, such as solid signet ring cell patterns and mucinous cribriform patterns; however, these features are not always observed in ALK⁺ lung cancers. We noticed that club cell (Clara cell)-like cells (CLCs) were frequently present in the papillary portion of ALK⁺ lung adenocarcinomas. In this study, we investigated the importance of CLCs in papillary patterns of ALK⁺ lung cancers. We compared the histological features of 18 ALK⁺ cases with 62 control cases (22 epidermal growth factor receptor-positive (EGFR⁺ ) and 40 ALK- and EGFR-negative (ALK^- /EGFR^- ) cases). The present study analyzed presence of papillary pattern, proportion of papillary pattern area, presence of micropapillary pattern, frequency of CLCs and lengths of snout. The frequency of CLCs in ALK⁺ cases was significantly higher than that in EGFR⁺ cases and ALK^- /EGFR^- cases. Micropapillary pattern was more frequently observed in ALK⁺ cases than that in ALK^- /EGFR^- cases (P < 0.001). The present study indicated that the high frequency of CLCs in papillary patterns was significantly associated with ALK⁺ cases. When solid signet ring cell patterns and mucinous cribriform patterns are absent, the high frequency of CLCs in papillary adenocarcinoma could be a useful histological marker for ALK⁺ lung cancers.

Surfactant Protein D Is Altered in Experimental Malaria-Associated Acute Lung Injury/Acute Respiratory Distress Syndrome

Surfactant protein D (SP-D) is in the collectin family of C-type lectins and plays an important role in the regulation of inflammation and the innate immune defense against pathogens. This protein has been proposed as a biomarker for acute lung injury. However, the expression of SP-D in the lung and the circulating levels of SP-D during malaria infection have received limited attention. Therefore, the aim of this study was to determine the location and expression of the SP-D protein in lung tissue and to measure the plasma level of SP-D in experimental malaria-associated acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Malaria-infected mice induced by Plasmodium berghei ANKA were classified into two groups, namely, the ALI/ARDS and non-ALI/ARDS groups, according to lung histopathology. The lungs of uninfected mice were used as a control group. The location and expression of SP-D in the lung tissues were investigated by immunohistochemical staining and Western blot analysis. In addition, the level of SP-D in plasma and lung homogenate was measured by an enzyme-linked immunosorbent assay. Immunohistochemical staining of SP-D was significantly increased in the lung tissues of the malaria-infected mice in the ALI/ARDS group compared with that in the malaria-infected mice in the non-ALI/ARDS group and the mice in the control group (p < 0.05). The levels of SP-D in the plasma and lung homogenate were significantly increased in the malaria-infected mice in the ALI/ARDS group compared with those in the malaria-infected mice in the non-ALI/ARDS group and the mice in the control group (p < 0.05). There was a significant positive correlation between SP-D in the plasma and SP-D in the lung homogenate (r _s = 0.900, p = 0.037). In conclusion, this study demonstrated increased expression levels of SP-D in the lung tissue and high levels of plasma SP-D in the malaria-infected mice with ALI/ARDS compared with those in the mice in the other groups. The current study supports that the elevation of the plasma SP-D level may provide useful biological confirmation of the diagnosis of ALI/ARDS during malaria infection.

Human SP-D Acts as an Innate Immune Surveillance Molecule Against Androgen-Responsive and Androgen-Resistant Prostate Cancer Cells

Surfactant Protein D (SP-D), a pattern recognition innate immune molecule, has been implicated in the immune surveillance against cancer. A recent report showed an association of decreased SP-D expression in human prostate adenocarcinoma with an increased Gleason score and severity. In the present study, the SP-D expression was evaluated in primary prostate epithelial cells (PrEC) and prostate cancer cell lines. LNCaP, an androgen dependent prostate cancer cell line, exhibited significantly lower mRNA and protein levels of SP-D than PrEC and the androgen independent cell lines (PC3 and DU145). A recombinant fragment of human SP-D, rfhSP-D, showed a dose and time dependent binding to prostate cancer cells via its carbohydrate recognition domain. This study, for the first time, provides evidence of significant and specific cell death of tumor cells in rfhSP-D treated explants as well as primary tumor cells isolated from tissue biopsies of metatstatic prostate cancer patients. Viability of PrEC was not altered by rfhSP-D. Treated LNCaP (p53+/+) and PC3 (p53 -/-) cells exhibited reduced cell viability in a dose and time dependent manner and were arrested in G2/M and G1/G0 phase of the cell cycle, respectively. rfhSP-D treated LNCaP cells showed a significant upregulation of p53 whereas a significant downregulation of pAkt was observed in both PC3 and LNCaP cell lines. The rfhSP-D-induced apoptosis signaling cascade involved upregulation of Bax:Bcl2 ratio, cytochrome c and cleaved products of caspase 7. The study concludes that rfhSP-D induces apoptosis in prostate tumor explants as well as in androgen dependent and independent prostate cancer cells via p53 and pAkt pathways.

Surfactant Protein D in Respiratory and Non-Respiratory Diseases

Surfactant protein D (SP-D) is a multimeric collectin that is involved in innate immune defense and expressed in pulmonary, as well as non-pulmonary, epithelia. SP-D exerts antimicrobial effects and dampens inflammation through direct microbial interactions and modulation of host cell responses via a series of cellular receptors. However, low protein concentrations, genetic variation, biochemical modification, and proteolytic breakdown can induce decomposition of multimeric SP-D into low-molecular weight forms, which may induce pro-inflammatory SP-D signaling. Multimeric SP-D can decompose into trimeric SP-D, and this process, and total SP-D levels, are partly determined by variation within the SP-D gene, SFTPD. SP-D has been implicated in the development of respiratory diseases including respiratory distress syndrome, bronchopulmonary dysplasia, allergic asthma, and chronic obstructive pulmonary disease. Disease-induced breakdown or modifications of SP-D facilitate its systemic leakage from the lung, and circulatory SP-D is a promising biomarker for lung injury. Moreover, studies in preclinical animal models have demonstrated that local pulmonary treatment with recombinant SP-D is beneficial in these diseases. In recent years, SP-D has been shown to exert antimicrobial and anti-inflammatory effects in various non-pulmonary organs and to have effects on lipid metabolism and pro-inflammatory effects in vessel walls, which enhance the risk of atherosclerosis. A common SFTPD polymorphism is associated with atherosclerosis and diabetes, and SP-D has been associated with metabolic disorders because of its effects in the endothelium and adipocytes and its obesity-dampening properties. This review summarizes and discusses the reported genetic associations of SP-D with disease and the clinical utility of circulating SP-D for respiratory disease prognosis. Moreover, basic research on the mechanistic links between SP-D and respiratory, cardiovascular, and metabolic diseases is summarized. Perspectives on the development of SP-D therapy are addressed.

Immunohistochemical study on the distribution of β-defensin 1 and β-defensin 2 throughout the respiratory tract of healthy rats

The distributions of β-defensin 1 and 2 in secretory host defense system throughout respiratory tract of healthy rats were immunohistochemically investigated. In the nasal epithelium, a large number of non-ciliated and non-microvillous cells (NCs) were immunopositive for both β-defensin 1 and 2, whereas a small number of goblet cells (GCs) were immunopositive only for β-defensin 1. Beta-defensin 2-immunopositive GCs were few. In the nasal glands, a small number of acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the laryngeal and tracheal epithelia, a very few NCs and GCs were immunopositive for both β-defensins. In laryngeal and tracheal glands, a very few acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the extra-pulmonary bronchus, a small number of NCs were immunopositive for both β-defensins. A small number of GCs were immunopositive for β-defensin 1, whereas few GCs were immunopositive for β-defensin 2. From the intra-pulmonary bronchus to alveoli, a very few or no epithelial cells were immunopositive for both β-defensins. In the mucus and periciliary layers, β-defensin 1 was detected from the nose to the extra-pulmonary bronchus, whereas β-defensin 2 was weakly detected only in the nose and the larynx. These findings suggest that the secretory sources of β-defensin 1 and 2 are mainly distributed in the nasal mucosa and gradually decrease toward the caudal airway in healthy rats.

Surfactant protein D is a causal risk factor for COPD: results of Mendelian randomisation

Surfactant protein D (SP-D) is produced primarily in the lung and is involved in regulating pulmonary surfactants, lipid homeostasis and innate immunity. Circulating SP-D levels in blood are associated with chronic obstructive pulmonary disease (COPD), although causality remains elusive.In 4061 subjects with COPD, we identified genetic variants associated with serum SP-D levels. We then determined whether these variants affected lung tissue gene expression in 1037 individuals. A Mendelian randomisation framework was then applied, whereby serum SP-D-associated variants were tested for association with COPD risk in 11 157 cases and 36 699 controls and with 11 years decline of lung function in the 4061 individuals.Three regions on chromosomes 6 (human leukocyte antigen region), 10 (SFTPD gene) and 16 (ATP2C2 gene) were associated with serum SP-D levels at genome-wide significance. In Mendelian randomisation analyses, variants associated with increased serum SP-D levels decreased the risk of COPD (estimate -0.19, p=6.46×10^-03) and slowed the lung function decline (estimate=0.0038, p=7.68×10^-3).Leveraging genetic variation effect on protein, lung gene expression and disease phenotypes provided novel insights into SP-D biology and established a causal link between increased SP-D levels and protection against COPD risk and progression. SP-D represents a very promising biomarker and therapeutic target for COPD.

Tsp1 promotes alveolar stem cell proliferation and its down-regulation relates to lung inflammation in intralobar pulmonary sequestration

An aberrant systemic artery supply results in recurrent infections in the abnormal lung lobe of intralobar pulmonary sequestration (ILS). The mechanisms underlying such persistent inflammation are unknown. Here, we hypothesize that alteration of an endothelial cell niche for alveolar epithelial cells results in the impaired proliferation potential of alveolar progenitor cells, leading to the defective defense mechanism in intralobar pulmonary sequestration. Paraffin sections of lung tissues from patients with intralobar pulmonary sequestration or from healthy controls were collected for analysis of alveolar epithelial alterations in intralobar pulmonary sequestration by quantitative RT-PCR or immunofluorescent staining. Differential transcripts were identified between human pulmonary artery endothelial cells and human aortic endothelial cells by microarray. Validation of microarray data by quantitative PCR analysis indicated that thrombospondin-1 expression level is low in near-lesion part but high in lesion part of ILS lobe as compared to healthy controls. In vitro 3-D matrigel culture was adopted to evaluate the regulation of alveolar progenitor cells by thrombospondin-1 and CD36. We found that the proliferative potential of alveolar type 2 stem/progenitor cells was impaired in intralobar pulmonary sequestration. Mechanistically, we discovered that endothelial thrombospondin-1 promotes alveolar type 2 cell proliferation through the interaction with CD36. These data demonstrate that alveolar stem cells are impaired in the abnormal lobe from patients with intralobar pulmonary sequestration and imply that restoring epithelial integrity can be beneficial for the future treatments of recurrent infections in lung pathologies.

Serum surfactant protein D predicts the outcome of patients with idiopathic pulmonary fibrosis treated with pirfenidone

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a fatal pulmonary disease with poor prognosis. Pirfenidone, the first antifibrotic drug, suppresses the decline in forced vital capacity (FVC) and improves prognosis in some, but not all, patients with IPF; therefore, an indicator for identifying improved outcomes in pirfenidone therapy is desirable. This study aims to clarify whether baseline parameters can be predictors of disease progression and prognosis in patients with IPF treated with pirfenidone.

METHODS

We retrospectively investigated patients with IPF who started treatment with pirfenidone between December 2008 and November 2014 at the Sapporo Medical University Hospital. Patients treated with pirfenidone for ≥6 months were enrolled in this study and were observed until November 2015. We investigated the association of clinical characteristics, pulmonary function test results, and blood examination results at the start of pirfenidone with the outcome of patients.

RESULTS

Sixty patients were included in this study. In multivariate logistic regression analysis, % predicted FVC and serum surfactant protein (SP)-D levels were predictors of a ≥10% decline in FVC in the initial 12 months. In the Cox proportional hazards model, these two factors predicted progression-free survival. Pack-years, % predicted diffusing capacity for carbon monoxide, and SP-D levels predicted overall survival.

CONCLUSIONS

The serum SP-D level was a predictor of disease progression and prognosis in patients with IPF treated with pirfenidone. In addition, this analysis describes the relative usefulness of other clinical parameters at baseline in estimating the prognosis of patients with IPF who are candidates for pirfenidone therapy.

Human amniotic membrane as newly identified source of amniotic fluid pulmonary surfactant

Pulmonary surfactant (PS) reduces surface tension at the air-liquid interface in the alveolar epithelium of the lung, which is required for breathing and for the pulmonary maturity of the developing foetus. However, the origin of PS had never been thoroughly investigated, although it was assumed to be secreted from the foetal developing lung. Human amniotic membrane (hAM), particularly its epithelial cell layer, composes the amniotic sac enclosing the amniotic fluid. In this study, we therefore aimed to investigate a potential contribution of the cellular components of the hAM to pulmonary surfactant found in amniotic fluid. We identified that cells within the native membrane contain lamellar bodies and express all four surfactant proteins as well as ABCA3. Lipidomic profiling by nanoESI – MS/MS revealed the presence of the essential lipid species as found in PS. Also, the biophysical activity of conditioned cell culture supernatant obtained from hAM was tested with captive bubble surfactometry. hAM supernatant showed the ability to reduce surface tension, similar to human PS obtained from bronchoalveolar lavage. This means that hAM produces the essential PS-associated components and can therefore contribute as second potential source of PS in amniotic fluid aside from the foetal lung.

Lung surfactant metabolism: early in life, early in disease and target in cell therapy

Lung surfactant is a complex mixture of lipids and proteins lining the alveolar epithelium. At the air-liquid interface, surfactant lowers surface tension, avoiding alveolar collapse and reducing the work of breathing. The essential role of lung surfactant in breathing and therefore in life, is highlighted by surfactant deficiency in premature neonates, which causes neonatal respiratory distress syndrome and results in early death after birth. In addition, defects in surfactant metabolism alter lung homeostasis and lead to disease. Special attention should be paid to two important key cells responsible for surfactant metabolism: alveolar epithelial type II cells (AE2C) and alveolar macrophages (AM). On the one hand, surfactant deficiency coming from abnormal AE2C function results in high surface tension, promoting alveolar collapse and mechanical stress in the epithelium. This epithelial injury contributes to tissue remodeling and lung fibrosis. On the other hand, impaired surfactant catabolism by AM leads to accumulation of surfactant in air spaces and the associated altered lung function in pulmonary alveolar proteinosis (PAP). We review here two recent cell therapies that aim to recover the activity of AE2C or AM, respectively, therefore targeting the restoring of surfactant metabolism and lung homeostasis. Applied therapies successfully show either transplantation of healthy AE2C in fibrotic lungs, to replace injured AE2C cells and surfactant, or transplantation of bone marrow-derived macrophages to counteract accumulation of surfactant lipid and proteinaceous material in the alveolar spaces leading to PAP. These therapies introduce an alternative treatment with great potential for patients suffering from lung diseases.

Pulmonary surfactant metabolism in the alveolar airspace: Biogenesis, extracellular conversions, recycling

Pulmonary surfactant is a lipid-protein complex that lines and stabilizes the respiratory interface in the alveoli, allowing for gas exchange during the breathing cycle. At the same time, surfactant constitutes the first line of lung defense against pathogens. This review presents an updated view on the processes involved in biogenesis and intracellular processing of newly synthesized and recycled surfactant components, as well as on the extracellular surfactant transformations before and after the formation of the surface active film at the air-water interface. Special attention is paid to the crucial regulation of surfactant homeostasis, because its disruption is associated with several lung pathologies.

The ceramide inhibitor fumonisin B1 mitigates the pulmonary effects of low-dose diesel exhaust inhalation in mice

Recent studies have suggested that inhalation of diesel exhaust (DE), a major source of air pollution, results in pulmonary alterations; however, the effects of DE at low concentrations are poorly understood. Therefore, this study was conducted to elucidate the pulmonary effects of low-level exposure to DE and the potential role of a ceramide de novo biosynthesis inhibitor, fumonisin B1 (FB1) to ameliorate the DE-toxicity. Male C57BL/6J mice underwent 1- or 7-day experiments (4 equal groups/experiment) and were assigned to the control, DE (0.1mg/m(3)), FB1 (6.75mg/kg body weight SC at days 0, 3 and 6) or DE+FB1 groups. DE and/or FB1 treatment had no effect on the expression of Nos2, a biomarker of oxidative stress. Ceramide production in the bronchial epithelial cells and Sphk1 mRNA expression were induced in the lung after the 7-day DE exposure and were partially suppressed by the FB1 treatment. Additionally, the effects of DE on SP-A and SP-D mRNA expression were also suppressed by the FB1 treatment. These results suggest that ceramide and Sphk1 may be sensitive biomarkers for low-level DE-induced pulmonary effects. Collectively, ceramide likely contributes to the DE-induced early stage of airway inflammation, which is considered a potential pulmonary target during low-level DE exposure.

Role of surfactant protein D (SP-D) in innate immunity in the gastric mucosa: evidence of interaction with Helicobacter pylori lipopolysaccharide

Surfactant protein D (SP-D) is a collagenous glycoprotein, a collectin, which functions as a pathogen-associated molecular pattern (PAMP) recognition receptor in the innate immune response. Although originally identified in the lung as a component of surfactant, SP-D also occurs in the gastric mucosa at the luminal surface and within gastric pits of mucus-secreting cells. Infection with the gastroduodenal pathogen Helicobacter pylori up-regulates expression of SP-D in human patients with gastritis, and its influence on colonization has been demonstrated in a Helicobacter SP-D-deficient (SP-D—/ —) mouse model. SP-D binds and agglutinates H. pylori cells in a lectin-specific manner, and has been shown to bind H. pylori lipopolysaccharide. Furthermore, evidence indicates that H. pylori varies LPS O-chain structure to evade SP-D binding which is speculated aids persistence of this chronic infection.

The Role of Surfactant in Lung Disease and Host Defense against Pulmonary Infections

Pulmonary surfactant is essential for life as it lines the alveoli to lower surface tension, thereby preventing atelectasis during breathing. Surfactant is enriched with a relatively unique phospholipid, termed dipalmitoylphosphatidylcholine, and four surfactant-associated proteins, SP-A, SP-B, SP-C, and SP-D. The hydrophobic proteins, SP-B and SP-C, together with dipalmitoylphosphatidylcholine, confer surface tension-lowering properties to the material. The more hydrophilic surfactant components, SP-A and SP-D, participate in pulmonary host defense and modify immune responses. Specifically, SP-A and SP-D bind and partake in the clearance of a variety of bacterial, fungal, and viral pathogens and can dampen antigen-induced immune function of effector cells. Emerging data also show immunosuppressive actions of some surfactant-associated lipids, such as phosphatidylglycerol. Conversely, microbial pathogens in preclinical models impair surfactant synthesis and secretion, and microbial proteinases degrade surfactant-associated proteins. Deficiencies of surfactant components are classically observed in the neonatal respiratory distress syndrome, where surfactant replacement therapies have been the mainstay of treatment. However, functional or compositional deficiencies of surfactant are also observed in a variety of acute and chronic lung disorders. Increased surfactant is seen in pulmonary alveolar proteinosis, a disorder characterized by a functional deficiency of the granulocyte-macrophage colony-stimulating factor receptor or development of granulocyte-macrophage colony-stimulating factor antibodies. Genetic polymorphisms of some surfactant proteins such as SP-C are linked to interstitial pulmonary fibrosis. Here, we briefly review the composition, antimicrobial properties, and relevance of pulmonary surfactant to lung disorders and present its therapeutic implications.

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Proteomic analysis reveals down-regulation of surfactant protein B in murine type II pneumocytes infected with influenza A virus

Infection of type II alveolar epithelial (ATII) cells by influenza A viruses (IAV) correlates with severe respiratory disease in humans and mice. To understand pathogenic mechanisms during IAV infection of ATII cells, murine ATII cells were cultured to maintain a differentiated phenotype, infected with IAV-PR8, which causes severe lung pathology in mice, and proteomics analyses were performed using liquid chromatography-mass spectrometry. PR8 infection increased levels of proteins involved in interferon signaling, antigen presentation, and cytoskeleton regulation. Proteins involved in mitochondrial membrane permeability, energy metabolism, and chromatin formation had reduced levels in PR8-infected cells. Phenotypic markers of ATII cells in vivo were identified, confirming the differentiation status of the cultures. Surfactant protein B had decreased levels in PR8-infected cells, which was confirmed by immunoblotting and immunofluorescence assays. Analysis of ATII cell protein profiles will elucidate cellular processes in IAV pathogenesis, which may provide insight into potential therapies to modulate disease severity.

OSCAR is a receptor for surfactant protein D that activates TNF-α release from human CCR2+ inflammatory monocytes

Surfactant protein D (SP-D) is critical for maintenance of lung homeostasis and provides a first line of defense to pathogens at mucosal surfaces. Polymorphisms in the SP-D-encoding gene SFTPD have been associated with chronic obstructive pulmonary disease and ulcerative colitis. Identification of the immunoreceptors that bind SP-D is essential for understanding its contribution to lung homeostasis and mucosal defense. We located a putative binding motif for the osteoclast-associated receptor (OSCAR) within the SP-D collagenous domain. An OSCAR-Fc fusion protein specifically bound to the collagenous region of recombinant SP-D and captured native SP-D from human bronchoalveolar lavage. OSCAR localized in an intracellular compartment of alveolar macrophages together with SP-D. Moreover, we found OSCAR on the surface of interstitial lung and blood CCR2(+) inflammatory monocytes, which secreted TNF-α when exposed to SP-D in an OSCAR-dependent fashion. OSCAR and SP-D did not exclusively colocalize in lung, as they were also highly expressed in atherosclerotic plaques of human aorta, supporting a role for this interaction in atherosclerosis. Our results identify the OSCAR:SP-D interaction as a potential therapeutic target in chronic inflammatory diseases of the lung as well as other diseases involving tissue accumulation of SP-D, infiltration of inflammatory monocytes, and release of TNF-α.

The roles of direct recognition by animal lectins in antiviral immunity and viral pathogenesis

Lectins are a group of proteins with carbohydrate recognition activity. Lectins are categorized into many families based on their different cellular locations as well as their specificities for a variety of carbohydrate structures due to the features of their carbohydrate recognition domain (CRD) modules. Many studies have indicated that the direct recognition of particular oligosaccharides on viral components by lectins is important for interactions between hosts and viruses. Herein, we aim to globally review the roles of this recognition by animal lectins in antiviral immune responses and viral pathogenesis. The different classes of mammalian lectins can either recognize carbohydrates to activate host immunity for viral elimination or can exploit those carbohydrates as susceptibility factors to facilitate viral entry, replication or assembly. Additionally, some arthropod C-type lectins were recently identified as key susceptibility factors that directly interact with multiple viruses and then facilitate infection. Summarization of the pleiotropic roles of direct viral recognition by animal lectins will benefit our understanding of host-virus interactions and could provide insight into the role of lectins in antiviral drug and vaccine development.

Eosinophil-associated lung diseases. A cry for surfactant proteins A and D help?

Surfactant proteins (SP)-A and SP-D (SP-A/-D) play important roles in numerous eosinophil-dominated diseases, including asthma, allergic bronchopulmonary aspergillosis, and allergic rhinitis. In these settings, SP-A/-D have been shown to modulate eosinophil chemotaxis, inhibit eosinophil mediator release, and mediate macrophage clearance of apoptotic eosinophils. Dysregulation of SP-A/-D function in eosinophil-dominated diseases is also not uncommon. Alterations in serum SP-A/-D levels are associated with disease severity in allergic rhinitis and chronic obstructive pulmonary disease. Furthermore, oligimerization of SP-A/-D, necessary for their proper function, can be perturbed by reactive nitrogen species, which are increased in eosinophilic disease. In this review, we highlight the associations of eosinophilic lung diseases with SP-A and SP-D levels and functions.

Distinct compartmentalization of SP-A and SP-D in the vasculature and lungs of patients with idiopathic pulmonary fibrosis

Background

Surfactant proteins SP-A and SP-D are useful biomarkers in diagnosis, monitoring, and prognosis of idiopathic pulmonary fibrosis (IPF). Despite their high structural homology, their serum concentrations often vary in IPF patients. This retrospective study aimed to investigate distinct compartmentalization of SP-A and SP-D in the vasculature and lungs by bronchoalveolar lavage fluid (BALF)/serum analysis, hydrophilicity and immunohistochemistry.

Methods

We included 36 IPF patients, 18 sarcoidosis (SAR) patients and 20 healthy subjects. Low-speed centrifugal supernatants of BALF (Sup-1) were obtained from each subject. Sera were also collected from each patient. Furthermore, we separated Sup-1 of IPF patients into hydrophilic supernatant (Sup-2) and hydrophobic precipitate (Ppt) by high-speed centrifugation. We measured SP-A and SP-D levels of each sample with the sandwich ELISA technique. We analyzed the change of the BALF/serum level ratios of the two proteins in IPF patients and their hydrophilicity in BALF. The distribution in the IPF lungs was also examined by immunohistochemical staining.

Results

In BALF, SP-A levels were comparable between the groups; however, SP-D levels were significantly lower in IPF patients than in others. Although IPF reduced the BALF/serum level ratios of the two proteins, the change in concentration of SP-D was more evident than SP-A. This suggests a higher disease impact for SP-D. Regarding hydrophilicity, although more than half of the SP-D remained in hydrophilic fractions (Sup-2), almost all of the SP-A sedimented in the Ppt with phospholipids. Hydrophilicity suggests that SP-D migrates into the blood more easily than SP-A in IPF lungs. Immunohistochemistry revealed that SP-A was confined to thick mucus-filling alveolar space, whereas SP-D was often intravascular. This data also suggests that SP-D easily leaks into the bloodstream, whereas SP-A remains bound to surfactant lipids in the alveolar space.

Conclusions

The current study investigated distinct compartmentalization of SP-A and SP-D in the vasculature and lungs. Our results suggest that serum levels of SP-D could reflect pathological changes of the IPF lungs more incisively than those of SP-A.

Surfactant protein D, Club cell protein 16, Pulmonary and activation-regulated chemokine, C-reactive protein, and Fibrinogen biomarker variation in chronic obstructive lung disease

Chronic obstructive pulmonary disease (COPD) is a multifaceted condition that cannot be fully described by the severity of airway obstruction. The limitations of spirometry and clinical history have prompted researchers to investigate a multitude of surrogate biomarkers of disease for the assessment of patients, prediction of risk, and guidance of treatment. The aim of this review is to provide a comprehensive summary of observations for a selection of recently investigated pulmonary inflammatory biomarkers (Surfactant protein D (SP-D), Club cell protein 16 (CC-16), and Pulmonary and activation-regulated chemokine (PARC/CCL-18)) and systemic inflammatory biomarkers (C-reactive protein (CRP) and fibrinogen) with COPD. The relevance of these biomarkers for COPD is discussed in terms of their biological plausibility, their independent association to disease and hard clinical outcomes, their modification by interventions, and whether changes in clinical outcomes are reflected by changes in the biomarker.

Persistence of silver nanoparticles in the rat lung: Influence of dose, size, and chemical composition

Increasing silver nanoparticle (AgNP) use in sprays, consumer products, and medical devices has raised concerns about potential health effects. While previous studies have investigated AgNPs, most were limited to a single particle size or surface coating. In this study, we investigated the effect of size, surface coating, and dose on the persistence of silver in the lung following exposure to AgNP. Adult male rats were intratracheally instilled with four different AgNPs: 20 or 110 nm in size and coated with either citrate or polyvinylpyrrolidone (PVP) at 0.5 or 1.0 mg/kg doses. Silver retention was assessed in the lung at 1, 7, and 21 d post exposure. ICP-MS quantification demonstrated that citrate-coated AgNPs persisted in the lung to 21 d with retention greater than 90%, while PVP-coated AgNP had less than 30% retention. Localization of silver in lung tissue at 1 d post exposure demonstrated decreased silver in proximal airways exposed to 110 nm particles compared with 20 nm AgNPs. In terminal bronchioles 1 d post exposure, silver was localized to surface epithelium but was more prominent in the basement membrane at 7 d. Silver positive macrophages in bronchoalveolar lavage fluid decreased more quickly after exposure to particles coated with PVP. We conclude that PVP-coated AgNPs had less retention in the lung tissue over time and larger particles were more rapidly cleared from large airways than smaller particles. The 20 nm citrate particles showed the greatest effect, increasing lung macrophages even 21 d after exposure, and resulted in the greatest silver retention in lung tissue.

Generation of multiciliated cells in functional airway epithelia from human induced pluripotent stem cells

Despite therapeutic advancement, pulmonary disease still remains a major cause of morbidity and mortality around the world. Opportunities to study human lung disease either in vivo or in vitro are currently limited. Using induced pluripotent stem cells (iPSCs), we generated mature multiciliated cells in a functional airway epithelium. Robust multiciliogenesis occurred when notch signaling was inhibited and was confirmed by (i) the assembly of multiple pericentrin-stained centrioles at the apical surface, (ii) expression of transcription factor forkhead box protein J1, and (iii) presence of multiple acetylated tubulin-labeled cilia projections in individual cells. Clara, goblet, and basal cells were all present, confirming the generation of a complete polarized epithelial-cell layer. Additionally, cAMP-activated and cystic fibrosis transmembrane regulator inhibitor 172-sensitive cystic fibrosis transmembrane regulator currents were recorded in isolated epithelial cells. Our report demonstrating the generation of mature multiciliated cells in respiratory epithelium from iPSCs is a significant advance toward modeling a number of human respiratory diseases in vitro.

Restoration of lung surfactant protein D by IL-6 protects against secondary pneumonia following hemorrhagic shock

OBJECTIVES

To identify novel approaches to improve innate immunity in the lung following trauma complicated by hemorrhagic shock (T/HS) for prevention of nosocomial pneumonia.

METHODS

We developed a rat model of T/HS followed by Pseudomonas aeruginosa (PA) pneumonia to assess the effect of alveolar epithelial cell (AEC) apoptosis, and its prevention by IL-6, on lung surfactant protein (SP)-D protein levels, lung bacterial burden, and survival from PA pneumonia, as well as to determine whether AEC apoptosis is a consequence of the unfolded protein response (UPR). Lung UPR transcriptome analysis was performed on rats subjected to sham, T/HS, and T/HS plus IL-6 protocols. Group comparisons were performed via Kaplan-Meier or ANOVA.

RESULTS

T/HS decreased lung SP-D by 1.8-fold (p < 0.05), increased PA bacterial burden 9-fold (p < 0.05), and increased PA pneumonia mortality by 80% (p < 0.001). IL-6, when provided at resuscitation, normalized SP-D levels (p < 0.05), decreased PA bacterial burden by 4.8-fold (p < 0.05), and prevented all mortality from PA pneumonia (p < 0.001). The UPR transcriptome was significantly impacted by T/HS; IL-6 treatment normalized the T/HS-induced UPR transcriptome changes (p < 0.05).

CONCLUSIONS

Impaired innate lung defense occurs following T/HS and is mediated, in part, by reduction in SP-D protein levels, which, along with AEC apoptosis, may be mediated by the UPR, and prevented by use of IL-6 as a resuscitation adjuvant.

Pulmonary surfactant protein D in first-line innate defence against influenza A virus infections

Influenza A viruses (IAV) cause respiratory tract infections annually associated with excess mortality and morbidity. Nonspecific, innate immune mechanisms play a key role in protection against viral invasion at early stages of infection. A soluble protein present in mucosal secretions of the lung, surfactant protein D (SP-D), is an important component of this initial barrier that helps to prevent and limit IAV infections of the respiratory epithelium. This collagenous C-type lectin binds IAVs and thereby inhibits attachment and entry of the virus but also contributes to enhanced clearance of SP-D-opsonized virus via interactions with phagocytic cells. In addition, SP-D modulates the inflammatory response and helps to maintain a balance between effective neutralization/killing of IAV, and protection against alveolar damage resulting from IAV-induced excessive inflammatory responses. The mechanisms of interaction between SP-D and IAV not only depend on the structure and binding properties of SP-D but also on strain-specific features of IAV, and both issues will be discussed. SP-D from pigs exhibits distinct anti-IAV properties and is discussed in more detail. Finally, the potential of SP-D as a prophylactic and/or therapeutic antiviral agent to protect humans against infections by IAV is discussed.

Characterization of the lung epithelium of wild-type and TLR9(-/-) mice after single and repeated exposures to chicken barn air

Exposure to chicken barn air causes lung injury resulting in lower and upper respiratory symptoms in the poultry workers, and mechanisms of which are not fully understood. The lung injury can initiate modifications such as proliferation of the airway epithelial cells such as Clara cells, type II alveolar (T2) cells and mucus producing goblet cells as part of the innate immune response. Toll-like receptors (TLR) have been suggested to play a role in cell division and proliferation. To understand the effect of TLR9 on Clara cells, T2 and mucus-producing goblet cells, we quantified the numbers of these cells in the lungs of wild-type (WT) and TLR9(-/-) mice exposed to chicken barn air. The mice were exposed for either one day or five or 20 days for 8 h/day. Clara cells and T2 cells were labelled with antibodies, and the mucus cells were identified with Periodic-acid Schiff stain, and quantified in per unit tissue section area. The data show decrease in the number of Clara cells and increase in mucus-producing goblet cells after exposure to chicken barn air in both WT and TLR9(-/-) mice. Numbers of T2 cells increased and decreased in WT and TLR9(-/-) mice, respectively, after exposure to poultry barn air. These data show that exposure to chicken barn air can affect major lung epithelial cells, and allude to the role of TLR9 in regulation of some of these responses.

Segmental allergen challenge alters multimeric structure and function of surfactant protein D in humans

RATIONALE

Surfactant protein D (SP-D), a 43-kD collectin, is synthesized and secreted by airway epithelia as a dodecamer formed by assembly of four trimeric subunits. We have previously shown that the quaternary structure of SP-D can be altered during inflammatory lung injury through its modification by S-nitrosylation, which in turn alters its functional behavior producing a proinflammatory response in effector cells.

OBJECTIVES

We hypothesized that alterations in structure and function of SP-D may occur in humans with acute allergic inflammation.

METHODS

Bronchoalveolar lavage (BAL) fluid was collected from 15 nonsmoking patients with mild intermittent allergic asthma before and 24 hours after segmental provocation with saline, allergen, LPS, and mixtures of allergen and LPS. Structural modifications of SP-D were analyzed by native and sodium dodecyl sulfate gel electrophoresis.

MEASUREMENTS AND MAIN RESULTS

The multimeric structure of native SP-D was found to be disrupted after provocation with allergen or a mixture of allergen and LPS. Interestingly, under reducing conditions, sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that 7 of 15 patients with asthma developed an abnormal cross-linked SP-D band after segmental challenge with either allergen or a mixture of allergen with LPS but not LPS alone. Importantly, patients with asthma with cross-linked SP-D demonstrated significantly higher levels of BAL eosinophils, nitrogen oxides, IL-4, IL-5, IL-13, and S-nitrosothiol-SP-D compared with patients without cross-linked SP-D.

CONCLUSIONS

We conclude that segmental allergen challenge results in changes of SP-D multimeric structure and that these modifications are associated with an altered local inflammatory response in the distal airways.

Serum SP-D levels as a biomarker of lung injury in respiratory syncytial virus bronchiolitis

To evaluate whether SP-D concentration is a useful biomarker of the severity of respiratory syncytial virus (RSV) bronchiolitis, we determined SP-D concentrations in patients with RSV bronchiolitis with or without chronic heart disease. We enrolled 52 patients who had been diagnosed with RSV bronchiolitis and required admission to the hospital at the Department of Pediatrics of Fukushima Medical University School of Medicine from 2004 through 2005. These patients were divided into two groups: Group 1 consisted of patients without any underlying disease and Group 2 consisted of patients with chronic heart disease. These patients were assigned to one of three categories. Stage A consisted of patients without oxygen dosage, Stage B of patients who required oxygen dosage, and Stage C of patients required artificial respiration. We evaluated baseline characteristics, clinical features, and serum SP-D concentration in Group 1, Group 2, and a control group (healthy infants without infection). Mean serum SP-D concentrations in patients with RSV bronchiolitis were higher than those in the control group (125.8 ± 49.3 and 44.2 ± 20.1 ng/ml, respectively). Mean serum SP-D concentration was also higher in Group 2 than in Group 1 patients (160.4 ± 56.4 and 112.3 ± 39.4 ng/ml, respectively). Mean serum SP-D concentrations were higher in Stage C than in Stages A or B patients, and mean serum SP-D concentrations were higher in Stage B than in Stage A. These findings suggest that serum SP-D is associated with the severity of RSV bronchiolitis and that it may be a useful biomarker for the severity of RSV bronchiolitis.

Serum levels of surfactant protein D predict the anti-tumor activity of gefitinib in patients with advanced non-small cell lung cancer

PURPOSE

Gefitinib is an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) that has dramatic effects in selective patients with non-small cell lung cancer (NSCLC). A simple non-invasive method for predicting the efficacy of gefitinib is preferable in clinical settings. In this study, we evaluated prospectively whether surfactant protein-A (SP-A) and -D (SP-D) may be new conventional predictors of the efficacy of gefitinib treatment.

METHODS

We measured serum SP-A and SP-D levels on days 0 and 29 in 40 patients with advanced NSCLC treated with 250 mg gefitinib daily. Eligibility criteria included performance status ≤3, age ≤80 years, and stage IIIB-IV disease. In addition, EGFR mutations were analyzed in 24 patients.

RESULTS

Multivariate analysis showed that favorable progression-free survival (PFS) after gefitinib treatment was associated with adenocarcinoma and high serum SP-D levels before treatment. EGFR mutation analysis of 24 patients showed that 16 patients had exon 19 deletion and/or exon 21 point mutations. EGFR mutations were significantly correlated with response to gefitinib and serum SP-D levels before treatment was significantly high in patients with the EGFR mutations. Serum SP-A levels were not associated with PFS.

CONCLUSIONS

The present study showed that measurement of serum SP-D levels before treatment in patients with NSCLC may be a new surrogate marker for predicting the response to gefitinib.

Long-term stability and circadian variation in circulating levels of surfactant protein D

Surfactant protein D (SP-D) is an oligomeric calcium-dependent lectin with important roles in innate host defence against infectious microorganisms. Several studies have shown that patients with inflammatory lung disease have elevated levels of circulating SP-D, and serum SP-D has been suggested to be used as a biomarker for disease e.g. in COPD. We aimed to investigate the variation of circulating SP-D in healthy individuals in and between days for 6 months. In addition, we studied the SP-D response to a standardized physical exercise programme. SP-D was measured in serum using a 5-layered ELISA technique. We found that circulating SP-D remained constant over a 6-month period. However, during the course of one day SP-D varied significantly. Median SP-D peaked at 10 a.m. at 1009 ng/ml (95% CI: 803-1497), subsequently decreasing to nadir at 10 p.m. at 867 ng/ml (95% CI: 650-1148)(P<0.00005). Median pre-exercise level of SP-D was 746 ng/ml (95% CI: 384-2035), and immediately after cessation of physical activity the median SP-D level was 767 ng/ml (95% CI: 367-1885) (P=0.248). Our findings underscore the importance of standardized blood sampling conditions in future studies on the potential role of SP-D as a biomarker. Importantly, stable measures of systemic SP-D over a prolonged period support that SP-D is suitable for biomarker studies.

Global transcriptional characterization of a mouse pulmonary epithelial cell line for use in genetic toxicology

Prior to its application for in vitro toxicological assays, thorough characterization of a cell line is essential. The present study uses global transcriptional profiling to characterize a lung epithelial cell line (FE1) derived from MutaMouse [White, P.A., Douglas, G.R., Gingerich, J., Parfett, C., Shwed, P., Seligy, V., Soper, L., Berndt, L., Bayley, J., Wagner, S., Pound, K., Blakey, D., 2003. Development and characterization of a stable epithelial cell line from Muta Mouse lung. Environmental and Molecular Mutagenesis 42, 166-184]. Results presented here demonstrate the origin of the FE1 lung cell line as epithelial, presenting both type I and type II alveolar phenotype. An assessment of toxicologically-relevant genes, including those involved in the response to stress and stimuli, DNA repair, cellular metabolism, and programmed cell death, revealed changes in expression of 22-27% of genes in one or more culture type (proliferating and static FE1 cultures, primary epithelial cultures) compared with whole lung isolates. Gene expression analysis at 4 and 24h following benzo(a)pyrene exposure revealed the induction of cyp1a1, cyp1a2, and cyp1b1 in FE1 cells and lung isolates. The use of DNA microarrays for gene expression profiling allows an improved understanding of global, coordinated cellular events arising in cells under different physiological conditions. Taken together, these data indicate that the FE1 cell line is derived from a cell type relevant to toxic responses in vivo, and shows some similarity in response to chemical insult as the original tissue.

Eosinophilic Inclusions in Rat Clara Cells and the Effect of an Inhaled Corticosteroid

Large eosinophilic cytoplasmic inclusions (ECIs) are occasionally seen in untreated rat Clara cells. Following inhalation exposure to a corticosteroid, the number of ECIs was increased. This is the first histopathological description of rat ECIs and attempted characterization by immunohistochemistry, in situ hybridization, and electron microscopy. ECIs were strongly positive for surfactant protein D (SP-D) and weakly positive for Clara cell specific protein (CCSP). Clara cell cytoplasm was positive for CCSP mRNA regardless of ECIs, but not within ECIs. Corticosteroid treatment and ECI presence did not affect the immunohistochemistry and in situ hybridization staining intensities. Electron microscopy revealed large intracytoplasmic granules with an irregular limiting membrane. The ECI number was microscopically quantified in rats from three-, six-, and twenty-four-month studies. The mean ECI counts in treated rats increased from three- to fifty-four-fold with a positive dose-related trend, when compared with vehicle controls. Although the mechanism is unclear, SP-D and to a lesser extent CCSP accumulate in the ECIs. As human bronchial epithelium does not appear to contain structures analogous to the ECI, it is suggested that the observation of an increased number of ECIs in the treated rats is not likely to be relevant for human clinical risk assessment.