Expression and regulation of PLUNC in human nasal epithelium

Non-Reflex Defense Mechanisms of Upper Airway Mucosa: Possible Clinical Application

The sinonasal mucosa has an essential role in defense mechanisms of the upper respiratory tract. The innate immune system presents the primary defense against noxious microorganisms followed by induction of the adaptive immune mechanisms as a consequence of the presence of pathogens. This well-known activation of adaptive immune system in response to presence of the antigen on mucosal surfaces is now broadly applicated in vaccinology research. Prevention of infectious diseases belongs to substantial challenges in maintaining the population health. Non-invasive, easily applicable mucosal vaccination purposes various research opportunities that could be usable in daily practice. However, the existence of multiple limitations such as rapid clearance of vaccine from nasal mucosa by means of mucociliary transport represents a great challenge in development of safe and efficient vaccines. Here we give an updated view on nasal functions with focus on nasal mucosal immunity and its potential application in vaccination in nearly future.

An in vitro model of murine middle ear epithelium

Otitis media (OM), or middle ear inflammation, is the most common paediatric disease and leads to significant morbidity. Although understanding of underlying disease mechanisms is hampered by complex pathophysiology it is clear that epithelial abnormalities underpin the disease. There is currently a lack of a well-characterised in vitro model of the middle ear (ME) epithelium that replicates the complex cellular composition of the middle ear. Here, we report the development of a novel in vitro model of mouse middle ear epithelial cells (mMECs) at an air–liquid interface (ALI) that recapitulates the characteristics of the native murine ME epithelium. We demonstrate that mMECs undergo differentiation into the varied cell populations seen within the native middle ear. Proteomic analysis confirmed that the cultures secrete a multitude of innate defence proteins from their apical surface. We showed that the mMECs supported the growth of the otopathogen, nontypeable Haemophilus influenzae (NTHi), suggesting that the model can be successfully utilised to study host–pathogen interactions in the middle ear. Overall, our mMEC culture system can help to better understand the cell biology of the middle ear and improve our understanding of the pathophysiology of OM. The model also has the potential to serve as a platform for validation of treatments designed to reverse aspects of epithelial remodelling that underpin OM development.

Summary: Development and systematic characterisation of an in vitro otopathogenic infection model of the murine middle ear epithelium as a tool to better understand the complex pathophysiology of Otitis media.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Increased susceptibility to otitis media in a Splunc1-deficient mouse model

Otitis media (inflammation of the middle ear) is one of the most common diseases of early childhood. Susceptibility to otitis is influenced by a number of factors, including the actions of innate immune molecules secreted by the epithelia lining the nasopharynx, middle ear and Eustachian tube. The SPLUNC1 (short palate, lung, nasal epithelial clone 1) protein is a highly abundant secretory product of the mammalian nasal, oral and respiratory mucosa that is thought to play a multifunctional role in host defense. In this study we investigated Splunc1 expression in the ear of the mouse, and examined whether this protein contributes to overall host defense in the middle ear and/or Eustachian tube. We found that Splunc1 is highly expressed in both the surface epithelium and in submucosal glands in these regions in wild-type mice. In mice lacking Splunc1, we noted histologically an increased frequency of otitis media, characterized by the accumulation of leukocytes (neutrophils with scattered macrophages), proteinaceous fluid and mucus in the middle ear lumens. Furthermore, many of these mice had extensive remodeling of the middle ear wall, suggesting a chronic course of disease. From these observations, we conclude that loss of Splunc1 predisposes mice to the development of otitis media. The Splunc1^−/− mouse model should help investigators to better understand both the biological role of Splunc1 as well as host defense mechanisms in the middle ear.

Summary: We document expression of the innate immune factor Splunc1 in the murine middle ear and Eustachian tube, and describe spontaneous development of otitis media in mice lacking functional Splunc1.

PLUNC proteins positivity in patients with chronic rhinosinusitis: a case-control study

Introduction. Innate immunity is the first protection against microorganisms. Nowadays, there is a growing interest in innate immune molecule known as palate, lung, nasal epithelial clone (PLUNC). PLUNC is a specific product of the airways, of approximately 25 kDa, encoded by adjacent genes found within a 300 kb region of chromosome 20; these proteins must be detected predominantly in the upper respiratory tract. Materials and Methods. We performed a case-control study to investigate the presence of this protein in nasal tissue of patients affected by chronic rhinosinusitis. 59 patients were enrolled (44 cases, 15 controls). We have examined the correlation between the presence of pathology and the PLUNC proteins positivity. Results. 100% of controls have a +++ rated PLUNC proteins positivity, while cases have a lower percentage of positivity. We used χ² statistical test to analyze the results of the study and there is a difference statistically significant between cases and controls in PLUNC proteins positivity. Conclusions. These observations suggest that, in response to agents or chemical factors, nasal mucosal epithelium will react and produce PLUNC proteins. So PLUNC proteins have a protective function on upper airways mucosa, as we can see by evaluating the high positivity in control group.

Decreased PLUNC expression in nasal polyps is associated with multibacterial colonization in chronic rhinosinusitis patients

PLUNC (palate, lung, and nasal epithelium clone) is an epithelium-secreted protein that plays a crucial role in the host's defense against bacterial infection. The function of PLUNC in the sinus remains poorly understood. To examine whether the expression levels of PLUNC could serve as a predictive outcome biomarker for patients with CRSwNP and bacterial colonization, we investigated the association of PLUNC expression levels with bacterial colonization in the sinuses. A total of 174 patients who underwent sinus surgery for chronic rhinosinusitis with nasal polyps (CRSwNP) were enrolled in this study. The tissue samples obtained from patients were examined using preoperative sinus computed tomography (CT) scans, postoperative bacterial cultures, and nasal polyp examinations. PLUNC mRNA and protein expression were quantified using RT-PCR and immunohistochemistry. We identified that decreased PLUNC expression is associated with multibacterial colonization (P = 0.0001), specifically those mediated by Staphyloccocus aureus (P = 0.037) and Pseudomonas aeruginosa (P = 0.002). The patients who required repeated sinus surgeries for recurrent or persistent sinusitis also presented much lower PLUNC expression than those who did not require repeated sinus surgery (P = 0.001). However, gender, age, and CT scores were not associated with PLUNC expression. These results suggest that reduced PLUNC expression is associated with bacterial colonization as well as treatment outcome in CRSwNP patients. Investigation of the association between PLUNC expressions and chronic rhinosinusitis may lead to the development of a novel biomarker for treatment outcome in CRSwNP patients.

Decreased SPLUNC1 expression is associated with Pseudomonas infection in surgically treated chronic rhinosinusitis patients who may require repeated sinus surgery

OBJECTIVES/HYPOTHESIS

Chronic rhinosinusitis colonized with Pseudomonas aruginosa is difficult to treat and is related to biofilm formation. Repeated sinus surgery is often required for these patients. Short palate, lung, and nasal epithelial clone 1 (SPLUNC1) is an epithelium-secreted protein that is involved in innate immunity and has anti-Pseudomonas and antibiofilm functions. This study examined if SPLUNC1 expression was related to sinusitis with bacterial culture positive for Pseudomonas and the possibility of using SPLUNC1 to predict treatment outcomes for sinusitis.

STUDY DESIGN

Nonrandomized retrospective study.

METHODS

This was a retrospective study of patients at a tertiary referral center. Pseudomonas aruginosa infection was compared to clinical variables such as SPLUNC1 mRNA expression levels, immunohistochemical (IHC) stain intensity, Lund-Mackay sinus computed tomography scores, rapid recurrent sinusitis, requirement for repeat sinus surgery, Phadiatop test results, age, gender, nasal polyp(s), and patients' presence/absence of diabetes mellitus. Comparisons between groups were performed using the χ(2) test or Fisher exact test when one confronter was <5. The statistical analyses were carried out with SPSS version 13.

RESULTS

P. aeruginosa sinus infections were associated with lower sinus mucosa SPLUNC1 expression (P = .0018), weaker SPLUNC1 IHC staining intensity (P = .011), and poor postoperative outcome (i.e., need repeated sinus surgery) (P < .001). Other factors were not associated with Pseudomonas sinus infection.

CONCLUSIONS

Sinusitis with positive P. aeruginosa bacterial culture is associated with decreased SPLUNC1 sinus mucosa expression. Repeated sinus surgeries are more frequently needed for these patients.

What is the Relationship between the Localization of Maxillary Fungal Balls and Intranasal Anatomic Variations?

Objectives

Although the mechanisms underlying the initiation and maintenance of inflammation in unilateral maxillary fungal balls (FBs) are poorly understood, the relationship between intranasal anatomy and maxillary FB is thought to play an important role. The aim of this study was to investigate the relationship between anatomic variations and FB.

Methods

We enrolled 140 patients who were composed of 56 patients with FB, 56 patients with unilateral chronic rhinosinusitis (CRS), and 28 patients with no sinus disease. Computed tomography scans were retrospectively analyzed to identify and compare the associated nasal anatomic abnormalities. To measure the volume of the nasal cavity and middle meatus, computed tomography scans were reconstructed into three-dimensional images.

Results

The relatively larger volume of the middle meatus was associated with the localization of the FB in contrast with the CRS. However, the nasal-cavity volume, nasal valve area, and nasal septal deviation were not significantly associated with localization of FB. The mean volumetric and areal measurements such as nasal cavity, middle meatus, and nasal valve in FB-ipsilateral sides were not significantly different from those in contralateral sides as well as other groups.

Conclusion

The middle meatus bears the major part of the inspiratory nasal airflow, and its volume may influence the occurrence of FB.

Expression and Clinical Significance of Plunc Protein in Nasal Polyp and Chronic Sinusitis Tissue

We conducted a study to validate the expression of PLUNC (palate, lung, and nasal epithelial clone) protein in nasal polyp and chronic sinusitis tissue by immunohistochemistry. We also explored the relationship between the intensity of positive immunohistochemical staining for PLUNC protein and postoperative therapeutic efficacy. Our study population consisted of 34 patients with nasal polyps and 30 with chronic sinusitis who had undergone surgical treatment, along with 18 healthy controls who did not undergo surgery. All samples were stained according to the streptavidin-peroxidase immunohistochemical method to examine PLUNC protein expression. The surgical patients were evaluated for clinical therapeutic efficacy 6 months postoperatively. The association between efficacy and the intensity of PLUNC protein positivity was examined by the Spearman rank correlation analysis. Intensity was rated as either +++ (>50% positive cells), ++ (26 to 50% positive cells), + (≤25% positive cells), or - (no positive cells). We found that the most common levels of PLUNC positivity were + in the patients with nasalpolyps, +++ in the patients with chronic sinusitis, and ++ in the controls (p < 0.01). Analysis of the Spearman rank correlation indicated that the intensity of PLUNC protein expression was significantly correlated with postoperative therapeutic efficacy (p < 0.001). We conclude that PLUNC protein is an essential factor in the innate defense mechanism of the nasal mucosa. The immunohistochemical staining of PLUNC protein could have clinical benefit in terms of predicting therapeutic efficacy and outcomes in patients with nasalpolyps or chronic sinusitis.

Expression pattern of PLUNC proteins as an auxiliary tool for the diagnosis of high-grade mucoepidermoid carcinoma of the salivary gland

BACKGROUND

Mucoepidermoid carcinomas are the most frequent malignant neoplasia of the salivary glands and are histologically classified as low, intermediate, and high grade. At present, histochemical stains such as periodic acid-Schiff or mucicarmine are useful tools in making a diagnosis. Recently, expression of the PLUNC proteins has been described in mucin-producing salivary gland tumors, with the suggestion that they could provide a powerful tool for the diagnosis of difficult cases.

METHODS

This study evaluates the expression of PLUNC proteins in 30 cases of salivary gland mucoepidermoid carcinomas. Tumors were reviewed and classified according to histological grade. Periodic acid-Schiff, mucicarmine, and immunohistochemical staining for SPLUNC1, LPLUNC1, SPLUNC2, and LPLUNC2 were carried out. Immunostaining was classified as positive or negative.

RESULTS

The majority of the tumors (63%) were classified as low grade, 13% were intermediate grade, and 23% were high grade. SPLUNC1 (90%) and LPLUNC1 (93%) were positive in the majority of cases, mainly in mucous cells, mucin plugs, and intermediate cells. SPLUNC2 and LPLUNC2 did not present significative expression within the tumors; however, LPLUNC2 was found to stain positively in mast cells in 83% of the samples.

CONCLUSIONS

SPLUNC1 and LPLUNC1 showed a similar pattern of expression and could prove useful in the diagnosis of high-grade cases because of the differential staining in intermediate and epidermoid cells. The expression of LPLUNC2 in mast cells has not previously been reported, but further studies are necessary to validate this finding and to determine its significance.

Functional roles of SPLUNC1 in the innate immune response against Gram-negative bacteria

PLUNC (palate, lung and nasal epithelium clone)-associated gene originally referred to one gene, but now has been extended to represent a gene family that consists of a number of genes with peptide sequence homologies and predicted structural similarities. PLUNC-like proteins display sequence homology with BPI (bactericidal/permeability-increasing protein), a 456-residue cationic protein produced by precursors of polymorphonuclear leucocytes that have been shown to possess both bactericidal and LPS (lipopolysaccharide)-binding activities. The human PLUNC is also known as LUNX (lung-specific X protein), NASG (nasopharyngeal carcinoma-related protein) and SPURT (secretory protein in upper respiratory tract). The gene originally named PLUNC is now recognized as SPLUNC1. Its gene product SPLUNC1 is a secretory protein that is abundantly expressed in cells of the surface epithelium in the upper respiratory tracts and secretory glands in lung, and in the head and the neck region. The functional role of SPLUNC1 in innate immunity has been suggested but not clearly defined. The present review describes recent findings that support antimicrobial and anti-inflammatory functions of SPLUNC1 in Gram-negative bacteria-induced respiratory infection.

Expression of SPLUNC1 protein in nasal polyp epithelial cells in air-liquid interface culture treated with IL-13

BACKGROUND

Short palate, lung, and nasal epithelium clone 1 (SPLUNC1) protein is an airway epithelial cell-derived molecule exerting host defense against pathogen. However, the function and regulation of SPLUNC1 in nasal epithelial cells are still unclear. Chronic rhinosinusitis with nasal polyps (CRSwNPs) is a disorder characterized by eosinophilic Th2 inflammation and frequent microbial colonization. The pathogenesis has been postulated as a disturbed mucosal immune response. This study investigates the SPLUNC1 expression of nasal polyp epithelial cells in air-liquid interface (ALI) culture and after treating with Th2 inflammatory cytokines IL-13.

METHODS

Human nasal polyp epithelial cells isolated from patients with CRSwNPs were put in different cell culture models at days 0 and 21 and were assessed for expression of SPLUNC1 by microarray. Cultured cells in ALI plus retinoic acid (ALI + RA) model were then incubated with 0, 1, 10, and 100 ng/mL human recombinant IL-13 for up to 5 days. The expression of SPLUNC1 was assessed by real-time quantitative polymerase chain reaction (RT-Q-PCR), reverse-transcriptase PCR (RT-PCR) and Western blot analysis.

RESULTS

ALI + RA culture model harvesting ciliary differentiated nasal epithelial cells constitutively expressed high levels of SPLUNC1. In contrast, SPLUNC1 is reduced under classic submerged single layer culture. SPLUNC1 is also dose-responsively down-regulated after incubation with IL-13.

CONCLUSION

A microenvironmental milieu containing IL-13 may be detrimental to the host innate immunity response, at least in part, through the inhibition of SPLUNC1 production.

The role of innate immunity in the pathogenesis of chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a heterogeneous inflammatory condition with a multifactorial basis. Infectious triggers of CRS have been proposed, but demonstration remains elusive. Evolving research suggests that abnormal host mucosal immune responses, rather than specific pathogens themselves, may underlie the chronic inflammatory state. Despite constant contact with airborne particulates and microorganisms, the sinonasal epithelium maintains mucosal homeostasis through innate and adaptive immune mechanisms that eliminate potential threats. Innate immunity encompasses a broad collection of constitutive and inducible processes that can be nonspecific or pathogen directed. Some innate immune pathways are closely intertwined with tissue growth and repair. The persistent inflammation observed in CRS may result from a pathologic imbalance in innate immune interactions between the host and the environment. Impairment of critical innate immune protection renders the sinonasal mucosal surface susceptible to colonization and potential injury, stimulating the prominent adaptive immune response that characterizes CRS.

Differential epithelial expression of the putative innate immune molecule SPLUNC1 in cystic fibrosis

INTRODUCTION

Short PLUNC1 (SPLUNC1) is the founding member of a family of proteins (PLUNCS) expressed in the upper respiratory tract and oral cavity, which may function in host defence. It is one of the most highly expressed genes in the upper airways and the protein has been detected in sputum and nasal secretions. The biology of the PLUNC family is poorly understood but in keeping with the putative function of the protein as an immune defence protein, a number of RNA and protein studies have indicated that SPLUNC1 is increased in inflammatory/infectious conditions such as Cystic Fibrosis (CF), COPD and allergic rhinitis.

METHODS

We used immunohistochemistry to localise SPLUNC1 in lung tissue from patients with CF and a range of other lung diseases. We used a range of additional markers for distinct cell types to try to establish the exact site of secretion of SPLUNC1. We have complemented these studies with a molecular analysis of SPLUNC1 gene expression in primary human lung cell cultures and isolated inflammatory cell populations.

RESULTS

In CF, expression of SPLUNC1 is significantly elevated in diseased airways and positive staining was noted in some of the inflammatory infiltrates. The epithelium of small airways of CF lung exhibit significantly increased SPLUNC1 staining compared to similar sized airways in non-CF lungs where staining is absent. Strong staining was also seen in mucous plugs in the airways, these included many inflammatory cells. No alveolar epithelial staining was noted in CF tissue. Airway epithelial staining did not co-localise with MUC5AC suggesting that the protein was not produced by goblet cells. Using serial sections stained with neutrophil elastase and CD68 we could not demonstrate co-localisation of SPLUNC1 with either neutrophils or macrophages/monocytes, indicating that these cells were not a source of SPLUNC1 in the airways of CF lungs. No change in staining pattern was noted in the small airways or lung parenchyma of other lung diseases studied including, COPD, emphysema or pneumonia where significant NE and CD68 staining was noted. Cultures of primary tracheobronchial epithelial cells were analysed by RT-PCR and showed that pro-inflammatory mediators did not induce expression of SPLUNC1. We have also shown that SPLUNC1 gene expression was not seen in isolated human mononuclear cells, macrophages or neutrophils.

CONCLUSION

These studies show that SPLUNC1 is specifically and significantly increased in the small airways of lungs from patients with CF. They further suggest that it is the airway epithelium that is responsible for the increased levels of SPLUNC1 in CF and not inflammatory cells; this could be a defensive response to the infectious component of the disease.