Perspectives on the etiology of chronic rhinosinusitis: an immune barrier hypothesis

BACKGROUND

Chronic rhinosinusitis (CRS) has been defined as persistent symptomatic inflammation of the nasal and sinus mucosa resulting from the interaction of multiple host and environmental factors. Recent studies have implicated Alternaria fungi or toxigenic Staphylococcus aureus as critical agents in CRS pathogenesis. The emphasis on environmental agents in CRS etiology has focused interest toward elimination of those agents as the prime mechanism of therapy. This viewpoint is in marked contrast to the current perspective on some other chronic inflammatory epithelial disorders that afflict the skin, lungs, and gut, wherein host factors are believed to predispose to disease expression in the presence of ubiquitous environmental agents.

METHODS

The current review evaluates CRS etiology from this perspective and considers that CRS develops, in part, as an outcome of a dysfunctional host response. Specifically, evidence from our laboratory and others will be reviewed indicating that CRS is associated with a failure of the mechanical and immunologic barriers across the nasal mucosa. The hypothesis would further propose that genetic and epigenetic variation predisposes susceptible individuals to barrier failure in the presence of environmental stress leading to CRS.

RESULTS

From this unifying perspective, bacteria and fungi are seen as disease modifiers rather than primary etiologic agents.

CONCLUSION

The goal is to place concepts of CRS pathophysiology in a framework consistent with a current understanding of chronic inflammation in general and epithelial disease in particular.

Epithelial genes in chronic rhinosinusitis with and without nasal polyps

BACKGROUND

Genetic studies on chronic inflammatory diseases have resulted in an emphasis on the epithelial interface with the environment and the genes that influence this interaction. This study examines the expression of key epithelial genes implicated in the pathogenesis of other inflammatory disorders for their role in chronic rhinosinusitis (CRS).

METHODS

Epithelial cells were collected from the inferior turbinate, middle turbinate, and/or uncinate from 62 subjects undergoing sinonasal surgery. Patient groups included 21 CRS patients with nasal polyposis, 23 CRS patients without nasal polyposis, and 18 controls. Samples were analyzed for S100A7, S100A8, S100A9, SLC9A3R1, G-protein-coupled receptor for asthma, and serine protease inhibitor kazal type 5 (SPINK5) by quantitative real-time polymerase chain reaction. Immunohistochemistry (IHC) was performed to analyze expression of SPINK5 lympho epithelial kazal-type inhibitor (LEKTI) in sinonasal samples.

RESULTS

Expression of S100A7 and S100A8 was significantly decreased in CRS with and without nasal polyps when compared with controls. S100A9 expression was significantly decreased in CRS without nasal polyps, and SPINK5 expression was significantly decreased in CRS with nasal polyps. SPINK5 (LEKTI) protein was detected in sinonasal tissue and was significantly decreased in polyp samples using IHC.

CONCLUSION

This study shows marked reductions in the level of expression of several genes involved in epithelial barrier maintenance and repair in the inflammatory state of CRS.

Innate immunity in the paranasal sinuses: a review of nasal host defenses

BACKGROUND

Chronic rhinosinusitis (CRS) is a common inflammatory disorder of the paranasal sinuses. An abnormal host response to common bacterial or fungal pathogens is thought to be an important factor in the disease process. Host sinonasal epithelium plays an important role in initially recognizing the presence of microbes and responding by increasing production of antimicrobial peptides and cytokines, with recruitment of phagocytes and lymphocytes of the adaptive immune system, to eliminate the infection. Recently, the innate immune system and its complex interplay with the adaptive immune system are increasingly being recognized as important in the pathogenesis of chronic inflammatory diseases such as asthma and CRS.

METHODS

Review of recent findings on innate immunity in the pathogenesis of CRS.

RESULTS

New areas of research into potentially novel therapies for CRS are highlighted in this review, with emphasis on toll-like receptors, antimicrobial peptides (cathelicidins and defensins), and surfactant proteins.

CONCLUSION

This review provides an overview of innate immunity in the sinonasal tract and discusses potential use of innate immune peptides as treatments against fungi, biofilms, and superantigens in CRS.

Chronic rhinosinusitis with nasal polyps is associated with decreased expression of mucosal interleukin 22 receptor

INTRODUCTION

Chronic rhinosinusitis with nasal polyps (CRSwNP) is an inflammatory disorder of the sinonasal mucosa that is frequently associated with microbial colonization. Innate defense mechanisms at the mucosal surface are critical in protecting the host from airborne environmental pathogens. Recent studies of skin and gastrointestinal tract inflammatory diseases have shown that stimulation of the interleukin-22 receptor (IL-22R1) nonspecifically increases innate immune responses. The potential role of IL-22R1 in the pathogenesis of CRSwNP has never been explored.

STUDY DESIGN

Prospective.

METHODS

Nine controls and 19 subjects with CRS were prospectively enrolled prior to undergoing endoscopic sinus surgery. Nasal epithelial cells were cultured from surgically obtained ethmoid mucosa and IL-22R1 protein expression was examined via flow cytometry. RNA was extracted from whole mucosal samples and real-time polymerase chain reaction (PCR) was employed to determine expression of IL22 and IL-22R1. Subjects were followed for at least 6 months postoperative to assess for recurrence or persistence of polyps.

RESULTS

Flow cytometry demonstrated the expression of IL-22R1 protein on the surface of cultured nasal epithelial cells. IL-22R1 mRNA was expressed in 100% of the controls and CRSsNP. However, IL-22R1 was only expressed in 55% of patients with recalcitrant CRSwNP. Additionally, levels of IL22R1 were significantly lower in recalcitrant CRSwNP compared to controls and CRSsNP. IL22 levels did not reach statistical significance.

CONCLUSIONS

In this study, we demonstrate IL-22R1 mRNA and protein expression on nasal epithelial cells. Failure of medical and surgical therapy in CRSwNP is associated with significantly decreased expression of IL-22R1. Further research is needed to determine the potential of IL-22R1 as a therapeutic target in CRSwNP.

The cigarette smoke component acrolein inhibits expression of the innate immune components IL-8 and human beta-defensin 2 by sinonasal epithelial cells

BACKGROUND

Tobacco use is associated with poorer outcomes of medical and surgical therapy for chronic rhinosinusitis (CRS), although the underlying mechanism is unknown. Acrolein (AC) is a major component of cigarette smoke that has been shown to suppress innate immune gene expression by human bronchial epithelial cells and murine macrophages. In this study, we explore whether exposure of human sinonasal epithelial cells (HSNECs) to AC similarly reduces their innate immune gene expression.

METHODS

Primary HSNECs from CRS patients were grown in culture, either differentiated or submerged. HSNECs were treated for 30 minutes with 0-50 microM of AC and were subsequently analyzed by real-time polymerase chain reaction and ELISA to determine IL-8 and human beta-defensin (HBD) 2 expression. Total glutathione was measured to see the oxidative stress within the treatment range.

RESULTS

In primary HSNEC, IL-8 mRNA levels decreased dose dependently in the range of 10-50 microM of AC with an eightfold decrease at 50 microM. In addition, a 125-fold decrease at 50 microM for IL-8 protein was observed. HBD-2 mRNA decreased twofold and HBD-2 protein decreased fourfold at 50 microM of AC in primary HSNEC. However, differentiated HSNEC showed a marginal decrease in a dose-dependent manner for both IL-8 and HBD-2 within the range of 10-50 microM of AC. There was no oxidative stress observed over this range of AC concentration.

CONCLUSION

The tobacco smoke component AC has the capacity to suppress the inflammatory and innate immune function of sinonasal epithelial cells. Whether this effect contributes to the negative clinical impact of smoking on CRS outcomes merits additional investigation.

Innate immunity of the sinonasal cavity and its role in chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is one of the most common health problems in the United States. Medical therapy and surgery are successful in treating the majority of patients with sinusitis; however, CRS patients recalcitrant to traditional therapy are increasingly prevalent. Although traditionally this illness could be explained by sinus ostial obstruction and persistent bacterial infection, the rhinologic literature over the years has suggested a significant underlying inflammatory component. Adaptive immune components, including lymphocytes and their associated cytokines, have been the subject of most research in chronic nasal inflammation. A recent appreciation of the importance of the innate immune system is leading to new areas of investigation regarding the pathogenesis of CRS. This review will outline our current knowledge of sinonasal innate immunity, the role of innate immunity in the pathogenesis of CRS, and potential therapeutic targets in the innate immune system.

Sinonasal epithelial cell expression of toll-like receptor 9 is decreased in chronic rhinosinusitis with polyps

BACKGROUND

Innate immune recognition of pathogens by sinonasal epithelial cells may play an important role in the pathogenesis of chronic rhinosinusitis (CRS). Previous studies have indicated that toll-like receptor (TLR) mRNA is present in sinonasal mucosa, and levels of TLR9 expression are decreased in recalcitrant CRS with nasal polyps (CRSwNP). However, the cellular source and function of TLR9 in the sinonasal epithelium is not known. In this study, primary epithelial cell cultures were analyzed from control subjects and CRSwNP patients to determine the presence and function of TLR9 protein.

METHODS

Primary epithelial cell cultures were established from 5 controls and 10 CRSwNP patients undergoing sinus surgery. Flow cytometry was used to confirm purity of epithelial cells and to assess expression of TLR9 protein. Epithelial cells were stimulated with TLR9 agonist, and mRNA was analyzed by real-time PCR for expression of human beta-defensin (HBD) 2 and interleukin (IL)-8.

RESULTS

Flow cytometry showed TLR9 protein in 100% of epithelial cells from controls and CRSwNP patients. The level of expression was 50% lower in CRS patients than in controls. Stimulation of epithelial cells with TLR9 agonist produced a 1.5- to 9-fold increase in HBD-2 and IL-8 mRNA expression.

CONCLUSION

Functional TLR9 protein is expressed by normal and diseased sinonasal epithelial cells. The level of TLR9 expression is decreased in CRSwNP patients, consistent with the previous finding of decreased TLR9 mRNA in whole sinonasal tissue. These findings suggest that impaired innate immune responses to pathogens via TLR9 on sinonasal epithelial cells may represent a critical mechanism in chronic inflammatory sinus disease.

Increased expression of acidic mammalian chitinase in chronic rhinosinusitis with nasal polyps

BACKGROUND

Chitin is an abundant polysaccharide found in fungi, insects, and parasitic nematodes. Innate immune host defense against chitin-containing pathogens include production of chitinases. In human lower airways, acidic mammalian chitinase (AMCase) is produced in epithelial cells via a Th2-specific, IL-13-dependent pathway, and may act as an inflammatory mediator in asthma. The role of AMCase in chronic rhinosinusitis (CRS) has not been studied previously.

METHODS

Eleven controls and 22 subjects with medically recalcitrant CRS were prospectively enrolled before undergoing endoscopic sinus surgery. RNA was extracted from surgically obtained ethmoid mucosa, and real-time PCR was used to determine expression of AMCase, eotaxin, and IL-13. Subjects were followed for at least 6 months postoperatively to assess for polyp recurrence. Based on the presence or absence of polyps, the subjects were classified as either recalcitrant or responsive to therapy.

RESULTS

AMCase mRNA was detected in the sinus mucosa of 72% of control subjects and in 72% of patients with eosinophilic CRS with nasal polyps (CRSwNP). The expression of AMCase was significantly greater in recalcitrant CRSwNP than it was in treatment-responsive CRSwNP. There was no significant difference in IL-13 expression between these two groups.

CONCLUSION

AMCase may be an important mediator in the pathogenesis of Th2 inflammatory diseases of the respiratory tract. Failure of medical and surgical therapy in CRSwNP is associated with significantly increased expression of AMCase, but not the Th2 cytokines IL-13 and eotaxin. Additional studies are needed to determine the potential of AMCase as a therapeutic target in CRSwNP.