Models for the study of nasal and sinus physiology in health and disease: A review of the literature

Objective

Chronic sinusitis is a very common yet poorly understood medical condition with significant morbidity. Hence, it remains an entity that is difficult to treat with unsatisfactory outcomes of current management options. This necessitates research into the etiology and pathophysiology of the condition to enhance our knowledge and the therapeutic options. Unfortunately, this kind of research is not always feasible on human subjects due to practical and ethical limitations. Therefore, an alternative model that simulates the disease had to be found in order to overcome these limitations. These models could either be in vivo or in vitro. The aim of our review is to summarize the research findings and key discoveries of both in vivo and in vitro models of chronic sinusitis that have enhanced our understanding of the condition today and have paved the way for the future research of tomorrow.

Data Sources: PubMed literature review.

Methods

A review of the literature was conducted to identify the main successful in vivo and in vitro models for chronic sinusitis.

Results

Creating a successful model for chronic sinusitis is no easy task. Over the years, both in vivo animal models and in vitro tissue culture models were proposed, with each model having its accolades and pitfalls, with the ideal model remaining elusive to this day. However, advancing three‐dimensional cell culturing techniques seems to be a promising new way to find a more accurate model.

Conclusion

None of the current models is perfect for a thorough study of chronic sinusitis. However, three‐dimensional cell cultures have the potential to bridge the gap between in vivo and in vitro studies.

Level of Evidence

NA

Rat Model of Platelet-Activating Factor-Induced Rhinosinusitis

Platelet-activating factor (PAF) is known to be a potent inflammatory mediator, especially in allergic inflammation. However, the exact role of PAF in the pathogenesis of rhinosinusitis has not been clearly established. To understand the role of PAF in the pathogenesis of rhinosinusitis, it is necessary to develop an animal model of PAF-induced rhinosinusitis. The aim of this study was to develop a rat model of rhinosinusitis induced by intranasally applied PAF. Fifty microliters of 16 μg/mL PAF was applied intranasally through each naris in 4-week-old Sprague-Dawley rats, and the same amount of vehicle was applied in control rats. At 1, 3, or 5 days, the animals were painlessly sacrificed, and the nasal cavity and sinuses were prepared for histologic investigation. The histologic sections were examined in a blind manner for the appearance of neutrophil clusters in the sinonasal air space, and the numbers of eosinophils, areas of epithelial loss, goblet cells, and inducible nitric oxide synthase (iNOS)–positive inflammatory cells in the mucosa. Neutrophil clusters were observed in the air space, and the number of eosinophils, areas of epithelial loss, goblet cells, and iNOS-positive inflammatory cells in the mucosa were increased significantly in the PAF-applied rats. The amount of inflammation varied according to the time interval, showing a peak at day 3. We conclude that intranasally applied PAF induces rhinosinusitis in rats. The histologic evidence of rhinosinusitis revealed the appearance of neutrophil clusters in the sinonasal air space, infiltration of eosinophils and iNOS-positive inflammatory cells in the mucosa, areas of epithelial loss, and goblet cell hyperplasia in the epithelium. This rat model of PAF-induced rhinosinusitis may be applied for better understanding of the role of PAF in the pathogenesis of rhinosinusitis.

Reovirus serotypes elicit distinctive patterns of recall immunity in humans

Mammalian orthoreoviruses (reoviruses) are ubiquitous viral agents that infect cells in respiratory and enteric tracts. The frequency and nature of human cellular immunoregulatory responses against reovirus are unknown. Here we establish systems to detect and quantify reovirus-induced cytokine and chemokine recall responses using primary cultures of virus-infected peripheral blood mononuclear cells (PBMC) and two widely used reovirus serotypes, type 1 Lang (T1L) and type 3 Dearing (T3D) reexposure in vitro. In cultures from 44 healthy adults, reovirus induced exceptionally strong CD4 and CD8 T-cell-dependent gamma interferon (IFN-gamma) recall responses concomitant with intense interleukin 10 (IL-10) production. These responses were elicited independently of viral replication. Surprisingly, paired analyses of subject responses to these two common serotypes revealed that while both elicit intense Th1-dominated immunity, median T3D-driven responses were 2.2-fold weaker (P = 0.0004) than those elicited by T1L. Recall responses evoked by these viral serotypes differed markedly in their mechanism of regulation. T3D IL-10 and IFN-gamma responses were CD4 and CD8 dependent and blocked by interfering with CD86 costimulation but were CD80 independent. T1L responses were consistently CD28 and CD80/86 independent. Thus, despite extensive genetic and morphological similarities between reovirus serotypes, the nature and intensity of the human recall responses as well as the control mechanisms regulating them are clearly distinct.

Persistent inflammation and hyperresponsiveness following viral rhinosinusitis

OBJECTIVES

To develop a murine model of viral rhinosinusitis.

STUDY DESIGN

Randomized, controlled, animal model.

METHODS

Mice were intranasally inoculated with Sendai virus (SeV) or ultraviolet (UV)-inactivated virus. On days 3 and 10 postinfection, nasal lavage fluid was obtained for viral culture. On days 4, 10, and 38 postinfection, sinus mucosa was harvested and analyzed by flow cytometry for CD3-, CD4-, CD8-, CD25-, CD11b-, CCR3-, and GR1-positive cells. Nasal hyperresponsiveness to histamine challenge was measured on days 8 and 36 postinoculation.

RESULTS

On day 3, viral cultures were positive from all SeV-inoculated mice but from none of the UV-inactivated mice (P<or=.0039). There was no growth of virus from either group on day 10. On day 4, flow cytometry on SeV-infected sinus cells showed a significant increase in macrophages (P<or=.03) and neutrophils (P<or=.02) compared with controls. This inflammation resolved by day 10. On day 38, mice inoculated with SeV had significantly more CD8+ (P<or=.044) and CD4+CD25+ (P<or=.017) cells than did controls. On day 8, there was a significant increase in both sneezing (P<or=.002) and nasal rubbing (P<or=.002) in the SeV-infected group to histamine challenge compared with controls. This difference continued to day 36.

CONCLUSIONS

Inoculation with SeV results in an acute infection that resolves spontaneously within 10 days. Infected mice develop a significant increase in T-suppressor and T-regulatory cells after resolution of the acute infection, which persists for at least 38 days. The persistence of these T cells is associated with hyperresponsiveness to histamine. This mouse model has some parallels to chronic rhinosinusitis after a viral infection in humans and should allow us to clarify the pathophysiology of this disease.

Survey anatomy of the paranasal sinuses in the normal mouse

OBJECTIVE

To provide researchers with a survey atlas of normal paranasal sinus anatomy in the mouse as well as to standardize the reporting of data within the murine nose and sinuses.

STUDY DESIGN

Histologic and radiographic study in mice.

METHODS

C57BL/6 mice were killed and their heads sectioned in the axial and coronal planes as well as imaged using a small animal micro-computed tomography (CT) scanner. Distinctive regions within the nose and paranasal sinuses were delineated and labeled A to G for identification.

RESULTS

Definable regions within the normal murine nose and paranasal sinuses include A) the nasal airway, B) the superior nasal vault, C) the osteomeatal complex, D) the anterior ethmoid sinuses, E) the posterior ethmoid sinuses, F) the true maxillary sinus, and G) the secondary maxillary sinus. Mice also possess discernible sphenoid sinuses. CT scans confirmed the histologic plane of section.

CONCLUSIONS

A survey atlas of normal murine sinonasal anatomy shall provide laboratories seeking to use mice in sinus research a reference for beginning their work. As new transgenic and gene knockout mice become available, phenotypic changes in sinonasal architecture can be more easily discerned using such a reference. Defining specific regions (A-G) within the sinuses will standardize the nomenclature used for reporting data.

Animal models of sinusitis: relevance to human disease

Experimental animal models are necessary to assess the efficacy of both medical and surgical procedures. The researcher who wishes to confirm and publish his results must overcome controversies concerning the validity of his model and, therefore, needs guidelines for standardization. Various models are offered in the literature. In this article, the rabbit and murine models of experimental sinusitis and their relevance to human disease with anatomical, histopathologic, and microbiologic aspects are discussed.