A mouse model for acute otitis media

Resolution of otitis media in a humanized mouse model

Otitis media (OM) is one of the largest public health problems of children and has devastating impacts in developing countries. The substantial medical and human costs involved have led to research to understand the disease and improve treatment. Animal models of OM have yielded critical information about the immune, inflammatory and genetic mechanisms of OM. However, it is important to link animal studies to human immune and inflammatory responses. In recent years, "humanized" mice have become a valuable tool to study the human immune system in an animal model. Here we describe the first use of humanized mice to study OM. We demonstrate that humanized mice with a sufficient degree of engraftment recapitulate a normal middle ear (ME) inflammatory response to bacterial infection, including the recruitment of human immune cells, and exhibit normal recovery. Moreover, these animals exhibit regulated expression of human-specific immune and inflammatory genes in the ME. In contrast, mice with insufficient engraftment fail to resolve OM. This model has many potential uses in OM research, including using hematopoietic stem cells from patients with differing degrees of OM susceptibility, to understand the role of human immune responses in proneness to this common childhood disease.

Essential Role of the Innate Immune Adaptor RIP2 in the Response to Otitis Media

Intracellular nucleotide binding and oligomerization domain (NOD) and Toll-like (TLR) receptors have emerged as pivotal sensors of infection. Both Nod1 and Nod2 contain a caspase activation and recruitment domain (CARD) that interacts with the adaptor protein RIP2 (receptor-interaction protein-2). This leads to ubiquitination of RIP2 and in turn to the activation of NFκB and MAPK transcription factors, to command the host defensive response against pathogenic infections. RIP2 is also activated by TLRs 2 and 4, although the mechanism of this activation is less. The role of RIP2 in otitis media (OM) pathogenesis has yet to be examined. Herein, we used in vivo animal models including C57BL/6 wild-type (WT) and RIP2^−/− knockout mice inoculated in the middle ear (ME) with non-typeable Haemophilus influenzae (NTHi), a common human OM pathogen, to evaluate the expression of RIP2 and its signaling genes at the cellular level to determine the role of RIP2 in OM pathogenesis and recovery. The Nod1, Nod2, and Ripk2 genes are minimally expressed in the normal ME. However, they are strongly upregulated during acute OM, as are many genes related to RIP2 signaling. However, while signaling genes were expressed by various ME cell types, only mucosal epithelial and stromal cells expressed the NODs, RIP2, and signaling genes required for the activation of the host defensive response. Whereas WT mice clear ME bacteria and recover from OM within 5 days after infection, RIP2-deficient mice show persistent ME bacterial carriage and inflammation to at least 15 days. This includes significantly prolonged mucosal hyperplasia and ME leukocytic infiltration. Recruitment of macrophages is also delayed in comparison to WT mice. Thus, RIP2 is required to elicit a robust innate immune response that promotes bacterial clearance and increases host innate resistance. The results also identify the structural cells of the ME mucosa, as opposed to leukocytes, as the primary sites of NOD/RIP2 activity in the infected ME.

Probing Immune-Mediated Clearance of Acute Middle Ear Infection in Mice

Acute otitis media (AOM) is commonly caused by bacterial pathobionts of the nasopharynx that ascend the Eustachian tube to cause disease in the middle ears. To model and study the various complexities of AOM, common human otopathogens are injected directly into the middle ear bullae of rodents or are delivered with viral co-infections which contribute to the access to the middle ears in complex and partially understood ways. Here, we present the novel observation that Bordetella bronchiseptica, a well-characterized respiratory commensal/pathogen of mice, also efficiently ascends their Eustachian tubes to colonize their middle ears, providing a flexible mouse model to study naturally occurring AOM. Mice lacking T and/or B cells failed to resolve infections, highlighting the cooperative role of both in clearing middle ear infection. Adoptively transferred antibodies provided complete protection to the lungs but only partially protected the middle ears, highlighting the differences between respiratory and otoimmunology. We present this as a novel experimental system that can capitalize on the strengths of the mouse model to dissect the molecular mechanisms involved in the generation and function of immunity within the middle ear.

Leukotriene B4 Is a Major Determinant of Leukocyte Recruitment During Otitis Media

Background

Pathogens of otitis media (OM) induce inflammatory responses in the middle ear (ME), characterized by mucosal hyperplasia, leukocyte infiltration, and inflammatory mediators, including arachidonic acid metabolites. We studied the role of the eicosanoid leukotriene B4 (LTB4) in OM.

Methods

Expression of LTB4-related genes was evaluated by gene array and single-cell RNA-Seq in MEs infected with nontypeable Haemophilus influenzae (NTHi). An inhibitor of LTB4 receptor 1 (i.e. U75302) was also used to block LTB4 responses.

Results

ME expression of LTB4-related genes was observed by gene arrays and scRNA-Seq. However, not all genes involved in LTB4 generation occurred in any one specific cell type. Moreover, LTB4 receptor inhibition significantly reduced mucosal hyperplasia and virtually eliminated leukocyte infiltration.

Conclusions

ME expression of LTB4-related genes suggest a functional role in OM disease. The fact that LTB4-generation is spread across different cell types is consistent with a transcellular pathway of eicosanoid biosynthesis involving cell-to-cell signaling as well as transfer of biosynthetic intermediates between cells. The dramatic reduction in ME leukocyte infiltration caused by U75302 indicates that LTB4 plays a major role in ME inflammatory cell recruitment, acting via the LTB4R1 receptor. Given that there are many other chemotactic factors that occur in the ME during OM, the ability of LTB4 to activate leukocytes and stimulate their extravasation may explain the effects of inhibition. Reduction in mucosal hyperplasia due to U75302 administration may be secondary to the reduction in leukocytes since LTB4R1 is not expressed by mucosal epithelial or stromal cells. The results suggest that LTB4 receptor antagonists could be useful in treating OM.

Macrophage Depletion in CCR2-/- Mice Delays Bacterial Clearance and Enhances Neutrophil Infiltration in an Acute Otitis Media Model

BACKGROUND

Otitis media (OM) is a common and potentially serious disease of childhood. Although OM is multifactorial on origin, bacterial infection is a unifying component. Many studies have established a critical role for innate immunity in bacterial clearance and OM resolution. A key component of innate immunity is the recruitment of immune and inflammatory cells, including macrophages.

METHODS

To explore the role of macrophages in OM, we evaluated the expression of genes related to macrophage function during a complete episode of acute OM in the mouse caused by middle ear (ME) inoculation with Haemophilus influenzae. We also combined CCR2 deficiency with chlodronate liposome toxicity to deplete macrophages during OM.

RESULTS

Macrophage genes were robustly regulated during OM. Moreover, macrophage depletion enhanced and prolonged the infiltration of neutrophils into the infected ME and increased the persistence of bacterial infection.

CONCLUSIONS

The results illustrate the critical role played by macrophages in OM resolution.

From Evidence to Clinical Guidelines in Antibiotic Treatment in Acute Otitis Media in Children

Acute otitis media (AOM) in children represents a public health concern, being one of the leading causes of health care visits and antibiotic prescriptions worldwide. The overall aim of this paper is to unravel the major current insights into the antibiotic treatment of AOM in children. Our approach is three-fold: 1. a preclinical evaluation of antibiotics in animal models of AOM stressing on the advantages of different species when testing for different schemes of antibiotics; 2. an overview on the new antimicrobial agents whose efficacy has been demonstrated in refractory cases of AOM in children; and 3. an analysis of the different guidelines stressing on the differences and similarities between the various schemes of antibiotic treatment. The preferred therapeutic agents remain amoxicillin and the amoxicillin-clavulanate combination for AOM caused by Streptococcus pneumoniae, whereas oral cephalosporin is preferred in AOM due to Moraxella catarrhalis and Haemophilus influenzae. As for the second and third line antimicrobial treatments, there is a wide variety of suggested antibiotic classes with variations in duration and posology. The decision to prescribe antimicrobial treatment as a first-line choice is based on the severity of the symptoms in 16 of the guidelines included in this review.

A kinase inhibitor screen identifies signaling pathways regulating mucosal growth during otitis media

Otitis media, the most common disease of childhood, is characterized by extensive changes in the morphology of the middle ear cavity. This includes hyperplasia of the mucosa that lines the tympanic cavity, from a simple monolayer of squamous epithelium into a greatly thickened, respiratory-type mucosa. The processes that control this response, which is critical to otitis media pathogenesis and recovery, are incompletely understood. Given the central role of protein phosphorylation in most intracellular processes, including cell proliferation and differentiation, we screened a library of kinase inhibitors targeting members of all the major families in the kinome for their ability to influence the growth of middle ear mucosal explants in vitro. Of the 160 inhibitors, 30 were found to inhibit mucosal growth, while two inhibitors enhanced tissue proliferation. The results suggest that the regulation of infection-mediated tissue growth in the ME mucosa involves multiple cellular processes that span the kinome. While some of the pathways and processes identified have been previously implicated in mucosa hyperplasia others are novel. The results were used to generate a global model of growth regulation by kinase pathways. The potential for therapeutic applications of the results are discussed.

NOD1/NOD2-mediated recognition of non-typeable Haemophilus influenzae activates innate immunity during otitis media

Pathogen recognition following infection in mammals depends mainly on TLRs and NLRs. Herein, we evaluate the role of NOD1 and NOD2 signaling in the inflammatory responses of the middle ear (ME) mucosa and leukocytes recruitment to infection site during otitis media (OM). OM is a common pediatric disease with prevalent repercussions on hearing health. While many risk factors have been implicated to OM proneness, immunity and the triggering of inflammation are central to OM pathology. We observed that many genes encoding members of the NOD leucine-rich repeat and their downstream adaptor/effector molecules were strongly regulated during the course of OM. When compared to wild type C57BL/6 mice, NOD1- and NOD2-deficient mice were susceptible to prolonged OM infection by non-typeable Haemophilus influenza. NOD1-deficient mice appeared to have reduced macrophage enlistment with a delayed inflammatory response by neutrophils and prolonged mucosal hyperplasia, whereas NOD2 knockouts exhibited an overall reduction in the number of leukocytes recruited to the ME, leading to delayed bacterial clearance. Altogether, these data show that the NODs play a role in the pathogenesis and recovery of OM and reinforce the importance of innate immune signaling in the protective host response.

Innate immunity of surfactant protein A in experimental otitis media

Surfactant protein A (SP-A) plays an important role in innate immune response and host defense against various microorganisms through opsonization and complement activation. To investigate the role of SP-A in non-typeable Haemophilus influenzae (NTHi)-induced acute otitis media, this study used wild type C57BL/6 (WT) and SP-A knockout (KO) mice. We divided mice into an infection group in which the middle ear (ME) was injected with NTHi and a control group that received the same treatment using normal saline. Mice were sacrificed on d 1, 3, and 7 after treatment. Temporal bone samples were fixed for histological, cellular, and molecular analyses. Ear washing fluid (EWF) was collected for culture and analyses of pro-inflammatory cytokines and inflammatory cells. SP-A-mediated bacterial aggregation and killing and phagocytosis by macrophages were studied in vitro. SP-A expression was detected in the ME and Eustachian tube mucosa of WT mice but not KO mice. After infection, KO mice showed more severe inflammation evidenced by increased ME mucosal thickness and inflammatory cell infiltration and higher NF-κB activation compared to WT mice. The levels of IL-6 and IL-1β in the EWF of infected KO mice were higher compared to infected WT mice on d 1. Our studies demonstrated that SP-A mediated NTHi aggregation and killing and enhanced bacterial phagocytosis by macrophages in vitro and modulated inflammation of the ME in otitis media in vivo.

A model of chronic, transmissible Otitis Media in mice

Infection and inflammation of the middle ears that characterizes acute and chronic otitis media (OM), is a major reason for doctor visits and antibiotic prescription, particularly among children. Nasopharyngeal pathogens that are commonly associated with OM in humans do not naturally colonize the middle ears of rodents, and experimental models in most cases involve directly injecting large numbers of human pathogens into the middle ear bullae of rodents, where they induce a short-lived acute inflammation but fail to persist. Here we report that Bordetella pseudohinzii, a respiratory pathogen of mice, naturally, efficiently and rapidly ascends the eustachian tubes to colonize the middle ears, causing acute and chronic histopathological changes with progressive decrease in hearing acuity that closely mimics otitis media in humans. Laboratory mice experimentally inoculated intranasally with very low numbers of bacteria consistently have their middle ears colonized and subsequently transmit the bacterium to cage mates. Taking advantage of the specifically engineered and well characterized immune deficiencies available in mice we conducted experiments to uncover different roles of T and B cells in controlling bacterial numbers in the middle ear during chronic OM. The iconic mouse model provides significant advantages for elucidating aspects of host-pathogen interactions in otitis media that are currently not possible using other animal models. This natural model of otitis media permits the study of transmission between hosts, efficient early colonization of the respiratory tract, ascension of the eustachian tube, as well as colonization, pathogenesis and persistence in the middle ear. It also allows the combination of the powerful tools of mouse molecular immunology and bacterial genetics to determine the mechanistic basis for these important processes.

Animal models of acute otitis media - A review with practical implications for laboratory research

Considerable animal research has focused on developing new strategies for the prevention and treatment of acute otitis media (AOM). Several experimental models of AOM have thus been developed. A PubMed search of the English literature was conducted from 1975 to July 2016 using the search terms "animal model" and "otitis media" from which 91 published studies were included for analysis, yielding 123 animal models. The rat, mouse and chinchilla are the preferred animals for experimental AOM models with their individual advantages and disadvantages. The most common pathogens used to create AOM are Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Streptococcus pneumoniae (types 3, 23 and 6A) and non-typeable Haemophilus influenzae (NTHi) are best options for inoculation into rat and mouse models. Adding viral pathogens such as RSV and Influenza A virus, along with creating ET dysfunction, are useful adjuncts in animal models of AOM. Antibiotic prophylaxis may interfere with the inflammatory response without a significant reduction in animal mortality.

Otitis Media and Nasopharyngeal Colonization in ccl3-/- Mice

We previously found CC chemokine ligand 3 (CCL3) to be a potent effector of inflammation during otitis media (OM): exogenous CCL3 rescues the OM phenotype of tumor necrosis factor-deficient mice and the function of macrophages deficient in several innate immune molecules. To further delineate the role of CCL3 in OM, we evaluated middle ear (ME) responses of ccl3^-/-mice to nontypeable Haemophilus influenzae (NTHi). CCL chemokine gene expression was evaluated in wild-type (WT) mice during the complete course of acute OM. OM was induced in ccl3^-/- and WT mice, and infection and inflammation were monitored for 21 days. Phagocytosis and killing of NTHi by macrophages were evaluated by an in vitro assay. The nasopharyngeal bacterial load was assessed in naive animals of both strains. Many CCL genes showed increased expression levels during acute OM, with CCL3 being the most upregulated, at levels 600-fold higher than the baseline. ccl3^-/- deletion compromised ME bacterial clearance and prolonged mucosal hyperplasia. ME recruitment of leukocytes was delayed but persisted far longer than in WT mice. These events were linked to a decrease in the macrophage capacity for NTHi phagocytosis and increased nasopharyngeal bacterial loads in ccl3^-/- mice. The generalized impairment in inflammatory cell recruitment was associated with compensatory changes in the expression profiles of CCL2, CCL7, and CCL12. CCL3 plays a significant role in the clearance of infection and resolution of inflammation and contributes to mucosal host defense of the nasopharyngeal niche, a reservoir for ME and upper respiratory infections. Therapies based on CCL3 could prove useful in treating or preventing persistent disease.

The Role of the Notch Signal Pathway in Mucosal Cell Metaplasia in Mouse Acute Otitis Media

Otitis media (OM) is a major cause of morbidity in pediatric and adult patients. This inflammatory condition is characterized by mucous cell hyperplasia that is thought to produce mucins from the middle ear mucosa. We are interested in the role of Notch signalling pathway in this inflammatory process. Using an acute otitis media (AOM) mouse model through injection of Streptococcus Pneumoniae into the middle ear, histopathologic examination and quantitative RT-PCR, acute inflammation with the thickness of mucosa, Goblet cell hyperplasia, and cilia loss were determined and gene expression related to the Notch signaling pathway were evaluated. Upregulation of the mucous cell markers, Argr2 and Muc5AC, and downregulation of the cilia cell marker, Foxj1 and Dnai2, were observed in AOM. In addition, genes encoding Notch receptors and ligands (Notch1, Notch2, Notch3, Notch4 and Dll1) and the Notch target genes (Hes1, Hes5, Hey1, NRARP) in AOM decreased significantly. The expression of the Notch1 and Jagged1 also showed down-regulation throughout the mouse middle ear epithelium. Taken together, this study suggests that downregulation of the Notch signaling pathway is involved in the mucosa hyperplasia during AOM.

Trivalent pneumococcal protein vaccine protects against experimental acute otitis media caused by Streptococcus pneumoniae in an infant murine model

BACKGROUND

Currently licensed serotype-based pneumococcal vaccines are effective in preventing invasive pneumococcal diseases, but less effective in preventing non-bacteremic pneumonia and acute otitis media (AOM). We previously reported that a trivalent pneumococcal protein recombinant vaccine (PPrV) protected against pneumonia in a murine model. Here we evaluated PPrV protection against AOM in an infant murine model.

METHODS

C57BL/6J mice were intramuscularly vaccinated at 1-3weeks of age with monovalent pneumococcal histidine triad protein D (PhtD), or pneumococcal choline binding protein A (PcpA), or detoxified pneumolysin (PlyD1), or trivalent vaccine, and transtympanically challenged at 7-8weeks of age with 1×10²CFU of pneumococcal strain BG7322 (6A) or 1×10⁴CFU of pneumococcal nontypeable strain 0702064MEF. Serum IgG titers were determined by ELISA. At 24 and 48h post infection (hpi), animals were sacrificed and middle ear fluid (MEF) samples were collected to determine pneumococcal CFUs.

RESULTS

We found that vaccination of infant mice with monovalent and trivalent pneumococcal proteins elicited significant serum IgG antibody responses to corresponding component proteins. Vaccination with PhtD reduced BG7322 bacterial burdens in MEF at both 24 (p=0.05) and 48hpi (p=0.16). Vaccination with PcpA significantly reduced the bacterial burdens in MEF at both 24 (p=0.02) and 48hpi (p=0.004), and PlyD1 significantly reduced bacterial burden in MEF at 48hpi (p=0.02). Vaccination with trivalent PPrV (PhtD, PcpA and PlyD1) significantly reduced Spn burdens in MEF at both 24 (p=0.001) and 48hpi (p<0.0001). Similar reductions of bacterial burdens were found when the vaccinated animals were challenged with a non-typeable Spn strain. Vaccinated mice had significantly milder inflammatory cytokine levels (IL-1β, IL-6, TNF-α, MIP-2 and KC) in middle ears at 24hpi (all p values<0.05).

CONCLUSION

Trivalent PPrV confers protection against pneumococcal AOM in an infant murine model.

TLR2 promotes macrophage recruitment and Streptococcus pneumoniae clearance during mouse otitis media

BACKGROUND

The natural course of otitis media (OM) in most children is acute and self-limiting; however, approximately 10-20% of children can experience persistent or recurrent OM. Determining the host factors that influence outcome of OM will help us design better therapies. This study focused on the role of Toll-like receptor 2 (TLR2) in a pneumococcal OM mouse model.

METHODS

The middle ears (MEs) of wild-type (WT) and TLR2^-/- mice were inoculated with Streptococcus pneumoniae (Spn) serotype 19F via transbullar injection. ME TLR2 expression in WT mice was determined by qRT-PCR and immunofluorescence. ME pathological manifestations, inflammatory response, and pneumococcal clearance between WT and TLR2^-/- mice were compared after Spn inoculation.

RESULTS

TLR2 expression in ME mucosa was markedly enhanced following infection with Spn in WT mice. In contrast to WT mice, TLR2^-/- mice exhibited unaffected early ME inflammatory response. During late stage of ME infection, however, the absence of TLR2 can lead to reduced macrophage recruitment, impaired Spn clearance, and prolonged ME inflammation.

CONCLUSION

Our results demonstrate that TLR2 signaling is critical for bacterial clearance and timely resolution of inflammation in OM induced by Spn.

The transcriptome of a complete episode of acute otitis media

BACKGROUND

Otitis media is the most common disease of childhood, and represents an important health challenge to the 10-15% of children who experience chronic/recurrent middle ear infections. The middle ear undergoes extensive modifications during otitis media, potentially involving changes in the expression of many genes. Expression profiling offers an opportunity to discover novel genes and pathways involved in this common childhood disease. The middle ears of 320 WBxB6 F1 hybrid mice were inoculated with non-typeable Haemophilus influenzae (NTHi) or PBS (sham control). Two independent samples were generated for each time point and condition, from initiation of infection to resolution. RNA was profiled on Affymetrix mouse 430 2.0 whole-genome microarrays.

RESULTS

Approximately 8% of the sampled transcripts defined the signature of acute NTHi-induced otitis media across time. Hierarchical clustering of signal intensities revealed several temporal gene clusters. Network and pathway enrichment analysis of these clusters identified sets of genes involved in activation of the innate immune response, negative regulation of immune response, changes in epithelial and stromal cell markers, and the recruitment/function of neutrophils and macrophages. We also identified key transcriptional regulators related to events in otitis media, which likely determine the expression of these gene clusters. A list of otitis media susceptibility genes, derived from genome-wide association and candidate gene studies, was significantly enriched during the early induction phase and the middle re-modeling phase of otitis but not in the resolution phase. Our results further indicate that positive versus negative regulation of inflammatory processes occur with highly similar kinetics during otitis media, underscoring the importance of anti-inflammatory responses in controlling pathogenesis.

CONCLUSIONS

The results characterize the global gene response during otitis media and identify key signaling and transcription factor networks that control the defense of the middle ear against infection. These networks deserve further attention, as dysregulated immune defense and inflammatory responses may contribute to recurrent or chronic otitis in children.

Heparin binding-epidermal growth factor-like growth factor for the regeneration of chronic tympanic membrane perforations in mice

We aim to explore the role of epidermal growth factor (EGF) ligand shedding in tympanic membrane wound healing and to investigate the translation of its modulation in tissue engineering of chronic tympanic membrane perforations. Chronic suppurative otitis media (CSOM) is an infected chronic tympanic membrane perforation. Up to 200 million suffer from its associated hearing loss and it is the most common cause of pediatric hearing loss in developing countries. There is a need for nonsurgical treatment due to a worldwide lack of resources. In this study, we show that EGF ligand shedding is essential for tympanic membrane healing as it's inhibition, with KB-R7785, leads to chronic perforation in 87.9% (n=58) compared with 0% (n=20) of controls. We then show that heparin binding-EGF-like growth factor (5 μg/mL), which acts to shed EGF ligands, can regenerate chronic perforations in mouse models with 92% (22 of 24) compared with 38% (10 of 26), also with eustachian tube occlusion with 94% (18 of 19) compared with 9% (2 of 23) and with CSOM 100% (16 of 16) compared with 41% (7 of 17). We also show the nonototoxicity of this treatment and its hydrogel delivery vehicle. This provides preliminary data for a clinical trial where it could be delivered by nonspecialist trained healthcare workers and fulfill the clinical need for a nonsurgical treatment for chronic tympanic membrane perforation and CSOM.

C-Jun N-terminal kinase (JNK) isoforms play differing roles in otitis media

BACKGROUND

Innate immunity and tissue proliferation play important roles in otitis media (OM), the most common disease of childhood. CJUN terminal kinase (JNK) is potentially involved in both processes.

RESULTS

Genes involved in both innate immune and growth factor activation of JNK are upregulated during OM, while expression of both positive and negative JNK regulatory genes is altered. When compared to wildtypes (WTs), C57BL/6 mice deficient in JNK1 exhibit enhanced mucosal thickening, with delayed recovery, enhanced neutrophil recruitment early in OM, and delayed bacterial clearance. In contrast, JNK2-/- mice exhibit delayed mucosal hyperplasia that eventually exceeds that of WTs and is slow to recover, delayed recruitment of neutrophils, and failure of bacterial clearance.

CONCLUSIONS

The results suggest that JNK1 and JNK2 play primarily opposing roles in mucosal hyperplasia and neutrophil recruitment early in OM. However, both isoforms are required for the normal resolution of middle ear infection.

A mouse model of otitis media identifies HB-EGF as a mediator of inflammation-induced mucosal proliferation

Objective

Otitis media is one of the most common pediatric infections. While it is usually treated without difficulty, up to 20% of children may progress to long-term complications that include hearing loss, impaired speech and language development, academic underachievement, and irreversible disease. Hyperplasia of middle ear mucosa contributes to the sequelae of acute otitis media and is of important clinical significance. Understanding the role of growth factors in the mediation of mucosal hyperplasia could lead to the development of new therapeutic interventions for this disease and its sequelae.

Methods

From a whole genome gene array analysis of mRNA expression during acute otitis media, we identified growth factors with expression kinetics temporally related to hyperplasia. We then tested these factors for their ability to stimulate mucosal epithelial growth in vitro, and determined protein levels and histological distribution in vivo for active factors.

Results

From the gene array, we identified seven candidate growth factors with upregulation of mRNA expression kinetics related to mucosal hyperplasia. Of the seven, only HB-EGF (heparin-binding-epidermal growth factor) induced significant mucosal epithelial hyperplasia in vitro. Subsequent quantification of HB-EGF protein expression in vivo via Western blot analysis confirmed that the protein is highly expressed from 6 hours to 24 hours after bacterial inoculation, while immunohistochemistry revealed production by middle ear epithelial cells and infiltrating lymphocytes.

Conclusion

Our data suggest an active role for HB-EGF in the hyperplasia of the middle ear mucosal epithelium during otitis media. These results imply that therapies targeting HB-EGF could ameliorate mucosal growth during otitis media, and thereby reduce detrimental sequelae of this childhood disease.

The inflammasome adaptor ASC contributes to multiple innate immune processes in the resolution of otitis media

This study was designed to understand the contribution of the inflammasome and IL-1β activation in otitis media (OM). We examined the middle ear (ME) response to non-typeable Haemophilus influenzae (NTHi) in wild type (WT) mice using gene microarrays and a murine model of acute OM. Expression of members of the NOD domain-like receptor family of inflammasome genes was significantly up-regulated early in NTHi infection of the ME, potentially activating specific downstream regulatory cascades that contribute to the proliferative inflammatory response observed during OM. Expression of the pro-forms of the inflammasome targets IL-1β and IL-18 were also up-regulated. To evaluate the role of inflammasome-mediated cytokine maturation, NTHi-induced OM was examined in Asc(-/-)-deficient mice and compared with that seen in WT mice. Mice lacking the Asc gene showed near absence of IL-1β maturation in the ME and a reduction in leukocyte recruitment and infiltration to the cavity, and their macrophages exhibited reduced phagocytosis of NTHi. These inflammatory defects were linked to an increase in the degree and duration of mucosal epithelial hyperplasia in the ME of Asc(-/-) mice, as well as a delay in bacterial clearance from their MEs. These data demonstrate an important role for the inflammasome and cytokine processing in the course and resolution of OM.

What have we learned from murine models of otitis media?

Otitis media (OM) is a common cause of childhood hearing loss. The large medical costs involved in treating this condition have meant that research to understand the pathology of this disease and identify new therapeutic interventions is important. There is evidence that susceptibility to OM has a significant genetic component, although little is known about the key genetic pathways involved. Mouse models for disease have become an important resource to understand a variety of human pathologies, including OM, due to the ability to easily manipulate their genetic components. This has enabled researchers to create models of acute OM, and has aided in the identification of a number of new genes associated with chronic disease, through the use of mutagenesis programs. The use of mouse models has identified a number of key molecular signalling pathways involved in the development of this condition, with genes identified from models shown to be associated with human OM.

Factors affecting loss of tympanic membrane mobility in acute otitis media model of chinchilla

Recently we reported that middle ear pressure (MEP), middle ear effusion (MEE), and ossicular changes each contribute to the loss of tympanic membrane (TM) mobility in a guinea pig model of acute otitis media (AOM) induced by Streptococcus pneumoniae (Guan and Gan, 2013). However, it is not clear how those factors vary along the course of the disease and whether those effects are reproducible in different species. In this study, a chinchilla AOM model was produced by transbullar injection of Haemophilus influenzae. Mobility of the TM at the umbo was measured by laser vibrometry in two treatment groups: 4 days (4D) and 8 days (8D) post inoculation. These time points represent relatively early and later phases of AOM. In each group, the vibration of the umbo was measured at three experimental stages: unopened, pressure-released, and effusion-removed ears. The effects of MEP and MEE and middle ear structural changes were quantified in each group by comparing the TM mobility at one stage with that of the previous stage. Our findings show that the factors affecting TM mobility do change with the disease time course. The MEP was the dominant contributor to reduction of TM mobility in 4D AOM ears, but showed little effect in 8D ears when MEE filled the tympanic cavity. MEE was the primary factor affecting TM mobility loss in 8D ears, but affected the 4D ears only at high frequencies. After the release of MEP and removal of MEE, residual loss of TM mobility was seen mainly at low frequencies in both 4D and 8D ears, and was associated with middle ear structural changes. Our findings establish that the factors contributing to TM mobility loss in the chinchilla ear were similar to those we reported previously for the guinea pig ears with AOM. Outcomes did not appear to differ between the two major bacterial species causing AOM in these animal models.

Bioluminescent Imaging of Pneumococcal Otitis Media in Chinchillas

Objectives:

Bioluminescent imaging has emerged as a powerful tool for monitoring the pathological process of infections in animals. The purpose of this study was to harness this new tool for objective assessment of acute otitis media (AOM) in animals with and without antibiotic interventions.

Methods:

Thirty-six healthy chinchillas, free of middle ear infections, were randomly divided into a control group and a group that received amoxicillin treatment. Bioluminescent Streptococcus pneumoniae (Xen 10) was injected into the epitympanic bullae of chinchillas (50 colony-forming units each) for induction of AOM. The infectious process of Xen 10 in the bullae of living animals with and without antibiotic interventions was monitored in real time with bioluminescence equipment.

Results:

A dynamic change of bioluminescent signals in the bullae of chinchillas from days 1 to 14 was observed after Xen 10 injection. Amoxicillin treatment reduced the bioluminescent signals in the bullae of chinchillas compared with controls. The AOM persisted for 14 days, and middle ear effusion for 6 weeks, in the control animals, whereas AOM lasted for 2 days, and effusion for 6 to 12 days, in the antibiotic-treated animals.

Conclusions:

Bioluminescent imaging provides an innovative method for assessment of the bacterial loads in the middle ear of chinchillas in a real-time manner and is very useful for objective evaluation of the efficacy of therapeutic interventions.

Protective anti-outer membrane protein immunity against Pasteurella pneumotropica infection of mice

The ability of recombinant outer membrane proteins of Pasteurella pneumotropica to vaccinate against the infections of mice was studied. The proteins examined were the homologues of the P4, P6, P26, and D15 proteins of Haemophilus influenzae. Intranasal vaccination with P4 and P6 produced protection against pneumonia. P6 vaccination, which was most studied, reduced the peak bacteria load in lungs by 50-fold and caused a rapid resolution of an infection that lasted for at least 5 days in unvaccinated animals. Protection could be partially transferred with CD4(+) T cells and pulmonary challenge with the P6 antigen induced interferon-γ and the Th17 cytokine IL-21. This is the first demonstration of the ability of a recombinant P6 to mediate protective immunity to a pathogen in its natural host and it is proposed that it would not only have utility for mouse breeding but also for investigating how to improve the efficacy of vaccination with homologous proteins for related species.

Pili play an important role in enhancing the bacterial clearance from the middle ear in a mouse model of acute otitis media with Moraxella catarrhalis

Moraxella catarrhalis is a Gram-negative aerobic diplococcus that is currently the third most frequent cause of bacterial acute otitis media (AOM) in children. In this study, we developed an experimental murine AOM model by inoculating M. catarrhalis in the middle ear bulla and studied the local response to this inoculation, and modulation of its course by the pili of M. catarrhalis. The pili-positive and pili-negative M. catarrhalis showed differences in bacterial clearance and infiltration of inflammatory cells in the middle ear. Pili-negative M. catarrhalis induced a more delayed and prolonged immune response in the middle ear than that of pili-positive M. catarrhalis. TLR2, -4, -5 and -9 mRNA expression was upregulated in neutrophils that infiltrated the middle ear cavity during AOM caused by both pili-positive and pili-negative bacteria. TLR5 mRNA expression and TLR5 protein in the neutrophils were induced more robustly by pili-positive M. catarrhalis. This immune response is likely to be related to neutrophil function such as toll-like 5-dependent phagocytosis. Our results show that mice may provide a useful AOM model for studying the role of M. catarrhalis. Furthermore, we show that pili play an important role in enhancing M. catarrhalis clearance from the middle ear that is probably mediated through neutrophil-dependent TLR5 signaling.

The role of vascular endothelial growth factors and fibroblast growth factors in angiogenesis during otitis media

The middle ear response to otitis media includes transformation and hyperplasia of the mucosal epithelium and subepithelial connective tissue. Significant neovascularization is also noted, which occurs both to support the hypertrophied mucosa and to mediate the increased trafficking of leukocytes. We investigated the role of two known potent angiogenic growth factor families, the fibroblast growth factors (FGFs) and vascular endothelial growth factors (VEGFs), in middle ear mucosal angiogenesis. DNA microarrays were used to evaluate the expression of FGFs and VEGFs, as well as their receptors and unique signaling proteins, in the middle ears of mice undergoing a complete course of acute bacterial otitis media. In addition, a member of each family was introduced to the middle ear submucosal compartment of the normal middle ears of guinea pigs, by a continuous-release osmotic minipump system over 1 week. During the course of bacterial otitis media, a significant regulation of a number of genes important for angiogenesis was identified. Histologic evaluation of middle ear mucosa following micropump infusion of both FGF1 and VEGF-A showed significant angiogenesis at the site of infusion in comparison to control saline infusion. These results support a role for FGFs and VEGFs in the neovascularization of the middle ear mucosa during otitis media, and offer a potential avenue for therapeutic intervention.

TNFA deletion alters apoptosis as well as caspase 3 and 4 expression during otitis media

Background

Tumor necrosis factor (TNFA) is the canonical member of the TNF superfamily, which plays a major role in both inflammation and apoptosis. To evaluate the role of TNFs in otitis media (OM), the most common disease of childhood, we evaluated middle ear (ME) expression of genes encoding the TNF and TNF receptor superfamilies during bacterial OM in the mouse, characterized OM in TNFA-deficient mice, and assessed apoptosis during OM in normal versus TNF-deficient MEs.

Results

TNFs and TNF receptors were broadly regulated during OM, with TNFA showing the highest level of up-regulation. TNF deficient mice exhibited mucosal hyperplasia even in the absence of infection and exuberant growth of the mucosa during OM, including the formation of mucosal polyps. Mucosal recovery during OM was also delayed, in parallel with a delay in mucosal apoptosis and reduced caspase gene expression.

Conclusions

The TNF and TNF receptor superfamilies mediate both inflammation and apoptosis during OM. TNF appears to be critical for the maintenance of mucosal architecture in both the normal and infected ME, since excessive accumulation of mucosal tissue is seen in TNFA^-/- MEs both before and after bacterial inoculation of the ME. TNFA is also required for appropriate regulation of caspase genes.

The role of DNA sensing and innate immune receptor TLR9 in otitis media

Otitis media (OM), a common infectious disease in children, is associated with bacterial middle ear (ME) infection. Toll-like receptors (TLRs) are important mediators of innate immune responses, and TLR9 specifically recognizes the unmethylated cytidine-phosphate-guanosine (CpG) motifs in bacterial DNA. Additional sensors of foreign DNA have recently been identified. The role of DNA sensing and TLR9 was investigated in a murine model of OM induced by non-typeable Haemophilus influenzae (NTHi). Expression of genes related to DNA-sensing pathways involved in innate immunity was assessed via DNA microarray, qPCR and immunohistochemistry. Middle ear responses to NTHi were examined in wild-type and TLR9(-/-) mice by histopathology and bacterial culture. Expression of TLR9 signaling genes was modestly up-regulated during OM, as was TLR9 protein in both ME mucosal cells and infiltrating leukocytes. However, genes known to be regulated by CpG DNA were dramatically up-regulated, as were genes involved in DNA sensing by DIA, Pol-III and AIM2. Toll-like receptor 9 deletion significantly prolonged the inflammatory response induced by NTHi in the ME and delayed bacterial clearance. The results suggest that DNA sensing via TLR9 plays a role in OM pathogenesis and recovery. Alternative forms of DNA sensing may also contribute to OM.

CC chemokine ligand 3 overcomes the bacteriocidal and phagocytic defect of macrophages and hastens recovery from experimental otitis media in TNF-/- mice

Innate immune mechanisms are crucial in defense against bacterial illnesses in humans, as evidenced by abnormal antibacterial responses due to defects in TLR signaling, seen in children with MyD88 or IL-1R-associated kinase 4 deficiency. Otitis media (OM) is the most common disease of childhood, and the role of innate immune molecules in this disorder remains unclear. In a murine model of OM, we show that, in the absence of TNF, a key effector of innate immunity, this disease is prolonged after middle ear infection with nontypeable Haemophilus influenzae (NTHi). In the absence of TNF, mice fail to upregulate both TLRs and downstream genes and proteins, such as CCL3, resulting in defects in both inflammatory cell recruitment and macrophage function. Peritoneal macrophages of mice lacking TNF have a diminished ability to phagocytose and kill NTHi, and this defect is partially corrected in vitro by exogenous rTNF. Addition of rCCL3 alone or in combination with rTNF restores phagocytosis and killing by TNF-deficient macrophages to that of unstimulated wild-type macrophages. In vivo administration of rCCL3 to animals deficient in TNF fully restores the ability to control OM due to NTHi, whereas a CCL3-blocking Ab impaired the ability of wild-type mice to recover from OM. Thus, CCL3 is a potent downstream effector of TNF-mediated inflammation in vitro and in vivo. Manipulation of CCL3 and/or TNF may prove to be effective therapeutic approaches in OM or other conditions associated with defective TNF generation.

Development of a non-invasive murine infection model for acute otitis media

Otitis media (OM) is one of the most frequent diseases in childhood, and Streptococcus pneumoniae is among the main causative bacterial agents. Since current experimental models used to study the bacterial pathogenesis of OM have several limitations, such as the invasiveness of the experimental procedures, we developed a non-invasive murine OM model. In our model, adapted from a previously developed rat OM model, a pressure cabin is used in which a 40 kPa pressure increase is applied to translocate pneumococci from the nasopharyngeal cavity into both mouse middle ears. Wild-type pneumococci were found to persist in the middle ear cavity for 144 h after infection, with a maximum bacterial load at 96 h. Inflammation was confirmed at 96 and 144 h post-infection by IL-1beta and TNF-alpha cytokine analysis and histopathology. Subsequently, we investigated the contribution of two surface-associated pneumococcal proteins, the streptococcal lipoprotein rotamase A (SlrA) and the putative proteinase maturation protein A (PpmA), to experimental OM in our model. Pneumococci lacking the slrA gene, but not those lacking the ppmA gene, were significantly reduced in virulence in the OM model. Importantly, pneumococci lacking both genes were significantly more attenuated than the DeltaslrA single mutant. This additive effect suggests that SlrA and PpmA exert complementary functions during experimental OM. In conclusion, we have developed a highly reproducible and non-invasive murine infection model for pneumococcal OM using a pressure cabin, which is very suitable to study pneumococcal pathogenesis and virulence in vivo.

The toll-Like receptor adaptor TRIF contributes to otitis media pathogenesis and recovery

Background

Toll-like receptor (TLR) signalling is crucial for innate immune responses to infection. The involvement of TLRs in otitis media (OM), the most prevalent childhood disease in developed countries, has been implicated by studies in middle ear cell lines, by association studies of TLR-related gene polymorphisms, and by altered OM in mice bearing mutations in TLR genes. Activated TLRs signal via two alternative intracellular signaling molecules with differing effects; MyD88 (Myeloid differentiation primary response gene 88) inducing primarily interleukin expression and TRIF (Tir-domain-containing adaptor inducing interferon β) mediating type I interferon (IFN) expression. We tested the hypothesis that TRIF and type I IFN signaling play a role in OM, using a murine model of OM induced by non-typeable Haemophilus influenzae (NTHi). The ME inflammatory response to NTHi was examined in wild-type (WT) and TRIF-/- mice by qPCR, gene microarray, histopathology and bacterial culture.

Results

Expression of TRIF mRNA was only modesty enhanced during OM, but both type I IFN signalling genes and type I IFN-inducible genes were significantly up-regulated in WT mice. TRIF-deficient mice showed reduced but more persistent mucosal hyperplasia and less leukocyte infiltration into the ME in response to NTHi infection than did WT animals. Viable bacteria could be cultured from MEs of TRIF-/- mice for much longer in the course of disease than was the case for middle ears of WT mice.

Conclusion

Our results demonstrate that activation of TRIF/type I IFN responses is important in both the pathogenesis and resolution of NTHi-induced OM.

TLR4-mediated induction of TLR2 signaling is critical in the pathogenesis and resolution of otitis media

Otitis media is the most prevalent childhood disease in developed countries. The involvement of Toll-like receptors (TLRs) in otitis media pathophysiology has been implicated by studies in cell lines and association studies of TLR gene polymorphisms. However, precise functions of TLRs in the etiology of otitis media in vivo have not been examined. We investigated the inflammatory response to nontypeable Haemophilus influenzae using a model of otitis media in wild-type, TLR2(- /-) and TLR4(-/ -) mice by gene microarray, qPCR, immunohistochemistry, Western blot analysis and histopathology. Toll-like receptor-2(- /-) and TLR4(- /-) mice exhibited a more profound, persistent inflammation with impaired bacterial clearance compared to controls. While wild-type mice induced tumor necrosis factor-a (TNF) after non-typeable H. influenzae challenge, TLR2(-/-) and TLR4(-/-) mice lack TNF induction in the early phase of otitis media. Moreover, lack of TLR2 resulted in a late increase in IL-10 expression and prolonged failure to clear bacteria. Toll-like receptor-4(-/- ) mice showed impaired early bacterial clearance and loss of TLR2 induction in early otitis media. Our results demonstrate that both TLR2 and TLR4 signalling are critical to the regulation of infection in non-typeable H. influenzae-induced otitis media. Toll-like receptor-4 signalling appears to induce TLR2 expression, and TLR2 activation is critical for bacterial clearance and timely resolution of otitis media.

Natural antibody to conserved targets of Haemophilus influenzae limits colonization of the murine nasopharynx

Nasopharyngeal colonization represents the initial interaction between Haemophilus influenzae and its human host. Factors that influence bacterial carriage likely affect transmission and incidence of infection. Therefore, we investigated host factors involved in limiting H. influenzae colonization in BALB/c mice, as colonization can be established in this genetic background. Unlike what is observed in the C57BL/6 background, initial colonization of BALB/c mice was mainly limited by adaptive immune components. This effect on colonization did not require either CD4- or CD8-positive T cells. Instead, initial colonization by genetically diverse strains was limited by preexisting natural antibody with a lesser contribution of complement activity and the presence of neutrophils. Natural serum immunoglobulin from mice was able to bind to the bacterial surface and exhibited complement-dependent bactericidal activity against these genetically diverse H. influenzae strains. Moreover, natural immunoglobulin G (IgG) recognizing these strains was detected at the nasopharyngeal mucosal surface. This antibody-mediated effect required exposure to the normal mouse microbial flora, since mice raised under germfree (GF) conditions showed increased levels of H. influenzae colonization that were not limited by adaptive immunity. In addition, serum IgG from GF mice exhibited less surface binding to H. influenzae, suggesting that natural antibody, induced through prior exposure to the microbial flora, mediated the observed reduction in initial colonization. The broad effect of natural IgG against genetically diverse isolates suggests the presence of conserved species-wide protective targets of antibody.

Role for Toll-like receptor 2 in the immune response to Streptococcus pneumoniae infection in mouse otitis media

Streptococcus pneumoniae is the most common pathogen associated with otitis media. To examine the role of Toll-like receptor 2 (TLR2) in host defense against Streptococcus pneumoniae infection in the middle ear, wild-type (WT; C57BL/6) and TLR2-deficient (TLR2(-/-)) mice were inoculated with Streptococcus pneumoniae (1 x 10(6) CFU) through the tympanic membrane. Nineteen of 37 TLR2(-/-) mice showed bacteremia and died within 3 days after the challenge, compared to only 4 of 32 WT mice that died. Of those that survived, more severe hearing loss in the TLR2(-/-) mice than in the WT mice was indicated by an elevation in auditory-evoked brain stem response thresholds at 3 or 7 days postinoculation. The histological pathology was characterized by effusion and tissue damage in the middle ear, and in the TLR2(-/-) mice, the outcome of infection became more severe at 7 days. At both 3 and 7 days postchallenge, the TLR2(-/-) mice had higher blood bacterial titers than the WT mice (P < 0.05), and typical bacteria were identified in the effusion from both ears of both mouse groups by acridine orange staining. Moreover, by 3 days postchallenge, the mRNA accumulation levels of NF-kappaB, tumor necrosis factor alpha, interleukin 1beta, MIP1alpha, Muc5ac, and Muc5b were significantly lower in the ears of TLR2(-/-) mice than in WT mice. In summary, TLR2(-/-) mice may produce relatively low levels of proinflammatory cytokines following pneumococcal challenge, thus hindering the clearance of bacteria from the middle ear and leading to sepsis and a high mortality rate. This study provides evidence that TLR2 is important in the molecular pathogenesis and host response to otitis media.

Mouse models for human otitis media

Otitis media (OM) remains the most common childhood disease and its annual costs exceed $5 billion. Its potential for permanent hearing impairment also emphasizes the need to better understand and manage this disease. The pathogenesis of OM is multifactorial and includes infectious pathogens, anatomy, immunologic status, genetic predisposition, and environment. Recent progress in mouse model development is helping to elucidate the respective roles of these factors and to significantly contribute toward efforts of OM prevention and control. Genetic predisposition is recognized as an important factor in OM and increasing numbers of mouse models are helping to uncover the potential genetic bases for human OM. Furthermore, the completion of the mouse genome sequence has offered a powerful set of tools for investigating gene function and is generating a rich resource of mouse mutants for studying the genetic factors underlying OM.

Myeloid differentiation primary response gene 88 is required for the resolution of otitis media

BACKGROUND

Signaling defects in the Toll-like receptor (TLR) pathway, such as interleukin-1 receptor-associated kinase 4 deficiency, highlight the prominence of TLR signaling in the defense against bacterial disease. Because myeloid differentiation primary response gene 88 (MyD88) can transduce signals from almost all TLRs, we studied its role in otitis media (OM), the most common upper respiratory tract bacterial infectious disease in young children.

METHODS

The middle ears (MEs) of wild-type (WT) and MyD88(-/-) mice were inoculated with nontypeable Haemophilus influenzae (NTHi). ME infection and inflammation were monitored for 21 days after surgery. Bone marrow-derived macrophages from WT and MyD88(-/-) mice were infected with NTHi in vitro to assess their interaction with bacteria.

RESULTS

In WT mice, MyD88 expression was detected in the ME stroma at baseline. MyD88(-/-) mice displayed prolonged ME mucosal thickening and delayed recruitment of neutrophils and macrophages. Although WT mice cleared NTHi within 5 days, viable NTHi were isolated for up to 21 days in MyD88(-/-) mice. The interaction between macrophages and NTHi was significantly altered in MyD88(-/-) mice.

CONCLUSIONS

In this mouse model, MyD88-mediated signaling was important for clearance of infection and resolution of inflammation in acute OM due to NTHi. The role played by innate signaling in children susceptible to chronic or recurrent OM deserves further study.

Animal models of Streptococcus pneumoniae disease

SUMMARY

Streptococcus pneumoniae is a colonizer of human nasopharynx, but it is also an important pathogen responsible for high morbidity, high mortality, numerous disabilities, and high health costs throughout the world. Major diseases caused by S. pneumoniae are otitis media, pneumonia, sepsis, and meningitis. Despite the availability of antibiotics and vaccines, pneumococcal infections still have high mortality rates, especially in risk groups. For this reason, there is an exceptionally extensive research effort worldwide to better understand the diseases caused by the pneumococcus, with the aim of developing improved therapeutics and vaccines. Animal experimentation is an essential tool to study the pathogenesis of infectious diseases and test novel drugs and vaccines. This article reviews both historical and innovative laboratory pneumococcal animal models that have vastly added to knowledge of (i) mechanisms of infection, pathogenesis, and immunity; (ii) efficacies of antimicrobials; and (iii) screening of vaccine candidates. A comprehensive description of the techniques applied to induce disease is provided, the advantages and limitations of mouse, rat, and rabbit models used to mimic pneumonia, sepsis, and meningitis are discussed, and a section on otitis media models is also included. The choice of appropriate animal models for in vivo studies is a key element for improved understanding of pneumococcal disease.

Free Bioverit ® II Implants Coated with a Nanoporous Silica Layer in a Mouse Ear Model — A Histological Study

The objective of this study is to evaluate the suitability of a mouse middle ear model for testing ossicular replacement materials. Twenty-four BALB/c mice are implanted with the bioglass-ceramic Bioverit® II which is coated with a silica-nanostructure or with plain Bioverit® II as a control. After 2, 6, and 12 weeks, 4 mice per group are sacrificed and both complete petrous bones are analyzed histologically. All implants revealed in situ an incipient growth of thin connective tissue layers over the surface, followed by a spreading of epithelial cells. The osseogenic response which is increasing with time is more intense in the coated Bioverit ® II specimens. The absence of inflammatory cells suggests an excellent biocompatibility of the silica nano structure. As the results are comparable to a study with the same materials in rabbits, the mouse model described is highly suitable for evaluation of new ossicular replacement materials. Additionally, by gene expression analysis a more detailed insight into cellular interactions of the middle ear is offered.

Lysozyme M deficiency leads to an increased susceptibility to Streptococcus pneumoniae-induced otitis media

Background

Lysozyme is an antimicrobial innate immune molecule degrading peptidoglycan of the bacterial cell wall. Lysozyme shows the ubiquitous expression in wide varieties of species and tissues including the tubotympanum of mammals. We aim to investigate the effects of lysozyme depletion on pneumococcal clearance from the middle ear cavity.

Methods

Immunohistochemistry was performed to localize lysozyme in the Eustachian tube. Lysozyme expression was compared between the wild type and the lysozyme M^-/- mice using real time quantitative RT-PCR and western blotting. Muramidase activity and bactericidal activity of lysozyme was measured using a lysoplate radial diffusion assay and a liquid broth assay, respectively. To determine if depletion of lysozyme M increases a susceptibility to pneumococal otitis media, 50 CFU of S. pneumoniae 6B were transtympanically inoculated to the middle ear and viable bacteria were counted at day 3 and 7 with clinical grading of middle ear inflammation.

Results

Immunolabeling revealed that localization of lysozyme M and lysozyme P is specific to some/particular cell types of the Eustachian tube. Lysozyme P of lysozyme M^-/- mice was mainly expressed in the submucosal gland but not in the tubal epithelium. Although lysozyme M^-/- mice showed compensatory up-regulation of lysozyme P, lysozyme M depletion resulted in a decrease in both muramidase and antimicrobial activities. Deficiency in lysozyme M led to an increased susceptibility to middle ear infection with S. pneumoniae 6B and resulted in severe middle ear inflammation, compared to wild type mice.

Conclusion

The results suggest that lysozyme M plays an important role in protecting the middle ear from invading pathogens, particularly in the early phase. We suggest a possibility of the exogenous lysozyme as an adjuvant therapeutic agent for otitis media, but further studies are necessary.

Interleukin-10 is an essential modulator of mucoid metaplasia in a mouse otitis media model

OBJECTIVES

Inflammatory cytokines are involved in the development of mucous cell metaplasia and hyperplasia (MCM) in otitis media (OM). However, which cytokines play an essential role in the MCM of OM is not clear at the moment.

METHODS

In this study, we hypothesized that interleukin-10 (IL-10) played an indispensable role in the MCM of bacterial OM, and we used IL-10 knockout mice to test this hypothesis.

RESULTS

In wild-type mice, both Streptococcus pneumoniae and Haemophilus influenzae triggered the development of MCM in the middle ear mucosa. In IL-10 knockout mice, the number of goblet cells and mucin-producing cells in the middle ear was significantly reduced after bacterial middle ear infection compared with that in wild-type mice.

CONCLUSIONS

We conclude that IL-10 plays an essential role in the MCM of bacterial OM. Interleukin-10 is a potential target for the treatment of MCM in OM.

Mouse models of otitis media

PURPOSE OF REVIEW

Otitis media is one of the most prevalent inflammatory diseases in the pediatric population. The personal and societal costs for otitis media are significant. Problems arising from antibiotic use have led to considerable animal research efforts to better understand the mechanisms of acute otitis media and to develop new strategies for its prevention and treatment.

RECENT FINDINGS

Various animal models induce acute otitis media from a variety of interventions, including direct injection of whole bacteria or their products into the middle ear. The mouse model has begun to emerge as a model for otitis media. The mouse affords many advantages for in-vivo research, including ease of genetic manipulation, availability of numerous inbred and transgenic strains, and an extensively studied immune system. Experimental reagents for cellular and molecular studies are widely available for the mouse. The mouse is an excellent model for investigating the genetics and molecular bases for otitis media due to the extensive understanding of the mouse genome.

SUMMARY

With the increased availability of knockout and transgenic mice, and the large amount of data to indicate that human disease is accurately modeled in the mouse, the mouse model is increasingly becoming a model of choice.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

Tympanometry assessment of 61 inbred strains of mice

Otitis media (OM) accounts for more than 20 million clinic visits in the United States every year. Resistance to antibiotics has hampered current management of the disease. Identification of genetic factors underlying susceptibility to OM is greatly needed in order to develop alternative treatment strategies. Genetically defined inbred mouse strains offer a powerful tool for dissecting genetic and environmental factors that may lead to OM in mice. Here, we report a study of middle ear function of 61 genetically diverse inbred strains of mice using tympanometry. Of the 61 inbred strains tested, the 129P1/ReJ, 129P3/J, 129S1/SvImJ, 129X1/SvJ, A/HeJ, BALB/cJ, BUB/BnJ, C57L/J, EL/SuzSeyFrkJ, FVB/NJ, I/LnJ, LP/J, NZB/BlNJ, PL/J and YBR/Ei strains exhibited tympanograms that were statistically different from other healthy strains according to parameters including middle ear pressure, volume and compliance. These differences are most likely the result of genetic factors that, when understood, will facilitate prevention and treatment of otitis media in humans. In addition, a negative correlation between age and compliance of the tympanic membrane was discovered. This is the first report to successfully use tympanometry to measure mouse middle ear function, which has been a challenge for the hearing research field because of the mouse's tiny ear size.

Spontaneous otitis media in Wistar rats: an overlooked pathology in otological research

The rat is commonly employed in otological research, but spontaneous ear infections can confound the results of experimental procedures--wasting time, money, and animals. The authors focus on the incidence of spontaneous otitis media in Wistar rats. They compare disease incidence in animals housed in standard cages with those housed in barrier units, showing that 20% of their conventionally housed animals developed spontaneous otitis media, whereas only 5% of their animals housed in isolated units were infected. These results underscore the importance of strict control of the shipping, housing conditions, and manipulation of animals to be used in otological research.

Evaluation of the mouse model for acute otitis media

Various animal models have been employed for otitis media research. The mouse has been studied less, in spite of its many advantages. To better understand the suitability of the mouse for studies of otitis media, an evaluation was made of its middle ear inflammatory processes following inoculation with heat-killed Streptococcus pneumoniae (strain 6A), one of the three most common bacteria to cause otitis media in the human. A total of 94 BALB/c mice were injected transtympanically with three concentrations of heat-killed bacteria (10(4), 10(6), and 10(9) organisms per ml) and inflammation evaluated with both histologic examination and auditory brainstem response audiometry. Dose-related measures of the time course of inflammation showed it was maximal at 3 days. PBS-injected control mice also demonstrated some degree of middle ear inflammation. Therefore, inflammation measures from PBS injected mice were used as the threshold above which histologic inflammatory changes would be considered a response to bacteria. These quantitative comparisons of bacterial and PBS inoculations revealed the most significant middle ear measures of inflammation were amount of fluid in the middle ear, tympanic membrane thickness, and number of inflammatory cells. The induction of middle ear inflammation in the mouse demonstrated the applicability of this model for investigations of otitis media.

Mouse models of induced otitis media

The mouse has seen limited use as a model for experimental otitis media, due primarily to the small size of its middle ear. However, the genetic resources of this species offer substantial potential benefits. These include detailed genomic information, a wealth of genetic models, and gene arrays that represent virtually all mouse genes. This has led to the development of methods for inducing otitis in mice. These include surgical approaches to the middle ear, documentation of the murine middle ear response to various pathogens and inflammatory factors, as well as characterization of induced otitis media in several mouse strains. The results indicate that induced otitis media in the normal mouse is in most respects comparable to that observed in other animal models and in humans. They further suggest that the considerable genetic resources of this species can be harnessed to increase our understanding of this disease.

Intranasal vaccination of neonatal mice with polysaccharide conjugate vaccine for protection against pneumococcal otitis media

Streptococcus pneumoniae is the leading bacterial cause of acute otitis media (OM) in young children, and can often produce invasive disease. Typical intramuscular routes of vaccination are poorly protective against development of OM. In the present study, we intranasally (i.n.) inoculated neonatal 1-week-old mice with pneumococcal polysaccharide conjugate vaccine using IL-12 as a mucosal adjuvant. The protective efficacy of this treatment was tested by challenging immunized infant (3-week-old) mice with bacteria to induce OM and invasive disease. i.n. vaccination was found to enhance levels of specific antibodies in middle ear (ME) washes and sera from wild-type (but not IFN-gamma(-/-)) mice. Immunization in the presence of IL-12 resulted in enhanced clearance of S. pneumoniae from the ME. Opsonization of bacteria with ME wash fluids or sera from immunized mice caused increased bacterial clearance from the ME of naïve mice. In addition, immunized mice demonstrated 89% survival after OM-induced invasive pneumococcal infection, compared to 22% survival in unvaccinated mice. These results indicate that i.n. vaccination of neonatal mice in the presence of IL-12 is able to enhance IFN-gamma dependent ME mucosal and systemic immune responses to pneumococci and efficiently protect against both OM and invasive infection.

Role of mast cells in otitis media

BACKGROUND

New pathophysiologic concepts are needed to explain the clinically observed connection between the allergic diathesis and otitis media. Although mast cells, unlike lymphocytes, are common in the normal middle ear mucosa, their potential role in innate immunity of the middle ear and in the expression of inflammatory responses in that space to bacterial challenge, as opposed to allergy, has received relatively little attention.

OBJECTIVE

In the current study, we examine the contributions of mast cells to the pathogenesis of bacterially induced inflammation in the middle ear and thus to otitis media.

METHODS

Wild-type mice, mast cell-deficient mice, and mast cell-deficient mice whose mast cell populations were restored by transplantation of bone marrow-derived mast cells were challenged by using models of bacterial and allergic middle ear inflammation.

RESULTS

Our results indicate that mast cells account for a substantial proportion of the innate immune response to bacteria in the middle ear.

CONCLUSION

This mechanism may link responses to allergy and infection in the middle ear mucosa, and thus the mast cell may be a critical control element in the pathogenesis of otitis media.