Cellular Immune Response against Nontypeable Haemophilus influenzae Infecting the Preinflamed Middle Ear of the Junbo Mouse

An infant mouse model of influenza-driven nontypeable Haemophilus influenzae colonization and acute otitis media suitable for preclinical testing of novel therapies

Nontypeable Haemophilus influenzae (NTHi) is a major otitis media (OM) pathogen, with colonization a prerequisite for disease development. Most acute OM is in children <5 years old, with recurrent and chronic OM impacting hearing and learning. Therapies to prevent NTHi colonization and/or disease are needed, especially for young children. Respiratory viruses are implicated in driving the development of bacterial OM in children. We have developed an infant mouse model of influenza-driven NTHi OM, as a preclinical tool for the evaluation of safety and efficacy of clinical therapies to prevent NTHi colonization and the development of OM. In this model, 100% of infant BALB/cARC mice were colonized with NTHi, and all developed NTHi OM. Influenza A virus (IAV) facilitated the establishment of dense (1 × 105 CFU/mL) and long-lasting (6 days) NTHi colonization. IAV was essential for the development of NTHi OM, with 100% of mice in the IAV/NTHi group developing NTHi OM compared with 8% of mice in the NTHi only group. Histological analysis and cytokine measurements revealed that the inflammation observed in the middle ear of the infant mice with OM reflected inflammation observed in children with OM. We have developed the first infant mouse model of NTHi colonization and OM. This ascension model uses influenza-driven establishment of OM and reflects the clinical pathology of bacterial OM developing after a respiratory virus infection. This model provides a valuable tool for testing therapies to prevent or treat NTHi colonization and disease in young children.

PANEL 3: Otitis media animal models, cell culture, tissue regeneration & pathophysiology

OBJECTIVE

To review and summarize recently published key articles on the topics of animal models, cell culture studies, tissue biomedical engineering and regeneration, and new models in relation to otitis media (OM).

DATA SOURCE

Electronic databases: PubMed, National Library of Medicine, Ovid Medline.

REVIEW METHODS

Key topics were assigned to the panel participants for identification and detailed evaluation. The PubMed reviews were focused on the period from June 2019 to June 2023, in any of the objective subject(s) or keywords listed above, noting the relevant references relating to these advances with a global overview and noting areas of recommendation(s). The final manuscript was prepared with input from all panel members.

CONCLUSIONS

In conclusion, ex vivo and in vivo OM research models have seen great advancements in the past 4 years. From the usage of novel genetic and molecular tools to the refinement of in vivo inducible and spontaneous mouse models, to the introduction of a wide array of reliable middle ear epithelium (MEE) cell culture systems, the next five years are likely to experience exponential growth in OM pathophysiology discoveries. Moreover, advances in these systems will predictably facilitate rapid means for novel molecular therapeutic studies.

Otitis media: Interactions between host and environment, immune and inflammatory responses

OBJECTIVE

To review and highlight progress in otitis media (OM) research in the areas of immunology, inflammation, environmental influences and host-pathogen responses from 2019 to 2023. Opportunities for innovative future research were also identified.

DATA SOURCES

PubMed database of the National Library of Medicine.

REVIEW METHODS

Key topics were assigned to each panel member for detailed review. Search of the literature was from June 2019 until February 2023. Draft reviews were collated, circulated, and discussed among panel members at the 22nd International Symposium on Recent Advances in Otitis Media in June 2023. The final manuscript was prepared and approved by all the panel members.

CONCLUSIONS

Important advances were identified in: environmental influences that enhance OM susceptibility; polymicrobial middle ear (ME) infections; the role of adaptive immunity defects in otitis-proneness; additional genes linked to OM; leukocyte contributions to OM pathogenesis and recovery; and novel interventions in OM based on host responses to infection. Innovative areas of research included: identification of novel bacterial genes and pathways important for OM persistence, bacterial adaptations and evolution that enhance chronicity; animal and human ME gene expression, including at the single-cell level; and Sars-CoV-2 infection of the ME and Eustachian tube.

Gene expression analysis reveals immune and metabolic candidate pathways in the pathogenesis of chronic otitis media

OBJECTIVES

Chronic otitis media (COM) is a common disease and causes significant hearing impairment in many adults. Our study aimed to investigate the immune response in COM adult patients through RNA sequencing.

METHODS

In this study, we enrolled four adult COM patients and five healthy controls (HCs) to analyze and compare the mRNA signatures in their peripheral blood mononuclear cells (PBMCs). Gene Ontology functional enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses were performed on the differentially expressed genes between the COM patients and the HCs. Furthermore, the immune cell proportions of the two groups were estimated by CIBERSORT. The GSE125532, GSE27990, and GSE23140 gene expression profiles were also retrieved and analyzed for comparison with our results.

RESULTS

Many immune pathways and genes were upregulated in the COM patients, including the IL-17 pathway and NLRP3. Monocytes and macrophages increased (P=0.005 and P=0.033, respectively), and the CD8+ T cells decreased (P=0.033) in the COM patients compared to the HCs. The COM patients' signatures also reflected a hypoxic state.

CONCLUSIONS

Our findings emphasized the roles of several immune pathways and a hypoxic state in interpreting host responses during COM, and may enable the development of novel therapeutic tools for the disease.

A Bacterial Epigenetic Switch in Non-typeable Haemophilus influenzae Modifies Host Immune Response During Otitis Media

Non-typeable Haemophilus influenzae (NTHi) causes multiple diseases of the human airway and is a predominant bacterial pathogen of acute otitis media and otitis media in which treatment fails. NTHi utilizes a system of phase variable epigenetic regulation, termed the phasevarion, to facilitate adaptation and survival within multiple sites of the human host. The NTHi phasevarion influences numerous disease-relevant phenotypes such as biofilm formation, antibiotic resistance, and opsonization. We have previously identified an advantageous selection for a specific phasevarion status, which significantly affects severity and chronicity of experimental otitis media. In this study, we utilized pure cultures of NTHi variants in which modA was either locked ON or locked OFF, and thus modA was unable to phase vary. These locked variants were used to assess the progression of experimental otitis media and define the specific immune response induced by each subpopulation. Although the initial disease caused by each subpopulation was similar, the immune response elicited by each subpopulation was unique. The modA2 OFF variant induced significantly greater activation of macrophages both in vitro and within the middle ear during disease. In contrast, the modA2 ON variant induced a greater neutrophil extracellular trap response, which led to greater killing of the modA2 ON variant. These data suggest that not only does the NTHi phasevarion facilitate adaptation, but also allows the bacteria to alter immune responses during disease. Understanding these complex bacterial-host interactions and the regulation of bacterial factors responsible is critical to the development of better diagnostic, treatment, and preventative strategies for these bacterial pathogens.

Phase variation with altering phosphorylcholine expression of nontypeable Haemophilus influenzae affects bacteria clearance and mucosal immune response in the middle ear and nasopharynx

OBJECTIVES

Nontypeable Haemophilus influenzae (NTHi) is a chief pathogen in both acute otitis media and otitis media with effusion. Phosphorylcholine (ChoP) is expressed on lipooligosaccharides, and ChoP has phase variation, which is related to its adhesion to and invasion of epithelial cells in the upper airway. However, little is known about the role of ChoP expression. We examined the kinetics of the mucosal clearance of NTHi from the nose and middle ear and the mucosal immune response to NTHi infection by comparing ChoP(+) and ChoP(-) strains in a mouse model of middle ear and nasal challenge.

METHODS

Six-week-old male BALB/c mice were subjected to bacterial challenge in the middle ear and nasopharynx. Mice were inoculated with a suspension of a ChoP(+) strain or ChoP(-) strain of NTHi. On days 1, 3, and 7 after inoculation, the middle ear wash (MEW) and nasal wash (NW) were harvested from each group. The samples were used for bacterial counts and the supernatant was used to measure the level of cytokines and C-reactive protein (CRP).

RESULTS

MEWs in the ChoP(+) strain group had significantly higher bacterial counts than those in the ChoP(-) strain group on day 1. However, bacteria were eradicated in the ChoP(+) strain group on day 7. NWs in the ChoP(+) strain group had higher bacterial counts than those in the ChoP(-) strain group during the experiment, however, there was no significant difference between the two strains. The levels of cytokines were significantly higher in the ChoP(-) strain group than in the ChoP(+) strain group in MEWs, but these cytokine levels were low in NWs. The CRP concentration in the ChoP(-) group was high on day 7 in the MEWs. In NWs, the CRP concentration was low in all groups during the experiment.

CONCLUSION

ChoP expression of NTHi changes the organism susceptible to killing by CRP, and the ChoP(+) strain might be gradually eradicated from the middle ear via the CRP-complement cascade, but not from nasopharynx. Based on our findings, phase variation by altering Phosphorylcholine expression of nontypeable Haemophilus influenzae affects bacteria clearance and mucosal immune response in the middle ear and nasopharynx.