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

Abstract

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.

Adaptive immune protection of the middle ears differs from that of the respiratory tract

“…and no bacteria were recovered from the MEs by day 56 p.i., indicating complete clearance. Histological examination of HE stained sections from previous studies (Dewan et al, 2022) showed evidence of inflammation and hypercellularity at day 7 p.i (peak of infection) (Figure 1B). Here we find that by day 56 inflammation had subsided.…”

“…We next turned our attention to examining the contributions of humoral and cellular components of adaptive immunity on convalescent protection. We had previously observed (Dewan et al, 2022) that when immune serum collected from convalescent WT mice (day 56 p.i.) was intraperitoneally injected into naive Rag-1 -/mice and challenged, bacterial CFUs in the MEs were reduced by ~100-fold compared to untreated Rag-1 -/mice.…”

“…Over the course of conducting studies on the respiratory tract pathogens belonging to the genus Bordetella ( Linz et al., 2019 ), we observed and reported that two mouse pathogens, Bordetella pseudohinzii ( Dewan et al., 2019 ) and Bordetella bronchiseptica ( Dewan et al., 2022 ) can rapidly and efficiently ascend the ET from the nasopharynx to colonize and infect the MEs of mice. While infections by B. pseudohinzii are chronic and persist in the MEs, eventually leading to the deafness of the mice, B. bronchiseptica is controlled and subsequently cleared from the MEs over a period of convalescence coincident with the generation of a robust immune response.…”

Contribution of a Novel Pertussis Toxin-Like Factor in Mediating Persistent Otitis Media

“…Mice infected with B. bronchiseptica experienced a steep decline (>95% reduction) in bacterial numbers between 7 and 14 dpi. This decline continued to 56 dpi, and B. bronchiseptica was cleared from the middle ears by 100 dpi ( Dewan et al, 2022 ) by the generation of a robust adaptive immune response ( Dewan et al, 2022 ). In contrast, B. pseudohinzii persisted in the middle ears at high numbers, approximately 10,000 CFU, until at least day 100, the end of this timecourse, with no apparent decline, suggesting infection is chronic, potentially life-long ( Figure 1 and data not shown).…”

“…In addition to its strengths as a model for OM, B. pseudohinzii has also been investigated as an upper respiratory tract pathogen that forms biofilms ( Clark et al., 2016 ) and is cytotoxic to ciliated epithelial cells ( Perniss et al., 2018 ). In contrast to B. pseudohinzii , a related species, B. bronchiseptica , can highly efficiently colonize both nasal cavity and middle ears of mice, and persists for life in the noses but is cleared from the middle ears by processes that involve adaptive immunity ( Dewan et al., 2019 ; Dewan et al, 2022 ).…”