Monocyte-dependent innate immunity prevents severe complications of acute bacterial infection in the middle ear in a murine model

Abstract

Introduction: Acute otitis media (AOM) is a common middle ear infection. The role of immune cells, particularly monocytes, in preventing complications of AOM remains unclear. Therefore, this study aimed to investigate the role of monocytes in immune response to bacterial AOM using a murine model. Methods: Wild-type C57BL/6 mice were infected with GFP-tagged Pseudomonas aeruginosa (PA01) via intratympanic (IT) middle ear injection to mimic bacterial AOM. Monocyte depletion (MD) was performed using clodronate liposomes. Results: The survival rate after PA01 IT injection was significantly lower (p = 0.018) in the MD group (50.0 %, n = 18) than in the control group (100 %, n = 9). The MD group exhibited severe hearing loss 2 weeks after PA01 injection, whereas the control group showed transient hearing loss resolving by 2 weeks. Bacterial growth was significantly greater in the MD group than in the control group (p < 0.001). Conclusion: MD causes uncontrolled bacterial growth and leads to more severe complications. Monocytemediated immune responses play a critical role in preventing the severe complications of AOM, suggesting a potential target for future therapeutic strategies.