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Role of phagocytes in antimicrobial defence of the middle ear
1Department of Otolaryngology, Medical College of Oita, Japan.
Abstract:
The role of phagocytes in the antimicrobial defence of the middle ear was investigated in this experiment, using Hartley strain guinea pigs with an experimental otitis media. Otitis media was induced with an inoculation of Streptococcus pneumoniae into the tympanic cavity through the ear drum. For depletion of peripheral blood phagocyte population such as monocytes and polymorphonuclear neutrophils (PMNs), whole body irradiation (250 rad or 500 rad) was carried out on guinea pigs three days before S. pneumoniae inoculation into the middle ears. Carrageenan was also used for selective depletion of mononuclear cells, to distinguish their role from polymorphonuclear neutrophils. In control animals, otitis media was induced reproducibly with middle ear inoculation of more than 10(6) S. pneumoniae. In irradiated animals, which underwent 10(2) or 10(4) S. pneumoniae inoculation, the incidence of otitis media because of S. pneumoniae infection became higher in accordance with the dosage of irradiation. However, no significant difference was seen in the occurrence of otitis media and the number of viable bacteria recovered from bulla washings between controls and carrageenan-treated animals. These results suggest that phagocytes, particularly neutrophils, are essential for antimicrobial defense at the early phase of the middle ear infection with S. pneumoniae.
Insights
Phagocytes, especially neutrophils, are crucial for fighting middle ear infections caused by Streptococcus pneumoniae. Depleting these cells increases infection severity, highlighting their essential role in early defense.
Area of Science:
- Immunology
- Microbiology
- Otolaryngology
Background:
- Otitis media is a common middle ear infection.
- Phagocytes play a key role in the immune response to bacterial pathogens.
Purpose of the Study:
- To investigate the role of phagocytes in the antimicrobial defense of the middle ear against Streptococcus pneumoniae.
- To differentiate the roles of monocytes and polymorphonuclear neutrophils (PMNs) in otitis media.
Main Methods:
- Experimental otitis media was induced in Hartley strain guinea pigs by inoculating Streptococcus pneumoniae.
- Peripheral blood phagocyte populations were depleted using whole-body irradiation (250 or 500 rad) or carrageenan.
- Infection incidence and bacterial load were assessed in control, irradiated, and carrageenan-treated animals.
Main Results:
- Irradiated guinea pigs showed a higher incidence of otitis media with increased S. pneumoniae inoculation doses.
- Carrageenan treatment did not significantly alter otitis media occurrence or bacterial counts compared to controls.
- Phagocyte depletion via irradiation correlated with increased susceptibility to S. pneumoniae infection.
Conclusions:
- Phagocytes, particularly neutrophils, are essential for early antimicrobial defense in the middle ear during Streptococcus pneumoniae infections.
- Neutrophils are critical in combating the initial stages of middle ear bacterial infections.