Infiltration of immunocompetent cells in the middle ear during acute otitis media: a temporal study.

HYPOTHESIS

The inflammatory response to acute otitis media (AOM) is a chain reaction involving, among others, macrophages, B lymphocytes, and T lymphocytes that vary in number on different days during the infection. The response is thought to eventually contribute to tympanosclerosis (TS).

BACKGROUND

In humans, TS and myringosclerosis (MS) are obscure sequelae of chronic otitis media. MS is also commonly seen in children who have had acute purulent otitis media or secretory otitis media or after treatment with ventilation tubes in the tympanic membrane (TM). It causes hearing disability, especially if the ossicles or the inner ear are affected. No successful treatment is available. This study was performed to evaluate the inflammatory stages that may lead to TS or MS.

METHODS

Sprague Dawley rats were exposed to a Pneumococcus type 3 solution into the middle ear. Groups of rats were killed at 3, 6, and 10 days after inoculation. Sections from the TM specimen were stained immunohistochemically according to the avidin-biotin method. Antibodies used were directed against macrophages, T cells, and B cells. Positive cells were counted and a mean value was estimated for each slide and section for each antibody in each rat.

RESULTS

Results showed that macrophages, T cells, and B cells were presented time-dependently in the acute inflammatory response in AOM. At day 3, dendritic cells, macrophages, T cells, B cells, and other major histocompatibility complex (MHC)-restricted cells were richly expressed in the whole submucosal layer and especially in the annulus fibrosus. At day 6, the amount of all positive cells decreased except for B cells and other MHC-restricted cells, which slightly increased in number. At day 10, all of the cells were lower in number than at days 3 and 6. Macrophages and possible T cells could be detected in the TM, which has not been observed earlier. Large osteoclastlike cells were present close to the bone.

CONCLUSIONS

Macrophages were the first cells to invade the tissue after AOM induction. Some cells were found in the TM. Large osteoclastlike cells could be seen adjacent to the bone in the submucosa. T cells and B cells were seen in the submucosa.