An animal model for the study of genetic predisposition in the pathogenesis of middle ear inflammation

Chronic otitis media with effusion (COME) is the most prevalent inflammatory disease in children and is associated with numerous adverse long-term sequelae. Many factors have been associated with an increased risk of developing COME, one of which may be a genetic predisposition to the disease. To study the role that genetics play in the pathogenesis of COME, we used an animal model to compare the middle ear inflammatory responses in two different strains of rats (Lewis and Fisher).

In earlier studies, we demonstrated that exposure of the middle ear to endotoxin caused early extensive exudation and, later, goblet cell hyperplasia and mucin hypersecretion. In the present study, the animals were divided into six groups. In each group the animals were given transtympanic injection with gram-positive bacterial cell wall product (peptidoglycan-polysaccharide [PG-PS]). The middle ear bullae were studied at 1 week and 3 weeks after infection, and after systemic reinfection. Comparisons were made of the quantity of mucin exudate by enzyme-linked immunosorbent assay and by histological evaluation of the middle ear epithelial thickness.

Our data demonstrate a statistically significant difference in middle ear inflammation and effusion formation between the two genetically different strains of rats.

These data support the hypothesis that the middle ear response to PG-PS may be genetically determined and therefore suggest that genetic predisposition may play a role in the pathogenesis of COME.