OBJECTIVE: This study addresses the interaction of bacterial antigens, spec
ifically peptidoglycan-polysaccharide (PG-PS) and lipopolysaccharide (LPS),
in the induction and reactivation of mucoid middle ear effusions.
METHODS: Twenty-seven rats underwent eustachian tube obstruction before ino
culation of the middle ear bulla with PG-PS. Three weeks later, after resol
ution of all middle ear effusions, 6 rats were randomly selected and euthan
ized as the first control group (control I). The remaining 21 animals were
randomly assigned to 3 groups that received intravenous injections of Krebs
Ringer (control II), PG-PS, and LPS, respectively. These rats were euthani
zed 2 days after intravenous injection. Middle ear mucin production and his
tologic changes were measured in all animals.
RESULTS: The mean concentrations of mucin were 0.94 +/- 0.52 mg/mL, 0.41 +/
- 0.87 mg/mL, 16.33 +/- 3.67 mg/mL, and 1.15 +/- 0.41 mg/mL in the control
I, control II, PG-PS, and LPS groups, respectively. Thus the mean concentra
tion of mucin in the middle ear lavage samples was significantly greater in
rats that were injected intravenously with PG-PS than in rats in other gro
ups (P < 0.05). Histologic analyses demonstrated a greater degree of goblet
cell hyperplasia in the PG-PS group than in other groups.
CONCLUSIONS: This is the first animal model of recurring otitis media with
effusion in which a systemic injection of PG-PS was used to reactivate a mi
ddle ear effusion in rats previously primed with a transtympanic injection
of PG-PS, This study suggests that after otitis media with effusion has res
olved, it may be reactivated by the presence of bacterial antigens and/or c
ytokines in the systemic circulation.