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It is known that the endotoxin of gram negative bacteria is not only antigenic, but also has many biological activities. In this study, endotoxin in human middle ear effusions (MEE) was measured quantitatively by the chromogenic substrate method which is more sensitive and accurate than Limulus assay.Fifty samples of MEE from 46 patients aged 2 to 84 years were classified into two groups, 24 mucoid and 26 serous. The endotoxin in the mucoid group was significantly higher (264.6pg/ml) than that in the serous group (27.5pg/ml). This suggests that bacterial endotoxin contributes greatly to induce otitis media with mucoid effusion.Audiometry showed that the majority of those with otitis media and mucoid effusion had conductive type deafness, while mixed type deafness was more common in those with serous effusion.

In order to investigate otitis media with effusion from the systemic perspective, we have studied histological reactions of the mucous membrane in the both middle ears in the sensitized animals. Guinea pigs were initially immunized by injection of BSA conjugated with alum (BSA-alum) into unilateral tympanic cavity. The second challenge of BSA-alum was performed on the seventh day after primary sensitization under an appropriate schedule. The guinea pigs were sacrificed for histological examination at 3 days after the second administration. Histological changes of the middle ear mucosa in the sensitized ear were characterized by hypertrophy of mucosa with fibrosis. Numerous mononuclear cells also existed. In non-sensitized ear (opposite side), the changes were edema of the mucosa showing mild proliferation of fibroblast and vasodilation. Mainly mononuclear cells were scattered. It was noted that these reactions were weaker than those of the sensitized ear.