Study On The Mechanism Of Otitis Media With Effusion Induced By Ovalbumin In A Rat Model

Objective: 1,To establish a rat model of otitis media with effusion (OME) sensitized and challenged by ovalbumin (OVA), observing histological characteristics and its dynamic changes.2,To determine the secretion and variation of interleukin-4 (IL-4), interleukin-5 (IL-5) and cysteinyl leukotrienes (CysLTs) relevant to late-phase allergy in allergic otitis media. 3,To discover the expression and possible modulation mechanism of cysteinyl leukotriene receptors, CysLTR1 and CysLTR2 in the middle ear mucosa of OME, and further to explore the role of receptor antagonist montelukast in inhibiting secretion and expression of IL-4, IL-5 and mucins (MUC2, MUC5AC).Methods: Thirty-five clean Sprague-Dawley rats were randomly divided into 4 groups―negative controlⅠ(C1), negative controlⅡ(C2),model(M) and treated(T). The model group was further subdivided into 3 subgroups including M1,M2 and M3, according to different observed day (2 days,5 days and 10 days after challenged respectively). Rats from the model group were sensitized to OVA via intraperitoneal injection once a week for two weeks then challenged transbullarly. T group rats were handled according to the model group management procedure and were treated once daily with 30mg/kg of Montelukast by intragastric administration for 5 days starting 2 days before challenged.C1 group were allergic rats but transbullarly injected with PBS and C2 group were nonallergic rats transbullarly injected with OVA. The histomorphology of middle ear mucosa were observed with histochemical technique. The levels of IL-4, IL-5 and CysLTs were measured by enzyme-linked immunosorbent assay in each model subgroups. And the effect of montelukast on the secretion levels of IL-4, IL-5 was noted also. Middle ear mucosa was harvested and assayed for CysLTR1, CysLTR2, MUC2 and MUC5AC mRNA expressions by semi-quantitative reverse transcription-polymerase chain reaction in each experimental group. The variation of different target gene expression between each group was noted also. Results: Tympanal mucosa in control group is composed of flat epithelia or ciliated columnar epithelia and thin connection tissue underneath located few fibrocytes and lymphocytes. Eustachian tube mucosa in control group rats was composed of ciliated columnar epithelia and inflammatory cells infiltrated into submucosa was sparse. Tympanal and Eustachian tube mucosa in M1 group rats thickened significantly and epithelium cilia disarranged in some region. Meanwhile, inflammatory cells infiltrated obviously and blood capillaries hyperplasted evidently were dilated and congested under hydropsia mucosa. Such histologic findings were abated to absent in M2 and M3 groups. The levels of IL-4, IL-5 and CysLTs in M1 group rats were higher significantly than that in M2 and M3 group ones. OVA challenge up-regulated significantly the expressions of CysLTR1 and CysLTR2 mRNA and increased MUC2 and MUC5AC mRNA expressions as well. As for the animals that pretreated with montelukast, histological observations revealed that the degree of mucosal edema was minimal and the intensity of cellular infiltration subsided. Concurrently, montelukast could inhibit MUC2 and MUC5AC mRNA expressions and decrease the levels of cytokine IL-4, IL-5.Conclusion: 1,The middle ear itself was capable of mounting an allergic inflammation. A one-time presentation of allergen brought about a self-limited pathological change.2,Besides histamine-mediated acute-phase allergy, late-phase allergy-induced inflammation mediated and characterized by a host of inflammatory mediators and cytokines such as TH2-cytokines(IL-4 and IL-5),cysteinyl leukotriene and infiltration of inflammatory cells including mainly eosinophils and lymphocytes play an important role in the development of OME. 3, Cysteinyl leukotriene receptors mRNA expressions presented as baseline production in the control group rats, whereas allergic inflammation was able to spur the receptors expressions.4,Montelukast partly inhibited the secretions of IL-4 and IL-5 and the expressions of mucin, meanwhile lessening the middle ear inflammation reaction.