A Mouse Model of Mosquito Allergy for Study of Antigen–Specific IgE and IgG Subclass Responses, Lymphocyte Proliferation, and IL–4 and IFN–Á Production

To date, there are no ideal animal models for study of natural sensitization leading to IgE– and lymphocyte–mediated hypersensitivities. We established such a model in which four BALB/c mice were each sensitized by exposure to at least 16 mosquito Aedes aegypti bites, twice a week for 4 weeks. Four non–exposed control mice were also studied. Mosquito A. aegypti head and thorax extract, saliva, and two recombinant salivary allergens (rAed a 1 and rAed a 2) were used in vitro as antigens. Intradermal tests were performed. Serum mosquito antigen–specific IgG, IgG1, IgG2a, and total IgE were measured by ELISA; specific IgE was measured by passive cutaneous anaphylaxis (PCA). IgE responses to each antigen in the saliva were analyzed using Western blotting. Spleen lymphocyte proliferation assays were performed to determine the cell–mediated hypersensitivity response. Antigen–induced IL–4 and IFN–γ production in the spleen lymphocytes were evaluated using ELISA. After 4 weeks, all 4 mosquito–sensitized mice developed a positive immediate wheal 20 min after skin tests with mosquito antigens, and a positive delayed papule 24 h later, while control mice did not. Also, the sensitized mice had a positive PCA response, which correlated significantly with total IgE levels (r = 0.84, p<0.05), confirming the presence of antigen–specific IgE, while none of control mice had a positive response. Antigen–specific IgG1, but not IgG2a, was increased in the sensitized mice (p<0.01). Western blotting showed that 5 of the 8 antigens which elicited mouse IgE responses, including 2 major antigens, also elicited human IgE responses. The mean lymphocyte proliferation response to mosquito antigens also elicited human IgE responses. The mean lymphocyte proliferation response to mosquito antigens was significantly increased in the sensitized mice (p<0.05). IL–4 production was significantly increased and IFN–γ production was decreased, further suggesting that a Th2 immune response predominates despite the development of the delayed skin reaction. This new model of natural sensitization without using an adjuvant is potentially useful for the study of other allergic disorders as well as mosquito allergy.