Induction of IgE Responses Using a Recombinant Mosquito Salivary Allergen rAed a 2 without Adjuvant in Mice

Background: Reactions to mosquito bites are a global problem. Several salivary proteins from Aedes (Ae.) aegypti, the most common mosquito species, have been cloned and expressed. Plasmid DNA vaccination has been shown to be effective in the downregulation of IgE responses. To investigate the in vivo antigenicity of these recombinant proteins and to study the mechanisms underlying plasmid DNA vaccination, a mouse model sensitized with a recombinant antigen has been developed. Methods: BALB/c and C57BL/6 mice were injected intradermally with a 37–kD recombinant Ae. aegypti salivary allergen (rAed a 2) in the absence of adjuvant twice weekly for 8 weeks and then challenged twice with rAed a 2 at weeks 10 and 12. Serum rAed a 2–specific IgE, IgG1 and IgG2a were measured by ELISA. Intradermal tests were performed every 4 weeks. The binding capacity of rAed a 2–specific IgE to the native Aed a 2 was examined by immunoblotting. Results: In both strains, sensitization with rAed a 2 induced a significant increase in IgE and IgG1, but not IgG2a. In all sensitized mice, a positive immediate skin reaction was apparent, while delayed–type hypersensitivity reactions were not observed. BALB/c mice produced significantly higher levels of IgE and IgG1 and larger wheals than C57BL/6 mice. The IgE antibodies elicited by rAed a 2 bound to not only rAed a 2 but also its natural form in mosquito saliva. Conclusion: (1) Repeated injections of rAed a 2 without adjuvant induce predominant Th2–type responses in mice. (2) BALB/c mice are better responders for IgE production than C57BL/6 mice. (3) rAed a 2 has identical allergenicity to its natural form.