Efficacy of a therapeutic treatment using gas-filled microbubble-associated phospholipase A2 in a mouse model of honeybee venom allergy.

Background: Venom immunotherapy is efficient to desensitize people suffering from insect sting allergies. However, the numerous injections required over several years and important risks of severe side reactions complicate the widespread use of immunotherapy. In the search for novel approaches to blunt the overwhelming pro-allergic Th2 response, we evaluated the therapeutic efficacy of a treatment based on a denatured form of the major allergen, phospholipase A2, associated with microbubbles (PLA2(denat)-MB) in a mouse model of honeybee venom allergy. Methods: Antibodies measured by ELISA, T-cell responses assessed by CFSE-based proliferation assays and ELISA, and basophil degranulation were examined after PLA2(denat)-MB-based therapeutic treatment of sensitized mice. Mice were challenged with a lethal dose of PLA2 to evaluate protection against anaphylaxis. Results: Therapeutic subcutaneous administration of two different PLA2(denat)-MB formulations, in contrast to PLA2(denat) alone, reduced allergic symptoms and protected all mice from anaphylaxis-mediated death after allergen challenge. At the functional level, the use of PLA2(denat) decreased IgE-mediated basophil degranulation as compared to the native form of the allergen. In comparison with PLA2(denat) alone, both PLA2(denat)-MB formulations decreased allergen-specific Th2 CD4 T-cell reactivity. At the mechanistic level, PLA2(denat)-MB containing 20% palmitic acid and PEG induced PLA2-specific IgA and increased Foxp3(+) Treg frequencies and TGF-beta production, whereas the formulation bearing 80% palmitic acid triggered the production of IFN-gamma, IgG2a, and IgG3. Conclusions: In contrast to conventional PLA2 subcutaneous immunotherapy, the therapeutic administration of PLA2-MB treatment to mice that already had established allergy to PLA2 protects all subsequently challenged animals.