Prophylactic immunization of mice with phospholipase A2-loaded gas-filled microbubbles is protective against Th2-mediated honeybee venom allergy.

BACKGROUND:People suffering from honeybee venom allergy can be treated by venom immunotherapy, which consists in the subcutaneous injection of increasing doses of allergen extracts over a period of 3-5 years. Such a procedure is time-consuming, and the risks of severe side reactions are important. Approaches based on the use of novel adjuvants to blunt pro-allergic Th2-type immune responses represent a sound alternative. OBJECTIVES:In this study, we evaluated in a mouse model of honeybee venom allergy the protection induced by the prophylactic use of the major allergen phospholipase A2 (PLA2) associated with microbubbles (MB). METHODS:Antibody (Ab) and T cell responses, as detected by ELISA and CFSE-based proliferation assays, were first examined after prophylactic immunization of CBA/J mice with PLA2-MB, and second after sensitization with native PLA2. Mice were eventually challenged with a lethal dose of PLA2 to assess protection against anaphylaxis. RESULTS:Prophylactic immunization with PLA2-MB induced PLA2-specific IgG and IgA Ab, triggered the production of IFN-γ and IL-10 and the differentiation of PLA2-specific Foxp3(+) Treg. Immunized/sensitized mice displayed the following: (1) increased titres of potent blocking IgG1, IgG2a and IgG3 Ab, (2) both reduced allergen-specific T cell proliferation and Th2-type cytokine production and (3) elevated frequencies of specific Foxp3(+) Treg and increased production of TGF-β, as compared to naïve/sensitized animals. Immunomodulation correlated with reduced signs of anaphylaxis after allergen challenge. CONCLUSIONS AND CLINICAL RELEVANCE:Our data demonstrate the ability of PLA2-MB to prophylactically protect mice against subsequent sensitization and death-inducing PLA2 challenge for up to 4 months, revealing so far unravelled immunomodulatory properties of MB. These data, combined with the safe use of MB as contrast agents for in situ imaging in humans, render them an immunotherapeutic agent of great interest for further evaluation.