Antigen-Independent Suppression of the Allergic Immune Response to Bee Venom Phospholipase A2 by DNA Vaccination in CBA/J Mice

Abstract

Phospholipase A2 (PLA2) is one of the major honey bee venom allergens for humans. To assess the long-term prevention of allergic reactions by DNA vaccination, a PLA2-CBA/J mouse model was employed using empty or PLA2 sequence-carrying DNA plasmids. Early skin application of either DNA construct before (prophylactic approach) or after (therapeutic approach) sensitization with PLA2/alum led to reduced PLA2-specific IgE and IgG1 titers at 7 mo, with concomitant rise in IgG2a and IgG3. Splenocytes recovered at 5–6 mo after the last DNA administration exhibited a sustained IFN-γ and IL-10 secretion and reduced IL-4 production. Recall challenge with PLA2 boosted IFN-γ and IL-10 secretion, suggesting the reactivation of quiescent memory Th1 lymphocytes. Mice from the prophylactic groups were fully protected against anaphylaxis, whereas 65% of the animals recovered in the therapeutic groups. Th1-polarized immune responses were also active in mice vaccinated with an empty plasmid 32 wk before sensitization with another Ag (OVA). This is the first demonstration that the Ag-coding sequence in DNA vaccine is not necessary to promote immune modulation in naive and sensitized animals for a prolonged period, and has relevance for the understanding of the innate and induced mechanisms underlying gene immunotherapy in long-term treatment of allergy.