Isoforms of the major allergen of birch pollen induce different immune responses after genetic immunization

Background: Recent publications indicate that immunization with plasmid DNA encoding allergens might represent a potential approach in allergen-specific immunotherapy, Objective: In the present study we have compared the immune responses induced by plasmid DNA encoding for two isoforms of Bet v 1,the major allergen of birch pollen. Methods: BALB/c mice were injected intradermally with plasmid DNA encoding for the genes of Bet v la (pCMV-Beta) and Bet v Id (pCMV-Betd). In addition, the effect of immunostimulatory DNA sequences was investigated by appending and/or coinjecting CpG motifs. Antibody responses and IFN-gamma and IL-4 levels were measured by ELISA. Allergen-specific proliferation was determined by incorporation of [H-3]thymidine. Results: The two isoforms induced a similar humoral response. The lack of any IgE production and the ratio of IgG1 to IgG2a clearly indicated a Th-l-type response. The antisera against both isoforms were highly cross-reactive, which was supported by the energy plot indicating similar folding of the two protein isoforms. However, determination of IFN-gamma and IL-4 in the serum elicited a strikingly different cytokine profile during the course of the immune response. In contrast to pCMV-Beta, pCMV-Betd caused no significant allergen-specific proliferation and induced only marginal levels of the key cytokines. Conclusions: Based on the assumption that the induction of a strong Th-l type response is a prerequisite for successful treatment of allergy, our results favor the use of isoform Bet v la in combination with CpG motifs for a novel type of allergen immunotherapy based on plasmid DNA immunization. Additionally, the data also confirm the assumption that the antigen itself can have a marked influence on the immune response after genetic immunization.