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-specif ic immunotherapy, Objective: In the present study we have compared the immu ne responses induced by plasmid DNA encoding for two isoforms of Bet v 1,th e major allergen of birch pollen. Methods: BALB/c mice were injected intrad ermally 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 seq uences was investigated by appending and/or coinjecting CpG motifs. Antibod y responses and IFN-gamma and IL-4 levels were measured by ELISA. Allergen- specific proliferation was determined by incorporation of [H-3]thymidine. R esults: The two isoforms induced a similar humoral response. The lack of an y IgE production and the ratio of IgG1 to IgG2a clearly indicated a Th-l-ty pe response. The antisera against both isoforms were highly cross-reactive, which was supported by the energy plot indicating similar folding of the t wo protein isoforms. However, determination of IFN-gamma and IL-4 in the se rum elicited a strikingly different cytokine profile during the course of t he immune response. In contrast to pCMV-Beta, pCMV-Betd caused no significa nt 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 al lergy, our results favor the use of isoform Bet v la in combination with Cp G motifs for a novel type of allergen immunotherapy based on plasmid DNA im munization. Additionally, the data also confirm the assumption that the ant igen itself can have a marked influence on the immune response after geneti c immunization.