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Background: DNA immunization and protein immunization with CpG motifs as adjuvants represent promising approaches in allergen-specific immunotherapy. Objective: We investigated the effect of coinjection or prepriming with CpG-ODN on Th2-type responses induced by gene gun and protein immunization. Methods: BALB/c mice were immunized with the gene gun using plasmid DNA containing the cDNAs coding for the genes of Bet v 1a, Phl p 2 and β-galactosidase or with the purified Al(OH)₃-adsorbed proteins. In addition, CpG-ODN were applied by coinjection or by prepriming treatment. Antibody and cytokine responses were measured by ELISA, proliferative and cytotoxic responses were determined by standard labeling procedures. Furthermore, the allergenic activity of sera was measured by passive cutaneous anaphylaxis. Results: Gene gun immunization and protein immunization induced a clear Th2-type response for all antigens. The Th1-promoting effect of CpG-ODN coinjection together with gene gun immunization was restricted to β-galactosidase as indicated by the increase of IgG2a and a marked expression of IFN-γ. CpG motifs also increased the specific cytotoxic response against β-galactosidase. Prepriming with CpG-ODN and gene gun or protein immunization with Bet v 1a exhibited no significant difference to the non-CpG control group. However, sera from mice preprimed with CpG-ODN induced no anaphylaxis with gene gun immunization, but with protein immunization. Conclusions: The effect of CpG motifs in vivo depends on a variety of parameters like the nature of the antigen and the immunization modality. Furthermore, our studies indicate that a combination of CpG + DNA immunization may be more effective in antagonizing Th2 responses than the combination of CpG + protein immunization.

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