DNA vaccines encoding low-molecular-weight allergens have been used to prevent IgE responses. A high-molecular-weight mite allergen Der f 11 that was hardly to be purified for immunotherapy was used to develop a DNA vaccine here. Vaccination of mice with plasmid DNA encoding Df11 (pDf11) induced Th1 responses characterized by IgG2a responses and spleen cell secretion of IFN-gamma. In contrast, sensitization with recombinant Der f 11 (rDf11) and alum induced Th2 responses characterized by IgE responses and spleen cell secretion of IL-4 and IL-5. Vaccination with pDf11 prevented the induction of IgE responses. Moreover, it could inhibit on-going IgE responses. The debate whether CD4+ or CD8+ T cells were the regulatory cells to inhibit IgE responses by DNA vaccination was also examined. First, sensitization of pDf11-vaccinated mice after depletion of CD8+ T cells still showed suppression of IgE responses. Secondly, adoptive transfer of either CD4- or CD8-depleted spleen cells from pDf11-vaccinated mice suppressed IgE responses. In conclusion, this is the first report to confirm the therapeutic effect of a DNA vaccine encoding a strong allergen on specific IgE responses. Both CD4+ and CD8+ T cells are crucial for the immunomodulation of IgE responses by pDf11.