One experimental approach for the treatment of allergic reactions is the stimulation of immunoregulatory NKT cells with the synthetic glycolipid αgalactosylceramide. For a first evaluation of the immunomodulatory potential of αGalCerMPEG a human in vitro allergy model was exploited. Acting as an adjuvant, the glycolipid induced an enhanced Th1-biased allergen-specific immune response of autologous lymphocytes. In a mouse model of allergic airway inflammation, αGalCerMPEG-activated NKT cells promoted a cytokine environment in the spleen, leading to priming of Th1 cells. The shift towards a Th1-dominated allergen-specific immune response thus might mediate the abrogation of allergic airway inflammation and thereby might provide a valid option for therapeutic intervention.