Production of Both IL-27 and IFN-γ after the Treatment with a Ligand for Invariant NK T Cells Is Responsible for the Suppression of Th2 Response and Allergic Inflammation in a Mouse Experimental Asthma Model

Using an allergen-induced airway inflammation model, we show that an injection of α-galactosylceramide (α-GalCer), a ligand for invariant NK T (iNKT) cells, induced IL-27 and that this process is essential for the attenuation of the Th2 response. After the systemic administration of α-GalCer into the mice primed with OVA in alum, Th2 cytokine production of OVA-primed CD4+ T cells in their lymph nodes, IgG1 and IgE Ab formation, and infiltration of eosinophils in bronchoalveolar lavage after the OVA challenge were suppressed. Systemic administration of rIFN-γ into OVA-primed mice could not reproduce these effects of α-GalCer. IL-27p28 was detected both in the culture supernatant of α-GalCer-stimulated spleen cells and in the serum of the α-GalCer-treated mice, but not in the iNKT cell-deficient mice. Splenic iNKT cells produced IL-27p28 in the culture supernatant upon stimulation with PMA plus ionomycin, although the transcript of IL-27p28 in the iNKT cells was constitutively expressed regardless of the stimulation. By contrast, the transcript of IL-27EBI3 was induced in the iNKT cells upon stimulation with PMA plus ionomycin in vitro and with α-GalCer treatment in vivo, suggesting that IL-27 (p28/EBI3) could be produced by iNKT cells in an activation-dependent manner. Although repeated injections of rIL-27 did not substitute for the effects of a single injection of α-GalCer, administration of rIL-27 along with rIFN-γ reproduced in vivo effects of the α-GalCer injection. These data indicate that production of both IL-27 and IFN-γ by the α-GalCer treatment is responsible for suppression of the Th2 response and allergic inflammation.