Risa Nozawa

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.

Characterization of the immature dendritic cells and cytotoxic cells both expanded after activation of invariant NKT cells with α-galactosylceramide in vivo

Invariant natural killer T (iNKT) cells can perform multiple functions characteristic of both innate and acquired immunity. Activation of iNKT cells in vivo by repeated alpha-GalCer injections can induce immune tolerance, but the mechanisms responsible for such immunoregulation remain unclear. We prepared alpha-GalCer-liposomes, a single injection of which into mice resulted in the expansion of splenic CD11c(low)CD45RB(high) cells, which consists of two populations, CD180(+) and CD49b(+). Expansion of these cells was not observed in alpha-GalCer-liposome-treated mice deficient in IL-10 or iNKT cells. MHC and co-stimulatory molecules were down-regulated in CD11c(low)CD180(+) cells compared with conventional dendritic cells (cDCs), suggesting that the former possess characteristics of immature DCs. Meanwhile, the CD11c(low)CD49b(+) cells expressed IL-10 and Ctla4, and possessed greater lytic activity than resting NK cells. These observations suggest that both immature DCs (CD11c(low)CD180(+)) and cytotoxic cells (CD11c(low)CD49b(+)) might be expanded by alpha-GalCer-activated iNKT cells and could therefore be involved in immune tolerance.