The interface between innate and acquired immunity: glycolipid antigen presentation by CD1d-expressing dendritic cells to NKT cells induces the differentiation of antigen-specific cytotoxic T lymphocytes.

In vivo administration of NKT cell ligand, alpha-galactosylceramide (alpha-GalCer), caused the activation of NKT cells to induce a strong NK activity and cytokine production by CD1d-restricted mechanisms. Surprisingly, we also found that alpha-GalCer induced the activation of immunoregulatory cells involved in acquired immunity. Specifically, in vivo administration of alpha-GalCer resulted in the induction of the early activation marker CD69 on CD4(+) T cells, CD8(+) T cells and B cells in addition to macrophages and NKT cells. However, no significant induction of CD69 was observed on cells from CD1d- or V(alpha)14 NKT-deficient mice, indicating an essential role for the interaction between NKT cells and CD1d-expressing dendritic cells (DC) in the activation of acquired immunity in response to alpha-GalCer. Indeed, in vivo injection of alpha-GalCer resulted not only in the activation of NKT cells but also in the generation of CD69(+)CD8(+) T cells possessing both cytotoxic T lymphocyte (CTL) activity and IFN-gamma-producing ability. Tumor-specific CTL generation was also accelerated by alpha-GalCer. The critical role of CD40-CD40 ligand (CD40L)-mediated NKT-DC interaction during the development of CD69(+)CD8(+) CTL by alpha-GalCer was demonstrated by blocking experiments using anti-CD40L mAb. These findings provide direct evidence for a critical role of CD1d-restricted NKT cells and DC in bridging innate and acquired immunity.