The mechanism by which CD1d-restricted Valpha14 natural killer T (NKT) cells participate in transplant tolerance has yet to be completely clarified. Recently, we showed that repeated activation of NKT cells by their specific glycolipid ligand, alpha-galactosylceramide, leads to a change in function to an immune regulatory role with IL-10 production. Moreover, these cells were shown to be able to induce regulatory dendritic cells (DCs). In this study, we showed that NKT cells from transplant tolerant recipients of cardiac allograft produced higher levels of IL-10, which is required for the maintenance of tolerance; this was proved by adoptive transfer experiments. In addition, DCs from wild-type (WT) tolerant recipients but not NKT cell-deficient recipients showed a higher IL-10-producing profile, a more immature phenotype, and tolerogenic capability. CD4 T cells from WT tolerant recipients but not NKT cell-deficient recipients also produced higher levels of IL-10 upon alloantigen stimulation and showed lower proliferative activity that was reversed by blocking the IL-10 receptor. These data indicate the existence of IL-10-dependent immune regulatory interplay among NKT cells, DCs, and CD4 T cells, even in the absence of artificial stimulation of NKT cells with synthetic glicolipids, which is required for the maintenance of transplant tolerance.

We report that stimulation of Mycobacterium tuberculosis secretory antigen- and tumor necrosis factor alpha-matured BALB/c mouse bone marrow dendritic cells (BMDCs) with anti-CD80 monoclonal antibody up-regulated CD86 levels on the cell surface. Coculture of these BMDCs with naïve, allogeneic T cells now down-regulated T helper cell type 1 (Th1) responses and up-regulated suppressor responses. Similar results were obtained with splenic CD11c(+)/CD8a(-) DCs but not to the same extent with CD11c(+)/CD8a(+) DCs. Following coculture with T cells, only BMDCs and CD11c(+)/CD8a(-) DCs and not CD11c(+)/CD8a(+) DCs displayed increased levels of surface CD86, and further, coculturing these DCs with a fresh set of T cells attenuated Th1 responses and increased suppressor responses. Not only naïve but even antigen-specific recall responses of the Th1-committed cells were modulated by DCs expressing up-regulated surface CD86. Further analyses showed that stimulation with anti-CD80 increased interleukin (IL)-10 and transforming growth factor-beta-1 levels with a concomitant reduction in IL-12p40 and interferon-gamma levels from BMDCs and CD11c(+)/CD8a(-) DCs and to a lesser extent, from CD11c(+)/CD8a(+) DCs. These results suggest that cross-talk between costimulatory molecules differentially regulates their relative surface densities leading to modulation of Th responses initiated from some DC subsets, and Th1-committed DCs such as CD11c(+)/CD8a(+) DCs may not allow for such modulation. Cognate antigen-presenting cell (APC):T cell interactions then impart a level of polarization on APCs mediated via cross-regulation of costimulatory molecules, which govern the nature of subsequent Th responses.