Distinct Endosomal Trafficking Requirements for Presentation of Autoantigens and Exogenous Lipids by Human CD1d Molecules

CD1d molecules present both self Ags and microbial lipids to NKT cells. Previous studies have established that CD1d lysosomal trafficking is required for presentation of autoantigens to murine invariant NKT cells. We show in this study that this is not necessary for autoantigen presentation by human CD1d, but significantly affects the presentation of exogenous Ags. Wild-type and tail-deleted CD1d molecules stimulated similar autoreactive responses by human NKT clones, whereas presentation of exogenous lipids by tail-deleted CD1d was highly inefficient. Chloroquine treatment markedly inhibited exogenous Ag presentation by wild-type CD1d transfectants, but did not affect NKT autoreactive responses. Conversely, APC expression of HLA-DRalphabeta and the invariant chain (Ii) was associated with faster internalization of CD1d into the endocytic system and enhanced CD1d-mediated presentation of exogenous Ags, but did not appear to augment NKT autoreactivity. Knockdown of the Ii by small interfering RNA resulted in reduced CD1d surface expression and slower internalization in HLA-DR+ APCs, but not HLA-DR- APCs, demonstrating a direct effect of MHC/Ii complexes on CD1d trafficking. CD1d-mediated presentation of exogenous Ags was much more efficient in immature dendritic cells, which actively recycle MHC class II molecules through the endocytic system, than in mature dendritic cells that have stabilized MHC class II expression at the cell surface, suggesting a physiological role for MHC/Ii complexes in modulating CD1d function. These results indicate that autoantigens and exogenous lipids are acquired by human CD1d at distinct cellular locations, and that Ii trafficking selectively regulates CD1d-mediated presentation of extracellular Ags.