Lysosomal recycling terminates CD1d-mediated presentation of short and polyunsaturated variants of the NKT cell lipid antigen αGalCer

Abstract

Short or polyunsaturated lipid variants of the NKT cell antigen ␣-galactosylceramide (␣GC) exhibit decreased potency and a Th2 bias in vivo despite conserved TCR contact residues and stable binding to CD1d at neutral and acidic pH. Using reagents to directly visualize lipids in their free or CD1d-bound form, we determined that, contrary to predictions, these lipids reached the lysosome better than ␣GC. However, in contrast with ␣GC, they loaded CD1d at the cell surface and underwent immediate pH-dependent dissociation upon recycling to the lysosome. In cell-free assays, ultrafast dissociation of preformed complexes could be induced at acidic pH only when free competitor lipids were added, suggesting active lipid displacement. These findings provide a common cell biological explanation for the decreased stimulatory properties of short and polyunsaturated ␣GC variants. They also suggest that direct lipid displacement is a potent mechanism underlying highly dynamic lipid exchange reactions in the lysosomal compartment that shape the repertoire of lipids associated with CD1d.

Enhanced Tumor Metastasis in Response to Blockade of the Chemokine Receptor CXCR6 Is Overcome by NKT Cell Activation

“…7), consistent with the ability of repeated doses to attenuate Th1/Th17-mediated autoimmune disease (40,41). ␣-GalCer, ␣-C-GalCer, and OCH all induced hyporesponsiveness despite differences in their processing, stability and affinity for CD1d (39,(45)(46)(47). However, IFN-␥ responses appeared to be more sensitive to multiple glycolipid treatments as OCH still induced low levels of other cytokines.…”

Dendritic cells tolerized with adenosine A2AR agonist attenuate acute kidney injury

“…To examine whether the suppressive effect of ATL313 on DCmediated NKT cell activation might be due to alterations in cellular processing and antigen presentation of the CD1d/glycolipid complex, we used an antibody (L363) that recognizes CD1d/glycolipid complex intracellularly and on the cell surface, indicative of antigen presentation (39,40). Labeling with antibody L363, as revealed by FACS, increased significantly both intracellularly (data not shown) and on the surface of WT or Adora2a -/-DCs after priming with αGC but was not altered by ATL313 treatment of WT DCs-αGC ( Figure 5B) or Adora2a -/-DCs-αGC (not shown).…”

Saposins modulate human invariant Natural Killer T cells self-reactivity and facilitate lipid exchange with CD1d molecules during antigen presentation

“…We speculate that saposin B molecules, dimeric at neutral and low pH and with a large hydrophobic cavity (31), may readily solubilize lipids and offer them to recycling CD1d molecules throughout the endocytic compartment, actively promoting lipid exchange in the groove of CD1d molecules by increasing the off-rate of already bound ligands. Lipid transfer proteins might be required to facilitate exchange of complex lipids bound to CD1d molecules, but the acidic pH in the presence of competing lipids (naturally present in the lysosome) already induces rapid, spontaneous dissociation of iNKT cell agonists with shorter acyl or phytosphingosine chains (62). In conclusion, in concert with their ability to promote glycosphingolipid degradation, the four members of the saposin family may use different strategies to facilitate access of a variety of endogenous and microbial lipid antigens to the CD1d groove, thus shaping the repertoire of agonists available for iNKT cell recognition.…”