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

Short or polyunsaturated lipid variants of the NKT cell antigen a-galactosylceramide (sGC) 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 αGC. However, in contrast with αGC, they loaded CD1 d 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 αGC 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. [ABSTRACT FROM AUTHOR]