Adaptability of the semi-invariant natural killer T-cell receptor towards structurally diverse CD1d-restricted ligands

The semi-invariant natural killer (NK) T-cell receptor (NKTcr) recognises structurally diverse glycolipid antigens presented by the monomorphic CD1d molecule. While the α-chain of the NKTcr is invariant, the Β-chain is more diverse, but how this diversity enables the NKTcr to recognise diverse antigens, such as an α-linked monosaccharide (α-galactosylceramide and α-galactosyldiacylglycerol) and the Β-linked trisaccharide (isoglobotriaosylceramide), is unclear. We demonstrate here that NKTcrs, which varied in their Β-chain usage, recognised diverse glycolipid antigens with a similar binding mode on CD1d. Nevertheless, the NKTcrs recognised distinct epitopic sites within these antigens, including α-galactosylceramide, the structurally similar α-galactosyldiacylglycerol and the very distinct isoglobotriaosylceramide. We also show that the relative roles of the CDR loops within the NKTcr Β-chain varied as a function of the antigen. Thus, while NKTcrs characteristically use a conserved docking mode, the NKTcr Β-chain allows these cells to recognise unique aspects of structurally diverse CD1d-restricted ligands.