Recognition of CD1d-sulfatide mediated by a type II natural killer T cell antigen receptor

Natural killer T cells (NKT cells) recognize lipid antigens presented by CD1d. Zajonc and Rossjohn and their colleagues describe molecular interactions between type II NKT cell antigen receptors and CD1d-ligand complexes, which demonstrate distinct modes of recognition used by the receptors. Natural killer T cells (NKT cells) are divided into type I and type II subsets on the basis of differences in their T cell antigen receptor (TCR) repertoire and CD1d-antigen specificity. Although the mode by which type I NKT cell TCRs recognize CD1d-antigen has been established, how type II NKT cell TCRs engage CD1d-antigen is unknown. Here we provide a basis for how a type II NKT cell TCR, XV19, recognized CD1d-sulfatide. The XV19 TCR bound orthogonally above the A′ pocket of CD1d, in contrast to the parallel docking of type I NKT cell TCRs over the F′ pocket of CD1d. At the XV19 TCR–CD1d-sulfatide interface, the TCRα and TCRβ chains sat centrally on CD1d, where the malleable CDR3 loops dominated interactions with CD1d-sulfatide. Accordingly, we highlight the diverse mechanisms by which NKT cell TCRs can bind CD1d and account for the distinct antigen specificity of type II NKT cells.