Natural killer T (NKT) cells recognize glycosphingolipids presented by CD1d molecules and have been linked to defense against microbial infections. Previously defined foreign glycosphingolipids recognized by NKT cells are uniquely found in nonpathogenic sphingomonas bacteria. Here we show that mouse and human NKT cells also recognized glycolipids, specifically a diacylglycerol, from Borrelia burgdorferi, which causes Lyme disease. The B. burgdorferi-derived, glycolipid-induced NKT cell proliferation and cytokine production and the antigenic potency of this glycolipid was dependent on acyl chain length and saturation. These data indicate that NKT cells recognize categories of glycolipids beyond those in sphingomonas and suggest that NKT cell responses driven by T cell receptor-mediated glycolipid recognition may provide protection against diverse pathogens.

Natural killer T (NKT) cells recognize glycolipid antigens presented by CD1d. These cells express an evolutionarily conserved, invariant T cell receptor (TCR), but the forces driving TCR conservation have remained uncertain. Here we show that NKT cells recognize diacylglycerol-containing glycolipids from Streptococcus pneumoniae, the leading cause of community-acquired pneumonia, and group B Streptococcus, which causes neonatal sepsis and meningitis. Furthermore, CD1d-dependent responses by NKT cells are required for activation and host protection. The glycolipid response was dependent on vaccenic acid, which is found at a low level in mammalian cells. Our results show how microbial lipids position the sugar for recognition by the invariant TCR, and most important, they extend the range of microbes recognized by this conserved TCR to several clinically important bacteria.

NKT cells express a conserved, semi-invariant αβ T cell receptor, which has specificity for a selfglycosphingolipids and microbial cell wall α-glycuronosylceramide antigens presented by CD1d molecules. Here we report the crystal structure of CD1d in complex with a short-chain synthetic variant of α-galalctosylceramide at 2.2 Å resolution. This structure elucidated the basis for the high specificity of these microbial ligands and explained the restriction of the α-linkage as a unique pathogen-specific pattern recognition motif. Comparison of the binding of altered lipid ligands to CD1d and TCR shows the differential T H 1-and T H 2-like properties of NKT cells may originate primarily from marked differences in their loading in different cell-types and, hence, in their tissue distribution in vivo.NKT cells are a conserved lymphocyte lineage expressing a semi-invariant TCR (V α 14-J α 18-V β 8, 7 or 2 in mouse and V α 24-J α 18-V β 11 in human . They are important in regulating a variety of microbial, allergic, autoimmune and tumor conditions through the rapid and substantial secretion of T H 1 and T H 2 cytokines and chemokines 1 . Unlike other T cells, NKT cells are restricted to a non-MHC molecule, CD1d, which binds lipids and glycolipids instead of peptides. Whereas other CD1 isotypes in humans can present a large variety of bacterial compounds that stimulate individual T cell clones expressing diverse TCRs 2 , CD1d appears to have specialized in the presentation of a limited set of lipids for recognition by the entire, or a large fraction of, NKT cell population. Two major classes of agonist ligands of mouse and human NKT cells have been uncovered, a self glycosphingolipid (GSL) isoglobotrihexosylceramide (iGb3) 3 , and a family of α-glycuronosylceramides that substitute for LPS in the cell wall of some Gram-negative LPS-negative bacteria including Sphingomonas 4-6 . Although iGb3 appears to be the only required ligand for NKT cell development, the dual specificity for self and foreign ligands, a general feature of many innatelike lymphocyte subsets 7 , underlies the recruitment and activation of NKT cells in various disease conditions, including microbial infections 5 . Another microbial ligand present in the *Corresponding authors: lteyton@scripps.edu, Phone: (858) 784-2728, Fax: (858) wilson@scripps.edu, Phone: (858) Fax: (858) NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript cell wall of mycobacteria, phosphatidylinositol mannoside (PIM 4 ) also appears to be a natural ligand of NKT cells 8 .Microbial α-glycuronosylceramides are of particular interest because of their relevance in the context of infection in vivo and their very close structural homology with a highly potent agonist of human and murine NKT cells, α-galactosyl ceramide (α-GalCer) 9 , that was previously isolated from marine sponges. These molecules are both α-stereo isomers, a stereochemistry absent from mammalian glycosphingolipids, and phyto-ceramides due to the additional hydroxyl group at the C 4 posi...

CD1 antigens bind a variety of self and foreign lipid and glycolipid antigens for presentation to CD1-restricted T cell receptors (TCRs). Here we report the crystal structure of human CD1a in complex with a sulfatide self antigen at a resolution of 2.15 A. The lipid adopts an S-shaped conformation, with the sphingosine chain completely buried in the A' pocket and the fatty acid chain emerging from the interface of the A' pocket into the more exposed F' pocket. The headgroup is anchored in the A'-F' junction and protrudes into the F' pocket for TCR recognition. Because the A' pocket is narrow with a fixed terminus, it can act as a molecular 'ruler' to select alkyl chains of a particular length.