Structure and function of a potent agonist for the semi-invariant natural killer T cell receptor

Abstract

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...

Differential alteration of lipid antigen presentation to NKT cells due to imbalances in lipid metabolism

“…Two mechanisms describing how the accumulating lipids might inhibit CD1d antigen presentation can be envisaged. First, they could hinder unloading of the spacer molecules that are associated with CD1d [43]. However, this possibility is not supported by the results obtained with the C 8 a-GalCer analogue.…”

“…However, this possibility is not supported by the results obtained with the C 8 a-GalCer analogue. This lipid antigen can effectively bind to CD1d in the presence of spacers [43]. Nevertheless, it does not restore the presentation capacity of NPC2 -/-APC.…”

“…To test for the first possibility, lipid antigens with short alkyl chains were used together with NPC2 -/-DC. Indeed, a-GalCer containing a C 8 alkyl chain binds to CD1d also in the presence of spacer molecules inserted in the A 0 pocket [43]. We compared the Va14i NKT cell stimulatory capacity of two a-GalCer molecules containing a C 8 and a C 26 alkyl chain, respectively.…”

Glucocerebroside: an evolutionary advantage for patients with Gaucher disease and a new immunomodulatory agent

“…81,82 The ability of NKT cells to generate either Improves insulin resistance [76][77][78]137 Promotion of mechanisms of mucosal immunity Oral GC as an immunomodulatory agent 135 Replacement of natural NKT cell ligands Th1 or Th2 responses shows their importance as immunoregulatory cells and the complexity of their immunomodulatory machinerydifferent responses can be generated by the same ligands. 72,83 Several glycosphingolipids and phospholipids derived from mammalian, bacterial, protozoan and plant species have been identified as possible natural ligands for NKT cells, 84,85 and phospholipids, such as phosphatidylcholine and phosphatidylinositol. 86,87 The semi-invariant TCRs can recognize iGb3 (isoglobotrihexosylceramide), a mammalian glycosphingolipid, and a microbial a-glycuronylceramide found in the cell wall of Gram-negative, lipopolysaccharide-negative bacteria.…”

The cellular and biochemical rules of lipid antigen presentation

“…CD1b binds PC together with a 42-44 carbon-long molecule that remains embedded into the lipid-binding groove [25]. Mouse CD1d associates with PC and a C 16 -long fatty acid [32,38]. These spacers partially occupy one lipid-binding pocket, still allowing accommodation of lipids with short acyl chains.…”