Many other endogenous glycosphingolipids (GSL) have been extracted from CD1d, with fluorescent labelling of glycan headgroups and HPLC used to profile the eluted GSL.[37] Although GSL are important for iNKT-cell activation, as shown by work with a GSL synthesis inhibitor,[30] iNKT-cell antigens are not exclusively GSL. CD1d has been found associated with glycosylphosphatidylinositol,[38] and engineered forms of CD1d (protease-cleavable or tail-less, secreted CD1d) have been used to extract endogenous FDA-approved Drug Library screening CD1d-associated non-GSL species.[39, 40] Secreted CD1d presents over 150 species, though only lysophosphatidylcholine was subsequently shown to be stimulatory.[41] It remains

possible that these molecules activate type 2 NKT cells. By transfecting GSL-deficient cell lines with CD1d and characterizing the iNKT stimulatory properties of cell extracts, and confirming their results with sphingolipid-specific hydrolases, which

left the antigenic activity of their extracts unaffected, Pei et al.[42] confirmed that endogenous iNKT-cell antigens need not be GSL. Lipids isolated from thymocytes include ether-bonded mono-alkyl glycerophosphates, which are able to activate iNKT thymocytes in a CD1d-dependent manner. Mice deficient in ether-bonded lipids are partially deficient in their ability to select iNKT cells, so these molecules form an essential part of the endogenous iNKT-cell antigen repertoire.[43] AZD1208 concentration CD1d is also capable of binding long hydrophobic peptides.[44, 45] Despite its potency as an iNKT antigen, αGalCer-based therapy has not become established in any disease indication. There is now strong interest in developing agonist ligands to bias iNKT-cell responses towards a Th1 or Th2 cytokine profile,[9] or to create a reduced response,[46, 47] allowing fine control of immune activation. The iNKT-cell TCR functions as a pattern-recognition receptor for both pathogens and altered levels of self-antigen. Structures of the iNKT TCR in complex with ligand-CD1d illuminate how it recognizes diverse

antigens. The footprint of the iNKT TCR on CD1d runs parallel to its binding cleft, unlike the diagonal footprint on MHC characterized for many Teicoplanin peptide–MHC-specific TCR, and covers a small surface area.[48] Just as conventional TCRs have a germline-encoded predisposition to recognize peptide–MHC,[49] so the iNKT TCR uses conserved sequence to recognize antigen–CD1d.[50] CD1d–ligand recognition is largely mediated by complementarity-determining regions (CDR) 3α, 1α and 2β, and structures of various human and mouse iNKT TCR alone[51, 52] and in TCR–antigen–CD1d ternary complexes[53-56] show how CD1d–ligand recognition by the iNKT TCR is highly conserved. CDR2β forms polar interactions with CD1d, CDR1α interacts exclusively with ligand, and CDR3α contacts both.[48, 53] Mouse Vβ8.