Structural Features of the Acyl Chain Determine Self-phospholipid Antigen Recognition by a CD1d-restricted Invariant NKT (iNKT) Cell

Abstract

Little is known about the antigen specificity of CD1d-restricted T cells, except that they frequently recognize CD1d-expressing antigen-presenting cells in the absence of exogenous antigen. We previously demonstrated that the 24.8.A iNKT cell hybridoma was broadly reactive with CD1d-transfected cell lines and recognized the polar lipid fraction of a tumor cell extract. In the present study, the antigen recognized by the 24.8.A iNKT cell hybridoma was purified to homogeneity and identified as palmitoyl-oleoyl-sn-glycero-3-phosphoethanolamine (16:0 -18:1 PE). The 24.8.A iNKT cell hybridoma recognized synthetic 16:0-18:1[cis] PE, confirming that this phospholipid is antigenic. Recognition correlated with the degree of unsaturation of the acyl chains. Using a panel of synthetic PEs, the 24.8.A iNKT cell hybridoma was shown to be activated by PEs that contained at least one unsaturated acyl chain. The configuration of the double bonds was important, as the 24.8.A iNKT cell hybridoma recognized unsaturated acyl chains in the cis, but not the trans, configuration. PEs with multiple double bonds were recognized better than those with a single double bond, and increasing acyl chain unsaturation correlated with increased binding of PE to CD1d. These data illustrate the potential importance of the acyl chain structure for phospholipid antigen binding to CD1d.

Retracted: α‐GalCer ameliorates listeriosis by accelerating infiltration of Gr‐1+ cells into the liver

“…a-glucuronosylceramide from Sphingomonas sp. [26][27][28][29] and Ehrlichia sp.[28], a-galactosyldiacylglycerol from Borrelia sp.[30], phosphatidylinositol mannoside from Mycobacterium sp.[31] and phosphoethanolamine [32] have recently been identified as ligands for iNKT cells, although all of these activate iNKT cells to a lesser degree than a-GalCer. Although lysosomal glycosphingolipid, isoglobotrihexosylceramide has been reported as a possible endogenous ligand for iNKT cells [28,33], a recent study argues against this possibility [34].…”

“…[31] and phosphoethanolamine [32] have recently been identified as ligands for iNKT cells, although all of these activate iNKT cells to a lesser degree than a-GalCer. Although lysosomal glycosphingolipid, isoglobotrihexosylceramide has been reported as a possible endogenous ligand for iNKT cells [28,33], a recent study argues against this possibility [34].…”

Saposins utilize two strategies for lipid transfer and CD1 antigen presentation

“…These chemical groups have a major effect on the shape of lipids, which is commonly underappreciated. Acyl chain unsaturations (alkene groups) generate a kink and limit flexibility in the acyl chain structure (30). Thus, alkene groups or other acyl-chain modifications may cause lipids to adopt a shape that is not compatible with the dimensions of the SapB hydrophobic pocket or may prevent acyl chains from adoptively fitting into the hydrophobic pocket by restricting its chain.…”

Time to Face the Fats: What Can Mass Spectrometry Reveal about the Structure of Lipids and Their Interactions with Proteins?

“…Not surprisingly, the gross geometric differences between isomeric lipids with cis and trans double bonds have a significant impact on molecular structure and, thus, their biophysical and biochemical properties. For example, Rauch et al showed that the configuration of the double bond in PE 16:0/18:1 was a critical determinant of its recognition as a protein-presented antigen for T cells [37]. Despite its recognized importance, the ability to rapidly establish double bond stereochemistry in complex lipids presents a significant analytical challenge.…”