Lipid binding orientation within CD1d affects recognition of Borrelia burgorferi antigens by NKT cells

Abstract

Invariant natural killer T cells (iNKT cells) respond to CD1d-presented glycolipids from Borrelia burgdorferi , the causative agent of Lyme disease. Although mouse and human iNKT cells respond to different antigens based on subtle differences in their fatty acids, the mechanism by which fatty acid structure determines antigenic potency is not well understood. Here we show that the mouse and human CD1d present glycolipids having different fatty acids, based in part upon a difference at a single amino acid position that is involved in positioning the sugar epitope. CD1d also can bind nonantigenic lipids, however, but unexpectedly, mouse CD1d orients the two aliphatic chains of a nonantigenic lipid rotated 180°, causing a dramatic repositioning of the exposed sugar. Therefore, our data reveal the biochemical basis for the high degree of antigenic specificity of iNKT cells for certain fatty acids, and they suggest how microbes could alter fatty acid biosynthesis as an immune evasion mechanism.

Lipid and Carbohydrate Modifications of α-Galactosylceramide Differently Influence Mouse and Human Type I Natural Killer T Cell Activation

“…GCK127 (K D ϭ 247 Ϯ 86 nM) and GCK152 (K D ϭ 197 Ϯ 22 nM) show the lowest V␣14V␤8.2 TCR affinity. This is similar to the affinity reported for the parent ␣-C-GalCer (K D ϭ 247 nM) (36) but is ϳ10-fold weaker than ␣GalCer, which in our hands ranges in affinity from 11 to 25 nM (18,29). Of note, the binding affinity is still high compared with mouse TCR affinities for MHC-presented peptides, which most often are in the micromolar range (39,40).…”

“…SPR Kinetic Analysis-Biotinylated CD1d was processed and purified, and studies were conducted using a BIAcore 3000 (GE Healthcare) as reported previously (29), and lipid loading was done as described above. Following overnight GSL loading, ϳ300 response units of the CD1d-GSL complex were immobilized onto a streptavidin sensor chip surface by injecting the CD1d-GSL mixture at 5 l/min using HBS (10 mM HEPES, 150 mM NaCl, 3.0 mM EDTA, pH 7.4) running buffer.…”

Activation of iNKT cells by a distinct constituent of the endogenous glucosylceramide fraction

“…1A), but no activity was detected in the GlcCer fraction from soy milk in this mouse-based assay system. Although iNKT cells are highly conserved, and even function to some degree across species, differences in the recognition of lipid antigens by mouse and human iNKT cells have been reported (11,14,15). To investigate the antigenicity of GlcCer lipid fractions on human iNKT cells, we tested the GlcCer fractions from different milk sources using human iNKT cells and human antigen-presenting cells.…”

Reduced Immune Response to Borrelia burgdorferi in the Absence of γδ T Cells

“…Finally, we measured the Borrelia burden from ear DNA using qPCR of the recA gene, which is chromosomal, whereas the previous study measured ospA, which is episomal. ␥␦ T cells share several parallels with invariant NKT (iNKT) cells, which also respond to B. burgdorferi, although the response by iNKT cells is via direct recognition of borrelial diacylglycerol antigens in a CD1d-restricted manner (17,37,40). Nonetheless, both ␥␦ and iNKT cell subsets rapidly produce various cytokines in response to infection (18,42), both manifest a previously activated phenotype in vivo as reflected in CD44 expression and a high turnover rate (16,35), and there is evidence in both for their indirect activation via TLR signaling on DC, which may enable the ␥␦ and iNKT cells to better activate both innate and adaptive immune responses (8,21,22).…”