The emergence of multidrug-resistant tuberculosis (TB) and problems with the BCG tuberculosis vaccine to protect humans against TB have prompted investigations into alternative approaches to combat this disease by exploring novel bacterial drug targets and vaccines. Phosphatidylinositol mannosides (PIMs) are biologically important glycoconjugates and represent common essential precursors of more complex mycobacterial cell wall glycolipids including lipomannan (LM), lipoarabinomannan (LAM), and mannan capped lipoarabinomannan (ManLAM). Synthetic PIMs constitute important biochemical tools to elucidate the biosynthesis of this class of molecules, to reveal PIM interactions with host cells, and to investigate the function of PIMs as potential antigens and/or adjuvants for vaccine development. Here, we report the efficient synthesis of all PIMs including phosphatidylinositol (PI) and phosphatidylinositol mono- to hexa-mannoside (PIM1 to PIM6). Robust synthetic protocols were developed for utilizing bicyclic and tricyclic orthoesters as well as mannosyl phosphates as glycosylating agents. Each synthetic PIM was equipped with a thiol-linker for immobilization on surfaces and carrier proteins for biological and immunological studies. The synthetic PIMs were immobilized on microarray slides to elucidate differences in binding to the dendritic cell specific intercellular adhesion molecule-grabbing nonintegrin (DC-SIGN) receptor. Synthetic PIMs served as immune stimulators during immunization experiments in C57BL/6 mice when coupled to the model antigen keyhole-limpet hemocyanin (KLH).
Deficiencies in enzymes of the lysosomal glycosphingolipid degradation pathway or in lysosomal lipid transfer proteins cause an imbalance in lipid metabolism and induce accumulation of certain lipids. A possible impact of such an imbalance on the presentation of lipid antigens to lipid-reactive T cells has only been hypothesized but not extensively studied so far. Here we demonstrate that presentation of lipid antigens to, and development of, lipid-reactive CD1d-restricted NKT cells, are impaired in mice deficient in the lysosomal enzyme b-galactosidase (bGal) or the lysosomal lipid transfer protein Niemann-Pick C (NPC) 2. Importantly, the residual populations of NKT cells selected in bGal -/-and NPC2 -/-mice showed differential TCR and CD4 repertoire characteristics, suggesting that differential selecting CD1d:lipid antigen complexes are formed. Furthermore, we provide direct evidence that accumulation of lipids impairs lipid antigen presentation in both cases. However, the mechanisms by which imbalanced lipid metabolism affected lipid antigen presentation were different. Based on these results, the impact of lipid accumulation should be generally considered in the interpretation of immunological deficiencies found in mice suffering from lipid metabolic disorders.Supporting information for this article is available at http://www.wiley-vch.de/contents/jc_2040/2007/37160_s.pdf IntroductionDefects in lysosomal lipid trafficking or degradation result in a severe imbalance of lipid metabolism. Little is known about the consequences of such an imbalance on the presentation of lipid antigens to lipid-reactive T cells, e.g., the important immunoregulatory invariant (i) NKT cell subset (Va14i and Va24i NKT cells in mice and humans, respectively), which recognizes glycolipid antigens presented by the MHC class I-like molecule Abbreviations: a-GalCer: a-galactosylceramide (KRN7000) Á a/bGal: a/b-galactosidase Á DN: CD4 -CD8 -double negative Á DP: CD4 + CD8 + double positive Á Hex: hexosaminidase Á HSA: heat-stable Ag Á i: invariant Á iGb3: isoglobotrihexosylceramide Á NB-DNJ: N-butyldeoxynojirimycin Á NPC: NiemannPick C Eur. J. Immunol. 2007Immunol. . 37: 1431Immunol. -1441 CD1d. In mice, the TCR of Va14i NKT cells is composed of an invariant Va14-Ja18 chain, paired preferentially with a restricted b chain, mostly containing Vb8.2 or Vb7 (the human equivalents are Va24-Ja18 and Vb11) [1][2][3][4]. Va14i NKT cells are implicated in the regulation of antitumor immunity, antimicrobial responses, and the balance between tolerance and autoimmunity [5,6]. Va14i NKT cells, which can be either CD4 + or CD4 -CD8 -double negative (DN), are a thymus-dependent population derived from CD4 + CD8 + double-positive (DP) thymocytes [7][8][9][10][11]. Different maturation stages of developing thymic Va14i NKT cells have been described, characterized by the sequential acquisition of CD44 and NK1.1 in C57BL/6 mice [12][13][14]. Unlike conventional MHC-dependent T cells, Va14i NKT cells are not positively selected by thymic epithelial cell...
A new practical synthesis of alpha-GalCer and of its analogues is presented, opening the chance to easily modify the sphingosine chain. The common precursor is a disaccharide, obtained by coupling tetra-O-benzyl-D-galactose with allyl 2,3-O-isopropylidene-D-lyxofuranoside. Introduction of alkyl chains via Wittig reaction (for alpha-GalCer and OCH) or via Williamson reaction (for oxa analogues) followed by standard synthetic steps allows one to efficiently obtain such compounds. The analogues are able to activate iNKT cells when presented by CD1d expressing cells.
The synthesis and some examples of glycosylations of a properly protected sphingosine is presented. This compound is suitable for the preparation of glycosphingolipids. It has been used for the synthesis of a-mannosylceramide and sulfatide exploiting the anchimeric assistance to address the stereochemistry of the glycosidic bond.
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