Preparation of anti-vicinal amino alcohols: asymmetric synthesis of D-erythro-Sphinganine, (+)-spisulosine and D-ribo-phytosphingosine

Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM-ether directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor D-erythro-sphinganine and the antitumor agent (+)-spisulosine, while the Overman rearrangement of chiral allylic trichloroacetimidates generated by asymmetric reduction of an alpha,beta-unsaturated methyl ketone allowed rapid access to both D-ribo-phytosphingosine and L-arabino-phytosphingosine

Recognition of Lyso-Phospholipids by Human Natural Killer T Lymphocytes

Natural killer T (NKT) cells are a subset of T lymphocytes with potent immunoregulatory properties. Recognition of self-antigens presented by CD1d molecules is an important route of NKT cell activation; however, the molecular identity of specific autoantigens that stimulate human NKT cells remains unclear. Here, we have analyzed human NKT cell recognition of CD1d cellular ligands. The most clearly antigenic species was lyso-phosphatidylcholine (LPC). Diacylated phosphatidylcholine and lyso-phosphoglycerols differing in the chemistry of the head group stimulated only weak responses from human NKT cells. However, lyso-sphingomyelin, which shares the phosphocholine head group of LPC, also activated NKT cells. Antigen-presenting cells pulsed with LPC were capable of stimulating increased cytokine responses by NKT cell clones and by freshly isolated peripheral blood lymphocytes. These results demonstrate that human NKT cells recognize cholinated lyso-phospholipids as antigens presented by CD1d. Since these lyso-phospholipids serve as lipid messengers in normal physiological processes and are present at elevated levels during inflammatory responses, these findings point to a novel link between NKT cells and cellular signaling pathways that are associated with human disease pathophysiology.</p

Production and characterization of monoclonal antibodies against complexes of the NKT cell ligand α-galactosylceramide bound to mouse CD1d

The α-galactosylceramide (α-GalCer) known as KRN7000 remains the best studied ligand of the lipid-binding MHC class I-like protein CD1d. The KRN7000:CD1d complex is highly recognized by invariant natural killer T (iNKT) cells, an evolutionarily conserved subset of T lymphocytes that express an unusual semi-invariant T cell antigen receptor, and mediate a variety of proinflammatory and immunoregulatory functions. To facilitate the study of glycolipid antigen presentation to iNKT cells by CD1d, we undertook the production of mouse monoclonal antibodies (mAbs) specific for complexes of KRN7000 bound to mouse CD1d (mCD1d) proteins. Three such monoclonal antibodies were isolated that bound only to mCD1d proteins that were loaded with KRN7000 or closely-related forms of α-GalCer. These mAbs showed no reactivity with mCD1d proteins that were not loaded with α-GalCer, nor did they bind to complexes formed by loading mCD1d with the self-glycolipid and putative iNKT cell ligand isoglobotrihexosylceramide. These complex-specific monoclonal antibodies allow the direct detection and monitoring of complexes formed by the binding of KRN7000 and other α-GalCer analogues to mCD1d. The availability of these mAbs should facilitate a wide range of studies on the biology and potential clinical applications of CD1d-restricted iNKT cells

Rapid identification of immunostimulatory alpha-galactosylceramides using synthetic combinatorial libraries

Two 60+-membered libraries of (alpha-galactosylceramides have been prepared by reactions between activated ester resins and two core, fully deprotected galactosylated sphingoid bases. The libraries were evaluated for their ability to stimulate CD1d-restricted NKT cells, using in vitro stimulation of a murine NKT cell hybridoma line and for their ability to induce the expansion of NKT cells from peripheral blood mononuclear cells (PBMC of a normal human subject. bur results showed that many compounds constructed on a C18-phytosphingosine base had significant stimulatory activity in both assays. Because no. product purification was required, this approach is particularly attractive as a method for rapid synthesis of large libraries of potential immunomodulatory glycosylceramides.1111sciescopu

Recognition of lyso-phospholipids by human natural killer T lymphocytes.

Natural killer T (NKT) cells are a subset of T lymphocytes with potent immunoregulatory properties. Recognition of self-antigens presented by CD1d molecules is an important route of NKT cell activation; however, the molecular identity of specific autoantigens that stimulate human NKT cells remains unclear. Here, we have analyzed human NKT cell recognition of CD1d cellular ligands. The most clearly antigenic species was lyso-phosphatidylcholine (LPC). Diacylated phosphatidylcholine and lyso-phosphoglycerols differing in the chemistry of the head group stimulated only weak responses from human NKT cells. However, lyso-sphingomyelin, which shares the phosphocholine head group of LPC, also activated NKT cells. Antigen-presenting cells pulsed with LPC were capable of stimulating increased cytokine responses by NKT cell clones and by freshly isolated peripheral blood lymphocytes. These results demonstrate that human NKT cells recognize cholinated lyso-phospholipids as antigens presented by CD1d. Since these lyso-phospholipids serve as lipid messengers in normal physiological processes and are present at elevated levels during inflammatory responses, these findings point to a novel link between NKT cells and cellular signaling pathways that are associated with human disease pathophysiology

A Rapid Fluorescence-Based Assay for Classification of iNKT Cell Activating Glycolipids

Structural variants of alpha-galactosylceramide (alpha GC) that activate invariant natural killer T cells (iNKT cells) are being developed as potential immunomodulatory agents for a variety of applications. Identification of specific forms of these glycolipids that bias responses to favor production of proinflammatory vs anti-inflammatory cytokines is central to current efforts, but this goal has been hampered by the lack of in vitro screening assays that reliably predict the in vivo biological activity of these compounds. Here we describe a fluorescence-based assay to identify functionally distinct alpha GC analogues. Our assay is based on recent findings showing that presentation of glycolipid antigens by CD1d molecules localized to plasma membrane detergent-resistant microdomains (lipid rafts) is correlated with induction of interferon-gamma secretion and Th1-biased cytokine responses. Using an assay that measures lipid raft residency of CD1d molecules loaded with alpha GG, we screened a library of similar to 200 synthetic alpha GC analogues and identified 19 agonists with potential Th1-biasing activity. Analysis of a subset of these novel candidate Th1 type agonists in vivo in mice confirmed their ability to induce systemic cytokine responses consistent with a Th1 type bias. These results demonstrate the predictive value of this novel in vitro assay for assessing the in vivo functionality of glycolipid agonists and provide the basis for a relatively simple high-throughput assay for identification and functional classification of iNKT cell activating glycolipids.1117sciescopu

Kinetics and Cellular Site of Glycolipid Loading Control the Outcome of Natural Killer T Cell Activation

CD1d-restricted natural killer T cells (NKT cells) possess a wide range of effector and regulatory activities that are related to their ability to secrete both T helper 1 (Th1) cell- and Th2 cell-type cytokines. We analyzed presentation of NKT cell activating α galactosylceramide (αGalCer) analogs that give predominantly Th2 cell-type cytokine responses to determine how ligand structure controls the outcome of NKT cell activation. Using a monoclonal antibody specific for αGalCer-CD1d complexes to visualize and quantitate glycolipid presentation, we found that Th2 cell-type cytokine-biasing ligands were characterized by rapid and direct loading of cell-surface CD1d proteins. Complexes formed by association of these Th2 cell-type cytokine-biasing αGalCer analogs with CD1d showed a distinctive exclusion from ganglioside-enriched, detergent-resistant plasma membrane microdomains of antigen-presenting cells. These findings help to explain how subtle alterations in glycolipid ligand structure can control the balance of proinflammatory and anti-inflammatory activities of NKT cells