krn-7000 and isoglobotrihexosylceramide

Invariant NKT (iNKT) cells are a unique subset of lymphocytes that recognize glycolipid antigens presented by a monomorphic glycoprotein CD1d. Numerous works have shown that iNKT cells may serve as regulatory cells in autoimmune diseases including multiple sclerosis (MS). However, recent studies have revealed that the presence of iNKT cells accelerates some inflammatory conditions, implying that their protective role against autoimmunity is not predetermined. Here we review recent information concerning the mechanism of how iNKT cells intervene or promote autoimmune inflammation. Although iNKT cells are thought to be specific for a limited set of glycolipids, they may cross-react to self and non-self ligands. Regarding the response to non-self, it is now known that iNKT cells produce enormous amounts of proinflammatory cytokines during the course of infectious diseases, which is triggered by TCR ligation by microbial lipids, cytokines produced from APCs or both. Whereas the strongly activated iNKT cells play a beneficial role in combating environmental pathogens, they could play a deleterious role in autoimmunity by producing disease-promoting cytokines. However, iNKT cells in the steady state would retain an ability to produce anti-inflammatory cytokines, which is needed for terminating the ongoing inflammation. Though an initial trigger for their regulatory responses remains elusive, our recent work indicates that iNKT cells may start regulating inflammation after sensing the presence of IL-2 in addition to recognizing a ubiquitous endogenous ligand. Understanding of how iNKT cells regulate autoimmunity should lead to a more sophisticated strategy for controlling autoimmune diseases.

Topics: Animals; Antigen-Presenting Cells; Autoimmune Diseases; Autoimmunity; Cytokines; Galactosylceramides; Globosides; Humans; Killer Cells, Natural; Th1 Cells; Th2 Cells; Trihexosylceramides

Isoglobotrihexosylceramide (iGb3) is an endogenous antigen of mammalian cells and can stimulate invariant natural killer T (iNKT) cells to evoke autoimmune activities by the release of T helper 1 (Th1) and Th2 cytokines. Th1 cytokines are correlated with the antitumor and antiviral response, while Th2 cytokines are correlated with the amelioration of autoimmune diseases. iGb3 is a very weak agonist compared to the exogenous alpha-galactosylceramide; however, modification of the ceramide moiety has been advocated as one of the approaches to improve its stimulatory activity and to change the bias of release of Th1 and Th2 cytokines. Two analogues of iGb3, 2H-iGb3 and HO-iGb3 with different ceramide moieties, were synthesized. Bioassay results showed that HO-iGb3 was much more effective in stimulating iNKT cells than iGb3 at low concentration. The assay also showed that the CD1d/2H-iGb3 complexes are remarkably efficient in stimulating iNKT cells.

Topics: Antigens, CD1; Antigens, CD1d; Carbohydrate Sequence; Cell Line; Globosides; Humans; Interferon-gamma; Interleukin-4; Killer Cells, Natural; Lymphocyte Activation; Models, Molecular; Molecular Sequence Data; Protein Binding; Receptors, Antigen, T-Cell; Stereoisomerism; Structure-Activity Relationship; Trihexosylceramides

A burst release of cytokines by Valpha14 invariant NKT (iNKT) cells upon their TCR engagement critically regulates innate and adaptive immune responses. However, it remains unclear in vivo why iNKT cells respond efficiently to microbial or intracellular lipid Ags that are at low levels or that possess suboptimal antigenicity. We found that dendritic cells (DCs) potentiated iNKT cells to respond to a minimal amount of ligand alpha-galactosylceramide (alphaGalCer) through CD1d-dependent autoreactive responses that require endosomal processing and CD1d trafficking. The ability of potentiation of NKT cells was DC specific and did not depend on costimulatory signals and IL-12 production by DCs. However, DCs that failed to synthesize a major endogenous lipid Ag isoglobotrihexosylceramide were unable to potentiate NKT cells for efficient activation. Further analysis showed that differences in the level and pattern of endogenous lipid Ag presentation differentiate DCs and B cells for effective potentiation and subsequent activation of iNKT cells in the presence of an exogenous Ag. Thus, CD1d-dependent potentiation by DCs may be crucial for iNKT cell-mediated immunity against infectious agents.

Topics: Animals; Antigen Presentation; Antigens; Antigens, CD1; Antigens, CD1d; B-Lymphocytes; Dendritic Cells; Endosomes; Galactosylceramides; Globosides; Immunity, Cellular; Interleukin-12; Killer Cells, Natural; Lymphocyte Activation; Mice; Mice, Inbred BALB C; Mice, Knockout; Mice, SCID; Protein Transport; Receptors, Antigen, T-Cell, alpha-beta; Self Tolerance; Signal Transduction; T-Lymphocytes; Trihexosylceramides

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 beta-galactosidase (betaGal) or the lysosomal lipid transfer protein Niemann-Pick C (NPC) 2. Importantly, the residual populations of NKT cells selected in betaGal-/- 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.

Topics: 1-Deoxynojirimycin; Animals; Antigen Presentation; Antigens, CD1; Antigens, CD1d; beta-Galactosidase; CD4 Antigens; Dendritic Cells; Enzyme Inhibitors; Galactosylceramides; Globosides; Glycolipids; Humans; Lipid Metabolism; Lipid Metabolism Disorders; Liver; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Knockout; Receptors, Antigen, T-Cell; Spleen; T-Lymphocyte Subsets; Thymus Gland; Trihexosylceramides; Vesicular Transport Proteins

Efficient chemoenzymatic syntheses of iGb3 and Gb3 have been developed. Isoglobotrihexose and globotrihexose were enzymatically synthesized by a three-enzyme system in both solid and solution phases. Then iGb3 and Gb3 were chemically synthesized by coupling of the corresponding trisaccharides with lipid.

Topics: Animals; Carbohydrate Sequence; Galactosylceramides; Globosides; Glycosylation; Humans; Killer Cells, Natural; Mice; Phosphoric Diester Hydrolases; Trihexosylceramides; Trisaccharides