Natural killer T (NKT) lymphocytes express an invariant T cell antigen receptor (TCR) encoded by the Valpha14 and Jalpha281 gene segments. A glycosylceramide-containing alpha-anomeric sugar with a longer fatty acyl chain (C26) and sphingosine base (C18) was identified as a ligand for this TCR. Glycosylceramide-mediated proliferative responses of Valpha14 NKT cells were abrogated by treatment with chloroquine-concanamycin A or by monoclonal antibodies against CD1d/Vbeta8, CD40/CD40L, or B7/CTLA-4/CD28, but not by interference with the function of a transporter-associated protein. Thus, this lymphocyte shares distinct recognition systems with either T or NK cells.

http://science.sciencemag.org/content/sci/278/5343/1626.full.pdf

CD1d-restricted and TCR-mediated activation of valpha14 NKT cells by glycosylceramides.

Recognized more than a decade ago, NKT cells differentiate from mainstream thymic precursors through instructive signals emanating during TCR engagement by CD1d-expressing cortical thymocytes. Their semi-invariant αβ TCRs recognize isoglobotrihexosylceramide, a mammalian glycosphingolipid, as well as microbial α-glycuronylceramides found in the cell wall of Gram-negative, lipopolysaccharide-negative bacteria. This dual recognition of self and microbial ligands underlies innate-like antimicrobial functions mediated by CD40L induction and massive Th1 and Th2 cytokine and chemokine release. Through reciprocal activation of NKT cells and dendritic cells, synthetic NKT ligands constitute promising new vaccine adjuvants. NKT cells also regulate a range of immunopathological conditions, but the mechanisms and the ligands involved remain unknown. NKT cell biology has emerged as a new field of research at the frontier between innate and adaptive immunity, providing a powerful model to study fundamental aspects of the cell and structural biology of glycolipid trafficking, processing, and recognition.

The biology of NKT cells.

Natural products to drugs: natural product derived compounds in clinical trials

Experimental autoimmune encephalomyelitis (EAE) is a prototype autoimmune disease mediated by type 1 helper T (TH1) cells and under the control of regulatory cells. Here we report that a synthetic glycolipid ligand for CD1d-restricted natural killer T (NKT) cells expressing the semi-invariant T-cell receptor (Valpha14+) is preventive against EAE. The ligand is an analogue of alpha-galactosylceramide (alpha-GC), a prototype NKT cell ligand, with a truncated sphingosine chain. alpha-GC causes NKT cells to produce both interferon (IFN)-gamma and interleukin (IL)-4 (refs 4, 5). However, this new ligand can induce a predominant production of IL-4 by the NKT cells. A single injection of this glycolipid, but not of alpha-GC, consistently induced TH2 bias of autoimmune T cells by causing NKT cells to produce IL-4, leading to suppression of EAE. The lack of polymorphism of CD1d and cross-reactive response of mouse and human NKT cells to the same ligand indicates that targeting NKT cells with this ligand may be an attractive means for intervening in human autoimmune diseases such as multiple sclerosis.

A synthetic glycolipid prevents autoimmune encephalomyelitis by inducing TH2 bias of natural killer T cells.

NKT cells: facts, functions and fallacies

Agelasphin-9b, (2S,3S,4R)-1-O-(alpha-D-galactopyranosyl)-16-methyl-2- [N-((R)-2- hydroxytetracosanoyl)-amino]- 1,3,4-heptadecanetriol, is a potent antitumor agent isolated from the marine sponge Agelas mauritianus. Various analogues of agelasphin-9b (a lead compound) were synthesized, and the relationship between their structures and biological activities was examined using several assay systems. From the results, KRN7000, (2S,3S,4R)-1-O-(alpha-D- galactopyranosyl)-2-(N-hexacosanoylamino)-1,3,4-octadecanetriol , was selected as a candidate for clinical application.

Structure-Activity Relationship of .alpha.-Galactosylceramides against B16-Bearing Mice

Agelasphins, novel antitumor and immunostimulatory cerebrosides from the marine sponge Agelas mauritianus

The first, enantiospecific total syntheses of pyranonaphthoquinone antibiotics, nanaomycins D and A, and their enantiomers, kalafungin and 4-deoxykalafunginic acid are described by an “enantiodivergent” strategy from a common optically active intermediate, (1S,3RS,4S)-3,4-dihydro-5,9,10-trimethoxy-1-methyl-1H-naphtho[2,3-c]pyran-3,4-diol, which has been derived from L-rhamnose via condensation of 4-methoxy-3(phenylsulfonyl)-1(3H)-isobenzofuranone and methyl 3,4,6-trideoxy-α-L-glycero-hex-3-enopyranosid-2-ulose.

Enantiodivergent total syntheses of nanaomycins and their enantiomers, kalafungins

Ten kinds of monoglycosylceramides (MonoCers), having the same ceramide portion and different sugar moieties, were synthesized and their immunostimulatory and antitumor activities were examined. The manner of combination between sugar and ceramide has been demonstrated to affect the manifestation of immunostimulatory and resultant antitumor activities of MonoCers, and in the case of D-MonoCers having the D-sugar, alpha-D-MonoCers (sugar combined to ceramide in an alpha-configuration) show stronger activities than beta-D-MonoCers. Furthermore, the form of sugar, not the furanose-form but the pyranose-form, and the 2"- and 4"-hydroxyl groups of the pyranose-form of sugar, seemed to play an important role in the manifestation of the activities of alpha-D-MonoCers.

Kohji Akimoto

Papers

Structure-Activity Relationship of .alpha.-Galactosylceramides against B16-Bearing Mice

Agelasphins, novel antitumor and immunostimulatory cerebrosides from the marine sponge Agelas mauritianus

Enantiodivergent total syntheses of nanaomycins and their enantiomers, kalafungins

Immunostimulatory and Antitumor Activities of Monoglycosylceramides Having Various Sugar Moieties

A new, stereocontrolled synthesis of cis,anti,cis-tricyclo[6.3.0.02,6]undecanes. Total synthesis of (.+-.)-hirsutene