Photoactivable Glycolipid Antigens Generate Stable Conjugates with CD1d for Invariant Natural Killer T Cell Activation.

Activation of invariant natural killer T lymphocytes (iNKT cells) by α-galactosylceramide (α-GC) elicits a range of pro-inflammatory or anti-inflammatory immune responses. We report the synthesis and characterization of a series of α-GC analogues with acyl chains of varying length and a terminal benzophenone. These bound efficiently to the glycolipid antigen presenting protein CD1d, and upon photoactivation formed stable CD1d-glycolipid covalent conjugates.

Identification of a Potent Microbial Lipid Antigen for Diverse NKT Cells.

Semi-invariant/type I NKT cells are a well-characterized CD1d-restricted T cell subset. The availability of potent Ags and tetramers for semi-invariant/type I NKT cells allowed this population to be extensively studied and revealed their central roles in infection, autoimmunity, and tumor immunity. In contrast, diverse/type II NKT (dNKT) cells are poorly understood because the lipid Ags that they recognize are largely unknown.

Recognition of microbial and mammalian phospholipid antigens by NKT cells with diverse TCRs.

CD1d-restricted natural killer T (NKT) cells include two major subgroups. The most widely studied are Vα14Jα18(+) invariant NKT (iNKT) cells that recognize the prototypical α-galactosylceramide antigen, whereas the other major group uses diverse T-cell receptor (TCR) α-and β-chains, does not recognize α-galactosylceramide, and is referred to as diverse NKT (dNKT) cells. dNKT cells play important roles during infection and autoimmunity, but the antigens they recognize remain poorly understood.

Structural basis of inhibition of Mycobacterium tuberculosis DprE1 by benzothiazinone inhibitors.

Resistance against currently used antitubercular therapeutics increasingly undermines efforts to contain the worldwide tuberculosis (TB) epidemic. Recently, benzothiazinone (BTZ) inhibitors have shown nanomolar potency against both drug-susceptible and multidrug-resistant strains of the tubercle bacillus. However, their proposed mode of action is lacking structural evidence.

Saposins utilize two strategies for lipid transfer and CD1 antigen presentation.

Transferring lipid antigens from membranes into CD1 antigen-presenting proteins represents a major molecular hurdle necessary for T-cell recognition. Saposins facilitate this process, but the mechanisms used are not well understood. We found that saposin B forms soluble saposin protein-lipid complexes detected by native gel electrophoresis that can directly load CD1 proteins.

Innate and cytokine-driven signals, rather than microbial antigens, dominate in natural killer T cell activation during microbial infection.

Invariant natural killer T cells (iNKT cells) are critical for host defense against a variety of microbial pathogens. However, the central question of how iNKT cells are activated by microbes has not been fully explained. The example of adaptive MHC-restricted T cells, studies using synthetic pharmacological α-galactosylceramides, and the recent discovery of microbial iNKT cell ligands have all suggested that recognition of foreign lipid antigens is the main driver for iNKT cell activation during infection.

Identification of arylamine N-acetyltransferase inhibitors as an approach towards novel anti-tuberculars.

New anti-tubercular drugs and drug targets are urgently needed to reduce the time for treatment and also to identify agents that will be effective against Mycobacterium tuberculosis persisting intracellularly. Mycobacteria have a unique cell wall. Deletion of the gene for arylamine N-acetyltransferase (NAT) decreases mycobacterial cell wall lipids, particularly the distinctive mycolates, and also increases antibiotic susceptibility and killing within macrophage of Mycobacterium bovis BCG.

Crystal structure of bovine CD1b3 with endogenously bound ligands.

The CD1 family of Ag-presenting molecules is able to display lipids to T cells by binding them within a hydrophobic groove connected to the protein surface. In particular, the CD1b isotype is capable of binding ligands with greatly varying alkyl chain lengths through a complex network of interconnected hydrophobic pockets. Interestingly, mycobacterial lipids such as glucose monomycolate exclusively bind to CD1b.

Novel generation mycobacterial adjuvant based on liposome-encapsulated monomycoloyl glycerol from Mycobacterium bovis bacillus Calmette-Guérin.

The immunostimulatory activity of lipids associated with the mycobacterial cell wall has been recognized for several decades and exploited in a large variety of different adjuvant preparations. Previously, we have shown that a mycobacterial lipid extract from Mycobacterium bovis bacillus Calmette-Guérin delivered in cationic liposomes was a particular efficient Th1-inducing adjuvant formulation effective against tuberculosis. Herein, we have dissected the adjuvant activity of the bacillus Calmette-Guérin lipid extract showing that the majority of the activity was attributable to the apolar lipids and more specifically to a single lipid, monomycoloyl glycerol (MMG), previously also shown to stimulate human dendritic cells.

Adjuvant properties of a simplified C32 monomycolyl glycerol analogue.

A simplified C(32) monomycolyl glycerol (MMG) analogue demonstrated enhanced immunostimulatory activity in a dioctadecyl ammonium bromide (DDA)/Ag85B-ESAT-6 formulation. Elevated levels of IFN-gamma and IL-6 were produced in spleen cells from mice immunised with a C(32) MMG analogue comparable activity to the potent Th1 adjuvant, trehalose 6,6'-di-behenate (TDB).

A simple mycobacterial monomycolated glycerol lipid has potent immunostimulatory activity.

It is a long held belief that the strong immunostimulatory activity of the Mycobacterium bovis bacillus Calmette-Guérin vaccine and Freund's complete adjuvant is due to specific mycobacterial cell envelope components, such as lipids and polysaccharides. Implicated mycobacterial lipids include, among others, the so-called cord factor or trehalose dimycolate, but limited information is available regarding the precise molecular nature of the stimulatory components responsible for the interaction with human APCs. In this regard, the majority of research aimed at identifying and characterizing individual immunostimulatory mycobacterial lipids has been performed in the murine system using bone marrow-derived dendritic cells.

Tuberculosis: a balanced diet of lipids and carbohydrates.

In spite of effective antibiotics to treat TB (tuberculosis) since the early 1960s, we enter the new millennium with TB currently the leading cause of death from a single infectious agent, killing more than 3 million people worldwide each year. Thus an understanding of drug-resistance mechanisms, the immunobiology of cell wall components to elucidate host-pathogen interactions and the discovery of new drug targets are now required for the treatment of TB. Above the plasma membrane is a classical chemotype IV peptidoglycan to which is attached the macromolecular structure, mycolyl-arabinogalactan via a unique diglycosylphosphoryl bridge.

Synthesis and biological evaluation of NAS-21 and NAS-91 analogues as potential inhibitors of the mycobacterial FAS-II dehydratase enzyme Rv0636.

The identification of potential new anti-tubercular chemotherapeutics is paramount due to the recent emergence of extensively drug-resistant strains of Mycobacterium tuberculosis (XDR-TB). Libraries of NAS-21 and NAS-91 analogues were synthesized and evaluated for their whole-cell activity against Mycobacterium bovis BCG. NAS-21 analogues 1 and 2 demonstrated enhanced whole-cell activity in comparison to the parental compound, and an M.

New drugs and vaccines for drug-resistant Mycobacterium tuberculosis infections.

Tuberculosis remains the most common cause of death due to a single infective organism. Despite the availability of a vaccine and chemotherapeutic options, the global disease burden remains relatively unaffected. The ability of the mycobacterial etiological agents to adopt a semidormant, phenotypically drug-resistant state requires that chemotherapy is both complex and lengthy.

Flavonoid inhibitors as novel antimycobacterial agents targeting Rv0636, a putative dehydratase enzyme involved in Mycobacterium tuberculosis fatty acid synthase II.

Flavonoids comprise a large group of bioactive polyphenolic plant secondary metabolites. Several of these possess potent in vivo activity against Escherichia coli and Plasmodium falciparum, targeting enzymes involved in fatty acid biosynthesis, such as enoyl-ACP-reductase, beta-ketoacyl-ACP reductase and beta-hydroxyacyl-ACP dehydratase. Herein, we report that butein, isoliquirtigenin, 2,2',4'-trihydroxychalcone and fisetin inhibit the growth of Mycobacterium bovis BCG.

Synthesis and biological evaluation of a C5-biphenyl thiolactomycin library.

Fifteen novel C5 analogues of thiolactomycin (13 biphenyl analogues and two biphenyl mimics) have been synthesised and assessed for their in vitro mtFabH and whole cell Mycobacterium bovis BCG activity, respectively. Analysis of the 15 compounds revealed that six possessed enhanced in vitro activity in a direct mtFabH assay. Encouragingly analogues 11, 12 and 13 gave a significant enhancement in in vitro activity against mtFabH.

EthA, a common activator of thiocarbamide-containing drugs acting on different mycobacterial targets.

Many of the current antimycobacterial agents require some form of cellular activation unmasking reactive groups, which in turn will bind to their specific targets. Therefore, understanding the mechanisms of activation of current antimycobacterials not only helps to decipher mechanisms of drug resistance but may also facilitate the development of alternative activation strategies or of analogues that do not require such processes. Herein, through the use of genetically defined strains of Mycobacterium bovis BCG we provide evidence that EthA, previously shown to activate ethionamide, also converts isoxyl (ISO) and thiacetazone (TAC) into reactive species.

Symmetrical and unsymmetrical analogues of isoxyl; active agents against Mycobacterium tuberculosis.

Symmetrical and unsymmetrical analogues of the antimycobacterial agent isoxyl have been synthesized and tested against Mycobacterium tuberculosis H37Rv and Mycobacterium bovis BCG, some showing an increased bactericidal effect. In particular, compounds 1-(p-n-butylphenyl)-3-(4-propoxy-phenyl) thiourea (10) and 1-(p-n-butylphenyl)-3-(4-n-butoxy-phenyl) thiourea (11) showed an approximate 10-fold increase in in vitro potency compared to isoxyl, paralleled by increased inhibition of mycolic acid biosynthesis in M. bovis BCG.