Linkage disequilibrium between minisatellite loci supports clonal evoluation of <I>Mycobacterium tuberculosis</I> in a high tuberculosis incidence area.

GesondheidswetenskappeMolekul�re Biologie & MensgenetikaPlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]

Mycolic acid biosynthesis and enzymic characterization of the beta-ketoacyl-ACP synthase A-condensing enzyme from Mycobacterium tuberculosis.

Mycolic acids consist of long-chain alpha-alkyl-beta-hydroxy fatty acids that are produced by successive rounds of elongation catalysed by a type II fatty acid synthase (FAS-II). A key feature in the elongation process is the condensation of a two-carbon unit from malonyl-acyl-carrier protein (ACP) to a growing acyl-ACP chain catalysed by a beta-ketoacyl-ACP synthase (Kas). In the present study, we provide evidence that kasA from Mycobacterium tuberculosis encodes an enzyme that elongates in vivo the meromycolate chain, in both Mycobacterium smegmatis and Mycobacterium chelonae. We demonstrate that KasA belongs to the FAS-II system, which utilizes primarily palmitoyl-ACP rather than short-chain acyl-ACP primers. Furthermore, in an in vitro condensing assay using purified recombinant KasA, palmitoyl-AcpM and malonyl-AcpM, KasA was found to express Kas activity. Also, mutated KasA proteins, with mutation of Cys(171), His(311), Lys(340) and His(345) to Ala abrogated the condensation activity of KasA in vitro completely. Finally, purified KasA was highly sensitive to cerulenin, a well-known inhibitor of Kas, which may lead to the development of novel anti-mycobacterial drugs targeting KasA

The Natural Cytotoxicity Receptor NKp46 Is Dispensable for IL-22-Mediated Innate Intestinal Immune Defense against Citrobacter rodentium

Natural cytotoxicity receptors (including NKp30, NKp44, and NKp46 in humans and NKp46 in mice) are type I transmembrane proteins that signal NK cell activation via ITAM-containing adapter proteins in response to stress- and pathogen-induced ligands. Although murine NKp46 expression (encoded by Ncr1) was thought to be predominantly restricted to NK cells, the identification of distinct intestinal NKp46(+) cell subsets that express the transcription factor Rorc and produce IL-22 suggests a broader function for NKp46 that could involve intestinal homeostasis and immune defense. Using mice carrying a GFP-modified Ncr1 allele, we found normal numbers of gut CD3(-)GFP(+) cells with a similar cell surface phenotype and subset distribution in the absence of Ncr1. Splenic and intestinal CD3(-)NKp46(+) cell subsets showed distinct patterns of cytokine secretion (IFN-gamma, IL-22) following activation via NK1.1, NKp46, IL-12 plus IL-18, or IL-23. However, IL-22 production was sharply restricted to intestinal CD3(-)GFP(+) cells with the CD127(+)NK1.1(-) phenotype and could be induced in an Ncr1-independent fashion. Because NKp46 ligands can trigger immune activation in the context of infectious pathogens, we assessed the response of wild-type and Ncr-1-deficient Rag2(-/-) mice to the enteric pathogen Citrobacter rodentium. No differences in the survival or clinical score were observed in C. rodentium-infected Rag2(-/-) mice lacking Ncr1, indicating that NKp46 plays a redundant role in the differentiation of intestinal IL-22(+) cells that mediate innate defense against this pathogen. Our results provide further evidence for functional heterogeneity in intestinal NKp46(+) cells that contrast with splenic NK cells. The Journal of Immunology, 2009, 183: 6579-6587

Cutting edge: thymic NK cells develop independently from T cell precursors.

Although NK cells in the mouse are thought to develop in the bone marrow, a small population of NK cells in the thymus has been shown to derive from a GATA3-dependent pathway. Characteristically, thymic NK cells express CD127 and few Ly49 molecules and lack CD11b. Because these NK cells develop in the thymus, the question of their relationship to the T cell lineage has been raised. Using several different mouse models, we find that unlike T cells, thymic NK cells are not the progeny of Rorc-expressing progenitors and do not express Rag2 or rearrange the TCRγ locus. We further demonstrate that thymic NK cells develop independently of the Notch signaling pathway, supporting the idea that thymic NK cells represent bona fide NK cells that can develop independently of all T cell precursors