Tuberculosis (TB) is the leading cause of death by an infectious agent. Macrophages play a pivotal role in the control of Mycobacterium tuberculosis through the expression of nitric oxide (NO.) and TNFalpha. NO plays an important mycobactericidal role in murine TB and is increasingly recognized to be important in humans. The overall hypothesis of this proposal is that macrophages, by specific surface receptor(s), recognize mycobacterial cell wall products to initiate iNOS- and TNFa-induction. Hence, the focus of this proposal is to: i) determine the receptor and signaling mechanisms which regulate iNOS and TNFa following exposure to the mycobacterial cell wall component lipoarabinomannan (ManLAM) and ii) to determine the significance of each of these components in an in vitro model of infection. Based on experiments showing that macrophages from the Toll-like receptor 4 (TLR4)-mutant C3H/HeJ mice produced significantly lower levels of NO than TLR4-intact C3H/HeN macrophages in response to IFNg + ManLAM, we hypothesize that ManLAM engages a TLR to induce iNOS-NO*/ TNFa expression. Since non-mannose capped LAM (AraLAM) from M. smegmatis induced greater NO about expression than ManLAM, we hypothesize that ii) the exposed arabinose residues on ManLAM or AraLAM are the components of ManLAM that bind to its putative TLR. Since initial studies show that the mitogen-activated protein kinases (MAPKs) and NFkB signaling pathways regulate iNOS and TNFa expression, we hypothesize that the proximal kinase MAP/ERK kinase kinase (MEKK) is a pivotal regulator for ManLAM-induction of iNOS and TNFa. Lastly, because TLRs recognize pathogen-derived molecules and enhance host-defenses, we hypothesize that blocking one or more of the TLRs will enhance the growth of M. tuberculosis and inhibit NO* and TNFa expression. These hypotheses will be addressed by three specific aims: 1. To determine the ManLAM structures that mediate the induction of iNOS-NO*/TNFa and the receptor that mediates these ManLAM effects. 2. To investigate the role of the MAPK and NFkB signaling pathways in ManLAM- and other lipoglycan-induced iNOS-NO* and TNFa. 3. To elucidate the role of the TLRs, MAPK and NFkB signaling pathways, and ManLAM in controlling the growth of M. tuberculosis in mouse and human macrophages and to correlate effects on growth with NO* and TNFa expression.
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