The knockout of the lprG-Rv1410 operon produces strong attenuation of Mycobacterium tuberculosis

227

193

MHC class II (MHC-II)-restricted CD4+ T cells are essential for control of Mycobacterium tuberculosis infection. This report describes the identification and purification of LprG (Rv1411c) as an inhibitor of primary human macrophage MHC-II Ag processing. LprG is a 24-kDa lipoprotein found in the M. tuberculosis cell wall. Prolonged exposure (>16 h) of human macrophages to LprG resulted in marked inhibition of MHC-II Ag processing. Inhibition of MHC-II Ag processing was dependent on TLR-2. Short-term exposure (<6 h) to LprG stimulated TLR-2-dependent TNF-α production. Thus, LprG can exploit TLR-2 signaling to inhibit MHC-II Ag processing in human macrophages. Inhibition of MHC-II Ag processing by mycobacterial lipoproteins may allow M. tuberculosis, within infected macrophages, to avoid recognition by CD4+ T cells.

Section: Discussionsupporting

confidence: 68%

Mycobacterium tuberculosisLprG (Rv1411c): A Novel TLR-2 Ligand That Inhibits Human Macrophage Class II MHC Antigen Processing

Gehring

Dobos

Belisle

et al. 2004

227

193

“…In both Staphylococcus aureus and Mtb, genetic defects that cause global lipoprotein disruptions result in reduced virulence (27), although this may reflect impairments in general bacterial physiology as well as potential alterations in host-pathogen interactions. In a study targeting a specific lipoprotein, deletion of LprG (a close homolog of LprA) was shown to attenuate the virulence of Mtb H37Rv in a mouse model (53). These observations suggest that further study of Mtb lipoproteins and their activities is important to our understanding of Mtb virulence and host-pathogen interactions in Mtb infection.…”

Section: Discussionmentioning

confidence: 97%

Mycobacterium tuberculosis LprA Is a Lipoprotein Agonist of TLR2 That Regulates Innate Immunity and APC Function

Pecora¹,

Gehring

Canaday

et al. 2006

192

168

TLR2 recognizes components of Mycobacterium tuberculosis (Mtb) and initiates responses by APCs that influence both innate and adaptive immunity. Mtb lipoproteins are an important class of TLR2 ligand, but only two, LpqH and LprG, have been characterized to date. In this study, we characterize a third Mtb lipoprotein, LprA, and determine its effects on host macrophages and dendritic cells. LprA is a cell wall-associated lipoprotein with no homologs outside the slow-growing mycobacteria. Using Mycobacterium smegmatis as an expression host, we purified 6× His-tagged LprA both with and without its acyl modifications. Acylated LprA had agonist activity for both human and murine TLR2 and induced expression of TNF-α, IL-10, and IL-12. LprA also induced dendritic cell maturation as shown by increased expression of CD40, CD80, and class II MHC (MHC-II). In macrophages, prolonged (24 h) incubation with LprA decreased IFN-γ-induced MHC-II Ag processing and presentation, consistent with an observed decrease in MHC-II expression (macrophage viability was not affected and apoptosis was not induced by LprA). Reduced MHC-II Ag presentation may represent a negative feedback mechanism for control of inflammation that may be subverted by Mtb for immune evasion. Thus, Mtb LprA is a TLR2 agonist that induces cytokine responses and regulates APC function.

“…The M.Tb complexspecific 27-kDa lipoprotein is a mitogen for murine splenocytes (68) and drives a Th1-type immune response in vivo, but fails to ameliorate a simultaneous or subsequent infection with virulent M.Tb (69,70). In vivo, a 27-kDa deficient M.Tb strain was strongly attenuated as compared with the control strains in a mouse model of tuberculosis (71). M.Tb mutants lacking lipoprotein signal peptidase are deficient in the processing of all lipoproteins which results in impaired stimulation of TLR2-reporter cells (72).…”

Section: Discussionmentioning

confidence: 99%

Mycobacterial Lipopeptides Elicit CD4+ CTLs in Mycobacterium tuberculosis-Infected Humans

Bastian¹,

Braun

Bruns³

et al. 2008

In searching for immunogenic molecules with the potential to induce protective immune responses against tuberculosis, we developed an ex vivo model to study frequency, phenotype, and effector functions of human T lymphocytes recognizing hydrophobic Ags of Mycobacterium tuberculosis (M.Tb). To obtain unbiased results, we characterized T lymphocytes responding to a crude cell wall extract (chloroform methanol extract of M.Tb (M.Tb-CME)) containing a broad spectrum of mycobacterial glycolipids and lipopeptides. A significant proportion of T lymphocytes recognized M.Tb-CME (290 IFN-γ+ T cells/105 PBMCs) and developed to effector memory cells as determined by the expression of CD45RO and the chemokine receptors CXCR3 and CCR5. Expanded lymphocytes fulfilled all criteria required for an efficient immune response against tuberculosis: 1) release of macrophage-activating Th1 cytokines and chemokines required for the spatial organization of local immune responses, 2) cytolytic activity against Ag-pulsed macrophages, and 3) recognition of infected macrophages and killing of the intracellular bacteria. Phenotypically, M.Tb-CME-expanded cells were CD4+ and MHC class II restricted, challenging current concepts that cytotoxic and antimicrobial effector cells are restricted to the CD8+ T cell subset. Pretreatment of M.Tb-CME with protease or chemical delipidation abrogated the biological activity, suggesting that responses were directed toward mycobacterial lipopeptides. These findings suggest that lipidated peptides are presented by M.Tb-infected macrophages and elicit CD4+ cytolytic and antimicrobial T lymphocytes. Our data support an emerging concept to include hydrophobic microbial Ags in vaccines against tuberculosis.