Restoration of impaired free radical generation and proinflammatory cytokines by MCP-1 in mycobacterial pathogenesis

ESX Secretion-Associated Protein C From Mycobacterium tuberculosis Induces Macrophage Activation Through the Toll-Like Receptor-4/Mitogen-Activated Protein Kinase Signaling Pathway

Mycobacterium tuberculosis, as a facultative intracellular pathogen, can interact with host macrophages and modulate macrophage function to influence innate and adaptive immunity. Proteins secreted by the ESX-1 secretion system are involved in this relationship. Although the importance of ESX-1 in host-pathogen interactions and virulence is well-known, the primary role is ascribed to EsxA (EAST-6) in mycobacterial pathogenesis and the functions of individual components in the interactions between pathogens and macrophages are still unclear. Here, we investigated the effects of EspC on macrophage activation. The EspC protein is encoded by an espA/C/D cluster, which is not linked to the esx-1 locus, but is essential for the secretion of the major virulence factors of ESX-1, EsxA and EsxB. Our results showed that both EspC protein and EspC overexpression in M. smegmatis induced pro-inflammatory cytokines and enhanced surface marker expression. This mechanism was dependent on Toll-like receptor 4 (TLR4), as demonstrated using EspC-treated macrophages from TLR4^-/- mice, leading to decreased pro-inflammatory cytokine secretion and surface marker expression compared with those from wild-type mice. Immunoprecipitation and immunofluorescence assays showed that EspC interacted with TLR4 directly. Moreover, EspC could activate macrophages and promote antigen presentation by inducing mitogen-activated protein kinase (MAPK) phosphorylation and nuclear factor-κB activation. The EspC-induced cytokine expression, surface marker upregulation, and MAPK signaling activation were inhibited when macrophages were blocked with anti-TLR4 antibodies or pretreated with MAPK inhibitors. Furthermore, our results showed that EspC overexpression enhanced the survival of M. smegmatis within macrophages and under stress conditions. Taken together, our results indicated that EspC may be another ESX-1 virulence factor that not only modulates the host innate immune response by activating macrophages through TLR4-dependent MAPK signaling but also plays an important role in the survival of pathogenic mycobacteria in host cells.

Lipoarabinomannan Decreases Galectin-9 Expression and Tumor Necrosis Factor Pathway in Macrophages Favoring Mycobacterium tuberculosis Intracellular Growth

Lipoarabinomannan (LAM) is a lipid virulent factor secreted by Mycobacterium tuberculosis (Mtb). LAM can be found in the sputum and urine of patients with active tuberculosis. When human monocytes are differentiated into macrophages [monocyte-derived macrophages (MDM)] in the presence of LAM, MDM are poorly functional which may limit the immune response to Mtb infection. Our previous studies have shown that TIM3 and galectin (GAL)9 interaction induces anti-mycobacterial activity, and the expression levels of TIM3 and GAL9 are downregulated during Mtb infection. We postulated that LAM affects GAL9/TIM3 pathway, and, in consequence, the ability of the macrophage to control bacterial growth could be affected. In this work, we have generated MDM in the presence of LAM and observed that the expression of TIM3 was not affected; in contrast, GAL9 expression was downregulated at the transcriptional and protein levels. We observed that the cell surface and the soluble form of tumor necrosis factor (TNF) receptor 2 were decreased. We also found that when LAM-exposed MDM were activated with LPS, they produced less TNF, and the transcription factor proteinase-activated receptor-2 (PAR2), which is involved in host immune responses to infection, was not induced. Our data show that LAM-exposed MDM were deficient in the control of intracellular growth of Mtb. In conclusion, LAM-exposed MDM leads to MDM with impaired intracellular signal activation affecting GAL9, TNF, and PAR2 pathways, which are important to restrict Mtb growth.

Mycobacterium tuberculosis Rv2882c Protein Induces Activation of Macrophages through TLR4 and Exhibits Vaccine Potential

Macrophages constitute the first line of defense against Mycobacterium tuberculosis and are critical in linking innate and adaptive immunity. Therefore, the identification and characterization of mycobacterial proteins that modulate macrophage function are essential for understanding tuberculosis pathogenesis. In this study, we identified the novel macrophage-activating protein, Rv2882c, from M. tuberculosis culture filtrate proteins. Recombinant Rv2882c protein activated macrophages to secrete pro-inflammatory cytokines and express co-stimulatory and major histocompatibility complex molecules via Toll-like receptor 4, myeloid differentiation primary response protein 88, and Toll/IL-1 receptor-domain-containing adaptor inducing IFN-beta. Mitogen-activated protein kinases and NF-κB signaling pathways were involved in Rv2882c-induced macrophage activation. Further, Rv2882c-treated macrophages induced expansion of the effector/memory T cell population and Th1 immune responses. In addition, boosting Bacillus Calmette-Guerin vaccination with Rv2882c improved protective efficacy against M. tuberculosis in our model system. These results suggest that Rv2882c is an antigen that could be used for tuberculosis vaccine development.

Mycobacterium indicus pranii (MIP) mediated host protective intracellular mechanisms against tuberculosis infection: Involvement of TLR-4 mediated signaling

Mycobacterium tuberculosis infection inflicts the disease Tuberculosis (TB), which is fatal if left untreated. During M. tuberculosis infection, the pathogen modulates TLR-4 receptor down-stream signaling, indicating the possible involvement of TLR-4 in the regulation of the host immune response. Mycobacterium indicus pranii (MIP) possesses immuno-modulatory properties which induces the pro-inflammatory responses via induction of TLR-4-mediated signaling. Here, we observed the immunomodulatory properties of MIP against tuberculosis infection. We have studied the detailed signaling mechanisms employed by MIP in order to restore the host immune response against the in vitro tuberculosis infection. We observed that in infected macrophages MIP treatment significantly increased the TLR-4 expression as well as activation of its downstream signaling, facilitating the activation of P38 MAP kinase. MIP treatment was able to activate NF-κB via involvement of TLR-4 signaling leading to the enhanced pro-inflammatory cytokine and NO generation in the infected macrophages and generation of protective immune response. Therefore, we may suggest that, TLR4 may represent a novel therapeutic target for the activation of the innate immune response during Tuberculosis infection.

Mycobacterium tuberculosis-induced expression of granulocyte-macrophage colony stimulating factor is mediated by PI3-K/MEK1/p38 MAPK signaling pathway

Members of the colony stimulating factor cytokine family play important roles in macrophage activation and recruitment to inflammatory lesions. Among them, granulocyte-macrophage colony stimulating factor (GM-CSF) is known to be associated with immune response to mycobacterial infection. However, the mechanism through which Mycobacterium tuberculosis (MTB) affects the expression of GM-CSF is poorly understood. Using PMA-differentiated THP-1 cells, we found that MTB infection increased GM-CSF mRNA expression in a dosedependent manner. Induction of GM-CSF mRNA expression peaked 6 h after infection, declining gradually thereafter and returning to its basal levels at 72 h. Secretion of GM-CSF protein was also elevated by MTB infection. The increase in mRNA expression and protein secretion of GM-CSF caused by MTB was inhibited in cells treated with inhibitors of p38 MAPK, mitogen-activated protein kinase kinase (MEK-1), and PI3-K. These results suggest that up-regulation of GM-CSF by MTB is mediated via the PI3-K/MEK1/p38 MAPK-associated signaling pathway. [BMB Reports 2013; 46(4): 213-218]

Mannosylated lipoarabinomannans from Mycobacterium avium subsp. paratuberculosis alters the inflammatory response by bovine macrophages and suppresses killing of Mycobacterium avium subsp. avium organisms

Analysis of the mechanisms through which pathogenic mycobacteria interfere with macrophage activation and phagosome maturation have shown that engagement of specific membrane receptors with bacterial ligands is the initiating event. Mannosylated lipoarabinomannan (Man-LAM) has been identified as one of the ligands that modulates macrophage function. We evaluated the effects of Man-LAM derived from Mycobacterium avium subsp. paratuberculosis (MAP) on bovine macrophages. Man-LAM induced a rapid and prolonged expression of IL-10 message as well as transient expression of TNF-α. Preincubation with Man-LAM for up to 16 h did not suppress expression of IL-12 in response to interferon-γ. Evaluation of the effect of Man-LAM on phagosome acidification, phagosome maturation, and killing of Mycobacterium avium subsp. avium (MAA) showed that preincubation of macrophages with Man-LAM before addition of MAA inhibited phagosome acidification, phagolysosome fusion, and reduced killing. Analysis of signaling pathways provided indirect evidence that inhibition of killing was associated with activation of the MAPK-p38 signaling pathway but not the pathway involved in regulation of expression of IL-10. These results support the hypothesis that MAP Man-LAM is one of the virulence factors facilitating survival of MAP in macrophages.

Metabolic impact of 4-hydroxynonenal on macrophage-like RAW 264.7 function and activation

Metabolic profiling of macrophage metabolic response upon exposure to 4-hydroxynonenal (HNE) demonstrates that HNE does not simply inactivate superoxide-generating enzymes but also could be responsible for the impairment of downfield signaling pathways. Multianalyte microphysiometry (MAMP) was employed to simultaneously measure perturbations in extracellular acidification, lactate production, and oxygen consumption for the examination of aerobic and anaerobic pathways. Combining the activation of oxidative burst with phorbol myristate acetate (PMA) and the immunosuppression with HNE, the complex nature of HNE toxicity was determined to be concentration- and time-dependent. Further analysis was utilized to assess the temporal effect of HNE on reactive oxygen species (ROS) production and on protein kinase C (PKC). Increased levels of HNE with decreasing PKC activity suggest that PKC is a target for HNE adductation prior to oxidative burst. Additionally, localization of PKC to the cell membrane was prevented with the introduction of HNE, demonstrating a consequence of HNE adductation on NADPH activation. The impairment of ROS by HNE suggests that HNE has a greater role in foam cell formation and tissue damage than is already known. Although work has been performed to understand the effect of HNE's regulation of specific signaling pathways, details regarding its involvement in cellular metabolism as a whole are generally unknown. This study examines the impact of HNE on macrophage oxidative burst and identifies PKC as a key protein for HNE suppression and eventual metabolic response.

Mycobacterium tuberculosis Rv0652 stimulates production of tumour necrosis factor and monocytes chemoattractant protein-1 in macrophages through the Toll-like receptor 4 pathway

Mycobacterial proteins interact with host macrophages and modulate their functions and cytokine gene expression profile. The protein Rv0652 is abundant in culture filtrates of Mycobacterium tuberculosis K-strain, which belongs to the Beijing family, compared with levels in the H37Rv and CDC1551 strains. Rv0652 induces strong antibody responses in patients with active tuberculosis. We investigated pro-inflammatory cytokine production induced by Rv0652 in murine macrophages and the roles of signalling pathways. In RAW264.7 cells and bone marrow-derived macrophages, recombinant Rv0652 induced predominantly tumour necrosis factor (TNF) and monocyte chemoattractant protein (MCP)-1 production, which was dependent on mitogen-activated protein kinases and nuclear factor-κB. Specific signalling pathway inhibitors revealed that the extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and phosphatidylinositol 3-kinase (PI3K) pathways were essential for Rv0652-induced TNF production, whereas the ERK1/2 and PI3K pathways, but not the p38 pathway, were critical for MCP-1 production in macrophages. Rv0652-stimulated TNF and MCP-1 secretion by macrophages occurred in a Toll-like receptor 4-dependent and MyD88-dependent manner. In addition, Rv0652 significantly up-regulated the expression of the mannose receptor, CD80, CD86 and MHC class II molecules. These results suggest that Rv0652 can induce a protective immunity against M. tuberculosis through the macrophage activation.

A printed superoxide dismutase coated electrode for the study of macrophage oxidative burst

The miniaturization of electrochemical sensors allows for the minimally invasive and cost effective examination of cellular responses at a high efficacy rate. In this work, an ink-jet printed superoxide dismutase electrode was designed, characterized, and utilized as a novel microfluidic device to examine the metabolic response of a 2D layer of macrophage cells. Since superoxide production is one of the first indicators of oxidative burst, macrophage cells were exposed within the microfluidic device to phorbol myristate acetate (PMA), a known promoter of oxidative burst, and the production of superoxide was measured. A 46 ± 19% increase in current was measured over a 30 min time period demonstrating successful detection of sustained macrophage oxidative burst, which corresponds to an increase in the superoxide production rate by 9 ± 3 attomoles/cell/s. Linear sweep voltammetry was utilized to show the selectivity of this sensor for superoxide over hydrogen peroxide. This novel controllable microfluidic system can be used to study the impact of multiple effectors from a large number of bacteria or other invaders along a 2D layer of macrophages, providing an in vitro platform for improved electrochemical studies of metabolic responses.

Cytokine and chemokine responses to selected early secreted antigenic target-6 and culture filtrate protein-10 peptides in tuberculosis

Cytokine [tumor necrosis factor-α, interleukin-2 (IL-2), IL-4] and chemokine [regulated upon activation normal T cell expressed and secreted (RANTES), monocyte chemoattractant protein-1] responses to selected early secreted antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) peptides were studied in healthy household contacts and patients with pulmonary tuberculosis (PTB). It was observed that Th1 cytokines and chemokine RANTES positive T cells were elevated in response to the peptides Esp1, Esp6, Cfp6, and Cfp8 in healthy household contacts. IL-4 positive T cells were enhanced by Esp1 and Esp6 in PTB. Monocyte chemoattractant protein-1 positive monocytes increased in response to the peptides Esp1, Esp6, Cfp8, and Cfp9 in PTB. These peptides deserve attention for further immune studies.

Mycobacterium tuberculosis-induced expression of Leukotactin-1 is mediated by the PI3-K/PDK1/Akt signaling pathway

Chemokines function in the migration of circulating leukocytes to regions of inflammation, and have been implicated in chronic inflammatory conditions including mycobacterial infection. We investigated whether Leukotactin-1 (Lkn-1), a novel member of the CC-chemokines, is involved in the immune response of macrophages against Mycobacterium tuberculosis (MTB). In PMA-differentiated THP-1 cells, MTB infection increased mRNA expression of Lkn-1 in a dose-dependent manner. Lkn-1 induction peaked 12 h after infection, then declined gradually and returned to its basal level at 72 h. Secretion of Lkn-1 was elevated by MTB infection. The increase in expression and secretion of Lkn-1 caused by MTB was reduced in cells treated with inhibitors of phosphatidylinositol 3-kinase (PI3-K), 3-phosphoinositide-dependent kinase 1 (PDK1) and Akt. MTB-induced Akt phosphorylation was blocked by treatment with a PI3-K inhibitor or a PDK1 inhibitor, implying that PI3-K, PDK1, and Akt are associated with the signaling pathway that up-regulates Lkn-1 in response to MTB. These results suggest that Lkn-1 is novel member of the group of chemokines that is released by macrophages infected with MTB.

Association of reduced tumor necrosis factor alpha, gamma interferon, and interleukin-1beta (IL-1beta) but increased IL-10 expression with improved chest radiography in patients with pulmonary tuberculosis

Mycobacterium tuberculosis infection is a major world health issue. The early identification of patients at risk for a poor response to anti-M. tuberculosis therapy would help elucidate the key players in the anti-M. tuberculosis response. The objective of the present study was to correlate the modulation of cytokine expression (interleukin-1 [IL-1], IL-6, IL-8, IL-10, IL-12, gamma interferon [IFN-gamma], interferon-inducible protein [IP-10], and monocyte chemotactic protein 1 [MCP-1]) with the clinical response to 2 months of intensive therapy. From January to December 2007, 40 M. tuberculosis-infected patients and 40 healthy patients were recruited. After exclusion for diabetes, 32 patients and 36 controls were analyzed. The clinical responses of the M. tuberculosis-infected patients on the basis of the findings of chest radiography were compared to their plasma cytokine levels measured before and after 2 months of intensive anti-M. tuberculosis therapy and 6 months of therapy with human cytokine antibody arrays. Chest radiographs of 20 of 32 M. tuberculosis-infected patients showed improvement after 2 months of intensive therapy (early responders), while the M. tuberculosis infections in 12 of 32 of the patients resolved after a further 4 months (late responders). The levels of expression of TNF-alpha, MCP-1, IFN-gamma, and IL-1beta were decreased; and the level of IL-10 increased in early responders. After adjustment for age, gender, and the result of sputum culture for M. tuberculosis, significant differences in the levels of MCP-1 and IP-10 expression were observed between the early and the late responders after 2 months of intensive anti-M. tuberculosis therapy. Due to the interpatient variability in IP-10 levels, intrapatient monitoring of IP-10 levels may provide more insight into the M. tuberculosis responder status than comparison between patients. Plasma MCP-1 levels were normalized in patients who had resolved their M. tuberculosis infections. Further studies to evaluate the association of the modulation in MCP-1 levels with early and late responses are warranted.

Differential cytokine secretion and early treatment response in patients with pulmonary tuberculosis

Biomarkers for treatment response would facilitate the testing of urgently needed new anti-tuberculous drugs. The present study investigated the profiles of 30 proinflammatory, anti-inflammatory and angiogenic factors [epidermal growth factor, eotaxin, fractalkine, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, interleukin (IL)-1alpha, IL-1beta, IL-1ra, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12p40, IL-12p70, IL-13, IL-15, IL-17, interferon-gamma, interferon-inducible protein-10, Krebs von den Lungen-6, monocyte chemotactic protein-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, sCD40L, transforming growth factor-alpha, tumour necrosis factor-alpha and vascular endothelial growth factor] in the plasma of 12 healthy tuberculin skin test-positive community controls and 20 human immunodeficiency virus-negative patients with active tuberculosis (TB) and identified potential biomarkers for early treatment response. We showed differences in the level of circulating cytokines between healthy controls and TB patients, but also between fast responders and slow responders to anti-tuberculosis treatment. The general discriminant analysis based on pre-treatment and week 1 measurements identified 10 sets of three-variable models that could classify fast and slow responders with up to 83% accuracy. Overall, this study shows the potential of cytokines as indicators of anti-tuberculosis treatment response.

Expression and regulation of chemokines in mycobacterial infection

Chemokines are the key molecules that recruit immune cells by chemotaxis and act in leukocyte activation during mycobacterial diseases. Currently, tuberculosis is a leading infectious disease affecting millions of people worldwide. The purpose of this review is to describe a series of recent scientific evidence concerning to the protective role of some members of the CC- and the CXC chemokine subfamilies for the control of mycobacterial infection. The discussion will (1) highlight the effectiveness of some chemokines as potent immunoprophylactic tool for controlling the mycobacterial establishment within the host, (2) describe recent work on the relevance of cellular signaling pathways by which mycobacterial antigens mediate chemokine induction, and (3) summarize current progress in the understanding of the potential use of chemokines as potent adjuvants in antimycobacterial immune responses.