Infection of human THP-1 cells with dormant Mycobacterium tuberculosis

Kicking sleepers out of bed: Macrophages promote reactivation of dormant Cryptococcus neoformans by extracellular vesicle release and non-lytic exocytosis

Macrophages play a key role in disseminated cryptococcosis, a deadly fungal disease caused by Cryptococcus neoformans. This opportunistic infection can arise following the reactivation of a poorly characterized latent infection attributed to dormant C. neoformans. Here, we investigated the mechanisms underlying reactivation of dormant C. neoformans using an in vitro co-culture model of viable but non-culturable (VBNC; equivalent of dormant) yeast cells with bone marrow-derived murine macrophages (BMDMs). Comparative transcriptome analysis of BMDMs incubated with log, stationary phase or VBNC cells of C. neoformans showed that VBNC cells elicited a reduced transcriptional modification of the macrophage but retaining the ability to regulate genes important for immune response, such as NLRP3 inflammasome-related genes. We further confirmed the maintenance of the low immunostimulatory capacity of VBNC cells using multiplex cytokine profiling, and analysis of cell wall composition and dectin-1 ligands exposure. In addition, we evaluated the effects of classic (M1) or alternative (M2) macrophage polarization on VBNC cells. We observed that intracellular residence sustained dormancy, regardless of the polarization state of macrophages and despite indirect detection of pantothenic acid (or its derivatives), a known reactivator for VBNC cells, in the C. neoformans-containing phagolysosome. Notably, M0 and M2, but not M1 macrophages, induced extracellular reactivation of VBNC cells by the secretion of extracellular vesicles and non-lytic exocytosis. Our results indicate that VBNC cells retain the low immunostimulatory profile required for persistence of C. neoformans in the host. We also describe a pro-pathogen role of macrophage-derived extracellular vesicles in C. neoformans infection and reinforce the impact of non-lytic exocytosis and the macrophage profile on the pathophysiology of cryptococcosis.

Delayed host mortality and immune response upon infection with P. aeruginosa persister cells

Chronic infections are a heavy burden on healthcare systems worldwide. Persister cells are thought to be largely responsible for chronic infection due to their tolerance to antimicrobials and recalcitrance to innate immunity factors. Pseudomonas aeruginosa is a common and clinically relevant pathogen that contains stereotypical persister cells. Despite their importance in chronic infection, there have been limited efforts to study persister cell infections in vivo. Drosophila melanogaster has a well-described innate immune response similar to that of vertebrates and is a good candidate for the development of an in vivo model of infection for persister cells. Similar to what is observed in other bacterial strains, in this work we found that infection with P. aeruginosa persister cells resulted in a delayed mortality phenotype in Caenorhabditis elegans, Arabidopsis thaliana, and D. melanogaster compared to infection with regular cells. An in-depth characterization of infected D. melanogaster found that bacterial loads differed between persister and regular cells' infections during the early stages. Furthermore, hemocyte activation and antimicrobial peptide expression were delayed/reduced in persister infections over the same time course, indicating an initial suppression of, or inability to elicit, the fly immune response. Overall, our findings support the use of D. melanogaster as a model in which to study persister cells in vivo, where this bacterial subpopulation exhibits delayed virulence and an attenuated immune response.

Subversion of the Complement System by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen heavily implicated in chronic diseases. Immunocompromised patients that become infected with P. aeruginosa usually are afflicted with a lifelong chronic infection, leading to worsened patient outcomes. The complement system is an integral piece of the first line of defense against invading microorganisms. Gram-negative bacteria are thought to be generally susceptible to attack from complement; however, P. aeruginosa can be an exception, with certain strains being serum resistant. Various molecular mechanisms have been described that confer P. aeruginosa unique resistance to numerous aspects of the complement response. In this review, we summarize the current published literature regarding the interactions of P. aeruginosa and complement, as well as the mechanisms used by P. aeruginosa to exploit various complement deficiencies and the strategies used to disrupt or hijack normal complement activities.

Immune Response Modulation by Pseudomonas aeruginosa Persister Cells

Bacterial persister cells-a metabolically dormant subpopulation tolerant to antimicrobials-contribute to chronic infections and are thought to evade host immunity. In this work, we studied the ability of Pseudomonas aeruginosa persister cells to withstand host innate immunity. We found that persister cells resist MAC-mediated killing by the complement system despite being bound by complement protein C3b at levels similar to regular vegetative cells, in part due to reduced bound C5b, and are engulfed at a lower rate (10- to 100-fold), even following opsonization. Once engulfed, persister cells resist killing and, contrary to regular vegetative cells which induce a M1 favored (CD80⁺/CD86⁺/CD206^-, high levels of CXCL-8, IL-6, and TNF-α) macrophage polarization, they initially induce a M2 favored macrophage polarization (CD80⁺/CD86⁺/CD206⁺, high levels of IL-10, and intermediate levels of CXCL-8, IL-6, and TNF-α), which is skewed toward M1 favored polarization (high levels of CXCL-8 and IL-6, lower levels of IL-10) by 24 h of infection, once persister cells awaken. Overall, our findings further establish the ability of persister cells to evade the innate host response and to contribute chronic infections. IMPORTANCE Bacterial cells have a subpopulation-persister cells-that have a low metabolism. Persister cells survive antimicrobial treatment and can regrow to cause chronic and recurrent infections. Currently little is known as to whether the human immune system recognizes and responds to the presence of persister cells. In this work, we studied the ability of persister cells from Pseudomonas aeruginosa to resist the host defense system (innate immunity). We found that this subpopulation is recognized by the defense system, but it is not killed. The lack of killing likely stems from hindering the immune response regulation, resulting in a failure to distinguish whether a pathogen is present. Findings from this work increase the overall knowledge as to how chronic infections are resilient.

Immunological aspects of host-pathogen crosstalk in the co-pathogenesis of diabetes and latent tuberculosis

Introduction

Diabetes is a potent risk factor for the activation of latent tuberculosis and worsens the tuberculosis (TB) treatment outcome. The major reason for mortality and morbidity in diabetic patients is due to their increased susceptibility to TB. Thus, the study was conducted to understand the crosstalk between M. tuberculosis and its host upon latent tuberculosis infection and under hyperglycemic conditions or diabetes.

Methods

An animal model was employed to study the relationship between latent tuberculosis and diabetes. BCG immunization was done in mice before infection with M. tuberculosis, and latency was confirmed by bacillary load, histopathological changes in the lungs and gene expression of hspX, tgs1, tgs3 and tgs5. Diabetes was then induced by a single high dose of streptozotocin (150 mg/kg body weight). Host factors, like various cytokines and MMPs (Matrix metalloproteinases), which play an important role in the containment of mycobacterial infection were studied in vivo and in vitro.

Results

A murine model of latent TB was developed, which was confirmed by CFU counts (<10⁴ in the lungs and spleen) and granuloma formation in lungs in the latent TB group. Also, the gene expression of hspX, tgs1, and tgs5 was upregulated, and after diabetes induction, blood glucose levels were >200 mg/dl. An in vitro study employing a THP-1 macrophage model of latent and active tuberculosis under normal and high glucose conditions showed that dormant bacilli were better contained in the presence of 5.5 mM glucose concentration as compared with active bacilli. However, the killing and restriction efficiency of macrophages decreased, and CFU counts increased significantly with an increase in glucose concentration.

Discussion

The decreased levels of MCP-1, decreased expression of mmp-9, and increased expression of mmp-1 in the latent group at high glucose concentrations could explain the failure of granuloma formation at high glucose conditions.

Immune response modulation by Pseudomonas aeruginosa persister cells

Bacterial persister cells - a metabolically dormant subpopulation tolerant to antimicrobials - contribute to chronic infections and are thought to evade host immunity. In this work, we studied the ability of Pseudomonas aeruginosa persister cells to withstand host innate immunity. We found that persister cells resist MAC-mediated killing by the complement system despite being bound by complement protein C3b at levels similar to regular vegetative cells, in part due to reduced bound C5b - and are engulfed at a lower rate (10-100 fold), even following opsonization. Once engulfed, persister cells resist killing and, contrary to regular vegetative cells which induce a M1 favored (CD80+/CD86+/CD206-, high levels of CXCL-8, IL-6, and TNF-α) macrophage polarization, they initially induce a M2 favored macrophage polarization (CD80+/CD86+/CD206+, high levels of IL-10, and intermediate levels of CXCL-8, IL-6, and TNF-α), which is skewed towards M1 favored polarization (high levels of CXCL-8 and IL-6, lower levels of IL-10) by 24 hours of infection, once persister cells awaken. Overall, our findings further establish the ability of persister cells to evade the innate host response and to contribute chronic infections.

ChCl: Gly (DESs) Promote Environmentally Benign Synthesis of Xanthene Derivatives and Their Antitubercular Activity

A ChCl: Gly (DESs) promoted environmentally benign method was developed for the first time using the reaction of aryl aldehydes and dimedone to give excellent yields of xanthene analogues. The major application of this present protocol is the use of green solvent, a wide range of substrate, short reaction times, ease of recovery, the recyclability of the catalyst, high reaction yield, and ChCl: Gly as an alternative catalyst and solvent. In addition to this, all the synthesized compounds were evaluated for their in vitro antimycobacterial activity against M. tuberculosis H37Ra (MTB) and M. bovis BCG strains. The compounds 3d, 3e, 3f, and 3j showed significant antitubercular activity against MTB and M. bovis strains with minimum inhibitory concentration (MIC) values of 2.5−15.10 µg/mL and 0.26–14.92 µg/mL, respectively. The compounds 3e, 3f, and 3j were found to be nontoxic against MCF-7, A549, HCT 116, and THP-1 cell lines. All the prepared compounds were confirmed by ¹H NMR and ¹³C NMR analysis.

Human antibodies targeting a Mycobacterium transporter protein mediate protection against tuberculosis

Mycobacterium tuberculosis (Mtb) exposure drives antibody responses, but whether patients with active tuberculosis elicit protective antibodies, and against which antigens, is still unclear. Here we generate monoclonal antibodies from memory B cells of one patient to investigate the B cell responses during active infection. The antibodies, members of four distinct B cell clones, are directed against the Mtb phosphate transporter subunit PstS1. Antibodies p4-36 and p4-163 reduce Mycobacterium bovis-BCG and Mtb levels in an ex vivo human whole blood growth inhibition assay in an FcR-dependent manner; meanwhile, germline versions of p4-36 and p4-163 do not bind Mtb. Crystal structures of p4-36 and p4-170, complexed to PstS1, are determined at 2.1 Å and 2.4 Å resolution, respectively, to reveal two distinctive PstS1 epitopes. Lastly, a prophylactic p4-36 and p4-163 treatment in Mtb-infected Balb/c mice reduces bacterial lung burden by 50%. Our study shows that inhibitory anti-PstS1 B cell responses arise during active tuberculosis.

Synthesis of Novel Sulfamethaoxazole 4-Thiazolidinone Hybrids and Their Biological Evaluation

A search for potent antitubercular agents prompted us to design and synthesize sulfamethaoxazole incorporated 4-thiazolidinone hybrids (7a–l) by using a cyclocondensation reaction between 4-amino-N-(5-methylisoxazol-3-yl)benzenesulfonamide (4), aryl aldehyde (5a–l), and mercapto acetic acid (6) resulting in good to excellent yields. All the newly synthesized 4-thiazolidinone derivatives were screened for their in vitro antitubercular activity against M. Bovis BCG and M. tuberculosis H37Ra (MTB) strains. The compounds 7d, 7g, 7i, 7k, and 7l revealed promising antimycobacterial activity against M. Bovis and MTB strains with IC₉₀ values in the range of 0.058–0.22 and 0.43–5.31 µg/mL, respectively. The most active compounds were also evaluated for their cytotoxicity against MCF-7, HCT 116, and A549 cell lines and were found to be non-cytotoxic. Moreover, the synthesized compounds were also analyzed for ADME (absorption, distribution, metabolism, and excretion) properties and showed potential as good oral drug candidates.

Dissecting the Mechanism of Intracellular Mycobacterium smegmatis Growth Inhibition by Platelet Activating Factor C-16

Mycobacterium tuberculosis (M.tb) infection results in approximately 1.3 million human deaths each year. M.tb resides primarily inside macrophages, and maintains persistent infection. In response to infection and inflammation, platelet activating factor C-16 (PAF C-16), a phospholipid compound, is released by various cells including neutophils and monocytes. We have recently shown that PAF C-16 can directly inhibit the growth of two representative non-pathogenic mycobacteria, Mycobacterium bovis BCG and Mycobacterium smegmatis (M. smegmatis), by damaging the bacterial cell membrane. Here, we have examined the effect of PAF C-16 on M. smegmatis residing within macrophages, and identified mechanisms involved in their growth inhibitory function. Our results demonstrated that exogenous PAF C-16 inhibited the growth of M. smegmatis inside phagocytic cells of monocytic cell line, THP-1; this effect was partially blocked by PAF receptor antagonists, suggesting the involvement of PAF receptor-mediated signaling pathways. Arachidonic acid, a downstream metabolite of PAF C-16 signaling pathway, directly inhibited the growth of M. smegmatis in vitro. Moreover, the inhibition of phospholipase C and phospholipase A₂ activities, involved in PAF C-16 signaling pathway, increased survival of intracellular M. smegmatis. Interestingly, we also observed that inhibition of inducible nitric oxide synthase (iNOS) enzyme and antibody-mediated neutralization of TNF-α partially mitigated the intracellular growth inhibitory effect of PAF C-16. Use of a number of PAF C-16 structural analogs, including Lyso-PAF, 2-O-methyl PAF, PAF C-18 and Hexanolamino PAF, revealed that the presence of acetyl group (CH₃CO) at sn-2 position of the glycerol backbone of PAF is important for the intracellular growth inhibition activity against M. smegmatis. Taken together, these results suggest that exogenous PAF C-16 treatment inhibits intracellular M. smegmatis growth, at least partially, in a nitric oxide and TNF-α dependent manner.

Mycobacterium tuberculosis sensor kinase DosS modulates the autophagosome in a DosR-independent manner

Dormancy is a key characteristic of the intracellular life-cycle of Mtb. The importance of sensor kinase DosS in mycobacteria are attributed in part to our current findings that DosS is required for both persistence and full virulence of Mtb. Here we show that DosS is also required for optimal replication in macrophages and involved in the suppression of TNF-α and autophagy pathways. Silencing of these pathways during the infection process restored full virulence in MtbΔdosS mutant. Notably, a mutant of the response regulator DosR did not exhibit the attenuation in macrophages, suggesting that DosS can function independently of DosR. We identified four DosS targets in Mtb genome; Rv0440, Rv2859c, Rv0994, and Rv0260c. These genes encode functions related to hypoxia adaptation, which are not directly controlled by DosR, e.g., protein recycling and chaperoning, biosynthesis of molybdenum cofactor and nitrogen metabolism. Our results strongly suggest a DosR-independent role for DosS in Mtb.

A high content screening assay for identifying inhibitors against active and dormant state intracellular Mycobacterium tuberculosis

The antitubercular drug development pipeline could start with an in vitro investigation of several compounds to examine their effect on active and dormant state Mycobacterium tuberculosis (Mtb). However, in vitro screening of dormant state bacilli cannot provide enough information on the simultaneous effect of a compound on the host. Therefore, we developed a live cell fluorescence based screening protocol by utilizing the high content system for determining the effect of inhibitors against active and dormant state intracellular mycobacteria. THP-1 macrophages infected with an actively growing and hypoxia derived dormant Mtb culture were standardized to develop the screening protocol. The signal to noise ratio and the Z' factor of this assay were found to be 7.5-29 and 0.6-0.8, respectively, which confirm the robustness of the protocol. The protocol was then validated with standard inhibitors. This newly developed drug screening assay offers an easy, safe, image based high content screening tool to search for novel antitubercular inhibitors against both active and dormant state intracellular mycobacteria. Therefore, this assay could fill in the gap between in vitro and in vivo latent tuberculosis drug screening programs.

Evaluation of the expression of cytokines and chemokines in macrophages in response to rifampin-monoresistant Mycobacterium tuberculosis and H37Rv strain

Macrophages are the primary phagocytes in the lungs and a part of the host defense system against Mycobacterium tuberculosis (Mtb), involved in the primary immune response. While several studies have assessed the effects of resistance to rifampin on Mtb physiology, the consequences of mutations in genes encoding the beta subunit of RNA polymerase (rpoB) for host-pathogen interactions remain poorly understood. In this study, rifampin-monoresistant (RMR) Mtb and H37Rv strains were used to infect the THP-1-derived macrophages. Real-time quantitative reverse transcription PCR assay was carried out to determine mRNA expression in 84 cytokine and chemokine genes. Production of specific cytokines and chemokines was measured by ELISA assay. In conclusion, the current study shed more light on the fitness cost of RMR strain and the potential effects of rpoB gene mutations on Mtb-host interactions. These results initially demonstrate that the Mtb carrying the rpoB-S450L can modulate macrophage responses to mediate bacterial survival.

Cytokine Biomarkers Associated with Human Extra-Pulmonary Tuberculosis Clinical Strains and Symptoms

Background: The primary site of infection for Mycobacterium tuberculosis (Mtb) is the alveolar macrophages. However, Mtb can disseminate into other organs and causes extrapulmonary tuberculosis (EPTB). The diagnosis of EPTB is challenging due to relatively inaccessible infectious sites that may be paucibacillary and with clinical symptoms varying by site that are similar to those seen in other diseases. Hence, we sought to identify the expression patterns of a variety of cytokines that may be specific to EPTB from in vitro infections and in the plasma of TB patients. Methods: To define those cytokine secretions associated with EPTB, human THP-1 derived macrophages were first infected with Mtb clinical isolates from pulmonary and EPTB. Infected macrophages supernatants were harvested at different time points and cytokines known to play key roles in TB immune responses including TNF-α, IL-6, IL-10, IFN-γ, and VEGF-A were measured by ELISA. Those cytokines that were in vitro associated to EPTB were also measured in the plasma from patients with PTB, EPTB, non-EPTB-confirmed-like symptoms and healthy controls. Results: While all of the studied cytokine secretions varied after in vitro infection, higher levels of TNF-α and VEGF secretions were observed in vitro in the infected macrophages respectively in the PTB and EPTB infecting clinical isolates. Similar trends were observed from the plasma of patients where patients with PTB showed significantly higher level of TNF-α compared to EPTB and healthy control groups. The patients with EPTB showed higher plasma level of VEGF compared to those patients with the non-EPTB (p < 0.01) and to healthy controls group (p < 0.0001). Using Receiver Operating Curves (ROC), we showed that TNF-α and VEGF concentrations could distinguish EPTB from non-confirmed EPTB with high sensitivity and specificity. Conclusion: Pulmonary and extrapulmonary Mtb clinical isolates showed different cytokine induction pattern in human macrophages that is also found in the plasma level of the EPTB patients. Further investigations are needed to define cytokine secretions that can lead to the definition of bio-signatures to differentiate EPTB from other pathologies with confusing symptoms that hampered the diagnosis of TB.

Divergent macrophage responses to Mycobacterium bovis among naturally exposed uninfected and infected cattle

Mycobacterium bovis, the causative agent of bovine tuberculosis (TB), is a successful pathogen that remains an important global threat to livestock. Cattle naturally exposed to M. bovis normally become reactive to the M. bovis-purified protein derivative (tuberculin) skin test; however, some individuals remain negative, suggesting that they may be resistant to infection. To better understand host innate resistance to infection, 26 cattle from herds with a long history of high TB prevalence were included in this study. We investigated the bactericidal activity, the production of reactive oxygen and nitrogen species and the TB-related gene expression profile after in vitro M. bovis challenge of monocyte-derived macrophages from cattle with TB (n=17) and from non-infected, exposed cattle (in-contacts, n=9). The disease status was established based on the tuberculin skin test and blood interferon-gamma test responses, the presence of visible lesions at inspection on abattoirs and the histopathology and culture of M. bovis. Although macrophages from TB-infected cattle enabled M. bovis replication, macrophages from healthy, exposed cattle had twofold lower bacterial loads, overproduced nitric oxide and had lower interleukin (IL)-10 gene expression (P⩽0.05). Higher mRNA expression levels of inducible nitric oxide synthase, C-C motif chemokine ligand 2 and IL-12 were observed in macrophages from all in-contact cattle than in macrophages from their TB-infected counterparts, which expressed more tumour necrosis factor-α; however, the differences were not statistically significant owing to individual variation. These results confirm that macrophage bactericidal responses have a crucial role in innate resistance to M. bovis infection in cattle.

Mycobacterium oryzae sp. nov., a scotochromogenic, rapidly growing species is able to infect human macrophage cell line

Gram-stain-positive, acid-fast-positive, rapidly growing, rod-shaped bacteria (designated as strains JC290T, JC430 and JC431) were isolated from paddy cultivated soils on the Western Ghats of India. Phylogenetic analysis placed the three strains among the rapidly growing mycobacteria, being most closely related to Mycobacterium tokaiense 47503T (98.8 % 16S rRNA gene sequence similarity), Mycobacterium murale MA112/96T (98.8 %) and a few other Mycobacterium species. The level of DNA-DNA reassociation of the three strains with M. tokaiense DSM 44635T was 23.4±4 % (26.1±3 %, reciprocal analysis) and 21.4±2 % (22.1±4 %, reciprocal analysis). The three novel strains shared >99.9 % 16S rRNA gene sequence similarity and DNA-DNA reassociation values >85 %. Furthermore, phylogenetic analysis based on concatenated sequences (3071 bp) of four housekeeping genes (16S rRNA, hsp65, rpoB and sodA) revealed that strain JC290T is clearly distinct from all other Mycobacteriumspecies. The three strains had diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositolmannosides, unidentified phospholipids, unidentified glycolipids and an unidentified lipid as polar lipids. The predominant isoprenoid quinone for all three strains was MK-9(H2). Fatty acids were C17 : 1ω7c, C16 : 0, C18 : 1ω9c, C16 : 1ω7c/C16 : 1ω6c and C19 : 1ω7c/C19 : 1ω6c for all the three strains. On the basis of phenotypic, chemotaxonomic and phylogenetic data, it was concluded that strains JC290T, JC430 and JC431 are members of a novel species within the genus Mycobacterium and for which the name Mycobacterium oryzae sp. nov. is proposed. The type strain is JC290T (=KCTC 39560T=LMG 28809T).

Mycobacterium tuberculosis gene expression at different stages of hypoxia-induced dormancy and upon resuscitation

The physiology of dormant Mycobacterium tuberculosis was studied in detail by examining the gene expression of 51 genes using quantitative Reverse-Transcription Polymerase Chain Reaction. A forty-day period of dormancy in the Wayne culture model depicted four major transcription patterns. Some sigma factors and many metabolic genes were constant, whereas genes belonging to the dormancy regulon were activated on day 9. In particular, alpha-crystallin mRNA showed more than a 1,000-fold increase compared to replicating bacilli. Genes belonging to the enduring hypoxic response were up-regulated at day 16, notably, transcription factors sigma B and E. Early genes typical of log-phase bacilli, esat-6 and fbpB, were uniformly down-regulated during dormancy. Late stages of dormancy showed a drop in gene expression likely due to a lack of substrates in anaerobic respiration as demonstrated by the transcriptional activation observed following nitrates addition. Among genes involved in nitrate metabolism, narG was strongly up-regulated by nitrates addition. Dormant bacilli responded very rapidly when exposed to oxygen and fresh medium, showing a transcriptional activation of many genes, including resuscitation-promoting factors, within one hour. Our observations extend the current knowledge on dormant M. tuberculosis gene expression and its response to nutrients and to aerobic and anaerobic respiration.

Evaluation of the inflammatory response in macrophages stimulated with exosomes secreted by Mycobacterium avium-infected macrophages

Exosomes secreted from Mycobacterium avium-infected macrophages contain numerous antigens of both M. avium and the host cell and are involved in the induction and expression of the inflammatory responses in macrophages. The interaction between exosomes secreted from M. avium-infected macrophages and macrophage phagocytosis, cytokine secretion, immunostimulation, and apoptosis was analyzed. Upon stimulation with exosomes secreted from M. avium-infected macrophages, the phagocytosis of dextran by treated macrophages was increased. Furthermore, the expression of CD40, CD80, CD81, CD86, HLA-DR, and most notably CD195 was enhanced. Additionally, the secretion of IL-6, IL-8, IL-10, IFN-γ, and TNF-α was increased by stimulated macrophages. Exosome stimulation did not induce macrophage apoptosis when compared with macrophages infected with M. avium. Caspase expression, including that of caspases 3, 6, and 8, was also not altered in exosome stimulated macrophages. Thus exosomes trigger the inflammatory response in macrophages owing to the presence of bacterial antigens but have no effect on macrophage viability.

Differential macrophage response to slow- and fast-growing pathogenic mycobacteria

Nontuberculous mycobacteria (NTM) have recently been recognized as important species that cause disease even in immunocompetent individuals. The mechanisms that these species use to infect and persist inside macrophages are not well characterised. To gain insight concerning this process we used THP-1 macrophages infected with M. abscessus, M. fortuitum, M. celatum, and M. tuberculosis. Our results showed that slow-growing mycobacteria gained entrance into these cells with more efficiency than fast-growing mycobacteria. We have also demonstrated that viable slow-growing M. celatum persisted inside macrophages without causing cell damage and without inducing reactive oxygen species (ROS), as M. tuberculosis caused. In contrast, fast-growing mycobacteria destroyed the cells and induced high levels of ROS. Additionally, the macrophage cytokine pattern induced by M. celatum was different from the one induced by either M. tuberculosis or fast-growing mycobacteria. Our results also suggest that, in some cases, the intracellular survival of mycobacteria and the immune response that they induce in macrophages could be related to their growth rate. In addition, the modulation of macrophage cytokine production, caused by M. celatum, might be a novel immune-evasion strategy used to survive inside macrophages that is different from the one reported for M. tuberculosis.

Role of TNF in the altered interaction of dormant Mycobacterium tuberculosis with host macrophages

Mycobacterium tuberculosis (Mtb) persists within lung granulomas, despite being subjected to diverse stress conditions, including hypoxia. We hypothesized that the response of host phagocytes to Mtb experiencing hypoxia is radically altered and designed in vitro experiment to study this phenomenon. Hypoxia-stressed (Mtb-H) and aerobically grown Mtb (Mtb-A) were used to infect Rhesus Macaque Bone Marrow Derived Macrophages (Rh-BMDMs) and the comparative host response to Mtb infection studied. Mechanistic insights were gained by employing RNAi. Mtb-H accumulated significantly lower bacterial burden during growth in Rh-BMDMs, concomitantly generating a drastically different host transcriptional profile (with only <2% of all genes perturbed by either infection being shared between the two groups). A key component of this signature was significantly higher TNF and apopotosis in Mtb-H- compared to Mtb-A-infected Rh-BMDMs. Silencing of TNF by RNAi reversed the significant control of Mtb replication. These results indicate a potential mechanism for the rapid clearance of hypoxia-conditioned bacilli by phagocytes. In conclusion, hypoxia-conditioned Mtb undergo significantly different interactions with host macrophages compared to Mtb grown in normoxia. These interactions result in the induction of the TNF signaling pathway, activation of apoptosis, and DNA-damage stress response. Our results show that Mtb-H bacilli are particularly susceptible to killing governed by TNF.

Proteomic analysis and immune properties of exosomes released by macrophages infected with Mycobacterium avium

The role of exosomes shed from Mycobacterium avium sp. paratuberculosis-infected macrophages in intercellular communication processes was examined. We compared the responses of resting macrophages infected with M. avium sp. paratuberculosis with those of resting macrophages treated with exosomes previously released from macrophages infected with M. avium sp. paratuberculosis. Some proteins components of exosomes released from resting macrophages infected with M. avium sp. paratuberculosis showed a significantly differential expression compared with exosomes from uninfected-macrophages. Both M. avium sp. paratuberculosis and exosomes from infected-cells enhanced the expression of CD80 and CD86 and the secretion of TNF-α and IFN-γ by macrophages. This suggests that exosomes from infected macrophages may be carriers of molecules, e.g. bacterial antigens and/or components from infected macrophages, that can elicit responses in resting cells. Two-dimensional analysis of the proteins present in exosomes from M. avium sp. paratuberculosis-infected macrophages compared with those from resting cells resulted in the identification by MALDI-TOF/TOF mass spectrometry of the following differentially expressed proteins: two actin isoforms, guanine nucleotide-binding protein β-1, cofilin-1 and peptidyl-prolyl cis-trans isomerase A. The possible relevance of the changes observed and the biological functions of the proteins differentially present are discussed.

The prostaglandin E2 receptor EP4 is integral to a positive feedback loop for prostaglandin E2 production in human macrophages infected with Mycobacterium tuberculosis

Prostaglandin E2 (PGE2) is an important biological mediator involved in the defense against Mycobacterium tuberculosis (Mtb) infection. Previously, we reported that in macrophages (Mϕs), infection with avirulent Mtb H37Ra resulted in inhibition of necrosis by an inhibitory effect on mitochondrial permeability transition via the PGE2 receptor EP2. However, human Mϕs also express EP4, a PGE2 receptor functionally closely related to EP2 that also couples to stimulatory guanine nucleotide binding protein, but the functional differences between EP2 and EP4 in Mtb-infected Mϕs have been unclear. EP4 antagonist addition to H37Ra-infected Mϕs inhibited the expression of cyclooxygenase 2 (COX2) and microsomal prostaglandin E synthase-1 (mPGES-1), which are involved in PGE2 production. Moreover, H37Ra infection induced PGE2 production through the Toll-like receptor (TLR) 2/p38 mitogen-activated protein kinase (MAPK) signaling pathway. Induction of COX2 and mPGES-1 expression by TLR2 stimulation or Mtb infection was increased after additional stimulation with EP4 agonist. Hence, in Mtb-infected Mϕs, PGE2 production induced by pathogen recognition receptors/p38 MAPK signaling is up-regulated by EP4-triggered signaling to maintain an effective PGE2 concentration.

Dormant Mycobacterium tuberculosis fails to block phagosome maturation and shows unexpected capacity to stimulate specific human T lymphocytes

Dormancy is defined as a stable but reversible nonreplicating state of Mycobacterium tuberculosis. It is currently thought that dormant M. tuberculosis (D-Mtb) is responsible for latent tuberculosis (TB) infection. Recently, D-Mtb was also shown in sputa of patients with active TB, but the capacity of D-Mtb to stimulate specific immune responses was not investigated. We observed that purified protein derivative-specific human CD4(+) T lymphocytes recognize mycobacterial Ags more efficiently when macrophages are infected with D-Mtb instead of replicating M. tuberculosis (R-Mtb). The different Ag recognition occurs even when the two forms of mycobacteria equally infect and stimulate macrophages, which secrete the same cytokine pattern and express MHC class I and II molecules at the same levels. However, D-Mtb but not R-Mtb colocalizes with mature phagolysosome marker LAMP-1 and with vacuolar proton ATPase in macrophages. D-Mtb, unlike R-Mtb, is unable to interfere with phagosome pH and does not inhibit the proteolytic efficiency of macrophages. We show that D-Mtb downmodulates the gene Rv3875 encoding for ESAT-6, which is required by R-Mtb to block phagosome maturation together with Rv3310 gene product SapM, previously shown to be downregulated in D-Mtb. Thus, our results indicate that D-Mtb cannot escape MHC class II Ag-processing pathway because it lacks the expression of genes required to block the phagosome maturation. Data suggest that switching to dormancy not only represents a mechanism of survival in latent TB infection, but also a M. tuberculosis strategy to modulate the immune response in different stages of TB.