Analysis of nitric oxide synthase and nitrotyrosine expression in human pulmonary tuberculosis

Progress and new directions in genetics of tuberculosis: an NHLBI working group report

Tuberculosis (TB), along with AIDS and malaria, is one of the three major killers among infectious diseases. New approaches to preventing, diagnosing, and curing TB are needed, which depend on a better understanding of Mycobacterium tuberculosis and the host. The National Heart, Lung, and Blood Institute convened a working group to develop recommendations for future TB research, including genetic aspects of the disease. The following areas were identified: (1) animal model research to improve understanding of persistence, reactivation, and granulomatous reactions; (2) preclinical studies aimed at shortening treatment of TB; (3) new resources for manipulating and characterizing the M. tuberculosis genome, proteome chips for more specific diagnoses, and studies of genes that appear to be essential but whose functions are not known; (4) prospective studies associated with clinical trials in populations with or at risk of TB to advance development of diagnostics and prognostics; (5) new quantitative and bioinformatic approaches to study the interaction between M. tuberculosis and the infected host and how this influences the infection process; (6) molecular characterization of M. tuberculosis genome diversity and phylogenetic analysis; (7) coordinated studies of human genome scans; (8) genetic epidemiology studies; (9) activities to foster knowledge dissemination, education, and training; and (10) coordination between the National Institutes of Health, the Gates Foundation, the Global Alliance for Tuberculosis Drug Development, and other organizations.

Susceptibility of brushtail possums (Trichosurus vulpecula) infected with Mycobacterium bovis is associated with a transient macrophage activation profile

The Australian brushtail possums are highly susceptible to Mycobacterium bovis and are the principal wildlife reservoir of M. bovis in New Zealand. To better understand the disease process in these animals, brushtail possums were infected by the aerosol route with a virulent strain of M. bovis, and immune parameters measured. M. bovis replicated actively in the lungs of infected animals. Animals began developing macroscopic lung lesions at 4 and 5 weeks following infection, with some lesions appearing in the livers and spleens. Infection determined the emergence of blood lymphocytes which proliferated in response to bovine purified protein derivative from M. bovis (PPD-b) at 3, 4 and 5 weeks. The response to a mitogen (Concanavalin A) waned progressively with time. Infection was associated with a modest increase in the numbers of free lung cells. Nitrite was detectable in the lavage fluids of infected animals at 3 weeks postinfection, but not at 4 and 5 weeks. Macrophage activation in the lungs was evident as alveolar macrophages produced more oxidants, significant levels of nitric oxide (NO), as well as tumor necrosis factor alpha (TNF-alpha) bioactivity at 3 weeks postinfection. However, macrophages from infected animals lost the ability to generate nitrite- and TNF-alpha generation was depressed at 4 and 5 weeks postinfection, the time at which macroscopic lesions in the lungs became apparent. Alveolar macrophages from animals at 3 weeks postinfection blocked the replication of M. bovis in part via a NO-dependent mechanism, and were more refractory for M. bovis growth than cells from naïve animals to bacterial replication. Alveolar macrophages from animals at 4 and 5 weeks postinfection allowed substantial replication of M. bovis, and no NO-dependent bacteriostatic activity was apparent. Introduction of autologous lymphocytes from the blood of infected animals in co-cultures rendered infected macrophages more resistant to M. bovis replication. We conclude that M. bovis infection in brushtail possums is associated with a transient activation of alveolar macrophages, although in vitro exposure to sensitized T cells can enhance this profile.

Mycobacterium tuberculosis and the host response

Mycobacterium tuberculosis remains a leading cause of morbidity and mortality worldwide. Advances reported at a recent international meeting highlight insights and controversies in the genetics of M. tuberculosis and the infected host, the nature of protective immune responses, adaptation of the bacillus to host-imposed stresses, animal models, and new techniques.

Role of CD8+ T lymphocytes in control of Mycobacterium tuberculosis infection

Tuberculosis remains a global health concern. Control of infection is dependent on cell-mediated immune responses, with CD4+ T lymphocytes playing a central role. In this article, data supporting the importance of CD8+ T lymphocytes is reviewed, with an emphasis on the unique functional roles that this lymphocyte subset may play.

Vaccination of brushtail possums, Trichosurus vulpecula , with Bacille Calmette–Guerin induces T lymphocytes that reduce Mycobacterium bovis replication in alveolar macrophages via a contact‐dependent/nitric oxide‐independent mechanism

The permissiveness of alveolar macrophages from brushtail possums for the replication of Mycobacterium bovis was examined. Mycobacterium bovis replication was indirectly measured by assessing bacterial metabolism via the incorporation of [3-H]-uracil by bacilli released from lysed macrophages previously infected with mycobacteria. Alveolar macrophages allowed substantial replication of virulent M. bovis, in contrast to Bacille Calmette-Guerin (BCG) Pasteur, which replicated poorly. The addition of crude lymphokines enhanced the metabolic activity of phagocytosed M. bovis in possum macrophages. Possum lymphokines enhanced the ability of possum macrophages to generate reactive oxygen intermediates, measured by the reduction of nitroblue tetrazolium, which is indicative of an activation process. Similarly, the addition of recombinant possum TNF-alpha enhanced the permissiveness of alveolar macrophages for M. bovis. In contrast to mouse peritoneal macrophages, possum alveolar macrophages did not release significant levels of nitric oxide (NO) after stimulation with M. bovis and/or lymphokines. However, the uptake of virulent M. bovis by possum macrophages was associated with an enhanced ability of cells to release TNF-alpha, whereas very low levels of TNF-alpha were released after infection with BCG. The addition of a selective inhibitor of inducible NO synthase had no impact on the replication of M. bovis or BCG in possum macrophages in the presence or absence of lymphokines. Co-culturing infected possum alveolar macrophages with autologous blood mononuclear cells from BCG-vaccinated possums led to a significant decrease in the metabolic activity of intracellular M. bovis. This effect was contact dependent and NO independent and was mediated by a population of CD3+ cells. In addition, adding scavengers of reactive oxygen intermediates did not abrogate this phenomenon.

S-nitroso proteome of Mycobacterium tuberculosis: Enzymes of intermediary metabolism and antioxidant defense

The immune response to Mycobacterium tuberculosis (Mtb) includes expression of nitric oxide (NO) synthase (NOS)2, whose products can kill Mtb in vitro with a molar potency greater than that of many conventional antitubercular agents. However, the targets of reactive nitrogen intermediates (RNIs) in Mtb are unknown. One major action of RNIs is protein S-nitrosylation. Here, we describe, to our knowledge, the first proteomic analysis of S-nitrosylation in a whole organism after treating Mtb with bactericidal concentrations of RNIs. The 29 S-nitroso proteins identified are all enzymes, mostly serving intermediary metabolism, lipid metabolism, and/or antioxidant defense. Many are essential or implicated in virulence, including defense against RNIs. For each of two target enzymes tested, lipoamide dehydrogenase and mycobacterial proteasome ATPase, S-nitrosylation caused enzyme inhibition. Moreover, endogenously biotinylated proteins were driven into mixed disulfide complexes. Targeting of metabolic enzymes and antioxidant defenses by means of protein S-nitrosylation and mixed disulfide bonding may contribute to the antimycobacterial actions of RNIs.

Antimicrobial reactive oxygen and nitrogen species: concepts and controversies

Phagocyte-derived reactive oxygen and nitrogen species are of crucial importance for host resistance to microbial pathogens. Decades of research have provided a detailed understanding of the regulation, generation and actions of these molecular mediators, as well as their roles in resisting infection. However, differences of opinion remain with regard to their host specificity, cell biology, sources and interactions with one another or with myeloperoxidase and granule proteases. More than a century after Metchnikoff first described phagocytosis, and more than four decades after the discovery of the burst of oxygen consumption that is associated with microbial killing, the seemingly elementary question of how phagocytes inhibit, kill and degrade microorganisms remains controversial. This review updates the reader on these concepts and the topical questions in the field.

Aerosolized gamma interferon (IFN-gamma) induces expression of the genes encoding the IFN-gamma-inducible 10-kilodalton protein but not inducible nitric oxide synthase in the lung during tuberculosis

Gamma interferon (IFN-gamma) is critical in the immune response against Mycobacterium tuberculosis. In an ongoing trial of aerosol IFN-gamma in conjunction with standard drug therapy, we have observed activation of IFN signaling in bronchoalveolar lavage (BAL) cells from tuberculosis (TB) patients. We hypothesized that aerosol IFN-gamma treatment of pulmonary TB would increase expression of genes important for the control of TB. We investigated the expression of downstream genes by measuring inducible nitric oxide synthase (iNOS) and the chemokine IFN-inducible 10-kDa protein (IP-10) by real-time quantitative reverse transcription-PCR. In vitro, M. tuberculosis induced IP-10, and IFN-gamma stimulated this further, with no effect on iNOS expression. We studied 21 patients with pulmonary TB and 7 healthy subjects. Similar to the in vitro model, IP-10 mRNA was increased in BAL cells from TB patients and was augmented after treatment with aerosolized IFN-gamma. TB was also associated with elevated iNOS mRNA, but aerosolized IFN-gamma did not further enhance expression. Genomic analysis identified 1,300 of 4,058 genes expressed in BAL cells from six TB patients before and after 1 month of therapy, including aerosolized IFN-gamma. However, only 15 genes were differentially regulated by IFN-gamma. We conclude that iNOS and IP-10 mRNA expression is increased in TB but that aerosol IFN-gamma treatment increases expression of few genes in the human lung.

Two sensor kinases contribute to the hypoxic response of Mycobacterium tuberculosis

Current estimates indicate that nearly a third of the world's population is latently infected with Mycobacterium tuberculosis. Reduced oxygen tension and nitric oxide exposure are two conditions encountered by bacilli in vivo that may promote latency. In vitro exposure to hypoxia or nitric oxide results in bacterial stasis with concomitant induction of a 47-gene regulon controlled by the transcription factor DosR. In this report we demonstrate that both the dosS gene adjacent to dosR and another gene, dosT (Rv2027c), encode sensor kinases, each of which can autophosphorylate at a conserved histidine and then transfer phosphate to an aspartate residue of DosR. Mutant bacteria lacking both sensors are unable to activate expression of DosR-regulated genes. These data indicate that DosR/DosS/DosT comprise a two-component signaling system that is required for the M. tuberculosis genetic response to hypoxia and nitric oxide, two conditions that produce reversible growth arrest in vitro and may contribute to latency in vivo.

The immunological aspects of latency in tuberculosis

A unique feature of Mycobacterium tuberculosis is its ability to exist in the granuloma of an asymptomatic host in a latent state that can subsequently reactivate to cause active disease. The latent state of infection poses a major obstacle to eradicating tuberculosis. In latent tuberculosis, the host immune response is capable of controlling the infection and yet falls short of eradicating the pathogen. That the host immune response contributes to the maintenance of latent tuberculous infection is supported by the observation that certain immunodeficient states, including those associated with the human immunodeficiency virus and tumor necrosis factor neutralization therapy, are associated with increased risks for developing reactivation disease. Latent tuberculosis is the product of a complex set of interactions between M. tuberculosis and the host immune response. The molecular basis for the persistence phenotype of M. Tuberculosis and the pertinent host immune mechanisms that contribute to the maintenance of tuberculous latency are just beginning to be understood. This review discusses the interactions between M. tuberculosis and the macrophage, the primary host cell that the tubercle bacillus parasitizes.

The secret lives of the pathogenic mycobacteria

Pathogenic mycobacteria, including the causative agents of tuberculosis and leprosy, are responsible for considerable morbidity and mortality worldwide. A hallmark of these pathogens is their tendency to establish chronic infections that produce similar pathologies in a variety of hosts. During infection, mycobacteria reside in macrophages and induce the formation of granulomas, organized immune complexes of differentiated macrophages, lymphocytes, and other cells. This review summarizes our understanding of Mycobacterium-host cell interactions, the bacterial-granuloma interface, and mechanisms of bacterial virulence and persistence. In addition, we highlight current controversies and unanswered questions in these areas.

Evidence for a cluster of genes on chromosome 17q11–q21 controlling susceptibility to tuberculosis and leprosy in Brazilians

The region of conserved synteny on mouse chromosome 11/human 17q11-q21 is known to carry a susceptibility gene(s) for intramacrophage pathogens. The region is rich in candidates including NOS2A, CCL2/MCP-1, CCL3/MIP-1alpha, CCL4/MIP-1beta, CCL5/RANTES, CCR7, STAT3 and STAT5A/5B. To examine the region in man, we studied 92 multicase tuberculosis (627 individuals) and 72 multicase leprosy (372 individuals) families from Brazil. Multipoint nonparametric analysis (ALLEGRO) using 16 microsatellites shows two peaks of linkage for leprosy at D17S250 (Z(lr) score 2.34; P=0.01) and D17S1795 (Z(lr) 2.67; P=0.004) and a single peak for tuberculosis at D17S250 (Z(lr) 2.04; P=0.02). Combined analysis shows significant linkage (peak Z(lr) 3.38) at D17S250, equivalent to an allele sharing LOD score 2.48 (P=0.0004). To determine whether one or multiple genes contribute, 49 informative single nucleotide polymorphisms were typed in candidate genes. Family-based allelic association testing that was robust to family clustering demonstrated significant associations with tuberculosis susceptibility at four loci separated by intervals (NOS2A-8.4 Mb-CCL18-32.3 kb-CCL4-6.04 Mb-STAT5B) up to several Mb. Stepwise conditional logistic regression analysis using a case/pseudo-control data set showed that the four genes contributed separate main effects, consistent with a cluster of susceptibility genes across 17q11.2.

Morphometric analysis of Th1 and Th2 cytokine expression in human pulmonary tuberculosis

SETTING

Following infection with Mycobacterium tuberculosis, host cytokine responses influence disease manifestation. Differences in cytokine expression likely determine whether tuberculosis (TB) progresses, resolves, or becomes latent. In particular, the balance between Th(1) and Th(2) cytokine responses influences the expression of disease in individuals with pulmonary TB.

OBJECTIVE AND DESIGN

Since the cytokine microenvironment in pulmonary TB remains suboptimally defined, we utilized quantitative immunohistochemistry to compare the expression of Th(1) cytokines [interferon-gamma (IFNgamma) and interleukin-12 (IL-12)] and Th(2) cytokines [IL-4, IL-10, transforming growth factor-beta (TGFbeta)] in surgically resected lungs of seven TB patients and four control subjects. We also quantified IFNgamma-inducible protein 10 (IP-10) expression, a CXC chemokine for macrophages and T cells.

RESULTS

Morphometric analyses revealed increased IFNgamma, IL-12, IP-10, and TGFbeta in granulomas and in pneumonitis areas of TB lungs. In contrast, IL-10 and IL-4 expressions were globally reduced in TB lung tissues compared to controls.

CONCLUSION

Th(1) cytokines and TGFbeta are increased while Th(2) cytokines are decreased in well-formed pulmonary granulomas of TB patients compared to controls.

Nitric oxide regulation of L-arginine uptake in murine and human macrophages

L-arginine uptake systems in macrophages play a role in regulating nitric oxide synthesis via the inducible L-arginine nitric oxide pathway. This paper describes the association of L-arginine transport with nitric oxide production in human peripheral blood monocyte-derived macrophages and in peritoneal macrophages from control and inducible nitric oxide synthase knock out C57BL6 mice. Experiments performed with human macrophages suggested that little or no nitric oxide was produced in human macrophages in vitro and that human macrophages exhibit a different arginine transport-specific response to stimuli compared with rodent macrophages. We conclude that increased L-arginine transport in both human and murine macrophages is dependent on the requirement for intracellular nitric oxide.

Reactivation of latent tuberculosis infection in TNF-deficient mice

TNF-deficient mice are highly susceptible to Mycobacterium tuberculosis H37Rv infection. Here we asked whether TNF is required for postinfectious immunity in aerosol-infected mice. Chemotherapy for 4 wk commencing 2 wk postinfection reduced CFU to undetectable levels. While wild-type mice had a slight rise in CFU, but controlled infection upon cessation of chemotherapy, TNF-deficient mice developed reactivation of infection with high bacterial loads in lungs, spleen, and liver, which was fatal within 13-18 wk. The increased susceptibility of TNF-deficient mice was accompanied by diminished recruitment and activation of T cells and macrophages into the lung, with defective granuloma formation and reduced inducible NO synthase expression. Reduced chemokine production in the lung might explain suboptimal recruitment and activation of T cells and uncontrolled infection. Therefore, despite a massive reduction of the mycobacterial load by chemotherapy, TNF-deficient mice were unable to compensate and mount a protective immune response. In conclusion, endogenous TNF is critical to maintain latent tuberculosis infection, and in its absence no specific immunity is generated.

Inhibition of respiration by nitric oxide induces a Mycobacterium tuberculosis dormancy program

An estimated two billion persons are latently infected with Mycobacterium tuberculosis. The host factors that initiate and maintain this latent state and the mechanisms by which M. tuberculosis survives within latent lesions are compelling but unanswered questions. One such host factor may be nitric oxide (NO), a product of activated macrophages that exhibits antimycobacterial properties. Evidence for the possible significance of NO comes from murine models of tuberculosis showing progressive infection in animals unable to produce the inducible isoform of NO synthase and in animals treated with a NO synthase inhibitor. Here, we show that O2 and low, nontoxic concentrations of NO competitively modulate the expression of a 48-gene regulon, which is expressed in vivo and prepares bacilli for survival during long periods of in vitro dormancy. NO was found to reversibly inhibit aerobic respiration and growth. A heme-containing enzyme, possibly the terminal oxidase in the respiratory pathway, likely senses and integrates NO and O2 levels and signals the regulon. These data lead to a model postulating that, within granulomas, inhibition of respiration by NO production and O2 limitation constrains M. tuberculosis replication rates in persons with latent tuberculosis.

The effects of reactive nitrogen intermediates on gene expression in Mycobacterium tuberculosis

Nitric oxide (NO) and related reactive nitrogen intermediates (RNI) are effective antimycobacterial agents and signal-transducing molecules. The present study uses microarray analysis to examine the effects of RNI on Mycobacterium tuberculosis gene expression. A common set of 53 genes was regulated by two chemically distinct nitric oxide donors. For a subset of the RNI-inducible genes, evidence exists suggesting that they may play a role in promoting survival of the tubercle bacillus in the host. Results obtained from studies based on a murine experimental tuberculosis model involving nos2-deficient mice suggest that RNI could regulate M. tuberculosis gene expression in vivo. Finally, there is a remarkable overlap between the RNI-inducible regulon and that previously reported to be regulated by hypoxia; and both reactive nitrogen species and anaerobicity upregulate the expression of one and the same putative two-component regulatory response system. Together, the results of this study provide evidence suggesting that (i) RNI play a role in regulating M. tuberculosis gene expression in vivo; (ii) the reactive nitrogen species upregulate genes that may be conducive to the survival of the tubercle bacillus in the infected host; and (iii) RNI and hypoxia may regulate mycobacterial gene expression via overlapping signal transduction pathways.

Latent tuberculosis: mechanisms of host and bacillus that contribute to persistent infection

Most people infected with Mycobacterium tuberculosis contain the initial infection and develop latent tuberculosis. This state is characterised by evidence of an immune response against the bacterium (a positive tuberculin skin test) but no signs of active infection. It can be maintained for the lifetime of the infected person. However, reactivation of latent infection occurs in about 10% of infected individuals, leading to active and contagious tuberculosis. An estimated 2 billion people worldwide are infected with M tuberculosis--an enormous reservoir of potential tuberculosis cases. The establishment and reactivation of latent infection depend on several factors, related to both host and bacterium. Elucidation of the host immune mechanisms that control the initial infection and prevent reactivation has begun. The bacillus is well adapted to the human host and has a range of evasion mechanisms that contribute to its ability to avoid elimination by the immune system and establish a persistent infection. We discuss here current understanding of both host and bacterial factors that contribute to latent and reactivation tuberculosis.

Immune evasion by Mycobacterium tuberculosis: living with the enemy

Mycobacterium tuberculosis is successful as a pathogen because of its ability to persist in an immunocompetent host. This bacterium lives within the macrophage, a cell whose function is the elimination of microbes. Recent advances have improved our understanding of how M. tuberculosis evades two major antimicrobial mechanisms of macrophages: phagolysosome fusion and the production of toxic reactive nitrogen intermediates. M. tuberculosis also modulates antigen presentation to prevent the detection of infected macrophages by CD4(+) T cells.