Interferon-gamma-treated murine macrophages inhibit growth of tubercle bacilli via the generation of reactive nitrogen intermediates

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.

The monocyte locomotion inhibitory factor produced by Entamoeba histolytica inhibits induced nitric oxide production in human leukocytes

The monocyte locomotion inhibitory factor, an anti-inflammatory pentapeptide produced by Entamoeba histolytica, inhibits the in vitro production of nitric oxide induced by cytokines (INF-gamma, TNF-alpha) or PMA in human leukocytes. This can be added to the other previously reported functional effects of this factor, such as the inhibition of monocyte locomotion and the synthesis of reactive oxygen intermediates in both monocytes and neutrophils. The decreased nitric oxide production may interfere with the killing of amebas by neutrophils in the early invasive stages of amebiasis, when oxidative mechanisms are used [reactive oxygen and nitrogen intermediates either individually or synergistically via peroxynitrite (ONOO(-))], and in the advanced stages, when both non-oxidative and oxidative (including nitric oxide) mechanisms are employed by macrophages. Diminished nitric oxide production by leukocytes may also contribute to the paucity of late inflammatory components in amebic abscess of the liver and other amebic lesions.

Mycobacterium bovis AN5 antigens vary in their ability to induce nitric oxide production in blood monocytes of experimentally infected cattle

Reactive nitrogen intermediates (RNI) are the principal effector molecules of activated monocyte/macrophage populations, responsible for killing and inhibiting the growth of virulent mycobacteria. In vitro nitrite production by blood monocytes of cattle inoculated with live Mycobacterium bovis AN5 was assessed from 0 day through 45 weeks post inoculation (PI). High in vitro nitrite production was observed at the 8th and 12th weeks PI in sensitized cattle but reactivity had fallen by the 20th week PI. To assess the in vitro nitrite producing ability of monocytes induced by individual polypeptides within culture filtrate antigens (CFA) of M. bovis AN5, cellular blotting was performed using peripheral blood mononuclear cells (PBMC) at the 12th week PI. It was observed that polypeptides of MW 70, 65, 60, 25, 24 and 22 kDa of CFA induced high nitrite production by blood monocytes while many polypeptides had little or no effect.

High plasma osteopontin level and its relationship with interleukin-12-mediated type 1 T helper cell response in tuberculosis

Osteopontin (OPN, also known as Eta-1), a noncollagenous matrix protein produced by macrophages and T lymphocytes, is expressed in granulomatous lesions caused by Mycobacterium tuberculosis infection. In the present study, we compared plasma concentrations of OPN in patients with active pulmonary tuberculosis with those of healthy control subjects and patients with sarcoidosis, another disease associated with granuloma formation. Plasma OPN levels were significantly higher in patients with tuberculosis (n = 48) than in control subjects (n = 34) and patients with sarcoidosis (n = 20). OPN levels correlated well with severity of pulmonary tuberculosis, as indicated by the size of lung lesions on chest X-ray films. Furthermore, chemotherapy resulted in a significant fall in plasma OPN levels. In patients with tuberculosis, plasma OPN concentrations correlated significantly with those of interleukin (IL)-12. In vitro experiments showed that OPN production by peripheral blood mononuclear cells infected with Mycobacterium bovis bacillus Calmette-Guérin preceded the synthesis of IL-12 and interferon-gamma and that the neutralizing anti-OPN monoclonal antibody significantly reduced the production of IL-12 and interferon-gamma. Our results suggest that OPN may be involved in the pathologic process associated with active pulmonary tuberculosis by inducing IL-12-mediated type 1 T helper cell responses.

Bacterial kidney disease as a model for studies of cell mediated immunity in rainbow trout (Oncorhynchus mykiss)

A cell mediated immune (CMI) response was measured in vitro to heat-killed and to paraformaldehyde fixed Renibacterium salmoninarum (Rs) in rainbow trout (Oncorhynchus mykiss) experimentally challenged with live Rs. The mitogenic response to the T lymphocyte mitogen Concanavalin A (Con A) was reduced during samplings 4 to 6 weeks after immersion, but no effect of the response to the B lymphocyte mitogen lipopolysaccharide (LPS) was detected. The subpopulation of lymphocytes, detected by the monoclonal antibody 1C2, was decreased from the 4th week to the 5th week of infection, and remained at the decreased level up to 10 weeks post immersion. The proportion of Immunoglobulin (Ig) bearing lymphocytes was not affected during the Rs infection period. The humoral antibody level to heat-stable Rs-antigens was increased up to 10 weeks after immersion but after 27 weeks was reduced to a level similar to that of the non-challenged fish. An anamnestic response was demonstrated in challenged fish, as intraperitoneal injection of heat-treated Rs bacteria into Rs challenged fish elicited a stronger humoral antibody response compared with injection into non-challenged fish.

Surfactant protein A decreases nitric oxide production by macrophages in a tumor necrosis factor-alpha-dependent mechanism

Surfactant protein A (SP-A) modulates the lung defense system through regulation of cytokines and nitric oxide (NO) production by alveolar macrophages (AMs). Whether SP-A upregulates or downregulates production of proinflammatory cytokines and NO is controversial. This study demonstrates the molecular mechanism(s) by which SP-A suppresses NO production by activated murine AMs. NO production by interferon-gamma (IFN-gamma) and IFN-gamma plus Mycobacterium avium-stimulated AMs was mediated through tumor necrosis factor-alpha (TNF-alpha) production, as addition of neutralizing anti-TNF-alpha antibodies during AMs stimulation resulted in reduced NO production. SP-A suppressed NO production by activated AMs by inhibiting TNF-alpha production. The maximum inhibitory effect of SP-A on NO production was observed at 20 microg/ml of SP-A concentration. Furthermore, SP-A inhibited activation of nuclear factor-kappa B, a transcription factor required for induction of TNF-alpha and inducible NO synthase genes. These findings suggest that SP-A suppresses NO production by activated AMs by inhibiting TNF-alpha secretion and nuclear factor-kappa B activation. This study also highlights the importance of SP-A levels in the lung, as changes in SP-A levels may modulate the local lung defense system.

Multiple roles of nitric oxide in the airways

Nitric oxide is endogenously released in the airways by nitric oxide synthase. Functionally, two isoforms of this enzyme exist: constitutive and inducible. The former seems to protect airways from excessive bronchoconstriction while the latter has a modulatory role in inflammatory disorders of the airways such as asthma. This review explores the physiological and pathophysiological role of endogenous nitric oxide in the airways, and the clinical aspects of monitoring nitric oxide in exhaled air of patients with respiratory disease.

Virulent Mycobacterium fortuitum restricts NO production by a gamma interferon-activated J774 cell line and phagosome-lysosome fusion

The virulence of different isolates of Mycobacterium has been associated with two morphologically distinguishable colonial variants: opaque (SmOp) and transparent (SmTr). In this report we used an in vitro assay to compare macrophage (Mphi) responses to SmOp and SmTr Mycobacterium fortuitum variants, taking advantage of the fact that these variants were derived from the same isolate. Cells preactivated or not with gamma interferon (IFN-gamma) were infected with SmOp or SmTr M. fortuitum. We showed that SmOp and SmTr induced different levels of nitric oxide (NO) production by IFN-gamma-stimulated Mphi. Indeed, the amount of IFN-gamma-induced NO production by J774 cells was 4.8 to 9.0 times higher by SmOp (23.1 to 37.7 micro M) compared to SmTr infection (3.9 to 4.8 micro M) (P = 0.0332), indicating that virulent SmTr bacilli restricted NO production. In addition, IFN-gamma-induced NO production by Mphi was higher when correlated with reduction of only avirulent SmOp bacillus viability. SNAP (S-nitroso-N-acetyl-DL-penicillamine)-induced NO production did not modify SmTr viability, indicating its resistance to nitrogen radicals. Electron microscopy studies were performed to evaluate the capacity of phagosomes to fuse with lysosomes labeled with bovine serum albumin-colloidal gold particles. By 24 h postinfection, 69% more phagosome-containing SmOp variant had fused with lysosomes compared to the SmTr-induced phagosomes. In conclusion, these data indicate that virulent SmTr bacilli may escape host defense by restricting IFN-gamma-induced NO production, resisting nitrogen toxic radicals, and limiting phagosome fusion with lysosomes.

Prolonging organ allograft survival: potential role of nitric oxide scavengers

A growing number of studies suggest a key role of nitric oxide (NO) derived from the inducible NO synthase (iNOS) isoform as a signalling molecule leading to acute organ transplant rejection. Current theory suggests that NO targets certain tissue proteins for nitrosylation or nitration leading to inhibition of enzyme/protein function and to cell death via apoptosis. Gene expression of iNOS and formation of nitrotyrosine residues have been confirmed in biopsies of rejecting grafts in humans. Experimental attempts to delay graft rejection by treatment with iNOS enzyme inhibitors have yielded conflicting results. An alternative strategy to alter rejection mediated by NO is to scavenge and/or neutralise the actions of excess NO, thereby by-passing the inhibition of iNOS enzyme activity. This review summarises recent laboratory evidence that new experimental NO scavengers/neutralisers have potential value to prolong graft survival. To date, various metal-based NO scavenging/neutralising compounds have been shown to enhance cardiac allograft survival in the absence of immunosuppression. When used in combination with low-dose cyclosporin, these agents produce a synergistic action to enhance graft survival or even to produce "permanent graft survival" under certain prolonged drug regimens. A portion of this benefit may be accounted for by the property of some of these compounds to display immunosuppressant and anti-inflammatory activity in vivo. These properties are based on findings including the following: (i) attenuating cell infiltration into the graft; (ii) attenuating activation of NFkappaB (a transcription factor important for upregulation of various inflammatory genes); (iii) attenuating cyclin D3 gene expression (a marker of cell proliferation; (iv) antagonising autoimmune activation (as determined by attenuated cytokine gene expression in splenocytes isolated from treated animals but stimulated for several days ex vivo in mixed lymphocyte cultures).

Tumor necrosis factor alpha stimulates killing of Mycobacterium tuberculosis by human neutrophils

The ability of human neutrophils to aid in defense against pulmonary infection with Mycobacterium tuberculosis is controversial. In this study, we have shown that neutrophils respond to and phagocytose M. tuberculosis in human lesions. Neutrophils from healthy individuals were able to kill significant fractions of an inoculum of M. tuberculosis within 1 h of phagocytosis, and this ability was enhanced by tumor necrosis factor alpha but not by gamma interferon. The mycobactericidal mechanism was nonoxidative, as inhibitors of reactive oxygen or reactive nitrogen intermediates did not interfere with killing. However, the mycobactericidal mechanism was associated with increased exposure of intracellular M. tuberculosis to neutrophil defensins. In vitro, human neutrophil peptides 1 to 3 were not able to kill the bacilli even at much higher levels. These studies support the concept that human neutrophils are directly involved in defense against infection with M. tuberculosis.

CancerB increases production of nitric oxide and tumor necrosis factor-alpha in peritoneal macrophages

BACKGROUND

CancerB (CCB, IMSF-5), herbal combination, may be able to stimulate potential toxic mediators such as nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) in isolated mouse peritoneal macrophages.

METHODS

NO production was determined by Griess method, and TNF-alpha production by enzyme-linked immunosorbent assay. Amounts of proteins were observed by Western blotting.

RESULTS

CCB had no effect on NO production by itself, but CCB alone did stimulate the production of TNF-alpha. When CCB was used in combination with recombinant interferon-gamma (rIFN-gamma), there was a marked cooperative induction of NO production, TNF-alpha production and NF-kappa B activation. The increase in NO synthesis was reflected as an increased amount of inducible NO synthase protein. The increased production of NO from rIFN-gamma plus CCB-stimulated peritoneal macrophages was decreased by the treatment with N(G)-monomethyl-L-arginine or N(alpha)-Tosyl-Phe Chloromethyl Ketone. Nuclear factor-kappa B (NF-kappa B) inhibitor, pyrrolidine dithiocarbamate was able to completely inhibit the production of NO and TNF-alpha.

CONCLUSIONS

These findings demonstrate that CCB increases the production of NO and TNF-alpha by rIFN-gamma-primed peritoneal macrophages and suggest that NF-kappa B plays a critical role in mediating these effects of CCB.

Mycobacterium tuberculosis CDC1551 is resistant to reactive nitrogen and oxygen intermediates in vitro

Resistance to reactive oxygen intermediates and reactive nitrogen intermediates in vitro of a clinical isolate of Mycobacterium tuberculosis (CDC1551) that caused a large outbreak of tuberculosis was compared to that of M. tuberculosis strains CB3.3, H37Rv, H37Ra, Erdman, RJ2E, C.C. 13, and C.C. 22 as well as M. bovis strains Ravenel and BCG. CDC1551 and CB3.3 were significantly more resistant to both hydrogen peroxide (H(2)O(2)) and acidified sodium nitrite than were the other strains tested. This biological phenotype may serve as an in vitro marker for clinical strains of M. tuberculosis likely to cause a large outbreak of tuberculosis.

Production of antibodies against glycolipids from the Mycobacterium tuberculosis cell wall in aerosol murine models of tuberculosis

Evolution of antibodies against glycolipids from the Mycobacterium tuberculosis cell wall has been studied for the first time in experimental murine models of tuberculosis induced by aerosol, in which infection, reinfection, reactivation, prophylaxis and treatment with antibiotics have been assayed. Results show a significant humoral response against these antigens, where diacyltrehaloses (DAT) and sulpholipid I (SL-I) elicited higher antibody levels than protein antigens like antigen 85 protein complex (Ag85), culture filtrate proteins (CFP) and purified protein derivative (PPD). Only immunoglobulin M (IgM) antibodies have been detected against DAT and SL-I. Their evolution has a positive correlation with bacillary concentration in tissues.

Transmembrane TNF induces an efficient cell-mediated immunity and resistance to Mycobacterium bovis bacillus Calmette-Guérin infection in the absence of secreted TNF and lymphotoxin-alpha

The contribution of a transmembrane (Tm) form of TNF to protective immunity against Mycobacterium bovis bacillus Calmette-Guérin (BCG) was studied in transgenic (tg) mice expressing a noncleavable Tm TNF but lacking the TNF/lymphotoxin-alpha (LT-alpha) locus (Tm TNF tg mice). These mice were as resistant to BCG infection as wild-type mice, whereas TNF/LT-alpha(-/-), TNF(-/-), and LT-alpha(-/-) mice succumbed. Tm TNF tg mice developed granulomas of smaller size but at 2- to 4-fold increased frequencies compared with wild-type mice. Granulomas were mainly formed by monocytes and activated macrophages expressing Tm TNF mRNA and accumulating acid phosphatase. NO synthase 2 activation as a key macrophage bactericidal mechanism was low during the acute phase of infection in Tm TNF tg mice but was still sufficient to limit bacterial growth and increased in late infection. While infection with virulent Mycobacterium tuberculosis resulted in very rapid death of TNF/LT-alpha(-/-) mice, it also resulted in survival of Tm TNF tg mice which presented an increase in the number of CFU in spleen (5-fold) and lungs (10-fold) as compared with bacterial load of wild-type mice. In conclusion, the Tm form of TNF induces an efficient cell-mediated immunity and total resistance against BCG even in the absence of LT-alpha and secreted TNF. However, Tm TNF-mediated protection against virulent M. tuberculosis infection can also be efficient but not as strong as in BCG infection, in which cognate cellular interactions may play a more predominant role in providing long-term surveillance and containment of BCG-infected macrophages.

Reduced NK activity in pulmonary tuberculosis patients with/without HIV infection: identifying the defective stage and studying the effect of interleukins on NK activity

SETTING

A study was undertaken to understand the non-major histocompatibility restricted cytotoxicity in order to delineate the role of natural killer (NK) cells towards the development of host immunity to tuberculosis.

OBJECTIVE

(a) Enumeration of NK cell numbers and activity in normal individuals (35), pulmonary tuberculosis patients (32), HIV-infected TB patients (20) and patient contacts (10), (b) effect of treatment on NK status, (c) enumeration of effector-target conjugates and (d) effect of in vitro cytokine stimulation on NK activity.

DESIGN

NK cells were enumerated by flow cytometry. NK activity was assessed by chromium release assay before and after treatment for tuberculosis and after stimulation with IL-2/IL-12. Novel flow cytometric method was standardized to enumerate effector-target conjugates.

RESULTS

No changes were seen between different groups as far as number of NK cells and relative proportions of different conjugate types were concerned, but there was a decrease in NK activity in TB patients which increased after treatment. Augmentation of NK activity was observed after cytokine stimulation.

CONCLUSION

Lowered NK activity during tuberculosis infection is probably the 'effect' and not the 'cause' for the disease as demonstrated by the follow-up study. Similar number of conjugates in both groups indicates no defect in the recognition/binding step but probably at subsequent steps of the cytotoxic process. Augmentation of NK activity with cytokines implicates them as potential adjuncts to tuberculosis chemotherapy.

Fibronectin facilitates Mycobacterium tuberculosis attachment to murine alveolar macrophages

Mycobacterium tuberculosis remains a major cause of pulmonary infection worldwide. Attachment of M. tuberculosis organisms to alveolar macrophages (AMs) represents the earliest phase of primary infection in pulmonary tuberculosis. In this study fibronectin (Fn), an adhesive protein, is shown to bind M. tuberculosis organisms and facilitates attachment of M. tuberculosis to murine AMs. A monoclonal antibody (MAb) specific to the heparin binding domain (HBD) of Fn decreases (125)I-Fn binding to M. tuberculosis; whereas MAbs specific to either the cell binding domain (CBD) or the gelatin binding domain (GBD) have no effect on Fn binding to M. tuberculosis. In the presence of exogenous Fn (10 microg/ml) M. tuberculosis attachment to AMs increased significantly from control levels (means +/- standard errors of the means) of 11.5% +/- 1.1% to 44.2% +/- 4.2% (P < 0.05). Fn-enhanced attachment was significantly decreased from 44.2% +/- 4.2% to 10.8% +/- 1.2% (P < 0.05) in the presence of anti-Fn polyclonal antibodies. The attachment is also inhibited in the presence of MAbs specific for the HBD and CBD, whereas MAbs specific to GBD did not affect the attachment. Further, an Fn cell binding peptide, Arg-Gly-Asp-Ser (RGDS), decreased the attachment from 44.2% +/- 4.2% to 15.3% +/- 1.2% (P < 0.05), whereas addition of a control peptide, Arg-Gly-Glu-Ser (RGES) did not affect the attachment (40.5% +/- 1.8%). These results suggest that Fn-mediated attachment of M. tuberculosis can occur through the binding of Fn to the AM via the CBD and to M. tuberculosis organisms via the HBD.

A ruthenium (III) polyaminocarboxylate complex, a novel nitric oxide scavenger, enhances graft survival and decreases nitrosylated heme protein in models of acute and delayed cardiac transplant rejection

Nitric oxide (NO) derived from the up-regulation of inducible NO synthase (iNOS) is believed to play an important role in organ rejection. In experimental models of acute cardiac transplant rejection (i.e., without immunosuppression), treatment using NOS inhibitors to prevent acute rejection have yielded conflicting results. This is most likely due to potential inhibition of constitutive NOS. Accordingly, agents that trap NO directly may have some advantage. In the current study, we evaluated the actions of a ruthenium-based NO scavenger, AMD6221, to inhibit the nitrosylation of myocardial protein and to prolong cardiac allograft survival in a model of acute cardiac transplant rejection (without immunosuppression). In addition, we evaluated the efficacy of AMD6221 used in combination with low-dose cyclosporine (CsA) (i.e., a model of delayed graft rejection). Heterotopic abdominal cardiac transplantation was performed using rat strains with disparities at major and minor histocompatibility loci. Grafts were harvested on postoperative day 6 for histologic examination or analysis of myocardial protein nitrosylation using electron paramagnetic resonance (EPR) spectroscopy. Other animals were monitored twice daily to determine rejection times. Plasma was also taken at postoperative day 6 for determining the concentration of NO by-products (nitrate plus nitrite). Treatment with AMD6221 either prolonged graft survival and/or caused a marked decrease in myocardial nitrosylprotein formation as determined by EPR spectroscopy. In vivo scavenging of NO by AMD6221 was verified by high-performance liquid chromatography analysis of nitrosylated-drug in plasma samples. Low-dose CsA given alone or in combination with AMD6221 completely blocked formation of myocardial nitrosylprotein complexes. Whereas low-dose CsA alone prolonged graft survival, combination therapy with CsA plus AMD6221 produced a synergistic effect on graft survival. These studies indicate that treatment with a ruthenium-based NO scavenger, such as AMD6221, may be an effective regimen used alone or in combination with CsA to protect myocardial proteins from posttranscriptional modification and to prolong cardiac graft survival.

Reactive nitrogen and oxygen intermediates and bacterial defenses: unusual adaptations in Mycobacterium tuberculosis

The production of reactive oxygen and reactive nitrogen intermediates is an important host defense mechanism mediated in response to infection by bacterial pathogens. Not surprisingly, intracellular pathogens have evolved numerous defense strategies to protect themselves against the damaging effects of these agents. In enteric bacteria, exposure to oxidative or nitrosative stress induces expression of numerous pathways that allow the bacterium to resist the toxic effects of these compounds during growth in the host. In contrast, members of pathogenic mycobacterial species, including the frank human pathogens Mycobacterium tuberculosis and Mycobacterium leprae, are dysfunctional in aspects of the oxidative and nitrosative stress response, yet they remain able to establish and maintain productive acute and persistent infections in the host. This article reviews the current knowledge regarding reactive oxygen and nitrogen intermediates, and compares the adaptative mechanisms utilized by enteric organisms and mycobacterial species to resist the bactericidal and bacteriostatic effects resulting from exposure to these compounds.

Fish monocytes as a model for mycobacterial host-pathogen interactions

Mycobacterium marinum, a relatively rapid-growing fish and human pathogen, has become an important model for the investigation of mycobacterial pathogenesis. M. marinum is closely related to the Mycobacterium tuberculosis complex and causes a disease in fish and amphibians with pathology similar to tuberculosis. We have developed an in vitro model for the study of M. marinum virulence mechanisms using the carp monocytic cell line CLC (carp leukocyte culture). We found that fish monocytes can differentiate between pathogenic and nonpathogenic mycobacterial species. Interestingly, M. marinum enters fish monocytes at a 40- to 60-fold-higher rate than Mycobacterium smegmatis. In addition, M. marinum survives and replicates in fish monocytes while M. smegmatis is killed. We also found that M. marinum inhibits lysosomal fusion in fish monocytes, indicating that these cells may be used to dissect the mechanisms of intracellular trafficking in mycobacteria. We conclude from these observations that monocytic cells from fish, a natural host for M. marinum, provide an extremely valuable model for the identification and characterization of mycobacterial virulence determinants in the laboratory.

Modulation of Mycobacterium bovis-specific responses of bovine peripheral blood mononuclear cells by 1,25-dihydroxyvitamin D(3)

Historically, administration of vitamin D has been considered beneficial in the treatment of tuberculosis. The interaction of this vitamin [i.e., 1,25-dihdroxyvitamin D(3) [1,25(OH)(2)D(3)]] with the antitubercular immune response, however, is not clear. In the present study, in vitro recall responses of peripheral blood mononuclear cells (PBMC) from cattle infected with Mycobacterium bovis were used to study the immune-modulatory effects of 1,25(OH)(2)D(3) on M. bovis-specific responses in vitro. Addition of 1 or 10 nM 1,25(OH)(2)D(3) inhibited M. bovis-specific proliferative responses of PBMC from M. bovis-infected cattle, affecting predominantly the CD4(+) cell subset. In addition, 1,25(OH)(2)D(3) inhibited M. bovis-specific gamma interferon (IFN-gamma) production yet enhanced M. bovis-specific nitric oxide (NO) production. Lymphocyte apoptosis, measured by flow cytometry using annexin-V staining, was diminished by addition of 1,25(OH)(2)D(3) to PBMC cultures. These findings support the current hypothesis that 1,25(OH)(2)D(3) enhances mycobacterial killing by increasing NO production, a potent antimicrobial mechanism of activated macrophages, and suggest that 1,25(OH)(2)D(3) limits host damage by decreasing M. bovis-induced IFN-gamma production.

Immunostimulatory DNA from Paracoccidioides brasiliensis acts as T-helper 1 promoter in susceptible mice

Th1 immune responses afford protection against some pathogens like the fungus P. brasiliensis (P.b.), etiological agent of Paracoccidioidomycosis (PCM). It is well known that nonmethylated CpG sequences from bacterial DNA have immunomodulatory properties and can be used as a Th1-promoting adjuvant. By analyzing the available gene sequences of P.b. we observed a high number of unmethylated CpG dinucleotides. In a murine model of the PCM infection, the isogenic mouse strain known to be susceptible presents a predominant Th2 pattern. In order to access the possibility of the genomic DNA to act as a Th1-promoting adjuvant, in vitro assays were made and indicated a significant increase in phagocytosis when the macrophages were stimulated with DNA from P.b. and in vivo assays of a decreased production of antibodies antigp43, the main antigen of the PCM system. The analysis of the antibody isotypes and the cytokine production suggested a Th1 modulation in the susceptible animals. Thus, when mice were infected with fungus plus synthetic oligodeoxynucleotide (ODN), made from the available sequence of gp43, a decrease in the fungus dissemination was observed. Results herein described suggest that genomic DNA from P.b. could have a immunostimulatory function as a Th-1-promoting adjuvant in susceptible mice.

Induction of iNOS in human monocytes infected with different Legionella species

The contribution of nitric oxide (NO) radicals to the suppression of intracellular replication of Legionella has been well established in rodents but remained questionable in humans. Considering the fact that human monocytes do not exhibit a high-output NO production, we used sensitive methods such as detection of inducible NO synthase (iNOS) mRNA by reverse transcription-PCR and demonstration of iNOS protein expression by means of flow cytometry and Western blot to compare the levels of iNOS induced by Legionella species which, in accordance to their human prevalence, show different multiplication rates within human monocytic cells. The expression of iNOS in Mono Mac 6 (MM6) cells showed an only moderate inverse correlation to the intracellular replication rate of a given Legionella species in the protein expression assays. However, stimulation of host cells with 1,25-dihydroxyvitamin D(3) to enhance NO production and inhibition of NO production by treatment of host cells with N(G)-methyl-L-arginine were not able to modify the intracellular multiplication of legionellae within MM6 cells. Therefore, NO production does not seem to play a crucial role for the restriction of intracellular replication of Legionella bacteria within human monocytic cells. Rodent models in investigations which are supposed to clarify the involvement of NO radicals in defense mechanisms against Legionella infections in humans are of doubtful significance.

Oestrus ovis (Diptera: Oestridae): effects of larval excretory/secretory products on nitric oxide production by murine RAW 264.7 macrophages

Larvae of Oestrus ovis (Insecta: Diptera: Oestridae) are common parasites of nasal and sinus cavities of sheep and goats. Previous studies revealed that crude extracts of larvae modify NO synthesis by ovine monocyte derived macrophages. The aim of this study was to investigate the larval excretory/secretory products effects on nitric oxide production by murine tumour macrophages RAW 264.7. Stimulation of RAW macrophages by excretory/secretory products of the three instars larvae (25 microg/ml) significantly increased nitrite concentrations in culture supernatants compared to negative and positive Escherichia coli lipopolysaccharide control. This effect was time and dose dependent. Nitrite production in culture supernatants was due to induction of isoform NOS-2 because both NG monomethyl L-arginine (100 microM) and dexamethasone (20 microM) inhibited, by 60 and 50%, respectively, nitrite accumulation in culture supernatants. First steps of purification, by ion exchange chromatography, indicated that one protein of 29 kDa was able to induce NO synthesis by macrophages. Further studies are needed for a better characterization of these molecule and to investigate their immunogenicity for a vaccine approach.

Deletion of the putative antioxidant noxR1 does not alter the virulence of Mycobacterium tuberculosis H37Rv

SETTING

The cloned M. tuberculosis noxR1 gene has been shown to confer resistance to reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) upon Escherichia coli and Mycobacterium smegmatis.

OBJECTIVE

To investigate the role of noxR1 in resistance to RNI and virulence of M. tuberculosis.

DESIGN

The noxR1 gene was deleted from M. bovis BCG and M. tuberculosis H37Rv by allelic exchange. The mutants were compared to wild type strains with respect to resistance to chemically generated RNI. The virulence of the M. tuberculosis mutant was investigated in a murine model of infection.

RESULTS

The NoxR1 mutants grew normally in Sautons and 7H9 broths. The BCG mutant demonstrated decreased resistance to in vitro generated RNI compared to the wild type. Resistance to RNI could be restored to the mutant by reintroduction of the noxR1 locus on a replicating plasmid. However, deletion of noxR1 from M. tuberculosis H37Rv did not result in decreased resistance to RNI nor a difference in growth and survival of the bacterium during murine infection.

CONCLUSION

The noxR1 gene locus in M. bovis BCG bestows ability to resist RNI generated in vitro. In M. tuberculosis H37Rv, however, noxR1 is either not involved in RNI resistance and virulence or is better compensated for by other mechanisms.

Fate of Mycobacterium tuberculosis within murine dendritic cells

The interaction of microbes with dendritic cells (DCs) is likely to have an enormous impact on the initiation of the immune response against a pathogen. In this study, we compared the interaction of Mycobacterium tuberculosis with murine bone marrow-derived DCs and macrophages (M phi) in vitro. M. tuberculosis grew equally well within nonactivated DCs and M phi. Activation of DCs and M phi with gamma interferon and lipopolysaccharide inhibited the growth of the intracellular bacteria in a nitric oxide synthase-dependent fashion. However, while this activation enabled M phi to kill the intracellular bacteria, the M. tuberculosis bacilli within activated DCs were not killed. Thus, DCs could restrict the growth of the intracellular mycobacteria but were less efficient than M phi at eliminating the infection. These results may have implications for priming immune responses to M. tuberculosis. In addition, they suggest that DCs may serve as a reservoir for M. tuberculosis in tissues, including the lymph nodes and lungs.

Interferon-gamma and interleukin-12 pathway defects and human disease

A genetic component to human mycobacterial disease susceptibility has long been postulated. Over the past five years, mutations in the interferon-gamma (IFNgamma) receptor, IL-12 receptor beta1 (IL-12Rbeta1), and IL-12 p40 genes have been recognized. These mutations are associated with heightened susceptibility to disease caused by intracellular pathogens including nontuberculous mycobacteria, vaccine-associated bacille Calmette Guerin (BCG), Salmonella species, and some viruses. We describe the genotype-phenotype correlations in IFNgamma receptor, IL-12Rbeta1, and IL-12 p40 deficiency, and discuss how study of these diseases has enhanced knowledge of human host defense against mycobacteria and other intracellular pathogens.

Modulation of polymorphonuclear leukocytes function by nitric oxide

Recognition of the endothelium-derived relaxation factor as nitric oxide (NO) gave rise to an impression that NO was synthesised only by the endothelial lining of the vessel wall. Later it was found that NO is synthesized constitutively by the enzyme nitric oxide synthase (NOS) in various cells. However, inflammatory cytokines can induce NOS (known as inducible NOS [iNOS]) activity in all the somatic cells. Blood cells, such as eosinophils, platelets, neutrophils, monocytes, and macrophages, also synthesize NO. Among them, polymorphonuclear leukocytes (PMNs) constitute an important proportion and are also the major participants in a number of pathological conditions with suggestive involvement of NO. PMNs can synthesize NO at rates similar to endothelial cells, thus suggesting the importance of PMN-derived NO in various physiological and pathological conditions. Most of the studies so far focus on the peripheral PMNs, while studies on PMNs after emigration are limited, thus warranting systematic studies on PMNs from both sources. The role of the endothelial NOS (eNOS) and functions of NO derived from the endothelial cells has been studied extensively. However, understanding of the PMNs NOS and its regulatory role in their function is unraveling. The present review summarizes the modulatory role of NO on PMNs functions and points out the discrepancies relating to presence of NOS in PMNs. This information will be helpful in understanding the importance of NO in physiological and pathological conditions associated with PMNs.

Nitric oxide synthesis enhances human immunodeficiency virus replication in primary human macrophages

Macrophages are suspected to play a major role in human immunodeficiency virus (HIV) infection pathogenesis, not only by their contribution to virus dissemination and persistence in the host but also through the dysregulation of immune functions. The production of NO, a highly reactive free radical, is thought to act as an important component of the host immune response in several viral infections. The aim of this study was to evaluate the effects of HIV type 1 (HIV-1) Ba-L replication on inducible nitric oxide synthase (iNOS) mRNA expression in primary cultures of human monocyte-derived macrophages (MDM) and then examine the effects of NO production on the level of HIV-1 replication. Significant induction of the iNOS gene was observed in cultured MDM concomitantly with the peak of virus replication. However, this induction was not accompanied by a measurable production of NO, suggesting a weak synthesis of NO. Surprisingly, exposure to low concentrations of a NO-generating compound (sodium nitroprusside) and L-arginine, the natural substrate of iNOS, results in a significant increase in HIV replication. Accordingly, reduction of L-arginine bioavailability after addition of arginase to the medium significantly reduced HIV replication. The specific involvement of NO was further demonstrated by a dose-dependent inhibition of viral replication that was observed in infected macrophages exposed to N(G)-monomethyl L-arginine and N(G)-nitro-L-arginine methyl ester (L-NAME), two inhibitors of the iNOS. Moreover, an excess of L-arginine reversed the addition of L-NAME, confirming that an arginine-dependent mechanism is involved. Finally, inhibitory effects of hemoglobin which can trap free NO in culture supernatants and in biological fluids in vivo confirmed that endogenously produced NO could interfere with HIV replication in human macrophages.

Role of inducible nitric oxide synthase in resistance to Mycobacterium leprae in mice

The manifestation of leprosy in humans is largely determined by host immunity to Mycobacterium leprae and is a model for immunoregulation in a human disease. However, animal models available for exploration of the leprosy spectrum are inadequate. This study explored M. leprae infection in mice deficient in inducible nitric oxide synthase, and this report describes elements resembling borderline tuberculoid leprosy in humans.

Aerosol infection of mice with recombinant BCG secreting murine IFN-gamma partially reconstitutes local protective immunity

To better understand the contribution of interferon-gamma (IFN-gamma) to the immune response during the first 60 days of mycobacterial infection in the lungs, IFN-gamma gene disrupted (IFN-gamma-/-) mice were infected via aerosol with recombinant Mycobacterium bovis Bacillus Calmette-Guerin (BCG) secreting murine IFN-gamma (BCG-IFN-gamma) and compared to mice infected with recombinant BCG containing the vector only (BCG-vector). When IFN-gamma-/- mice were infected with BCG-vector, increasing bacillary loads and large undifferentiated granulomas that did not express inducible nitric oxide synthase (iNOS) were observed in the lungs. In contrast, infection with BCG-IFN-gamma resulted in reduced bacillary load and better differentiated granulomas containing epithelioid macrophages expressing iNOS as well as reduced levels of interleukin 10 (IL-10) mRNA. However, local production of IFN-gamma by the recombinant BCG did not protect IFN-gamma-/- mice from subsequent challenge with M. tuberculosis. Infection of IFN-gamma-/- peritoneal macrophages in vitro with BCG-IFN-gamma led to induction of iNOS expression and lower IL-10 mRNA levels. Nevertheless, the growth of the intracellular BCG was unaffected. Since IFN-gamma induced-iNOS protein and reduced IL-10 production were insufficient to control mycobacterial growth in vitro, the results suggest that additional mediator(s) present in vivo are required for control of mycobacterial growth.

Surfactant protein A enhances mycobacterial killing by rat macrophages through a nitric oxide-dependent pathway

Surfactant-associated protein A (SP-A) is involved in surfactant homeostasis and host defense in the lung. We have previously demonstrated that SP-A specifically binds to and enhances the ingestion of bacillus Calmette-Guerin (BCG) organisms by macrophages. In the current study, we investigated the effect of SP-A on the generation of inflammatory mediators induced by BCG and the subsequent fate of ingested BCG organisms. Rat macrophages were incubated with BCG in the presence and absence of SP-A. Noningested BCG organisms were removed, and the release of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide were measured at varying times. TNF-alpha and nitric oxide production induced by BCG were enhanced by SP-A. In addition, SP-A enhanced the BCG-induced increase in the level of inducible nitric oxide synthase protein. Addition of antibodies directed against SPR210, a specific macrophage SP-A receptor, inhibited the SP-A-enhanced mediator production. BCG in the absence of SP-A showed increased growth over a 5-day period, whereas inclusion of SP-A dramatically inhibited BCG growth. Inhibition of nitric oxide production blocked BCG killing in the presence and absence of SP-A. These results demonstrate that ingestion of SP-A-BCG complexes by rat macrophages leads to production of inflammatory mediators and increased mycobacterial killing.

Reactive oxygen and nitrogen intermediates in the relationship between mammalian hosts and microbial pathogens

This review summarizes recent evidence from knock-out mice on the role of reactive oxygen intermediates and reactive nitrogen intermediates (RNI) in mammalian immunity. Reflections on redundancy in immunity help explain an apparent paradox: the phagocyte oxidase and inducible nitric oxide synthase are each nonredundant, and yet also mutually redundant, in host defense. In combination, the contribution of these two enzymes appears to be greater than previously appreciated. The remainder of this review focuses on a relatively new field, the basis of microbial resistance to RNI. Experimental tuberculosis provides an important example of an extended, dynamic balance between host and pathogen in which RNI play a major role. In diseases such as tuberculosis, a molecular understanding of host-pathogen interactions requires characterization of the defenses used by microbes against RNI, analogous to our understanding of defenses against reactive oxygen intermediates. Genetic and biochemical approaches have identified candidates for RNI-resistance genes in Mycobacterium tuberculosis and other pathogens.

Cytokine profile and natural killer cell activity in Listeria monocytogenes infected mice treated orally with Petiveria alliacea extract

In this work, we investigated the effects of Petiveria alliacea extract on the production of Th1-type and Th2-type cytokines and on NK cells activity in normal and Listeria monocytogenes infected mice. Our results demonstrated that in normal/non-infected mice P. alliacea administration led to increased levels of Interleukin-2 (IL-2). The infection alone enhanced INF-gamma levels and NK cell activity at 48 and 72 hours of infection. The treatment with five consecutive doses of 1000 mg/kg/day of P. alliacea extract, given previously to infection, led to further increases in IL-2 levels, in relation to normal/non-infected/P. alliacea treated controls, and in INF-gamma levels at 72 h of infection, compared to infected mice. On the other hand, the production of IL-4 and IL-10 were not altered either by the infection or by the treatment with P. alliacea extract. NK cells activity increased at 48 h and 72 h following the inoculation of the bacteria. When mice were treated with P. alliacea previously to infection, NK activity was higher than that observed at 48 h, 72 h and 120 h of infection in the infected animal. Based on these findings we suggest that P. alliacea up-regulates anti-bacterial immune response by enhancing both Th1 function and the activity of NK cells.

A pre-existing infection by Mycobacterium avium subsp. avium modulates anti-Cryptococcus neoformans and anti-Candida albicans activities in human macrophages

Mycobacterium avium is a facultative intracellular microorganism, able to survive and multiply within mammalian macrophages by circumventing antimicrobial mechanisms. In this study we hypothesize that pre-existing M. avium infection could result in macrophage superinfections by other microorganisms. We found that 24 h after ingestion of M. avium at a low multiplicity of infection, macrophages are unable to efficiently produce superoxide anions when over-stimulated with phorbol esters, and that the generation of oxidative burst is only partially restored 72 h after bacteria ingestion. We also demonstrate that intracellular killing of Cryptococcus neoformans is markedly impaired in human macrophages that have previously ingested M. avium (but not other bacteria such as Escherichia coli). This inhibitory effect is observed with live mycobacteria, but not when heat-inactivated bacteria are ingested. In contrast, when Candida albicans is given to macrophages instead of C. neoformans, an enhancement of intracellular killing is observed, suggesting that cytocidal mechanisms other than respiratory burst are involved in the anti- Candidacidal activity of macrophages.

In vitro T-cell activation of monocyte-derived macrophages by soluble messengers or cell-to-cell contact in bovine tuberculosis

The macrophage plays a dual role in tuberculosis, promoting not only protection against mycobacteria, but also survival of the pathogen. Macrophages inhibit multiplication of mycobacteria but also act in concert with lymphocytes through presentation of antigens to T cells. Studies in animal and human infections have suggested a correlation of in vitro growth rates of mycobacteria with in vivo virulence, using uracil uptake to assess mycobacterial metabolism. This study found that blood-derived, non-activated bovine macrophages were capable of controlling Mycobacterium bovis bacillus Calmette-Gurin growth for up to 96 hr, but were permissive to intracellular growth of virulent M. bovis. The present investigation compared the in vitro modulation of these macrophage activities by cytokine-rich T-cell supernatants or cell-to-cell contact. On the one hand, treatment of cultured monocytes with mitogen-produced T-cell supernatants promoted morphological changes suggestive of an activation status, enhanced the antigen presentation capabilities of monocytes and up-regulated major histocompatibility complex class II expression. However, this activation was not associated with enhanced anti-M. bovis activity. On the other hand, incubation of infected monocytes with T-cell populations resulted in proportionally increased inhibition of M. bovis uracil uptake. This inhibition was also seen using cells from uninfected animals and indicated the necessity for cell-to-cell contact to promote antimycobacterial capability.

Interferon-gamma and tumor necrosis factor-alpha determine resistance to Paracoccidioides brasiliensis infection in mice

To investigate the role of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the resistance to Paracoccidioides brasiliensis (Pb) infection, mice with homologous disruption of the IFN-gamma (GKO) or TNF-alpha receptor p55 (p55KO) were infected with the parasite. GKO and p55KO, but not wild-type (WT) mice, were unable to control the growth of yeast cells and the mice succumbed to infection by days 16 and 90 after infection, respectively. Typical inflammatory granulomas were found only in WT mice. In contrast, knockout mice presented an inflammatory infiltrate composed of a few neutrophils, mononuclear, epithelioid, and multinuclear giant cells forming incipient granulomas in GKO mice and without granuloma formation in p55KO mice. Besides, both groups of knockout mice exhibited elevated numbers of yeast forms in agreement with colony-forming unit counts in organs. Compared with WT, splenocytes from infected GKO mice cultured with the Pb F1 fraction produced lower TNF-alpha levels, whereas leukocytes from infected p55KO mice produced similar amounts of TNF-alpha but higher levels of IFN-gamma. Moreover, splenocytes from infected WT mice produced higher levels of nitric oxide (NO) resulting in a lower T-cell proliferative response to Con A than uninfected WT, or infected p55KO and GKO mice. On the contrary, the addition of IFN-gamma to splenocytes from infected GKO mice resulted in higher NO production and lower T cell proliferation. Taken together, these findings suggests that endogenous TNF-alpha, acting through the p55 receptor, and IFN-gamma mediate resistance to Pb infection and induce NO production that determines marked T cell unresponsiveness.

Nitric oxide mediates intestinal pathology but not immune expulsion during Trichinella spiralis infection in mice

The relationship between intestinal pathology and immune expulsion of gastrointestinal (GI) nematodes remains controversial. Although immune expulsion of GI helminth parasites is usually associated with Th2 responses, the effector mechanisms directly responsible for parasite loss have not been identified. We have previously shown that while the intestinal pathology accompanying the expulsion of the GI parasite Trichinella spiralis may be dependent on IL-4 and mediated by TNF, parasite loss is independent of TNF. In contrast, intestinal pathology in other disease models has been attributed to Th1 cytokines, although it closely resembles that seen in helminth infections. Whereas production of inducible NO synthase (iNOS) in the gut is important for both homeostasis of the epithelial layer and in protection against pathogenic microorganisms, overproduction of NO has been implicated in the pathogenesis of a number of inflammatory conditions. We therefore investigated the role of NO in T. spiralis infection using iNOS-deficient mice. iNOS-/- and iNOS-/+ mice were infected with T. spiralis, and parasite expulsion and intestinal pathology were followed. Parasite expulsion proceeded similarly in both groups of animals, but significant intestinal pathology was only observed in the heterozygous mice. Thus it appears that, although the protective effects of Th2 responses in GI helminth infection do not require NO, this mediator contributes substantially to the associated enteropathy. NO may therefore be an important mediator of enteropathy in both Th1- and Th2-inducing conditions.

Roles of interleukin-12 and gamma interferon in murine Chlamydia pneumoniae infection

BALB/c and strain 129 mice infected intranasally with Chlamydia pneumoniae displayed a moderate-to-severe inflammation in the lungs and produced interleukin-12 (IL-12), gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and IL-10, with peak levels on days 1 to 3 postinfection (p.i.), returning to basal levels by day 16 p.i. Anti-IL-12 treatment resulted in less-severe pathological changes but higher bacterial titers on days 3 and 7 p.i. By day 16 p.i., the inflammatory responses of control antibody-treated mice subsided. The bacterial titers of both anti-IL-12- and control antibody-treated mice decreased within 3 weeks to marginally detectable levels. Anti-IL-12 treatment significantly reduced lung IFN-gamma production and in vitro spleen cell IFN-gamma production in response to either C. pneumoniae or concanavalin A. In gamma-irradiated infected mice, cytokine production was delayed, and this delay correlated with high bacterial titers in the lungs. Following C. pneumoniae infection, 129 mice lacking the IFN-gamma receptor alpha chain gene (G129 mice) produced similar IL-12 levels and exhibited similarly severe pathological changes but had higher bacterial titers than 129 mice. However, by day 45 p.i., bacterial titers became undetectable in both wild-type 129 and G129 mice. Thus, during C. pneumoniae lung infection, IL-12, more than IFN-gamma, plays a role in pulmonary-cell infiltration. IFN-gamma and IL-12, acting mostly through its induction of IFN-gamma and Th1 responses, play an important role in controlling acute C. pneumoniae infection in the lungs, but eventually all mice control the infection to undetectable levels by IL-12- and IFN-gamma-independent mechanisms.

Inhibitory effects of nitric oxide and gamma interferon on in vitro and in vivo replication of Marek's disease virus

The replication of Marek's disease herpesvirus (MDV) and herpesvirus of turkeys (HVT) in chicken embryo fibroblast (CEF) cultures was inhibited by the addition of S-nitroso-N-acetylpenicillamine, a nitric oxide (NO)-generating compound, in a dose-dependent manner. Treatment of CEF culture, prepared from 11-day-old embryos, with recombinant chicken gamma interferon (rChIFN-gamma) and lipopolysaccharide (LPS) resulted in production of NO which was suppressed by the addition of N(G)-monomethyl L-arginine (NMMA), an inhibitor of inducible NO synthase (iNOS). Incubation of CEF cultures for 72 h prior to treatment with rChIFN-gamma plus LPS was required for optimal NO production. Significant differences in NO production were observed in CEF derived from MDV-resistant N2a (major histocompatibility complex [MHC], B(21)B(21)) and MDV-susceptible S(13) (MHC, B(13)B(13)) and P2a (MHC, B(19)B(19)) chickens. N2a-derived CEF produced NO earlier and at higher levels than CEF from the other two lines. The lowest production of NO was detected in P2a-derived CEF. NO production in chicken splenocyte cultures followed a similar pattern, with the highest levels of NO produced in cultures from N2a chickens and the lowest levels produced in cultures from P2a chickens. Replication of MDV and HVT was significantly inhibited in CEF cultures treated with rChIFN-gamma plus LPS and producing NO. The addition of NMMA to CEF treated with rChIFN-gamma plus LPS reduced the inhibition. MDV infection of chickens treated with S-methylisothiourea, an inhibitor of iNOS, resulted in increased virus load compared to nontreated chickens. These results suggest that NO may play an important role in control of MDV replication in vivo.

Toxicity of nitrogen oxides and related oxidants on mycobacteria: M. tuberculosis is resistant to peroxynitrite anion

OBJECTIVE

To test the toxicity of reactive nitrogen intermediates (RNI), including authentic nitric oxide (NO), nitrogen dioxide (NO2), and peroxynitrite anion (ONOO-), a potent oxidant derived from NO and superoxide anion, on various mycobacterial strains including M. tuberculosis.

DESIGN

Relatively avirulent mycobacteria including M. smegmatis and BCG, as well as the pathogenic M. Bovis Ravenel and M. tuberculosis Erdman and the clinical isolate M160 (also known as the C strain) were tested for their susceptibility to the toxic effects of NO, NO2, and ONOO-, Deaerated, NO-saturated solutions as well as an anaerobic in vitro system in which mycobacteria can be exposed to desired concentrations of authentic NO or NO2, were employed in these studies. An in vitro ONOO- killing assay was used to examine the adverse effects of this NO-derived oxidant on the various strains of mycobacteria.

RESULTS

Both NO and NO2 exhibit antimycobacterial activity, with the former being more potent. Results obtained using ONOO- killing assay revealed that while avirulent mycobacteria including BCG and M. smegmatis are susceptible to this NO-derived oxidant, the virulent Erdman strain of M. tuberculosis and M. bovis, as well as the clinical tuberculous isolate M160, are remarkably resistant.

CONCLUSION

These results suggest that the interactions between RNI and various species of mycobacteria could be highly specific. And since activated macrophages produce peroxynitrite, the significance of the ONOO- resistance of M. tuberculosis strains in relation to intracellular survival deserves further investigation.

Involvement of endogenously synthesized interleukin (IL)-18 in the protective effects of IL-12 against pulmonary infection with Cryptococcus neoformans in mice

We previously demonstrated that interleukin (IL)-12 protected mice against fatal pulmonary infection with a highly virulent strain of Cryptococcus neoformans, which correlated well with the production of interferon (IFN)-gamma as well as IL-18 in the primary infected site. In the present study, we examined the role of endogenously synthesized IL-18 in IL-12-induced host resistance to this pathogen. There was little or no production of IFN-gamma and IL-18 both at mRNA and protein levels in lungs of mice infected with C. neoformans, while treatment with IL-12 induced a marked production of these cytokines. Caspase-1 mRNA was expressed in infected mice even without IL-12 treatment. Administration of neutralizing anti-IFN-gamma monoclonal antibody (mAb) clearly inhibited production of IFN-gamma and IL-18 induced by IL-12, while control IgG did not show such an effect. However, administration of IFN-gamma did not induce the production of both cytokines in infected mice, although tumor necrosis factor (TNF)-alpha and IFN-gamma-inducible protein (IP)-10 were synthesized by the same treatment. Finally, neutralizing anti-IL-18 antibody (Ab) significantly interfered with the production of IFN-gamma and elimination of the microorganism from the lung induced by IL-12 treatment. Furthermore, both IFN-gamma synthesis and host protection caused by IL-12 were profoundly diminished in IL-18 gene-disrupted mice. Considered collectively, our results indicated that host protection against C. neoformans induced by IL-12 involved endogenously synthesized IL-18 and that the production of IL-18 was mediated at least in part by endogenous IFN-gamma.

Inhibition of multiplication of Mycobacterium leprae in mouse foot pads by recombinant Bacillus Catmette-Guérin (BCG)

Immunization of mice with recombinant Mycobacterium bovis Bacillus Calmette-Guérin (rBCG) which over-produces a putative protective antigen candidate, the A component of antigen 85 complex (Ag85A), reduced the multiplication of Mycobacterium leprae in the foot pads of mice. The inhibition by this rBCG (rBCG/85A) was more evident than that with parental BCG. Repeated rBCG/85A immunization significantly could reduce M. leplae multiplication in mice. This is first report of rBCG to control mycobacterial infection in animal model. Therefore, rBCG technique may be useful for the development of a more effective mycobacteria vaccine.

A role for lymphotoxin beta receptor in host defense against Mycobacterium bovis BCG infection

To investigate the role of membrane lymphotoxin (LT)alpha1 / beta2 and its LTbeta receptor (LTbetaR) in the protective immune response to Mycobacterium bovis bacillus Calmette-Guérin (BCG) infection, we have used a soluble fusion molecule (LTbetaR-IgG1). LTbetaR-Ig treatment interferes with granuloma formation mainly in the spleen by inhibiting macrophage activation and nitric oxide synthase activity. In addition, a large accumulation of eosinophils was observed in the spleen of LTbetaR-Ig-treated infected mice. Decreased blood levels of IFN-gamma and increased IL-4 were also observed, suggesting that the LTbetaR pathway is important in BCG infection to favor a Th1 type of immune response. The treatment of transgenic mice expressing high blood levels of a soluble TNFR1-IgG3 fusion protein with LTbetaR-Ig resulted in a still higher sensitivity to BCG infection, and extensive necrosis in the spleen. In conclusion, these results suggest that the LTbetaR and the TNFR pathways are not redundant in the course of BCG infection and protective granuloma formation: the LTbetaR pathway appears to be important in spleen granuloma formation, whereas the TNFR pathway has a predominant role in other tissues.

Attenuation of MHC Class II Expression in Macrophages Infected with Mycobacterium bovis Bacillus Calmette-Guerin Involves Class II Transactivator and Depends on the Nramp1 Gene

The natural resistance associated macrophage protein 1 (Nramp1) gene determines the ability of murine macrophages to control infection with a group of intracellular pathogens, including Salmonella typhimurium, Leishmania donovani, and Mycobacterium bovis bacillus Calmette-Guérin (BCG). The expression of the resistant allele of the Nramp1 gene in murine macrophages is associated with a more efficient expression of several macrophage activation-associated genes, including class II MHC loci. In this study, we investigated the molecular mechanisms involved in IFN-γ-induced MHC class II expression in three types of macrophages: those expressing a wild-type allele of the Nramp1 gene (B10R and 129/Mφ), those carrying a susceptible form of the Nramp1 gene (B10S), and those derived from 129-Nramp1-knockout mice (129/Nramp1-KO). Previously, we published results showing that Ia protein expression is significantly higher in the IFN-γ-induced B10R macrophages, compared with its susceptible counterpart. In this paper, we also show that the higher expression of Ia protein in B10R cells is associated with higher I-Aβ mRNA expression, which correlates with a higher level of IFN-γ-induced phosphorylation of the STAT1-α protein and subsequently with elevated expression of class II transactivator (CIITA) mRNA, compared with B10S. Furthermore, we demonstrate that the infection of macrophages with M. bovis BCG results in a down-regulation of CIITA mRNA expression and, consequently, in the inhibition of Ia induction. Therefore, our data explain, at least in part, the molecular mechanism involved in the inhibition of I-Aβ gene expression in M. bovis BCG-infected macrophages activated with IFN-γ.

The effects of Chlorella vulgaris in the protection of mice infected with Listeria monocytogenes. Role of natural killer cells

In this work we have demonstrated the effects of oral administration of Chlorella vulgaris (CV) on Natural Killer cells (NK) activity of mice infected with a sublethal dose of viable Listeria monocytogenes. The treatment with C. vulgaris produced a significant increase on NK cells activity in normal (non-infected) animals compared to the animals that received only vehicle (water) (p < 0.0001). Similarly, the infection alone produced a significant increase on NK cells activity, which was observed at 48 and 72 hours after the inoculation of L. monocytogenes. Moreover, when CV was administered in infected animals, there was an additional increase in NK cells activity which was significantly higher than that found in the infected groups (p < 0.0001). CV treatment (50 and 500mg/Kg) of mice infected with a dose of 3 x 10(5) bacteria/animal, which was lethal for all the non-treated controls, produced a dose-response protection which led to a 20% and 55% survival, respectively (p < 0.0001).

Early emergence of CD8(+) T cells primed for production of type 1 cytokines in the lungs of Mycobacterium tuberculosis-infected mice

Several lines of evidence suggest that CD8 T cells are important in protection against tuberculosis. To understand the function of this cell population in the immune response against Mycobacterium tuberculosis, T cells from lungs of M. tuberculosis-infected mice were examined by flow cytometry. The kinetics of the appearance of CD8 T cells in lungs of infected mice closely paralleled that of CD4 T cells. Both CD4(+) and CD8(+) T cells displaying an activated phenotype were found in the lungs as early as 1 week postinfection. By 2 weeks, total cell numbers in the lungs had tripled and percentages of T cells were increased two- to threefold; the percentages of CD4(+) T cells were ca. twofold higher than those of CD8(+) T cells. Short-term stimulation with M. tuberculosis-infected antigen-presenting cells induced cytokine production by primed CD4(+) and CD8(+) T cells. Intracellular cytokine staining revealed that 30% +/- 5% of CD4(+) and 23% +/- 4% of CD8(+) T cells were primed for production of gamma interferon (IFN-gamma). However, a difference in in vivo IFN-gamma production by T cells was observed with approximately 12% of CD4(+) T cells and approximately 5% of CD8(+) T cells secreting cytokine in the lungs at any given time during infection. The data presented indicate that although early in infection the majority of IFN-gamma is produced by CD4(+) T cells, cytokine-producing CD8(+) T cells are readily available when triggered by the appropriate stimuli.

T-Cell hyporesponsiveness induced by activated macrophages through nitric oxide production in mice infected with Mycobacterium tuberculosis

In active tuberculosis, T-cell response to Mycobacterium tuberculosis is known to be reduced. In the course of Mycobacterium tuberculosis infection in mice, we observed that T-cell proliferation in response to M. tuberculosis purified protein derivative (PPD) reached the maximum level on day 7, then declined to the minimal level on day 14, and persisted at a low level through day 28 postinfection. The frequency of PPD-specific CD4 T cells in the spleen on day 28 decreased to one-sixth on day 7. To further investigate the mechanism of this T-cell hyporesponsiveness, we next analyzed the suppressive activity of spleen macrophages on T-cell function. The nonspecific proliferative response of naive T cells and the PPD-specific proliferative response of T cells were suppressed by day 28 macrophages, but not by day 7 macrophages or naive macrophages. This reduction of proliferative response was restored by addition of nitric oxide synthesis inhibitor, NG-monoethyl-L-arginine monoacetate, but not by monoclonal antibody against interleukin 10 or transforming growth factor beta. These data indicate that the macrophages from mice chronically infected with M. tuberculosis suppress T-cell response through production of nitric oxide, suggesting that nitric oxide-induced elimination mediated by activated macrophages may reduce the T-cell response and the number of mycobacterium-specific CD4 T cells in vivo.

Immunosuppressant FK506 inhibits inducible nitric oxide synthase gene expression at a step of NF-kappaB activation in rat hepatocytes

BACKGROUND/AIMS

Recent evidence indicates that an increase in nitric oxide production after liver transplantation is associated with acute allograft rejection. Nitric oxide mediates cellular injury under various pathological conditions in the liver. Studies were performed to determine whether the immunosuppressants FK506 and cyclosporin A directly influence gene expression of inducible nitric oxide synthase by interleukin 1beta in hepatocytes.

METHODS

Primary cultures of rat hepatocytes were treated with interleukin 1beta in the presence and absence of FK506 or cyclosporin A. Release of nitrite (nitric oxide metabolite) into culture medium, levels of inducible nitric oxide synthase protein and mRNA, and activation of nuclear factor-kappaB were compared with the two drugs.

RESULTS

Interleukin 1beta increased levels of inducible nitric oxide synthase protein and inducible nitric oxide synthase mRNA, as well as nitric oxide production, in the cultured hepatocytes. Nuclear factor-kappaB, an important transcription factor in inducible nitric oxide synthase gene expression in response to inflammation, also appeared in the nuclear fraction of hepatocytes after addition of interleukin 1beta. FK506 markedly inhibited the nitric oxide formation, inducible nitric oxide synthase protein synthesis and inducible nitric oxide synthase mRNA expression induced by interleukin 1beta, but cyclosporin A had no effects. Furthermore, FK506 inhibited nuclear factor-kappaB activation and decreased mRNA levels of the p50/p65 subunits of nuclear factor-kappaB.

CONCLUSIONS

These results demonstrate that FK506, but not cyclosporin A, inhibits the induction of inducible nitric oxide synthase expression during nuclear factor-kappaB activation. FK506 may influence liver function during diseases by modulating the nitric oxide pathway, in addition to its immunosuppressive effect.

Mycobacterium tuberculosis CDC1551 Induces a More Vigorous Host Response In Vivo and In Vitro, But Is Not More Virulent Than Other Clinical Isolates

Mycobacterium tuberculosis CDC1551, a clinical isolate reported to be hypervirulent and to grow faster than other isolates, was compared with two other clinical isolates (HN60 and HN878) and two laboratory strains (H37Rv and Erdman). The initial (1–14 days) growth of CDC1551, HN60, HN878, and H37Rv was similar in the lungs of aerosol-infected mice, but growth of Erdman was slower. Thereafter, the growth rate of CDC1551 decreased relative to the other strains which continued to grow at comparable rates up to day 21. In the lungs of CDC1551-infected mice, small well-organized granulomas with high levels of TNF-α, IL-6, IL-10, IL-12, and IFN-γ mRNA were apparent sooner than in lungs of mice infected with the other strains. CDC1551-infected mice survived significantly longer. These findings were confirmed in vitro. The growth rates of H37Rv and CDC1551 in human monocytes were the same, but higher levels of TNF-α, IL-10, IL-6, and IL-12 were induced in monocytes after infection with CDC1551 or by exposure of monocytes to lipid fractions from CDC1551. CD14 expression on the surface of the monocytes was up-regulated to a greater extent by exposure to the lipids of CDC1551. Thus, CDC1551 is not more virulent than other M. tuberculosis isolates in terms of growth in vivo and in vitro, but it induces a more rapid and robust host response.