Evidence for a reduced chemokine response in the lungs of beige mice infected with Mycobacterium avium

Immunogenicity and protection against Mycobacterium avium with a heterologous RNA prime and protein boost vaccine regimen

Prophylactic efficacy of two different delivery platforms for vaccination against Mycobacterium avium (M. avium) were tested in this study; a subunit and an RNA-based vaccine. The vaccine antigen, ID91, includes four mycobacterial antigens: Rv3619, Rv2389, Rv3478, and Rv1886. We have shown that ID91+GLA-SE is effective against a clinical NTM isolate, M. avium 2-151 smt. Here, we extend these results and show that a heterologous prime/boost strategy with a repRNA-ID91 (replicon RNA) followed by protein ID91+GLA-SE boost is superior to the subunit protein vaccine given as a homologous prime/boost regimen. The repRNA-ID91/ID91+GLA-SE heterologous regimen elicited a higher polyfunctional CD4+ TH1 immune response when compared to the homologous protein prime/boost regimen. More significantly, among all the vaccine regimens tested only repRNA-ID91/ID91+GLA-SE induced IFN-γ and TNF-secreting CD8+ T cells. Furthermore, the repRNA-ID91/ID91+GLA-SE vaccine strategy elicited high systemic proinflammatory cytokine responses and induced strong ID91 and an Ag85B-specific humoral antibody response a pre- and post-challenge with M. avium 2-151 smt. Finally, while all prophylactic prime/boost vaccine regimens elicited a degree of protection in beige mice, the heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen provided greater pulmonary protection than the homologous protein prime/boost regimen. These data indicate that a prophylactic heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen augments immunogenicity and confers protection against M. avium.

Subunit vaccine protects against a clinical isolate of Mycobacterium avium in wild type and immunocompromised mouse models

The nontuberculous mycobacteria (NTM) Mycobacterium avium is a clinically significant pathogen that can cause a wide range of maladies, including tuberculosis-like pulmonary disease. An immunocompromised host status, either genetically or acutely acquired, presents a large risk for progressive NTM infections. Due to this quietly emerging health threat, we evaluated the ability of a recombinant fusion protein ID91 combined with GLA-SE [glucopyranosyl lipid adjuvant, a toll like receptor 4 agonist formulated in an oil-in-water stable nano-emulsion] to confer protection in both C57BL/6 (wild type) and Beige (immunocompromised) mouse models. We optimized an aerosol challenge model using a clinical NTM isolate: M. avium 2-151 smt, observed bacterial growth kinetics, colony morphology, drug sensitivity and histopathology, characterized the influx of pulmonary immune cells, and confirmed the immunogenicity of ID91 in both mouse models. To determine prophylactic vaccine efficacy against this M. avium isolate, mice were immunized with either ID91 + GLA-SE or bacillus Calmette-Guérin (BCG). Immunocompromised Beige mice displayed a delayed influx of innate and adaptive immune cells resulting in a sustained and increased bacterial burden in the lungs and spleen compared to C57BL/6 mice. Importantly, both ID91 + GLA-SE and BCG vaccines significantly reduced pulmonary bacterial burden in both mouse strains. This work is a proof-of-concept study of subunit vaccine-induced protection against NTM.

Animal Models of Mycobacteria Infection

This manuscript describes the infection of mice and guinea pigs with mycobacteria via various routes, as well as necropsy methods for the determination of mycobacterial loads within target organs. Additionally, methods for cultivating mycobacteria and preparing stocks are described. The protocols outlined are primarily used for M. tuberculosis, but can also be used for the study of other non-tuberculosis mycobacterial species. A wide variety of animal models have been used to test new vaccines, drugs, and the impact of cigarette exposure. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Aerosol infection of mice with mycobacteria Basic Protocol 2: Aerosol infection of guinea pig with mycobacteria using a Madison chamber Alternate Protocol 1: Cigarette exposure prior to infection of mice with mycobacteria Alternate Protocol 2: Intravenous infection of mice with mycobacteria Basic Protocol 3: Necropsy methods for animals experimentally infected with mycobacteria Basic Protocol 4: Following the course of infection Basic Protocol 5: Measuring the animal immune response to infection Support Protocol: Cultivation of mycobacteria for use in animal experiments.

NK Cell-Derived IFN-γ Protects against Nontuberculous Mycobacterial Lung Infection

In developed countries, pulmonary nontuberculous mycobacteria (NTM) infections are more prevalent than Mycobacterium tuberculosis infections. Given the differences in the pathogenesis of NTM and M. tuberculosis infections, separate studies are needed to investigate the pathological effects of NTM pathogens. Our previous study showed that anti-IFN-γ autoantibodies are detected in NTM-infected patients. However, the role of NK cells and especially NK cell-derived IFN-γ in this context has not been studied in detail. In the current study, we show that NK1.1 cell depletion increases bacterial load and mortality in a mouse model of pulmonary NTM infection. NK1.1 cell depletion exacerbates NTM-induced pathogenesis by reducing macrophage phagocytosis, dendritic cell development, cytokine production, and lung granuloma formation. Similar pathological phenomena are observed in IFN-γ-deficient (IFN-γ^-/-) mice following NTM infection, and adoptive transfer of wild-type NK cells into IFN-γ^-/- mice considerably reduces NTM pathogenesis. Injection of rIFN-γ also prevents NTM-induced pathogenesis in IFN-γ^-/- mice. We observed that NK cells represent the main producers of IFN-γ in the lungs and production starts as soon as 1 d postinfection. Accordingly, injection of rIFN-γ into IFN-γ^-/- mice 1 d (but not 2 wk) postinfection significantly improves immunity against NTM infection. NK cells also stimulate mycobacterial killing and IL-12 production by macrophages. Our results therefore indicate that IFN-γ production by NK cells plays an important role in activating and enhancing innate and adaptive immune responses at early stages of pulmonary NTM infection.

CD11d Antibody Treatment Improves Recovery in Spinal Cord-Injured Mice

Acute administration of a monoclonal antibody (mAb) raised against the CD11d subunit of the leukocyte CD11d/CD18 integrin after spinal cord injury (SCI) in the rat greatly improves neurological outcomes. This has been chiefly attributed to the reduced infiltration of neutrophils into the injured spinal cord in treated rats. More recently, treating spinal cord-injured mice with a Ly-6G neutrophil-depleting antibody was demonstrated to impair neurological recovery. These disparate results could be due to different mechanisms of action utilized by the two antibodies, or due to differences in the inflammatory responses between mouse and rat that are triggered by SCI. To address whether the anti-CD11d treatment would be effective in mice, a CD11d mAb (205C) or a control mAb (1B7) was administered intravenously at 2, 24, and 48 h after an 8-g clip compression injury at the fourth thoracic spinal segment. The anti-CD11d treatment reduced neutrophil infiltration into the injured mouse spinal cord and was associated with increased white matter sparing and reductions in myeloperoxidase (MPO) activity, reactive oxygen species, lipid peroxidation, and scar formation. These improvements in the injured spinal cord microenvironment were accompanied by increased serotonin (5-HT) immunoreactivity below the level of the lesion and improved locomotor recovery. Our results with the 205C CD11d mAb treatment complement previous work using this anti-integrin treatment in a rat model of SCI.

Animal models of mycobacteria infection

This unit describes the infection of mice and guinea pigs with mycobacteria via various routes, as well as necropsy methods for the determination of mycobacterial loads within target organs. Additionally, methods for cultivating mycobacteria and preparing stocks are described. The protocols outlined are primarily used for M. tuberculosis, but can also be used for the study of other non-tuberculosis mycobacterial species.

Neutrophil granule proteins tune monocytic cell function

Polymorphonuclear leukocytes (PMNs) release the contents of granules during their migration to inflammatory sites. On liberation from the first leukocyte to enter injured tissue, the granule proteins play a central role in the early inflammatory response. In particular, mononuclear phagocytes interact intimately with PMNs and their secretion products. PMN granule proteins enhance the adhesion of monocytes to the endothelium and stimulate subsequent extravasation of inflammatory monocytes. At the site of inflammation, PMN granule proteins activate macrophages to produce and release cytokines and to phagocytose IgG-opsonized bacteria. Furthermore, by direct cell-cell contacts, PMNs activate monocyte-derived dendritic cells, thereby enhancing antigen presentation. Efforts in this field might lead to the development of drugs for specific modulation of innate immune functions.

Mechanisms underlying neutrophil-mediated monocyte recruitment

Extravasation of polymorphonuclear leukocytes (PMNs) to the site of inflammation precedes a second wave of emigrating monocytes. That these events are causally connected has been established a long time ago. However, we are now just beginning to understand the molecular mechanisms underlying this cellular switch, which has become even more complex considering the emergence of monocyte subsets, which are affected differently by signals generated from PMNs. PMN granule proteins induce adhesion as well as emigration of inflammatory monocytes to the site of inflammation involving beta(2)-integrins and formyl-peptide receptors. Furthermore, modification of the chemokine network by PMNs and their granule proteins creates a milieu favoring extravasation of inflammatory monocytes. Finally, emigrated PMNs rapidly undergo apoptosis, leading to the discharge of lysophosphatidylcholine, which attracts monocytes via G2A receptors. The net effect of these mechanisms is the accumulation of inflammatory monocytes, thus promoting proinflammatory events, such as release of inflammation-sustaining cytokines and reactive oxygen species. As targeting PMNs without causing serious side effects seems futile, it may be more promising to aim at interfering with subsequent PMN-driven proinflammatory events.

Lung Lesions in SCID-bo and SCID-bg Mice after Intratracheal Inoculation with Wild-type or Leucotoxin-deficient Mutant Strains of Mannheimia haemolytica Serotype 1

The purpose of this study was to investigate SCID-bg mice engrafted with bovine haematolymphoid tissues (SCID-bo) as a model for studying bovine Mannheimia haemolytica serotype 1- induced pneumonia, in which leucotoxin (LKT) plays a major role. In experiment A, SCID-bo and SCID-bg mice were inoculated intratracheally with either (1) phosphate-buffered saline (PBS), (2) M. haemolytica wild-type strain 89010807N ("LKT(+)WT"), (3) a M. haemolytica leucotoxin-deficient mutant of strain 89010807N ("LKT(-)mutant"), or (4) the M. haemolytica wild-type Oklahoma strain. Mice were killed for examination at intervals between 20 and 44h after inoculation. Lung lesions consisted of thickened alveolar septa and neutrophil and macrophage infiltrates in the bronchioles and alveoli. Lung lesion scores in the SCID-bo mice inoculated with LKT(+)WT or LKT(-) mutant were significantly (P<0.05) greater than those of the PBS control group, but the two bacterial strains produced results that did not differ significantly. M. haemolytica was isolated from lung, liver and spleen after inoculation but less frequently as time progressed. In experiment B, SCID-bg mice were inoculated intratracheally with live LKT(+)WT or formalin-killed LKT(+)WT and killed 24, 48 or 96 h later. Lung lesions were histologically similar to those observed in experiment A; however, there were no significant differences in the lung lesion scores between groups. It was concluded that the lesions seen in this study were probably not due to LKT, and that the SCID-bo mouse does not provide a good rodent model for bovine pneumonia.

Members of the 30- to 32-kilodalton mycolyl transferase family (Ag85) from culture filtrate of Mycobacterium avium subsp. paratuberculosis are immunodominant Th1-type antigens recognized early upon infection in mice and cattle

The characterization of protective antigens is essential for the development of an effective, subunit-based vaccine against paratuberculosis. Surface-exposed and secreted antigens, present abundantly in mycobacterial culture filtrate (CF), are among the well-known protective antigens of Mycobacterium tuberculosis and Mycobacterium bovis. Culture filtrate, prepared from Mycobacterium avium subsp. paratuberculosis ATCC 19698 grown as a surface pellicle on synthetic Sauton medium, was strongly and early recognized in experimentally infected B6 bg/bg beige mice and cattle, as indicated by elevated spleen cell gamma interferon (IFN-gamma) secretion and lymphoproliferative responses of peripheral blood mononuclear cells, respectively. Strong proliferative and ex vivo IFN-gamma responses against antigen 85 (Ag85) complex (a major protein component from M. bovis BCG culture filtrate) could be detected in cattle as early as 10 weeks after oral M. avium subsp. paratuberculosis infection. Synthetic peptides from the Ag85A and Ag85B components of this complex were strongly recognized, whereas T-cell responses were weaker against peptides from the Ag85C protein. A promiscuous T-cell epitope spanning amino acids 145 to 162 of Ag85B (identical sequence in M. bovis and M. avium subsp. paratuberculosis) was identified in experimentally infected cattle. Finally, young calves, born from cows with confirmed paratuberculosis, demonstrated proliferative responses to purified, recombinant Ag85A and Ag85B from M. avium subsp. paratuberculosis. These results indicate that the M. avium subsp. paratuberculosis Ag85 homologues are immunodominant T-cell antigens that are recognized early in experimental and natural infection of cattle.

Intranasal interleukin-12 treatment for protection against respiratory infection with the Francisella tularensis live vaccine strain

Francisella tularensis is a gram-negative intracellular bacterium that can induce lethal respiratory infection in humans and rodents. However, little is known about the role of innate or adaptive immunity in protection from respiratory tularemia. In the present study, the role of interleukin-12 (IL-12) in inducing protective immunity in the lungs against intranasal infection of mice with the live vaccine strain (LVS) of F. tularensis was investigated. It was found that gamma interferon (IFN-gamma) and IL-12 were strictly required for protection, since mice deficient in IFN-gamma, IL-12 p35, or IL-12 p40 all succumbed to LVS doses that were sublethal for wild-type mice. Furthermore, exogenous IL-12 treatment 24 h before intranasal infection with a lethal dose of LVS (10,000 CFU) significantly decreased bacterial loads in the lungs, livers, and spleens of wild-type BALB/c and C57BL/6 mice and allowed the animals to survive infection; such protection was not observed in IFN-gamma-deficient mice. The resistance induced by IL-12 to LVS infection was still observed in NK cell-deficient beige mice but not in CD8-/- mice. These results demonstrate that exogenous IL-12 delivered intranasally can prevent respiratory tularemia through a mechanism that is at least partially dependent upon the expression of IFN-gamma and CD8 T cells.

Proposed pathway for the biosynthesis of serovar-specific glycopeptidolipids in Mycobacterium avium serovar 2

Members of the Mycobacterium avium complex are distinguished by the presence of highly antigenic surface molecules called glycopeptidolipids (GPLs) and the oligosaccharide portion of the serovar-specific GPL defines the 28 serovars. Previously, the genomic region (ser2) encoding the enzymes responsible for the glycosylation of the lipopeptide core to generate the serovar-2-specific GPLs has been described. In this work, the ser2 gene clusters of M. avium serovar 2 strains 2151 and TMC 724 were fully sequenced and compared to the homologous regions of M. avium serovar 1 strain 104, M. avium subsp. paratuberculosis and M. avium subsp. silvaticum. It was also determined that 104Rg, a mutant of strain 104 that produces truncated GPLs, lost several GPL biosynthesis genes by deletion. This comparison, together with analysis of protein similarities, supports a biosynthetic model in which serovar-2-specific GPLs are synthesized from a serovar-1-specific GPL intermediate that is derived from a non-specific GPL precursor. We also identified a gene encoding an enzyme that is necessary for the biosynthesis of serovar-3- and 9-specific GPLs, but not serovar-2-specific GPLs, suggesting that the different serovars may have evolved from the acquisition or loss of genetic information. In addition, a subcluster of genes for the biosynthesis and transfer of fucose, which are needed to make serovar-specific GPLs such as those of serovar 2, is found in the non-GPL-producing M. avium subspecies paratuberculosis and silvaticum.

Characterization of virulence, colony morphotype and the glycopeptidolipid of Mycobacterium avium strain 104

SETTING

Members of the Mycobacterium avium complex (MAC) are responsible for mycobacterial disease in children, the aged and in immunocompromised individuals. The complex consists of different species, serovars and morphologic forms that vary in virulence. One isolate of the MAC is currently being sequenced (MAC 104) and was chosen based on its derivation from an AIDS patient and the fact that it could be genetically manipulated.

OBJECTIVE

MAC 104 was therefore analyzed for virulence, colony morphotype and expression of the glycopeptidolipid (GPL) responsible for serotying differences and the rough to smooth morphological switch.

RESULTS

The isolate was found to be virulent in the murine model of low-dose aerosol infection in that it could colonize the lung, proliferate within the tissue and disseminate to other organs. MAC 104 expressed a variety of colony morphotypes, the most prevalent of which were smooth opaque, smooth transparent and rough. All three morphotypes could persist in the lung; however, the transparent and rough morphotypes grew more rapidlyinvivo. The rough morphotype was unusual in that it expressed an atypical form of the GPL usually absent from rough morphotypes.

CONCLUSION

This characterization complements the genome data and confirms that MAC 104 behaves similarly to other MAC isolates.

Pathogenesis of nontuberculous mycobacteria infections

M avium is a microorganism well adapted to living in the environment and in different hosts. During the past 15 years, a substantial amount of information has been accumulated about the mechanisms used by M avium to cross the host's mucosal barrier, replicate inside cells, circumvent the host's immune response, and persist inside the host. It turns out that M avium is a fascinating pathogen after all. The increasing knowledge about M avium pathogenesis may one day provide means for a more effective prophylaxis as well as for treatment of the infection.

Inflammation in atherosclerosis: lesion formation in LDL receptor-deficient mice with perforin and Lyst(beige) mutations

OBJECTIVE

Natural killer (NK) cells have been identified in human vascular pathologies. In this study, we identified NK cells in aortic root atherosclerotic lesions of low density lipoprotein (LDL) receptor-deficient (LDLr-/-) mice. To characterize the role of NK cell-mediated cytolysis in atherosclerosis, we generated C57Bl/6 double-mutant mice by crossing LDLr-/- mice with NK cell-defective Lyst(beige) mice (creating beige,LDLr-/- mice) and with perforin-deficient mice (creating Pfp-/-,LDLr-/- mice).

METHODS AND RESULTS

Male mice (8 to 10 weeks old) were fed a high-fat diet to induce atherosclerosis. Compared with LDLr-/- mice, beige,LDLr-/- mice had impaired NK cell cytolytic activity and significantly increased atherosclerosis (P<0.05). Pfp-/-,LDLr-/- mice had impaired NK cell cytolytic activity, yet they had lesions that were similar to those of control mice. This suggested that NK cell cytolysis did not play a significant role in atherosclerosis and that the exacerbated atherosclerosis of the beige,LDLr-/- mouse was independent of impaired NK cell cytolytic activity. Therefore, we investigated the role of T and B lymphocytes in atherosclerosis of beige mice by crossing them with recombinase activator gene 1-deficient LDLr-/- mice (Rag1-/-,LDLr-/- mice), thus creating beige,Rag1-/-, LDLr-/- mice. As in the double-mutant study, beige,Rag1-/-,LDLr-/- mice had significantly increased lesions compared with Rag1-/-,LDLr-/- control mice.

CONCLUSIONS

Therefore, the Lyst(beige) mutation in LDLr-/- mice has proatherogenic properties that are independent of NK cell-mediated cytolysis and lymphocyte-mediated acquired immunity.

The involvement of the chemokine receptor CXCR2 in neutrophil recruitment in LPS-induced inflammation and in Mycobacterium avium infection

Knockout mice for CXC receptor 2 (CXCR2) chemokine receptor were used to study the recruitment of neutrophils during acute and chronic inflammatory responses. When treated with lipopolysaccharide (LPS), either intraperitoneally or intratracheally, these animals had a significant reduction in the neutrophil recruitment in the first 24-48 h as compared with control mice. During 15 days of intraperitoneal infection by Mycobacterium avium, the knockout mice showed significantly reduced numbers of neutrophils in the peritoneal cavity as compared with the control mice. In contrast, the recruitment of neutrophils to the lungs during an aerogenic M. avium infection was not affected by the CXCR2 mutation throughout the 60 days of the study. Finally, we could not find any impact of the mutation on the mycobacterial growth of the infected animals. These findings indicate that CXCR2 may be essentially involved in acute inflammatory responses where an early and rapid recruitment of neutrophils is observed.

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.

Animal models of mycobacteria infection

This unit describes the infection of mice and guinea pigs with mycobacteria via the aerogenic route, or of mice via the intravenous route, as well as necropsy methods for the determination of mycobacterial loads within target organs. Additionally, methods for cultivating mycobacteria and preparing stocks are described. The protocols outlined are primarily used for M. tuberculosis, but can also be used for the study of other opportunistic Mycobacterial species.

Release of monocyte chemoattractant protein (MCP)-1 by a human alveolar epithelial cell line in response to mycobacterium avium

Clinical strains of Mycobacterium avium isolated from patients with acquired immunodeficiency syndrome, but not a non-clinical laboratory strain (ATCC 25291), were found to stimulate the human alveolar epithelial cell line A549, to produce monocyte chemoattractant protein (MCP)-1. A549 cells were also found to produce elevated levels of MCP-1 in response to sonicates of the clinical strains of M. avium, and surprisingly, the non-clinical strain as well. However, sonic extracts of the clinical strains were found to induce significantly higher levels of MCP-1 production compared to extracts of the non-clinical strain (P < 0.001). These data suggest the existence of strain-related differences in antigen expression by M. avium. The clinical and non-clinical strains of M. avium were found to attach and invade, but not replicate in A549 cells indicating that MCP-1 production by A549 cells does require the presence of viable, replicating organisms. Activation of alveolar epithelial cells by exposure to M. avium resulting in the production of chemokines which recruit inflammatory cells to the site of infection may be an important regulatory pathway for the activation of pulmonary host defense.

Protection against Mycobacterium avium by DNA vaccines expressing mycobacterial antigens as fusion proteins with green fluorescent protein

Mycobacterium avium causes disseminated disease in humans with AIDS, paratuberculosis in ruminants, lymphadenopathy in swine, and tuberculosis in birds. We constructed DNA vaccines expressing mycobacterial antigens as fusion proteins with enhanced green fluorescent protein (EGFP). Plasmids p65K-EGFP, p85A-EGFP, and p85B-EGFP expressed the M. avium 65-kDa antigen, the Mycobacterium bovis BCG 85A antigen, and the M. avium 85B antigen, respectively, as EGFP fusion proteins. We visualized protein expression directly in cultured murine fibroblasts and intact muscle. p65K-EGFP expressed fusion protein in a diffuse cytoplasmic pattern, and p85A-EGFP and p85B-EGFP produced a speckled pattern. We vaccinated C57BL/6 mice with three doses of plasmid DNA and then challenged them intraperitoneally with M. avium. Negative controls received saline, and positive controls received one dose of BCG vaccine. Mice in all groups developed disseminated infection with a high burden of organisms. Compared to negative controls, mice vaccinated with p85A-EGFP had an eightfold reduction in spleen M. avium CFU at 4 weeks after infection and a fourfold reduction at 8 weeks, reductions similar to those generated by BCG vaccine. Mice vaccinated with p65K-EGFP had a fourfold CFU reduction at 4 weeks and no effect at 8 weeks. This is the first report of DNA vaccines expressing foreign antigens as fusion proteins with EGFP and the first report of successful DNA vaccination against M. avium.

Elevated chemokine concentrations in sera of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative patients with tuberculosis: a possible role for mycobacterial lipoarabinomannan

Levels of interleukin 8 (IL-8), gamma interferon-inducible protein 10 (IP-10), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory protein 1beta (MIP-1beta) were elevated in patients with tuberculosis. IP-10 and MCP-1 levels were higher in human immunodeficiency virus (HIV)-seropositive patients than in HIV-seronegative patients with tuberculosis. Lipoarabinomannan induced IL-8, MCP-1, and MIP-1beta in vitro, which was partly inhibited by anti-tumor necrosis factor antibody.

Role of CD40 ligand in Mycobacterium avium infection

Mycobacterium avium is a common opportunistic pathogen in immunocompromised patients such as those infected with human immunodeficiency virus. Although M. avium is an intracellular organism replicating predominantly in macrophages, disseminated M. avium infection is seen in AIDS patients with CD4(+) cell counts of <50 cells/microliters, suggesting a possible involvement of a T cell-macrophage interaction for the elimination of M. avium. To determine whether CD40-CD40 ligand (CD40L) interactions play a role in M. avium infection, we studied the ability of CD40L to restrict M. avium replication in human monocyte-derived macrophages (MDM) in vitro. MDM were infected with M. avium and cocultured with CD40L-transfected 293 cells for 7 days. Intracellular growth of M. avium in these MDM was assessed by colony counting. CD40L-expressing cells inhibited growth of M. avium in MDM by 86.5% +/- 4.2% compared to MDM cultured with control cells. These findings were verified by assays using purified, soluble recombinant human CD40L (CD40LT). CD40LT (5 micrograms/ml) inhibited intracellular growth of M. avium by 76.9% +/- 18.0% compared to cells treated with medium alone. Inhibition by CD40LT was reduced by monoclonal antibodies (MAbs) against CD40 and CD40L. The inhibitory effect of CD40LT was not accompanied by enhancement of interleukin-12 (IL-12) production by M. avium-infected MDM, while CD40L-expressing cells stimulated IL-12 production by these cells. Treatment of M. avium-infected mice with MAb against murine CD40L resulted in recovery of larger numbers of organisms (0.8 to 1.0 log) from the spleens, livers, and lungs of these animals compared to infected mice which received normal immunoglobulin G. These results indicate that CD40-CD40L signaling may be an important step in host immune response against M. avium infection.

Resistance of virulent Mycobacterium avium to gamma interferon-mediated antimicrobial activity suggests additional signals for induction of mycobacteriostasis

The cytokine gamma interferon (IFN-gamma) plays a major role in the control of Mycobacterium avium infections. We assessed whether the progressive growth of virulent strains of M. avium was associated with alterations in the production of this cytokine as evaluated by reverse transcription-PCR and detection of immunoreactive cytokine in the serum and in spleen homogenates. We found that IFN-gamma was induced during infection by a virulent strain of M. avium to similar or even higher extents than the levels found during infections by a less virulent strain whose growth was controlled. IFN-gamma produced during infection by both mycobacterial strains was partly derived from T cells and led to activation of macrophages, namely, those that were infected. Concomitant with the development of the infection with the virulent strain of M. avium there was an extensive depletion of lymphocytes in the spleen. Thymectomy alone promoted the proliferation of the virulent, but not of the less virulent, strain of M. avium. Our data indicate that virulent strains of M. avium resist the antimicrobial mechanisms of IFN-gamma-activated macrophages and raise the possibility that a second, T-cell-dependent signal is required for the effective control of mycobacterial replication inside macrophages.

CRL-1072 enhances antimycobacterial activity of human macrophages through interleukin-8

CRL-1072 is a poloxamer surfactant that kills mycobacteria more effectively within macrophages than in broth cultures. Human macrophages treated with CRL-1072 synthesized interleukin-8 (IL-8), tumor necrosis factor-alpha (TNF-alpha), and granulocyte-macrophage colony-stimulating factor (GM-CSF) in a dose-dependent manner. About 3000 pg of IL-8 per million human macrophages accumulated in cultures treated with 100-1500 ng of poloxamer, with mRNA message for IL-8 induced as early as 2 h. As macrophages do not have IL-RA receptors, a transwell culture was used to study the chemotactic and activating effects of IL-8 between CRL-1072-treated human macrophage effectors and polymorphonuclear neutrophil (PMN) targets. PMN were activated by IL-8 and secreted hydrogen peroxide and myeloperoxidase (MPO). MPO derived from PMN, in turn, activated monocytes for an enhanced killing of intracellular Mycobacterium avium. The ability of CRL-1072 to modulate macrophage-mediated activation of neutrophils and receive a feedback activation signal may form one mechanism by which its antimycobacterial activity is achieved in vivo.

Role of gamma delta T cells in immunopathology of pulmonary Mycobacterium avium infection in mice

Several studies have shown that gamma delta T cells influence granuloma development after infection with intracellular pathogens. The role of gamma delta T cells in controlling the influx of inflammatory cells into the lung after Mycobacterium avium infection was therefore examined with gene-disrupted mice (K/O). The mice were infected with either M. avium 724, a progressively replicating highly virulent strain of M. avium, or with M. avium 2-151 SmT, a virulent strain that induces a chronic infection. gamma delta-K/O mice infected with M. avium 2-151 SmT showed early enhanced bacterial growth within the lung compared to the wild-type mice, although granuloma formation was similar in both strains. gamma delta-K/O mice infected with M. avium 724 showed identical bacterial growth within the lung compared to the wild-type mice, but they developed more-compact lymphocytic granulomas and did not show the extensive neutrophil influx and widespread tissue necrosis seen in wild-type mice. These data support the hypothesis that isolates of M. avium that induce protective T-cell-specific immunity are largely unaffected by the absence of gammadelta T cells. Whereas with bacterial strains that induce poor protective immunity, the absence of gamma delta T cells led to significant reductions in both the influx of neutrophils and tissue damage within the lungs of infected mice.

Lack of Both Types 1 and 2 Cytokines, Tissue Inflammatory Responses, and Immune Protection During Pulmonary Infection by Mycobacterium bovis Bacille Calmette-Guérin in IL-12-Deficient Mice

Understanding of key cytokines and the nature of protective immune responses in pulmonary mycobacterial diseases remains a task of paramount importance. In this study, both wild-type (wt) and IL-12-deficient (IL-12−/−) mice were infected by airways inoculation of live Mycobacterium bovis bacille Calmette-Guérin (BCG). The type 1 cytokines IL-12, IFN-γ, and TNF-α, but not the type 2 cytokines IL-4 and granulocyte macrophage (GM)-CSF, markedly increased in the lung and peripheral blood of wt mice postinfection, which resulted in the development of intense granulomatous responses and the effective control of mycobacterial infection in the lung. In contrast, IL-12−/− mice demonstrated a lack of both types 1 and 2 cytokines in the lung and blood and a severely impaired tissue immune-inflammatory response lacking not only macrophages and neutrophils but CD4 and CD8 T cells and NK cells in the lung throughout the entire course of study. Total lung mononuclear cells isolated from these mice, in contrast to wt mice, had an impaired recall immune response to Ag challenge in vitro. These impaired responses resulted in an uncontrolled local growth and systemic spread of bacilli. Our findings reveal that IL-12 plays an irreplaceable role in the initiation of Th1 responses, and the loss of its function cannot be compensated for by alternative mechanisms in the lung. This cytokine, together with IFN-γ and TNF-α, and granulomatous inflammation are critically required for the effective control of pulmonary mycobacterial infection. Our results also indicate that the absence of type 1 cytokines does not necessarily favor a Th2 response.