Comparison of 15 laboratory and patient-derived strains of Mycobacterium avium for ability to infect and multiply in cultured human macrophages

Agent-based model indicates chemoattractant signaling caused by Mycobacterium avium biofilms in the lung airway increases bacterial loads by spatially diverting macrophages

Incidence and prevalence of MAC infections are increasing globally, and reinfection is common. Thus, MAC infections present a significant public health challenge. We quantify the impact of MAC biofilms and repeated exposure on infection progression using a computational model of MAC infection in lung airways. MAC biofilms aid epithelial cell invasion, cause premature macrophage apoptosis, and limit antibiotic efficacy. In this computational work we develop an agent-based model that incorporates the interactions between bacteria, biofilm, and immune cells. In this computational model, we perform virtual knockouts to quantify the effects of the biofilm sources (deposited with bacteria vs. formed in the airway), and their impacts on macrophages (inducing apoptosis and slowing phagocytosis). We also quantify the effects of repeated bacterial exposures to assess their impact on infection progression. Our simulations show that chemoattractants released by biofilm-induced apoptosis bias macrophage chemotaxis towards pockets of infected and apoptosed macrophages. This bias results in fewer macrophages finding extracellular bacteria, allowing the extracellular planktonic bacteria to replicate freely. These spatial macrophage trends are further exacerbated with repeated deposition of bacteria. Our model indicates that interventions to abrogate macrophages' apoptotic responses to bacterial biofilms and/or reduce frequency of patient exposure to bacteria will lower bacterial load, and likely overall risk of infection.

The Role of Biofilms, Bacterial Phenotypes, and Innate Immune Response in Mycobacterium avium Colonization to Infection

Mycobacterium avium complex (MAC), is known for colonizing and infecting humans following inhalation of the bacteria. MAC pulmonary disease is notoriously difficult to treat and prone to recurrence. Both the incidence and prevalence MAC pulmonary disease have been increasing globally. MAC is well known to form biofilms in the environment, and in vitro, these biofilms have been shown to aid MAC in epithelial cell invasion, protect MAC from phagocytosis, and cause premature apoptosis in macrophages. In vivo, the system of interactions between MAC, biofilms and host macrophages is complex, difficult to replicate in vitro and in animal models, has not been fully characterized. Here we present a three-dimensional agent-based model of a lung airway to help understand how these interactions evolve in the first 14 days post-bacterial inhalation. We parameterized the model using published data and performed uncertainty analysis to characterize outcomes and parameters' effects on those outcomes. Model results show diverse outcomes, including wide ranges of macrophage recruitment levels, and bacterial loads and phenotype distribution. Though most bacteria are phagocytosed by macrophages and remain intracellular, there are also many simulations in which extracellular bacteria continue to drive the colonization and infection. Initial parameters dictating host immune levels, bacterial loads introduced to the airway, and biofilm conditions have significant and lasting impacts on the course of these results. Additionally, though macrophage recruitment is key for suppressing bacterial loads, there is evidence of significant excess recruitment that fail to impact bacterial numbers. These results highlight a need and identify a path for further exploration into the inhalation events in MAC infection. Early infection dynamics could have lasting impacts on the development of nodular bronchiectatic or fibrocavitary disease as well as inform possible preventative and treatment intervention targeting biofilm-macrophage interactions.

Genetic Variation/Evolution and Differential Host Responses Resulting from In-Patient Adaptation of Mycobacterium avium

Members of the Mycobacterium avium complex (MAC) are characterized as nontuberculosis mycobacteria and are pathogenic mainly in immunocompromised individuals. MAC strains show a wide genetic variability, and there is growing evidence suggesting that genetic differences may contribute to a varied immune response that may impact the infection outcome.

Members of the Mycobacterium avium complex (MAC) are characterized as nontuberculosis mycobacteria and are pathogenic mainly in immunocompromised individuals. MAC strains show a wide genetic variability, and there is growing evidence suggesting that genetic differences may contribute to a varied immune response that may impact the infection outcome. The current study aimed to characterize the genomic changes within M.avium isolates collected from single patients over time and test the host immune responses to these clinical isolates. Pulsed-field gel electrophoresis and whole-genome sequencing were performed on 40 MAC isolates isolated from 15 patients at the Department of Medical Microbiology at St. Olavs Hospital in Trondheim, Norway. Isolates from patients (patients 4, 9, and 13) for whom more than two isolates were available were selected for further analysis. These isolates exhibited extensive sequence variation in the form of single-nucleotide polymorphisms (SNPs), suggesting that M. avium accumulates mutations at higher rates during persistent infections than other mycobacteria. Infection of murine macrophages and mice with sequential isolates from patients showed a tendency toward increased persistence and the downregulation of inflammatory cytokines by host-adapted M. avium strains. The study revealed the rapid genetic evolution of M. avium in chronically infected patients, accompanied by changes in the virulence properties of the sequential mycobacterial isolates.

Mycobacterium avium Complex Disease

Despite the ubiqitous nature of Mycobacterium avium complex (MAC) organisms in the environment, relatively few of those who are infected develop disease. Thus, some degree of susceptibility due to either underlying lung disease or immunosuppression is required. The frequency of pulmonary MAC disease is increasing in many areas, and the exact reasons are unknown. Isolation of MAC from a respiratory specimen does not necessarily mean that treatment is required, as the decision to treatment requires the synthesis of clinical, radiographic, and microbiologic information as well as a weighing of the risks and benefits for the individual patient. Successful treatment requires a multipronged approach that includes antibiotics, aggressive pulmonary hygiene, and sometimes resection of the diseased lung. A combination of azithromycin, rifampin, and ethambutol administered three times weekly is recommend for nodular bronchiectatic disease, whereas the same regimen may be used for cavitary disease but administered daily and often with inclusion of a parenteral aminoglycoside. Disseminated MAC (DMAC) is almost exclusively seen in patients with late-stage AIDS and can be treated with a macrolide in combination with ethambutol, with or without rifabutin: the most important intervention in this setting is to gain HIV control with the use of potent antiretroviral therapy. Treatment outcomes for many patients with MAC disease remain suboptimal, so new drugs and treatment regimens are greatly needed. Given the high rate of reinfection after cure, one of the greatest needs is a better understanding of where infection occurs and how this can be prevented.

Tofacitinib versus methotrexate in rheumatoid arthritis

BACKGROUND

Methotrexate is the most frequently used first-line antirheumatic drug. We report the findings of a phase 3 study of monotherapy with tofacitinib, an oral Janus kinase inhibitor, as compared with methotrexate monotherapy in patients with rheumatoid arthritis who had not previously received methotrexate or therapeutic doses of methotrexate.

METHODS

We randomly assigned 958 patients to receive 5 mg or 10 mg of tofacitinib twice daily or methotrexate at a dose that was incrementally increased to 20 mg per week over 8 weeks; 956 patients received a study drug. The coprimary end points at month 6 were the mean change from baseline in the van der Heijde modified total Sharp score (which ranges from 0 to 448, with higher scores indicating greater structural joint damage) and the proportion of patients with an American College of Rheumatology (ACR) 70 response (≥70% reduction in the number of both tender and swollen joints and ≥70% improvement in three of five other criteria: the patient's assessment of pain, level of disability, C-reactive protein level or erythrocyte sedimentation rate, global assessment of disease by the patient, and global assessment of disease by the physician).

RESULTS

Mean changes in the modified total Sharp score from baseline to month 6 were significantly smaller in the tofacitinib groups than in the methotrexate group, but changes were modest in all three groups (0.2 points in the 5-mg tofacitinib group and <0.1 point in the 10-mg tofacitinib group, as compared with 0.8 points in the methotrexate group [P<0.001 for both comparisons]). Among the patients receiving tofacitinib, 25.5% in the 5-mg group and 37.7% in the 10-mg group had an ACR 70 response at month 6, as compared with 12.0% of patients in the methotrexate group (P<0.001 for both comparisons). Herpes zoster developed in 31 of 770 patients who received tofacitinib (4.0%) and in 2 of 186 patients who received methotrexate (1.1%). Confirmed cases of cancer (including three cases of lymphoma) developed in 5 patients who received tofacitinib and in 1 patient who received methotrexate. Tofacitinib was associated with increases in creatinine levels and in low-density and high-density lipoprotein cholesterol levels.

CONCLUSIONS

In patients who had not previously received methotrexate or therapeutic doses of methotrexate, tofacitinib monotherapy was superior to methotrexate in reducing signs and symptoms of rheumatoid arthritis and inhibiting the progression of structural joint damage. The benefits of tofacitinib need to be considered in the context of the risks of adverse events. (Funded by Pfizer; ORAL Start ClinicalTrials.gov number, NCT01039688.).

Characterization of clinical and environmental Mycobacterium avium spp. isolates and their interaction with human macrophages

Members of the Mycobacterium avium complex (MAC) are naturally occurring bacteria in the environment. A link has been suggested between M. avium strains in drinking water and clinical isolates from infected individuals. There is a need to develop new screening methodologies that can identify specific virulence properties of M. avium isolates found in water that predict a level of risk to exposed individuals. In this work we have characterized 15 clinical and environmental M. avium spp. isolates provided by the US Environmental Protection Agency (EPA) to improve our understanding of the key processes involved in the binding, uptake and survival of these isolates in primary human macrophages. M. avium serovar 8 was predominant among the isolates studied. Different amounts and exposure of mannose-capped lipoarabinomannan (ManLAM) and glycopeptidolipids (GPLs), both major mycobacterial virulence factors, were found among the isolates studied. Reference clinical isolate 104 serovar 1 and clinical isolates 11 and 14 serovar 8 showed an increased association with macrophages. Serum opsonization increased the cell association and survival at 2 h post infection for all isolates. However, only the clinical isolates 104 and 3 among those tested showed an increased growth in primary human macrophages. The other isolates varied in their survival in these cells. Thus we conclude that the amounts of cell envelope ManLAM and GPL, as well as GPL serovar specificity are not the only important bacterial factors for dictating the early interactions of M. avium with human macrophages.

The mycobacterial glycopeptidolipids: structure, function, and their role in pathogenesis

Glycopeptidolipids (GPLs) are a class of glycolipids produced by several nontuberculosis-causing members of the Mycobacterium genus including pathogenic and nonpathogenic species. GPLs are expressed in different forms with production of highly antigenic, typeable serovar-specific GPLs in members of the Mycobacterium avium complex (MAC). M. avium and M. intracellulare, which comprise this complex, are slow-growing mycobacteria noted for producing disseminated infections in AIDS patients and pulmonary infections in non-AIDS patients. Previous studies have defined the gene cluster responsible for GPL biosynthesis and more recent work has characterized the function of the individual genes. Current research has also focused on the GPL's role in colony morphology, sliding motility, biofilm formation, immune modulation and virulence. These topics, along with new information on the enzymes involved in GPL biosynthesis, are the subject of this review.

Selective killing of Mycobacterium avium-infected macrophages by inhibition of phosphorylated signal transducer and activator of transcription type 1

Mycobacterium avium infects mononuclear phagocytes, which thereby become reservoirs for this pathogen. Currently recommended therapy does not ensure the eradication of intracellular bacteria. Here, we report that M. avium infection in macrophages activates the signal transducer and activator of transcription type 1 (STAT-1) signaling pathway. Fludarabine, an antileukemic drug active against cells that express STAT-1, selectively kills M. avium-infected macrophages. These findings suggest that phosphorylated STAT-1 can enhance the survival of macrophages, promoting their role as persistent reservoirs of M. avium. This work invites research on new combination therapeutic approaches that consist of fludarabine, to kill the macrophage reservoir, and antibacterial agents, to eliminate mycobacteria released from the dead cells.

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.

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.

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.

Sliding motility in mycobacteria

Mycobacteria are nonflagellated gram-positive microorganisms. Previously thought to be nonmotile, we show here that Mycobacterium smegmatis can spread on the surface of growth medium by a sliding mechanism. M. smegmatis spreads as a monolayer of cells which are arranged in pseudofilaments by close cell-to-cell contacts, predominantly along their longitudinal axis. The monolayer moves away from the inoculation point as a unit with only minor rearrangements. No extracellular structures such as pili or fimbriae appear to be involved in this process. The ability to translocate over the surface correlates with the presence of glycopeptidolipids, a mycobacterium-specific class of amphiphilic molecules located in the outermost layer of the cell envelope. We present evidence that surface motility is not restricted to M. smegmatis but is also a property of the slow-growing opportunistic pathogen M. avium. This form of motility could play an important role in surface colonization by mycobacteria in the environment as well as in the host.

Role of complement receptors in uptake of Mycobacterium avium by macrophages in vivo: evidence from studies using CD18-deficient mice

Mycobacterium avium is an intracellular pathogen that has been shown to invade macrophages by using complement receptors in vitro, but mycobacteria released from one cell can enter a second macrophage by using receptors different from complement receptors. Infection of CD18 (beta(2) integrin) knockout mice and the C57 BL/6 control mice led to comparable levels of tissue infection at 1 day, 2 days, 1 week, and 3 weeks following administration of bacteria. A histopathological study revealed similar granulomatous lesions in the two mouse strains, with comparable numbers of organisms. In addition, transmission electron microscopy of spleen tissues from both strains of mice showed bacteria inside macrophages. Our in vivo findings support the hypothesis that M. avium in the host is likely to use receptors other than CR3 and CR4 receptors to enter macrophages with increased efficiency.

Isolation of two subpopulations of Mycobacterium avium within human macrophages

Mycobacterium avium is an intracellular pathogen that is associated with disseminated infection in acquired immunodeficiency syndrome (AIDS) patients. Human monocyte-derived macrophages were infected with M. avium strain 101 and a quinolone (Bay y 3118) was used at 8 micrograms ml-1, a concentration that kills growing bacteria but fails to eliminate static organisms. Infected monolayers were treated with Bay y 3118 for 4 days and viable bacteria obtained from the lysis of macrophages were used to infect other macrophages without passage in media. The procedure was repeated five times, after which seven different subpopulations that failed to grow within macrophages were identified. While the DNA fingerprinting confirmed that all came from the same strain, three protein profiles were observed. Static subpopulations were not killed by cytokine-stimulated macrophages, in contrast to the replicating subpopulation. Three of the static subpopulation strains were shown to be auxotrophic for glutamic acid or methionine. All seven non-duplicating subpopulation strains grew well in complete 7H10 agar. The importance of a static subpopulation of M. avium within macrophages is presently unknown. It is possible, however, that the non-growing bacteria would persist within macrophages.

Observed differences in virulence-associated phenotypes between a human clinical isolate and a veterinary isolate of Mycobacterium avium

Mycobacterium avium, the most common opportunistic pathogen in patients with AIDS, is frequently isolated from a variety of environmental sources, but rarely can these environmental isolates be epidemiologically linked with isolates known to cause human disease. Using a number of in vitro tissue culture assays, we found significant pathogenic differences between a serotype 4 human clinical M. avium isolate and a serotype 2 veterinary isolate. Cell association of the patient strain with a human intestinal cell line was 1.7 times that of the veterinary strain. Growth of this clinical strain in human peripheral blood mononuclear cell-derived macrophages increased from 12-fold higher than that of the veterinary isolate after 2 days to 200-fold higher after 4 days. By the conclusion of each experiment, lysis of all examined host cell types and accumulation of cell debris were observed in infections with the human isolate, but monolayers remained relatively intact in the presence of the animal isolate. The two strains also differed in the ability to stimulate human immunodeficiency virus replication in coinfected host cells, with p24 antigen levels after 6 days threefold higher in the cells coinfected with the clinical strain than in those infected with the veterinary strain. If the genetic differences responsible for the phenotypes observed in these assays can be identified and characterized, it may be possible to determine which M. avium strains in the environment are potential human pathogens.

Heterodimer-loaded erythrocytes as bioreactors for slow delivery of the antiviral drug azidothymidine and the antimycobacterial drug ethambutol

Disseminated infection with Mycobacterium avium complex (MAC) remains the most common serious bacterial infection in patients with advanced AIDS. The organisms that make up this complex are found ubiquitously in the environment, yet rarely cause disseminated disease in nonimmunocompromised human patients; on the contrary, up to 50% of patients with AIDS may ultimately develop the pathology. Hence, therapeutic strategies able to inhibit HIV and Mycobacterium replication are needed. Because of the rapid plasma elimination and toxicity of the most commonly used drugs, daily multiple-drug therapies must often be continued throughout life, frequently causing major side effects and, as a consequence, poor patient compliance. Therefore, alternative strategies that reduce the toxicity of the drugs and allow prolonged application intervals are sorely needed. Since erythrocytes (RBCs) can behave as bioreactors able to convert impermeant prodrugs to membrane-releasable active drugs, new compounds (AZTpEMB, AZTpEMBpAZT, and AZTp2EMB) consisting of both an antiretroviral and an antimicrobial drug were designed and synthesized. Among these, only AZTp2EMB was hydrolyzed by erythrocyte enzymes and could be encapsulated inside RBCs. AZTp2EMB-loaded RBCs slowly released AZT and EMB in culture medium, reducing its concentration by one-half about every 48 hr of incubation at 37 degrees C. Moreover, when AZTp2EMB-loaded erythrocytes were incubated for 6 days in the presence of human macrophages infected with Mycobacterium avium (M. avium) a marked bactericidal effect (>1 log) was observed. Thus, AZTp2EMB-loaded erythrocytes could be used as endogenous bioreactors for AZT and EMB delivery in the treatment of HIV and M. avium infection.

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.

Change in colony morphology influences the virulence as well as the biochemical properties of the Mycobacterium avium complex

Factors that influence colony morphology are of crucial importance for drug development as well as for understanding the virulence of Mycobacterium avium complex (MAC) strains. The MAC 101 strain used in the present study grows as smooth transparent (SmT) colonies that tend to become opaque and pigmented when incubated for long periods of time. However, when MAC was passaged in animals, two types of colonies were recovered. The new rough transparent (RgT) colony morphology appeared more flat and transparent, having a central spot, irregular edges at times, and a dry, granular appearance like that of the rough mutants. In animal studies, the RgT bacilli multiplied at a much faster rate than that of the SmT bacilli, causing 60-80% mortality compared with the 10% mortality observed in mice infected with SmT. In vitro studies indicated that the SmT MAC did not grow and multiply as well in resident peritoneal macrophages as the RgT MAC did. The two morphotypes did not differ in their growth ratesin vitro but the RgT MAC failed to reduce dimethylthiazol-diphenyltetrazolium bromide (MTT), alamar blue and neutral red, suggesting that there might be significant changes in the cell wall or elsewhere causing changes in cellular permeability. These two morphotypes could serve as models for studying the biochemical markers or the identification of factors responsible for the virulence of the MAC.

The macrophage-induced gene mig as a marker for clinical pathogenicity and in vitro virulence of Mycobacterium avium complex strains

The capacity of 20 Mycobacterium avium complex isolates to multiply intracellularly in human monocyte-derived macrophages was assessed and correlated to the clinical relevance of each isolate and its reactivity with several candidate genetic virulence markers. The strongest correlation with a virulence phenotype was found for a conserved coding sequence of the macrophage-induced gene mig identified by a specific mig restriction fragment length polymorphism type.

Treatment with recombinant granulocyte colony-stimulating factor (Filgrastin) stimulates neutrophils and tissue macrophages and induces an effective non-specific response against Mycobacterium avium in mice

A role of neutrophils in the host response against Mycobacterium avium (MAC) has recently been suggested. To investigate this matter further, we determined the effect of granulocyte colony-stimulating factor (G-CSF) on the outcome of MAC infection in mice. C57BL/6bg+/bg- black mice were intravenously infected with 1 x 10(7) MAC and then divided into four experimental groups to receive G-CSF as follows: (i) 10 micrograms/kg/day; (ii) 50 micrograms/kg/day; (iii) 100 micrograms/kg/day; (iv) placebo control. Mice were killed at 2 and 4 weeks of treatment to determine the bacterial load of liver and spleen. Treatment with G-CSF at both 10 and 50 micrograms/kg/day doses significantly decreased the number of viable bacteria in liver and spleen after 2 weeks (approximately 70.5% and 69.0%, respectively), and after 4 weeks (approximately 53% and 52%, respectively, P < 0.05 compared with placebo control). Treatment with 100 micrograms/kg/day did not result in decrease of bacterial colony-forming units in the liver and spleen after 4 weeks. Administration of G-CSF induced interleukin-10 (IL-10) and IL-12 production by splenocytes. To examine if the protective effect of G-CSF was accompanied by the activation of phagocytic cells, blood neutrophils and splenic macrophages were purified from mice receiving G-CSF and their ability to kill MAC was examined ex vivo. Neutrophils and macrophages from G-CSF-treated mice were able to inhibit the growth of or to kill MAC ex vivo, while phagocytic cells from untreated control mice had no anti-MAC effect. These results suggest that activation of neutrophils appears to induce an effective non-specific host defence against MAC, and further studies should aim for better understanding of the mechanisms of protection.

The interaction between Mycobacterium and the macrophage analyzed by two-dimensional polyacrylamide gel electrophoresis

The intramacrophage pathogen Mycobacterium avium resides in a vacuole which displays unusual fusion characteristics, expressed as both a failure to mature into phagolysosomes and a continued access to the early recycling pathway. In contrast, compartments containing inert IgG-opsonized latex beads mature to phagolysosomes. Techniques were developed for the isolation of these particle-containing phagosomes from macrophages to facilitate analysis of phagosomal constituents by electrophoresis and autoradiography. Metabolic labeling of macrophages followed by phagosome isolation and two-dimensional polyacrylamide gel electrophoresis revealed only minor differences in the protein profiles between the M. avium and IgG-bead phagosomes despite the marked differences in the fusigenicity of the respective vacuoles. Pulse-chase labeling experiments revealed greater differences in the accessibility of Mycobacterium avium and IgG-bead phagosomes to newly synthesized proteins. These phagosome isolation techniques were extended to analyze the protein synthesis profile of intracellular M. avium for comparison with bacteria that were metabolically labeled in broth culture. Not surprisingly, the majority of polypeptides in the bacilli were common to both growth conditions. However, despite these similarities, intracellular M. avium express several unique proteins, most notably one abundant protein with a molecular weight of 51 kDa. In addition, the bacteria manifest a restricted set of proteins expressed while in stasis shortly after infection.

Mycobacterial growth and sensitivity to H2O2 killing in human monocytes in vitro

The intracellular growth and susceptibilities to killing by H2O2 in cultured human monocytes of a number of mycobacterial species including laboratory strains and clinical isolates of Mycobacterium tuberculosis, and Mycobacterium bovis bacillus Calmette-Guerin (BCG) and a clinical isolate of Mycobacterium avium-M. intracellulare were examined. The clinical isolate of M. avium-M. intracellulare did not replicate in freshly explanted monocytes (generation time of >400 h); BCG replicated with a generation time of 95 h, and M. tuberculosis strains CDC551, H37Rv, and H37Ra replicated with generation times of 24, 35, and 37 h, respectively, during the 4-day growth assay. When cultured in monocytes for 4 days, the mycobacteria were variably sensitive to H2O2-induced killing. A positive correlation between the generation time and percent killing of intracellular bacilli was observed. By comparison, mycobacterial strains were similarly sensitive to H2O2 treatment in cell-free culture media and in sonicated cell suspensions. Using a number of inhibitors of reactive oxygen intermediates we determined that other than catalase the inhibitors tested did not affect H2O2-induced killing of intracellular mycobacteria. Our studies suggest that the killing of mycobacteria growing in human monocytes in vitro by the addition of exogenous H2O2 is dependent on the susceptibility to a peroxide-induced killing pathway as well as on the intracellular growth rate of the mycobacteria.

Cloning, sequencing, and expression of the mig gene of Mycobacterium avium, which codes for a secreted macrophage-induced protein

Mycobacterium avium is an intracellular pathogen that has evolved to be a frequent cause of disseminated infection in immunocompromised patients. Although these bacilli are readily phagocytized, they are able to survive and even multiply within human macrophages. The process whereby mycobacteria circumvent the lytic functions of the macrophages is currently not well understood, but this is a key aspect in the pathogenicity of all pathogenic mycobacteria. Previously, we identified a gene in M. avium, designated mig (for macrophage-induced gene), the expression of which is induced when the bacilli grow in human macrophages (G. Plum and J. E. Clark-Curtiss, Infect. Immun. 62:476-483, 1994). In the present study we show that (i) the nucleotide sequence of the mig gene has an open reading frame of 295 amino acids with a strong bias for mycobacterial codon usage, (ii) the mig gene also codes for a putative signal peptide of 19 amino acid residues, (iii) mig is induced by acidity to be expressed as an early-secreted 30-kDa protein, and (iv) the Mig protein exhibits an AMP-binding domain signature. However, beyond this motif which is common to enzymes that activate a large variety of substrates, no homologies to known sequences are found. We also show that (v) Mycobacterium smegmatis strains expressing the Mig protein have a limited advantage for survival in macrophages. These findings may be concordant with a role of the mig gene in the virulence of M. avium.

Altered IL-1 expression and compartmentalization in monocytes from patients with AIDS stimulated with Mycobacterium avium complex

The pathophysiologic basis for the exuberant intracellular growth of Mycobacterium avium complex (MAC) in AIDS patients is unclear but may relate to altered expression of modulatory cytokines. Interleukin (IL)-1, IL-6, and TNF-alpha expression by monocytes from AIDS patients and healthy subjects (HS) stimulated with isogeneic MAC strains (SmT, smooth-transparent, virulent; SmD, smooth-domed, avirulent) was examined. Spontaneous cytokine production was not observed in patients with AIDS. MAC strains induced less IL-1 alpha and IL-1 beta release in AIDS patients than HS (P < 0.05). The ratio of cell-associated to supernatant IL-1 alpha also was increased in AIDS patients (P = 0.03). IL-1 beta mRNA expression paralleled protein release in either group of subjects. In both HS and AIDS patients, stimulation with SmD induced more IL-1 and TNF-alpha release by monocytes compared to SmT. In AIDS patients, SmD also induced greater IL-6 release than SmT (P < 0.01). Alterations in monocyte expression and compartmentalization of the regulatory cytokines IL-1 and IL-6 may enhance bacterial replication and contribute to the pathogenesis of MAC infection in AIDS.

Interaction of Mycobacterium avium with environmental amoebae enhances virulence

Environmental mycobacteria are a common cause of human infections. Recently, contaminated domestic water supplies have been suggested as a potential environmental source of several mycobacterial diseases. Since many of these mycobacterial species replicate best intracellularly, environmental hosts have been sought. In the present study, we examined the interaction of Mycobacterium avium with a potential protozoan host, the water-borne amoeba Acanthamoeba castellanii. We found that M. avium enters and replicates in A. castellanii. In addition, similar to that shown for mycobacteria within macrophages, M. avium inhibits lysosomal fusion and replicates in vacuoles that are tightly juxtaposed to the bacterial surfaces within amoebae. In order to determine whether growth of M. avium in amoebae plays a role in human infections, we tested the effects of this growth condition on virulence. We found that growth of M. avium in amoebae enhances both entry and intracellular replication compared to growth of bacteria in broth. Furthermore, amoeba-grown M. avium was also more virulent in the beige mouse model of infection. These data suggest a role for protozoa present in water environments as hosts for pathogenic mycobacteria, particularly M. avium.

Growth within macrophages increases the efficiency of Mycobacterium avium in invading other macrophages by a complement receptor-independent pathway

Infections caused by organisms of the Mycobacterium avium complex occur in approximately 50 to 60% of patients with AIDS. M. avium is an intracellular pathogen that survives and multiplies within mononuclear phagocytes. In this study, we investigated the uptake of M. avium grown within macrophages (intracellular growth M. avium [IG]) by a second macrophage compared with M. avium cultured in broth (extracellular growth M. avium [EG]). The results showed that IG was six- to eightfold more efficient than EG in entering macrophages. In addition, while an anti-CR3 antibody was able to inhibit approximately 60% of EG uptake by macrophages, it failed to inhibit the entry of IG. In contrast to EG, IG uptake into macrophages was significantly inhibited in the presence of anti-beta1-integrin and anti-transferrin receptor antibodies. Entry into macrophages by alternate receptors was associated with resistance to tumor necrosis factor alpha (TNF-alpha) stimulation. While stimulation with TNF-alpha resulted in inhibition of the growth of EG, it was not associated with inhibition of intracellular growth of IG. Investigation of the reason why M. avium is able to sense the changes in the intracellular environment triggering a change to the invasive phenotype suggests a direct relationship with macrophage apoptosis. These results suggest that intracellular growth is associated with novel mechanisms of M. avium uptake of macrophages and that those mechanisms appear to offer advantages to the bacteria in escaping the host defense.

Regulation of the expression of Mycobacterium avium complex proteins differs according to the environment within host cells

Mycobacterium avium is an intracellular organism that can infect a number of cell types such as macrophages and epithelial cells. Each one of these cells represents a different environment that requires specific adaptation from the bacterium. The effect of uptake of M. avium and M. smegmatis by both human monocyte-derived macrophages in culture for 6 days, and HT-29 intestinal mucosal cell line on the bacterial synthesis of proteins were comparatively examined. Incorporation of [35S]-methionine by the bacterium was measured at 30 min, 2, 4, and 24 h after infection. Effect of the uptake by cells was compared with bacteria not exposed to cells and bacteria submitted to different stresses such as heat, hyperosmolarity and acid pH. Uptake of M. avium by macrophages triggered the synthesis of 93, 65, 55 and 33 kDa, among other proteins in the bacteria. Between 2 and 4 h of exposure to the intracellular millieu, a number of additional proteins have their synthesis up-regulated such as 39, 31, 43, 42, 61 and 70 kDa. In contrast, uptake by epithelial cells is associated with the up-regulation of 27, 65, 71 and 72 kDa proteins, among others. In this case, exposure to the intracellular environment was associated with expression of a number of proteins that do not vary with time. The results of this study suggest that regulation of the expression of proteins in M, avium varies according to the mammalian cell bacteria they are exposed to, and is influenced by the stage of intracellular infection.

Mechanism of UVB-induced suppression of the immune response to Mycobacterium bovis bacillus Calmette-Guerin: role of cytokines on macrophage function

Previously we demonstrated that treatment of mice with either UVB radiation or supernatants derived from UVB-irradiated PAM 212 keratinocytes decreased the induction of the delayed-type hypersensitivity (DTH) response to Mycobacterium bovis bacillus Calmette-Guerin (BCG), impaired the clearance of bacteria from their lymphoid organs and also altered macrophage functions. In order to characterize the cytokines involved in these phenomena, UV-irradiated mice were injected with antibodies to interleukin-10 (IL-10), transforming growth factor-beta 1 (TGF-beta 1), or tumor necrosis factor-alpha (TNF-alpha). Injection of UVB-irradiated mice with anti-IL-10 immediately after UV irradiation restored the DTH response and reversed the UV-induced inhibition of bacterial clearance. Injection of UV-irradiated mice with anti-TGF-beta only partially restored the DTH response although it allowed a better clearance of BCG than injection of mice with the control antibody. In contrast, injection of anti-TNF-alpha did not affect the UVB-induced suppression of DTH or impaired bacterial clearance. Similarly, the ability of macrophages to phagocytose BCG and kill the intracellular organisms was restored to almost normal levels after injecting UV-irradiated mice with antibodies specific for IL-10 or TGF-beta. Injection of mice with either recombinant IL-10 or TGF-beta mimicked the effect of whole-body UV irradiation on immune function. These results suggest that IL-10 has a major role in UV-induced suppression of both DTH to BCG and impairment in the clearance of bacteria and that TGF-beta has a more significant role in blocking bacterial clearance. Furthermore, these cytokines seem to modulate immune responses by altering macrophage functions in UVB-irradiated mice.

H2O2 induces monocyte apoptosis and reduces viability of Mycobacterium avium-M. intracellulare within cultured human monocytes

Mycobacterium avium-M. intracellulare, an intracellular parasite of mononuclear phagocytes, rarely causes disease in immunocompetent individuals. In contrast, in human immunodeficiency virus type 1-infected patients, M. avium-M. intracellulare can infect almost every tissue and organ. This suggests that immunocompetent individuals have a protective mechanism to control or prevent the infection. How mycobacterial may be killed by the host immune response is unclear. We have recently reported that induction of apoptosis of Mycobacterium bovis BCG-infected macrophages with ATP4- was associated with killing of the intracellular mycobacteria. In the present study, a long-term culture of M. avium-M. intracellulare-infected monocytes was used to further evaluate the interaction between M. avium-M. intracellulare and primary human monocytes. In our system, M. avium-M. intracellulare parasitized the human monocytes and appeared to replicate slowly over 14 days within the host cells. To examine the role of apoptotic mechanisms in survival or death of intracellular mycobacteria, M. avium-M. intracellulare-infected human monocytes were treated with a monoclonal antibody to Fas receptor (APO-1/CD95) or with various concentrations of H2O2. Although both of these exogenous agents induced monocyte apoptosis, optimal killing (65% reduction in CFU) of intracellular M. avium-M. intracellulare was observed only when M. avium-M. intracellulare-infected cells were treated with 10 mM H2O2. Fas-induced apoptosis did not affect M. avium-M. intracellulare viability. Our results suggest that not all stimuli of monocyte apoptosis induce killing of intracellular M. avium-M. intracellulare. Since release of H2O2 following phagocytosis of mycobacteria has been documented, H2O2-induced apoptotic death of M. avium-M. intracellulare-infected monocytes and its association with killing of the intracellular bacilli may be a physiological mechanism of host defense against M. avium-M. intracellulare.

Interleukin-12-stimulated natural killer cells can activate human macrophages to inhibit growth of Mycobacterium avium

Interleukin-12 (IL-12) is a critical cytokine that affects many of the biological functions of NK cells and T cells. We have previously shown that both human and murine NK cells are important in host defense against Mycobacterium avium complex and act by secreting cytokines that induce macrophages to inhibit the growth of intracellular M. avium. To define the role of IL-12 in M. avium complex infection, we stimulated human NK cells with recombinant human IL-12 at 0.01 to 1 ng/ml for 24 h and used the tissue culture supernatant to treat human monocyte-derived macrophage monolayers infected with M. avium. IL-12 had no direct effect on M. avium-infected macrophages, but culture supernatant from IL-12-treated NK cells activated macrophages to inhibit the growth of intracellular M. avium in a dose-dependent manner. Stimulation of NK cells with IL-12 in combination with tumor necrosis factor alpha (TNF-alpha) or IL-1 increased the ability of supernatant from NK-cell culture to limit M. avium growth within macrophages, compared with that of culture supernatant from IL-12-treated NK cells. Results with supernatant from nonstimulated NK cells were similar to those with supernatant from untreated controls. Treatment of supernatant from IL-12-stimulated NK cells with anti-TNF-alpha, anti-granulocyte-macrophage colony-stimulating factor, but not anti-gamma interferon antibodies decreased the ability of NK-cell supernatant to induce anti-M. avium activity in infected macrophages. Treatment of macrophage monolayers with anti-transforming growth factor beta antibody before adding supernatant from IL-12-stimulated NK cells was associated with an increase of anti-M. avium activity compared with that of supernatant from IL-12-treated NK cells. These results suggest that IL-12 has a role in host defense against M. avium and that the effect of IL-12 is dependent chiefly on TNF-alpha and granulocyte-macrophage colony-stimulating factor.

Activities of poloxamer CRL8131 against Mycobacterium tuberculosis in vitro and in vivo

A poloxamer surfactant, CRL8131, was evaluated for activity against Mycobacterium tuberculosis (Erdman) by itself and in combination with antibiotics in broth culture, in a macrophage cell line assay, and in testing with mice. In the broth culture, CRL8131 suppressed the growth of M. tuberculosis and produced synergistic effects in combination with isoniazid, rifampin, and streptomycin. It also displayed synergy with isoniazid and rifampin against two drug-resistant isolates. In the macrophage cell line assay, CRL8131 produced a synergistic effect on intracellular killing of M. tuberculosis by isoniazid, rifampin, streptomycin, pyrazinamide, thiacetazone, D-cycloserine, ethionamide, amikacin, clindamycin, and p-aminosalicylic acid. It demonstrated no synergy or antagonism with ethambutol, gentamicin, kanamycin, ciprofloxacin, or nalidixic acid. Finally, with C57BL/6 mice infected with M. tuberculosis, a combination of CRL8131 and either thiacetazone or pyrazinamide produced 100% survival at 40 days whereas the antibiotics produced only 33% survival and CRL8131 produced 0% survival when used as single agents. This improved survival rate was associated with a significant reduction in the number of organisms in the lungs and spleens of infected mice.

Activities of roxithromycin against Mycobacterium avium infections in human macrophages and C57BL/6 mice

The activity of roxithromycin against three clinical isolates of Mycobacterium avium was compared with that of clarithromycin both in a model of infection of human monocyte-derived macrophages and in a model of established infection of C57BL/6 mice. In the cell culture model, roxithromycin and clarithromycin were bactericidal for strains MO-1 and N-92159 and bacteriostatic for strain N-93043. For the three strains, the differences between the intracellular activities of roxithromycin and clarithromycin were not singificant after 7 days of treatment. Mice were infected with the MO-1 strain. Drugs were given by gavage at a dosage of 200 mg/kg of body weight 6 days per week for 16 weeks starting 5 weeks after infection. At the end of treatment, clarithromycin was more effective than roxithromycin in lungs; roxithromycin was as effective as clarithromycin in spleens. Thus, the activity of roxithromycin was comparable to that of clarithromycin both in vitro and in vivo.

Enhancement of antibiotic susceptibility and suppression of Mycobacterium avium complex growth by poloxamer 331

The resistance of Mycobacterium avium complex (MAC) to antibiotics is thought to be enhanced by its outer glycolipid layer, which protects the organisms from antibiotics and host defense mechanisms. We hypothesized that surfactants which disrupt the lipid barrier might be of therapeutic value. We evaluated the ability of 10 poloxamer surfactants to inhibit the growth of MAC organisms and to potentiate antimycobacterial drug activity in broth culture using a radiometric assay. Very large, small, or hydrophilic poloxamers had little or no effect. However, certain hydrophobic poloxamers, especially P331, retarded the growth of most isolates of MAC and produced a synergistic effect with rifampin. The MIC of rifampin required to inhibit the growth of MAC was reduced from a mean of 14.6 micrograms/ml (range, 4 to > 32 micrograms/ml) to 1.4 micrograms/ml (range, < 1.125 to 4 micrograms/ml) by 1.0 mg of P331 per ml (P < 0.01). Enhancement of antibiotic susceptibility was observed with concentrations of poloxamer as low as 10 micrograms/ml. These studies suggest that P331 might be useful in increasing the effectiveness of antibiotic therapy of MAC infections.

Response to stimulation with recombinant cytokines and synthesis of cytokines by murine intestinal macrophages infected with the Mycobacterium avium complex

Current evidence suggests that the gut is the chief portal of entry for organisms of the Mycobacterium avium complex (MAC) in AIDS patients. Bacterial invasion of intestinal mucosa presumably occurs through epithelial cells, and M cells in the Peyer's patches, where the bacteria have contact with immunocompetent cells such as macrophages and T and B lymphocytes. As mucosal macrophages are probably the first line of defense against MAC, we examined their ability to inhibit intracellular growth of MAC when properly stimulated. Mouse intestinal macrophages were purified, infected with MAC 101, serovar 1, and MAC 86-2686, serovar 16, and subsequently stimulated with recombinant tumor necrosis factor alpha (TNF-alpha), gamma interferon (IFN-gamma), granulocyte-macrophage colony-stimulating factor (GM-CSF), or macrophage colony-stimulating factor (M-CSF). Viable intracellular bacteria were quantitated at 24 h after infection and again after 4 days of infection. Stimulation with TNF-alpha, IFN-gamma, and GM-CSF, but not M-CSF, was associated with mycobacteriostatic and/or mycobactericidal activity in macrophages. Treatment with 10(3) U of TNF-alpha, GM-CSF, and IFN-gamma per ml at 24 h prior to infection with MAC resulted in a significant enhancement in killing of MAC at 4 days after infection, compared with that observed for macrophages exposed to cytokines after infection. When stimulated with lipopolysaccharide or live MAC, intestinal macrophages had produced significantly less TNF-alpha and transforming growth factor beta than had splenic and peritoneal macrophages, although the levels of production of interleukin 6 and interleukin 10 among the three populations of cells were similar. Intestinal macrophages can be stimulated with cytokines to inhibit the intracellular growth of MAC, but they have differentiated abilities to produce cytokines which can modulate the anti-MAC immune response.

Recombinant cytokines for controlling mycobacterial infections

Knowing how mycobacteria exploit host cytokines to survive and which cytokines have important roles in host defense against mycobacteria should allow the use of these molecules in the treatment of mycobacterial infections. Both interleukin 2 and interferon gamma have been used to treat patients with leprosy, and granulocyte-macrophage colony-stimulating factor is presently being administered to AIDS patients infected with Mycobacterium avium.

A bone marrow-derived murine macrophage model for evaluating efficacy of antimycobacterial drugs under relevant physiological conditions

Even though the macrophage is the host cell for the intracellular bacterial parasite Mycobacterium avium, macrophages have undergone only limited evaluation as models for determining the capacities of antimycobacterial drugs to inhibit the growth of M. avium within this relevant intracellular environment. In the present study, we demonstrated that a panel of M. avium isolates could actively infect homogeneous monolayers of murine bone marrow-derived macrophages. A number of established and experimental antimycobacterial drugs were then added to these cultures at a range of concentrations, and their effects on the numbers of surviving bacilli were determined 8 days later. By plotting such numbers versus drug concentrations it was then possible to clearly distinguish between compounds with bactericidal activity (such as rifabutin and PD 125354) and those with bacteriostatic effects (such as clarithromycin), even though several of these compounds had very similar MICs. In addition, an estimate of the potential therapeutic efficiency of each drug could be made by determining the concentration needed to destroy an arbitrary percentage of the inoculum (in this case, the bactericidal concentration destroying 99% of the inoculum). Such values were considerably in excess of the MICs and may more realistically reflect the concentrations in serum required to effectively reduce the bacterial burden in vivo.

Characterization of the virulence of Mycobacterium avium complex (MAC) isolates in mice

The virulence of different isolates of MAC was studied in naturally susceptible BALB/c mice. In preliminary experiments, MAC bacteria forming smooth transparent colonies on solid media (SmT variants) were found to be virulent for BALB/c mice, causing progressive infection; smooth opaque (SmOp) were generally avirulent, being slowly eliminated from the infected organs; and rough (Rg) variants were either avirulent or as virulent as SmT variants. We chose to compare the virulence of different isolates of MAC of different origins, studying only the SmT morphotype. Strains of MAC isolated from naturally infected animals were those that most consistently caused progressive infections. AIDS patients-derived isolates were of intermediate virulence or devoid of virulence in mice. The environmental strains were eliminated from mice or did not proliferate. Strains of MAC isolated from individuals who were not infected by HIV varied in virulence from completely avirulent to highly virulent. There was no close correlation between virulence and restriction fragment length polymorphism (RFLP) type, although all highly virulent strains were of the A/I type. There was also no correlation between virulence analysed in vivo and the ability to grow in cultured macrophages.

Use of liposome preparation to treat mycobacterial infections

Infections caused by organisms of the genus mycobacteria, such as tuberculosis M. avium disseminated infection in AIDS patients and leprosy, are extremely common around the world. Mycobacteria are intracellular organisms that invade and multiply chiefly within phagocytic cells. Antibiotic resistance among mycobacteria is a growing concern. M. tuberculosis resistant to INH and rifampin are increasing in major urban centers of the developed and in the developing world. M. avium is characteristically resistant to most anti-tuberculosis antibiotics. Furthermore, therapy of mycobacterial infections takes a long time and most of the drugs have potential side effects and toxicity. In addition, mycobacteria is found within cells and antimicrobials need to be able to achieve adequate concentration within the compartment where mycobacteria is located. Liposome preparations, containing antibiotics, have a theoretical advantage in being able to deliver high concentrations of antimicrobials into the infected cell. Studies done thus far, in vitro and in vivo, have confirmed this premise, when comparing drug entrapped in liposomes with free drug. This paper summarizes the results obtained using liposome preparations to treat mycobacterial infections.

Search for the molecular basis of morphological variation in Mycobacterium avium

Isolates of Mycobacterium avium exhibit three different colonial variations: smooth domed (SmD), smooth transparent (SmT), and rough (Rg). Because the discrimination between morphotypes is founded on morphological rather than molecular principles and because of the absence of consensus over the relevance of morphology to pathogenesis and drug sensitivity, a comparative study at the protein level was undertaken. By direct immunization of BALB/c mice with the soluble sonicate of one of the morphotypes of M. avium serovar 2, eight monoclonal antibodies (MAbs) were identified, of which one was M. avium specific. Cross immunization of syngeneic mice with serum-absorbed antigens allowed the generation of 15 further MAbs; 11 were M. avium or M. avium complex specific, but none of them was morphotype specific. Subcellular fractions analyzed by electrophoresis showed similar profiles, with the exception of a cytosolic protein with a relative molecular mass of ca. 66 kDa (protein SmT 66), which was most highly expressed in SmT variants of M. avium serotypes 2 and 4. Because a well-known, ubiquitous stress-heat shock protein (hsp65) has a similar molecular mass, protein SmT 66 was compared with hsp65. Western blot (immunoblot) analyses using several cross-reacting MAbs and N-terminal amino acid sequencing established that this protein was not the ubiquitous stress protein. Thus, SmT 66 is the first product to be described which might be associated with the SmT morphotype.

Induction of Mycobacterium avium gene expression following phagocytosis by human macrophages

Little is known about the bacterial factors that enable pathogenic mycobacteria to survive and multiply within the macrophages of the infected host. By preparing cDNA from Mycobacterium avium bacilli grown in human-derived macrophages and in broth culture and using subtractive hybridization to remove commonly expressed genes, a procedure was developed to identify genes of M. avium that are specifically expressed when the bacilli are growing within macrophages. Total RNA was isolated from M. avium recovered 5 days after infection of human macrophages and from bacilli grown in vitro in broth. Mycobacterial mRNAs were converted to cDNA by reverse transcription. Biotin-modified cDNAs prepared from M. avium grown in broth culture were used to subtract the housekeeping genes from the cDNAs of the macrophage-derived M. avium. After each round of subtraction, a sample of the unsubtracted cDNA was amplified, labeled, and hybridized to cosmid clones of M. avium DNA. After three rounds of subtraction, the amplified DNA hybridized to approximately 1% of the cosmid clones under stringent conditions. Although the majority of the genes that are induced in phagocytized M. avium cells are expressed in the broth-grown bacilli, one DNA fragment that was identified coded for an mRNA that is highly specific for M. avium in phagosomes. This procedure will be especially useful for identifying genes that are expressed in response to growth in specific environments from organisms with genetic systems that are not well characterized.

Interleukin-1 is involved in mouse resistance to Mycobacterium avium

In this study, we examined the contribution of the monokine interleukin-1 (IL-1) in mouse resistance to the intracellular pathogen Mycobacterium avium. The effect of neutralizing endogenous IL-1 in mouse macrophage resistance to M. avium infection was investigated. Infection of mouse peritoneal macrophages with M. avium B101 was shown to result in significant IL-1 beta release by cells at 4 and 7 days postinfection. Addition of IL-1 receptor antagonist (IL-1ra) at doses of 5 micrograms daily, which neutralized endogenous IL-1, failed to significantly modify the intracellular growth of M. avium. Mice were injected with M. avium B101 by the intravenous route, and the growth of the mycobacteria was monitored in the organs of intact mice and in those of mice that received repeated high doses of IL-1ra. The infection with M. avium elicited the production of large amounts of IL-1 in the lungs, livers, and spleens. Repeated injections of IL-1ra into M. avium-infected mice resulted in moderately enhanced growth of the bacilli in the livers and spleens but in much enhanced growth in the lungs. The enhanced growth of M. avium in the lungs correlated with a diminished inflammatory influx of cells (particularly neutrophils) in the bronchoalveolar space. These data argue for a role for IL-1 in host resistance to M. avium infections.

Potential role of cytokines in disseminated mycobacterial infections

Organisms belonging to the Mycobacterium avium complex (MAC) are common pathogens in immunosuppressed and AIDS patients. This paper reviews the role of cytokines in the pathogenesis of MAC infection. MAC organisms mainly infect monocytes and macrophages, and the effect of HIV infection on susceptibility of macrophages to MAC infection is largely unknown. Both GM-CSF and tumour necrosis factor-alpha can induce mycobacteriostatic/mycobactericidal activity in MAC-infected macrophages. The activity of interferon-gamma on mycobacterial infection appears to be dependent on the type of macrophage: in murine peritoneal and human monocyte-derived macrophages, interferon-gamma does not inhibit the intracellular growth of MAC, whereas in intestinal macrophages interferon-gamma results in inhibition of MAC. Transforming growth factor-beta 1, interleukin-10 and interleukin-6 have all been shown to counteract the immunoactivating cytokines and MAC survival may be due to induction of these inhibitory cytokines within the macrophage. GM-CSF has been given to patients with disseminated MAC infection. Isolated macrophages from these patients demonstrated increased superoxide anion production and enhanced mycobacteriostatic/cidal activity compared with macrophages isolated from the same patients before GM-CSF treatment. These results suggest that GM-CSF may have potential in the treatment of MAC infection.

The Mycobacterium avium complex

Mycobacterium avium complex (MAC) disease emerged early in the epidemic of AIDS as one of the common opportunistic infections afflicting human immunodeficiency virus-infected patients. However, only over the past few years has a consensus developed about its significance to the morbidity and mortality of AIDS. M. avium was well known to mycobacteriologists decades before AIDS, and the MAC was known to cause disease, albeit uncommon, in humans and animals. The early interest in the MAC provided a basis for an explosion of studies over the past 10 years largely in response to the role of the MAC in AIDS opportunistic infection. Molecular techniques have been applied to the epidemiology of MAC disease as well as to a better understanding of the genetics of antimicrobial resistance. The interaction of the MAC with the immune system is complex, and putative MAC virulence factors appear to have a direct effect on the components of cellular immunity, including the regulation of cytokine expression and function. There now is compelling evidence that disseminated MAC disease in humans contributes to both a decrease in the quality of life and survival. Disseminated disease most commonly develops late in the course of AIDS as the CD4 cells are depleted below a critical threshold, but new therapies for prophylaxis and treatment offer considerable promise. These new therapeutic modalities are likely to be useful in the treatment of other forms of MAC disease in patients without AIDS. The laboratory diagnosis of MAC disease has focused on the detection of mycobacteria in the blood and tissues, and although the existing methods are largely adequate, there is need for improvement. Indeed, the successful treatment of MAC disease clearly will require an early and rapid detection of the MAC in clinical specimens long before the establishment of the characteristic overwhelming infection of bone marrow, liver, spleen, and other tissue. Also, a standard method of susceptibility testing is of increasing interest and importance as new effective antimicrobial agents are identified and evaluated. Antimicrobial resistance has already emerged as an important problem, and methods for circumventing resistance that use combination therapies are now being studied.

Infection with Mycobacterium avium induces production of interleukin-10 (IL-10), and administration of anti-IL-10 antibody is associated with enhanced resistance to infection in mice

Organisms of the Mycobacterium avium complex are associated with disseminated infection in patients with AIDS. The mechanisms that account for the survival of the intracellular bacteria are unknown. We document here that infection of C57BL/6 black mice with M. avium 101 triggered interleukin-10 (IL-10) production. The synthesis of IL-10 peaked after 2 weeks of infection and remained elevated throughout the period of infection. Treatment of M. avium-infected peritoneal macrophages with recombinant IL-10 suppressed the stimulatory effect of tumor necrosis factor alpha and granulocyte-macrophage colony-stimulating factor. To confirm the possible role of IL-10 in the infection in vivo, mice were infected with M. avium 101 and simultaneously received treatment with neutralizing anti-IL-10 antibody. After 4 weeks the animals were harvested and the numbers of viable bacteria were quantitated in the liver, spleen, and blood. The liver and spleen of animals receiving anti-IL-10 antibody had 2 to 3 log units fewer bacteria than did those of control animals. These results suggest a role for IL-10 in the pathogenesis of M. avium infection.

Impaired erythropoiesis in the acquired immunodeficiency syndrome with disseminated Mycobacterium avium complex

PURPOSE

Anemia is an important negative predictor for survival with disseminated Mycobacterium avium complex (MAC) infection in the acquired immunodeficiency syndrome (AIDS). We analyzed the differences in AIDS patients with and without MAC infection with regard to anemia, severity of human immunodeficiency virus (HIV) infection, bone marrow morphology, and bone marrow erythroid progenitor colony growth (BFU-E and CFU-E). In addition, we determined the in vitro effect of sera obtained from these patients on normal BFU-E and CFU-E. A possible role of macrophages in the suppression of erythropoiesis was examined by studying in vitro the effect of supernatants from MAC-infected macrophages on cultured BFU-E and CFU-E.

PATIENTS AND METHODS

Hematocrit, serum levels of p24 antigen, erythropoietin, and CD4-positive cell count were determined in 14 AIDS patients with and 24 without MAC infection. Bone marrow erythropoietic and granulocytic progenitor cells from 15 normal individuals, from 12 AIDS patients with MAC infection, and from 10 AIDS patients without MAC infection were cultured on methylcellulose. In addition, progenitor cells from normal individuals were cultured in the presence, and in the absence, of sera obtained from AIDS patients with (14), or without (24), MAC infection. Last, we studied the effect of supernatants (SNs) from MAC and Mycobacterium tuberculosis-infected macrophages on erythropoietic progenitor cell growth.

RESULTS

The anemia in AIDS patients with MAC infection was associated with a selective suppression of erythropoietic progenitors despite bone marrow morphology that was indistinguishable from that in patients without MAC infection. The degree of anemia could not be explained on the basis of severity of HIV infection or a deficiency of erythropoietin production. Bone marrow mononuclear cells from AIDS patients with MAC generated significantly fewer erythroid progenitor colonies (BFU-E and CFU-E) than equivalent cells from AIDS patients without MAC infection (p < 0.05). Sera from MAC-infected AIDS patients were markedly inhibitory to the erythroid progenitors as compared with sera from patients without MAC infection (p < 0.001). SNs from MAC-infected macrophages were markedly inhibitory to the erythroid progenitors (BFU-E and CFU-E) as compared with the myeloid progenitors (CFU-GM).

CONCLUSION

The profound anemia in MAC-infected AIDS patients is due to suppression of erythroid progenitors by a soluble factor(s) in the serum. The data suggest that the soluble factor(s) is probably elaborated by macrophages.

MICs and MBCs of clarithromycin against Mycobacterium avium within human macrophages

The inhibitory and bactericidal activities of clarithromycin were determined quantitatively against the intracellular populations of five Mycobacterium avium strains growing in monocyte-derived human macrophages. The MICs were 1.0 microgram/ml, and the MBCs ranged from 16.0 to 64.0 micrograms/ml; these values were similar to the MICs and MBCs found in broth cultures at pH 7.4 and were substantially lower than those found in broth cultures at pHs 6.8 and 5.0. Since the intracellular environment has a neutral or even an acidic pH, relatively low MICs and MBCs found in macrophage cultures can be associated with the fact that the drug concentrations in macrophages are substantially higher than those in the medium in which these cells are cultivated. Pretreatment of the macrophages 2 days prior to infection decreased the MICs twofold in comparison with results of experiments in which the drug was added to already infected macrophages.

Activity of defensins from human neutrophilic granulocytes against Mycobacterium avium-Mycobacterium intracellulare

We have examined the activity of defensins from human neutrophilic granulocytes against Mycobacterium avium-Mycobacterium intracellulare. M. avium-M. intracellulare at 2.5 x 10(6)/ml or 2.5 x 10(8)/ml was cultured in the presence of defensins at 37 degrees C from 4 to 48 h. After incubation, CFU were enumerated. Human neutrophil peptide 1 (HNP-1) at 5 micrograms/ml had the ability to kill M. avium-M. intracellulare. Treatment with HNP-1 resulted in significant (96.3 to 97.7%) killing of M. avium-M. intracellulare, even after taking clumping into consideration. This activity was not affected by the presence of calcium (0.5 and 1.0 mM), magnesium (0.5 and 1.0 mM), or sodium chloride (25, 50, and 100 mM). The optimal pH for bactericidal activity was higher than 5. We tested numerous M. avium-M. intracellulare strains, and HNP-1 was successful in killing every strain, although the degree of killing varied among them (34.2 to 87.2%). Additionally, this activity was independent of colonial morphology. We also examined the activity of HNP-2 and HNP-3 against M. avium-M. intracellulare and found that they were as effective in killing M. avium-M. intracellulare as HNP-1 was. These observations suggest that defensins may play an important role in the host defense against M. avium-M. intracellulare.