Immunomodulation of human peripheral blood mononuclear cell functions by defined lipid fractions of Mycobacterium avium

Acquired and genetic host susceptibility factors and microbial pathogenic factors that predispose to nontuberculous mycobacterial infections

Nontuberculous mycobacteria (NTM) are ubiquitous in the environment and human exposure is likely to be pervasive; yet, the occurrence of NTM-related diseases is relatively infrequent. This discrepancy suggests that host risk factors play an integral role in vulnerability to NTM infections. Isolated NTM lung disease (NTM-LD) is often due to underlying anatomical pulmonary or immune disorders, either of which may be acquired or genetic. However, many cases of NTM-LD have no known underlying risk factors and may be multigenic and/or multicausative. In contrast, extrapulmonary visceral or disseminated NTM diseases almost always have an underlying severe immunodeficiency, which may also be acquired or genetic. NTM cell wall components play a key role in pathogenesis and as inducers of the host immune response.

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.

Genetics of Capsular Polysaccharides and Cell Envelope (Glyco)lipids

This article summarizes what is currently known of the structures, physiological roles, involvement in pathogenicity, and biogenesis of a variety of noncovalently bound cell envelope lipids and glycoconjugates of Mycobacterium tuberculosis and other Mycobacterium species. Topics addressed in this article include phospholipids; phosphatidylinositol mannosides; triglycerides; isoprenoids and related compounds (polyprenyl phosphate, menaquinones, carotenoids, noncarotenoid cyclic isoprenoids); acyltrehaloses (lipooligosaccharides, trehalose mono- and di-mycolates, sulfolipids, di- and poly-acyltrehaloses); mannosyl-beta-1-phosphomycoketides; glycopeptidolipids; phthiocerol dimycocerosates, para-hydroxybenzoic acids, and phenolic glycolipids; mycobactins; mycolactones; and capsular polysaccharides.

Pathogenesis and risk factors for nontuberculous mycobacterial lung disease

Nontuberculous mycobacteria (NTM) infections are broadly classified as skin and soft tissue infections, isolated lung disease, and visceral or disseminated disease. The degree of underlying immune abnormalities varies between each classification. Skin and soft tissue infections are usually the result of iatrogenic or accidental inoculation of NTM in otherwise normal hosts. Visceral and disseminated NTM disease invariably occurs in individuals with more severe immunosuppression. Although the focus of this article is to discuss the pathogenesis of NTM lung disease, the risk factors of visceral/disseminated NTM disease are also summarized, as they provide insights into host-defense mechanisms against these organisms.

Mycobacterium tuberculosis keto-mycolic acid and macrophage nuclear receptor TR4 modulate foamy biogenesis in granulomas: a case of a heterologous and noncanonical ligand-receptor pair

The cell wall of Mycobacterium tuberculosis is configured of bioactive lipid classes that are essential for virulence and potentially involved in the formation of foamy macrophages (FMs) and granulomas. Our recent work established crosstalk between M. tuberculosis cell wall lipids and the host lipid-sensing nuclear receptor TR4. In this study, we have characterized, identified, and adopted a heterologous ligand keto-mycolic acid from among M. tuberculosis lipid repertoire for the host orphan NR TR4. Crosstalk between cell wall lipids and TR4 was analyzed by transactivation and promoter reporter assays. Mycolic acid (MA) was found to transactivate TR4 significantly compared with other cell wall lipids. Among the MA, the oxygenated form, keto-MA, was responsible for transactivation, and the identity was validated by TR4 binding assays followed by TLC and nuclear magnetic resonance. Isothermal titration calorimetry revealed that keto-MA binding to TR4 is energetically favorable. This keto-MA-TR4 axis seems to be essential to this oxygenated MA induction of FMs and granuloma formation as evaluated by in vitro and in vivo model of granuloma formation. TR4 binding with keto-MA features a unique association of host nuclear receptor with a bacterial lipid and adds to the presently known ligand repertoire beyond dietary lipids. Pharmacologic modulation of this heterologous axis may hold promise as an adjunct therapy to frontline tuberculosis drugs.

Cellular and humoral immunogenicity of Mycobacterium avium subsp. paratuberculosis specific lipopentapeptide antigens

Paratuberculosis caused by Mycobacterium avium subsp. paratuberculosis (MAP) is a chronic infectious disease affecting domestic and wild ruminants. Antigens currently used for the diagnosis of paratuberculosis are whole-cell derived crude preparations. The identification of MAP-specific antigens for the specific and early diagnosis of this infection is strongly needed. This study assessed the ability of the MAP-specific synthetic lipopeptide antigen Para-LP-01 to invoke specific serum antibody (Ab) and cell-mediated immune (CMI) responses in sheep experimentally exposed to MAP S strain. Responses were compared to those elicited by the crude whole-cell derived MAP 316v antigen (316v). Para-LP-01 induced a significant serum Ab response in MAP-infected sheep in comparison with unexposed or uninfected sheep, but failed to induce detectable CMI responses including production of IFN-γ, IL-10 and lymphoproliferation, unlike 316v which invoked both CMI and serum Ab responses in MAP-exposed sheep. Para-LP-01 is a suitable antigen for serodiagnosis of MAP-infection in sheep. The differential induction of humoral and CMI responses by lipid based antigens could enhance current understanding of the role played by cell-wall associated lipid antigens in the pathogenesis of MAP-infection.

Effect of lipoarabinomannan from Mycobacterium avium subsp avium in Freund's incomplete adjuvant on the immune response of cattle

The aim of the present study was to determine whether lipoarabinomannan (LAM), in combination with Freund's incomplete adjuvant (FIA), was able to improve cell-mediated and antibody-mediated immune responses against ovalbumin (OVA) in cattle. Twenty-three calves were assigned to four treatment groups, which were subcutaneously immunized with either OVA plus FIA, OVA plus FIA and LAM from Mycobacterium avium subsp avium, FIA plus LAM, or FIA alone. Lymphoproliferation, IFN-γ production and cell subpopulations on peripheral blood mononuclear cells before and 15 days after treatment were evaluated. Delayed hypersensitivity was evaluated on day 57. Specific humoral immune response was measured by ELISA. Inoculation with LAM induced higher levels of lymphoproliferation and IFN-γ production in response to ConA and OVA (P < 0.05). Specific antibody titers were similar in both OVA-immunized groups. Interestingly, our results showed that the use of LAM in vaccine preparations improved specific cell immune response evaluated by lymphoproliferation and IFN-γ production by at least 50 and 25%, respectively, in cattle without interfering with tuberculosis and paratuberculosis diagnosis.

Mannose receptor-dependent delay in phagosome maturation by Mycobacterium avium glycopeptidolipids

The ability of pathogenic mycobacteria to block phagosome-lysosome fusion is critical for its pathogenesis. The molecules expressed by mycobacteria that inhibit phagosome maturation and the mechanism of this inhibition have been extensively studied. Recent work has indicated that mannosylated lipoarabinomannan (ManLAM) isolated from Mycobacterium tuberculosis can function to delay phagosome-lysosome fusion and that this delay requires the interaction of ManLAM with the mannose receptor (MR). However, the molecules expressed by other pathogenic mycobacteria that function to inhibit phagosome maturation have not been well described. In the present study, we show that phagosomes containing silica beads coated with glycopeptidolipids (GPLs), a major surface component of Mycobacterium avium, showed limited acidification and delayed recruitment of late endosomal/lysosomal markers compared to those of phosphatidylcholine-coated beads. The carbohydrate component of the GPLs was required, as beads coated only with the lipopeptide core failed to delay phagosome-lysosome fusion. Moreover, the ability of GPLs to delay phagosome maturation was dependent on the macrophage expression of the MR. Using CHO cells expressing the MR, we confirmed that the GPLs bind this receptor. Finally, human monocyte-derived macrophages knocked down for MR expression showed increased M. avium phagosome-lysosome fusion relative to control cells. Together, the data indicate that GPLs can function to delay phagosome-lysosome fusion and suggest that GPLs, like ManLAM, work through the MR to mediate this activity.

Polyphasic taxonomic analysis establishes Mycobacterium indicus pranii as a distinct species

Background

Mycobacterium indicus pranii (MIP), popularly known as Mw, is a cultivable, non-pathogenic organism, which, based on its growth and metabolic properties, is classified in Runyon Group IV along with M. fortuitum, M. smegmatis and M. vaccae. The novelty of this bacterium was accredited to its immunological ability to undergo antigen driven blast transformation of leukocytes and delayed hypersensitivity skin test in leprosy patients, a disease endemic in the Indian sub-continent. Consequently, MIP has been extensively evaluated for its biochemical and immunological properties leading to its usage as an immunomodulator in leprosy and tuberculosis patients. However, owing to advances in sequencing and culture techniques, the citing of new strains with almost 100% similarity in the sequences of marker genes like 16S rRNA, has compromised the identity of MIP as a novel species. Hence, to define its precise taxonomic position, we have carried out polyphasic taxonomic studies on MIP that integrate its phenotypic, chemotaxonomic and molecular phylogenetic attributes.

Methodology/Principal Findings

The comparative analysis of 16S rRNA sequence of MIP by using BLAST algorithm at NCBI (nr database) revealed a similarity of ≥99% with M. intracellulare, M. arosiense, M. chimaera, M. seoulense, M. avium subsp. hominissuis, M. avium subsp. paratuberculosis and M. bohemicum. Further analysis with other widely used markers like rpoB and hsp65 could resolve the phylogenetic relationship between MIP and other closely related mycobacteria apart from M. intracellulare and M. chimaera, which shares ≥99% similarity with corresponding MIP orthologues. Molecular phylogenetic analysis, based on the concatenation of candidate orthologues of 16S rRNA, hsp65 and rpoB, also substantiated its distinctiveness from all the related organisms used in the analysis excluding M. intracellulare and M. chimaera with which it exhibited a close proximity. This necessitated further analysis of MIP with more sensitive and segregating parameters to ascertain its precise taxonomic position as a new species. The analysis of MIP and its comparison with other mycobacterial reference strains based on cellular and biochemical features, growth characteristics and chemotaxonomic studies like FAME profiling confirmed that MIP is uniquely endowed with diverse metabolic attributes that effectively distinguishes it from all the closely related mycobacteria including M. intracellulare and M. chimaera.

Conclusion

The results presented in this study coupled with the non-pathogenic nature and different biochemical and immunomodulatory properties of MIP affirm it as a distinct species belonging to M. avium complex (MAC). It is further proposed to use an earlier suggested name Mycobacterium indicus pranii for this newly established mycobacterial species. This study also exemplifies the growing need for a uniform, consensus based broader polyphasic frame work for the purpose of taxonomy and speciation, particularly in the genus Mycobacterium.

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.

Diacyltrehalose ofMycobacterium tuberculosisinhibits lipopolysaccharide- and mycobacteria-induced proinflammatory cytokine production in human monocytic cells

The lipids located in the outer layer of Mycobacterium tuberculosis, which include sulfolipid, phthiocerol dimycocerosate (PDIM), diacyltrehalose, and polyacyltrehalose, may play a role in host-pathogen interactions. These lipids were purified using thin-layer chromatography, and their ability to induce proinflammatory cytokines in human monocytes and in a human acute monocytic leukemia cell line (THP-1) was examined. None of the lipids tested induced significant interleukin (IL)-12p40 or tumor necrosis factor (TNF)-alpha production in monocytic cells. Diacyltrehalose significantly inhibited lipopolysaccharide- and M. tuberculosis-induced IL-12p40, TNF-alpha, and IL-6 productions in human monocytes, whereas other lipids had no effect. However, diacyltrehalose was unable to inhibit peptidoglycan-induced IL-12p40 production. These results suggest that diacyltrehalose is a mycobacterial factor capable of modulating host immune responses.

Mycobacterium tuberculosis and Mycobacterium avium inhibit IFN- gamma -induced gene expression by TLR2-dependent and independent pathways

Mycobacteria-infected macrophages are poor responders to interferon-gamma (IFN-gamma), resulting in decreased expression of IFN-gamma-induced genes. In the present study, we examined the inhibition of IFN-gamma-induced gene expression by Mycobacterium tuberculosis and four different Mycobacterium avium strains in mouse RAW264.7 macrophages. Gamma-irradiated M. tuberculosis inhibited mRNA expression of a panel of six different IFN- gamma-induced genes. All four of the M. avium strains completely inhibited IFN-gamma-induced expression of MHC class II Aalpha and Ebeta mRNA. However, the Mac101 strain, which is serovar 1, inhibited IFN-gamma induction of IFN regulatory factor-1 (IRF-1) and guanylate-binding protein-1 (GBP-1) mRNA to a greater extent than the other M. avium strains, which are serovar 2. In this study, we also show that mycobacteria inhibit gene expression by both toll-like receptor 2 (TLR2)-dependent and independent pathways. The inhibition of IFN-gamma-induced gene expression by M. avium was reduced but not completely blocked in macrophages from TLR2(/) mice. IFN-gamma-induced gene expression was also inhibited by mycobacteria in RAW264.7 cells expressing dominantnegative TLR2 or myeloid differentiation factor 88 (MyD88), further indicating the existence of a pathway independent of TLR2 and MyD88. These data suggest that mycobacteria inhibit IFN-gamma-induced gene expression by multiple pathways involving both TLR2 and non-TLR receptors.

Serotype-specific modulation of human monocyte functions by glycopeptidolipid (GPL) isolated from Mycobacterium avium complex

Immunomodulating activity of glycopeptidolipids (GPL), separated from different serovars of Mycobacterium avium complex (MAC), on macrophage functions was compared. When peripheral blood mononuclear cells (PBMC), from healthy donors showing strongly positive reactions to mycobacterial purified protein derivatives (PPD), were incubated with heat-killed Staphylococcus aureus coated with GPL serovar 4, phagocytosis of monocytes increased in dose-dependent manner. However, coating with GPL serovar 9 did not show any effects. After phagocytosis of heat-killed S. aureus, the phagosome-lysosome (P-L) fusion in monocytes was inhibited dose-dependently by coating of S. aureus with GPL serovar 4, but not serovar 9. These results indicate that GPL serovar 4 facilitates invasion of MAC into monocytes and renders resistance to bactericidal reactions due to the inhibition of P-L fusion. Regarding accessory function of macrophages in proliferative responses of T cells, the addition of GPL serovar 4 to cultures resulted in significant inhibition of anti-CD3 monoclonal antibody (mAb)-induced proliferation, whereas both serovar GPLs did not cause reduction of cell viability. Furthermore, the PPD-specific T cell proliferative response was downregulated markedly by GPL serovar 4, but weakly suppressed by GPL serovar 9. These results indicated that the immunomodulating activity of GPL on macrophage functions is serovar-dependent.

Utilization of a ts-sacB selection system for the generation of a Mycobacterium avium serovar-8 specific glycopeptidolipid allelic exchange mutant

Background

Mycobacterium avium are ubiquitous environmental organisms and a cause of disseminated infection in patients with end-stage AIDS. The glycopeptidolipids (GPL) of M. avium are proposed to participate in the pathogenesis of this organism, however, establishment of a clear role for GPL in disease production has been limited by the inability to genetically manipulate M. avium.

Methods

To be able to study the role of the GPL in M. avium pathogenesis, a ts-sacB selection system, not previously used in M. avium, was employed as a means to achieve homologous recombination for the rhamnosyltransferase (rtfA) gene of a pathogenic serovar 8 strain of M. avium to prevent addition of serovar-specific sugars to rhamnose of the fatty acyl-peptide backbone of GPL. The genotype of the resultant rtfA mutant was confirmed by polymerase chain reaction and southern hybridization. Disruption in the proximal sugar of the haptenic oligosaccharide resulted in the loss of serovar specific GPL with no change in the pattern of non-serovar specific GPL moieties as shown by thin layer chromatography and gas chromatography/mass spectrometry. Complementation of wild type (wt) rtfA in trans through an integrative plasmid restored serovar-8 specific GPL expression identical to wt serovar 8 parent strain.

Results

In this study, we affirm our results that rtfA encodes an enzyme responsible for the transfer of Rha to 6d-Tal and provide evidence of a second allelic exchange mutagenesis system suitable for M. avium.

Conclusion

We report the second allelic exchange system for M. avium utilizing ts-sacB as double-negative and xylE as positive counter-selection markers, respectively. This system of allelic exchange would be especially useful for M. avium strains that demonstrate significant isoniazid (INH) resistance despite transformation with katG. Through the construction of mutants in GPL or other mycobacterial components, their roles in M. avium pathogenesis, biosynthesis, or drug resistance can be studied in a consistent manner.

Biosynthetic specificity of the rhamnosyltransferase gene of Mycobacterium avium serovar 2 as determined by allelic exchange mutagenesis

In prior studies, through recombinant expression inMycobacterium smegmatis, thertfAgene ofMycobacterium aviumwas shown to encode a rhamnosyltransferase that catalyses the addition of rhamnose (Rha) to the 6-deoxytalose of serovar 2-specific glycopeptidolipid (GPL). Whether RtfA also catalyses the transfer of Rha to the alaninol of the lipopeptide core is unknown. An isogenicrtfAmutant ofM. aviumserovar 2 strain TMC724 was derived using a novel allelic exchange mutagenesis system utilizing a multicopy plasmid that contained thekatGgene ofMycobacterium bovisand the gene encoding green fluorescent protein (gfp). Overexpression of KatG inM. aviumresulted in increased susceptibility to isoniazid, thus providing counter-selection by enriching for clones that had lost plasmid DNA. Plasmid loss was confirmed by screening forgfp-negative clones to select putative allelic exchange mutants. Two exchange mutants were created, confirmed by Southern hybridization, and demonstrated loss of serovar 2-specific GPL by thin-layer chromatography (TLC). Gas chromatography of alditol acetate derivatives revealed the loss of Rha and the terminal 2,3-O-Me-fucose and preservation of 3-O-Me-Rha and 3,4-O-Me-Rha substituents at the terminal alaninol of the lipopeptide core. Complementation ofrtfAin transthrough an integrative plasmid restored serovar 2-specific GPL expression identical to wild-type TMC724. This result shows thatrtfAencodes an enzyme responsible only for the transfer of Rha to the serovar 2-specific oligosaccharide and provides a system of allelic exchange forM. aviumas a tool for future genetic studies involving this species.

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.

How to establish a lasting relationship with your host: lessons learned from Mycobacterium spp

Mycobacterium spp. enjoy an intracellular lifestyle that is fatal to most microorganisms. Bacilli persist and multiply within mononuclear phagocytes in the face of defences ranging from toxic oxygen and nitrogen radicals, acidic proteases and bactericidal peptides. Uptake of Mycobacterium by phagocytes results in the de novo formation of a phagosome, which is manipulated by the pathogen to accommodate its needs for intracellular survival and replication. The present review describes the intracellular compartment occupied by Mycobacterium spp. and presents current ideas on how mycobacteria may establish this niche, placing special emphasis on the involvement of mycobacterial cell wall lipids.

Influence of the glycopeptidic moiety of mycobacterial glycopeptidolipids on their lateral organization in phospholipid monolayers

Glycopeptidolipids (GPLs) from the cell wall of opportunistic pathogenic mycobacteria are potential factors of pathogenicity which can interact with biological membranes. GPL suspensions uncouple oxidative phosphorylation of mitochondria and increase membrane permeability of liposomes. Heavily glycosylated GPLs are less active than lightly glycosylated ones. GPL-phospholipid interactions into preformed mixed films at the air-water interface were investigated in order to understand the permeabilization efficiency differences among GPLs. Polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) was used to determine, in situ, the organization of GPL and of 1,2-di(perdeuteropalmitoyl)phosphatidylcholine (DPPC) molecules in mixed films. Compression isotherms of GPL alone or mixed with DPPC in various proportions showed that the less the GPL was glycosylated the higher its miscibility with DPPC. PMIRRAS studies indicated that low miscibility may result from large self-association of GPL molecules in beta-sheet structures. Low glycosylated GPL molecules increased disorder of DPPC acyl chains. Based on these results, an explanatory model is proposed for membrane permeabilization. Increase of passive permeability may arise from disruption of phospholipid packing induced by GPL molecules. GPL segregation is proposed as the cause of low activity of GPL with high sugar content, by decreasing the number of GPL molecules interacting with phospholipids.

Exposure of human peripheral blood mononuclear cells to total lipids and serovar-specific glycopeptidolipids from Mycobacterium avium serovars 4 and 8 results in inhibition of TH1-type responses

Previous studies have suggested that large quantities of bacterial lipids may accumulate and persist within host cells during chronic stages of Mycobacterium avium infections. This study intended to assess the ability of purified M. avium lipids to affect TH-1-type responses in human peripheral blood mononuclear cells (PBMC) from healthy donors. PBMC were exposed to total lipids and serovar-specific glycopeptidolipids (GPL) extracted from M. avium serovars 4 and 8, which have been reported to predominate as opportunistic infection among AIDS patients. After 24 h exposure to lipids followed by PHA/PMA treatment, IL-2 and IFN-gamma were assayed in the supernatants. Reverse transcriptase polymerase chain reaction (RT-PCR) was used for a semiquantitative estimation of mRNA for IL-2 and IFN-gamma in cell pellets at various time points. Exposure of PBMC to M. avium total lipids significantly suppressed PHA/PMA-induced secretion of IL-2 and IFN-gamma as determined by ELISA. The GPL antigens from serovar 4 were more efficient at inhibiting TH-1 responses than GPL from serovar 8. CD4(+)T-lymphocyte enrichment of PBMC demonstrated that suppression by M. avium lipids was intact without the presence of other cell populations such as monocytes and B-cells. Preliminary RT-PCR experiments showed that the secretion of TH-1 cytokines was partially affected at the transcriptional level. The results obtained showed that M. avium lipids are indeed able to modify the induction of TH-1-type cytokines by human PBMC, and suggest that accumulation of M. avium lipids in the chronic stages of infection may play an important role in the pathogenesis of HIV infection.

Trafficking and release of mycobacterial lipids from infected macrophages

Analysis of infected macrophages revealed that lipid-containing moieties of the mycobacterial cell wall are actively trafficked out of the mycobacterial vacuole. To facilitate the analysis of vesicular trafficking from mycobacteria-containing phagosomes, surface-exposed carbohydrates were labeled with hydrazide-tagged markers. The distribution of labeled carbohydrate/lipid moieties and subsequent interaction with cellular compartments were analyzed by immunoelectron microscopy and by fluorescence microscopy of live cells. The released mycobacterial constituents were associated with several intracellular organelles and were enriched strikingly in tubular endocytic compartments. Subcellular fractionation of infected macrophages by density gradient electrophoresis showed temporal movement of labeled bacterial constituents through early and late endosomes. Thin layer chromatography analysis of these subcellular fractions confirmed their lipid nature and revealed five dominant bacteria-derived species. These mycobacterial lipids were also found in extracellular vesicles isolated from the medium and could be observed in un-infected 'bystander' cells. Their transfer to bystander cells could expand the bacteria's sphere of influence beyond the immediate confines of the host cell.

Lymphoproliferative responses to mitogens and prepared antigens of M. avium complex in patients with HIV infection

Published reports have demonstrated that antigens of Mycobacterium avium complex (MAC) can suppress the normal response to mitogens in lymphoproliferation assays. We therefore studied the lymphoproliferative (LP) function of PBMC from 55 HIV-infected patients and 16 controls in response to mitogens with and without MAC antigen. As expected, LP responses decline with progressive decline in CD4 count; MAC antigen in combination with PHA further suppresses that response in a dose-dependent manner. More relevant were the LP responses in those with CD4 counts less than 100. All patients with MAC disease had poor responses (stimulation index, SI < 10) to PHA or anti-CD3 with or without MAC antigen. Those who did not have nor subsequently developed MAC were both good (SI > 10) or poor responders (SI < 10). The suppressive effect of MAC on lymphocyte function may serve as a weak virulence factor which is only relevant in severely immunocompromised HIV patients.

Altered expression profile of the surface glycopeptidolipids in drug-resistant clinical isolates of Mycobacterium avium complex

Members of the Mycobacterium avium complex are the most frequently encountered opportunistic bacterial pathogens among patients in the advanced stage of AIDS. Two clinical isolates of the same strain, numbers 397 and 417, were obtained from an AIDS patient with disseminated M. avium complex infection before and after treatment with a regimen of clarithromycin and ethambutol. To identify the biochemical consequence of drug treatment, the expression and chemical composition of their major cell wall constituents, the arabinogalactan, lipoarabinomannan, and the surface glycopeptidolipids (GPL), were critically examined. Through thin layer chromatography, mass spectrometry, and chemical analysis, it was found that the GPL expression profiles differ significantly in that several apolar GPLs were overexpressed in the clinically resistant 417 isolate at the expense of the serotype 1 polar GPL, which was the single predominant band in the ethambutol-susceptible 397 isolate. Thus, instead of additional rhamnosylation on the 6-deoxytalose (6-dTal) appendage to give the serotype 1-specific disaccharide hapten, the accumulation of this nonextended apolar GPL probably provided more precursor substrate available for further nonsaccharide substitutions including a higher degree of O-methylation to give 3-O-Me-6-dTal and the unusual 4-O-sulfation on 6-dTal. Further data showed that this alteration effectively neutralized ethambutol, which is known to inhibit arabinan synthesis. Thus, in contrast with derived Emb-resistant mutants of Mycobacterium smegmatis or Mycobacterium tuberculosis, which are devoid of a surface GPL layer, the lipoarabinomannan from resistant 417 isolate grown in the presence of this drug was not apparently truncated.

Use of Mono Mac 6 human monocytic cell line and J774 murine macrophage cell line in parallel antimycobacterial drug studies

The Mono Mac 6 (MM6) human monocytic cell line was evaluated with the established J774 murine macrophage cell line to ascertain its effectiveness in determining the intracellular activities of antimycobacterial drugs. Cells were infected with Mycobacterium tuberculosis H37Ra and treated with drug concentrations corresponding to the MICs, as well as to threefold higher than and threefold less than the MICs. Changes in CFU were compared after 7 days to determine significant differences between treated and nontreated groups. The results suggest that MM6 will make a useful model for testing the intracellular activities of antituberculosis drugs.

T-cell lung granulomas induced by sepharose-coupled Mycobacterium tuberculosis protein antigens: immunosuppressive phenomena reversed with cyclophosphamide and indomethacin

We induced lung granulomas in BALB/c mice by intratracheal instillation of Sepharose beads coated with a Mycobacterium tuberculosis protein extract. Granulomas composed of macrophages and lymphocytes were induced. The granulomatous reaction reached its peak 3-7 days after challenge and lasted for approximately 1 month. Immunolabelling of tissue sections and bronchial washings revealed that granulomas were predominantly composed of T lymphocytes with the cytotoxic-suppressor phenotype (CD8+). Granulomas were associated with a significant decrease in anti-mycobacterial immunity manifested by a drop in delayed-type hypersensitivity reactions and antibody titres. The immunosuppressive phenomena were abolished with cyclophosphamide or indomethacin. Control granulomas induced with methylated bovine serum albumin (BSA) were smaller and composed by similar numbers of CD4+ and CD8+ cells. BSA granulomas did not alter antibody titres but they decreased delayed-type hypersensitivity to BSA which was restored to normal with indomethacin but not with cyclophosphamide. Our findings show that mycobacterial proteins anchored to Sepharose beads are granulomatogenic and that they preferentially recruit CD8+ cells which, together with locally produced prostaglandins, down-modulate cell-mediated and humoral immunity to mycobacterial antigens.

Immunomodulatory spectrum of lipids associated with Mycobacterium avium serovar 8

Lipid fractions obtained from Mycobacterium avium serovar 8 were assessed for the ability to affect various immune functions of human peripheral blood mononuclear cells (PBM). Lipids included a total lipid fraction and fractions eluted from silicic acid column separation of that total lipid fraction, using chloroform and chloroform-methanol combinations. Lipid fractions were assayed for total carbohydrate and total 6-deoxyhexose content and were assessed for the ability to influence human macrophage function and the capacity to induce secretion of prostaglandin E2 (PGE2) and tumor necrosis factor alpha in PBM. The total lipid and serovar-specific glycopeptidolipid (GPL) fractions both induced significant levels of tumor necrosis factor alpha, as well as PGE2, in PBM exposed to a sublethal concentration of 100 micrograms lipid per 2 x 10(6) cells. In addition, the same concentrations of the 5 to 7% and GPL fractions induced significant levels of leukotriene B4 in PBM. Comparison of carbohydrate and 6-deoxyhexose contents of each fraction suggested a relationship to carbohydrate content and ability of fractions to induce immune modulator secretion. Analysis of GPL fractions from M. avium serovars 4 and 20 revealed that those GPL lacked the ability to induce PGE2. These results are explained by considering the difference in the carbohydrate residues of the oligosaccharide moieties.

Potential drug targets for Mycobacterium avium defined by radiometric drug-inhibitor combination techniques

Previously established radiometric techniques were used to assess the effectiveness of combined antimicrobial drug-inhibitory drug (drug-inhibitor) treatment on two clinical isolates of the Mycobacterium avium complex representing three colony variants: smooth opaque (dome) (SmO), smooth transparent (SmT), and rough (Rg). All variants were identified as members of the M. avium complex; however, only the SmT colony type of strain 373 possessed characteristic serovar-specific glycopeptidolipid (GPL) antigens. MICs, determined radiometrically, of drugs with the potential to inhibit the biosynthesis of GPL antigens or other cell envelope constituents were similar for all strains. These drugs included cerulenin, N-carbamyl-DL-phenylalanine, N-carbamyl-L-isoleucine, trans-cinnamic acid, ethambutol, 1-fluoro-1-deoxy-beta-D-glucose, 2-deoxy-D-glucose, and m-fluoro-phenylalanine. The MICs of the antimicrobial drugs amikacin, sparfloxacin, and clarithromycin varied, but overall the MICs for the SmO variant were the lowest. Radiometric assessment of drug-inhibitor combinations by using established x/y determinations revealed enhanced activity when either ethambutol or cerulenin were used in combination with all antimicrobial agents for all variants except the Rg variant of strain 424, for which ethambutol was not effective. Enhanced activity with amino acid analogs was observed with the Rg colony variants of strains 373 and 424. Two potential sites for drug targeting were identified: fatty acid synthesis, for all strains assayed, and peptide biosynthesis, particularly for Rg colony variants that possess previously identified phenylalanine-containing lipopeptides as potential targets for future drug development.