Chemical and immunological studies on mycobacterial polysaccharides. 1. Purification and properties of polysaccharides from human tubercle bacilli

GlfT1 down-regulation affects Mycobacterium tuberculosis biofilm formation and its in-vitro and in-vivo survival

Mycobacterial galactan biosynthesis is critical for cell viability and growth, therefore an effort was made to study galactofuranosyl transferase 1, encoded by MRA_3822 in Mycobacterium tuberculosis H37Ra (Mtb-Ra). Galactofuranosyl transferases are involved in the biosynthesis of mycobacterial cell wall galactan chain and have been shown to be essential for in-vitro growth of Mycobacterium tuberculosis. In Mtb-Ra and Mycobacterium tuberculosis H37Rv (Mtb-Rv), two galactofuranosyl transferases are present, GlfT1 acts as initiator of galactan biosynthesis and GlfT2 continues with the subsequent polymerization events. GlfT2 has been well studied however GlfT1 inhibition/down-regulation and its effect on mycobacterial survival fitness has not been evaluated. To study the Mtb-Ra survival after GlfT1 silencing, Mtb-Ra knockdown and complemented strains were developed. In this study we show that GlfT1 down-regulation leads to increased susceptibility to ethambutol. Expression of glfT1 was up-regulated in the presence of ethambutol, and also in the presence of oxidative and nitrosative stress and upon exposure to low pH. Also, reduced biofilm formation, increased accumulation of ethidium bromide, and reduced tolerance to peroxide, nitric oxide and acid stress, were observed. The present study also demonstrates that GlfT1 down-regulation leads to reduced survival of Mtb-Ra in macrophages and in mice.

Strategies for Using Muramyl Peptides - Modulators of Innate Immunity of Bacterial Origin - in Medicine

The spread of infectious diseases is rampant. The emergence of new infections, the irrational use of antibiotics in medicine and their widespread use in agriculture contribute to the emergence of microorganisms that are resistant to antimicrobial drugs. By 2050, mortality from antibiotic-resistant strains of bacteria is projected to increase up to 10 million people per year, which will exceed mortality from cancer. Mutations in bacteria and viruses are occurring faster than new drugs and vaccines are being introduced to the market. In search of effective protection against infections, new strategies and approaches are being developed, one of which is the use of innate immunity activators in combination with etiotropic chemotherapy drugs. Muramyl peptides, which are part of peptidoglycan of cell walls of all known bacteria, regularly formed in the body during the breakdown of microflora and considered to be natural regulators of immunity. Their interaction with intracellular receptors launches a sequence of processes that ultimately leads to the increased expression of genes of MHC molecules, pro-inflammatory mediators, cytokines and their soluble and membrane-associated receptors. As a result, all subpopulations of immunocompetent cells are activated: macrophages and dendritic cells, neutrophils, T-, B- lymphocytes and natural killer cells for an adequate response to foreign or transformed antigens, manifested both in the regulation of the inflammatory response and in providing immunological tolerance. Muramyl peptides take part in the process of hematopoiesis, stimulating production of colony-stimulating factors, which is the basis for their use in the treatment of oncological diseases. In this review we highlight clinical trials of drugs based on muramyl peptides, as well as clinical efficacy of drugs mifamurtide, lycopid, liasten and polimuramil. Such a multifactorial effect of muramyl peptides and a well-known mechanism of activity make them promising drugs in the treatment and preventing of infectious, allergic and oncological diseases, and in the composition of vaccines.

The Mycobacterial Cell Wall--Peptidoglycan and Arabinogalactan

The mycobacterial bacillus is encompassed by a remarkably elaborate cell wall structure. The mycolyl-arabinogalactan-peptidoglycan (mAGP) complex is essential for the viability of Mycobacterium tuberculosis and maintains a robust basal structure supporting the upper "myco-membrane." M. tuberculosis peptidoglycan, although appearing to be unexceptional at first glance, contains a number of unique molecular subtleties that become particularly important as the TB-bacilli enters into nonreplicative growth during dormancy. Arabinogalactan, a highly branched polysaccharide, serves to connect peptidoglycan with the outer mycolic acid layer, and a variety of unique glycolsyltransferases are used for its assembly. In this review, we shall explore the microbial chemistry of this unique heteropolysacchride, examine the molecular genetics that underpins its fabrication, and discuss how the essential biosynthetic process might be exploited for the development of future anti-TB chemotherapies.

Polysaccharides of Mycobacterium bovis Ushi 10, Mycobacterium smegmatis, Mycobacterium phlei, and Atypical Mycobacterium P1

Four kinds of polysaccharides, glucan, mannan, arabinomannan, and arabinogalactan, were purified from the defatted cells of four strains of mycobacteria. By the chemical and immunological analyses, we concluded that arabinomannan and arabinogalactan are common serologically active polysaccharides in mycobacteria.

Mycobacterial lipoarabinomannan: an extraordinary lipoheteroglycan with profound physiological effects

Detailed structural and functional studies over the last decade have led to current recognition of the mycobacterial lipoarabinomannan (LAM) as a phosphatidylinositol anchored lipoglycan with diverse biological activities. Fatty acylation has been demonstrated to be essential for LAM to maintain its functional integrity although the focus has largely been on the arabinan motifs and the terminal capping function. It has recently been shown that the mannose caps may be involved not only in attenuating host immune response, but also in mediating the binding of mycobacteria to and subsequent entry into macrophages. This may further be linked to an intracellular trafficking pathway through which LAM is thought to be presented by CD1 to subsets of T-cells. The implication of LAM as major histocompatibility complex (MHC)-independent T-cell epitope and the ensuing immune response is an area of intensive studies. Another recent focus of research is the biosynthesis of arabinan which has been shown to be inhibitable by the anti-tuberculosis drug, ethambutol. The phenomenon of truncated LAM as synthesized by ethambutol resistant strains provides an invaluable handle for dissecting the array of arabinosyltransferases involved, as well as generating much needed structural variants for further structural and functional studies. It is hoped that with more systematic investigations based on clinical isolates and human cell lines, the true significance of LAM in the immunopathogenesis of tuberculosis and leprosy can eventually be explained.

Biosynthesis of mycobacterial lipoarabinomannan

The mycobacterial lipoglycans, lipomannan (LM) and lipoarabinomannan (LAM), are potent immunomodulators in tuberculosis and leprosy. Little is known of their biosynthesis, other than being based on phosphatidylinositol (PI), and they probably originate in the phosphatidylinositol mannosides (PIMs; PIMans). A novel form of cell-free incubation involving in vitro and in situ labeling with GDP-[14C]Man of the polyprenyl-P-mannoses (C35/C50-P-Man) and the simpler PIMs of mycobacterial membranes, reisolation of the [14C]Man-labeled membranes, and in situ chase demonstrated the synthesis of a novel alpha(1-->6)-linked linear form of LM at the expense of the C35/C50-P-Man. There was little or no synthesis under these conditions of PIMan5 with its terminal alpha(1-->2)Man unit or the mature LM or LAM with copious alpha(1-->2)Man branching. Synthesis of the linear LM, but not of the simpler PIMan2, was susceptible to amphomycin, a lipopeptide antibiotic that specifically inhibits polyprenyl-P-requiring translocases. A mixture of P[3H]I and P[3H]IMan2 was incorporated into the linear LM, supporting other evidence that, like the PIMs, LM and LAM, it is a lipid-linked mannooligosaccharide and a new member of the mycobacterial glycosylphosphatidylinositol lipoglycan/glycolipid class. Hence, the simpler PIMs originate in PI and GDP-Man, but further growth of the linear backbone emanates from C35-/C50-P-Man and is amphomycin-sensitive. The origin of the alpha(1-->2)Man branches of mature PIMan5, LM, and LAM is not known at this time but is probably GDP-Man.

Leprosy

Leprosy affects over 10 million people in the world. The disease is a model of graded cell-mediated immunity, in this case to the causative organism, Mycobacterium leprae. The clinical manifestations are due to (i) bacterial progression, (ii) immunologic responses of the host, (iii) peripheral nerve damage due to either or both bacterial progression and immunologic responses of the host, and (iv) preventable secondary deformities following nerve damage, which account for most of the stigma of the disease. Treatment modalities are now available to control or minimize the effects of bacterial progression, harmful immunologic responses of the host, peripheral nerve damage, and secondary deformities. Unique biochemical characteristics of M. leprae reside in the cell wall and associated macromolecules. Some of these molecules are potent immunogens in humans, while others constitute the structural integrity of the bacillus. Proteins of M. leprae are currently under intensive investigation as a result of deoxyribonucleic acid cloning of M. leprae genes. Structure-function and antigenic relationships of M. leprae proteins should become available by using recombinant deoxyribonucleic acid procedures coupled with T- and B-cell cloning to advance our understanding of the immunologic reactions encountered in Hansen's disease. Until recently, the study of the immunology of leprosy has been stymied by the lack of immunologically specific M. leprae antigens. The definition of specific antigens and production of recombinant and synthetic immunologic reagents have fostered state-of-the-art research efforts into new immunodiagnostic procedures and development of a leprosy vaccine. Also discussed is progress in understanding of the mechanism(s) underlying the M. leprae-specific immunodeficiency associated with lepromatous leprosy, including the role of suppressor T cells and defective macrophage function. Metabolic studies of M. leprae suggest intact catabolic pathways and energy generation with purine bases and catalase as possible growth factors. Special attention may also need to be given to biophysical parameters for eventual in vitro cultivation. Rapid in vitro systems, using quantitation of bacillary metabolic activity, may soon replace the lengthy mouse footpad test for determining the viability and drug susceptibility of the leprosy bacillus.

Lipoarabinomannan and lipid-free arabinomannan antigens of Mycobacterium paratuberculosis

Lipoarabinomannan (LAM) and lipid-free arabinomannan (AM) were prepared from Mycobacterium paratuberculosis. Purification of LAM was done by ultracentrifugation of the phenol-water-extracted crude polysaccharide, followed by affinity and anion exchange chromatography. AM was purified from the supernatant of the ultracentrifuged polysaccharide or from alkaline-extracted material by gel filtration and anion exchange chromatography. Chemical analysis revealed arabinose and mannose in LAM (1.4:1) and AM (3.5:1) and the presence of palmitic, stearic, and tuberculostearic acids for a total of 7.8% lipid in LAM. Traces of phosphorus were found in the AMs, particularly LAM (0.05%). Nuclear magnetic resonance confirmed the presence of alpha-arabinosyl residues and the acylated nature of LAM. LAM exhibited lipid-dependent aggregation, as indicated by a Triton-induced decrease in molecular weight. By using bovine sera, LAM was found to be active in the complement fixation test, whereas AM was inactive and inhibited this activity. Thus, the presence of AM in crude polysaccharide could explain the variable complement fixation results. Triton-dissociated LAM exhibited a precipitin (Cl) in common with that of AM, confirming shared determinants. LAM in its lipid-dependent aggregated form, however, exhibited a second precipitin (C2), which may be due to the disparity in antigen size or a novel epitope. The lipid content of LAM rendered it 100 times more effective for coating plates in the enzyme immunoassay than lipid-free AM.

Characterization of the immune response to an epitope on Mycobacterium leprae antigen 7 defined by a monoclonal antibody

A mouse monoclonal antibody (038D-C6) was shown by crossed immunoelectrophoresis and radioimmunoassay to react with an epitope on the Mycobacterium leprae antigen 7. This epitope was highly crossreactive with BCG/M. tuberculosis and of a non-arabinogalactan-arabinomannan nature. A solid-phase radioimmunoassay (SPRIA) was applied, based on competitive inhibition by human sera of antigen binding by this anti-M. leprae monoclonal antibody. Inhibitory activity determined by this assay decreased markedly upon treatment in both lepromatous and tuberculoid leprosy patients. A correlation was found between the bacterial load of the patient and the inhibitory activity measured in the SPRIA assay. Serum-inhibitory activity could therefore perhaps be used as a follow-up test for patients on treatment or as a screening method to detect infective cases. A dot enzyme-linked immunosorbent assay based, like the SPRIA assay, on competitive inhibition by human sera, was explored as an inexpensive and technically simple alternative also applicable under field conditions.

Biological, chemical, immunological and staining properties of bacteria isolated from tissues of leprosy patients

Two kinds of microorganisms are found in tissue of leprosy patients: Mycobacterium leprae (ML) and leprosy derived corynebacteria (LDC). ML from untreated patients has an alcohol-acid-fastness, which is lost upon treatment with antibiotics and immune response (tuberculoid leprosy). Vulnerable ML thus produced can be reversibly de-stained by organic solvent: in tissue sections from tuberculoid and treated patients, more bacteria are, thus, revealed by the Wade-Fite than by the Ziehl-Neelsen procedure. Organisms of genera Corynebacterium, Mycobacterium and Nocardia (CMN group), have DNA with %GC contents of 50-70, 69-72, and 68-70 respectively. GC values of DNA from ML and LDC are close to 56%. DNA from different LDC strains display high homology among them and low homology with reference corynebacteria. CMN cell wall consists of interconnected peptidoglycan and polysaccharide-mycolate complex. Peptidoglycan of LDC (and known CMN) has the polysaccharide backbone linked to a tetrapeptide of L-Ala, D-Glu, m-DAP (meso-diaminopimelate), D-Ala. In ML, L-Ala is replaced by glycine. Mycobacterial wall polysaccharides (that of ML is unknown) are branched arabinogalactans with end arabinoses linked to C70 to C90 mycolates. LDC peripheral polysaccharides are arabinogalactomannans with arabinose and mannose lateral strands. Mycolic acids of LDC are of corynomycolic type (C32, C34 and C36 with 1-4 double bonds) and those of ML are of mycobacterial type. Components of CMN wall and cytoplasm are immunologically active as antigens (polysaccharides, proteins), haptens (lipids) and adjuvants (peptidoglycans). Strong intrageneric and weak intergenera crossreactions are observed among CMN bacteria: LDC preparations, however, crossreact strongly with ML and mycobacteria, and weakly with reference corynebacteria. LDC in leprosy tissues can, thus, be revealed as well by fluorescent anti-LDC antisera as by anti-ML antisera. The main crossreacting component is antigen M1 of LDC, which corresponds to antigens Ag 7 of ML and Ag60 of BCG, the active components of lepromin and tuberculin (known reagents for cutaneous tests). Antigen M1 has a polysaccharide moiety crossreacting with the wall polysaccharide of LDC.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental epithelioid cell granulomas, tubercle formation and immunological competence: an ultrastructural analysis

An ultrastructural study of the cells comprising tubercles in experimental mycobacterial granulomas in rats is presented. Tubercle formation was compared in: (1) primary infections due to BCG at 49 days, (2) reinfection with BCG at 7 days, 8 months after primary infection and (3) lesions due to preformed BCG/anti-BCG complexes in antibody excess in unprimed animals at 10 days. The most rapid elimination of antigen with resolution of the lesion in the reinfection lesions, was effected by the early recruitment of cells morphologically characteristic of activated macrophages and immature epithelioid cells. The next best performance was in the immune complex lesion which at its height was maintained by a roughly constant size due to promonocytes, monocytes, macrophages, activated macrophages and immature epithelioid cells accumulated at the site. True epithelioid cells were rare. The slowest rate of healing in the primary 49 day granulomas, was associated with the whole spectrum of mononuclear phagocyte series of cells. All granulomas were surrounded by a cuff of mixed lymphocytes, interdigitating cells and fibroblasts. The rapid resolution of the reinfection lesions appeared as a loosely compacted infiltration of cells which allowed intimate contact of lymphocytes and macrophages. This was distinct from the tightly compared and compartmentalised zones of lymphocytes and macrophages which inhibited contact in the most slowly resolving lesions. An intermediate arrangement was seen in the immune complex granuloma. Another factor which predisposed to rapid resolution was the high vascularity of the central region of the granulomas. In the slow resolving group vascularity was diminished and peripherally situated.

Tuberculin purified protein derivative-reactive T cells in cord blood lymphocytes

Lymphocytes obtained from cord blood of newborn babies who were born of healthy mothers were studied in vitro for their responsiveness to purified protein derivative (PPD) of tuberculin. Cord blood lymphocytes proliferated in vitro by stimulation with PPD, despite wide variations in the results. Studies with fractionated lymphocytes revealed that PPD-responding cells belonged to E-rosetting, nylon wool-nonadherent T lymphocytes. Non-E-rosetting B lymphocytes alone did not proliferate at all after stimulation with PPD. In addition, bromodeoxyuridine and light treatment of in vitro PPD-stimulated lymphocytes eliminated the responsiveness to PPD. These results suggest that T lymphocytes do exist in cord blood and respond in vitro to stimulation with PPD. A possible role for PPD-reactive T lymphocytes in cell-mediated protective immunity in newborns is discussed.

Structural and immunochemical characterization of the acidic arabinomannan of Mycobacterium smegmatis

A serologically active, acidic arabinomannan has been isolated from Mycobacterium smegmatis. The polysaccharide contains approximately 56 arabinosyl and 11 mannosyl residues, and 2 phosphate, 6 monoesterified succinate, and 4 ether-linked lactate groups. After saponification to remove succinyl groups, the polysaccharide can be separated into phosphorylated (55%) and nonphosphorylated (45%) forms, the former containing a little more arabinose and a little less mannose than the latter. The structures of these polysaccharides were investigated by 1H- and 13C-n.m.r. spectroscopy and methylation analysis, before and after selective cleavage of furanosyl linkages. The phosphorylated and nonphosphorylated forms of the polysaccharide were found to have similar, if not identical, structures. The main structural feature of the polysaccharides is the presence of chains of contiguous arabinofuranosyl residues linked alpha-(1 leads to 5). These chains are attached at 0-4 of arabinopyranosyl residues that are present in a core region of the polysaccharide that also contains mannopyranosyl residues. Immunochemical studies demonstrated that the polysaccharide is an effective, precipitating antigen with antisera from rabbits immunized with cell walls or heat-killed cells of M. smegmatis. The polysaccharide is, however, more effective as a precipitating antigen after removal of the succinate groups, and completely ineffective after removal of arabinofuranosyl residues. The polysaccharide therefore contains an important antigen in common with the arabinogalactan lipopolysaccharide of the cell wall of the bacterium, i.e., chains of contiguous alpha-(1 leads to 5)-linked arabinofuranosyl residues.

Immunosuppression by mycobacterial arabinomannan

The means by which mycobacteria elude host defence mechanisms to cause human disease is unknown. This report provides the initial demonstration of a soluble product of Mycobacterium tuberculosis with immunosuppressive activity which may contribute to the pathogenicity of this organism.

Mycobacterial D-arabino-D-mannan (AM), purified from culture filtrates of M. tuberculosis by Concanavalin A-Sepharose affinity chromatography did not itself induce ³H-thymidine incorporation or migration inhibitory factor production by peripheral blood mononuclear cells from tuberculin skin-test-positive healthy humans although it produced weak delayed skin-test reactions in these subjects. However, this mycobacterial cell wall polysaccharide suppressed the response of human lymphocytes to mycobacterial and other antigens as assessed with these in vitro correlates of delayed hypersensitivity. Immunosuppression by arabinomannan was not contingent upon prior exposure of the individual to M. tuberculosis, since it occurred with lymphocytes from tuberculin skin-test non-reactive as well as reactive subjects. Nor was it due to cytotoxicity, an antimitotic effect of the polysaccharide preparation or generation of suppressor cells. Rather, AM seemed to suppress macrophage-dependent, antigen-induced activation of human lymphocytes. This immunosuppressive substance elaborated by mycobacteria has potential relevance to the pathogenesis of human tuberculosis and the nature and limitation of the resulting host response.

Mycobacterial antigens: a review of their isolation, chemistry, and immunological properties

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Binding between components of the tubercle bacillus and humoral antibodies

Studies were undertaken to find a substance or substances for use in primary binding types of tests to detect humoral antibodies in rabbits and monkeys exposed to the tubercle bacillus that would distinguish between strains of mycobacteria. The antigen employed was a component of the 5159 strain of Mycobacterium tuberculosis that was obtained following sonification, ultracentrifugation, electrophoresis, and elution from a preparative polyacrylamide column. When the antigen was labeled with (131)I, specific binding was observed in sera from immunized rabbits and BCG-protected rhesus monkeys by the radio-gel electrophoresis and ammonium sulfate tests. This component was partially characterized, and its major antigenic determinants were associated with anionic mucopolysaccharides. Electrophoretically at pH 8.3 it migrated anodally to albumin, its molecular weight was between 9,000 and 12,000, and it was soluble in 50% saturated ammonium sulfate. Binding to antibody was destroyed after treatment with Pronase, but not after DNase or RNase. Inhibition of the reaction, as measured by the ammonium sulfate test, between the (131)I-labeled component and antisera from rabbits that had been immunized with sonicated 5159 organisms, was studied. These experiments demonstrated a capacity to define subtle similarities and differences among different mycobacteria and mycobacterial components. Some microorganisms not clearly related to mycobacteria also partially inhibited this reaction, suggesting that they shared antigenic groups with the component derived from 5159 organisms. The studies described suggested the advisability of using direct primary tests and purified components of mycobacteria to differentiate further the antigenic groups between individual pathogenic mycobacteria and between pathogenic and nonpathogenic organisms.

Isolation and characterization of arabinose mycolate from firmly bound lipids of mycobacteria

The glycolipid, d-arabinose-5-mycolate, was purified from bound lipids of mycobacteria. The significance of this glycolipid in the chemical structure of cell wall and wax D is discussed. The hypothetical chemical structure of mycolic acid-arabinogalactan portion of cell wall and wax D is proposed.