IL-4 and T cells are required for the generation of IgG1 isotype antibodies against cardiolipin

Infection with Mycobacterium tuberculosis induces Abs against a vast array of mycobacterial lipids and glycolipids. One of the most prominent lipid Ags recognized is cardiolipin (CL). The kinetics of the generation of anti-CL Abs during infection reveals that IgM titers to CL increase over time. Interestingly, at day 30 postinfection CL-specific IgG1 appears, an isotype usually dependent on T cell help. Using an immunization schedule with CL/anti-CL Ab complexes, which induces antiphospholipid syndrome in mice, we show that the generation of IgG1 to CL requires IL-4 and that optimal production is T cell dependent. IgG1 production to CL was impaired in nude (nu/nu) mice devoid in conventional T cells, but was not affected in mice deficient for either alphabeta TCR(+), gammadelta TCR(+), CD4(+), CD8(+), or NK1.1(+) T cells. We conclude that IgG1 production to CL depends on T cell help and IL-4, which can be provided by different T cell populations. This is the first report that IL-4 is indispensable for the induction of IgG1 Abs to lipid Ags.

Mycobacterial lysocardiolipin is exported from phagosomes upon cleavage of cardiolipin by a macrophage-derived lysosomal phospholipase A2

Pathogenic mycobacteria are able to survive and proliferate in phagosomes within host macrophages (Mphi). This capability has been attributed in part to their cell wall, which consists of various unique lipids. Some of these are important in the host-pathogen interaction, such as resistance against microbicidal effector mechanisms and modulation of host cell functions, and/or are presented as Ags to T cells. Here we show that two lipids are released from the mycobacterial cell wall within the phagosome of infected Mphi and transported out of this compartment into intracellular vesicles. One of these lipids was identified as lysocardiolipin. Lysocardiolipin was generated through cleavage of mycobacterial cardiolipin by a Ca2+-independent phospholipase A2 present in Mphi lysosomes. This result indicates that lysosomal host cell enzymes can interact with released mycobacterial lipids to generate new products with a different intracellular distribution. This represents a novel pathway for the modification of bacterial lipid Ags.

Identification of proteins from Mycobacterium tuberculosis missing in attenuated Mycobacterium bovis BCG strains

A proteome approach, combining high-resolution two-dimensional electrophoresis (2-DE) with mass spectrometry, was used to compare the cellular protein composition of two virulent strains of Mycobacterium tuberculosis with two attenuated strains of Mycobacterium bovis Bacillus Calmette-Guerin (BCG), in order to identify unique proteins of these strains. Emphasis was given to the identification of M. tuberculosis specific proteins, because we consider these proteins to represent putative virulence factors and interesting candidates for vaccination and diagnosis of tuberculosis. The genome of M. tuberculosis strain H37Rv comprises nearly 4000 predicted open reading frames. In contrast, the separation of proteins from whole mycobacterial cells by 2-DE resulted in silver-stained patterns comprising about 1800 distinct protein spots. Amongst these, 96 spots were exclusively detected either in the virulent (56 spots) or in the attenuated (40 spots) mycobacterial strains. Fifty-three of these spots were analyzed by mass spectrometry, of which 41 were identified, including 32 M. tuberculosis specific spots. Twelve M. tuberculosis specific spots were identified as proteins, encoded by genes previously reported to be deleted in M. bovis BCG. The remaining 20 spots unique for M. tuberculosis were identified as proteins encoded by genes that are not known to be missing in M. bovis BCG.

CD1 molecules and CD1-dependent T cells in bacterial infections: a link from innate to acquired immunity?

The MHC class I-like, non-polymorphic CD1 molecules represent a novel system for the presentation of glycolipid antigens to T lymphocytes. CD1-mediated T cell responses appear to play distinct roles during bacterial infections such as in tuberculosis. This review deals with two aspects of CD1-mediated immune reactions. First we discuss the role of group II CD1-dependent NK T cells in bacterial infection. Second, we provide an insight into differential intracellular meeting points for antigen processing between group I CD1 molecules, mycobacteria and mycobacterial glycolipid antigens.

CD1 and CD1-restricted T cells in infections with intracellular bacteria

Glycolipid-specific, CD1a-, b- and c-dependent cytotoxic T cells have recently been shown to be involved in the host response against tuberculosis. These CD1 molecules 'sample' mycobacterial glycolipids from different intracellular sites in the infected cell. Additionally, upon microbial encounter, CD1d-dependent natural killer T cells promptly produce cytokines and perform regulatory activities. Here, we discuss the intracellular localization of CD1 molecules and mycobacterial lipids and the role of CD1-mediated T-cell responses in mycobacterial infections.

Isolation of RNA from mycobacteria grown under in vitro and in vivo conditions

Isolation of RNA from mycobacteria is very difficult to perform, and the yields are generally very low. We describe an approach to isolate RNA from mycobacterial species which combines the disruption of mycobacterial cells by a silica/ceramic matrix in a reciprocal shaker with the ease and efficiency of subsequent RNA purification on spin columns with silica gel-based membranes. This method is rapid, easy to perform and yields high amounts of pure, intact total RNA. Due to its safety, this method is applicable even to group 3 biological hazard organisms like Mycobacterium tuberculosis. By combining a method for the isolation of phagosomal bacteria from infected primary macrophages with the novel RNA isolation technique, we are able to monitor gene expression during infection even in bacteria which are rather resistant to genetic manipulation, like Mycobacterium bovis.

Intersection of group I CD1 molecules and mycobacteria in different intracellular compartments of dendritic cells

Human CD1a, CD1b, and CD1c molecules can present mycobacterial glycolipids to T cells. Because phagosomes containing viable mycobacteria represent early endosomal compartments, we studied where mycobacterial glycolipids intersect with CD1 molecules in infected APC. CD1b and CD1c, but not CD1a, localized to late endosomes/lysosomes. CD1a and CD1c were predominantly expressed on the cell surface and in mycobacterial phagosomes of the early endosomal stage. In contrast, CD1b was present in a subset of mycobacterial phagosomes representing mature phagolysosomes. Released mycobacterial glycolipids including lipoarabinomannan and phosphatidylinositol mannosides were transported from the phagosome into late endosomes/lysosomes and to uninfected bystander cells. The macrophage mannose receptor, which has been implicated in glycolipid uptake by APC for CD1b-mediated presentation, was absent from mycobacterial phagosomes and may therefore not be involved in trafficking of glycolipids between phagosomes and late endosomes/lysosomes. In conclusion, all three CD1 molecules have access to mycobacteria and glycolipids thereof, but at different intracellular sites. This allows sampling by CD1a, CD1b, and CD1c of mycobacterial glycolipids from different intracellular sites of the infected cell, which has important implications for processing and presentation of such Ags during mycobacterial infections.

Comparative proteome analysis of Mycobacterium tuberculosis and Mycobacterium bovis BCG strains: towards functional genomics of microbial pathogens

In 1993, the WHO declared tuberculosis a global emergency on the basis that there are 8 million new cases per year. The complete genome of the strain H37Rv of the causative microorganism, Mycobacterium tuberculosis, comprising 3924 genes has been sequenced. We compared the proteomes of two non-virulent vaccine strains of M. bovis BCG (Chicago and Copenhagen) with two virulent strains of M. tuberculosis (H37Rv and Erdman) to identify protein candidates of value for the development of vaccines, diagnostics and therapeutics. The mycobacterial strains were analysed by two-dimensional electrophoresis (2-DE) combining non-equilibrium pH gradient electrophoresis (NEPHGE) with SDS-PAGE. Distinct and characteristic proteins were identified by mass spectrometry and introduced into a dynamic 2-DE database (http://www.mpiib-berlin.mpg.de/2D-PAGE). Silver-stained 2-DE patterns of mycobacterial cell proteins or culture supernatants contained 1800 or 800 spots, respectively, from which 263 were identified. Of these, 54 belong to the culture supernatant. Sixteen and 25 proteins differing in intensity or position between M. tuberculosis H37Rv and Erdman, and H37Rv and M. bovis BCG Chicago, respectively, were identified and categorized into protein classes. It is to be hoped that the availability of the mycobacterial proteome will facilitate the design of novel measures for prevention and therapy of one of the great health threats, tuberculosis.

A dynamic two-dimensional polyacrylamide gel electrophoresis database: the mycobacterial proteome via Internet

Proteome analysis by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and mass spectrometry, in combination with protein chemical methods, is a powerful approach for the analysis of the protein composition of complex biological samples. Data organization is imperative for efficient handling of the vast amount of information generated. Thus we have constructed a 2-D PAGE database to store and compare protein patterns of cell-associated and culture-supernatant proteins of different mycobacterial strains. In accordance with the guidelines for federated 2-DE databases, we developed a program that generates a dynamic 2-D PAGE database for the World-Wide-Web to organise and publish, via the internet, our results from proteome analysis of different Mycobacterium tuberculosis as well as Mycobacterium bovis BCG strains. The uniform resource locator for the database is http://www.mpiib-berlin.mpg.de/2D-PAGE and can be read with a Java compatible browser. The interactive hypertext markup language documents displayed are generated dynamically in each individual session from a rational data file, a 2-D gel image file and a map file describing the protein spots as polygons. The program consists of common gateway interface scripts written in PERL, minimizing the administrative workload of the database. Furthermore, the database facilitates not only interactive use, but also worldwide active participation of other scientific groups with their own data, requiring only minimal computer hardware and knowledge of information technology.

Parasitophorous vacuoles of Leishmania mexicana acquire macromolecules from the host cell cytosol via two independent routes

The intracellular parasite Leishmania survives and proliferates in host macrophages. In this study we show that parasitophorous vacuoles of L. mexicana gain access to cytosolic material via two different routes. (1) Small anionic molecules such as Lucifer Yellow are rapidly transported into the vacuoles by an active transport mechanism that is sensitive to inhibitors of the host cell's organic anion transporter. (2) Larger molecules such as fluorescent dextrans introduced into the host cell cytosol are also delivered to parasitophorous vacuoles. This transport is slower and sensitive to modulators of autophagy. Infected macrophages were examined by two novel assays to visualize and quantify this process. Immunoelectron microscopy of cells loaded with digoxigenin-dextran revealed label in multivesicular endosomes, which appeared to fuse with parasitophorous vacuoles. The inner membranes of the multivesicular vesicles label strongly with antibodies against lysobisphosphatidic acid, suggesting that they represent a point of confluence between the endosomal and autophagosomal pathways. Although the rate of autophagous transfer was comparable in infected and uninfected cells, infected cells retained hydrolyzed cysteine proteinase substrate to a greater degree. These data suggest that L. mexicana-containing vacuoles have access to potential nutrients in the host cell cytosol via at least two independent mechanisms.

Early IL-4 Induction in Bone Marrow Lymphoid Precursor Cells by Mycobacterial Lipoarabinomannan

IL-4 is produced promptly in response to certain infections and plays a key role in the Th1/Th2 T cell dichotomy; however, the cellular source remains a matter of debate. Here we describe the induction of IL-4 in bone marrow cells of normal and RAG−/− mice by both Mycobacterium tuberculosis and its major cell wall glycolipid, lipoarabinomannan. Characterization of the cell type responsible indicated that it was distinct from the NK1+ or CD4+ T cell previously ascribed the function of rapid IL-4 secretion. Cell-sorting experiments identified CD19+/B220+ precursor cells, presumably pre-B cells that produced IL-4 constitutively and whose frequency was rapidly and markedly up-regulated by lipoarabinomannan. Thus, pathogenic mycobacteria and their glycolipids may influence hemopoiesis by rapidly inducing IL-4 secretion in the bone marrow.

Early IL-4 induction in bone marrow lymphoid precursor cells by mycobacterial lipoarabinomannan

IL-4 is produced promptly in response to certain infections and plays a key role in the Th1/Th2 T cell dichotomy; however, the cellular source remains a matter of debate. Here we describe the induction of IL-4 in bone marrow cells of normal and RAG-/- mice by both Mycobacterium tuberculosis and its major cell wall glycolipid, lipoarabinomannan. Characterization of the cell type responsible indicated that it was distinct from the NK1+ or CD4+ T cell previously ascribed the function of rapid IL-4 secretion. Cell-sorting experiments identified CD19+/B220+ precursor cells, presumably pre-B cells that produced IL-4 constitutively and whose frequency was rapidly and markedly up-regulated by lipoarabinomannan. Thus, pathogenic mycobacteria and their glycolipids may influence hemopoiesis by rapidly inducing IL-4 secretion in the bone marrow.

Cytokine Activation Leads to Acidification and Increases Maturation of Mycobacterium avium-Containing Phagosomes in Murine Macrophages

Mycobacterium avium (MAC) organisms multiply in phagosomes that have restricted fusigenicity with lysosomes, do not acidify due to a paucity of vacuolar proton-ATPases, yet remain accessible to recycling endosomes. During the course of mycobacterial infections, IFN-γ-mediated activation of host and bystander macrophages is a key mechanism in the regulation of bacterial growth. Here we demonstrate that in keeping with earlier studies, cytokine activation of host macrophages leads to a decrease in MAC viability, demonstrable by bacterial esterase staining with fluorescein diacetate as well as colony-forming unit counts from infected cells. Analysis of the pH of MAC phagosomes demonstrated that the vacuoles in activated macrophages equilibrate to pH 5.2, in contrast to pH 6.3 in resting phagocytes. Biochemical analysis of MAC phagosomes from both resting and activated macrophages confirmed that the lower intraphagosomal pH correlated with an increased accumulation of proton-ATPases. Furthermore, the lower pH is reflected in the transition of MAC phagosomes to a point no longer accessible to transferrin, a marker of the recycling endosomal system. These alterations parallel the coalescence of bacterial vacuoles from individual bacilli in single vacuoles to communal vacuoles with multiple bacilli. These data demonstrate that bacteriostatic and bactericidal activities of activated macrophages are concomitant with alterations in the physiology of the mycobacterial phagosome.

Cytokine activation leads to acidification and increases maturation of Mycobacterium avium-containing phagosomes in murine macrophages

Mycobacterium avium (MAC) organisms multiply in phagosomes that have restricted fusigenicity with lysosomes, do not acidify due to a paucity of vacuolar proton-ATPases, yet remain accessible to recycling endosomes. During the course of mycobacterial infections, IFN-gamma-mediated activation of host and bystander macrophages is a key mechanism in the regulation of bacterial growth. Here we demonstrate that in keeping with earlier studies, cytokine activation of host macrophages leads to a decrease in MAC viability, demonstrable by bacterial esterase staining with fluorescein diacetate as well as colony-forming unit counts from infected cells. Analysis of the pH of MAC phagosomes demonstrated that the vacuoles in activated macrophages equilibrate to pH 5.2, in contrast to pH 6.3 in resting phagocytes. Biochemical analysis of MAC phagosomes from both resting and activated macrophages confirmed that the lower intraphagosomal pH correlated with an increased accumulation of proton-ATPases. Furthermore, the lower pH is reflected in the transition of MAC phagosomes to a point no longer accessible to transferrin, a marker of the recycling endosomal system. These alterations parallel the coalescence of bacterial vacuoles from individual bacilli in single vacuoles to communal vacuoles with multiple bacilli. These data demonstrate that bacteriostatic and bactericidal activities of activated macrophages are concomitant with alterations in the physiology of the mycobacterial phagosome.

Why intracellular parasitism need not be a degrading experience for Mycobacterium

The success of mycobacteria as pathogens hinges on their ability to infect and persist within the macrophages of their host. However, activation of host macrophages by cytokines from a productive cellular immune response can stimulate the cells to kill their resident pathogens. This suggests that the interaction between host cell and microbe is in delicate balance, which can be tipped in favour of either organism. Biochemical analysis of mycobacterial vacuoles has shown them to be integral to the host cell's recycling endosomal system. As such they show limited acidification and hydrolytic activity despite possession of known lysosomal constituents such as cathepsins D, B and L, and LAMP 1. Even in established infections, they remain dynamic compartments accessible to several plasmalemma-derived constituents. Once the macrophage has been activated by IFN-gamma and TNF-alpha the vacuoles coalesce and acidify. This marks a distinct alteration in vacuole physiology and leads to stasis and death of the mycobacteria. Mycobacteria have developed several strategies to avoid this outcome. Most notably, live bacilli-induce sustained release of IL-6 from infected macrophages. IL-6 blocks the ability of both polyclonal primary T cells and T-cell hybridomas to respond to appropriate stimuli. Such an activity could render the centres of infection foci, such as granulomas, anergic and thus avoid release of macrophage-activating cytokines. This paper discusses both the mechanisms by which mycobacteria try to ensure their success as intracellular pathogens and the relevance of these strategies to the overall understanding of mycobacterial diseases.

Transfer of phagocytosed particles to the parasitophorous vacuole of Leishmania mexicana is a transient phenomenon preceding the acquisition of annexin I by the phagosome

The eukaryotic intracellular pathogen Leishmania mexicana resides inside macrophages contained within a membrane bound parasitophorous vacuole which, as it matures, acquires the characteristics of a late endosomal compartment. This study reports the selectivity of fusion of this compartment with other particle containing vacuoles. Phagosomes containing zymosan or live Listeria monocytogenes rapidly fused with L. mexicana parasitophorous vacuoles, while those containing latex beads or heat killed L. monocytogenes failed to do so. Fusigenicity of phagosomes was not primarily dependent on the receptor utilized for ingestion, as opsonization with defined ligands could not overcome the exclusion of either latex beads or heat killed organisms. However modulation of intracellular pH by pharmacological agents such as chloroquine and ammonium chloride increased delivery of live Listeria and also induced transfer of previously excluded particles. The absence of fusion correlated with the acquisition of annexin I, a putative lysosomal targeting, molecule, on the phagosome membrane. We propose that the acquisition of cellular membrane constituents such as annexin I during phagosome maturation can ultimately direct the fusion pathway of the vesicles formed and have described a model system to further document changes in vesicle fusigenicity within cells.

Mycobacterium-containing phagosomes are accessible to early endosomes and reflect a transitional state in normal phagosome biogenesis

The success of Mycobacterium as a pathogen hinges on its ability to modulate its intracellular environment. Mycobacterium avium reside in vacuoles with limited proteolytic activity, maintain cathepsin D in an immature form and remain accessible to internalized transferrin. Artificial acidification of isolated phagosomes facilitated processing of cathepsin D, demonstrating that pH alone limits proteolysis in these vacuoles. Moreover, analysis of IgG-bead phagosomes at early time points during their formation indicates that these phagosomes also acquire LAMP 1 and cathepsin D prior to the accumulation of proton-ATPases, and are transiently accessible to sorting endosomes. This suggests that the anomolous distribution of endosomal proteins in M. avium-containing vacuoles results from their arrested differentiation in an early transitional stage through which all phagosomes pass.

Infestation of rodents with larval Ixodes ricinus (Acari: Ixodidae) is an important factor in the transmission cycle of Borrelia burgdorferi s.l. in German woodlands

The ecology of Borrelia burgdorferi Johnson et al. s.l. was investigated from 1987 to 1993 in a preserved woodland in western Germany near Bonn. In selected biotopes, host-seeking Ixodes ricinus L. were regularly collected by blanket dragging in 1987, 1988, and 1989 and screened for infection with B. burgdorferi. Rodents were trapped monthly between April and October in 1988, 1990, 1991, and in the winter of 1992-1993, examined for antibodies to B. burgdorferi s.l., and inspected for feeding ticks. Ticks collected from rodents were screened for spirochete infection. High numbers of host-seeking nymphs were consistently collected within a biotope characterized by humid and acid soils. The mean number of ticks was significantly lower in biotopes with permeable soils. All small mammals captured belonged to the species Apodemus flavicollis Melchior, A. sylvaticus L., and Clethrionomys glareolus Schreber. Of 11,680 ticks obtained from rodents, 11,674 were I. ricinus, with 97.9% of the ticks being larvae, 2.0% nymphs, and 0.1% females. Mean numbers of feeding ticks ranged from 3.4 to 117 larvae per rodent and from 0.0 to 0.64 nymph per rodent, respectively. High levels of larval infestation on rodents were recorded in the same biotope where high numbers of host-seeking nymphs were present. Members of the genus Apodemus were more heavily infested with I. ricinus larvae than C. glareolus. The mean infection prevalence in host-seeking ticks was found to be 1% for larvae, 5% for nymphs, and 10-20% for adults. The infection prevalence in host-seeking nymphs ranged from 1.1 to 15.4% according to the particular biotope. The values for specific infectivity for the Apodemus populations were positively correlated with the mean larval infestation, but not with nymphal infestation. The respective estimates for C. glareolus were much higher than those for Apodemus spp. in biotopes with low tick densities. However, specific infectivity of C. glareolus was substantially reduced at sites with high tick abundances. In biotopes with high numbers of infected I. ricinus, significantly more rodents were found to have antibodies to B. burgdorferi than in biotopes with low abundances of ticks. The data show that C. glareolus plays a different role as reservoir host species compared with the 2 Apodemus species. This and previous studies suggest that the degree of infestation with larval I. ricinus differentially modulates infectivity of host species for ticks. We conclude that immune processes in natural reservoir hosts induced by B. burgdorferi or I. ricinus bites (or both) are important regulatory factors in the transmission cycle(s) of B. burgdorferi.

Studies on early events of Borrelia burgdorferi-induced cytokine production in immunodeficient SCID mice by using a tissue chamber model for acute inflammation

Lyme arthritis, one of the common features of Borrelia burgdorferi infection in the human, is associated with the production of various monocyte derived cytokines. To investigate the expression and regulation of cytokines during the acute phase of spirochete induced inflammation, a perforated Teflon chamber was implanted under the dorsal skin of severe combined immunodeficiency (SCID) and immunocompetent co-isogenic C.B-17 mice. The histology of the surrounding chamber tissue exhibited sterile inflammation with several features reminiscent of an inflamed synovium, i.e. infiltration of polymorphonuclear and mononuclear cells, fibroblast-like cells and neovascularization. The experimental inoculation of Borrelia burgdorferi into the chamber resulted in the production of TNF-alpha, IL-1 and IL-6 into the chamber exudate, in both the immunodeficient, disease susceptible SCID and the immunocompetent, disease resistant C.B-17 mice. Peak levels of TNF-alpha were reached at 2 hours and of IL-1 and IL-6 at 6 hours after infection; by 24 hours, cytokine levels were only marginal (IL-1, IL-6) or non-detectable (TNF-alpha). Experimental infection by s.c. injection distant from the tissue chamber led to colonization of the spirochetes into the chamber, suggesting a tropism of the bacteria for this tissue. Thus, this model provides a system for studying acute events of Borellia burgdorferi induced cytokine regulation in a complex cellular, synovium-like environment that the bacterium encounters in vivo.

The outer surface lipoprotein A of Borrelia burgdorferi provides direct and indirect augmenting/co-stimulatory signals for the activation of CD4+ and CD8+ T cells

Naive CD4+ and CD8+ T cells require two distinct signals to proliferate and to express effector functions [1]. One is provided by the antigen receptor on the T cell (TCR) after its encounter with antigenic peptides associated with class I or II major histocompatibility complex (MHC) molecules on antigen-presenting cells (APC) [2]. The second signal, which is not antigen-specific but essential for proliferation and differentiation of naive T cells, is provided by co-stimulatory structures. The major co-stimulatory molecules for CD4+ T cells seem to be B7 [3], B7.2 [4,5], and heat-stable antigen (HSA) [6]. These molecules are expressed on a variety of naive and/or activated APC and bind to CD28 and CTLA-4 and possibly other, as yet undefined, TCRs [3,7]. Optimal T cell activation only occurs when co-stimulatory molecules and ligands for the TCR are expressed on the same APC [8,9]. However, co-stimulation for T cells may also be provided via bystander cells [8,9] or by glycoproteins of the extracellular matrix, like fibronectin [10] and laminin [11]. In this case, T-cell VLA integrins function as signaling molecules [10,11]. This indicates that antigen-specific T-cell activation may also occur in areas where antigens are presented in association with extracellular matrix proteins. The recent finding that the invasion protein of Yersinia spp. delivers co-stimulatory signals to anti-CD3-activated human T cells, most probably through the b1 integrins, suggests that bacterial products can also bind to contribute to the activation of T cells [12].(ABSTRACT TRUNCATED AT 250 WORDS)