Lipoarabinomannan induced cytotoxic effects in human mononuclear cells

Corynebacterium diphtheriae 67-72p hemagglutinin, characterized as the protein DIP0733, contributes to invasion and induction of apoptosis in HEp-2 cells

Although Corynebacterium diphtheriae has been classically described as an exclusively extracellular pathogen, there is growing evidence that it may be internalized by epithelial cells. The aim of the present report was to investigate the nature and involvement of the surface-exposed non-fimbrial 67-72 kDa proteins (67-72p), previously characterized as adhesin/hemagglutinin, in C. diphtheriae internalization by HEp-2 cells. Transmission electron microscopy and bacterial internalization inhibition assays indicated the role of 67-72p as invasin for strains of varied sources. Cytoskeletal changes with accumulation of polymerized actin in HEp-2 cells beneath adherent 67-72p-adsorbed microspheres were observed by the Fluorescent actin staining test. Trypan blue staining method and Methylthiazole tetrazolium reduction assay showed a significant decrease in viability of HEp-2 cells treated with 67-72p. Morphological changes in HEp-2 cells observed after treatment with 67-72p included vacuolization, nuclear fragmentation and the formation of apoptotic bodies. Flow cytometry revealed an apoptotic volume decrease in HEp-2 cells treated with 67-72p. Moreover, a double-staining assay using Propidium Iodide/Annexin V gave information about the numbers of vital vs. early apoptotic cells and late apoptotic or secondary necrotic cells. The comparative analysis of MALDI-TOF MS experiments with the probes provided for 67-72p CDC-E8392 with an in silico proteome deduced from the complete genome sequence of C. diphtheriae identified with significant scores 67-72p as the protein DIP0733. In conclusion, DIP0733 (67-72p) may be directly implicated in bacterial invasion and apoptosis of epithelial cells in the early stages of diphtheria and C. diphtheriae invasive infection.

Organelle membrane proteomics reveals differential influence of mycobacterial lipoglycans on macrophage phagosome maturation and autophagosome accumulation

The mycobacterial cell wall component lipoarabinomannan (LAM) has been described as one of the key virulence factors of Mycobacterium tuberculosis. Modification of the terminal arabinan residues of this lipoglycan with mannose caps in M. tuberculosis or with phosphoinositol caps in Mycobacterium smegmatis results in distinct host immune responses. Given that M. tuberculosis typically persists in the phagosomal vacuole after being phagocytosed by macrophages, we performed a proteomic analysis of that organelle after treatment of macrophages with LAMs purified from the two mycobacterial species. The quantitative changes in phagosomal proteins suggested a distinct role for mannose-capped LAM in modulating protein trafficking pathways that contribute to the arrest of phagosome maturation. Enlightened by our proteomic data, we performed further experiments to show that only the LAM from M. tuberculosis inhibits accumulation of autophagic vacuoles in the macrophage, suggesting a new function for this virulence-associated lipid.

LAM has been described as one of the key virulence factors of Mycobacterium tuberculosis. Modification of the terminal arabinan residues of this lipoglycan with mannose caps in M. tuberculosis or with phosphoinositol caps in Mycobacterium smegmatis results in distinct host immune responses. Given that M. tuberculosis typically persists in the phagosomal vacuole after being phagocytosed by macrophages, we performed a proteomic analysis of that organelle after treatment of macrophages with LAMs purified from the two mycobacterial species.

Epitope-Based Immunome-Derived Vaccines: A Strategy for Improved Design and Safety

Vaccine science has extended beyond genomics to proteomics and has come to also encompass ‘immunomics,’ the study of the universe of pathogen-derived or neoplasm-derived peptides that interface with B and T cells of the host immune system. It has been theorized that effective vaccines can be developed using the minimum essential subset of T cell and B cell epitopes that comprise the ‘immunome.’ Researchers are therefore using bioinformatics sequence analysis tools, epitope-mapping tools, microarrays, and high-throughput immunology assays to discover the minimal essential components of the immunome. When these minimal components, or epitopes, are packaged with adjuvants in an appropriate delivery vehicle, the complete package comprises an epitope-based immunome-derived vaccine. Such vaccines may have a significant advantage over conventional vaccines, as the careful selection of the components may diminish undesired side effects such as have been observed with whole pathogen and protein subunit vaccines. This chapter will review the pre-clinical and anticipated clinical development of computer-driven vaccine design and the validation of epitope-based immunome-derived vaccines in animal models; it will also include an overview of heterologous immunity and other emerging issues that will need to be addressed by vaccines of all types in the future.

Arabinosylated lipoarabinomannan modulates the impaired cell mediated immune response in Mycobacterium tuberculosis H37Rv infected C57BL/6 mice

Mycobacterium tuberculosis is a facultative intracellular pathogen that flourishes inside the host macrophages. This organism has the ability to deactivate the cell-mediated immune responses involving the down-regulation of pro-inflammatory cytokines, T cell proliferation, apoptosis of CD4+T cells and impairment of the expression of MHC Class II molecules. We observed that Arabinosylated Lipoarabinomannan (Ara-LAM), a glycolipid present in the cell wall of the avirulent Mycobacterium smegmatis, could effectively restrict the growth of tubercle bacilli, induced the transcription of Th1 cytokines in alveolar macrophages (AMs) and splenocytes, enhanced the frequency of CD4+T cells secreting IFN-gamma and induced the expression of MHC Class II molecules on the splenocyte membrane, compared to that of Mycobacterium tuberculosis H37Rv infected C57BL/6 mice. Collectively our findings strongly suggest that Ara-LAM had the potency to restore the impaired cell mediated immune responses in mice infected with Mycobacterium tuberculosis H37Rv, and hence could be utilized as an effective immuno-prophylactic tool in the control of tuberculosis.

An unusual pro-inflammatory role of interleukin-10 induced by arabinosylated lipoarabinomannan in murine peritoneal macrophages

Various species of Mycobacteria produce a major cell wall-associated lipoglycan, called Lipoarabinomannan (LAM), which is involved in the virulence of Mycobacterial species. In this study, we tried to establish the role of the increased IL-10 secretion under Arabinosylated-LAM (Ara-LAM) treatment, the LAM that induces apoptosis in host macrophages or PBMC. We have studied the survival and apoptotic factors by western blotting, and estimated nitrite generation by Griess reaction, quantified iNOS mRNA by semi-quantitative RT-PCR, and ultimately the fate of the cells were studied by Flow Cytometric Analysis of AnnexinV-FITC binding. As per our observations, neutralization of released IL-10 in C57BL/6 peritoneal macrophages prior to Ara-LAM treatment, as well as macrophages from IL-10 knockout (KO) mice treated with Ara-LAM, showed significant down regulation of pro-apoptotic factors and up regulation of survival factors. These effects were strikingly similar to those when peritoneal macrophages were subjected to TNF-alpha and IL-12 neutralization followed by Ara-LAM-treatment. However, under similar conditions virulent Mannosylated-LAM (from Mycobacterium tuberculosis) treatment of macrophages clearly depicts the importance of IL-10 in the maintenance of pathogenesis, proving its usual immunosuppressive role. Thus, from our detailed investigations we point out an unusual pro-inflammatory action of IL-10 in Ara-LAM treated macrophages, where it behaves in a similar manner as the known Th1 cytokines TNF- alpha and IL-12.

Modulation of eukaryotic cell apoptosis by members of the bacterial order Actinomycetales

Apoptosis, or programmed cell death, is normally responsible for the orderly elimination of aged or damaged cells, and is a necessary part of the homeostasis and development of multicellular organisms. Some pathogenic bacteria can disrupt this process by triggering excess apoptosis or by preventing it when appropriate. Either event can lead to disease. There has been extensive research into the modulation of host cell death by microorganisms, and several reviews have been published on the phenomenon. Rather than covering the entire field, this review focuses on the dysregulation of host cell apoptosis by members of the order Actinomycetales, containing the genera Corynebacterium, Mycobacterium, Rhodococcus, and Nocardia.

Recent advances towards identification of new drug targets for Mycobacterium tuberculosis

Mycobacterium tuberculosis is a very successful pathogen that remains a leading infectious killer worldwide. The global situation has become precarious due to various factors such as the variable efficacy of the Bacille Calmette-Guerin (BCG) vaccine, drug resistance, delay in diagnosis, association with HIV, and other factors, creating a long-lasting reservoir of impending disease and infection. Surprisingly, no new drugs have been developed in the past 30 years. The release of the complete genome sequence of M. tuberculosis and the availability of advanced genetic tools have provided the powerful repertoire of potential drug targets that are now in hand and can be explored in a more rational and directional manner. In this review, the authors highlight some possible therapeutic targets in M. tuberculosis. The gene products involved in various processes, such as mycobacterial cell wall synthesis, ability to acquire or obtain essential nutrients, persistence, transcription regulation, energy metabolism and others, such as the PE-PGRS family and culture filtrate proteins, would be potential targets for the development of new drugs. Apart from these categories, the importance of signal transduction events in the virulence of mycobacteria is discussed in relation to their potential as therapeutic targets. The potential of all of these therapeutic targets should be investigated together with the potential of being able to synthesise future chemotherapeutic agents.

Mycobacterial lipoarabinomannan and related lipoglycans: from biogenesis to modulation of the immune response

The cell wall component lipoarabinomannan (ManLAM) from Mycobacterium tuberculosis is involved in the inhibition of phagosome maturation, apoptosis and interferon (IFN)-gamma signalling in macrophages and interleukin (IL)-12 cytokine secretion of dendritic cells (DC). All these processes are important for the host to mount an efficient immune response. Conversely, LAM isolated from non-pathogenic mycobacteria (PILAM) have the opposite effect, by inducing a potent proinflammatory response in macrophages and DCs. LAMs from diverse mycobacterial species differ in the modification of their terminal arabinose residues. The strong proinflammatory response induced by PILAM correlates with the presence of phospho-myo-inositol on the terminal arabinose. Interestingly, recent work indicates that the biosynthetic precursor of LAM, lipomannan (LM), which is also present in the cell wall, displays strong proinflammatory effects, independently of which mycobacterial species it is isolated from. Results from in vitro assays and knock-out mice suggest that LM, like PILAM, mediates its biological activity via Toll-like receptor 2. We hypothesize that the LAM/LM ratio might be a crucial factor in determining the virulence of a mycobacterial species and the outcome of the infection. Recent progress in the identification of genes involved in the biosynthesis of LAM is discussed, in particular with respect to the fact that enzymes controlling the LAM/LM balance might represent targets for new antitubercular drugs. In addition, inactivation of these genes may lead to attenuated strains of M. tuberculosis for the development of new vaccine candidates.

Mycobacterium tuberculosis lipomannan induces apoptosis and interleukin-12 production in macrophages

The mycobacterial cell wall component lipoarabinomannan (LAM) has been described as a virulence factor of Mycobacterium tuberculosis, and modification of the terminal arabinan residues of this compound with mannose caps (producing mannosyl-capped LAM [ManLAM]) in M. tuberculosis or with phosphoinositol caps (producing phosphoinositol-capped LAM [PILAM]) in Mycobacterium smegmatis has been implicated in various functions associated with these lipoglycans. A structure-function analysis was performed by using LAMs and their biosynthetic precursor lipomannans (LMs) isolated from different mycobacterial species on the basis of their capacity to induce the production of interleukin-12 (IL-12) and/or apoptosis of macrophage cell lines. Independent of the mycobacterial species, ManLAMs did not induce IL-12 gene expression or apoptosis of macrophages, whereas PILAMs induced IL-12 secretion and apoptosis. Interestingly, uncapped LAM purified from Mycobacterium chelonae did not induce IL-12 secretion or apoptosis. Furthermore, LMs, independent of their mycobacterial origins, were potent inducers of IL-12 and apoptosis. The precursor of LM, phosphatidyl-myo-inositol dimannoside, had no activity, suggesting that the mannan core of LM was required for the activity of LM. The specific interaction of LM with Toll-like receptor 2 (TLR-2) but not with TLR-4 suggested that these responses were mediated via the TLR-2 signaling pathway. Our experiments revealed an important immunostimulatory activity of the biosynthetic LAM precursor LM. The ratio of LAM to LM in the cell wall of mycobacteria may be an important determinant of virulence, and enzymes that modify LM could provide targets for development of antituberculosis drugs and for derivation of attenuated strains of M. tuberculosis.

Lipoarabinomannan-induced cell signaling involves ceramide and mitogen-activated protein kinase

Lipoarabinomannan (LAM) is a major cell wall-associated lipoglycan, produced in large amounts (15 mg/g of bacteria) in different species of mycobacteria. Our laboratory has previously reported that LAM from Mycobacterium smegmatis exerts its cytotoxic activity via inhibition of protein kinase C, a key signaling molecule inside the mononuclear cells (S. Ghosh, S. Pal, S. Das, S. K. Dasgupta, and S. Majumdar, FEMS Immunol. Med. Microbiol. 21:181-188, 1998). In this study we report that LAM from Mycobacterium tuberculosis induces a signal transduction pathway in favor of survivability of the host cells via the generation of ceramide, a novel second messenger. The endogenous ceramide level in mononuclear cells was found to be enhanced during LAM treatment. The effects of LAM on protein tyrosine phosphorylation in human peripheral blood mononuclear cells were examined. LAM enhanced the tyrosine phosphorylation of p42 mitogen-activated protein kinase and phosphoinositol 3-kinase (PI3 kinase) and dephosphorylation of stress-activated protein kinase. LAM-induced phosphorylation of p42 (extracellular signal-regulated kinase 2) was further enhanced by wortmannin, a PI3 kinase inhibitor. To examine whether these effects are due to elevation of endogenous ceramide, we exposed the cells to cell-permeative C(2)-ceramide exogenously and studied the activities of different protein kinases. Fluorescence-activated cell sorter analysis and morphological studies showed that LAM induces cell survival. Therefore, these results suggest the ability of LAM to induce ceramide in the altered signaling pathway and help in cell survival.

Immuno-informatics: Mining genomes for vaccine components

The complete genome sequences of more than 60 microbes have been completed in the past decade. Concurrently, a series of new informatics tools, designed to harness this new wealth of information, have been developed. Some of these new tools allow researchers to select regions of microbial genomes that trigger immune responses. These regions, termed epitopes, are ideal components of vaccines. When the new tools are used to search for epitopes, this search is usually coupled with in vitro screening methods; an approach that has been termed computational immunology or immuno-informatics. Researchers are now implementing these combined methods to scan genomic sequences for vaccine components. They are thereby expanding the number of different proteins that can be screened for vaccine development, while narrowing this search to those regions of the proteins that are extremely likely to induce an immune response. As the tools improve, it may soon be feasible to skip over many of the in vitro screening steps, moving directly from genome sequence to vaccine design. The present article reviews the work of several groups engaged in the development of immuno-informatics tools and illustrates the application of these tools to the process of vaccine discovery.