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PubMed2005

Immune evasion by hepatitis C virus NS3/4A protease-mediated cleavage of the Toll-like receptor 3 adaptor protein TRIF.

Toll-like receptors (TLRs) bind pathogen-specific ligands early in infection, initiating signaling pathways that lead to expression of multiple protective cellular genes. Many viruses have evolved strategies that block the effector mechanisms induced through these signaling pathways, but viral interference with critical proximal receptor interactions has not been described. We show here that the NS3/4A serine protease of hepatitis C virus (HCV), a virus notorious for its ability to establish persistent intrahepatic infection, causes specific proteolysis of Toll-IL-1 receptor domain-containing adaptor inducing IFN-beta (TRIF or TICAM-1), an adaptor protein linking TLR3 to kinases responsible for activating IFN regulatory factor 3 (IRF-3) and NF-kappaB, transcription factors controlling a multiplicity of antiviral defenses. NS3/4A-mediated cleavage of TRIF reduces its abundance and inhibits polyI:C-activated signaling through the TLR3 pathway before its bifurcation to IRF-3 and NF-kappaB. This uniquely broad mechanism of immune evasion potentially limits expression of multiple host defense genes, thereby promoting persistent infections with this medically important virus.

Adaptor Proteins, Vesicular Transport↗

PubMed2006

Apoptosis-inducing factor participation in bovine macrophage Mycobacterium bovis-induced caspase-independent cell death.

Mycobacterium tuberculosis complex species survive and replicate in phagosomes of the host cell. Cell death (CD) has been highlighted as one of the probable outcomes in this host-pathogen interaction. Previously, our group demonstrated macrophage apoptosis as a consequence of Mycobacterium bovis infection. In this study, we aimed to identify the contribution of apoptotic effector elements in M. bovis-induced CD. Bovine macrophages were either infected with M. bovis (multiplicity of infection, 10:1) or treated with an M. bovis cell extract (CFE). Structural changes compatible with CD were evaluated. Chromatin condensation was increased three times by the CFE. On the other hand, a terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay demonstrated that levels of DNA fragmentation induced by M. bovis and CFE were 53.7% +/- 24% and 38.9% +/- 14%, respectively, whereas control cells had a basal proportion of 8.9% +/- 4.1%. Rates of DNA fragmentation were unaffected by the presence of the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp (z-VAD). Cells treated with 100 mug of CFE for 12 h had a fivefold decrease in the level of mitochondrial outer membrane permeabilization compared to that of untreated cells. Neither M. bovis infection nor CFE treatment induced activation of caspase 3, 8, or 9. Translocation of apoptosis-inducing factor (AIF) to the nucleus was identified in 32% +/- 3.5% and 26.3% +/- 4.9% of M. bovis-infected and CFE-treated cells, respectively. Incubation of macrophages with z-VAD prior to infection did not alter the percentage of cells showing AIF translocation. Our data suggest that M. bovis-induced CD in bovine macrophages is caspase independent with AIF participation.

Animals↗

PubMed2006

The Legionella pneumophila effector SidJ is required for efficient recruitment of endoplasmic reticulum proteins to the bacterial phagosome.

The virulence of Legionella pneumophila is dependent on the Dot/Icm type IV protein secretion system, which translocates effectors into infected cells. A large number of such translocated proteins have been identified, but few of these proteins are necessary for intracellular replication of the pathogen, making it difficult to correlate these genes with specific cell-biological events associated with L. pneumophila infection. We report here the identification and characterization of a family of two substrates, SidJ and SdjA, with distinctive phenotypes. In contrast to many Dot/Icm substrates, whose expression levels are elevated when bacteria are grown to postexponential phase, SidJ is produced at a constant rate during the entire bacterial growth cycle. Mutation in sidJ causes a significant growth defect in both macrophage and amoeba hosts, but an sdjA mutant is detectably defective only in protozoan hosts. However, in the amoeba host a mutant lacking both sidJ and sdjA does not display a more severe growth defect than the sidJ mutant. Despite its significant intracellular growth defect, the sidJ mutant is still able to effectively evade fusion with lysosomes. Importantly, recruitment of endoplasmic reticulum (ER) proteins by vacuoles containing the sidJ mutant was considerably delayed in both mammalian and amoeba cells. Our results suggest that SidJ modulates host cellular pathways, contributing to the trafficking or retention of ER-derived vesicles to L. pneumophila vacuoles.

Animals↗

PubMed1995

Endogenous expression of type II cGMP-dependent protein kinase mRNA and protein in rat intestine. Implications for cystic fibrosis transmembrane conductance regulator.

Certain pathogenic bacteria produce a family of heat stable enterotoxins (STa) which activate intestinal guanylyl cyclases, increase cGMP, and elicit life-threatening secretory diarrhea. The intracellular effector of cGMP actions has not been clarified. Recently we cloned the cDNA for a rat intestinal type II cGMP dependent protein kinase (cGK II) which is highly enriched in intestinal mucosa. Here we show that cGK II mRNA and protein are restricted to the intestinal segments from the duodenum to the proximal colon, with the highest amounts of cGK II protein in duodenum and jejunum. cGK II mRNA and protein decreased along the villus to crypt axis in the small intestine, whereas substantial amounts of both were found in the crypts of cecum. In intestinal epithelia, cGK II was specifically localized in the apical membrane, a major site of ion transport regulation. In contrast to cGK II, cGK I was localized in smooth muscle cells of the villus lamina propria. Short circuit current (ISC), a measure of Cl- secretion, was increased to a similar extent by STa and by 8-Br-cGMP, a selective activator of cGK, except in distal colon and in monolayers of T84 human colon carcinoma cells in which cGK II was not detected. In human and mouse intestine, the cyclic nucleotide-regulated Cl- conductance can be exclusively accounted for by the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. Viewed collectively, the data suggest that cGK II is the mediator of STa and cGMP effects on Cl- transport in intestinal-epithelia.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2004

The role of CD94/NKG2 in innate and adaptive immunity.

CD94/NKG2 is a heterodimer expressed on natural killer (NK) and a small subset of T cells. This receptor varies in function as an inhibitor or activator depending on which isoform of NKG2 is expressed. The ligand for CD94/NKG2 is HLA-E in human and its homolog, Qa1 in mouse, which are both nonclassical class I molecules that bind leader peptides from other class I molecules. Although <5% of CD8 T cells express the receptor in a naïve mouse, its expression is upregulated upon specific recognition of antigen. Similar to NK cells, most CD8 T cells that express high levels of CD94 co-express NKG2A, the inhibitory isoform. The engagement of this receptor can lead to a blocking of cytotoxicity. However, these receptors have also been implicated in the cell survival of both NK and CD8 T cells. The level of CD94 expression is inversely correlated with the level of apoptosis in culture. Thus, CD94/NKG2 receptors may regulate effector functions and cell survival of NK cells and CD8 T cells, thereby playing a crucial role in the innate and adaptive immune response to a pathogen.

Animals↗

PubMed1996

The immune system: a look from a distance.

The self-nonself discrimination is germline encoded for defense mechanisms, but it is somatically learned for the immune system and this is the fundamental difference between the two. When referring to the defense mechanisms of vertebrates, immunologists like to use the term "innate immune systems" to describe the germline encoded class of defense mechanism. It was the acquisition of a somatically learned S-NS discrimination during vertebrate evolution that permitted the immune system to develop large recognitive repertoires compared to those of defense mechanisms. This seemingly boundless immune repertoire has fascinated immunologists for almost a century. Today we have a better understanding of the size and function of the antibody repertoire. Humoral antibody effector functions depend upon secreted immunoglobulin and the concentration of antibody must reach a minimum effective threshold in a short enough time to stop a growing pathogen before it becomes lethal. This requires that initially an equivalent number of B-cells per ml respond to the pathogen. This number of B-cells must respond for each and every milliliter of animal. Consequently, the humoral immune system must be iterated. This straightforward conclusion has far reaching implications, some of which are explored in this review.

Animals↗

PubMed1997

Laccase and melanin in the pathogenesis of Cryptococcus neoformans.

Cryptococcosis, caused by an encapsulated fungus, Cryptococcus neoformans, has emerged as a life threatening infection in HIV positive individuals and other immunocompromised hosts. The present review describes laccase and its product melanin as an important virulence factor of Cryptococcus neoformans and illustrates the approaches used in elucidating the pathogenesis of cryptococcosis. Characterization of the biochemical pathways leading to melanin synthesis is summarized using biochemical and biomolecular approaches. Melanin synthesis is dependent on a single copper-dependent enzyme, laccase. Since the mammalian host does not contain this enzyme, laccase is an attractive candidate for the study of fungal pathogenesis, as well as a drug target. The cloning of the CNLAC1 gene and construction of CNLAC1 gene knock-out strains has confirmed its role in the virulence of Cryptococcus. Also described is the role of melanin in the host-pathogen interactions. Melanin may protect Cryptococcus cells by a variety of methods including anti-oxidant or cell wall surface effects thereby offering protection against numerous effectors of cellular immunity.

Antioxidants↗

PubMed2004

A signal through OX40 (CD134) allows anergic, autoreactive T cells to acquire effector cell functions.

To study mechanisms of peripheral self-tolerance, we injected small numbers of naive CD4(+) TCR-transgenic T cells into mice expressing the MHC/peptide ligand under the control of an MHC class II promoter. The donor T cells expand rapidly to very large numbers, acquire memory markers, and go out into tissues, but the animals remain healthy, and the accumulated T cells are profoundly anergic to restimulation with Ag in vitro. Provision of a costimulatory signal by coinjection of an agonist Ab to OX40 (CD134), a TNFR family member expressed on activated CD4 T cells, results in death of the mice within 12 days. TCR-transgenic T cells recovered at 5 days from anti-OX40-treated mice have a unique phenotype: they remain unresponsive to Ag in vitro, but they are larger, more granular, and strongly IL-2R positive. Some spontaneously secrete IFN-gamma directly ex vivo, and the majority make IFN-gamma in response to PMA and ionomycin. Although they are anergic by conventional tests requiring Ag recognition, they respond vigorously to cytokines, proliferating in response to IL-2, and secreting IFN-gamma when TCR signaling is bypassed with IL-12 and IL-18. We conclude that the costimulatory signal through OX40 allows otherwise harmless, proliferating, autoreactive T cells to acquire effector cell functions. The ability of these T cells to respond to cytokines by synthesizing additional inflammatory cytokines without a TCR signal may drive the fatal pathogenic process in vivo.

Animals↗

PubMed1992

[Effects of antioxidant emoxipin on lipid metabolism in the lungs during development of pulmonary edema].

Trials in white rats have shown, that intravenous injection of pituitrin (10 U/kg), challenging marked pulmonary edema, resulted in decrease of general lipids in them, as well as cholesterol, phospholipids and free fatty acids with accumulation of lipid peroxidation (LP) products. Preliminary administration of antioxidant emoxipin prevented the decrease in the level of general lipids, phospholipids and fatty acids, promoted a further decrease in cholesterol concentration in them and strongly inhibited lipid peroxidation processes. All this was combined with the development of more pronounced pulmonary edema. Intratracheal administration of a strong inductor of LP--Butyl hydroperoxide has never resulted in the development of pulmonary edema in white rats. These and earlier obtained data ground the statement, that LP--products are not pathogenic in the development of pulmonary edema. Inhibition of their formation may increase its development due to intensification of the signal from the receptor towards intracellular effector systems.

Animals↗

PubMed1987

[The role of T-lymphocytes in organ-specific autoimmune diseases].

Chronic debilitating diseases such as multiple sclerosis, demyelinating inflammatory polyradiculoneuropathy, rheumatoid arthritis, diabetes mellitus type I, Hashimoto thyroiditis, forms of uveitis and interstitial nephritis, share many characteristics. They are all organ-specific inflammatory diseases of unknown etiology but with strong evidence of tissue-destructive activity of the cellular immune system in the organs respectively affected, i.e. the central or peripheral nervous system, the joints, the islets of Langerhans, the thyroid gland, the retina, or the tubulo-interstitial renal tissue. Recognized animal models of all these diseases are experimentally induced autoimmune conditions that are transferable with autoreactive T-lymphocytes, in contrast to autoantibodies in humoral autoimmune diseases. In recent years, disease-transferring T-lymphocytes, have been successfully grown as lines and clones in vitro, thus finally proving the primary pathogenic role of autoreactive T-lymphocytes in these animal models. Such T-cell lines are valuable tools in further defining autoantigens, studying mechanisms of T-cell activation in vitro, following T-cell migration and organ-specific homing in vivo, and analyzing effector functions in the infiltrated organs. In addition, questions concerning the breakdown of immunological selftolerance and the basic principles of resistance to disease can be addressed, and possibilities of treatment can be approached. Although the basic etiology of the human organ-specific immune diseases is still unknown, these animal models have helped to throw light on some of the pathogenic mechanisms common to these various diseases.

Animals↗

PubMed2002

Molecular basis of non-self recognition by the horseshoe crab tachylectins.

The self/non-self discrimination by innate immunity through simple ligands universally expressed both on pathogens and hosts, such as monosaccharides and acetyl group, depends on the density or clustering patterns of the ligands. The specific recognition by the horseshoe crab tachylectins with a propeller-like fold or a propeller-like oligomeric arrangement is reinforced by the short distance between the individual binding sites that interact with pathogen-associated molecular patterns (PAMPs). There is virtually no conformational change in the main or side chains of tachylectins upon binding with the ligands. This low structural flexibility of the propeller structures must be very important for specific interaction with PAMPs. Mammalian lectins, such as mannose-binding lectin and ficolins, trigger complement activation through the lectin pathway in the form of opsonins. However, tachylectins have no effector collagenous domains and no lectin-associated serine proteases found in the mammalian lectins. Furthermore, no complement-like proteins have been found in horseshoe crabs, except for alpha(2)-macroglobulin. The mystery of the molecular mechanism of the scavenging pathway of pathogens in horseshoe crabs remains to be solved.

Animals↗

PubMed2002

The presence of diverse IS elements and an avrPphD homologue that acts as a virulence factor on the pathogenicity plasmid of Erwinia herbicola pv. gypsophilae.

The pathogenicity of Erwinia herbicola pv. gypsophilae (Ehg) and Erwinia herbicola pv. betae (Ehb) is dependent on a native plasmid (pPATH(Ehg) or pPATH(Ehb)) that harbors the hrp gene cluster, genes encoding type III effectors, phytohormones, biosynthetic genes, and several copies of IS1327. Sequence analysis of the hrp-flanking region in pPATH(Ehg) (cosmid pLA150) revealed a cluster of four additional IS elements designated as ISEhel, ISEhe2, ISEhe3, and ISEhe4. Two copies of another IS element (ISEhe5) were identified on the upstream region of the indole-3-acetic acid operon located on the same cosmid. Based on homology of amino acids and genetic organization, ISEhe1 belongs to the IS630 family, ISEhe2 to the IS5 family, ISEhe3 and ISEhe4 to different groups of the IS3 family, and ISEhe5 to the IS1 family. With the exception of ISEhe4, one to three copies of all the other IS elements were identified only in pathogenic strains of Erwinia herbicola pv. gypsophilae and Erwinia herbicola pv. betae whereas ISEhe4 was present in both pathogenic and nonpathogenic strains. An open reading frame that exhibited high identity (89% in amino acids) to AvrPphD of Pseudomonas syringae pv. phaseolicola was present within the cluster of IS elements. An insertional mutation in the AvrPphDEh, reduced gall size in gypsophila by approximately 85%. In addition, remnants of known genes from four different bacteria were detected on the same cosmid.

Bacterial Proteins↗

PubMed2001

Yersinia outer protein P of Yersinia enterocolitica simultaneously blocks the nuclear factor-kappa B pathway and exploits lipopolysaccharide signaling to trigger apoptosis in macrophages.

Exposure of macrophages to bacteria or LPS mediates activation of signaling pathways that induce expression of self defense-related genes. Pathogenic Yersinia species impair activation of transcription factor NF-kappaB and trigger apoptosis in macrophages. In this study, we dissected the mechanism of apoptosis induction by Yersinia. Selectively, Yersinia enterocolitica strains producing the effector protein Yersinia outer protein P (YopP) hampered NF-kappaB activation and subsequently conferred apoptosis to J774A.1 macrophages. Thereby, YopP bound and inhibited the macrophage NF-kappaB-activating kinase IKKbeta. YopP- and Yersinia-, but not Salmonella-induced apoptosis was specifically prevented by transient overexpression of NF-kappaB p65, giving evidence that YopP mediates cell death by disrupting the NF-kappaB signaling pathway. Transfection of J774A.1 macrophages with YopP induced a moderate, but significant degree of apoptosis (40-50% of transfected cells). This effect was strongly enhanced by additional initiation of LPS signaling (80-90%), indicating a synergism between LPS-induced signal transduction and inhibition of NF-kappaB by YopP. This reflects a strategy of a bacterial pathogen that takes advantage of LPS, serving as cofactor, to impair the macrophage.

Adhesins, Bacterial↗

PubMed2026

Precision Engineering of Evolution-Resilient Rice against Bacterial Blight.

The persistent conflict between rice and Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial blight, exemplifies a dynamic genetic arms race in agriculture. The cyclical deployment and erosion of major resistance (R) genes highlight the high adaptive potential of Xoo and the need for strategies that are durable rather than absolute. This review synthesizes a paradigm shift from reactive, single R-gene deployment toward proactive engineering of evolution-resilient resistance. We explore the molecular-genetic basis of Xoo adaptability, including TAL effector diversification, non-TAL virulence functions, genome variation, and immune suppression mechanisms. In response, we propose a framework for durable disease management with three connected components: precision disarmament through editing of susceptibility-gene effector-binding elements and executor/decoy designs; smart induction through targeted delivery and immune priming; and ecological fortification through protective microbiomes. We also discuss the limits, trade-offs, and field-validation requirements of these approaches. Integrating frontier technologies with evolutionary genetics, predictive genomics, and pathogen population dynamics can help develop rice varieties and deployment systems that are more difficult for Xoo populations to overcome.

CRISPR↗

PubMed2006

Pseudomonas aeruginosa type III-secreted toxin ExoT inhibits host-cell division by targeting cytokinesis at multiple steps.

Pseudomonas aeruginosa is an opportunistic pathogen that requires preexisiting epithelial injury to cause acute infections. We report that P. aeruginosa inhibits mammalian cytokinesis in a type III secretion system and exotoxin T (ExoT)-dependent manner. ExoT is a bifunctional type III secretion system effector protein that contains an N-terminal GTPase-activating protein domain and a C-terminal ADP-ribosyl transferase domain. Each of its domains inhibits cytokinesis in a kinetically, morphologically, and mechanistically distinct manner. The GTPase-activating protein-mediated inhibition of cytokinesis occurs early, likely as a consequence of its inhibitory effect on RhoA. The ADP-ribosyl transferase domain inhibits late steps of cytokinesis by blocking syntaxin-2 localization to the midbody, an event essential for completion of cytokinesis. These findings provide an example of a bacterial pathogen targeting cytokinesis.

ADP Ribose Transferases↗

PubMed2003

Anti-neuronal nuclear autoantibody type 2: paraneoplastic accompaniments.

We identified the IgG autoantibody ANNA-2 ("anti-Ri") in 34 patients in a 12-year period by immunofluorescence screening of sera from approximately 75000 patients with subacute neurological disorders that were suspected to be paraneoplastic. Detailed clinical information was available for 28 patients (10 men, 18 women). Cancer was diagnosed in 24 patients (86%); 21 had histologically proven carcinoma (10 lung, 9 breast, 1 cervical, 1 bladder), and 3 had an intrathoracic imaging abnormality. Cancer anteceded neurological symptoms in 4 of 28 patients. Cancer detection frequency increased with continued surveillance. Neurological disorders, in decreasing frequency, were brainstem syndrome (including opsoclonus, myoclonus, or both), cerebellar syndrome, myelopathy, peripheral neuropathy, cranial neuropathy, movement disorder, encephalopathy, Lambert-Eaton syndrome, and seizures. Four patients had laryngospasm and four had jaw opening dystonia (two with neck dystonia). Nine (32%) were wheelchair-bound 1 month after neurological symptom onset. Most improved neurologically after immunomodulatory or tumor-directed therapy. Accompanying autoantibodies, found in 73% of sera, included ANNA-1, ANNA-3, CRMP-5-IgG, P/Q-type and N-type Ca(2+) channel antibodies, and muscle-type acetylcholine receptor antibody. Some neurological accompaniments of ANNA-2 may reflect potentially pathogenic humoral or cell-mediated responses to coimmunogenic tumor antigens, for example, Lambert-Eaton syndrome (P/Q-type Ca(2+) channel antibody) and peripheral neuropathy (ANNA-1 effector T cells).

Adult↗

PubMed2001

New approaches to dissect degeneracy and specificity in T cell antigen recognition.

The acquired immune system is a complex and very effective defense against invading pathogens such as bacteria and viruses. T cells are central to the acquired immune system by controlling B and T cell activation and induction of T cell effector functions. The key event for T cell activation is the recognition of a specific antigen by the T cell receptor. During the past decade antigen recognition of T cells has been investigated intensively leading to new insights into the molecular mechanisms of T cell activation. In addition to the resolution of the molecular structure of the trimolecular complex (T cell receptor, peptide, major histocompatibility complex) functional studies have demonstrated the flexibility of the T cell receptor interaction with its ligand. These observations have had strong implications for the understanding of T cell selection, maturation, and repertoire maintenance. In addition, the flexibility of the T cell receptor has provided the basis for novel methods to dissect antigen recognition and define the repertoire of ligands for a given receptor. Here, we summarize recent progress on T cell recognition and method innovations with respect to future studies in autoimmune diseases.

Animals↗

PubMed2001

Differential expression of granulysin and perforin by NK cells in cancer patients and correlation of impaired granulysin expression with progression of cancer.

Granulysin has been identified as an effector molecule co-localized with perforin in the cytotoxic granules of cytotoxic T lymphocytes and natural killer (NK) cells, and has been reported to kill intracellular pathogens in infected cells in the presence of perforin and to induce a cytotoxic effect against tumor cells. The aim of the present study was to elucidate whether intracellular expression of granulysin and perforin by NK cells might be associated with progression of cancer. Flow cytometric analysis demonstrated high levels of perforin and granulysin expression by CD3(-) CD16(+) cells in healthy controls. In contrast, cancer patients exhibited significantly decreased levels of granulysin expression ( P<0.005), despite having equally high levels of perforin expression in comparison with healthy controls. The tumor-free patients expressed granulysin at levels similar to healthy controls, while the progressive tumor-bearing patients expressed remarkably lower levels of granulysin compared to healthy controls ( P<0.0001). Similarly, patients with an advanced performance status had significantly fewer granulysin-positive NK cells than healthy controls. Meanwhile, a considerable number of the tumor-bearing patients showed a decrease in the number of circulating NK cells, and a correlation between impaired granulysin expression and reduced circulating NK cells was observed. These findings suggest that the tumor-bearing patients with impaired granulysin expression were in an immunosuppressive state. In conclusion, impaired expression of granulysin by NK cells correlates with progression of cancer, and determination of granulysin expression might prove informative for assessing the immunological condition of cancer patients.

Adult↗