Protein kinase A-mediated inhibition of gamma interferon-induced tyrosine phosphorylation of Janus kinases and latent cytoplasmic transcription factors in human monocytes by Ehrlichia chaffeensis

Epidemiologic, Clinical and Immunological Consequences of Co-Infections during Canine Leishmaniosis

Simple Summary

Canine leishmaniosis (CanL), the most severe, visceralizing form of disease caused by Leishmania infantum transmitted by phlebotomine sand flies. CanL is frequently diagnosed in the Mediterranean basin and South America, although it is also found in other regions, including the United States (U.S.). Dogs in these regions are at risk for co-infections, prominently tick-borne diseases. Our review examines epidemiologic, clinical, and immunologic mechanisms found during the most common eight CanL co-infections reported in published literature. Co-infections alter immunologic processes and disease progression impacting CanL diagnosis, therapeutic responses, and prognosis.

Abstract

Canine leishmaniosis (CanL) is a vector-borne, parasitic disease. CanL is endemic in the Mediterranean basin and South America but also found in Northern Africa, Asia, and the U.S. Regions with both competent sand fly vectors and L. infantum parasites are also endemic for additional infectious diseases that could cause co-infections in dogs. Growing evidence indicates that co-infections can impact immunologic responses and thus the clinical course of both CanL and the comorbid disease(s). The aim for this review is to summarize epidemiologic, clinical, and immunologic factors contributing to eight primary co-infections reported with CanL: Ehrlichia spp., Anaplasma spp., Borrelia spp., Babesia spp., Trypanosoma cruzi, Toxoplasma gondii, Dirofilaria immitis, Paracoccidioides braziliensis. Co-infection causes mechanistic differences in immunity which can alter diagnostics, therapeutic management, and prognosis of dogs with CanL. More research is needed to further explore immunomodulation during CanL co-infection(s) and their clinical impact.

Tick-Borne Emerging Infections: Ehrlichiosis and Anaplasmosis

Human ehrlichiosis and anaplasmosis are acute febrile tick-borne infectious diseases caused by various members from the genera Ehrlichia and Anaplasma. Ehrlichia chaffeensis is the major etiologic agent of human monocytotropic ehrlichiosis (HME), while Anaplasma phagocytophilum is the major cause of human granulocytic anaplasmosis (HGA). The clinical manifestations of HME and HGA ranges from subclinical to potentially life-threatening diseases associated with multi-organ failure. Macrophages and neutrophils are the major target cells for Ehrlichia and Anaplasma, respectively. The threat to public health is increasing with newly emerging ehrlichial and anaplasma agents, yet vaccines for human ehrlichioses and anaplasmosis are not available, and therapeutic options are limited. This article reviews recent advances in the understanding of HME and HGA.

PKA regulatory IIα subunit is essential for PGD2-mediated resolution of inflammation

The kinetic participation of macrophages is critical for inflammatory resolution and recovery from myocardial infarction (MI), particularly with respect to the transition from the M1 to the M2 phenotype; however, the underlying mechanisms are poorly understood. In this study, we found that the deletion of prostaglandin (PG) D2 receptor subtype 1 (DP1) in macrophages retarded M2 polarization, antiinflammatory cytokine production, and resolution in different inflammatory models, including the MI model. DP1 deletion up-regulated proinflammatory genes expression via JAK2/STAT1 signaling in macrophages, whereas its activation facilitated binding of the separated PKA regulatory IIα subunit (PRKAR2A) to the transmembrane domain of IFN-γ receptor, suppressed JAK2-STAT1 axis-mediated M1 polarization, and promoted resolution. PRKAR2A deficiency attenuated DP1 activation-mediated M2 polarization and resolution of inflammation. Collectively, PGD2-DP1 axis-induced M2 polarization facilitates resolution of inflammation through the PRKAR2A-mediated suppression of JAK2/STAT1 signaling. These observations indicate that macrophage DP1 activation represents a promising strategy in the management of inflammation-associated diseases, including post-MI healing.

Molecular Pathogenesis of Ehrlichia chaffeensis Infection

Ehrlichia chaffeensis is an obligatory intracellular and cholesterol-dependent bacterium that has evolved special proteins and functions to proliferate inside leukocytes and cause disease. E. chaffeensis has a multigene family of major outer membrane proteins with porin activity and induces infectious entry using its entry-triggering protein to bind the human cell surface protein DNase X. During intracellular replication, three functional pairs of two-component systems are sequentially expressed to regulate metabolism, aggregation, and the development of stress-resistance traits for transmission. A type IV secretion effector of E. chaffeensis blocks mitochondrion-mediated host cell apoptosis. Several type I secretion proteins are secreted at the Ehrlichia-host interface. E. chaffeensis strains induce strikingly variable inflammation in mice. The central role of MyD88, but not Toll-like receptors, suggests that Ehrlichia species have unique inflammatory molecules. A recent report about transient targeted mutagenesis and random transposon mutagenesis suggests that stable targeted knockouts may become feasible in Ehrlichia.

Hacker within! Ehrlichia chaffeensis Effector Driven Phagocyte Reprogramming Strategy

Ehrlichia chaffeensis is a small, gram negative, obligately intracellular bacterium that preferentially infects mononuclear phagocytes. It is the etiologic agent of human monocytotropic ehrlichiosis (HME), an emerging life-threatening tick-borne zoonosis. Mechanisms by which E. chaffeensis establishes intracellular infection, and avoids host defenses are not well understood, but involve functionally relevant host-pathogen interactions associated with tandem and ankyrin repeat effector proteins. In this review, we discuss the recent advances in our understanding of the molecular and cellular mechanisms that underlie Ehrlichia host cellular reprogramming strategies that enable intracellular survival.

The role of CD8 T lymphocytes in rickettsial infections

Arthropod-borne obligately intracellular bacteria pose a difficult challenge to the immune system. The genera Rickettsia, Orientia, Ehrlichia, and Anaplasma evolved mechanisms of immune evasion, and each interacts differently with the immune system. The roles of CD8 T cells include protective immunity and immunopathology. In Rickettsia infections, CD8 T cells are protective mediated in part by cytotoxicity toward infected cells. In contrast, TNF-α overproduction by CD8 T cells is pathogenic in lethal ehrlichiosis by induction of apoptosis/necrosis in hepatocytes. Yet, CD8 T cells, along with CD4 T cells and antibodies, also contribute to protective immunity in ehrlichial infections. In granulocytic anaplasmosis, CD8 T cells impact pathogen control modestly but could contribute to immunopathology by virtue of their dysfunction. While preliminary evidence indicates that CD8 T cells are important in protection against Orientia tsutsugamushi, mechanistic studies have been neglected. Valid animal models will enable experiments to elucidate protective and pathologic immune mechanisms. The public health need for vaccines against these agents of human disease, most clearly O. tsutsugamushi, and the veterinary diseases, canine monocytotropic ehrlichiosis (Ehrlichia canis), heartwater (Ehrlichia ruminantium), and bovine anaplasmosis (A. marginale), requires detailed immunity and immunopathology investigations, including the roles of CD8 T lymphocytes.

Recent molecular insights into rickettsial pathogenesis and immunity

Human infections with arthropod-borne Rickettsia species remain a major global health issue, causing significant morbidity and mortality. Epidemic typhus due to Rickettsia prowazekii has an established reputation as the 'scourge of armies', and as a major determinant of significant 'historical turning points'. No suitable vaccines for human use are currently available to prevent rickettsial diseases. The unique lifestyle features of rickettsiae include obligate intracellular parasitism, intracytoplasmic niche within the host cell, predilection for infection of microvascular endothelium in mammalian hosts, association with arthropods and the tendency for genomic reduction. The fundamental research in the field of Rickettsiology has witnessed significant recent progress in the areas of pathogen adhesion/invasion and host immune responses, as well as the genomics, proteomics, metabolomics, phylogenetics, motility and molecular manipulation of important rickettsial pathogens. The focus of this review article is to capture a snapshot of the latest developments pertaining to the mechanisms of rickettsial pathogenesis and immunity.

Commensal bacteria at the interface of host metabolism and the immune system

The mammalian gastrointestinal tract, the site of digestion and nutrient absorption, harbors trillions of beneficial commensal microbes from all three domains of life. Commensal bacteria, in particular, are key participants in the digestion of food, and are responsible for the extraction and synthesis of nutrients and other metabolites that are essential for the maintenance of mammalian health. Many of these nutrients and metabolites derived from commensal bacteria have been implicated in the development, homeostasis and function of the immune system, suggesting that commensal bacteria may influence host immunity via nutrient- and metabolite-dependent mechanisms. Here we review the current knowledge of how commensal bacteria regulate the production and bioavailability of immunomodulatory, diet-dependent nutrients and metabolites and discuss how these commensal bacteria-derived products may regulate the development and function of the mammalian immune system.

Anaplasma phagocytophilum, interferon gamma production and Stat1 signaling

Human granulocytic anaplasmosis is caused by the obligate intracellular bacterium, Anaplasma phagocytophilum. The proinflammatory cytokine, IFN-γ, is necessary for innate immunity and plays an important role in the induction of severe histopathology in A. phagocytophilum-infected mice, horses and humans. In this study, activation of signal transducer and activator of transcription (Stat) 1 phosphorylation associated with A. phagocytophilum infection was examined in mice and found to be markedly greater on day 7 post-infection than in mock-infected controls. This increase in phosphorylated Stat1 (pStat1) correlated significantly with IFN-γ production and inflammatory tissue injury. Because pStat1 operates as a transcription factor central to the generation of effectors of inflammatory injury, these data suggest that Stat1 signaling is involved in IFN-γ-mediated immunopathologic lesions and disease in A. phagocytophilum infection and could be an important target for intervention in this disease.

Ehrlichia chaffeensis tandem repeat proteins and Ank200 are type 1 secretion system substrates related to the repeats-in-toxin exoprotein family

Ehrlichia chaffeensis has type 1 and 4 secretion systems (T1SS and T4SS), but the substrates have not been identified. Potential substrates include secreted tandem repeat protein (TRP) 47, TRP120, and TRP32, and the ankyrin repeat protein, Ank200, that are involved in molecular host–pathogen interactions including DNA binding and a network of protein–protein interactions with host targets associated with signaling, transcriptional regulation, vesicle trafficking, and apoptosis. In this study we report that E. chaffeensis TRP47, TRP32, TRP120, and Ank200 were not secreted in the Agrobacterium tumefaciens Cre recombinase reporter assay routinely used to identify T4SS substrates. In contrast, all TRPs and the Ank200 proteins were secreted by the Escherichia coli complemented with the hemolysin secretion system (T1SS), and secretion was reduced in a T1SS mutant (ΔTolC), demonstrating that these proteins are T1SS substrates. Moreover, T1SS secretion signals were identified in the C-terminal domains of the TRPs and Ank200, and a detailed bioinformatic analysis of E. chaffeensis TRPs and Ank200 revealed features consistent with those described in the repeats-in-toxins (RTX) family of exoproteins, including glycine- and aspartate-rich tandem repeats, homology with ATP-transporters, a non-cleavable C-terminal T1SS signal, acidic pIs, and functions consistent with other T1SS substrates. Using a heterologous E. coli T1SS, this investigation has identified the first Ehrlichia T1SS substrates supporting the conclusion that the T1SS and corresponding substrates are involved in molecular host–pathogen interactions that contribute to Ehrlichia pathobiology. Further investigation of the relationship between Ehrlichia TRPs, Ank200, and the RTX exoprotein family may lead to a greater understanding of the importance of T1SS substrates and specific functions of T1SS in the pathobiology of obligately intracellular bacteria.

New insight into immunity and immunopathology of Rickettsial diseases

Human rickettsial diseases comprise a variety of clinical entities caused by microorganisms belonging to the genera Rickettsia, Orientia, Ehrlichia, and Anaplasma. These microorganisms are characterized by a strictly intracellular location which has, for long, impaired their detailed study. In this paper, the critical steps taken by these microorganisms to play their pathogenic roles are discussed in detail on the basis of recent advances in our understanding of molecular Rickettsia-host interactions, preferential target cells, virulence mechanisms, three-dimensional structures of bacteria effector proteins, upstream signalling pathways and signal transduction systems, and modulation of gene expression. The roles of innate and adaptive immune responses are discussed, and potential new targets for therapies to block host-pathogen interactions and pathogen virulence mechanisms are considered.

Ehrlichia chaffeensis TRP120 binds a G+C-rich motif in host cell DNA and exhibits eukaryotic transcriptional activator function

Ehrlichia chaffeensis is an obligately intracellular bacterium that modulates host cell gene transcription in the mononuclear phagocyte, but the host gene targets and mechanisms involved in transcriptional modulation are not well-defined. In this study, we identified a novel tandem repeat DNA-binding domain in the E. chaffeensis 120-kDa tandem repeat protein (TRP120) that directly binds host cell DNA. TRP120 was observed by immunofluorescent microscopy in the nucleus of E. chaffeensis-infected host cells and was detected in nuclear extracts by Western immunoblotting with TRP120-specific antibody. The TRP120 binding sites and associated host cell target genes were identified using high-throughput deep sequencing (Illumina) of immunoprecipitated DNA (chromatin immunoprecipitation and high-throughput DNA sequencing). Multiple em motif elicitation (MEME) analysis of the most highly enriched TRP120-bound sequences revealed a G+C-rich DNA motif, and recombinant TRP120 specifically bound synthetic oligonucleotides containing the motif. TRP120 target gene binding sites were mapped most frequently to intersecting regions (intron/exon; 49%) but were also identified in upstream regulatory regions (25%) and downstream locations (26%). Genes targeted by TRP120 were most frequently associated with transcriptional regulation, signal transduction, and apoptosis. TRP120 targeted inflammatory chemokine genes, CCL2, CCL20, and CXCL11, which were strongly upregulated during E. chaffeensis infection and were also upregulated by direct transfection with recombinant TRP120. This study reveals that TRP120 is a novel DNA-binding protein that is involved in a host gene transcriptional regulation strategy.

Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum

Anaplasma phagocytophilum persists in nature by cycling between mammals and ticks. Human infection by the bite of an infected tick leads to a potentially fatal emerging disease called human granulocytic anaplasmosis. A. phagocytophilum is an obligatory intracellular bacterium that replicates inside mammalian granulocytes and the salivary gland and midgut cells of ticks. A. phagocytophilum evolved the remarkable ability to hijack the regulatory system of host cells. A. phagocytophilum alters vesicular traffic to create an intracellular membrane-bound compartment that allows replication in seclusion from lysosomes. The bacterium downregulates or actively inhibits a number of innate immune responses of mammalian host cells, and it upregulates cellular cholesterol uptake to acquire cholesterol for survival. It also upregulates several genes critical for the infection of ticks, and it prolongs tick survival at freezing temperatures. Several host factors that exacerbate infection have been identified, including interleukin-8 (IL-8) and cholesterol. Host factors that overcome infection include IL-12 and gamma interferon (IFN-γ). Two bacterial type IV secretion effectors and several bacterial proteins that associate with inclusion membranes have been identified. An understanding of the molecular mechanisms underlying A. phagocytophilum infection will foster the development of creative ideas to prevent or treat this emerging tick-borne disease.

Molecular and cellular pathobiology of Ehrlichia infection: targets for new therapeutics and immunomodulation strategies

Ehrlichia are small obligately intracellular bacteria in the order Rickettsiales that are transmitted by ticks and associated with emerging life-threatening human zoonoses. Vaccines are not available for human ehrlichiosis, and therapeutic options are limited to a single antibiotic class. New technologies for exploring host-pathogen interactions have yielded recent advances in understanding the molecular interactions between Ehrlichia and the eukaryotic host cell and identified new targets for therapeutic and vaccine development, including those that target pathogen virulence mechanisms or disrupt the processes associated with ehrlichial effector proteins. Animal models have also provided insight into immunopathological mechanisms that contribute significantly to understanding severe disease manifestations, which should lead to the development of immunomodulatory approaches for treating patients nearing or experiencing severe disease states. In this review, we discuss the recent advances in our understanding of molecular and cellular pathobiology and the immunobiology of Ehrlichia infection. We identify new molecular host-pathogen interactions that can be targets of new therapeutics, and discuss prospects for treating the immunological dysregulation during acute infection that leads to life-threatening complications.

Haemophagocytic syndrome and rickettsial diseases

Haemophagocytic lymphohistiocytosis is a rare but potentially fatal disease resulting from dysregulated activation and proliferation of lymphocytes. We present a case of haemophagocytic syndrome occurring in a 5-year-old Italian boy as a complication of Mediterranean spotted fever. The characteristics of this case have been analysed and contextualized among those of another 15 cases of haemophagocytic syndrome associated with rickettsial diseases found through a systematic review of the international literature.

Progress and obstacles in vaccine development for the ehrlichioses

Ehrlichia are tick-borne obligately intracellular bacteria that cause significant diseases in veterinary natural hosts, including livestock and companion animals, and are now considered important zoonotic pathogens in humans. Vaccines are needed for these veterinary and zoonotic human pathogens, but many obstacles exist that have impeded their development. These obstacles include understanding genetic and antigenic variability, influence of the host on the pathogen phenotype and immunogenicity, identification of the ehrlichial antigens that stimulate protective immunity and those that elicit immunopathology, development of animal models that faithfully reflect the immune responses of the hosts and understanding molecular host-pathogen interactions involved in immune evasion or that may be blocked by the host immune response. We review the obstacles and progress in addressing barriers associated with vaccine development to protect livestock, companion animals and humans against these host defense-evasive and cell function-manipulative, vector-transmitted pathogens.

Mass spectrometric analysis of Ehrlichia chaffeensis tandem repeat proteins reveals evidence of phosphorylation and absence of glycosylation

BACKGROUND

Ehrlichia chaffeensis has a small subset of immunoreactive secreted, acidic (pI approximately 4), tandem repeat (TR)-containing proteins (TRPs), which exhibit abnormally large electrophoretic masses that have been associated with glycosylation of the TR domain.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined the extent and nature of posttranslational modifications on the native TRP47 and TRP32 using mass spectrometry. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) demonstrated that the mass of native TRP47 (33,104.5 Da) and TRP32 (22,736.8 Da) were slightly larger (179- and 288-Da, respectively) than their predicted masses. The anomalous migration of native and recombinant TRP47, and the recombinant TR domain (C-terminal region) were normalized by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) modification of negatively charged carboxylates to neutral amides. Exhaustive tandem mass spectrometric analysis (92% coverage) performed on trypsin and Asp-N digested native TRP47 identified peptides consistent with their predicted masses. Two TRP47 peptides not identified were located in the normally migrating amino (N)-terminal region of TRP47 and contained predicted phosphorylation sites (tyrosine and serine residues). Moreover, native TRP47 was immunoprecipitated from E. chaffeensis-infected cell lysate with anti-phosphotyrosine (anti-pTyr) antibody.

CONCLUSIONS/SIGNIFICANCE

TRP47 and TRP32 are not modified by glycans and the substantial net negative charge of the ehrlichial TRPs, and particularly the highly acidic TRs present within the ehrlichial TRPs, is responsible for larger-than-predicted masses. Furthermore, this study provides evidence that the N-terminal region of the TRP47 is tyrosine phosphorylated.

New insights into molecular Ehrlichia chaffeensis-host interactions

Ehrlichia chaffeensis is an obligately intracellular bacterium that exhibits tropism for mononuclear phagocytes and survives by reprogramming the host cell. Here we review new information regarding the newly characterized effector molecules and the complex network of molecular host-pathogen interactions that the organism exploits enabling it to thrive and persist intracellularly.

Molecular events involved in cellular invasion by Ehrlichia chaffeensis and Anaplasma phagocytophilum

Ehrlichia chaffeensis and Anaplasma phagocytophilum are obligatory intracellular bacteria that preferentially replicate inside leukocytes by utilizing biological compounds and processes of these primary host defensive cells. These bacteria incorporate cholesterol from the host for their survival. Upon interaction with host monocytes and granulocytes, respectively, these bacteria usurp the lipid raft domain containing GPI-anchored protein to induce a series of signaling events that result in internalization of the bacteria. Monocytes and neutrophils usually kill invading microorganisms by fusion of the phagosomes containing the bacteria with granules containing both antimicrobial peptides and lysosomal hydrolytic enzymes and/or through sequestering vital nutrients. However, E. chaffeensis and A. phagocytophilum alter vesicular traffic to create a unique intracellular membrane-bound compartment that allows their replication in seclusion from lysosomal killing. These bacteria are quite sensitive to reactive oxygen species (ROS), so in order to survive in host cells that are primary mediators of ROS-induced killing, they inhibit activation of NADPH oxidase and assembly of this enzyme in their inclusion compartments. Moreover, host phagocyte activation and differentiation, apoptosis, and IFN-gamma signaling pathways are inhibited by these bacteria. Through reductive evolution, lipopolysaccharide and peptidoglycan that activate the innate immune response, have been eliminated from these gram-negative bacteria at the genomic level. Upon interaction with new host cells, bacterial genes encoding the Type IV secretion apparatus and the two-component regulatory system are up-regulated to sense and adapt to the host environment. Thus dynamic signal transduction events concurrently proceed both in the host cells and in the invading E. chaffeensis and A. phagocytophilum bacteria for successful establishment of intracellular infection. Several bacterial surface-exposed proteins and porins are recently identified. Further functional studies on Ehrlichia and Anaplasma effector or ligand molecules and cognate host cell receptors will undoubtedly advance our understanding of the complex interplay between obligatory intracellular pathogens and their hosts. Such data can be applied towards treatment, diagnosis, and control of ehrlichiosis and anaplasmosis.

Nuclear translocated Ehrlichia chaffeensis ankyrin protein interacts with a specific adenine-rich motif of host promoter and intronic Alu elements

Ehrlichiae are obligately intracellular bacteria that reside and replicate in phagocytes by circumventing host cell defenses and modulating cellular processes, including host cell gene transcription. However, the mechanisms by which ehrlichiae influence host gene transcription have largely remained undetermined. Numerous ankyrin and tandem repeat-containing proteins associated with host-pathogen interactions have been identified in Ehrlichia species, but their roles in pathobiology are unknown. In this study, we determined by confocal immunofluorescence microscopy and by immunodetection in purified nuclear extracts that the ankyrin repeat-containing protein p200 is translocated to the nuclei of Ehrlichia-infected monocytes. Chromatin immunoprecipitation (ChIP) with DNA sequencing revealed an Ehrlichia chaffeensis p200 interaction located within host promoter and intronic Alu-Sx elements, the most abundant repetitive elements in the human genome. A specific adenine-rich (mid-A-stretch) motif within Alu-Sx elements was identified using electrophoretic mobility shift and NoShift assays. Whole-genome analysis with ChIP and DNA microarray analysis (ChIP-chip) determined that genes (n = 456) with promoter Alu elements primarily related to transcription, apoptosis, ATPase activity, and structural proteins associated with the nucleus and membrane-bound organelles were the primary targets of p200. Several p200 target genes (encoding tumor necrosis factor alpha, Stat1, and CD48) associated with ehrlichial pathobiology were strongly upregulated during infection, as determined by quantitative PCR. This is the first study to identify a nuclear translocation of bacterially encoded protein by E. chaffeensis and to identify a specific binding motif and genes that are primary targets of a novel molecular strategy to reprogram host cell gene expression to promote survival of the pathogen.

An Ehrlichia chaffeensis tandem repeat protein interacts with multiple host targets involved in cell signaling, transcriptional regulation, and vesicle trafficking

Ehrlichia chaffeensis is an obligately intracellular bacterium that exhibits tropism for mononuclear phagocytes forming cytoplasmic membrane-bound microcolonies called morulae. To survive and replicate within phagocytes, E. chaffeensis exploits the host cell by modulating a number of host cell processes, but the ehrlichial effector proteins involved are unknown. In this study, we determined that p47, a secreted, differentially expressed, tandem repeat (TR) protein, interacts with multiple host proteins associated with cell signaling, transcriptional regulation, and vesicle trafficking. Yeast two-hybrid analysis revealed that p47 interacts with polycomb group ring finger 5 (PCGF5) protein, Src protein tyrosine kinase FYN (FYN), protein tyrosine phosphatase non-receptor type 2 (PTPN2), and adenylate cyclase-associated protein 1 (CAP1). p47 interaction with these proteins was further confirmed by coimmunoprecipitation assays and colocalization in HeLa cells transfected with p47-green fluorescent fusion protein (AcGFP1-p47). Moreover, confocal microscopy demonstrated p47-expressing dense-cored (DC) ehrlichiae colocalized with PCGF5, FYN, PTPN2, and CAP1. An amino-terminally truncated form of p47 containing TRs interacted only with PCGF5 and not with FYN, PTPN2, and CAP1, indicating differences in p47 domains that are involved in these interactions. These results demonstrate that p47 is involved in a complex network of interactions involving numerous host cell proteins. Furthermore, this study provides a new insight into the molecular and functional distinction of DC ehrlichiae, as well as the effector proteins involved in facilitating ehrlichial survival in mononuclear phagocytes.

The IFNgamma-induced STAT1-CBP/P300 association, required for a normal response to the cytokine, is disrupted in Brucella-infected macrophages

To develop intracellularly within phagocytes and cause chronic infection, Brucella must overcome different steps of the host immune responses. IFNgamma is a key mediator of the innate and adaptive responses produced during Brucella infection. Therefore, Brucella would control host defenses by impairing macrophage responses to IFNgamma. We first showed that in infected human macrophages (VD3-differentiated THP-1 cells) Brucella escaped the microbicidal environment generated by IFNgamma. We then analyzed the IFNgamma-mediated signaling in Brucella-infected cells. We observed no decrease in STAT1 tyrosine or serine phosphorylation, or in dimerization of phosphorylated STAT1 (P-STAT1) and P-STAT1 translocation to the nucleus or in P-STAT1 binding to GAS, a minimal IFNgamma-response DNA sequence. In contrast, immuno-precipitation experiments indicated that the IFNgamma-mediated association of P-STAT1 with CBP/P300 transactivators was markedly reduced in infected macrophages, demonstrating that P-STAT1 was unable to normally recruit these transactivators. The host cell cAMP pathway triggered by Brucella could be responsible for this defect, CBP/P300 mobilization by phosphorylated CREB (P-CREB) disrupting the IFNgamma-induced STAT1-CBP/P300 association, required for a normal response of macrophages to IFNgamma. In any case, the inhibition of an essential protein-protein interaction probably lead to a deteriorated response to IFNgamma and thus participated in the pathogen's establishment within its host.

In spermatozoa, Stat1 is activated during capacitation and the acrosomal reaction

A role for sperm-specific proteins during the early embryonic development has been suggested by a number of recent studies. However, little is known about the participation of transcription factors in that stage. Here, we show that the signal transducer and activator of transcription 1 (Stat1), but not Stat4, was phosphorylated in response to capacitation and the acrosomal reaction (AR). Moreover, Stat1 phosphorylation correlated with changes in its localization: during capacitation, Stat1 moved from the cytoplasm to the theca/flagellum fraction. During AR, Stat1 phosphorylation increased again. In addition, blocking protein kinase A (PKA) and PKC during capacitation abolished both phosphorylation and migration of Stat1. Our results show tight spatio-temporal rearrangements of Stat1, suggesting that after fertilization Stat1 participates in the first rounds of transcription within the male pronucleus.

Ehrlichia under our noses and no one notices

Ehrlichia chaffeensis, an obligately intracellular bacterium, resides within a cytoplasmic vacuole in macrophages, establishes persistent infection in natural hosts such as white-tailed deer and canids, and is transmitted transstadially and during feeding by ticks, particularly Amblyomma americanum. Ehrlichial cell walls contain glycoproteins and a family of divergent 28 kDa proteins, but no peptidoglycan or lipopolysaccharide. The dense-cored ultrastructural form preferentially expresses certain glycoproteins, including a multiple repeat unit-containing adhesin. Ehrlichiae attach to L-selectin and E-selectin, inhibit phagolysosomal fusion, apoptosis, and JAK/STAT activation, and downregulate IL-12, IL-15, IL-18, TLR2 and 3, and CD14. Mouse models implicate overproduction of TNF-alpha by antigen-specific CD8 T lymphocytes in pathogenesis and strong type 1 CD4 and CD8 T lymphocyte responses, synergistic activities of IFN-gamma and TNF-alpha, and IgG2a antibodies in immunity. Human monocytotropic ehrlichiosis (HME) manifests as a flu-like illness that progresses in severity to resemble toxic shock-like syndrome, with meningoencephalitis or adult respiratory distress syndrome in some patients, and requires hospitalization in half. In immunocompromised patients, HME acts as an overwhelming opportunistic infection. In one family physician's practice, active surveillance for three years revealed an incidence of 1000 cases per million population. Diagnosis employs serology or polymerase chain reaction, which are not utilized sufficiently to establish the true impact of this emerging virus-like illness.

Ehrlichia subversion of host innate responses

Anaplasma (formerly Ehrlichia) phagocytophilum and Ehrlichia chaffeensis, upon infection of humans, replicate in host leukocyte granulocytes and monocytes/macrophages, respectively. These unusual Gram-negative bacteria lack genes for biosynthesis of the lipopolysaccharide and peptidoglycan that activate host leukocytes. Caveolae-mediated endocytosis directs A. phagocytophilum and E. chaffeensis to an intracellular compartment secluded from oxygen-dependent and -independent killing. Furthermore, these bacteria orchestrate a remarkable series of events that culminate in suppression of NADPH oxidase, phagocyte activation and differentiation pathways, apoptosis, and interferon-gamma signaling in host leukocytes. They offer a fascinating example of how pathogens employ intricate strategies to usurp and subvert host cell function.

Inhibition of eosinophil survival by a selective inhibitor of phosphodiesterase 4 via the induction of apoptosis

Selective inhibitors of phosphodiesterases (PDEs) have been suggested to have anti-inflammatory effects on bronchial asthma through the inhibition of chemotaxis, adhesion, degranulation, the respiratory burst, and survival prolongation of eosinophils. However, the mechanisms by which these agents inhibit eosinophil survival remain unclear. We therefore investigated the possible mechanisms of inhibitory effects of selective inhibitors of PDE 3 (cilostazol) and PDE 4 (rolipram) on granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated eosinophil survival. Purified blood eosinophils were cultured with medium alone or GM-CSF (0.01 ng/ml) in the presence or absence of the agents for up to 6 d. DNA was extracted from freshly isolated eosinophils and eosinophils cultured for 2 d with medium alone, GM-CSF, or GM-CSF in the presence of the agents, and analyzed using agarose gel electrophoresis. The presence of rolipram (10(-4), 10(-5), 10(-6) M), but not cilostazol, significantly inhibited eosinophil survival at days 2, 4, and 6. A laddering pattern was observed in the DNA of eosinophils cultured with medium alone and with GM-CSF in the presence of rolipram. The results reveal that selective PDE 4 inhibitors inhibit GM-CSF-mediated eosinophil survival through the induction of apoptosis.

Mycobacteria inhibition of IFN-gamma induced HLA-DR gene expression by up-regulating histone deacetylation at the promoter region in human THP-1 monocytic cells

Infection of macrophages with mycobacteria has been shown to inhibit the macrophage response to IFN-gamma. In the current study, we examined the effect of Mycobacteria avium, Mycobacteria tuberculosis, and TLR2 stimulation on IFN-gamma-induced gene expression in human PMA-differentiated THP-1 monocytic cells. Mycobacterial infection inhibited IFN-gamma-induced expression of HLA-DRalpha and HLA-DRbeta mRNA and partially inhibited CIITA expression but did not affect expression of IFN regulatory factor-1 mRNA. To determine whether inhibition of histone deacetylase (HDAC) activity could rescue HLA-DR gene expression, butyric acid and MS-275, inhibitors of HDAC activity, were added at the time of M. avium or M. tuberculosis infection or TLR2 stimulation. HDAC inhibition restored the ability of these cells to express HLA-DRalpha and HLA-DRbeta mRNA in response to IFN-gamma. Histone acetylation induced by IFN-gamma at the HLA-DRalpha promoter was repressed upon mycobacteria infection or TLR2 stimulation. HDAC gene expression was not affected by mycobacterial infection. However, mycobacterial infection or TLR2 stimulation up-regulated expression of mammalian Sin3A, a corepressor that is required for MHC class II repression by HDAC. Furthermore, we show that the mammalian Sin3A corepressor is associated with the HLA-DRalpha promoter in M. avium-infected THP-1 cells stimulated with IFN-gamma. Thus, mycobacterial infection of human THP-1 cells specifically inhibits HLA-DR gene expression by a novel pathway that involves HDAC complex formation at the HLA-DR promoter, resulting in histone deacetylation and gene silencing.

Cellular bioterrorism: how Brucella corrupts macrophage physiology to promote invasion and proliferation

Brucellosis is a worldwide human zoonosis caused by intracellular bacteria of the genus Brucella. Virulence factors play an important role in allowing Brucella infection and proliferation within macrophages. Brucella enters macrophages through lipid raft microdomains, avoids phagolysosome fusion, and inhibits TNF-alpha secretion and apoptosis. Furthermore, Brucella can perturb bactericidal activity in macrophages by influencing the host cell response to its advantage through its LPS or by activating the cAMP/PKA pathway. To date, small steps have been taken in defining and understanding the virulence factors of Brucella used in macrophage subversion, but further investigation is required to fully explain virulence and persistence.

Anaplasma phagocytophilum modulates gp91phox gene expression through altered interferon regulatory factor 1 and PU.1 levels and binding of CCAAT displacement protein

Infection of neutrophil precursors with Anaplasma phagocytophilum, the causative agent of human granulocytic ehrlichiosis, results in downregulation of the gp91(phox) gene, a key component of NADPH oxidase. We now show that repression of gp91(phox) gene transcription is associated with reduced expression of interferon regulatory factor 1 (IRF-1) and PU.1 in nuclear extracts of A. phagocytophilum-infected cells. Loss of PU.1 and IRF-1 correlated with increased binding of the repressor, CCAAT displacement protein (CDP), to the promoter of the gp91(phox) gene. Reduced protein expression of IRF-1 was observed with or without gamma interferon (IFN-gamma) stimulation, and the defect in IFN-gamma signaling was associated with diminished binding of phosphorylated Stat1 to the Stat1 binding element of the IRF-1 promoter. The diminished levels of activator proteins and enhanced binding of CDP account for the transcriptional inhibition of the gp91(phox) gene during A. phagocytophilum infection, providing evidence of the first molecular mechanism that a pathogen uses to alter the regulation of genes that contribute to an effective respiratory burst.

Bile acids are essential for porcine enteric calicivirus replication in association with down-regulation of signal transducer and activator of transcription 1

A porcine enteric calicivirus (PEC), strain Cowden in the family Caliciviridae (genus Sapovirus), can be propagated in a continuous cell line, LLC-PK cells, but only in the presence of an intestinal content fluid filtrate from gnotobiotic pigs. This cell culture system is presently the only in vitro model among caliciviruses that cause gastrointestinal disease, including members of the genera Sapovirus and Norovirus. We report here the identification of bile acids as active factors in intestinal content fluid essential for PEC growth. Bile acids that allowed PEC growth induced an increase in cAMP concentration in LLC-PK cells that was associated with down-regulation of IFN-mediated signal transducer and activator of transcription 1 phosphorylation, a key element in innate immunity. In addition, cAMP/protein kinase A pathway inhibitors, suramin, MDL12330A, or H89 suppressed bile acid-mediated PEC replication. We propose a mechanism for enteric calicivirus growth dependent on bile acids, ubiquitous molecules present in the intestine at the site of the virus replication that involves the protein kinase A cell-signaling pathway and a possible down-regulation of innate immunity.

Ehrlichia chaffeensis downregulates surface Toll-like receptors 2/4, CD14 and transcription factors PU.1 and inhibits lipopolysaccharide activation of NF-kappa B, ERK 1/2 and p38 MAPK in host monocytes

Microbial ligands, such as lipopolysaccharide (LPS), activate Toll-like receptors (TLRs) of mononuclear phagocytes, thus activating transcription factors including NF-kappa B and inducing antimicrobial activity. Ehrlichia chaffeensis, an obligatory intramonocytic Gram-negative bacterium, causes human monocytic ehrlichiosis. In the present study, we found that E. chaffeensis-infected human monocytes became progressively less responsive to Escherichia coli lipopolysaccharide (LPS) in activating NF-kappa B and mobilizing ehrlichiacidal activities. E. chaffeensis infection caused downregulation of the expression of several pattern recognition receptors, such as CD14, TLR2 and TLR4, as revealed by flow cytometry and/or reverse transcription polymerase chain reaction analysis. Electrophoretic mobility shift assay revealed that the activity of a transcription factor PU.1 was also downregulated by E. chaffeensis infection. ERK 1/2 and p38 MAPK were slightly activated at the early stage of E. chaffeensis infection; however, the activations of ERK 1/2 and p38 MAPK by LPS treatment were subsequently reduced in E. chaffeensis-infected monocytes compared with those in uninfected monocytes. Like E. chaffeensis, the p38 MAPK-specific inhibitor SB 203580 downregulated PU.1 activity and the expression of TLR2, TLR4 and CD14 in human monocytes, suggesting that the inhibition of p38 MAPK by E. chaffeensis is involved in the suppression of several downstream signalling pathways. These data point to a novel mechanism by which E. chaffeensis can survive by inhibiting critical signalling in monocyte activation pathways linked to pattern recognition receptors.

Mechanisms of immunity to Ehrlichia muris: a model of monocytotropic ehrlichiosis

Ehrlichia species can cause life-threatening infections or chronic persistent infections. Mechanisms of protective immunity were examined in an Ehrlichia muris mouse model of monocytotropic ehrlichiosis. C57BL/6 mice possessed strong genetic resistance to E. muris of an undetermined mechanism. CD8 T lymphocytes were particularly important, as revealed by 81% fatalities for E. muris-infected, major histocompatibility complex class I gene knockout mice compared with no deaths for wild-type C3H mice. Moreover, 80% of C3H mice depleted of CD8 and CD4 cells died of E. muris infection compared with only 44% of CD4 cell-depleted mice. CD8 T lymphocytes were demonstrated for the first time in an Ehrlichia infection to exhibit cytotoxic T-lymphocyte activity against Ehrlichia-infected target cells. Both gamma interferon and tumor necrosis factor were shown to play synergistic roles in protective immunity in vivo for the first time, as demonstrated by 75% fatalities when both cytokines were neutralized compared with minimal mortality when they were depleted separately. Passive transfer of antibodies, but not Fab fragments, to E. muris protected C3H/SCID mice against lethal infection. The mechanism of increased susceptibility (22% lethality) of C57BL/6 major histocompatibility complex class II gene knockout mice and CD4 cell-depleted C3H mice (i.e., through a gamma interferon or antibody mechanism), as well as the more important role of CD8 T lymphocytes (in the form of cytotoxic T-lymphocyte activity and/or gamma interferon production), remains to be elucidated. Protective immunity against monocytotropic E. muris is mediated by a combination of CD8 and CD4 T lymphocytes, gamma interferon, tumor necrosis factor alpha, and antibodies.

Ehrlichia chaffeensis: a prevalent, life-threatening, emerging pathogen

Ehrlichia chaffeensis are small, obligately intracellular, endosomal bacteria with tropism for macrophages. Persistent infection in reservoir white-tailed deer is transmitted by lone star ticks. Flu-like illness can progress to severe multisystem disease with toxic shock-like syndrome, meningitis, or ARDS. The case-fatality rate is 2.7%. Leukopenia and thrombocytopenia are diagnostically useful. Granulomas are associated with control of the infection. Ehrlichial proteins and glycoproteins have been sequenced and expressed for diagnostic serology and vaccine development. Mouse models (mild disease and persistent infection with E. muris and fatal monocytotropic ehrlichiosis with a Japanese tick isolate) revealed that CD4 and CD8 T type 1 lymphocyte responses, IFN-gamma, TNF-alpha, and antibodies play roles in protective immunity, while a weak CD4 T-helper response, overproduction of TNF-alpha, and very high IL-10 are associated with toxic shock-like mortality. Protection against fatal ehrlichiosis was achieved by prior infection with low virulence E. muris. Acute clinical diagnosis is difficult except by PCR. Response to doxycycline is dramatic.

Helicobacter pylori infection interferes with epithelial Stat6-mediated interleukin-4 signal transduction independent of cagA, cagE, or VacA

Helicobacter pylori is a bacterial pathogen evolved to chronically colonize the gastric epithelium, evade immune clearance by the host, and cause gastritis, peptic ulcers, and even gastric malignancies in some infected humans. In view of the known ability of this bacterium to manipulate gastric epithelial cell signal transduction cascades, we determined the effects of H. pylori infection on epithelial IL-4-Stat6 signal transduction. HEp-2 and MKN45 epithelial cells were infected with H. pylori strains LC11 or 8823 (type 1; cagA(+)/cagE(+)/VacA(+)), LC20 (type 2; cagA(-), cagE(-), VacA(-)), and cagA, cagE, and vacA isogenic mutants of strain 8823, with some cells receiving subsequent treatment with the Th2 cytokine IL-4, a known Stat6 activator. Immunofluorescence showed a disruption of Stat6-induced nuclear translocation by IL-4 in LC11-infected HEp-2 cells. IL-4-inducible Stat6 DNA binding in HEp-2 and MKN45 cells was abrogated by infection, but MKN45 cell viability was unaffected. A decrease in IL-4-mediated Stat6 tyrosine phosphorylation in nuclear and whole cell lysates was also observed following infection with strains LC11 and LC20, while neither strain altered IL-4 receptor chain alpha or Janus kinase 1 protein expression. Furthermore, parental strain 8823 and its isogenic cagA, cagE, and vacA mutants also suppressed IL-4-induced Stat6 tyrosine phosphorylation to comparable degrees. Thus, H. pylori did not directly activate Stat6, but blocked the IL-4-induced activation of epithelial Stat6. This may represent an evolutionarily conserved strategy to disrupt a Th2 response and evade the host immune system, allowing for successful chronic infection.

Inhibition of interferon (IFN) gamma-induced Jak-STAT1 activation in microglia by vasoactive intestinal peptide: inhibitory effect on CD40, IFN-induced protein-10, and inducible nitric-oxide synthase expression

Interferon (IFN)-gamma is one of the most important microglia stimulators in vivo participating in inflammation and Th1 activation/differentiation. IFN-gamma-mediated signaling involves the activation of the Jak/STAT1 pathway. The neuropeptides vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase activating polypeptide (PACAP) are two potent microglia-deactivating factors that inhibit the production of proinflammatory mediators in vitro and in vivo. The present study investigated the molecular mechanisms involved in the VIP/PACAP regulation of several IFN-gamma-induced microglia-derived factors, including IFN-gamma-inducible protein-10 (IP-10), inducible nitric-oxide synthase (iNOS), and CD40. The results indicate that VIP/PACAP inhibit Jak1-2 and STAT1 phosphorylation, and the binding of activated STAT1 to the IFN-gamma activated site motif in the IFN regulatory factor-1 and CD40 promoter and to the IFN-stimulated response element motif of the IP-10 promoter. Through its effect in the IFN-gamma-induced Jak/STAT1 pathway, VIP and PACAP are able to control the gene expression of IP-10, CD40, and iNOS, three microglia-derived mediators that play an essential role in several pathologies, i.e. inflammation and autoimmune disorders. The effects of VIP/PACAP are mediated through the specific receptor VPAC1 and the cAMP/protein kinase A transduction pathway. Because IFN-gamma is a major stimulator of innate and adaptive immune responses in vivo, the down-regulation of IFN-gamma-induced gene expression by VIP and PACAP could represent a significant element in the regulation of the inflammatory response in the central nervous system by endogenous neuropeptides.

Mechanisms to create a safe haven by members of the family Anaplasmataceae

Members of the family Anaplasmataceae are obligatory intracellular bacteria with unique host cell specificities. Depending on each bacterial species, granulocytes, platelets, endothelial cells, monocytes, macrophages, red blood cells, and cells of invertebrates are specifically infected. This unique host cell specificity has been the major hurdle to overcome in order to cultivate this group of bacteria. Because these bacteria cannot survive outside host cells, once released from a host cell, they need to rapidly induce signals for their own internalization into another host cell unique to each species. How these bacteria enter and continue to survive and replicate within the host milieu, then exit the host cell is largely unknown. Recently, however, unique strategies employed by some of these bacteria for successful parasitism of mammalian leukocytes have begun to be uncovered. When these bacteria interact with host cells, signals are transduced both inside the host cells and inside the bacteria. These signals disable the alarm system, as well as microbicidal mechanisms, of the leukocytes and condition the host cells to accept these intruders to share space and nutrient resources. Signals transduced inside the bacteria allow them to finely tune their metabolism and physiology in the new host cell environment and to disguise themselves as "insiders" so that their sojourn does not upset the host cell physiology until they have sufficiently multiplied. This paper discusses our recent findings on these topics.

Subversion and utilization of the host cell cyclic adenosine 5'-monophosphate/protein kinase A pathway by Brucella during macrophage infection

Brucella spp. are intramacrophage pathogens that induce chronic infections in a wide range of mammals, including domestic animals and humans. Therefore, the macrophage response to infection has important consequences for both the survival of phagocytosed bacteria and the further development of host immunity. However, very little is known about the macrophage cell signaling pathways initiated upon infection and the virulence strategy that Brucella use to counteract these responses and secure their survival. In a previous study, we have shown that macrophages activated by SR141716A, a ligand of the cannabinoid receptor CB1, acquired the capacity to control Brucella and observed that the CB1 receptor-triggering engages the microbicidal activity of phagocytes. To analyze the perturbation of cell signaling pathway during macrophage infection by Brucella, we hypothesized that SR141716A provides cell signaling that interferes with the bacterial message leading to inhibition of macrophage functions. As CB1 receptor belongs to the family of G protein-linked receptors, we explored the cAMP signaling pathway. In this study, we show that the CB1 ligand inhibited the bacteria-induced cell signaling. Taking advantage of this result, we then demonstrated that Brucella infection elicited a rapid activation of the cAMP/protein kinase A pathway. This activation resulted in a prolonged phosphorylation of the transcription factor CREB. We finally demonstrate that the activation of the cAMP/protein kinase A pathway is crucial for the survival and establishment of Brucella within macrophages. For the first time in phagocytes, we thus characterized a primordial virulence strategy of Brucella involving the host signaling pathway, a novel point of immune intervention of this virulent pathogen.

Enterohemorrhagic Escherichia coli O157:H7 disrupts Stat1-mediated gamma interferon signal transduction in epithelial cells

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a clinically important bacterial enteropathogen that manipulates a variety of host cell signal transduction cascades to establish infection. However, the effect of EHEC O157:H7 on Jak/Stat signaling is unknown. To define the effect of EHEC infection on epithelial gamma interferon (IFN-gamma)-Stat1 signaling, human T84 and HEp-2 epithelial cells were infected with EHEC O157:H7 and then stimulated with recombinant human IFN-gamma. Cells were also infected with different EHEC strains, heat-killed EHEC, enteropathogenic E. coli (EPEC) O127:H6, and the commensal strain E. coli HB101. Nuclear and whole-cell protein extracts were prepared and were assayed by an electrophoretic mobility shift assay (EMSA) and by Western blotting, respectively. Cells were also processed for immunofluorescence to detect the subcellular localization of Stat1. The EMSA revealed inducible, but not constitutive, Stat1 activation upon IFN-gamma treatment of both cell lines. The EMSA also showed that 6 h of EHEC O157:H7 infection, but not 30 min of EHEC O157:H7 infection, prevented subsequent Stat1 DNA binding induced by IFN-gamma, whereas infection with EPEC did not. Immunoblotting showed that infection with EHEC, but not infection with EPEC, eliminated IFN-gamma-induced Stat1 tyrosine phosphorylation in both dose- and time-dependent fashions and disrupted inducible protein expression of the Stat1-dependent gene interferon regulatory factor 1. Immunofluorescence revealed that EHEC infection did not prevent nuclear accumulation of Stat1 after IFN-gamma treatment. Also, Stat1 tyrosine phosphorylation was suppressed by different EHEC isolates, including intimin-, type III secretion- and plasmid-deficient strains, but not by HB101 and heat-killed EHEC. These findings indicate the novel disruption of host cell signaling caused by EHEC infection but not by EPEC infection.

Enterohemorrhagic Escherichia coli O157:H7 disrupts Stat1-mediated gamma interferon signal transduction in epithelial cells

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a clinically important bacterial enteropathogen that manipulates a variety of host cell signal transduction cascades to establish infection. However, the effect of EHEC O157:H7 on Jak/Stat signaling is unknown. To define the effect of EHEC infection on epithelial gamma interferon (IFN-gamma)-Stat1 signaling, human T84 and HEp-2 epithelial cells were infected with EHEC O157:H7 and then stimulated with recombinant human IFN-gamma. Cells were also infected with different EHEC strains, heat-killed EHEC, enteropathogenic E. coli (EPEC) O127:H6, and the commensal strain E. coli HB101. Nuclear and whole-cell protein extracts were prepared and were assayed by an electrophoretic mobility shift assay (EMSA) and by Western blotting, respectively. Cells were also processed for immunofluorescence to detect the subcellular localization of Stat1. The EMSA revealed inducible, but not constitutive, Stat1 activation upon IFN-gamma treatment of both cell lines. The EMSA also showed that 6 h of EHEC O157:H7 infection, but not 30 min of EHEC O157:H7 infection, prevented subsequent Stat1 DNA binding induced by IFN-gamma, whereas infection with EPEC did not. Immunoblotting showed that infection with EHEC, but not infection with EPEC, eliminated IFN-gamma-induced Stat1 tyrosine phosphorylation in both dose- and time-dependent fashions and disrupted inducible protein expression of the Stat1-dependent gene interferon regulatory factor 1. Immunofluorescence revealed that EHEC infection did not prevent nuclear accumulation of Stat1 after IFN-gamma treatment. Also, Stat1 tyrosine phosphorylation was suppressed by different EHEC isolates, including intimin-, type III secretion- and plasmid-deficient strains, but not by HB101 and heat-killed EHEC. These findings indicate the novel disruption of host cell signaling caused by EHEC infection but not by EPEC infection.

17beta-estradiol inhibits the production of interferon-induced protein of 10 kDa by human keratinocytes

The natural course of psoriasis is often modulated during pregnancy, indicating the regulatory effect of estrogen or progesterone on psoriasis. Interferon-induced protein of 10 kDa chemoattracts T helper 1 cells, and interferon-induced protein of 10 kDa production by keratinocytes is enhanced in psoriatic skin lesions. We examined in vitro effects of sex hormones on the interferon-induced protein of 10 kDa production by human keratinocytes. 17beta-estradiol inhibited interferon-gamma-induced interferon-induced protein of 10 kDa secretion, mRNA expression, and promoter activity. Interferon-stimulated response element on the promoter was responsible for the inhibition by 17beta-estradiol. Interferon-gamma-induced protein of 10 kDa production was also inhibited by anti-estrogens, ICI 182 780 and tamoxifen, and membrane-impermeable bovine serum albumin-conjugated 17beta-estradiol, suggesting the effects via membrane estrogen receptor, whereas 17alpha-estradiol, progesterone, and dihydrotestosterone had no effects. 17beta-estradiol and bovine serum albumin-conjugated 17beta-estradiol suppressed interferon-gamma-induced transcription through the interferon-stimulated response element and signal transducer and activator of transcription 1alpha binding to interferon-stimulated response element. 17beta-estradiol and bovine serum albumin-conjugated 17beta-estradiol suppressed interferon-gamma-induced tyrosine phosphorylation of signal transducer and activator of transcription 1alpha, and Janus tyrosine kinase 1 and 2. 17beta-estradiol-mediated suppression on the interferon-gamma-induced signal transducer and activator of transcription 1alpha activation and interferon-induced protein of 10 kDa synthesis was counteracted by adenylate cyclase inhibitor SQ22536. 17beta-estradiol, bovine serum albumin-conjugated 17beta-estradiol, ICI 182 780, and tamoxifen increased intracellular 3',5'-adenosine cyclic monophosphate level by activating adenylate cyclase in keratinocytes. Fluorescein isothiocyanate-labeled bovine serum albumin-conjugated 17beta-estradiol bound to the surface of keratinocytes, and mRNA for estrogen receptor beta but not for estrogen receptor alpha was detected in keratinocytes. These results suggest that 17beta-estradiol may interact with the membrane receptor on keratinocytes and generate 3',5'-adenosine cyclic monophosphate by activating adenylate cyclase, which may lead to the inhibition of interferon-gamma-induced signal transducer and activator of transcription 1alpha activation and interferon-induced protein of 10 kDa synthesis.

Monocytic activation of protein tyrosine kinase, protein kinase A and protein kinase C induced by porins isolated from Salmonella enterica serovar Typhimurium

OBJECTIVES

In the present study a monocytic cell line, U937, was used to investigate the possible involvement of protein tyrosine kinases (NT-PTKs), protein kinase A (PKA) and protein kinase C (PKC) in cell signaling pathways following Salmonella enterica serovar Typhimurium porin stimulation.

METHODS

Different concentrations of porins and lipopolysaccharide (LPS) were analysed to evaluate changes in PTK activity by a non radioactive tyrosine kinase assay and in PKA and PKC phosphorylation by Western blotting analysis. The inhibitors of PTK, PKA and PKC activation used, were: 3,4-dihydroxybenzylidene-malononitrile (tyrphostin 23), inhibitor of epidermal growth factor (EGF) receptor tyrosine kinase activity; dihychloride (H-89), a selective inhibitor of PKA which is useful to discriminate between the effects of PKC and PKA; diacylglycerol kinase inhibitor II (R59949), which is useful for elucidating roles of PKC; calphostin C, a specific inhibitor of PKC.

RESULTS

Porins of the outer membrane of the ST were isolated to be used as a stimulus in the performed experiments. Following porin treatment, a dose-dependent increase in PTK, PKA and PKC activation was observed. U937 monocytes pretreated with inhibitors induced an evident decrease in PTK activity and PKA and PKC phosphorylation pattern in porin stimulated monocytes.

CONCLUSIONS

Our data support the important role played by NT-PTK, PKA and PKC in transducing the activating signal in macrophages stimulated with porins through the activation of the mitogen-activated protein kinase (MAPK) pathway that participate in the regulation of gene expression.

Ehrlichia chaffeensis: a prototypical emerging pathogen

Ehrlichia chaffeensis is an obligately intracellular, tick-transmitted bacterium that is maintained in nature in a cycle involving at least one and perhaps several vertebrate reservoir hosts. The moderate to severe disease caused by E. chaffeensis in humans, first identified in 1986 and reported for more than 1,000 patients through 2000, represents a prototypical "emerging infection." Knowledge of the biology and natural history of E. chaffeensis, and of the epidemiology, clinical features, and laboratory diagnosis of the zoonotic disease it causes (commonly referred to as human monocytic ehrlichiosis [HME]) has expanded considerably in the period since its discovery. In this review, we summarize briefly the current understanding of the microbiology, pathogenesis, and clinical manifestations associated with this pathogen but focus primarily on discussing various ecological factors responsible for the recent recognition of this important and potentially life-threatening tick-borne disease. Perhaps the most pivotal element in the emergence of HME has been the staggering increases in white-tailed deer populations in the eastern United States during the 20th century. This animal serves as a keystone host for all life stages of the principal tick vector (Amblyomma americanum) and is perhaps the most important vertebrate reservoir host for E. chaffeensis. The contributions of other components, including expansion of susceptible human populations, growth and broadening geographical distributions of other potential reservoir species and A. americanum, and improvements in confirmatory diagnostic methods, are also explored.

Histamine inhibits the production of interferon-induced protein of 10 kDa in human squamous cell carcinoma and melanoma

Interferon-induced protein of (IP-10) inhibits tumor progression. Tumor cells can produce interferon-induced protein of IP-10 in response to interferon-g. Histamine in the vicinity of tumor cells may sustain the tumor progression. We examined the in vitro effects of histamine on interferon-induced protein of IP-10 production in human squamous cell carcinoma and melanoma. Histamine suppressed interferon-g-mediated interferon-induced protein of IP-10 secretion and mRNA expression in SV40-transformed keratinocytes, SCC15, SCC4, and melanoma WM115, WM266-4, and C32. Histamine suppressed interferon-g-induced interferon-mediated protein of IP-10 promoter activation in these cells, and the interferon-stimulated response element on the promoter was responsible for the suppression. Histamine suppressed interferon-g-mediated transcription through the interferon-stimulated response element and signal transducer and activator of transcription 1alpha binding to the interferon-stimulated response element. Histamine suppressed interferon-g-induced tyrosine phosphorylation of the signal transducer and activator of transcription 1alpha, Janus tyrosine kinase 1, and Janus tyrosine kinase 2. Histamine-mediated suppression on the interferon-g-induced interferon-mediated protein of IP-10 synthesis was counteracted by the H2 receptor antagonist cimetidine, adenylate cyclase inhibitor SQ22536, and protein kinase A inhibitor H-89, but were not affected by H1 receptor antagonist mepyramine. Cimetidine, SQ22536, and H-89 also counteracted histamine-mediated suppression on the interferon-g-induced transcription through the interferon-stimulated response element, signal transducer and activator of transcription 1alpha binding to the interferon-stimulated response element, and tyrosine phosphorylation of the signal transducer and activator of transcription 1alpha, Janus tyrosine kinase 1, and Janus tyrosine kinase 2. Histamine increased intracellular 3',5'-adenosine cyclic monophosphate level and protein kinase A activity in squamous cell carcinoma and melanoma, and the effects of histamine were blocked by cimetidine. These results suggest that histamine may interact with H2 receptor on squamous cell carcinoma and melanoma and generate 3',5'-adenosine cyclic monophosphate, which may activate protein kinase A. The cyclic 3',5'-adenosine monophosphate/protein kinase A signaling pathway induced by histamine may inhibit interferon-g-induced signal transducer and activator of transcription 1alpha activation and suppress interferon-induced protein of IP-10 synthesis.

Cyclooxygenase-2 inhibitor enhances whereas prostaglandin E2 inhibits the production of interferon-induced protein of 10 kDa in epidermoid carcinoma A431

Interferon-induced protein of 10 kDa (IP-10) induces antitumor immunity. Cyclooxygenase-2 and its metabolite prostaglandin E2 (PGE2) are overexpressed in tumor cells, which may suppress antitumor immunity. We examined the in vitro effects of cyclooxygenase-2 inhibitor NS398 on IP-10 production in human epidermoid carcinoma A431. NS398 enhanced interferon-gamma-induced IP-10 secretion, mRNA expression, and promoter activation in A431, and exogenous PGE2 antagonized the enhancement. Interferon-stimulated response element (ISRE) on IP-10 promoter was responsible for the transcriptional regulation by NS398 and PGE2. NS398 enhanced interferon-gamma-induced transcription through ISRE and binding of signal transducer and activator of transcription 1alpha (STAT1alpha to ISRE in A431, and PGE2 antagonized the enhancement. NS398 enhanced interferon-gamma-induced tyrosine phosphorylation of STAT1alpha, Janus tyrosine kinase 1, and Janus tyrosine kinase 2, and PGE2 antagonized the enhancement. PGE2-mediated suppression of IP-10 synthesis was counteracted by adenylate cyclase inhibitor SQ22536 and protein kinase A inhibitor H-89, and PGE2 receptor EP4 antagonist AH23848B. AH23848B, SQ22536, and H-89 counteracted the PGE2-mediated suppression of ISRE-dependent transcription, STAT1alpha binding to ISRE, and tyrosine phosphorylation of STAT1alpha, Janus tyrosine kinase 1, and Janus tyrosine kinase 2. PGE2 increased intracellular cAMP level and protein kinase A activity in A431 pretreated with NS398, and AH23848B blocked the effects of PGE2. These results suggest that A431-derived PGE2 may generate cAMP signal via EP4 in A431, which may activate protein kinase A, and may resultantly inhibit interferon-gamma-induced STAT1alpha activation and IP-10 synthesis. The results also suggest that NS398 may restore IP-10 synthesis by preventing PGE2 production in A431 and thus may be therapeutically useful for skin cancer.

Modulation of gamma interferon-induced major histocompatibility complex class II gene expression by Porphyromonas gingivalis membrane vesicles

Gamma interferon (IFN-gamma)-induced endothelial cells actively participate in initiating immune responses by interacting with CD4(+) T cells via class II major histocompatibility complex (MHC) surface glycoproteins. Previously, Porphyromonas gingivalis membrane vesicles were shown to selectively inhibit IFN-gamma-induced surface expression of HLA-DR molecules by human umbilical cord vascular endothelial cells. In this study, we demonstrated an absence of HLA-DR alpha mRNA from IFN-gamma-induced cells in the presence of P. gingivalis membrane vesicles by using reverse transcriptase-PCR and Southern blotting. Vesicles also prevented transcription of the gene encoding class II transactivator, a transactivator protein required for IFN-gamma-induced expression of MHC class II genes. In addition, the effects of vesicles on IFN-gamma signal transduction involving Jak and Stat proteins were characterized by using immunoprecipitation and Western blot analyses. Jak1 and Jak2 proteins could not be detected in endothelial cells treated with membrane vesicles. Consequently, IFN-gamma-induced phosphorylation of Jak1, Jak2, and Stat1 alpha proteins was prevented. The class II-inhibitory effect of the membrane vesicles could be eliminated by heating vesicles at 100 degrees C for 30 min or by treating them with a cysteine proteinase inhibitor. This indicates that the cysteine proteinases were most likely responsible for the absence of Jak proteins observed in vesicle-treated cells. The observed increased binding of radiolabeled IFN-gamma to vesicle-treated cells suggests that vesicles may also modulate the IFN-gamma interactions with the cell surface. However, no evidence was obtained demonstrating that vesicles affected the expression of IFN-gamma receptors. Thus, P. gingivalis membrane vesicles apparently inhibited IFN-gamma-induced MHC class II by disrupting the IFN-gamma signaling transduction pathway. Vesicle-inhibited class II expression also occurred in other IFN-gamma-inducible cells. This suggested that the ability of P. gingivalis membrane vesicles to modulate antigen presentation by key cells may be an important mechanism used by this particular bacterium to escape immunosurveillance, thereby favoring its colonization and invasion of host tissues.

Human ehrlichioses

Human ehrlichioses represent one of the best examples of newly emergent infectious diseases in which the classic triad of host, infectious agent, and environment are intertwined closely. These pathogens have existed for eons on the planet, and some were described as veterinary pathogens decades ago. Because of dramatic increases of deer and small mammal populations in certain areas and the subsequent increased populations of particular blood-feeding ticks, the risk of developing these diseases is higher than before. Increasing human populations in suburban areas and increased immunosuppressed populations (transplant patients, human immunodeficiency virus patients, and cancer survivors) also have increased risk of developing severe forms of these diseases.

Inhibition of IFN-gamma-induced janus kinase-1-STAT1 activation in macrophages by vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide

The vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase-activating polypeptide (PACAP), two immunomodulatory neuropeptides that affect both innate and acquired immunity, down-regulate IL-12 p40 and inducible NO synthase expression in LPS/IFN-gamma-stimulated macrophages. We showed previously that VIP/PACAP inhibit NF-kappaB nuclear translocation through the stabilization of IkappaB and reduce IFN regulatory factor-1 (IRF-1) binding to the regulatory elements found in the IL-12 p40 and inducible NO synthase promoters. In this paper we studied the molecular mechanisms involved in the VIP/PACAP regulation of IRF-1 transactivating activity. Our studies indicate that the inhibition in IRF-1 binding correlates with a reduction in IRF-1 protein and mRNA in IFN-gamma-treated Raw 264.7 macrophages. In agreement with the described Janus kinase (Jak)1/Jak2/STAT1/IRF-1 activation pathway, VIP/PACAP inhibit Jak1/Jak2, STAT1 phosphorylation, and the binding of STAT1 to the GAS sequence motif in the IRF-1 promoter. The effects of VIP/PACAP are mediated through the specific VIP/PACAP receptor-1 and the cAMP/protein kinase A (PKA) transduction pathway, but not through the induction of suppressor of cytokine signaling-1 or suppressor of cytokine signaling-3. Because IFN-gamma is a major stimulator of innate immune responses in vivo, the down-regulation of IFN-gamma-induced gene expression by VIP and PACAP could represent a significant element in the regulation of the inflammatory response by endogenous neuropeptides.

Expression of interleukin-1beta, tumor necrosis factor alpha, and interleukin-6 in human peripheral blood leukocytes exposed to human granulocytic ehrlichiosis agent or recombinant major surface protein P44

Human granulocytic ehrlichiosis (HGE) is an emerging febrile systemic disease caused by the HGE agent, an obligatory intracellular bacterium of granulocytes. The pathogenicity- and immunity-related mechanisms of HGE are unknown. In this study, several cytokines generated in human peripheral blood leukocytes (PBLs) incubated with the HGE agent or a recombinant 44-kDa major surface protein (rP44) of the HGE agent were examined by reverse transcription-PCR and a capture enzyme-linked immunosorbent assay. The HGE agent induced expression of interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and IL-6 mRNAs and proteins in PBLs in a dose-dependent manner to levels as high as those resulting from Escherichia coli lipopolysaccharide stimulation. The kinetics of induction of these three cytokines in PBLs by rP44 and by the HGE agent were similar. Proteinase K treatment of the HGE agent or rP44 eliminated the ability to induce these three cytokines. Induction of these cytokine mRNAs was not dependent on superoxide generation. These results suggest that P44 proteins have a major role in inducing the production of proinflammatory cytokines by PBLs. Expression of IL-8, IL-10, gamma interferon, transforming growth factor beta, and IL-2 mRNAs in response to the HGE agent was not remarkable. Among PBLs, neutrophils and lymphocytes expressed IL-1beta mRNA but not TNF-alpha or IL-6 mRNA in response to the HGE agent, whereas monocytes expressed all three of these cytokine mRNAs. These observations suggest that induction of proinflammatory-cytokine gene expression by the major outer membrane protein of the HGE agent in monocytes, which are not the primary host cells of the HGE agent, contributes to HGE pathogenesis and immunomodulation.

Intracellular infection by the human granulocytic ehrlichiosis agent inhibits human neutrophil apoptosis

In patients with human granulocytic ehrlichiosis (HGE), the HGE agent has been seen only in the peripheral blood granulocytes, which have a life span too short for ehrlichial proliferation. To determine if the HGE agent delays the apoptosis of human peripheral blood neutrophils for its advantage, peripheral blood granulocytes consisting mostly of neutrophils were incubated with freshly freed host cell-free HGE agent in vitro. The HGE agent induced a significant delay in morphological apoptosis and the cytoplasmic appearance of histone-associated DNA fragments in the granulocytes. This antiapoptotic effect was dose dependent. Although much weaker than the HGE agent freshly freed from the host cells, noninfectious purified HGE agent stored frozen and thawed also had antiapoptotic effect, which was lost with proteinase K treatment but not with periodate treatment. Treatment of neutrophils with a transglutaminase inhibitor, monodansylcadaverine, blocked the antiapoptotic effect of the HGE agent. Addition of oxytetracycline, however, did not prevent or reverse the antiapoptotic effect of the HGE agent. These results suggest that binding of a protein component(s) of the HGE agent to neutrophils and subsequent cross-linking and/or internalization of the receptor and ehrlichiae are required for antiapoptotic signaling, but ehrlichial protein synthesis and/or proliferation is not required. MG-132, a proteasome inhibitor, and cycloheximide accelerated the apoptosis of neutrophils and overrode the antiapoptotic effect of the HGE agent. Studies with specific inhibitors suggest that protein kinase A, NF-kappaB, and interleukin 1beta are not involved in the antiapoptotic mechanism of the HGE agent.