Virulence

Published by Taylor & Francis
Online ISSN: 2150-5608
Print ISSN: 2150-5594
Publications
Enteroaggregative Escherichia coli (EAEC) is a major pathogen worldwide, associated with diarrheal disease in both children and adults, suggesting the need for new preventive and therapeutic treatments. We investigated the role of the micronutrient zinc in the pathogenesis of an E. coli strain associated with human disease. A variety of bacterial characteristics-growth in vitro, biofilm formation, adherence to IEC-6 epithelial cells, gene expression of putative EAEC virulence factors as well as EAEC-induced cytokine expression by HCT-8 cells-were quantified. At concentrations (≤ 0.05 mM) that did not alter EAEC growth (strain 042) but that are physiologic in serum, zinc markedly decreased the organism's ability to form biofilm (P < 0.001), adhere to IEC-6 epithelial cells (P < 0.01), and express putative EAEC virulence factors (aggR, aap, aatA, virK) (P < 0.03). After exposure of the organism to zinc, the effect on virulence factor generation was prolonged (> 3 h). Further, EAEC-induced IL-8 mRNA and protein secretion by HCT-8 epithelial cells were significantly reduced by 0.05 mM zinc (P < 0.03). Using an in vivo murine model of diet-induced zinc-deficiency, oral zinc supplementation (0.4 µg/mouse daily) administered after EAEC challenge (10 ( 10) CFU/mouse) significantly abrogated growth shortfalls (by > 90%; P < 0.01); furthermore, stool shedding was reduced (days 9-11) but tissue burden of organisms in the intestine was unchanged. These findings suggest several potential mechanisms whereby physiological levels of zinc alter pathogenetic events in the bacterium (reducing biofilm formation, adherence to epithelium, virulence factor expression) as well as the bacterium's effect on the epithelium (cytokine response to exposure to EAEC) to alter EAEC pathogenesis in vitro and in vivo. These effects may help explain and extend the benefits of zinc in childhood diarrhea and malnutrition.
 
Escherichia coli ST131 is an important cause of multidrug-resistant infections. Thus, the aim of this study was to evaluate the concomitant presence of resistance plasmids and pathogenicity islands (PAIs) in ST131 E. coli. From 97 extra-intestinal E. coli characterized for antimicrobial susceptibility and extended-spectrum β-lactamase production, 16% of isolates were identified as CTX-M-15 producers. These strains were studied by PFGE, MLST, and phylogroups, plasmid groups, PAIs, and plasmid-mediated quinolone-resistance determinants. MLST identified one ST10 strain from phylogroup A and the remaining isolates were ST131, from group B2. Despite the genetic variability, 64% of ST131 strains presented a profile composed by PAI IV 536, PAI ICFT073, and PAI IICFT073, IncF plasmid, blaCTX-M-15, and aac(6')-lb-cr genes. The prevalent virulence and resistance profile detected among the strains may constitute an optimal combination of factors, which allow E. coli ST131 to maintain both features becoming concomitantly virulent and extremely resistant.
 
Involvement of IL-17 in protective immunity to intracellular pathogens 
The identification of a new T cell subset referred to as T helper 17 (Th17) cells and its role in protective immunity against extracellular bacterial infections is well established. In contrast, initial studies suggested that the IL-23-IL-17 pathway was not required for protection against intracellular pathogens such as mycobacterial infections. However, recent studies demonstrate that Th17-IL-23 pathway may play a crucial role in protective immunity against other intracellular pathogens by regulating the innate and adaptive immune responses. The current outlook on the role of IL-23-IL-17 pathway in protective immunity to intracellular pathogens is discussed here.
 
Th1-polarized host response, mediated by IFN-γ, has been associated with increased severity of periodontal disease as well as control of periodontal infection. The functional polymorphism TBX21-1993T/C (rs4794067) increases the transcriptional activity of the TBX21 gene (essential for Th1 polarization) resulting in a predisposition to a Th-1 biased immune response. Thus, we conducted a case-control study, including a population of healthy controls (H, n=218), chronic periodontitis (CP, n=197), and chronic gingivitis patients (CG, n=193), to investigate if genetic variations in TBX21 could impact the development of Th1 responses, and consequently influence the pattern of bacterial infection and periodontitis outcome. We observed that the polymorphic allele T was significantly enriched in the CP patients compared to CG subjects, while the H controls demonstrated and intermediate genotype. Also, investigating the putative functionality TBX21-1993T/C in the modulation of local response, we observed that the transcripts levels of T-bet, but not of IFN-γ, were upregulated in homozygote and heterozygote polymorphic subjects. In addition, TBX21-1993T/C did not influence the pattern of bacterial infection or the clinical parameters of disease severity, being the presence/absence of red complex bacteria the main factor associated with the disease status and the subrogate variable probing depth (PD) in the logistic regression analysis.
 
Influenza A viruses are the causative agents of annual epidemics and occasional pandemics. The pathogenicity of influenza viruses is determined by complex interplay of viral and host factors. While some knowledge exists on viral determinants of pathogenicity, little is known on the host factors involved. Here, we discuss our recent findings on host genetic variations involved in disease outcome. We found that 2009 pandemic H1N1 influenza A virus strains (pH1N1) are low pathogenic in BALB/c but display differential pathogenicities in C57BL/6J mice. In contrast, a highly pathogenic avian influenza A virus (HPAIV) strain of the H5N1 subtype isolated from a fatal human case was more virulent in BALB/c than C57BL/6J mice. As a control, we used a seasonal H1N1 influenza virus which showed marginal pathogenicity in both mouse strains. Thus, differences in pH1N1 virulence become visible in C57BL/6J mice, while intrinsic pH1N1 pathogenicity markers are masked in BALB/c mice. Further, increased pH1N1 virulence correlated with a depressed cytokine response in C57BL/6J mice, while increased H5N1 virulence correlated with an elevated proinflammatory cytokine response in BALB/c mice. These findings indicate that disease severity can be strongly regulated by the host genetic background. Moreover, our findings suggest that differential host determinants contribute to the pathogenesis of pH1N1 and human H5N1 influenza viruses. Further studies are needed to identify the responsible viral factors involved in enhanced pH1N1 virulence in C57BL/6J mice. Also, extensive studies are needed to identify and characterize cellular factors regulating pH1N1 or H5N1 susceptibility in a host dependent manner. These observations extend our knowledge on influenza virus pathogenicity and highlight the role of host dependent factors, especially in pH1N1 susceptibility. We propose the C57BL/6J mouse strain as a convenient small animal model to study pH1N1 virulence determinants. Furthermore, the C57BL/6J mouse strain might also represent a suitable model for the assessment of pH1N1 vaccine candidates or the evaluation of antiviral therapies.
 
illustration of the plausible interaction of contemporary seasonal human (h1/h3) and animal (swine, wild aquatic/migratory birds, domestic poultry) influenza viruses with the pandemic (h1n1) 2009 virus in intermediate hosts (pigs and/or turkey) and the potential generation of more virulent variants. Establishment and continued circulation of the pandemic (h1n1) 2009 virus in potential intermediate hosts such as pigs, continuously proposed as "genetic-mixing vessels," 21,22 present opportunities for reassortment with influenza A viruses from different lineage (mammalian and avian). On the other hand, turkeys readily infected with the pandemic virus also provide an alternative host to converge and recombine with other avian influenza viruses. Susceptible pigs and turkeys may also facilitate adaptation of the pandemic (h1n1) 2009 virus in these hosts by acquiring accumulated mutations in the viral genome which may lead to interspecies transmission. Solid lines represent existing reports of interspecies transmission while broken lines represent possible spread of potentially more virulent pandemic virus variants. Avian viruses highlighted in red fonts emphasize subtypes considered to be of pandemic potential.
Infections due to the pandemic (H1N1) 2009 influenza A viruses have been considerably mild relative to previous pandemics. However, its continued circulation among human and animal populations heightened concerns for the generation of virulent variants with greater threat to public health. Thus, we explored the potential role of the influenza viral polymerases, including known molecular markers, in altering the virulence phenotype of the 2009 pandemic A/California/04/09 (CA04, H1N1) virus. By examining in vitro polymerase activities and in vivo pathogenicities in mice model, we were able to show that individual or simultaneous expression of virulence factors in PB2, PB1, and PA might not significantly elevate pathogenicity. Nevertheless, we demonstrated that PB2(627K) or PA(97I) derived from different genetic backgrounds and other unknown polymerase markers have the potential to enhance virulence of CA04. Virus rescue and replication studies identified PA as a critical factor in maintaining genetic stability of the CA04 (H1N1) virus.
 
The rise of drug-resistant strains of Mycobacterium tuberculosis in a world where at least one third of the entire population is infected with the tuberculosis-causing infectious bacterial pathogen is a serious threat to human health.Integration of interdisciplinary approaches by academia and industry can herald a generation that can aim to be free from tuberculosis (TB).1 The challenges faced are varied and range from developing quicker, cheaper and more accurate diagnostic tools to establishing new effective strategies for therapy and identifying novel anti-tubercular agents. The conference, “Mycobacterium tuberculosis… can we beat it?” organized by Euroscicon, aimed at pooling together cutting-edge research performed in the fields of TB diagnostics and treatment from across the world. Scientists from various disciplines discussed their research and exchanged technical knowledge. The Royal College of Pathologists, located at heart of the cosmopolitan city of London, where TB incidences have been reported to be higher than HIV infections in the recent past, created the perfect environment to host the international meeting, which took place on 21 March 2013, commemorating World TB Day.
 
Median life span of 2-Me-treated/non-treated strains of mice 
Longevity of (NZW x NZB) F 1-hybrid male and female mice exposed to normal, 10-3 M or 10-2 M 2-Me drinking water. (a) Females. Treatment started at 28 days of age. Nontreated water shown in black (n = 9), 10-3 M 2-Me water in red (n = 8) and 10-2 M 2-Me water in blue (n = 11). (B) Males. Treatment started at 28 days of age. control (n = 15), 10-3 M 2-Me (n = 9), 10-2 M 2-Me (n = 11). (c) Males. Grandparents and parents on 10-3 M 2-Me their entire lives. at 28 days of age, water of offspring of these parents/ grandpaarents was switched to: nontreated water (n = 6), 10-2 M 2-Me (n = 7), or continued on 10-3 M 2-Me (n = 10) for the remainder of their lives. animals with solid tumors or ascites are designated by +.
Longevity of NZB and NZW mice not treated or treated with 10-3 or 10-2 M 2-Me. (a and B) Females. (c and D) Males. Treatment started at 28 days of age for control shown in black, 10-3 M 2-Me in red and 10-2 M 2-Me in blue. animals with solid tumors or ascites are designated by +.
Body weight and average daily intake of food, water and 2-Me by male (NZW x NZB) F 1 and c57BL10 mice at 210 days of age
In the preceding report, moderately lived-mice fed dietary 2-mercaptoethanol (2-Me) had their life extended, whereas long-lived mice were found to have the quality of life improved, but not extended, and did not develop high fat-diet obesity. In the present report, alteration of longevity of mice prone to develop spontaneous, systemic lupus erythematosus (SLE) by dietary 2-Me was determined. NZB, NZW, (NZW x NZB) F₁-hybrid, BXSB/MpJ, BXSB-Yaa+/J, MRL/MpJ and MRL/MpJ-Faslpr mice received drinking water, without or with 2-Me at concentrations of 10⁻³ or 10⁻² M. Therapeutic benefit was assessed by changes in longevity. The median survival of MRL/MpJ males was increased from 443 to 615 days and those of (NZW x NZB) F₁ and NZB males and females were increased approximately 2-fold. The most unexpected finding was that longevity of F₁ males was significantly extended irrespective of whether dietary exposure to 2-Me was initiated at 28 days of age, at 50 days of age, or initiated during gestation (and then terminated at weaning--28 days of age). Survival of F₁-hybrids in which treatment was initiated in utero or at 28 days of age was not significantly different, whereas if initiation was delayed until 50 days of age, survival was >200 days shorter. Survival of male MRL/MpJ-Fas lpr and BXSB/MpJ (Yaa-), two strains with genetically controlled accelerated SLE, was not altered by 2-Me when started at 50 days. Various alternatives are discussed regarding potential long-lasting mechanisms imprinted early in life. Even though present day treatments of rodent SLE are generally aimed at controlling specific immunological events, with or without survival benefits, or are procedures presently unsuitable for therapeutic use in humans, the findings presented herein seem worthy of clinical evaluation.
 
Kaplan-Meier plot of paratuberculosis parameters of calves undergoing different treatments. (A) calves (Group 1) were not treated (n = 8). (B) calves (Group 2) were treated with viable Dietzia for only the 1 st 2 days of life (n = 8). (c) calves (Group 4) were treated with viable Dietzia for the 1 st 2 days of life, followed by 58 days of Dietzia in the presence of antibiotics (n = 8). (D) calves (Group 3, n = 10) were treated with viable Dietzia for 60 days (-). Also shown is a compilation of the data for Groups 1, 2 and 4 (-) shown in (A-c) (n = 18). (+) represent the age at which each calf first tested sero-and/or fecal-paratuberculosis-positive and (Δ) the age at which an animal left the herd testing negative.
parameters for calves not fed Dietzia and for their paratuberculosis dams 
parameters for calves fed Dietzia for first two days of life and for their paratuberculosis dams 
parameters for calves fed Dietzia for 60 days and for their paratuberculosis dams 
The research reported herein was designed to assess whether the bacterium, Dietzia subspecies C79793-74, used as a probiotic, could prevent development of parameters indicative of bovine paratuberculosis after potential in utero, birthing and neonatal (colostrum) exposure to Mycobacterium avium subspecies paratuberculosis (MAP). Such exposure avenues are especially relevant for dairy farms practicing good management procedures since calves on these farms could be infected via dams that have yet to be identified as MAP-positive. Indeed, of 18 calves in the present study that became paratuberculosis parameter-positive, five had dams that were negative for all parameters pre-calving. Parameters used herein to define paratuberculosis status were serum ELISA, serum agar gel immunodiffusion, cultureable fecal MAP, histopathology at necropsy and clinical disease. Thirty-four newborn calves, whose dams were paratuberculosis-positive, were assigned to four different treatment groups. Ten were treated daily for 60 days with viable Dietzia added to their antibiotic-free milk feedings; none became positive for any parameter with age. In contrast, seven of eight calves that were not treated became positive for one or more paratuberculosis-associated parameter. Sixteen calves were treated with viable Dietzia for the first two days of life; eight were then not treated further, whereas the other eight were treated an additional 58 days with Dietzia added to tetracycline-fortified milk (Dietzia is sensitive to tetracycline). In these two groups, positivity developed in five of eight and six of eight, respectively. These results indicated that (a) a daily, 60-day treatment with viable Dietzia effectively prevented development of parameters indicative of paratuberculosis and (b) this treatment, in combination with good management practices, has the potential to eradicate MAP from animals/herds, which should curtail the spread of MAP. Such results should significantly reduce human exposure to MAP, which in turn, could have relevance for the controversial role of MAP in Crohn's disease, type-1 diabetes mellitus, sarcoidosis, Blau syndrome, ulcerative colitis, irritable bowel syndrome and multiple sclerosis.
 
Abstract Heat shock proteins (HSP) represent important antigenic targets for the immune response, playing an important role in the pathology and infectious diseases control. The purpose of this work was to investigate the levels of HSP60 and HSP70 specific antibodies in the bloodstream of patients with different bacterial infections and cancer, in order to evaluate their potential role as diagnosis markers of different infectious diseases. Detection of specific anti-HSP 60 and HSP 70 serum levels was performed by ELISA. Statistical analysis of data by multivariate logistic regression was performed using GraphPadPrism software and statistical tests based on chi-square and Student t-test. High levels of anti-HSP60 were found in patients with localized infections, while the levels of anti- HSP70 were higher in the group with generalized infections. The serum levels of both anti-HSP 60 and anti-HSP70 were significantly increased in patients with Gram-negative bacterial infections, as compared with patients harbouring infections produced by Gram-positive and fungal strains, demonstrating their potential use as additional diagnosis and prognosis markers in infections with this etiology.
 
The objective of the present investigation was to determine whether the bacterium Dietzia subsp. C79793-74, previously shown to inhibit growth of Mycobacterium subsp. paratuberculosis under in vitro culture conditions, has therapeutic value as a probiotic for adult cattle with paratuberculosis. Animals were obtained from several herds with evidence of disease based on seropositivity and/or fecal shedding. Sixty-eight cows with initial evidence of Stage II or III paratuberculosis and 2 with an initial Stage IV disease were evaluated longitudinally. Animals were either treated daily with variable, disease-dependent doses of Dietzia (n = 48) or left untreated (n = 22). Clinical aspects of disease (diarrhea, emaciated, cachectic and appetite) were recorded until the animal recovered or required euthanasia due to advanced clinical paratuberculosis or other severe conditions. Paratuberculosis parameters-antibody serology (ELISA, AGID) and fecal culture-were longitudinally monitored over the lifetime of each animal. The results indicated that daily treatment with Dietzia was therapeutic for paratuberculosis cows based on: (a) longitudinal decline in ELISA values only occurred in animals that were treated; (b) prolonged survival was dependant upon treatment--the length being directly associated with low initial ELISA values; and (c) treated animals were the only ones cured of disease. Further investigations are envisaged to determine optimal, long-term dosages that may result in even better therapeutic outcomes as well as to evaluate potential application for therapy of the Johne's disease, human-counterpart, Crohn's disease.
 
Abnormal expression of CEACAM6 is observed at the apical surface of the ileal epithelium in Crohn's disease (CD) patients, and CD ileal lesions are colonized by pathogenic adherent-invasive Escherichia coli (AIEC). The paper of Carvalho et al. recently reported that CD associated AIEC colonize and induce strong gut inflammation in transgenic mice expressing human CEACAM6 acting as a receptor for type 1 pili produced by AIEC bacteria. AIEC also induce CEACAM6 expression by intestinal epithelial cells directly by adhering to host cells and indirectly via increased secretion of TNF-α from AIEC-infected macrophages. Patients expressing a basal level of CEACAM6 in ileum could be predisposed to develop ileal CD and blocking interaction between type 1 pili and CEACAM6 might serve as a specific means of disrupting the colonization and the subsequent inflammatory amplification loop.
 
A new hypervirulent (hypermucoviscous) clinical variant of Klebsiella pneumoniae (hvKP) has emerged over the last decade. Our goal is to identify new mechanisms, which increase the virulence hvKP. It has been shown that hvKP strains produce more biofilm than "classical" stains of K. pneumoniae, therefore we hypothesized that biofilm formation may contribute to the pathogenesis of systemic infection. To test this hypothesis, transposon mutants of the model pathogen hvKP1 were generated and screened for decreased production of biofilm. Three mutant constructs with disruptions in glnA [putatively encodes glutamine synthetase, hvKP1 glnA:: EZ::TN < KAN-2 > (glnA::Tn)], sucD [putatively encodes succinyl-CoA synthase α subunit, hvKP1 sucD:: EZ::TN < KAN-2 > (sucD::Tn)], and tag [putatively encodes transcriptional antiterminator of glycerol uptake operon, hvKP1 tag:: EZ::TN < KAN-2 > (tag::Tn)] were chosen for further characterization and use in biologic studies. Quantitative assays performed in rich laboratory medium and human ascites confirmed the phenotype and a hypermucoviscosity assay established that capsule production was not affected. However, compared with its wild-type parent, neither planktonic cells nor biofilms of glnA::Tn, sucD::Tn and tag::Tn displayed a change to the bactericidal activity of 90% human serum. Likewise, when assessed in a rat subcutaneous abscess model, the growth and survival of glnA::Tn, sucD::Tn and tag::Tn in abscess fluid was similar to hvKP1. In this report we identify three new genes that contribute to biofilm formation in hvKP1. However, decreased biofilm production due to disruption of these genes does not affect the sensitivity of these mutant constructs to 90% human serum when in planktonic form or within a biofilm. Further, their virulence in an in vivo abscess model was unaffected.
 
Klebsiella pneumoniae liver abscess is an emerging infectious disease. This syndrome was unknown before the late 1980s when it was first recognized in Taiwan. Over the next two decades it increased in prevalence in Taiwan and was reported from other nations of East Asia. It was then that the rest of the world became aware of this interesting new syndrome. The disease is no longer confined to East Asia, and is now an emerging infection in North America and Europe. How did this come about? We now understand some of the genetic changes that turn commensal E. coli into extra-intestinal pathogens. K pneumoniae is another member of the Enterobacteriaceae that is usually normal flora in the gut, but we know relatively little about how it evolved into an invasive pathogen capable of causing abscesses in normal livers. The phenotype of the liver-invasive strains is hyperviscosity of the polysaccharide capsules, but while the gene that determines that property is required it is not sufficient to create the pathogen, and more research is needed to discover the other virulence genes, and thus to potentially target them therapeutically.
 
The yeast Candida parapsilosis has emerged as a major human pathogen. The fungus is found in diverse environments as well as in different mammalian hosts, indicative of a successful adaptation to various niches. Fatty acids are the building blocks of cell membranes. Thus, the yeast must have evolved efficient ways to assimilate fatty acids from different sources, such as glucose via de novo fatty acid synthesis or lipids via lipolysis. We have recently shown that blocking the fatty acid synthesis pathway or interfering with the production of secreted lipases impeded yeast growth in glucose and lipid-containing media, respectively. However, in a more complex media (e.g. presence of glucose and lipids), blockage of either pathway individually resulted in growth similar to wild-type yeast. Here, we demonstrate that dual inhibition of these pathways significantly decreased yeast growth in complex media. Therefore, we propose that simultaneously targeting secreted lipases and fatty acid pathways might be ideal to combat C. parapsilosis disease and perhaps other pathogenic fungi.
 
The ubiquitous apicomplexan parasite Toxoplasma gondii stimulates its host's immune response to achieve quiescent chronic infection. Central to this goal are host dendritic cells. The parasite exploits dendritic cells to disseminate through the body, produce pro-inflammatory cytokines, present its antigens to the immune system and yet at the same time subvert their signaling pathways in order to evade detection. This carefully struck balance by Toxoplasma makes it the most successful parasite on this planet. Recent progress has highlighted specific parasite and host molecules that mediate some of these processes particularly in dendritic cells and in other cells of the innate immune system. Critically, there are several important factors that need to be taken into consideration when concluding how the dendritic cells and the immune system deal with a Toxoplasma infection, including the route of administration, parasite strain and host genotype.
 
Differential dectin-1 binding on Aspergillus fumigatus and Aspergillus terreus phialidic conidia. soluble dectin-1 binding A. fumigatus and A. terreus phialidic conidia at various stages of germination (a) dormant conidia (B) swollen condia (c) early germ tube formation and (D) late germination. Differential interference microscopy (DIc) and fluorescence images were captured by microscopy at 40x (a) and 100x (B-D), and are representative of 3 experiments. scale bars denote 5 μm and 10 μm for 40x and 100x magnification, respectively.
Dectin-1 binding on phialidic conidia and accessory conidia at different germination stages. soluble dectin-1 binding on A. terreus phialidic and accessory conidia at (a) dormant conidia (B) swollen conidia, (c) early germ tube formation and (D) late germination. DIc and fluorescence images were captured by microscopy at 40x (a) and 100x (B-D), and are representative of 3 experiments. Within windows, arrows depict the ring-like staining pattern on ac at 100x (a). scale bars denote 5 μm and 10 μm for 40x and 100x magnification, respectively.
accessory conidia are multinucleated prior to germination. hoechst staining was performed on A. terreus accessory conidia, both attached (a) and detached (B) from the hyphae, and A. terreus pc (c) and A. fumigatus pc (D). DIc and UV images were captured by microscopy at 100x, and are representative of 3 experiments. scale bars denote 10 μm.
accessory conidia undergo hyperpolarization during germination. early germ tube formation and hoechst nuclei staining was assessed for A. terreus accessory conidia. DIc and UV images were captured by microscopy at 100x, and are representative of 3 experiments. scale bars denote 10 μm.
Aspergillus terreus accessory conidia elicit a heightened inflammatory response by alveolar macrophages. alveolar macrophages were co-cultured with A. terreus ac or pc. supernatants were collected at (a) 6 or (B) 20 h and assayed for chemokine/cytokine levels by Bio-plex or eLIsa. experiments were performed three times.  
In addition to phialidic conidia (PC), A. terreus produces accessory conidia (AC) both in vitro and in vivo. AC are distinct from PC in cell surface architecture, with the AC surfaces displaying more β-glucan, a molecule that can be a trigger for the induction of inflammatory responses. The present study follows β-glucan cell surface presentation throughout the course of germination of both types of conidia, and analyzes the differential capacity of AC and PC to elicit immune responses. Results show that AC display early, increased dectin-1 labeling on their cell surfaces compared to PC, and this differential dectin-1 labeling is sustained on the cell surface from the time of breaking dormancy through early germ tube emergence. Mouse alveolar macrophages showed a stronger inflammatory cytokine/chemokine response when challenged with AC than with PC in both ex vivo and in vivo experiments, correlating with the greater exposure of β-glucan exhibited by AC. Further, histopathologic staining of the lungs from mice challenged with AC demonstrated heightened cell recruitment and increased inflammatory response compared to the lungs of mice challenged with PC. Our study also demonstrates that AC are multinucleate structures with the ability to germinate rapidly, polarizing in multiple directions and producing several hyphal extensions. We present evidence that A. terreus AC are phenotypically distinct from PC and can be potent activators of the innate immune mechanism thus possibly playing a role in this organism's pathogenesis.
 
Avian influenza viruses (AIV) of H5 and H7 subtypes exhibit two different pathotypes in poultry: infection with low pathogenic (LP) strains results in minimal, if any, health disturbances, whereas highly pathogenic (HP) strains cause severe morbidity and mortality. LPAIV of H5 and H7 subtypes can spontaneously mutate into HPAIV. Ten outbreaks caused by HPAIV are known to have been preceded by circulation of a predecessor LPAIV in poultry. Three of them were caused by H5N2 subtype and seven involved H7 subtype in combination with N1, N3, or N7. Here, we review those outbreaks and summarize the genetic changes which resulted in the transformation of LPAIV to HPAIV under natural conditions. Mutations that were found directly in those outbreaks are more likely to be linked to virulence, pathogenesis, and early adaptation of AIV.
 
Strains and plasmids used in this study 
In vitro characterization of the DSTM1485. (A) and (B) Growth kinetics of the DSTM1485 and its parental strain at acidic pH. Growth kinetics was done in LB (A) and LPM (B) at pH 4.5 buffered with sodium citrate. Log (C) and stationary (D) phase acid tolerance response (ATR) of the DSTM1485 strain. Overnight grown cultures were sub cultured into LPM media at pH 7.0 to an OD 600 nm of 0.3 (log phase) or 1.5 (stationary). For adaptation, bacteria were resuspended in LPM media at pH 4.5 for 2 h, followed by shifting of pH to 3.0 and growth for 2 h. Unadapted cells were directly shifted to pH 3.0. Number of viable bacteria was enumerated by plating on selective LB plates. Shown is the data of two independent experiments. Filled circles, WT; open circles, DSTM1485; NS, not significant.  
STM1485 gene expression in in vitro grown bacteria and intracellular bacteria. (A) and (B) cDNA was synthesized from the RNA isolated from in vitro grown bacteria (in LB pH 7.0 and 4.5 for 4 h) and from infected RAW264.7 cells (4 h post-infection) with and without BAF treatment. STM1485 and spiC (representative from SPI-2 island) were amplified by PCR. 16s rRNA served as internal control. (C) Expression of the His tagged STM1485 protein from STM1485::6xHis knock in strain grown in LB at pH (4.5 and 7.0) by immunoblot. Ribosome Recycling Factor (RRF) probing was done to equalize the amount of bacterial protein loaded for the SDS PAGE. Numbers below the gels indicate the values of densitometric image analysis using Multi Guage software. Images are representative of two independent experiments.
Evaluation of STM1485 expression in epithelial cells (INT-407, Caco-2 and HeLa). STM1485 expression was studied using (A) RT-PCR assay. (B) Immunoblot method using the STM1485::6xHis tagged strain. Bacteria were isolated from the infected epithelial cells at 6th h post infection. Bacteria grown in DMEM at 37°C under 5% CO 2 were served as control to determine expression outside host cells. Numbers below the gels indicate the values of densitometric image analysis using Multi Guage software. Results are representative of two independent experiments.  
Intracellular survival assay of DSTM1485 in mouse macrophage cells (A) and complementation studies in INT-407 (B) and RAW264.7 (C). Cells were infected with WT or DSTM1485 or DSTM1485pQE601485 strains were lysed at 2 and 16 h post infection. Bacterial load was shown as fold increase in CFU from 2 h to 16 h. Graphs are representative of two independent experiments with similar results. Statistical significance was defined as follows (**p , 0.005) (Student's t-test).  
During the course of infection, Salmonella has to face several potentially lethal environmental conditions, one such being acidic pH. The ability to sense and respond to the acidic pH is crucial for the survival and replication of Salmonella. The physiological role of one gene (STM1485) involved in this response, which is upregulated inside the host cells (by 90- to 113-fold) is functionally characterized in Salmonella pathogenesis. In vitro, the ΔSTM1485 neither exhibited any growth defect at pH 4.5 nor any difference in the acid tolerance response. The ΔSTM1485 was compromised in its capacity to proliferate inside the host cells and complementation with STM1485 gene restored its virulence. We further demonstrate that the surface translocation of Salmonella pathogenicity island-2 (SPI-2) encoded translocon proteins, SseB and SseD were reduced in the ΔSTM1485. The increase in co-localization of this mutant with lysosomes was also observed. In addition, the ΔSTM1485 displayed significantly reduced competitive indices (CI) in spleen, liver and mesenteric lymph nodes in murine typhoid model when infected by intra-gastric route. Based on these results, we conclude that the acidic pH induced STM1485 gene is essential for intracellular replication of Salmonella.
 
The first stress that foodborne pathogens find upon ingestion is the very acidic pH of the stomach of the host. In addition, intracellular pathogens like Salmonella are submitted to low pH inside the host cells. Two general acid survival systems are found in these organisms: acid resistance mechanisms and acid tolerance responses. These mechanisms involve the synthesis of a series of acid shock proteins. Only a subset of these proteins is directly involved in acid survival. This is related to the fact that low pH is not only a stress to cope with, but it is also an important signal that indicates to the bacterium that it is in a potential host environment and that triggers the induction of many virulence genes. Asr is an acid shock protein that supports growth of Escherichia coli at moderate acidity. In this issue of Virulence, Allam et al. investigate the role of STM1485, the homologous of asr in Salmonella enterica serovar Typhimurium, in acid survival and virulence. Although STM1485 is not required for acid survival of S. enterica, it is necessary for intracellular replication in human epithelial cells and murine macrophages, and to prevent the progression of the Salmonella-containing vacuole along the degradative pathway. In addition, Allam et al. are able to show that the defects of the STM1485 mutant at the cellular level correlate with reduced virulence in the mouse model.
 
Acinetobacter baumannii (Ab) is a common cause of community-acquired pneumonia (CAP) in chronic alcoholics in tropical and sub-tropical climates and associated with a > 50% mortality rate. We demonstrated that exposure of J774.16 macrophage-like cells to physiological alcohol (EtOH) concentrations decreased phagocytosis and killing of Ab. EtOH-mediated macrophage phagocytosis dysfunction may be associated with reduced expression of GTPase-RhoA, a key regulator of the actin polymerization signaling cascade. EtOH inhibited nitric oxide (NO) generation via inducible NO-synthase inactivation, which enhanced Ab survival within macrophages. Additionally, EtOH alters cytokine production resulting in a dysregulated immune response. This study is a proof of principle which establishes that EtOH might exacerbate Ab infection and be an important factor enhancing CAP in individuals at risk.
 
Acinetobacter baumannii is an opportunistic bacterial pathogen primarily associated with hospital-acquired infections. The recent increase in incidence, largely associated with infected combat troops returning from conflict zones, coupled with a dramatic increase in the incidence of multidrug-resistant (MDR) strains, has significantly raised the profile of this emerging opportunistic pathogen. Herein, we provide an overview of the pathogen, discuss some of the major factors that have led to its clinical prominence and outline some of the novel therapeutic strategies currently in development.
 
NO-np inhibits Ab growth in vitro. The effect of NO on Ab growth kinetics was determined using Bioscreen c analysis. Ab was grown in the absence (untreated) or presence of nanoparticles with NO (NO-np) or without NO (np). each point represents the average of four measurements.
NO-np increased wound healing rate in mice. (A) Wounds of Balb/c mice untreated Ab-infected, np-treated Ab-infected, and Abinfected NO-np-treated, 3 days post-infection. scale bar: 5 mm. (B) Wound size analysis of Balb/c mice skin lesions. Time points are the averages of the results for five measurements, and error bars denote standard deviations. *p < 0.05; **p < 0.001 in comparing the NO-nptreated group with untreated and np-treated groups.
NO-nps decrease collagen degradation in skin lesions of Balb/c mice. (A) histological analysis of Balb/c mice untreated Ab-infected, np-treated Ab-infected, and Ab-infected treated with NO, day 3. Mice were infected with 5 x 10 7 bacterial cells. The blue stain indicates collagen. scale bar: 20 μm. (B) Quantitative measurements of collagen intensity in 10 representative fields of the same size for untreated Ab-infected, np-treated Ab-infected, and Ab-infected treated with NO wounds were taken using Image J software. Bars are the averages of the results, and error bars denote standard deviations. *p < 0.001 in comparing the NO-treated group with untreated and np-treated groups.
Acinetobacter baumannii (Ab) is a frequent cause of hospital acquired pneumonia and recently has increased in incidence as the causative agent of severe disease in troops wounded in Afghanistan and Iraq. Ab clinical isolates are frequently extremely resistant to antimicrobials, significantly complicating our capacity to treat infections due to this pathogen. Hence, the development of innovative therapeutics targeting mechanisms to which the bacteria are unlikely to evolve resistance is urgently needed. We examined the capacity of a nitric oxide-releasing nanoparticle (NO-np) to treat wounds infected with Ab. We found that the NO-nps were therapeutic in an experimental Ab murine wound model. Treatment with NO-nps significantly accelerated healing of infected wounds. Histological study demonstrated that NO-np treatment reduced suppurative inflammation, decreased microbial burden, and reduced the degradation of collagen. Furthermore, NO-np treatment alters the local cytokine milieu. In sum, we demonstrated that the NO-nps are an easily administered topical antimicrobial for the treatment of Ab wound infections, and our findings suggest that NO-nps may also be ideal for use in combat or disaster situations.
 
The Gram-negative coccobacillus Acinetobacter baumannii (Ab) has become an increasingly prevalent cause of hospital-acquired infections during the last two decades primarily resulting in pneumonia and complicated infections, including wound infections in troops injured in Afghanistan and Iraq. Moreover, the majority of clinical Ab isolates display high-level resistance to commonly utilized antimicrobial drugs, which severely compromises our capacity to care for patients with Ab disease. Thus, radically new approaches are urgently needed. This review focuses on novel therapies that can challenge the evolving ability of Ab to develop resistance and cause disease.
 
Mechanisms of resistance to E. faecium and E. faecalis (continued) 
Mechanisms of resistance to E. faecium and E. faecalis 
Enterococci have the potential for resistance to virtually all clinically useful antibiotics. Their emergence as important nosocomial pathogens has coincided with increased expression of antimicrobial resistance by members of the genus. The mechanisms underlying antibiotic resistance in enterococci may be intrinsic to the species or acquired through mutation of intrinsic genes or horizontal exchange of genetic material encoding resistance determinants. This paper reviews the antibiotic resistance mechanisms in Enterococcus faecium and Enterococcus faecalis and discusses treatment options.
 
Mice treated with anthrax lethal toxin (LT) exhibit hemorrhage caused by unknown mechanisms. Moreover, LT treatment in mice induced liver damage. In this study, we hypothesized that a suppressed coagulation function may be associated with liver damage, because the liver is the major producing source of coagulation factors. The hepatic expression of coagulant factors and the survival rates were analyzed after cultured cells or mice were exposed to LT. In agreement with our hypothesis, LT induces cytotoxicity against hepatic cells in vitro. In addition, suppressed expression of coagulation factor VIII (FVIII) in the liver is associated with a prolonged plasma clotting time in LT-treated mice, suggesting a suppressive role of LT in coagulation. Accordingly, we further hypothesized that a loss-of-function approach involving treatments of an anticoagulant should exacerbate LT-induced abnormalities, whereas a gain-of-function approach involving injections of recombinant FVIII to complement the coagulation deficiency should ameliorate the pathogenesis. As expected, a sublethal dose of LT caused mortality in the mice that were non-lethally pretreated with an anticoagulant (warfarin). By contrast, treatments of recombinant FVIII reduced the mortality from a lethal dose of LT in mice. Our results indicated that LT-induced deficiency of FVIII is involved in LT-mediated pathogenesis. Using recombinant FVIII to correct the coagulant defect may enable developing a new strategy to treat anthrax.
 
Streptococcus pyogenes (group A Streptococcus, GAS) is a human bacterial pathogen of global significance, causing severe invasive diseases associated with serious morbidity and mortality. To survive within the host and establish an infection, GAS requires essential nutrients, including iron. The streptococcal hemoprotein receptor (Shr) is a surface-localized GAS protein that binds heme-containing proteins and extracellular matrix components. In this study, we employ targeted allelic exchange mutagenesis to investigate the role of Shr in the pathogenesis of the globally disseminated serotype M1T1 GAS. The shr mutant exhibited a growth defect in iron-restricted medium supplemented with ferric chloride, but no significant differences were observed in neutrophil survival, antimicrobial peptide resistance, cell surface charge, fibronectin-binding or adherence to human epithelial cells and keratinocytes, compared with wild-type. However, the shr mutant displayed a reduction in human blood proliferation, laminin-binding capacity and was attenuated for virulence in in vivo models of skin and systemic infection. We conclude that Shr augments GAS adherence to laminin, an important extracellular matrix attachment component. Furthermore, Shr-mediated iron uptake contributes to GAS growth in human blood, and is required for full virulence of serotype M1T1 GAS in mouse models of invasive disease.
 
The blood-brain barrier (BBB) is a structural and functional barrier that protects the central nervous system (CNS) from invasion by blood-borne pathogens including parasites. However, some intracellular and extracellular parasites can traverse the BBB during the course of infection and cause neurological disturbances and/or damage which are at times fatal. The means by which parasites cross the BBB and how the immune system controls the parasites within the brain are still unclear. In this review we present the current understanding of the processes utilized by two human neuropathogenic parasites, Trypanosoma brucei spp and Toxoplasma gondii, to go across the BBB and consequences of CNS invasion. We also describe briefly other parasites that can invade the brain and how they interact with or circumvent the BBB. The roles played by parasite-derived and host-derived molecules during parasitic and white blood cell invasion of the brain are discussed.
 
Cyr1, Cap1 and G-actin form a tripartite complex. (A) Previous studies 15,25 suggest that Cap1 associates with Cyr1 and G-actin independently forming two heterodimeric complexes with distinct functions. We propose a tripartite complex with Cap1 acting as a scaffold holding Cyr1 and G-actin together. This tripartite complex may provide a mechanism for bidirectional signaling between the cellular actin status and cAMP levels. (B) We propose that both Cap1 and G-actin act as positive regulatory subunits in the tripartite complex and contribute to a proper activation of cAMP synthesis in response to hyphal induction. Whereas Cap1 can act without association with G-actin, the latter requires Cap1 to make functional contacts with Cyr1.
The fungal pathogen Candida albicans has a remarkable ability to switch growth forms. Particularly, the yeast-to-hyphae switch is closely linked with its virulence. A range of chemicals and conditions can promote hyphal growth including serum, peptidoglycan, CO2, neutral pH, and elevated temperature. All these signals act essentially through the adenylyl cyclase Cyr1 that synthesizes cAMP. Cells lacking Cyr1 are completely defective in hyphal growth. Recently, cellular actin status is found to influence cAMP synthesis. However, how Cyr1 senses and processes multiple external and internal signals to produce a contextually proper level of cAMP remains unclear. We hypothesized that Cyr1 itself possesses multiple sensors for different signals and achieves signal integration through a combined allosteric effect on the catalytic center. To test this hypothesis, we affinity-purified a Cyr1-containing complex and found that it could enhance cAMP synthesis upon treatment with serum, peptidoglycan or CO2 in vitro. The data indicate that the complex is an essentially intact sensor/effector apparatus for cAMP synthesis. The complex contains two more subunits, the cyclase-associated protein Cap1 and G-actin. We discovered that G-actin plays a regulatory role, rendering cAMP synthesis responsive to actin dynamics. These findings shed new lights on the mechanisms that regulate cAMP-mediated responses in fungi.
 
Clinical presentation of localized aggressive periodontitis. A 16-year old female presenting with radiographic alveolar bone loss associated with bone defects (marked with arrows) and probing attachment loss at 2 permanent first molars, left upper premolars and lower incisors. Clinical photographs buccal view (A-C). Radiographs (D-F). The clinical presentation shows sparse plaque accumulation and localized gingival inflammation with 48 mm periodontal crevices with bleeding on probing in the affected regions. The results from the microbial sampling are presented in the inserted table and the sampled sites are indicated. Microbiological analysis, by cultivation technique, confirmed the presence of high levels of A. actinomycetemcomitans in the 3 lesions sampled. Diagnosis: localized aggressive periodontitis (LAgP). 
(A) Interaction of A. actinomycetemcomitans leukotoxin (LtxA) with T-, B-lymphocytes, polymorphonuclear (PMN) leukocytes, and macrophages leads to cell lysis. (B) LtxA-induced cell death in macrophages involves several steps before the cell lysis occurs. LtxA binds to LFA-1 (1) and induces extracellular release of ATP (2). The released ATP binds to the P2X 7-receptor (3) that subsequently causes efflux of potassium (4). The inflammasome complex is formed and activated (5), which promotes the cleavage and activation of a cysteine proteinase called caspase-1 (6). The cleaved caspase1 is then responsible for activation (7) and release of abundant levels of active IL-1b and IL-18 (8). 
Abstract Periodontitis is an infection-induced inflammatory disease that causes loss of the tooth supporting tissues. Much focus has been put on comparison of the microbial biofilm in the healthy periodontium with the diseased one. The information arising from such studies is limited due to difficulties to compare the microbial composition in these two completely different ecological niches. A few longitudinal studies have contributed with information that makes it possible to predict which individuals have an increased risk of developing aggressive forms of periodontitis, and the predictors are either microbial or/and host-derived factors. The most conspicuous condition that is associated with disease risk is the presence of Aggregatibacter actinomycetemcomitans at the individual level. This Gram-negative bacterium has a great genetic variation with a number of virulence factors. In this review we focus in particular on the leukotoxin that, based on resent knowledge, might be one of the most important virulence factors of A. actinomycetemcomitans.
 
Bacterial pathogens release a number of toxins that are able to form pores in target host cells, which can result in their destruction. Due to this property of this subgroup of toxins, they are considered virulence factors. A lesser known ability of these toxins when present at lower concentrations that are insufficient for host cell lysis to occur, is their activation of host immune cells. The Panton-Valentine Leukocidin (PVL) secreted by an alarming percentage of Staphylococcus aureus causing community-acquired infections, is one such toxin. Due to the low inoculum of S. aureus we used to establish skin abscesses in a murine model of infection, lower amounts of PVL are likely to be present early in infection, hence, the proinflammatory properties of PVL may be more evident. Our data not only suggested that this was indeed the case, but we also showed that antibodies directed to PVL neutralized immune activation by this toxin resulting in a less robust host innate immune response. Thus, given the high levels of antibodies to PVL present in healthy individuals, these antibodies may directly enhance the virulence of PVLproducing S. aureus by dampening the innate immune response to infection. Since many pore-forming toxins share this dual property of concentration-dependent host cell lysis and immune activation, it is interesting to speculate that antibodies raised to some bacterial toxins may have the opposite intended outcome of directly enhancing bacterial virulence instead of controlling infection.
 
LPS/LTA-induced cytokine secretion in the presence and absence of different serum proteins. Human monocytes were incubated with 1 mg/ml of different serum proteins prior to incubation with either 100 ng/ml LPS or 10 mg/ml of LTA. Supernatant was collected and analyzed for TNF-a using a flow cytometric (Th1/Th2) bead array system (Becton Dickinson). T-test was performed comparing results against serum free values for LPS+ and LTA+, respectively. * and # denote statistical significance (p , 0.05). The results are representative from three independent experiments.
Bacterial cell wall components, such LPS and LTA, are potent initiators of an inflammatory response that can lead to septic shock. The advances in the past were centered around membrane-bound receptors and intracellular events, but our understanding of the initial interactions of these bacterial components with serum proteins as they enter the bloodstream remain unclear. In this study we identified several serum proteins, which are involved in the innate recognition of bacterial products. Using affinity chromatography and mass spectrometry we performed proteomic analysis of LPS- and LTA-binding serum proteins. We isolated proteins from normal serum that can interact with LPS and LTA. Fluorescent binding experiments and cytokine assays revealed that serum proteins, such as apolipoprotein, LDL, transferrin and holotransferrin could neutralize LPS/LTA binding as well as the subsequent inflammatory response, suggesting that serum proteins modulate LPS/LTA-induced responses. When compared with the proteomic profile of serum from septic patients it was shown that these proteins were in lower abundance. Investigation of serum proteins in 25 critically ill patients with a mortality rate of 40% showed statistically higher levels of these proteins in survivors. Patients surviving sepsis had statistically significant higher levels of apolipoprotein, albumin, LDL, transferrin and holotransferrin than individuals that succumbed, suggesting that these proteins have an inhibitory effect on LPS/LTA-induced inflammatory responses and in their absence there might be an augmented inflammatory response in sepsis.
 
summary of biomarkers and cited references, by disease
Endothelial dysfunction contributes to the pathogenesis of a variety of potentially serious infectious diseases and syndromes, including sepsis and septic shock, hemolytic-uremic syndrome, severe malaria, and dengue hemorrhagic fever. Because endothelial activation often precedes overt endothelial dysfunction, biomarkers of the activated endothelium in serum and/or plasma may be detectable before classically recognized markers of disease, and therefore, may be clinically useful as biomarkers of disease severity or prognosis in systemic infectious diseases. In this review, the current status of mediators of endothelial cell function (angiopoietins-1 and -2), components of the coagulation pathway (von Willebrand Factor, ADAMTS13, and thrombomodulin), soluble cell-surface adhesion molecules (soluble E-selectin, sICAM-1, and sVCAM-1), and regulators of vascular tone and permeability (VEGF and sFlt-1) as biomarkers in severe infectious diseases is discussed in the context of sepsis, E. coli O157:H7 infection, malaria, and dengue virus infection.
 
Larval hemocyte densities in response to A. fumigatus conidia infection. Larvae were injected with PBS or non-lethal doses of A. fumigatus ATCC 26933 and incubated at 30°C. Larvae were subsequently bled 24 h post-infection and hemocyte densities were ascertained by hemocytometry. The data shown are the mean of three independent experiments with standard error included. *p ≤ 0.05 relative to PBS injection; **p ≤ 0.028 relative to PBS injection.
Densitometric analysis of hemolymph proteins, from larvae previously exposed to non-lethal doses of conidia, showing dierential binding to conidia. The binding of three identied protein of interest from conidia-challenged larvae was analyzed by densitometry. Arylphorin, prophenoloxidase subunit 2 and apolipophorin III from the hemolymph of G. mellonella larvae injected with PBS or non-lethal inocula of conidia demonstrated varying levels of binding to A. fumigatus conidia under standardized conditions. The eect of immune priming was compared with the binding exhibited by untreated larvae (U.T.) which had been incubated at 30°C only. *p ≤ 0.028, **p ≤ 0.008, ***p ≤ 0.003
Larval hemolymph proteomic prole following challenge with non-lethal A. fumigatus conidia inocula. Untreated larvae (A) or larvae injected with PBS (B), 1 x 10 4 (C) or 1 x 10 5 (D) A. fumigatus ATCC26933 conidia were incubated at 30°C for 24 h. Protein was extracted and the proteomic prole was examined using 2-D electrophoresis as described. Alterations to relative protein expression following immune priming were compared.
Larvae of Galleria mellonella are useful models for studying the virulence of microbial pathogens or for evaluating the potency of antimicrobial agents. In this work we demonstrated that prior exposure of larvae to non-lethal doses of Aspergillus fumigatus conidia increases the resistance of larvae to a lethal dose (1 x 10⁷ 20 μl⁻¹) 24 h later. Exposure of larvae to a conidia concentration of 1 x 10⁴ 20 μl⁻¹ leads to an increase in haemocyte density but an inoculum of 1 x 10⁵ conidia leads to enhanced expression of antimicrobial peptides, increased binding of proteins (e.g. arylophorin, prophenoloxidase, apolipophorin ) to conidia and elevated hemocytes density. These results suggest that a low dose of conidia (1 x 10⁴) predominantly activates the cellular immune response but that a higher dose (1 x 10⁵) that is still not lethal activates a humoral immune response to the greatest extent. While insects have an immune system analogous to the innate immune response of mammals these results suggest that it is capable of assessing the extent of the microbial challenge and mounting a "proportionate" immune response, which may have important survival advantages.
 
Pathogenic bacteria produce virulence factors called effectors, which are important components of the infection process. Effectors aid in pathogenesis by facilitating bacterial attachment, pathogen entry into or exit from the host cell, immunoevasion, and immunosuppression. Effectors also have the ability to subvert host cellular processes, such as hijacking cytoskeletal machinery or blocking protein translation. However, host cells possess an evolutionarily conserved innate immune response that can sense the pathogen through the activity of its effectors and mount a robust immune response. This "effector triggered immunity" (ETI) was first discovered in plants but recent evidence suggest that the process is also well conserved in metazoans. We will discuss salient points of the mechanism of ETI in metazoans from recent studies done in mammalian cells and invertebrate model hosts.
 
Biomarkers of endothelial activation 
Biomarkers of endothelial activation 
Biomarkers of coagulation 
Biomarkers of coagulation 
Introduction: HIV infection is associated with vascular dysfunction and adverse cardiovascular outcomes. Our objective was to review the evidence regarding the clinical utility of endothelial activation and coagulation biomarkers for the prognosis of HIV-infected patients. Methods: We searched PubMed and Embase for publications using the keywords "HIV" or "HIV infection" and "endothelium" or "coagulation". We reviewed reference lists and hand-searched for additional relevant articles. All clinical studies that enrolled non-pregnant, HIV-infected adults, measured biomarkers reflecting endothelial activation or coagulation, and prospectively evaluated their associations with vascular dysfunction or clinical outcomes were included. Results: Seventeen studies were identified that fulfilled the inclusion criteria, of which 11 investigated endothelial activation biomarkers and 12 investigated coagulation biomarkers. Biomarkers and outcomes varied widely across studies. Overall, published studies support an association between P-selectin and venous thromboembolism in HIV-infected patients, an association between tissue-type plasminogen activator and death, and associations between D-dimer and several clinical outcomes, including venous thromboembolism, cardiovascular disease, and all-cause mortality. Conclusions: Several studies have demonstrated associations between biomarkers of endothelial activation and coagulation and clinically important outcomes in HIV-1 infection. Additional large-scale prospective investigations to determine the utility of endothelial activation and coagulation biomarkers for risk stratification and prediction of adverse outcomes are clearly warranted.
 
(A) endothelial cell barrier dysfunction. During severe infections, endothelial activation and dysfunction may lead to the loss of microvascular endothelial barrier integrity, resulting in edema, multiple organ failure and death. phosphorylation of adherens junction protein p120 catenin precipitates VE-cadherin internalization/junction disassembly. Endothelial integrity may also be compromised by rearrangements/degradation of the actin cytoskeleton. Molecular pathways implicated in this response include MYD88-aRNo binding that results in enhanced aRF6 signaling and decreased VE-cadherin localization at the cell surface. Endothelial activation may also cause an increase in the Ang-1 antagonist, Ang-2. Ang-2 binds to its cognate receptor, Tie2, and impedes the vascular stabilizing effects of Ang-1 by promoting proinflammatory endothelial responses and upregulating cell surface adhesion molecules. Vascular permeabilizing VEGF binds to VEGFR2 resulting in increased dissociation of VE-cadherin from the adherens junction through a veGFR2-Src-ve-cadherin signaling pathway. (B) endothelial cell barrier enhancement. SecinH3, a GeF (e.g., aRNo) inhibitor, inhibits ARF6-induced VE-cadherin internalization. Ang-1/Tie2 agonists activate Tie2 resulting in increased vascular quiescence via strengthening of endothelial cell junctions, downregulation of surface adhesion molecules and transdominate blockade of veGR2 signaling. Fibrinopeptide Bβ 15-42 provides barrier protection via maintenance of membrane ve-cadherin and inhibition of actin degradation via Rhoa signaling inhibition. upon binding its receptor Robo4, Slit2N reduces p120 catenin phosphorylation and inhibits aRF6, thereby increasing ve-cadherin retention at the cell surface. aNp administration decreases microvascular permeability via inhibition of Rhoa-induced actin degradation and NFκB/P38 MAPK inhibition. S1P agonist administration reinforces the endothelial barrier via Rac1 and α v β 3 integrin signaling, resulting in formation and stabilization of cortical actin. Administration of S1p agonist enhances cortical actin formation (via Rac1 and α v β 3 integrin signaling) and downregulates iFN-α, thereby decreasing cytokine/ chemokine production and enhancing endothelial cell barrier stability. 
Recent evidence suggests that loss of endothelial barrier function and resulting microvascular leak play important mechanistic roles in the pathogenesis of infection-related end-organ dysfunction and failure. Several distinct therapeutic strategies, designed to prevent or limit infection-related microvascular endothelial activation and permeability, thereby mitigating end-organ injury/dysfunction, have recently been investigated in pre-clinical models. In this review, these potential therapeutic strategies, namely, VEGFR2/Src antagonists, sphingosine-1-phosphate agonists, fibrinopeptide Bβ 15-42, slit2N, secinH3, angiopoietin-1/tie-2 agonists, angiopoietin-2 antagonists, statins, atrial natriuretic peptide, and mesenchymal stromal (stem) cells, are discussed in terms of their translational potential for the management of clinical infectious diseases.
 
Similarities and differences between dengue hemorrhagic fever and hantavirus pulmonary syndrome 
The loss of the endothelium barrier and vascular leakage play a central role in the pathogenesis of hemorrhagic fever viruses in general. This can be caused either directly by the viral infection and damage of the vascular endothelium, or indirectly by a dysregulated immune response resulting in an excessive activation of the endothelium. This article briefly reviews our knowledge of the importance of the disruption of the vascular endothelial barrier in two severe disease syndromes, dengue hemorrhagic fever and hantavirus pulmonary syndrome. Both viruses cause changes in vascular permeability without damaging the endothelium. Here we focus on our understanding of the virus interaction with the endothelium, the role of the endothelium in the induced pathogenesis, and the possible mechanisms by which each virus causes vascular leakage. Understanding the dynamics between viral infection and the dysregulation of the endothelial cell barrier will help us to define potential therapeutic targets for reducing disease severity.
 
The development of severe influenza has been attributed to a heightened innate immune response. Recent evidence suggests that endothelial activation, loss of barrier function, and consequent microvascular leak may also serve important mechanistic roles in the pathogenesis of severe influenza. The aim of this review is to summarize the current evidence in support of endothelial activation and dysfunction as a central feature preceding the development of severe influenza. We also discuss the effect of influenza on platelet-endothelial interactions.
 
Pathological intercourse between HcV and HiV-1 in the co-infected host. Proposed scheme of the main factors and their interactions in the pathogenic processes in HcV/HiV-1 co-infection.
Activation of innate and adaptive immune mechanisms in response to infection is necessary to control and clear infections. However, chronic immune activation in human immunodeficiency virus 1 (HIV-1) infection has a series of detrimental effects and is a major driving force in HIV-1 disease progression. We recently found that patients with chronic hepatitis C virus (HCV)/HIV-1 co-infection display sharply elevated immune activation as determined by expression of CD38 in T cells. High immune activation was observed despite that these patients were on effective antiretroviral therapy (ART), which usually brings down activation levels in HIV-infected people. HCV treatment with pegylated interferon-α (IFNα) and ribavirin reduced activation, and this was at first glance unexpected as IFNα is believed to be involved in driving activation. Here, we briefly summarize these findings and discuss them in context of the emerging roles of the gut barrier and the liver in chronic immune activation and viral disease progression.
 
P. aeruginosa is an opportunistic pathogen that occupies diverse environmental niches and is capable of causing a range of infections in humans. This versatility suggests that it has sophisticated mechanisms to sense and respond to the surrounding microenvironment. Two-component sensors are commonly used by bacteria to sense and respond to environmental stimuli and Pseudomonas aeruginosa has one of the largest sets of two-component sensors known in bacteria. We took advantage of a non-redundant transposon library and a recently characterized vertebrate model host, Danio rerio, that is amenable to higher throughput analysis than mammalian models, to systematically test the role of 60 two-component sensors that are required for P. aeruginosa virulence in acute infection. We found that the sensor kinase KinB is required for acute infection in zebrafish embryos and regulates a number of virulence related phenotypes in a manner independent of its kinase activity and its known response regulator, AlgB. Thus, the regulation of virulence by KinB highlights the increasing recognition of non-canonical two-component signaling mechanisms.
 
An important part of the innate immune response of the nematode C. elegans to fungal infection is the rapid induction of antimicrobial peptide gene expression. One of these genes, nlp‑29, is expressed at a low level in adults under normal conditions. Its expression is up-regulated in the epidermis by infection with Drechmeria coniospora, but also by physical injury and by osmotic stress. For infection and wounding, the induction is dependent on a p38 MAP kinase cascade, but for osmotic stress, this pathway is not required. To characterize further the pathways that control the expression of nlp‑29, we carried out a genetic screen for negative regulatory genes. We isolated a number of Peni (peptide expression no infection) mutants and cloned one. It corresponds to fasn‑1, the nematode ortholog of vertebrate fatty acid synthase. We show here that a pathway involving fatty acid synthesis and the evolutionary conserved wnk‑1 and gck‑3/Ste20/GCK‑VI kinases modulates nlp‑29 expression in the C. elegans epidermis, independently of p38 MAPK signaling. The control of the antimicrobial peptide gene nlp‑29 thus links different physiological processes, including fatty acid metabolism, osmoregulation, maintenance of epidermal integrity and the innate immune response to infection.
 
Top-cited authors
Bernhard Hube
  • Leibniz Institute for Natural Product Research and Infection Biology - Hans Knöll Institute
Duncan Wilson
  • University of Exeter
Derek C Angus
  • University of Pittsburgh
Andreas Vilcinskas
  • Justus-Liebig-Universität Gießen
Mark Shirtliff
  • University of Maryland, Baltimore