Trillions and Trillions: Herpes Simplex Virus-1 Hepatitis in an Immunocompetent Adult

We describe a case of acute liver failure and myopericarditis due to herpes simplex virus-1 (HSV-1) in an immunocompetent adult. We estimate that, at the height of viremia, the patient contained a quantity of HSV-1 virions approaching that of human cells. The patient recovered with acyclovir that was dose-adjusted for neurotoxicity and developed a vigorous anti-HSV-1 T-cell response.

Decoding the complexities of human malaria through systems immunology

The complexity of the Plasmodium parasite and its life cycle poses a challenge to our understanding of the host immune response against malaria. Studying human immune responses during natural and experimental Plasmodium infections can enhance our understanding of malaria-protective immunity and inform the design of disease-modifying adjunctive therapies and next-generation malaria vaccines. Systems immunology can complement conventional approaches to facilitate our understanding of the complex immune response to the highly dynamic malaria parasite. In this review, recent studies that used systems-based approaches to evaluate human immune responses during natural and experimental Plasmodium falciparum and Plasmodium vivax infections as well as during immunization with candidate malaria vaccines are summarized and related to each other. The potential for next-generation technologies to address the current limitations of systems-based studies of human malaria are discussed.

The Roles of MicroRNAs (miRNAs) in Avian Response to Viral Infection and Pathogenesis of Avian Immunosuppressive Diseases

MicroRNAs (miRNAs) are a class of non-coding small RNAs that play important roles in the regulation of various biological processes including cell development and differentiation, apoptosis, tumorigenesis, immunoregulation and viral infections. Avian immunosuppressive diseases refer to those avian diseases caused by pathogens that target and damage the immune organs or cells of the host, increasing susceptibility to other microbial infections and the risk of failure in subsequent vaccination against other diseases. As such, once a disease with an immunosuppressive feature occurs in flocks, it would be difficult for the stakeholders to have an optimal economic income. Infectious bursal disease (IBD), avian leukemia (AL), Marek’s disease (MD), chicken infectious anemia (CIA), reticuloendotheliosis (RE) and avian reovirus infection are on the top list of commonly-seen avian diseases with a feature of immunosuppression, posing an unmeasurable threat to the poultry industry across the globe. Understanding the pathogenesis of avian immunosuppressive disease is the basis for disease prevention and control. miRNAs have been shown to be involved in host response to pathogenic infections in chickens, including regulation of immunity, tumorigenesis, cell proliferation and viral replication. Here we summarize current knowledge on the roles of miRNAs in avian response to viral infection and pathogenesis of avian immunosuppressive diseases, in particular, MD, AL, IBD and RE.

Quantitative Proteomics Reveal Peroxiredoxin Perturbation Upon Persistent Lymphocytic Choriomeningitis Virus Infection in Human Cells

Experimental data indicate that during persistent infection, lymphocytic choriomeningitis virus (LCMV) may both directly or indirectly modulate regulatory cellular processes and alter cellular functions that are not critical for survival, but are essential for cell homeostasis. In order to shed more light on these processes, two-dimensional differential in-gel electrophoresis (2D-DIGE) and MALDI-TOF tandem mass spectrometry were used to determine the proteome response of the HeLa cell line to persistent LCMV infection. Quantitative analysis revealed 24 differentially abundant proteins. Functional analysis showed that LCMV-responsive proteins were primarily involved in metabolism, stress, and the defense response. Among identified proteins, we discovered significant changes for peroxiredoxins, a family of antioxidant enzymes. Decreased amount of these antioxidant proteins correlated with elevation of reactive oxygen species (ROS) in infected cells. Increased levels of ROS were accompanied by changes in the pattern of telomere restriction fragments (TRFs) in infected cells and mediated activation of hypoxia-inducible transcription factor-1 (HIF-1) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways. Moreover, treatment with antioxidants resulted in reduced levels of viral nucleoprotein, indicating a connection between ROS-dependent signaling and viral replication.

Molecular and biomarker-based diagnostics in early sepsis: current challenges and future perspectives

Introduction: Sepsis, defined as a life-threatening organ dysfunction resulting from dysregulated host response to infection, is still a major challenge for healthcare systems. Early diagnosis is highly needed, yet challenging, due to the non-specificity of clinical symptoms. Rapid and targeted application of therapy strategies is crucial for patient's outcome.Areas covered: Faster and better diagnostics with high accuracy is promised by novel host response biomarkers and a wide variety of direct pathogen identification technologies, which have emerged over the last years. This review will cover both - host response-guided diagnostics and methods for direct pathogen detection. Some of the markers and technologies are already market-ready, others are more likely aspirants. We will discuss them in terms of their performance and benefit for use in clinical diagnostics.Expert opinion: Latest technological advances enable the development of promising diagnostic tests, detecting the host response as well as identifying pathogens without the need of cultivation. However, the syndrome's heterogeneity makes it difficult to develop a universal test suitable for routine use. Moreover, the robustness of the biomarkers and technologies still has to be verified. Combining these technologies and clinical routine parameters with bioinformatic methods (e.g., machine-learning algorithms) may revolutionize sepsis diagnostics.

High Resolution Analysis of Respiratory Syncytial Virus Infection In Vivo

Human respiratory syncytial virus (HRSV) is a major cause of pediatric infection and also causes disease in the elderly and those with underlying respiratory problems. There is no vaccine for HRSV and anti-viral therapeutics are not broadly applicable. To investigate the effect of HRSV biology in children, nasopharyngeal aspirates were taken from children with different viral loads and a combined high throughput RNAseq and label free quantitative proteomics approach was used to characterize the nucleic acid and proteins in these samples. HRSV proteins were identified in the nasopharyngeal aspirates from infected children, and their abundance correlated with viral load (Ct value), confirming HRSV infection. Analysis of the HRSV genome indicated that the children were infected with sub-group A virus and that minor variants in nucleotide frequency occurred in discrete clusters along the HRSV genome, and within a patient clustered distinctly within the glycoprotein gene. Data from the samples were binned into four groups; no-HRSV infection (control), high viral load (Ct < 20), medium viral load (Ct = 20-25), and low viral load (Ct > 25). Cellular proteins associated with the anti-viral response (e.g., ISG15) were identified in the nasopharyngeal aspirates and their abundance was correlated with viral load. These combined approaches have not been used before to study HRSV biology in vivo and can be readily applied to the study the variation of virus host interactions.

Specifications for Innovative, Enabling Biomaterials Based on the Principles of Biocompatibility Mechanisms

In any engineering discipline, whenever products are designed, manufactured and ultimately utilized for the benefits of society, a series of specifications for the product are defined, and maybe refined, in order that they perform as effectively as possible, with due attention being paid to the safety, and economic aspects. These specifications are established with respect to all of the relevant properties, including those determined by mechanical, physical, chemical, manufacturing and environmental conditions, and the resulting design and materials selection reflects the optimal balance. In areas of medical technology, these specifications should be based on both functionality, which determines whether a device can actually perform as intended, and biocompatibility, which determines how the device interacts, both acutely and chronically, with the body. Unfortunately, whilst so much progress has been made with the development of superior functionality for the treatment and diagnosis of so many disease states, this is not the same for biocompatibility, where the single most-important currently adopted specification is that the device should do no harm, which falls far short of the ideal requirement. This paper addresses the profound need for biomaterials specifications to be based on the mechanisms of biocompatibility.

Antibody-Dependent Dengue Virus Entry Modulates Cell Intrinsic Responses for Enhanced Infection

Dengue is caused by infection with any one of four dengue viruses (DENV); the risk of severe disease appears to be enhanced by the cross-reactive or subneutralizing levels of antibody from a prior DENV infection. These antibodies opsonize DENV entry through the activating Fc gamma receptors (FcγR), instead of infection through canonical receptor-mediated endocytosis, to result in higher levels of DENV replication. However, whether the enhanced replication is solely due to more efficient FcγR-mediated DENV entry or is also through FcγR-mediated alteration of the host transcriptome response to favor DENV infection remains unclear. Indeed, more efficient viral entry through activation of the FcγR can result in an increased viral antigenic load within target cells and confound direct comparisons of the host transcriptome response under antibody-dependent and antibody-independent conditions. Herein, we show that, despite controlling for the viral antigenic load in primary monocytes, the antibody-dependent and non-antibody-dependent routes of DENV entry induce transcriptome responses that are remarkably different. Notably, antibody-dependent DENV entry upregulated DENV host dependency factors associated with RNA splicing, mitochondrial respiratory chain complexes, and vesicle trafficking. Additionally, supporting findings from other studies, antibody-dependent DENV entry impeded the downregulation of ribosomal genes caused by canonical receptor-mediated endocytosis to increase viral translation. Collectively, our findings support the notion that antibody-dependent DENV entry alters host responses that support the viral life cycle and that host responses to DENV need to be defined in the context of its entry pathway.IMPORTANCE Dengue virus is the most prevalent mosquito-borne viral infection globally, resulting in variable manifestations ranging from asymptomatic viremia to life-threatening shock and multiorgan failure. Previous studies have indicated that the risk of severe dengue in humans can be increased by a specific range of preexisting anti-dengue virus antibody titers, a phenomenon termed antibody-dependent enhancement. There is hence a need to understand how antibodies augment dengue virus infection compared to the alternative canonical receptor-mediated viral entry route. Herein, we show that, besides facilitating viral uptake, antibody-mediated entry increases the expression of early host dependency factors to promote viral infection; these factors include RNA splicing, mitochondrial respiratory chain complexes, vesicle trafficking, and ribosomal genes. These findings will enhance our understanding of how differences in entry pathways can affect host responses and offer opportunities to design therapeutics that can specifically inhibit antibody-dependent enhancement of dengue virus infection.

Future Research Directions in Pneumonia. NHLBI Working Group Report

Pneumonia is a complex pulmonary disease in need of new clinical approaches. Although triggered by a pathogen, pneumonia often results from dysregulations of host defense that likely precede infection. The coordinated activities of immune resistance and tissue resilience then dictate whether and how pneumonia progresses or resolves. Inadequate or inappropriate host responses lead to more severe outcomes such as acute respiratory distress syndrome and to organ dysfunction beyond the lungs and over extended time frames after pathogen clearance, some of which increase the risk for subsequent pneumonia. Improved understanding of such host responses will guide the development of novel approaches for preventing and curing pneumonia and for mitigating the subsequent pulmonary and extrapulmonary complications of pneumonia. The NHLBI assembled a working group of extramural investigators to prioritize avenues of host-directed pneumonia research that should yield novel approaches for interrupting the cycle of unhealthy decline caused by pneumonia. This report summarizes the working group's specific recommendations in the areas of pneumonia susceptibility, host response, and consequences. Overarching goals include the development of more host-focused clinical approaches for preventing and treating pneumonia, the generation of predictive tools (for pneumonia occurrence, severity, and outcome), and the elucidation of mechanisms mediating immune resistance and tissue resilience in the lung. Specific areas of research are highlighted as especially promising for making advances against pneumonia.

Importance of Virulence Factors for the Persistence of Oral Bacteria in the Inflamed Gingival Crevice and in the Pathogenesis of Periodontal Disease

Periodontitis is a chronic inflammation that develops due to a destructive tissue response to prolonged inflammation and a disturbed homeostasis (dysbiosis) in the interplay between the microorganisms of the dental biofilm and the host. The infectious nature of the microbes associated with periodontitis is unclear, as is the role of specific bacterial species and virulence factors that interfere with the host defense and tissue repair. This review highlights the impact of classical virulence factors, such as exotoxins, endotoxins, fimbriae and capsule, but also aims to emphasize the often-neglected cascade of metabolic products (e.g., those generated by anaerobic and proteolytic metabolism) that are produced by the bacterial phenotypes that survive and thrive in deep, inflamed periodontal pockets. This metabolic activity of the microbes aggravates the inflammatory response from a low-grade physiologic (homeostatic) inflammation (i.e., gingivitis) into more destructive or tissue remodeling processes in periodontitis. That bacteria associated with periodontitis are linked with a number of systemic diseases of importance in clinical medicine is highlighted and exemplified with rheumatoid arthritis, The unclear significance of a number of potential "virulence factors" that contribute to the pathogenicity of specific bacterial species in the complex biofilm-host interaction clinically is discussed in this review.

In Silico Modeling of Biofilm Formation by Nontypeable Haemophilus influenzae In Vivo

Biofilms formed by nontypeable Haemophilus influenzae (NTHI) bacteria play an important role in multiple respiratory tract diseases. Visual inspection of the morphology of biofilms formed during chronic infections shows distinct differences from biofilms formed in vitro To better understand these differences, we analyzed images of NTHI biofilms formed in the middle ears of Chinchilla lanigera and developed an in silico agent-based model of the formation of NTHI biofilms in vivo We found that, as in vitro, NTHI bacteria are organized in self-similar patterns; however, the sizes of NTHI clusters in vivo are more than 10-fold smaller than their in vitro counterparts. The agent-based model reproduced these patterns and suggested that smaller clusters occur due to elimination of planktonic NTHI cells by the host responses. Estimation of model parameters by fitting simulation results to imaging data showed that the effects of several processes in the model change during the course of the infection.IMPORTANCE Multiple respiratory illnesses are associated with formation of biofilms within the human airway by NTHI. However, a substantial amount of our understanding of the mechanisms that underlie NTHI biofilm formation is obtained from in vitro studies. Our in silico model that describes biofilm formation by NTHI within the middle ears of Chinchilla lanigera will help isolate processes potentially responsible for the differences between the morphologies of biofilms formed in vivo versus those formed in vitro Thus, the in silico model can be used to glean mechanisms that underlie biofilm formation in vivo and connect those mechanisms to those obtained from in vitro experiments. The in silico model developed here can be extended to investigate potential roles of specific host responses (e.g., mucociliary clearance) on NTHI biofilm formation in vivo The developed computational tools can also be used to analyze and describe biofilm formation by other bacterial species in vivo.

Phage Therapy of Pneumonia Is Not Associated with an Overstimulation of the Inflammatory Response Compared to Antibiotic Treatment in Mice

Supported by years of clinical use in some countries and more recently by literature on experimental models, as well as its compassionate use in Europe and in the United States, bacteriophage (phage) therapy is providing a solution for difficult-to-treat bacterial infections. However, studies of the impact of such treatments on the host remain scarce. Murine acute pneumonia initiated by intranasal instillation of two pathogenic strains of Escherichia coli (536 and LM33) was treated by two specific bacteriophages (536_P1 and LM33_P1; intranasal) or antibiotics (ceftriaxone, cefoxitin, or imipenem-cilastatin; intraperitoneal). Healthy mice also received phages alone. The severity of pulmonary edema, acute inflammatory cytokine concentration (blood and lung homogenates), complete blood counts, and bacterial and bacteriophage counts were determined at early (≤12 h) and late (≥20 h) time points. The efficacy of bacteriophage to decrease bacterial load was faster than with antibiotics, but the two displayed similar endpoints. Bacteriophage treatment was not associated with overinflammation but in contrast tended to lower inflammation and provided a faster correction of blood cell count abnormalities than did antibiotics. In the absence of bacterial infection, bacteriophage 536_P1 promoted a weak increase in the production of antiviral cytokines (gamma interferon [IFN-γ] and interleukin-12 [IL-12]) and chemokines in the lungs but not in the blood. However, such variations were no longer observed when bacteriophage 536_P1 was administered to treat infected animals. The rapid lysis of bacteria by bacteriophages in vivo does not increase the innate inflammatory response compared to that with antibiotic treatment.

Diagnosing and Managing Sepsis by Probing the Host Response to Infection: Advances, Opportunities, and Challenges

Sepsis is a major source of mortality and morbidity globally. Accurately diagnosing sepsis remains challenging due to the heterogeneous nature of the disease, and delays in diagnosis and intervention contribute to high mortality rates. Measuring the host response to infection enables more rapid diagnosis of sepsis than is possible through direct detection of the causative pathogen, and recent advances in host response diagnostics and prognostics hold promise for improving outcomes. The current review discusses recent advances in the technologies used to probe the host response to infection, particularly those based on transcriptomics. These are discussed in the context of contemporary approaches to diagnosing and prognosing sepsis, and recommendations are made for successful development and validation of host response technologies.

Lymphocytopenia as a Predictor of Mortality in Patients with ICU-Acquired Pneumonia

BACKGROUND

Intensive care unit-acquired pneumonia (ICU-AP) is a severe complication in patients admitted to the ICU. Lymphocytopenia is a marker of poor prognosis in patients with community-acquired pneumonia, but its impact on ICU-AP prognosis is unknown. We aimed to evaluate whether lymphocytopenia is an independent risk factor for mortality in non-immunocompromised patients with ICU-AP.

METHODS

Prospective observational cohort study of patients from six ICUs of an 800-bed tertiary teaching hospital (2005 to 2016).

RESULTS

Of the 473 patients included, 277 (59%) had ventilator-associated pneumonia (VAP). Receiver operating characteristic (ROC) analysis of the lymphocyte counts at diagnosis showed that 595 cells/mm³ was the best cut-off for discriminating two groups of patients at risk: lymphocytopenic group (lymphocyte count <595 cells/mm³, 141 patients (30%)) and non-lymphocytopenic group (lymphocyte count ≥595 cells/mm³, 332 patients (70%)). Patients with lymphocytopenia presented more comorbidities and a higher sequential organ failure assessment (SOFA) score at the moment of pneumonia diagnosis. Also, 28-day mortality and 90-day mortality were higher in patients with lymphocytopenia (28-day: 38 (27%) versus 59 (18%), 90-day: 74 (53%) versus 111 (34%)). In the multivariable model, <595 cells/mm³ resulted to be an independent predictor for 90-day mortality (Hazard Ratio 1.41; 95% Confidence Interval 1.02 to 1.94).

CONCLUSION

Lymphocytopenia is an independent predictor of 90-day mortality in non-immunocompromised patients with ICU-AP.

Polymeric Approaches to Reduce Tissue Responses Against Devices Applied for Islet-Cell Encapsulation

Immunoisolation of pancreatic islets is a technology in which islets are encapsulated in semipermeable but immunoprotective polymeric membranes. The technology allows for successful transplantation of insulin-producing cells in the absence of immunosuppression. Different approaches of immunoisolation are currently under development. These approaches involve intravascular devices that are connected to the bloodstream and extravascular devices that can be distinguished in micro- and macrocapsules and are usually implanted in the peritoneal cavity or under the skin. The technology has been subject of intense fundamental research in the past decade. It has co-evolved with novel replenishable cell sources for cure of diseases such as Type 1 Diabetes Mellitus that need to be protected for the host immune system. Although the devices have shown significant success in animal models and even in human safety studies most technologies still suffer from undesired tissue responses in the host. Here we review the past and current approaches to modulate and reduce tissue responses against extravascular cell-containing micro- and macrocapsules with a focus on rational choices for polymer (combinations). Choices for polymers but also choices for crosslinking agents that induce more stable and biocompatible capsules are discussed. Combining beneficial properties of molecules in diblock polymers or application of these molecules or other anti-biofouling molecules have been reviewed. Emerging are also the principles of polymer brushes that prevent protein and cell-adhesion. Recently also immunomodulating biomaterials that bind to specific immune receptors have entered the field. Several natural and synthetic polymers and even combinations of these polymers have demonstrated significant improvement in outcomes of encapsulated grafts. Adequate polymeric surface properties have been shown to be essential but how the surface should be composed to avoid host responses remains to be identified. Current insight is that optimal biocompatible devices can be created which raises optimism that immunoisolating devices can be created that allows for long term survival of encapsulated replenishable insulin-producing cell sources for treatment of Type 1 Diabetes Mellitus.

Heterologous Immunity between Adenoviruses and Hepatitis C Virus (HCV): Recombinant Adenovirus Vaccine Vectors Containing Antigens from Unrelated Pathogens Induce Cross-Reactive Immunity Against HCV Antigens

Host immune responses play an important role in the outcome of infection with hepatitis C virus (HCV). They can lead to viral clearance and a positive outcome, or progression and severity of chronic disease. Extensive research in the past >25 years into understanding the immune responses against HCV have still resulted in many unanswered questions implicating a role for unknown factors and events. In our earlier studies, we made a surprising discovery that peptides derived from structural and non-structural proteins of HCV have substantial amino acid sequence homologies with various proteins of adenoviruses and that immunizing mice with a non-replicating, non-recombinant adenovirus vector leads to induction of a robust cross-reactive cellular and humoral response against various HCV antigens. In this work, we further demonstrate antibody cross-reactivity between Ad and HCV in vivo. We also extend this observation to show that recombinant adenoviruses containing antigens from unrelated pathogens also possess the ability to induce cross-reactive immune responses against HCV antigens along with the induction of transgene antigen-specific immunity. This cross-reactive immunity can (a) accommodate the making of dual-pathogen vaccines, (b) play an important role in the natural course of HCV infection and (c) provide a plausible answer to many unexplained questions regarding immunity to HCV.

Multidimensional Assessment of the Host Response in Mechanically Ventilated Patients with Suspected Pneumonia

Rationale: The identification of informative elements of the host response to infection may improve the diagnosis and management of bacterial pneumonia. Objectives: To determine whether the absence of alveolar neutrophilia can exclude bacterial pneumonia in critically ill patients with suspected infection and to test whether signatures of bacterial pneumonia can be identified in the alveolar macrophage transcriptome. Methods: We determined the test characteristics of alveolar neutrophilia for the diagnosis of bacterial pneumonia in three cohorts of mechanically ventilated patients. In one cohort, we also isolated macrophages from alveolar lavage fluid and used the transcriptome to identify signatures of bacterial pneumonia. Finally, we developed a humanized mouse model of Pseudomonas aeruginosa pneumonia to determine if pathogen-specific signatures can be identified in human alveolar macrophages. Measurements and Main Results: An alveolar neutrophil percentage less than 50% had a negative predictive value of greater than 90% for bacterial pneumonia in both the retrospective (n = 851) and validation cohorts (n = 76 and n = 79). A transcriptional signature of bacterial pneumonia was present in both resident and recruited macrophages. Gene signatures from both cell types identified patients with bacterial pneumonia with test characteristics similar to alveolar neutrophilia. Conclusions: The absence of alveolar neutrophilia has a high negative predictive value for bacterial pneumonia in critically ill patients with suspected infection. Macrophages can be isolated from alveolar lavage fluid obtained during routine care and used for RNA-Seq analysis. This novel approach may facilitate a longitudinal and multidimensional assessment of the host response to bacterial pneumonia.

Defining Microbiome Health through a Host Lens

We are walking ecosystems, inoculated at birth with a unique set of microbes that are integral to the functioning of our bodies. The physiology of our commensal microbiota is intertwined with our metabolism, immune function, and mental state. The specifics of this entanglement remain largely unknown and are somewhat unique to individuals, and when any one piece of this complex system breaks, our health can suffer. There appear to be many ways to build a healthy, functional microbiome and several distinct ways in which it can break. Despite the hundreds of associations with human disease, there are only a handful of cases where the exact contribution of the microbiome to the etiology of disease is known. Our laboratory takes a systems approach, integrating dynamic high-throughput host phenotyping with eco-evolutionary dynamics and metabolism of gut microbiota to better define health and disease for each individual at the ecosystem level.

Differential Effects of Influenza Virus NA, HA Head, and HA Stalk Antibodies on Peripheral Blood Leukocyte Gene Expression during Human Infection

In this study, we examined the relationships between anti-influenza virus serum antibody titers, clinical disease, and peripheral blood leukocyte (PBL) global gene expression during presymptomatic, acute, and convalescent illness in 83 participants infected with 2009 pandemic H1N1 virus in a human influenza challenge model. Using traditional statistical and logistic regression modeling approaches, profiles of differentially expressed genes that correlated with active viral shedding, predicted length of viral shedding, and predicted illness severity were identified. These analyses further demonstrated that challenge participants fell into three peripheral blood leukocyte gene expression phenotypes that significantly correlated with different clinical outcomes and prechallenge serum titers of antibodies specific for the viral neuraminidase, hemagglutinin head, and hemagglutinin stalk. Higher prechallenge serum antibody titers were inversely correlated with leukocyte responsiveness in participants with active disease and could mask expression of peripheral blood markers of clinical disease in some participants, including viral shedding and symptom severity. Consequently, preexisting anti-influenza antibodies may modulate PBL gene expression, and this must be taken into consideration in the development and interpretation of peripheral blood diagnostic and prognostic assays of influenza infection.IMPORTANCE Influenza A viruses are significant human pathogens that caused 83,000 deaths in the United States during 2017 to 2018, and there is need to understand the molecular correlates of illness and to identify prognostic markers of viral infection, symptom severity, and disease course. Preexisting antibodies against viral neuraminidase (NA) and hemagglutinin (HA) proteins play a critical role in lessening disease severity. We performed global gene expression profiling of peripheral blood leukocytes collected during acute and convalescent phases from a large cohort of people infected with A/H1N1pdm virus. Using statistical and machine-learning approaches, populations of genes were identified early in infection that correlated with active viral shedding, predicted length of shedding, or disease severity. Finally, these gene expression responses were differentially affected by increased levels of preexisting influenza antibodies, which could mask detection of these markers of contagiousness and disease severity in people with active clinical disease.

Innate Immune Response and Outcome of Clostridium difficile Infection Are Dependent on Fecal Bacterial Composition in the Aged Host

Background

Clostridium difficile infection (CDI) is a serious threat for an aging population. Using an aged mouse model, we evaluated the effect of age and the roles of innate immunity and intestinal microbiota.

Methods

Aged (18 months) and young (8 weeks) mice were infected with C difficile, and disease severity, immune response, and intestinal microbiome were compared. The same experiment was repeated with intestinal microbiota exchange between aged and young mice before infection.

Results

Higher mortality was observed in aged mice with weaker neutrophilic mobilization in blood and intestinal tissue and depressed proinflammatory cytokines in early infection. Microbiota exchange improved survival and early immune response in aged mice. Microbiome analysis revealed that aged mice have significant deficiencies in Bacteroidetes phylum and, specifically, Bacteroides, Alistipes, and rc4-4 genera, which were replenished by cage switching.

Conclusions

Microbiota-dependent alteration in innate immune response early on during infection may explain poor outcome in aged host with CDI.

Candida parapsilosis: from Genes to the Bedside

Patients with suppressed immunity are at the highest risk for hospital-acquired infections. Among these, invasive candidiasis is the most prevalent systemic fungal nosocomial infection. Over recent decades, the combined prevalence of non-albicans Candida species outranked Candida albicans infections in several geographical regions worldwide, highlighting the need to understand their pathobiology in order to develop effective treatment and to prevent future outbreaks. Candida parapsilosis is the second or third most frequently isolated Candida species from patients. Besides being highly prevalent, its biology differs markedly from that of C. albicans, which may be associated with C. parapsilosis' increased incidence. Differences in virulence, regulatory and antifungal drug resistance mechanisms, and the patient groups at risk indicate that conclusions drawn from C. albicans pathobiology cannot be simply extrapolated to C. parapsilosis Such species-specific characteristics may also influence their recognition and elimination by the host and the efficacy of antifungal drugs. Due to the availability of high-throughput, state-of-the-art experimental tools and molecular genetic methods adapted to C. parapsilosis, genome and transcriptome studies are now available that greatly contribute to our understanding of what makes this species a threat. In this review, we summarize 10 years of findings on C. parapsilosis pathogenesis, including the species' genetic properties, transcriptome studies, host responses, and molecular mechanisms of virulence. Antifungal susceptibility studies and clinician perspectives are discussed. We also present regional incidence reports in order to provide an updated worldwide epidemiology summary.

Immunologic Pathways in Protective versus Maladaptive Host Responses to Attenuated and Pathogenic Strains of Mycoplasma gallisepticum

Mycoplasmas are small bacterial commensals or pathogens that commonly colonize host mucosal tissues and avoid rapid clearance, in part by stimulating inflammatory, immunopathogenic responses. We previously characterized a wide array of transcriptomic perturbations in avian host tracheal mucosae infected with virulent, immunopathologic Mycoplasma gallisepticum; however, mechanisms delineating these from protective responses, such as those induced upon vaccination, have not been thoroughly explored. In this study, host transcriptomic responses to two experimental M. gallisepticum vaccines were assessed during the first 2 days of infection. Relative to virulent infection, host metabolic and immune gene responses to both vaccines were greatly decreased, including early innate immune responses critical to disease development and subsequent adaptive immunity. These data specify host genes and potential mechanisms contributing to maladaptive versus beneficial host responses-information critical for design of vaccines efficacious in both limiting inflammation and enabling pathogen clearance.

A Cell Proliferation and Inflammatory Signature Is Induced by Lawsonia intracellularis Infection in Swine

Lawsonia intracellularis causes porcine proliferative enteropathy. This is an enteric disease characterized by thickening of the wall of the ileum that leads to decreased growth of animals and diarrhea. In this study, we investigated the host response to L. intracellularis infection by performing transcriptomic and pathway analysis of intestinal tissue samples from groups of infected and noninfected animals at 14, 21, and 28 days postchallenge. At the peak of infection, when animals developed the most severe lesions, infected animals had higher levels of several gene transcripts involved in cellular proliferation and inflammation, including matrix metalloproteinase-7 (MMP7), transglutaminase-2 (TGM2), and oncostatin M (OSM). Histomorphology also revealed general features of intestinal inflammation. This study identified important pathways associated with the host response in developing and resolving lesions due to L. intracellularis infection.IMPORTANCE Lawsonia intracellularis is among the most important enteric pathogens of swine, and it can also infect other mammalian species. Much is still unknown regarding its pathogenesis and the host response, especially at the site of infection. In this study, we uncovered several novel genes and pathways associated with infection. Differentially expressed transcripts, in addition to histological changes in infected tissue, revealed striking similarities between L. intracellularis infection and cellular proliferation mechanisms described in some cancers and inflammatory diseases of the gastrointestinal tract. This research sheds important light into the pathogenesis of L. intracellularis and the host response associated with the lesions caused by infection.

Clinical Characterization of Host Response to Simian Hemorrhagic Fever Virus Infection in Permissive and Refractory Hosts: A Model for Determining Mechanisms of VHF Pathogenesis

Simian hemorrhagic fever virus (SHFV) causes a fulminant and typically lethal viral hemorrhagic fever (VHF) in macaques (Cercopithecinae: Macaca spp.) but causes subclinical infections in patas monkeys (Cercopithecinae: Erythrocebus patas). This difference in disease course offers a unique opportunity to compare host responses to infection by a VHF-causing virus in biologically similar susceptible and refractory animals. Patas and rhesus monkeys were inoculated side-by-side with SHFV. Unlike the severe disease observed in rhesus monkeys, patas monkeys developed a limited clinical disease characterized by changes in complete blood counts, serum chemistries, and development of lymphadenopathy. Viral RNA was measurable in circulating blood 2 days after exposure, and its duration varied by species. Infectious virus was detected in terminal tissues of both patas and rhesus monkeys. Varying degrees of overlap in changes in serum concentrations of interferon (IFN)-γ, monocyte chemoattractant protein (MCP)-1, and interleukin (IL)-6 were observed between patas and rhesus monkeys, suggesting the presence of common and species-specific cytokine responses to infection. Similarly, quantitative immunohistochemistry of livers from terminal monkeys and whole blood flow cytometry revealed varying degrees of overlap in changes in macrophages, natural killer cells, and T-cells. The unexpected degree of overlap in host response suggests that relatively small subsets of a host's response to infection may be responsible for driving hemorrhagic fever pathogenesis. Furthermore, comparative SHFV infection in patas and rhesus monkeys offers an experimental model to characterize host⁻response mechanisms associated with viral hemorrhagic fever and evaluate pan-viral hemorrhagic fever countermeasures.