Correlation between the concentrations of tumor necrosis factor-alpha and the severity of disease in patients infected with Orientia tsutsugamushi

Lack of the IFN-γ signal leads to lethal Orientia tsutsugamushi infection in mice with skin eschar lesions

Scrub typhus is an acute febrile disease due to Orientia tsutsugamushi (Ot) infection and can be life-threatening with organ failure, hemorrhage, and fatality. Yet, little is known as to how the host reacts to Ot bacteria at early stages of infection; no reports have addressed the functional roles of type I versus type II interferon (IFN) responses in scrub typhus. In this study, we used comprehensive intradermal (i.d.) inoculation models and two clinically predominant Ot strains (Karp and Gilliam) to uncover early immune events. Karp infection induced sequential expression of Ifnb and Ifng in inflamed skin and draining lymph nodes at days 1 and 3 post-infection. Using double Ifnar1-/-Ifngr1-/- and Stat1-/- mice, we found that deficiency in IFN/STAT1 signaling resulted in lethal infection with profound pathology and skin eschar lesions, which resembled to human scrub typhus. Further analyses demonstrated that deficiency in IFN-γ, but not IFN-I, resulted in impaired NK cell and macrophage activation and uncontrolled bacterial growth and dissemination, leading to metabolic dysregulation, excessive inflammatory cell infiltration, and exacerbated tissue damage. NK cells were found to be the major cellular source of innate IFN-γ, contributing to the initial Ot control in the draining lymph nodes. In vitro studies with dendritic cell cultures revealed a superior antibacterial effect offered by IFN-γ than IFN-β. Comparative in vivo studies with Karp- and Gilliam-infection revealed a crucial role of IFN-γ signaling in protection against progression of eschar lesions and Ot infection lethality. Additionally, our i.d. mouse models of lethal infection with eschar lesions are promising tools for immunological study and vaccine development for scrub typhus.

Reverse vaccinology and immunoinformatics approach to design a chimeric epitope vaccine against Orientia tsutsugamushi

Scrub typhus is a vector-borne infectious disease caused by Orientia tsutsugamushi and it is reportedly associated with up to 20 % of hospitalized cases of febrile illnesses. The major challenge of vaccine development is the lack of identified antigens that can induce both heterotypic and homotypic immunity including the production of antibodies, cytotoxic T lymphocyte, and helper T lymphocytes. We employed a comprehensive immunoinformatic prediction algorithm to identify immunogenic epitopes of the 56-kDa type-specific cell membrane surface antigen and surface cell antigen A of O. tsutsugamushi to select potential candidates for developing vaccines and diagnostic assays. We identified 35 linear and 29 continuous immunogenic B-cell epitopes and 51 and 27 strong-binding T-cell epitopes of major histocompatibility complex class I and class II molecules, respectively, in the conserved and variable regions of the 56-kDa type-specific surface antigen. The predicted B- and T-cell epitopes were used to develop immunogenic multi-epitope candidate vaccines and showed to elicit a broad-range of immune protection. A stable interactions between the multi-epitope vaccines and the host fibronectin protein were observed using docking and simulation methods. Molecular dynamics simulation studies demonstrated that the multi-epitope vaccine constructs and fibronectin docked models were stable during simulation time. Furthermore, the multi-epitope vaccine exhibited properties such as antigenicity, non-allergenicity and ability to induce interferon gamma production and had strong associations with their respective human leukocyte antigen alleles of world-wide population coverage. A correlation of immune simulations and the in-silico predicted immunogenic potential of multi-epitope vaccines implicate for further investigations to accelerate designing of epitope-based vaccine candidates and chimeric antigens for development of serological diagnostic assays for scrub typhus.

Alterations in germinal center formation and B cell activation during severe Orientia tsutsugamushi infection in mice

Scrub typhus is a poorly studied but life-threatening disease caused by the intracellular bacterium Orientia tsutsugamushi (Ot). Cellular and humoral immunity in Ot-infected patients is not long-lasting, waning as early as one-year post-infection; however, its underlying mechanisms remain unclear. To date, no studies have examined germinal center (GC) or B cell responses in Ot-infected humans or experimental animals. This study was aimed at evaluating humoral immune responses at acute stages of severe Ot infection and possible mechanisms underlying B cell dysfunction. Following inoculation with Ot Karp, a clinically dominant strain known to cause lethal infection in C57BL/6 mice, we measured antigen-specific antibody titers, revealing IgG2c as the dominant isotype induced by infection. Splenic GC responses were evaluated by immunohistology, co-staining for B cells (B220), T cells (CD3), and GCs (GL-7). Organized GCs were evident at day 4 post-infection (D4), but they were nearly absent at D8, accompanied by scattered T cells throughout splenic tissues. Flow cytometry revealed comparable numbers of GC B cells and T follicular helper (Tfh) cells at D4 and D8, indicating that GC collapse was not due to excessive death of these cell subtypes at D8. B cell RNAseq analysis revealed significant differences in expression of genes associated with B cell adhesion and co-stimulation at D8 versus D4. The significant downregulation of S1PR2 (a GC-specific adhesion gene) was most evident at D8, correlating with disrupted GC formation. Signaling pathway analysis uncovered downregulation of 71% of B cell activation genes at D8, suggesting attenuation of B cell activation during severe infection. This is the first study showing the disruption of B/T cell microenvironment and dysregulation of B cell responses during Ot infection, which may help understand the transient immunity associated with scrub typhus.

Multiple Orientia clusters and Th1-skewed chemokine profile: a cross-sectional study in patients with scrub typhus from Nepal

OBJECTIVES

Scrub typhus is an emerging infectious disease in Asia caused by Orientia tsutsugamushi (Ot). From Nepal, only scant data on the genetic epidemiology of this agent is available, and determinants of immunoregulation are poorly understood.

METHODS

Patients (n = 238) referred to the National Public Health Laboratory (Kathmandu, Nepal) from all over Nepal for suspected scrub typhus were enrolled upon positive immunoglobulin (Ig)M testing between July and October 2015. From Ot 16S and 47 kD polymerase chain reaction (PCR)-positive samples, the variable domain I of the 56 kD gene was sequenced and phylogenetically analyzed. T helper (Th) cell-associated cytokines (n = 13) and chemokines (n = 12) were quantified by multiplex bead arrays.

RESULTS

In 93/238 (39.1%) IgM-positive samples, Ot DNA was detected by quantitative PCR. Phylogenetic analysis of 56 kD sequences revealed seven distinct clusters, six of them with high homologies to strains detected in other countries. The Th1-related cytokines interferon-γ and C-X-C motif chemokine ligand 10 were strongly upregulated and correlated with bacteremia, while levels of Th2-associated chemokines were reduced. Bacteremia also correlated with concentrations of interleukin (IL)-6 and IL-10 but not tumor necrosis factor-α.

CONCLUSION

We identified a considerable genetic heterogeneity of human-pathogenic Ot strains circulating in Nepal. Acute Nepalese scrub typhus patients showed strong Th1 but impaired Th2 responses, especially on the chemokine level.

Host transcriptomic profiling of CD-1 outbred mice with severe clinical outcomes following infection with Orientia tsutsugamushi

Orientia tsutsugamushi is an obligately intracellular bacterium with endothelial tropism and can cause mild to lethal scrub typhus in humans. No vaccine is available for this reemerging and severely neglected infection. Previous scrub typhus studies have utilized inbred mice, yet such models have intrinsic limitations. Thus, the development of suitable mouse models that better mimic human diseases is in great need for immunologic investigation and future vaccine studies. This study is aimed at establishing scrub typhus in outbred CD-1 mice and defining immune biomarkers related to disease severity. CD-1 mice received O. tsutsugamushi Karp strain via the i.v. route; major organs were harvested at 2-12 days post-infection for kinetic analyses. We found that for our given infection doses, CD-1 mice were significantly more susceptible (90-100% lethal) than were inbred C57BL/6 mice (0-10% lethal). Gross pathology of infected CD-1 mouse organs revealed features that mimicked human scrub typhus, including pulmonary edema, interstitial pneumonia, perivascular lymphocytic infiltrates, and vasculitis. Alteration in angiopoietin/receptor expression in inflamed lungs implied endothelial dysfunction. Lung immune gene profiling using NanoString analysis displayed a Th1/CD8-skewed, but Th2 repressed profile, including novel biomarkers not previously investigated in other scrub typhus models. Bio-plex analysis revealed a robust inflammatory response in CD-1 mice as evidenced by increased serum cytokine and chemokine levels, correlating with immune cell recruitment during the severe stages of the disease. This study provides an important framework indicating a value of CD-1 mice for delineating host susceptibility to O. tsutsugamushi, immune dysregulation, and disease pathogenesis. This preclinical model is particularly useful for future translational and vaccine studies for severe scrub typhus.

Spatiotemporal NF-κB dynamics encodes the position, amplitude, and duration of local immune inputs

Infected cells communicate through secreted signaling molecules like cytokines, which carry information about pathogens. How differences in cytokine secretion affect inflammatory signaling over space and how responding cells decode information from propagating cytokines are not understood. By computationally and experimentally studying NF-κB dynamics in cocultures of signal-sending cells (macrophages) and signal-receiving cells (fibroblasts), we find that cytokine signals are transmitted by wave-like propagation of NF-κB activity and create well-defined activation zones in responding cells. NF-κB dynamics in responding cells can simultaneously encode information about cytokine dose, duration, and distance to the cytokine source. Spatially resolved transcriptional analysis reveals that responding cells transmit local cytokine information to distance-specific proinflammatory gene expression patterns, creating "gene expression zones." Despite single-cell variability, the size and duration of the signaling zone are tightly controlled by the macrophage secretion profile. Our results highlight how macrophages tune cytokine secretion to control signal transmission distance and how inflammatory signaling interprets these signals in space and time.

A time-course comparative clinical and immune response evaluation study between the human pathogenic Orientia tsutsugamushi strains: Karp and Gilliam in a rhesus macaque (Macaca mulatta) model

BACKGROUND

Scrub typhus is a vector-borne febrile illness caused by Orientia tsutsugamushi transmitted by the bite of Trombiculid mites. O. tsutsugamushi has a high genetic diversity and is increasingly recognized to have a wider global distribution than previously assumed.

METHODOLOGY/PRINCIPLE FINDINGS

We evaluated the clinical outcomes and host immune responses of the two most relevant human pathogenic strains of O. tsutsugamushi; Karp (n = 4) and Gilliam (n = 4) in a time-course study over 80 days post infection (dpi) in a standardized scrub typhus non-human primate rhesus macaque model. We observed distinct features in clinical progression and immune response between the two strains; Gilliam-infected macaques developed more pronounced systemic infection characterized by an earlier onset of bacteremia, lymph node enlargement, eschar lesions and higher inflammatory markers during the acute phase of infection, when compared to the Karp strain. C-reactive protein (CRP) plasma levels, interferon gamma (IFN-γ, interleukin-1 receptor antagonist (IL-1ra), IL-15 serum concentrations, CRP/IL10- and IFN-γ/IL-10 ratios correlated positively with bacterial load in blood, implying activation of the innate immune response and preferential development of a T helper-type 1 immune response. The O. tsutsugamushi-specific immune memory responses in cells isolated from skin and lymph nodes at 80 dpi were more markedly elevated in the Gilliam-infected macaques than in the Karp-infected group. The comparative cytokine response dynamics of both strains revealed significant up-regulation of IFN-γ, tumor necrosis factor (TNF), IL-15, IL-6, IL-18, regulatory IL-1ra, IL-10, IL-8 and granulocyte-colony-stimulating factor (G-CSF). These data suggest that the clinical outcomes and host immune responses to scrub typhus could be associated with counter balancing effects of pro- and anti-inflammatory cytokine-mediated responses. Currently, no data on characterized time-course comparisons of O. tsutsugamushi strains regarding measures of disease severity and immune response is available. Our study provides evidence for the strain-specificity of host responses in scrub typhus, which supports our understanding of processes at the initial inoculation site (eschar), systemic disease progression, protective and/or pathogenic host immune mechanisms and cellular immune memory function.

CONCLUSIONS/SIGNIFICANCE

This study characterised an improved intradermal rhesus macaque challenge model for scrub typhus, whereby the Gilliam strain infection associated with higher disease severity in the rhesus macaque model than the previous Karp strain infection. Difficulties associated with inoculum quantitation for obligate-intracellular bacteria were overcome by using functional inoculum titrations in outbred mice. The Gilliam-based rhesus macaque model provides improved endpoint measurements and contributes towards the identification of correlates of protection for future vaccine development.

Distinct Role of TNFR1 and TNFR2 in Protective Immunity Against Orientia tsutsugamushi Infection in Mice

Infection with Orientia tsutsugamushi, an obligate intracellular bacterium, can cause mild or severe scrub typhus. Some patients develop acute lung injury, multi-organ failure, and fatal infection; however, little is known regarding key immune mediators that mediate infection control or disease pathogenesis. Using murine models of scrub typhus, we demonstrated in this study the requirement of TNF-TNFR signaling in protective immunity against this infection. Mice lacking both TNF receptors (TNFR1 and TNFR2) were highly susceptible to O. tsutsugamushi infection, displaying significantly increased tissue bacterial burdens and succumbing to infection by day 9, while most wild-type mice survived through day 20. This increased susceptibility correlated with poor activation of cellular immunity in inflamed tissues. Flow cytometry of lung- and spleen-derived cells revealed profound deficiencies in total numbers and activation status of NK cells, neutrophils, and macrophages, as well as CD4 and CD8 T cells. To define the role of individual receptors in O. tsutsugamushi infection, we used mice lacking either TNFR1 or TNFR2. While deficiency in either receptor alone was sufficient to increase host susceptibility to the infection, TNFR1 and TNFR2 played a distinct role in cellular responses. TNF signaling through TNFR1 promoted inflammatory responses and effector T cell expansion, while TNFR2 signaling was associated with anti-inflammatory action and tissue homeostasis. Moreover, TNFRs played an intrinsic role in CD8+ T cell activation, revealing an indispensable role of TNF in protective immunity against O. tsutsugamushi infection.

Systematic review of the scrub typhus treatment landscape: Assessing the feasibility of an individual participant-level data (IPD) platform

Background

Scrub typhus is an acute febrile illness caused by intracellular bacteria from the genus Orientia. It is estimated that one billion people are at risk, with one million cases annually mainly affecting rural areas in Asia-Oceania. Relative to its burden, scrub typhus is understudied, and treatment recommendations vary with poor evidence base. These knowledge gaps could be addressed by establishing an individual participant-level data (IPD) platform, which would enable pooled, more detailed and statistically powered analyses to be conducted. This study aims to assess the characteristics of scrub typhus treatment studies and explore the feasibility and potential value of developing a scrub typhus IPD platform to address unanswered research questions.

Methodology/principal findings

We conducted a systematic literature review looking for prospective scrub typhus clinical treatment studies published from 1998 to 2020. Six electronic databases (Ovid Embase, Ovid Medline, Ovid Global Health, Cochrane Library, Scopus, Global Index Medicus), ClinicalTrials.gov, and WHO ICTRP were searched. We extracted data on study design, treatment tested, patient characteristics, diagnostic methods, geographical location, outcome measures, and statistical methodology.

Among 3,100 articles screened, 127 were included in the analysis. 12,079 participants from 12 countries were enrolled in the identified studies. ELISA, PCR, and eschar presence were the most commonly used diagnostic methods. Doxycycline, azithromycin, and chloramphenicol were the most commonly administered antibiotics. Mortality, complications, adverse events, and clinical response were assessed in most studies. There was substantial heterogeneity in the diagnostic methods used, treatment administered (including dosing and duration), and outcome assessed across studies. There were few interventional studies and limited data collected on specific groups such as children and pregnant women.

Conclusions/significance

There were a limited number of interventional trials, highlighting that scrub typhus remains a neglected disease. The heterogeneous nature of the available data reflects the absence of consensus in treatment and research methodologies and poses a significant barrier to aggregating information across available published data without access to the underlying IPD. There is likely to be a substantial amount of data available to address knowledge gaps. Therefore, there is value for an IPD platform that will facilitate pooling and harmonisation of currently scattered data and enable in-depth investigation of priority research questions that can, ultimately, inform clinical practice and improve health outcomes for scrub typhus patients.

Scrub typhus is a febrile illness most commonly found in rural tropical areas. It is caused by a Gram-negative bacteria belonging to the family Rickettsiaceae and transmitted by mites when they feed on vertebrates. There is an estimate of one million cases annually, with an estimated one billion people at risk, mostly in Asia-Oceania. But relative to the scale of the problem, scrub typhus is largely understudied. Evidence-based treatment recommendations by policymakers vary or are non-existent. We searched databases and registries for prospective scrub typhus clinical treatment studies published from 1998 to 2020 and reviewed them. Data from clinical trials and particularly for specific groups, such as pregnant women and children, were minimal. The methods used to measure treatment efficacy were heterogeneous, making it difficult to directly compare or conduct a meta-analysis based on aggregated data. One way to improve the current level of evidence would be by pooling and analysing individual participant-level data (IPD), i.e. the raw data from individual participants in completed studies. This review demonstrated that there is scope for developing a database for individual participant data to enable more detailed analyses. IPD meta-analyses could be a way to address knowledge gaps such as optimum dosing for children and pregnant women.

Orientia tsutsugamushi modulates cellular levels of NF-κB inhibitor p105

Background

Scrub typhus is a neglected tropical disease that threatens more than one billion people. If antibiotic therapy is delayed, often due to mis- or late diagnosis, the case fatality rate can increase considerably. Scrub typhus is caused by the obligate intracellular bacterium, Orientia tsutsugamushi, which invades phagocytes and endothelial cells in vivo and diverse tissue culture cell types in vitro. The ability of O. tsutsugamushi to replicate in the cytoplasm indicates that it has evolved to counter eukaryotic host cell immune defense mechanisms. The transcription factor, NF-κB, is a tightly regulated initiator of proinflammatory and antimicrobial responses. Typically, the inhibitory proteins p105 and IκBα sequester the NF-κB p50:p65 heterodimer in the cytoplasm. Canonical activation of NF-κB via TNFα involves IKKβ-mediated serine phosphorylation of IκBα and p105, which leads to their degradation and enables NF-κB nuclear translocation. A portion of p105 is also processed into p50. O. tsutsugamushi impairs NF-κB translocation into the nucleus, but how it does so is incompletely defined.

Principal findings

Western blot, densitometry, and quantitative RT-PCR analyses of O. tsutsugamushi infected host cells were used to determine if the pathogen’s ability to inhibit NF-κB is linked to modulation of p105. Results demonstrate that p105 levels are elevated several-fold in O. tsutsugamushi infected HeLa and RF/6A cells with only a nominal increase in p50. The O. tsutsugamushi-stimulated increase in p105 is bacterial dose- and protein synthesis-dependent, but does not occur at the level of host cell transcription. While TNFα-induced phosphorylation of p105 serine 932 proceeds unhindered in infected cells, p105 levels remain elevated and NF-κB p65 is retained in the cytoplasm.

Conclusions

O. tsutsugamushi specifically stabilizes p105 to inhibit the canonical NF-κB pathway, which advances understanding of how it counters host immunity to establish infection.

Scrub typhus is a neglected disease that can be fatal and occurs predominantly in the Asia-Pacific, one of the most densely populated regions of the world. Notably, cases continue to emerge outside this area. The etiologic agent is Orientia tsutsugamushi, a bacterial pathogen that infects certain leukocytes and cells that line blood vessels in animals and humans. The success of O. tsutsugamushi to colonize these cells is at least partially attributable to its ability to counter host immunity. In this study, we demonstrate that O. tsutsugamushi stabilizes p105, a mammalian inhibitor of the transcription factor, NF-κB, which is otherwise key for activating proinflammatory and antimicrobial gene expression. O. tsutsugamushi is the first example of a bacterium that inhibits NF-κB by promoting elevated levels of p105 and impairing its degradation. Our findings provide fundamental information that helps explain how this important pathogen has evolved to stealthily establish infection in host cells.

Minocycline Induces Autophagy and Inhibits Cell Proliferation in LPS-Stimulated THP-1 Cells

Excessive activation and proliferation of inflammatory cell and uncontrolled release of cytokines and chemokines, also known as cytokine storm, is considered to be the main cause of sepsis. Accumulating evidence has indicated that autophagy may play an important role in regulating immune response and controlling excessive inflammation. Recent studies have showed that minocycline has immunomodulatory effects on cytokine and chemokine production. It has also been reported that minocycline can induce autophagy, suggesting that autophagy may be involved in the process of minocycline regulating inflammation and immune response. However, the precise mechanism is unclear. In the present study, we used enzyme-linked immunosorbent assays (ELISA) to measure the production of cytokines following minocycline treatment of lipopolysaccharide- (LPS-) stimulated THP-1 cells. Western blotting analysis was performed to confirm autophagy and the mTOR signal pathway. Cell proliferation was measured by WST-1 cell proliferation assay. We demonstrated that LPS induced autophagy in a tumor necrosis factor- (TNF-) α-mediated manner, and simultaneously, LPS induced the release of TNF-α to trigger inflammation and activated mammalian target of rapamycin (mTOR) to potentiate cell proliferation. Minocycline, which induces autophagy by inhibiting mTOR, suppresses cytokine production and cell proliferation and protects THP-1 cells from LPS toxicity. Further study demonstrated that there might be an intimate crosstalk between the inhibitor kappa B kinase (IKK)/nuclear factor-kappa B (NF-κB) signaling pathway and autophagy flux in modification of inflammatory responses. In addition, rapamycin, the mTOR inhibitor, has cooperative effect with minocycline on suppression of TNF-α release and induction of autophagy by repressing mTOR. Our data brought a novel clue to evaluate minocycline using as a potential therapeutic medicine for sepsis.

Complex Cytokine Responses in Imported Scrub Typhus Cases, Germany, 2010-2018

Scrub typhus is a life-threatening zoonotic disease, which is caused by Orientia tsutsugamushi, an obligatory intracellular Gram-negative bacterium. It is transmitted by Leptotrombidium mites in endemic regions of Southeast Asia. So far, data on imported scrub typhus cases to non-endemic areas and immunological descriptions are rare. Eleven scrub typhus cases that had been diagnosed by the German National Reference Center for Tropical Pathogens between 2010 and 2018 were retrospectively reviewed for clinical symptoms, laboratory changes, and travel destinations. Patient sera were included if follow-up samples showed simultaneous seroconversion for IgM and IgG antibody responses by immunofluorescence assays or concurrence with the first serum sample. The median of seroconversion was week 2 after symptom onset. Cytokine levels were measured over time, demonstrating simultaneously upregulated major Th1, Th2, and Th17 cytokines in the acute phase of infection followed by normalization during convalescence. This study underlines the complex mixed cytokine response elicited by scrub typhus and highlights clinical and diagnostic aspects of imported infections with O. tsutsugamushi.

Evaluation of Th1 and Th2 immune response in clinical and sub-clinical scrub typhus infection

Scrub typhus (ST), caused by a gram negative intracellular bacteria- Orientia tsutsugamushi, is one among the leading causes of febrile illness across Southeast Asia, including India. Clinical presentation can vary from asymptomatic to severely fatal. Th1-cell mediated immunity has been suggested to play an important role against ST infection in animal models. However, human data on protective immunity are limited. The present study was undertaken to identify host immune correlates that could confer protection in individuals that remain clinically asymptomatic/sub-clinical. Serum cytokine profiling and mRNA expression levels of Th1 (TNF-α, IFN-γ, IL-2) and Th2 (IL-10, IL-6, IL-4) cytokines was studied amongst the clinical and sub-clinical infections. It was observed that a Th1/Th2 pattern is not involved in human ST infection irrespective of being a symptomatic or asymptomatic presentation. However, significant difference was observed in IL-10 serum and gene expression levels. This study suggests a possible role of IL-10 in disease phenotypic presentation. Over-production of IL-10 was found to be a significant factor contributing to the severity of the disease whereas a protective immune mechanism might exist with a low level of IL-10 in ST infection.

Indicators of severe prognosis of scrub typhus: prognostic factors of scrub typhus severity

Background

Scrub typhus is an acute disease, characterized by symptoms of fever, which occurs due to infection by Orientia tsutsugamushi. In most cases, patients recover from the disease with appropriate treatment, but serious and fatal complications may occur. The present study examined laboratory findings and tumor necrosis factor-alpha (TNF-α) levels of scrub typhus patients to identify the prognostic predictors of disease severity.

Method

Patients whose scrub typhus diagnosis was confirmed by elevated indirect fluorescent antibody (IFA) levels and positive polymerase chain reaction (PCR) results were classified according to disease severity into one of three groups; i.e., deceased (n = 7), severe (n = 15), and mild (n = 15) retrospectively registered. Additionally, the usefulness of modified Acute Physiology and Chronic Health Evaluation II (APACHE II) score, C-reactive protein (CRP) level, white blood cell (WBC) count, and TNF-α level as prognostic predictors were examined.

Result

The mean TNF-α levels of the deceased, severe, and mild groups were 53.5 (range: 7.8–147.8), 26.0 (1.7–64.4), and 8.8 pg/mL (4.6–16.0), respectively. The results of Kruskal-Wallis tests showed statistically significant differences between the deceased and severe groups versus the mild group (p = 0.005). CRP level and Modified APACHE II score also differed significantly among the groups (p = 0.046 and 0.007, respectively); however, WBC count did not (p = 0.196).

Conclusion

An elevated serum TNF-α level in patients with scrub typhus could predict a severe condition or death and may be useful in predicting patient prognosis.

Dysregulated Th1 Immune and Vascular Responses in Scrub Typhus Pathogenesis

Scrub typhus is an emerging, insect-transmitted disease caused by Orientia tsutsugamushi, a Gram- and LPS-negative bacterium that replicates freely within professional phagocytes and endothelial cells. Scrub typhus is prevalent with high mortality rates, but information regarding its molecular pathogenesis, microbial virulence determinants, and key immune responses is limited. Improved animal models have recently been developed that respectively resemble the pathological features of self-limiting or severe scrub typhus in humans. Strong activation of Th1 and CD8, but not Th2 and regulatory T, immune responses, accompanied by altered angiopoietin/Tie2-related regulation, are hallmarks of lethal infection in murine models. This review, based primarily on recent advances from clinical and experimental studies, highlights tissue- and endothelial cell-specific biomarkers that are indicative of immune dysregulation. The potential roles of neutrophils and damage-associated molecular pattern molecules at late stages of disease are discussed in the context of vascular leakage, pulmonary and renal injury, and scrub typhus pathogenesis.

Orientia tsutsugamushi uses two Ank effectors to modulate NF-κB p65 nuclear transport and inhibit NF-κB transcriptional activation

Orientia tsutsugamushi causes scrub typhus, a potentially fatal infection that threatens over one billion people. Nuclear translocation of the transcription factor, NF-κB, is the central initiating cellular event in the antimicrobial response. Here, we report that NF-κB p65 nuclear accumulation and NF-κB-dependent transcription are inhibited in O. tsutsugamushi infected HeLa cells and/or primary macrophages, even in the presence of TNFα. The bacterium modulates p65 subcellular localization by neither degrading it nor inhibiting IκBα degradation. Rather, it exploits host exportin 1 to mediate p65 nuclear export, as this phenomenon is leptomycin B-sensitive. O. tsutsugamushi antagonizes NF-κB-activated transcription even when exportin 1 is inhibited and NF-κB consequently remains in the nucleus. Two ankyrin repeat-containing effectors (Anks), Ank1 and Ank6, each of which possess a C-terminal F-box and exhibit 58.5% amino acid identity, are linked to the pathogen's ability to modulate NF-κB. When ectopically expressed, both translocate to the nucleus, abrogate NF-κB-activated transcription in an exportin 1-independent manner, and pronouncedly reduce TNFα-induced p65 nuclear levels by exportin 1-dependent means. Flag-tagged Ank 1 and Ank6 co-immunoprecipitate p65 and exportin 1. Both also bind importin β1, a host protein that is essential for the classical nuclear import pathway. Importazole, which blocks importin β1 activity, abrogates Ank1 and Ank6 nuclear translocation. The Ank1 and Ank6 regions that bind importin β1 also mediate their transport into the nucleus. Yet, these regions are distinct from those that bind p65/exportin 1. The Ank1 and Ank6 F-box and the region that lies between it and the ankyrin repeat domain are essential for blocking p65 nuclear accumulation. These data reveal a novel mechanism by which O. tsutsugamushi modulates the activity and nuclear transport of NF-κB p65 and identify the first microbial proteins that co-opt both importin β1 and exportin 1 to antagonize a critical arm of the antimicrobial response.

Dissemination of Orientia tsutsugamushi, a Causative Agent of Scrub Typhus, and Immunological Responses in the Humanized DRAGA Mouse

Scrub typhus is caused by Orientia tsutsugamushi, an obligated intracellular bacterium that affects over one million people per year. Several mouse models have been used to study its pathogenesis, disease immunology, and for testing vaccine candidates. However, due to the intrinsic differences between the immune systems in mouse and human, these mouse models could not faithfully mimic the pathology and immunological responses developed by human patients, limiting their value in both basic and translational studies. In this study, we have tested for the first time, a new humanized mouse model through footpad inoculation of O. tsutsugamushi in DRAGA (HLA-A2.HLA-DR4.Rag1KO.IL2RγcKO.NOD) mice with their human immune system reconstituted by infusion of HLA-matched human hematopoietic stem cells from umbilical cord blood. Upon infection, Orientia disseminated into various organs of DRAGA mice resulted in lethality in a dose-dependent manner, while all C3H/HeJ mice infected by the same route survived. Tissue-specific lesions associated with inflammation and/or necroses were observed in multiple organs of infected DRAGA mice. Consistent with the intracellular nature of Orientia, strong Th1, but subdued Th2 responses were elicited as reflected by the human cytokine profiles in sera from infected mice. Interestingly, the percentage of both activated and regulatory (CD4⁺FOXP3⁺) human T cells were elevated in spleen tissues of infected mice. After immunization with irradiated whole cell Orientia, humanized DRAGA mice showed a significant activation of human T cells as evidenced by increased number of human CD4⁺ and CD8⁺ T cells. Specific human IgM and IgG antibodies were developed after repetitive immunization. The humanized DRAGA mouse model represents a new pre-clinical model for studying Orientia-human interactions and also for testing vaccines and novel therapeutics for scrub typhus.

The dynamic immunomodulatory effects of vitamin D3 during Mycobacterium infection

Mycobacterium tuberculosis ( Mtb), is a highly infectious airborne bacterium. Previous studies have found vitamin D₃ to be a key factor in the defense against Mtb infection, through its regulation of the production of immune-related cytokines, chemokines and effector molecules. Mycobacterium smegmatis was used in our study as a surrogate of Mtb. We hypothesized that the continuous presence of vitamin D₃, as well as the level of severity of infection would differentially modulate host cell immune response in comparison with control and the vehicle, ethanol. We found that vitamin D₃ conditioning promotes increased bacterial clearance during low-level infection, intracellular containment during high-level infection, and minimizes host cytotoxicity. In the presence of vitamin D₃ host cell production of cytokines and effector molecules was infection-level dependent, most notably IL-12, which increased during high-level infection and decreased during low-level infection, and NO, which had a rate of change positively correlated to IL-12. Our study provides evidence that vitamin D₃ modulation is context-dependent and time-variant, as well as highly correlated to level of infection. This study furthers our mechanistic understanding of the dual role of vitamin D₃ as a regulator of bactericidal molecules and protective agent against host cell damage.

An Update on Host-Pathogen Interplay and Modulation of Immune Responses during Orientia tsutsugamushi Infection

The obligate intracellular bacterium Orientia tsutsugamushi is the causative agent of scrub typhus in humans, a serious mite-borne disease present in a widespread area of endemicity, which affects an estimated 1 million people every year. This disease may exhibit a broad range of presentations, ranging from asymptomatic to fatal conditions, with the latter being due to disseminated endothelial infection and organ injury. Unique characteristics of the biology and host-pathogen interactions of O. tsutsugamushi, including the high antigenic diversity among strains and the highly variable, short-lived memory responses developed by the host, underlie difficulties faced in the pursuit of an effective vaccine, which is an imperative need. Other factors that have hindered scientific progress relative to the infectious mechanisms of and the immune response triggered by this bacterium in vertebrate hosts include the limited number of mechanistic studies performed on animal models and the lack of genetic tools currently available for this pathogen. However, recent advances in animal model development are promising to improve our understanding of host-pathogen interactions. Here, we comprehensively discuss the recent advances in and future perspectives on host-pathogen interactions and the modulation of immune responses related to this reemerging disease, highlighting the role of animal models.

Strong interferon-gamma mediated cellular immunity to scrub typhus demonstrated using a novel whole cell antigen ELISpot assay in rhesus macaques and humans

Scrub typhus is a febrile infection caused by the obligate intracellular bacterium Orientia tsutsugamushi, which causes significant morbidity and mortality across the Asia-Pacific region. The control of this vector-borne disease is challenging due to humans being dead-end hosts, vertical maintenance of the pathogen in the vector itself, and a potentially large rodent reservoir of unclear significance, coupled with a lack of accurate diagnostic tests. Development of an effective vaccine is highly desirable. This however requires better characterization of the natural immune response of this neglected but important disease. Here we implement a novel IFN-γ ELISpot assay as a tool for studying O. tsutsugamushi induced cellular immune responses in an experimental scrub typhus rhesus macaque model and human populations. Whole cell antigen for O. tsutsugamushi (OT-WCA) was prepared by heat inactivation of Karp-strain bacteria. Rhesus macaques were infected intradermally with O. tsutsugamushi. Freshly isolated peripheral blood mononuclear cells (PBMC) from infected (n = 10) and uninfected animals (n = 5) were stimulated with OT-WCA, and IFN-γ secreting cells quantitated by ELISpot assay at five time points over 28 days. PBMC were then assayed from people in a scrub typhus-endemic region of Thailand (n = 105) and responses compared to those from a partially exposed population in a non-endemic region (n = 14), and to a naïve population in UK (n = 12). Mean results at Day 0 prior to O. tsutsugamushi infection were 12 (95% CI 0–25) and 15 (2–27) spot-forming cells (SFC)/10⁶ PBMC for infected and control macaques respectively. Strong O. tsutsugamushi-specific IFN-γ responses were seen post infection, with ELISpot responses 20-fold higher than baseline at Day 7 (mean 235, 95% CI 200–270 SFC/10⁶ PBMC), 105-fold higher at Day 14 (mean 1261, 95% CI 1,097–1,425 SFC/10⁶ PBMC), 125-fold higher at Day 21 (mean 1,498, 95% CI 1,496–1,500 SFC/10⁶ PBMC) and 118-fold higher at Day 28 (mean 1,416, 95% CI 1,306–1,527 SFC/10⁶ PBMC). No significant change was found in the control group at any time point compared to baseline. Humans from a scrub typhus endemic region of Thailand had mean responses of 189 (95% CI 88–290) SFC/10⁶ PBMC compared to mean responses of 40 (95% CI 9–71) SFC/10⁶ PBMC in people from a non-endemic region and 3 (95% CI 0–7) SFC/10⁶ PBMC in naïve controls. In summary, this highly sensitive assay will enable field immunogenicity studies and further characterization of the host response to O. tsutsugamushi, and provides a link between human and animal models to accelerate vaccine development.

Scrub typhus is a disease caused by bacteria that invade cells in our immune system and blood vessels. It is transmitted by mites and is treatable with antibiotics. Unfortunately diagnosis is difficult and requires techniques that are not easily accessible everywhere. Currently, there is no scrub typhus vaccine available. In order to improve diagnostics and vaccine development in future, we need to better understand our immune response against these bacteria. In this study, we developed a test where these bacteria were killed and prepared by a new purification method to stimulate the immune cells in our blood -not antibodies. We evaluated this test in hospitalized patients with scrub typhus disease and also in non-human primates to study the responses over time. The test proved to be very accurate and useful to study natural immune responses, and we found differences in responses in areas where scrub typhus is common, compared to areas where it is not common. This test will allow us to investigate the immune response to scrub typhus more in-depth in the future, and will support the development of better diagnostic tests and vaccines against scrub typhus.

An Intradermal Inoculation Mouse Model for Immunological Investigations of Acute Scrub Typhus and Persistent Infection

Scrub typhus is a neglected tropical disease, caused by Orientia tsutsugamushi, a Gram-negative bacterium that is transmitted to mammalian hosts during feeding by Leptotrombidium mites and replicates predominantly within endothelial cells. Most studies of scrub typhus in animal models have utilized either intraperitoneal or intravenous inoculation; however, there is limited information on infection by the natural route in murine model skin or its related early host responses. Here, we developed an intradermal (i.d.) inoculation model of scrub typhus and focused on the kinetics of the host responses in the blood and major infected organs. Following ear inoculation with 6 x 104 O. tsutsugamushi, mice developed fever at 11-12 days post-infection (dpi), followed by marked hypothermia and body weight loss at 14-19 dpi. Bacteria in blood and tissues and histopathological changes were detected around 9 dpi and peaked around 14 dpi. Serum cytokine analyses revealed a mixed Th1/Th2 response, with marked elevations of MCP-1/CCL2, MIP-1α/CCL3 and IL-10 at 9 dpi, followed by increased concentrations of pro-inflammatory markers (IL-6, IL-12, IFN-γ, G-CSF, RANTES/CCL5, KC/CCL11, IL-1α/β, IL-2, TNF-α, GM-CSF), as well as modulatory cytokines (IL-9, IL-13). Cytokine levels in lungs had similar elevation patterns, except for a marked reduction of IL-9. The Orientia 47-kDa gene and infectious bacteria were detected in several organs for up to 84 dpi, indicating persistent infection. This is the first comprehensive report of acute scrub typhus and persistent infection in i.d.-inoculated C57BL/6 mice. This is a significant improvement over current murine models for Orientia infection and will permit detailed studies of host immune responses and infection control interventions.

Cross-Regulation of Proinflammatory Cytokines by Interleukin-10 and miR-155 in Orientia tsutsugamushi-Infected Human Macrophages Prevents Cytokine Storm

Scrub typhus is caused by the obligate intracellular bacterium Orientia tsutsugamushi. Macrophages are host cells for its replication and clearance. Severe complications in patients are mainly caused by a cytokine storm resulting from overproduction of proinflammatory cytokines; nevertheless, the molecular mechanism for the occurrence remains obscure. Herein, we investigate the interactive regulation of cytokines and micro-RNA (miR) in human macrophages infected with low and high doses of O. tsutsugamushi. During low dose infection, macrophages produce high levels of IL-10 through extracellular signal-regulated kinase activation, which inhibits proinflammatory cytokine production and facilitates pathogen replication. Increasing levels of pathogen results in reduced levels of IL-10, and macrophages begin to generate high levels of proinflammatory cytokines through NF-κB activation. However, during a high dose infection, macrophages produce high levels of miR-155 to slow the proinflammatory response. The extracellular signal-regulated kinase/IL-10 axis suppresses the NF-κB/tumor necrosis factor alpha axis via activation of signal transducer and activator of transcription 3. Both IL-10 and miR-155 inhibit the NF-κB signaling pathway. Furthermore, IL-10 is a potent inhibitor of miR-155. Patients susceptible to a cytokine storm, peripheral blood mononuclear cells showed significantly lower IL-10 and miR-155 responses to O. tsutsugamushi challenge. Thus, IL-10 and miR-155 operate inhibitory mechanisms to achieve a proper defense mechanism and prevent a cytokine storm.

Strategies for detecting rickettsiae and diagnosing rickettsial diseases

Rickettsial diseases and scrub typhus constitute a group of the oldest known vector-borne diseases. The cosmopolitan distribution of the vectors that transmit rickettsiae and orientiae leads to a worldwide prevalence of these diseases. Despite their significant historical status, detection and diagnosis of these diseases are still evolving today. Serological methods remain among the most prevalent techniques used for the detection/diagnosis of rickettsial diseases and scrub typhus. Molecular techniques have been instrumental in increasing the sensitivity/specificity of diagnosis, identifying new Rickettsia and Orientia species and have enhanced epidemiological capabilities when used in combination with serological methods. In this review, we discuss these techniques and their associated pros and cons.

The Rapid Effectiveness of Minocycline against Scrub Typhus Meningoencephalitis

Scrub typhus is associated with various clinical symptoms. However, the pathogenesis of scrub typhus infection remains to be elucidated. A 73-year-old man was admitted to our hospital with consciousness disturbance and suspected meningoencephalitis. The patient's laboratory data showed deterioration and were indicative of hemophagocytic lymphohistiocytosis (HLH). A whole body examination to detect the trigger disease revealed an eschar, which is a characteristic of scrub typhus, on his back. His symptoms showed dramatic improvement after the administration of minocycline (MINO). This case report highlights that the clinical course of a case of scrub typhus meningoencephalitis that was cured with MINO.

Tetracyclines downregulate the production of LPS-induced cytokines and chemokines in THP-1 cells via ERK, p38, and nuclear factor-κB signaling pathways

Recent reports have shown that antibiotics such as macrolide, aminoglycoside, and tetracyclines have immunomodulatory effects in addition to essential antibiotic effects. These agents may have important effects on the regulation of cytokine and chemokine production. However, the precise mechanism is unknown. This time, we used Multi Plex to measure the production of cytokines and chemokines following tetracycline treatment of lipopolysaccharide (LPS)-induced THP-1 cells. The signaling pathways were investigated with Western blotting analysis. Three tetracyclines significantly suppressed the expression of cytokines and chemokines induced by LPS. Minocycline (50 μg/ml), tigecycline (50 μg/ml), or doxycycline (50 μg/ml) were added after treatment with LPS (10 μg/ml). Tumor necrosis factor-α was downregulated to 16%, 14%, and 8%, respectively, after 60 min compared to treatment with LPS without agents. Interleukin-8 was downregulated to 43%, 32%, and 26% at 60 min. Macrophage inflammatory protein (MIP)-1α was downregulated to 23%, 33%, and 16% at 120 min. MIP-1β was downregulated to 21%, 11%, and 2% at 120 min. Concerning about signaling pathways, the mechanisms of the three tetracyclines might not be the same. Although the three tetracyclines showed some differences in the time course, tetracyclines modulated phosphorylation of the NF-κB pathway, p38 and ERK1/2/MAPK pathways, resulting in inhibition of cytokine and chemokine production. In addition, SB203580 (p38 inhibitor) and U0126 (ERK1/2 inhibitor) significantly suppressed the expression of TNF-α and IL-8 in LPS-stimulated THP-1 cells. And further, the NF-κB inhibitor, BAY11-7082, almost completely suppressed LPS-induced these two cytokines production. Thus, more than one signaling pathway may be involved in tetracyclines downregulation of the expression of LPS-induced cytokines and chemokines in THP-1 cells. And among the three signaling pathways, NF-κB pathway might be the dominant pathway on tetracyclines modification the LPS-induced cytokines production in THP-1 cells. In general, minocycline and doxycycline suppressed the production of cytokines and chemokines in LPS-stimulated THP-1 cell lines via mainly the inhibition of phosphorylation of NF-κB pathways. Tigecycline has the same structure as the other tetracyclines, however, it showed the different properties of cytokine modulation in the experimental time course.

Strong type 1, but impaired type 2, immune responses contribute to Orientia tsutsugamushi-induced pathology in mice

Scrub typhus is a neglected, but important, tropical disease, which puts one-third of the world's population at risk. The disease is caused by Orientia tsutsugamushi, an obligately intracellular Gram-negative bacterium. Dysregulation in immune responses is known to contribute to disease pathogenesis; however, the nature and molecular basis of immune alterations are poorly defined. This study made use of a newly developed murine model of severe scrub typhus and focused on innate regulators and vascular growth factors in O. tsutsugamushi-infected liver, lungs and spleen. We found no activation or even reduction in base-line expression for multiple molecules (IL-7, IL-4, IL-13, GATA3, ROR-γt, and CXCL12) at 2, 6 and 10 days post-infection. This selective impairment in type 2-related immune responses correlated with a significant activation of the genes for IL-1β, IL-6, IL-10, TNF-α, IFN-γ, as well as CXCR3- and CXCR1-related chemokines in inflamed tissues. The elevated angiopoietin (Ang)-2 expression and Ang-2/Ang-1 ratios suggested excessive inflammation and the loss of endothelial integrity. These alterations, together with extensive recruitment of myeloperoxidase (MPO)-expressing neutrophils and the influx of CD3+ T cells, contributed to acute tissue damage and animal death. This is the first report of selective alterations in a panel of immune regulators during early O. tsutsugamushi infection in intravenously inoculated C57BL/6 mice. Our findings shed new light on the pathogenic mechanisms associated with severe scrub typhus and suggest potential targets for therapeutic investigation.

Significantly higher cytokine and chemokine levels in patients with Japanese spotted fever than in those with Tsutsugamushi disease

Tetracyclines are administered to cure Japanese spotted fever (JSF) and tsutsugamushi disease (TD). It is generally said that the clinical course of JSF is worse than that of TD despite antibiotic treatment. The precise mechanism underlying the more severe clinical course of JSF is not fully understood. We therefore examined whether the differential cytokine profile between these two infectious diseases contributes to the difference in clinical severity. The serum concentrations of various cytokines (tumor necrosis factor alpha [TNF-α], interleukin-6 [IL-6], and gamma interferon [IFN-γ]) and chemokines (IL-8, interferon-inducible protein 10 [IP-10], monocyte chemoattractant protein 1 [MCP-1], macrophage inflammatory protein 1α [MIP-1α], MIP-1β, and eotaxin) were measured in 32 TD and 21 JSF patients. The results showed that serum levels of TNF-α in the acute phases of TD and JSF were significantly increased, with a higher concentration of TNF-α in patients with JSF (mean, 39.9 pg/ml) than in those with TD (mean, 13.8 pg/ml). Comparatively higher levels of other cytokines and chemokines (IL-6, IFN-γ, IL-8, IP-10, MCP-1, MIP-1α, and MIP-1β) were also observed in the acute phase of JSF. The clinical severity score (3.67 ± 1.71) of JSF patients was higher than that of TD patients (1.47 ± 0.77). Our findings revealed that the cytokine and chemokine levels in the acute phase of JSF were significantly higher than those in the acute phase of TD. The differential cytokine levels may be related to the difference in clinical severity between JSF and TD.

Cytokine network in scrub typhus: high levels of interleukin-8 are associated with disease severity and mortality

Background

Scrub typhus, caused by Orientia tsutsugamushi, is endemic in the Asia-Pacific region. Mortality is high if untreated, and even with treatment as high as 10–20%, further knowledge of the immune response during scrub typhus is needed. The current study was aimed at comparing plasma levels of a variety of inflammatory mediators in scrub typhus patients and controls in South India in order to map the broader cytokine profile and their relation to disease severity and clinical outcome.

Methodology/Principal Findings

We examined plasma levels of several cytokines in scrub typhus patients (n = 129) compared to healthy controls (n = 31) and infectious disease controls (n = 31), both in the acute phase and after recovery, by multiplex technology and enzyme immunoassays. Scrub typhus patients were characterized by marked changes in the cytokine network during the acute phase, differing not only from healthy controls but also from infectious disease controls. While most of the inflammatory markers were raised in scrub typhus, platelet-derived mediators such as RANTES were markedly decreased, probably reflecting enhanced platelet activation. Some of the inflammatory markers, including various chemokines (e.g., interleukin-8, monocyte chemoattractant peptide-1 and macrophage inflammatory protein-1β) and downstream markers of inflammation (e.g., C-reactive protein and pentraxin-3), were also associated with disease severity and mortality during follow-up, with a particular strong association with interleukin-8.

Conclusions/Significance

Our findings suggest that scrub typhus is characterized by a certain cytokine profile that includes dysregulated levels of a wide range of mediators, and that this enhanced inflammation could contribute to disease severity and clinical outcome.

Scrub typhus is a potentially fatal disease affecting at least 1 million people yearly, with 1 billion at risk in the Asia-Pacific region. Caused by the bacterium Orientia tsutsugamushi, which is transmitted by mites, people with more outdoor activities, like farmers and construction workers, often low-income populations, are at higher risk. The interaction between the bacteria and cells in the patient triggers inflammatory responses, including production of several cytokines, representing both beneficial and detrimental effects to the host. In order to develop better treatment and even a vaccine, we need a better understanding of the pathophysiological mechanisms of the disease. The current study was aimed at comparing levels of inflammatory mediators in scrub typhus patients, including recovered patients, in order to map the broader cytokine profile and see how this can be related to disease severity and clinical outcome. Our findings suggest that scrub typhus is characterized by a specific cytokine profile that includes dysregulated levels of a wide range of inflammatory mediators. Further studies on this issue may lead to much-needed new therapeutic targets and prognostic markers in scrub typhus patients.

Tsutsugamushi disease caused by Shimokoshi-type Orientia tsutsugamushi: the first report in Western Japan

An 85-year-old female farmer was admitted to our hospital for fever, general fatigue, and skin rash. Cephalosporin was not effective and minocycline was dramatically effective. An eschar was discovered on her inguinal region after the defervescence. Laboratory examination of serum taken 12 days after onset of the illness showed elevated titers of antibodies against the Shimokoshi strain of Orientia tsutsugamushi. The gene sequence analysis of specimen from the patient's eschar revealed high similarity to the Shimokoshi strain by nested polymerase chain reaction. Therefore, this patient was diagnosed as a case of Shimokoshi-type tsutsugamushi disease, which has not previously been reported in Western Japan. Recently, cases of this type have also been confirmed in northeastern Japan, suggesting the need for further epidemiological studies.

Minocycline modulates cytokine and chemokine production in lipopolysaccharide-stimulated THP-1 monocytic cells by inhibiting IκB kinase α/β phosphorylation

Minocycline, which is a member of the broad-spectrum bacteriostatic tetracycline antibiotics group, has also recently been shown to have additional effects that are separate from their antimicrobial function; however, the detailed mechanisms involved remain unknown. We examined the effects of minocycline on cytokine and chemokine production and the expression levels of intracellular phosphorylated proteins in a lipopolysaccharide (LPS)-induced cytokine response model in vitro. In the present study, 3 cytokines (tumor necrosis factor [TNF]-α, interleukin [IL]-6, and interferon [IFN]-γ) and 7 chemokines (IL-8, interferon inducible protein [IP]-10, monocyte chemoattractant protein [MCP]-1, macrophage inflammatory protein [MIP]-1α, MIP-1β, regulated upon activation normal T-cell expressed secreted [RANTES], and eotaxin) were suppressed by minocycline in a dose-dependent manner. Moreover, the phosphorylation of inhibitor of nuclear factor-κB alpha (IκBα) and IκB kinase (IKK)α/β, which is located upstream from IκBα, was significantly suppressed by minocycline, whereas the phosphorylation of extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK), p38, and TGF-β-activated kinase (TAK)1 were not affected. Thus, minocycline appears to inhibit the signaling pathway at the level of IKKα/β phosphorylation. In conclusion, minocycline was found to reduce the production of multiple cytokines and chemokines by inhibiting LPS-induced IKKα/β phosphorylation. That is, minocycline appears to be a potent inhibitor of IKKα/β phosphorylation. From a clinical and translational significance point-of view, these findings suggest that the use of minocycline offers the advantage of providing both antimicrobial and anti-inflammatory effects, which may be key in treating certain types of infectious diseases, particularly those that lead to hypercytokinemia and chronic inflammatory disorders.

Recent insights into microbial triggers of interleukin-10 production in the host and the impact on infectious disease pathogenesis

Since its initial description as a Th2-cytokine antagonistic to interferon-alpha and granulocyte-macrophage colony-stimulating factor, many studies have shown various anti-inflammatory actions of interleukin-10 (IL-10), and its role in infection as a key regulator of innate immunity. Studies have shown that IL-10 induced in response to microorganisms and their products plays a central role in shaping pathogenesis. IL-10 appears to function as both sword and shield in the response to varied groups of microorganisms in its capacity to mediate protective immunity against some organisms but increase susceptibility to other infections. The nature of IL-10 as a pleiotropic modulator of host responses to microorganisms is explained, in part, by its potent and varied effects on different immune effector cells which influence antimicrobial activity. A new understanding of how microorganisms trigger IL-10 responses is emerging, along with recent discoveries of how IL-10 produced during disease might be harnessed for better protective or therapeutic strategies. In this review, we summarize studies from the past 5 years that have reported the induction of IL-10 by different classes of pathogenic microorganisms, including protozoa, nematodes, fungi, viruses and bacteria and discuss the impact of this induction on the persistence and/or clearance of microorganisms in the host.

Severity predictors in eschar-positive scrub typhus and role of serum osteopontin

We prospectively evaluated severity predictors in terms of host, microorganism, and treatment factors in 153 eschar-positive scrub typhus patients. Severity was assessed with the Acute Physiology and Chronic Health Evaluation (APACHE) II score (< 10 versus ≥ 10) and predefined criteria of severe complications. Genotypes of Orientia tsutsugamushi were determined. Independent risk factors for severity (APACHE II score ≥ 10) were old age, diabetes mellitus, serum osteopontin > 100 ng/mL, and a group of underlying diseases (congestive heart failure, cerebrovascular disease, chronic liver disease, bronchial asthma, and chronic obstructive lung diseases). Anemia (≤ 10 g/dL) and C-reactive protein > 10 mg/dL were indicators of current severity. Neither the delay in antibiotics administration nor strain types (Boryong, Taguchi, or Kanda/Kawasaki) contributed to the severity. The risk factors for severe complications were similar. Serum osteopontin > 100 ng/mL had a negative predictive value of 96% for severe complications. This marker can be used to rule out severe disease status.

Non-therapeutic administration of a model antimicrobial growth promoter modulates intestinal immune responses

Background

The development of efficacious alternatives to antimicrobial growth promoters (AGP) in livestock production is an urgent issue, but is hampered by a lack of knowledge regarding the mode of action of AGP. The belief that AGP modulate the intestinal microbiota has become prominent in the literature; however, there is a lack of experimental evidence to support this hypothesis. Using a chlortetracycline-murine-Citrobacter rodentium model, the ability of AGP to modulate the intestinal immune system in mammals was investigated.

Results

C. rodentium was transformed with the tetracycline resistance gene, tetO, and continuous oral administration of a non-therapeutic dose of chlortetracycline to mice did not affect densities of C. rodentium CFU in feces throughout the experiment or associated with mucosal surfaces in the colon (i.e. at peak and late infection). However, chlortetracycline regulated transcription levels of Th1 and Th17 inflammatory cytokines in a temporal manner in C. rodentium-inoculated mice, and ameliorated weight loss associated with infection. In mice inoculated with C. rodentium, those that received chlortetracycline had less pathologic changes in the distal colon than mice not administered CTC (i.e. relative to untreated mice). Furthermore, chlortetracycline administration at a non-therapeutic dose did not impart either prominent or consistent effects on the colonic microbiota.

Conclusion

Data support the hypothesis that AGP function by modulating the intestinal immune system in mammals. This finding may facilitate the development of biorationale-based and efficacious alternatives to AGP.

New insight into immunity and immunopathology of Rickettsial diseases

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

Subversion of host cell signaling by Orientia tsutsugamushi

Progress has been made in deciphering the mechanisms on Orientia tsutsugamushi-host interaction. The genome sequencing, microarray and proteomic analyses of this ancient bacterium have provided a wealth of new information. This paper reviews the general characteristics of O. tsutsugamushi and recent developments especially in signaling events involved in the bacteria--host interaction.