Chemokine and cytokine production during Orientia tsutsugamushi infection in mice

Study on the Mechanism of Allergic Rhinitis Based on the Expression of FIB, PCT, hs-CRP, and Th17/Treg-IL10/IL-17 Axis Balance

BACKGROUND

The pathogenesis of allergic rhinitis (AR) is ambiguous, while it is clear that various immune cells and cytokines play crucial roles in its occurrence and development.

AIM

To investigate the effect of exogenous interleukin-10 (IL-10) on the expression of fibrinogen (FIB), procalcitonin (PCT), hypersensitive C-reactive protein (hs-CRP), and Th17/Treg-IL10/IL-17 axis balance in the nasal mucosa of rats with AR.

METHOD

In this study, 48 female-specific pathogen-free Sprague-Dawley rats were randomly divided into 3 groups: blank control group, AR group, and IL-10 intervention group. The AR model was established in the AR group and IL-10 group. The rats in the control group were treated with normal saline; the rats in the AR group were given 20 μL of saline containing 50 μg of ovalbumin (OVA) every day. The rats in the IL-10 intervention group were intraperitoneally injected with 1 mL of 40 pg/kg IL-10 and provided with OVA. The IL-10 intervention group was composed of mice with AR that received IL-10. The behavior of nasal allergic symptoms (such as nasal itching, sneezing, and runny nose) and the hematoxylin and eosin staining of nasal mucosa were observed. The levels of FIB, PCT, hs-CRP, IgE, and OVA sIgE in serum were determined by enzyme-linked immunosorbent assay. The levels of Treg and Th17 cells in serum were detected by flow cytometry. The protein levels of TGF-β, IL-10, and IL-17 in nasal mucosa were detected by the Western-blot method.

RESULTS

The scores of snots, nasal itching, and sneezing in the AR group were significantly higher than those in the control group, while the scores of the above symptoms in the IL-10 intervention group were lower than those in the AR group. The levels of FIB, PCT, hs-CRP, IgE, and OVA sIgE in serum and the protein levels of IL-10 and IL-17 in the nasal mucosa in the AR group were higher than those in the blank control group. Meanwhile, the levels of FIB, PCT, hs-CRP, IgE, and OVA sIgE in serum and IL-10 and IL-17 protein in the nasal mucosa in the IL-10 group were lower than those in the AR group.

CONCLUSION

IL-10 can relieve the allergy of AR rats by affecting the expression of FIB, PCT, and hs-CRP, as well as the balance of the Th17/Treg-IL10/IL-17 axis in the nasal mucosa of AR rats.

Endothelial Activation in Orientia tsutsugamushi Infection Is Mediated by Cytokine Secretion From Infected Monocytes

Scrub typhus, caused by Orientia tsutsugamushi, is a common systemic infection in Asia. Delay in diagnosis and treatment can lead to vasculitis in the visceral organs and other complications. The mechanisms that drive endothelial activation and the inflammatory response in O. tsutsugamushi infection remain unknown. In addition, the interaction between monocytes and endothelial cells is still unclear. Here we demonstrate that O. tsutsugamushi-infected human dermal microvascular endothelial cells produced moderate levels of chemokines and low levels of IL-6 and IFN-β, but not TNF or IL-1β. Recombinant TNF and cytokine-rich supernatants from infected monocytes markedly enhanced chemokine production in infected endothelial cells. We also show that TNF and monocyte supernatants, but not O. tsutsugamushi infection of endothelial cells per se, upregulated the endothelial cell surface expression of ICAM-1, E-selectin, and tissue factor. This finding was consistent with the inability of O. tsutsugamushi to induce cytokine secretion from endothelial cells. The upregulation of surface molecules after stimulation with monocyte supernatants was significantly reduced by neutralizing anti-TNF antibodies. These results suggest that endothelial cell activation and response are mainly mediated by inflammatory cytokines secreted from monocytes.

Comparison of Lethal and Nonlethal Mouse Models of Orientia tsutsugamushi Infection Reveals T-Cell Population-Associated Cytokine Signatures Correlated with Lethality and Protection

The antigenic diversity of Orientia tsutsugamushi as well as the interstrain difference(s) associated with virulence in mice impose the necessity to dissect the host immune response. In this study we compared the host response in lethal and non-lethal murine models of O. tsutsugamushi infection using the two strains, Karp (New Guinea) and Woods (Australia). The models included the lethal model: Karp intraperitoneal (IP) challenge; and the nonlethal models: Karp intradermal (ID), Woods IP, and Woods ID challenges. We monitored bacterial trafficking to the liver, lung, spleen, kidney, heart, and blood, and seroconversion during the 21-day challenge. Bacterial trafficking to all organs was observed in both the lethal and nonlethal models of infection, with significant increases in average bacterial loads observed in the livers and hearts of the lethal model. Multicolor flow cytometry was utilized to analyze the CD4+ and CD8+ T cell populations and their intracellular production of the cytokines IFNγ, TNF, and IL2 (single, double, and triple combinations) associated with both the lethal and nonlethal murine models of infection. The lethal model was defined by a cytokine signature of double- (IFNγ-IL2) and triple-producing (IL2-TNF-IFNγ) CD4+ T-cell populations; no multifunctional signature was identified in the CD8+ T-cell populations associated with the lethal model. In the nonlethal model, the cytokine signature was predominated by CD4+ and CD8+ T-cell populations associated with single (IL2) and/or double (IL2-TNF) populations of producers. The cytokine signatures associated with our lethal model will become depletion targets in future experiments; those signatures associated with our nonlethal model are hypothesized to be related to the protective nature of the nonlethal challenges.

The neglected challenge: Vaccination against rickettsiae

Over the last decades, rickettsioses are emerging worldwide. These diseases are caused by intracellular bacteria. Although rickettsioses can be treated with antibiotics, a vaccine against rickettsiae is highly desired for several reasons. Rickettsioses are highly prevalent, especially in poor countries, and there are indications of the development of antibiotic resistance. In addition, some rickettsiae can persist and cause recurrent disease. The development of a vaccine requires the understanding of the immune mechanisms that are involved in protection as well as in immunopathology. Knowledge about these immune responses is accumulating, and efforts have been undertaken to identify antigenic components of rickettsiae that may be useful as a vaccine. This review provides an overview on current knowledge of adaptive immunity against rickettsiae, which is essential for defense, rickettsial antigens that have been identified so far, and on vaccination strategies that have been used in animal models of rickettsial infections.

Dual RNA-seq of Orientia tsutsugamushi informs on host-pathogen interactions for this neglected intracellular human pathogen

Studying emerging or neglected pathogens is often challenging due to insufficient information and absence of genetic tools. Dual RNA-seq provides insights into host-pathogen interactions, and is particularly informative for intracellular organisms. Here we apply dual RNA-seq to Orientia tsutsugamushi (Ot), an obligate intracellular bacterium that causes the vector-borne human disease scrub typhus. Half the Ot genome is composed of repetitive DNA, and there is minimal collinearity in gene order between strains. Integrating RNA-seq, comparative genomics, proteomics, and machine learning to study the transcriptional architecture of Ot, we find evidence for wide-spread post-transcriptional antisense regulation. Comparing the host response to two clinical isolates, we identify distinct immune response networks for each strain, leading to predictions of relative virulence that are validated in a mouse infection model. Thus, dual RNA-seq can provide insight into the biology and host-pathogen interactions of a poorly characterized and genetically intractable organism such as Ot.

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.

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.

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.

Approaches to vaccines against Orientia tsutsugamushi

Scrub typhus is a severe mite-borne infection caused by Orientia tsutsugamushi, an obligately intracellular bacterium closely related to Rickettsia. The disease explains a substantial proportion of acute undifferentiated febrile cases that require hospitalization in rural areas of Asia, the North of Australia, and many islands of the Pacific Ocean. Delayed antibiotic treatment is common due to the lack of effective commercially available diagnostic tests and the lack of specificity of the early clinical presentation. The systemic infection of endothelial cells that line the vasculature with Orientia can lead to many complications and fatalities. In survivors, immunity does not last long, and is poorly cross-reactive among numerous strains. In addition, chronic infections are established in an unknown number of patients. All those characteristics justify the pursuit of a prophylactic vaccine against O. tsutsugamushi; however, despite continuous efforts to develop such a vaccine since World War II, the objective has not been attained. In this review, we discuss the history of vaccine development against Orientia to provide a clear picture of the challenges that we continue to face from the perspective of animal models and the immunological challenges posed by an intracellular bacterium that normally triggers a short-lived immune response. We finish with a proposal for development of an effective and safe vaccine for scrub typhus through a new approach with a strong focus on T cell-mediated immunity, empirical testing of the immunogenicity of proteins encoded by conserved genes, and assessment of protection in relevant animal models that truly mimic human scrub typhus.

Orientia tsutsugamushi subverts dendritic cell functions by escaping from autophagy and impairing their migration

Background

Dendritic cells (DCs) are the most potent antigen-presenting cells that link innate and adaptive immune responses, playing a pivotal role in triggering antigen-specific immunity. Antigen uptake by DCs induces maturational changes that include increased surface expression of major histocompatibility complex (MHC) and costimulatory molecules. In addition, DCs actively migrate to regional lymph nodes and activate antigen-specific naive T cells after capturing antigens. We characterize the functional changes of DCs infected with Orientia tsutsugamushi, the causative agent of scrub typhus, since there is limited knowledge of the role played by DCs in O. tsutsugamushi infection.

Methodology/Principal Finding

O. tsutsugamushi efficiently infected bone marrow-derived DCs and induced surface expression of MHC II and costimulatory molecules. In addition, O. tsutsugamushi induced autophagy activation, but actively escaped from this innate defense system. Infected DCs also secreted cytokines and chemokines such as IL-6, IL-12, MCP5, MIP-1α, and RANTES. Furthermore, in vitro migration of DCs in the presence of a CCL19 gradient within a 3D collagen matrix was drastically impaired when infected with O. tsutsugamushi. The infected cells migrated much less efficiently into lymphatic vessels of ear dermis ex vivo when compared to LPS-stimulated DCs. In vivo migration of O. tsutsugamushi-infected DCs to regional lymph nodes was significantly impaired and similar to that of immature DCs. Finally, we found that MAP kinases involved in chemotactic signaling were differentially activated in O. tsutsugamushi-infected DCs.

Conclusion/Significance

These results suggest that O. tsutsugamushi can target DCs to exploit these sentinel cells as replication reservoirs and delay or impair the functional maturation of DCs during the bacterial infection in mammals.

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi infection and is one of the main causes of febrile illness in the Asia-Pacific region. If not properly treated with antibiotics, patients often develop severe vasculitis that affects multiple organs, and the mortality rate of untreated patients reaches up to 30%. To understand the pathogenic mechanisms of the infectious disease, we characterized the functional changes of O. tsutsugamushi–infected dendritic cells (DCs), which play a pivotal role in orchestrating innate and adaptive immune responses. The obligate intracellular bacteria efficiently infected bone marrow-derived DCs and activated the cells as measured by induced surface expression of MHC II and costimulatory molecules, secretion of cytokines and chemokines, and autophagy induction. However, the live bacteria actively escaped from host autophagosomes and the migration of infected cells was severely impaired in vitro, ex vivo, and in vivo infection models. Finally, we found that MAP kinases involved in chemotactic signaling were differentially activated in O. tsutsugamushi-infected DCs. These results suggest that O. tsutsugamushi can target DCs to exploit these sentinel cells as replication reservoirs and delay or impair the functional maturation of DCs during the bacterial infection in mammals.

Phenotypic characterization of peripheral T cells and their dynamics in scrub typhus patients

Background

Scrub typhus, caused by Orientia tsutsugamushi infection, is one of the main causes of febrile illness in the Asia-Pacific region. Although cell-mediated immunity plays an important role in protection, little is known about the phenotypic changes and dynamics of leukocytes in scrub typhus patients.

Methodology/Principal Findings

To reveal the underlying mechanisms of immunological pathogenesis, we extensively analyzed peripheral blood leukocytes, especially T cells, during acute and convalescent phases of infection in human patients and compared with healthy volunteers. We observed neutrophilia and CD4⁺ T lymphopenia in the acute phase of infection, followed by proliferation of CD8⁺ T cells during the convalescent phase. Massive T cell apoptosis was detected in the acute phase and preferential increase of CD8⁺ T cells with activated phenotypes was observed in both acute and convalescent phases, which might be associated or correlated with elevated serum IL-7 and IL-15. Interestingly, peripheral Treg cells were significantly down-regulated throughout the disease course.

Conclusions/Significance

The remarkable decrease of CD4⁺ T cells, including Treg cells, during the acute phase of infection may contribute to the loss of immunological memory that are often observed in vaccine studies and recurrent human infection.

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi infection. It has been estimated that one billion people are at risk and one million new cases arise each year in Asian-pacific region. Despite of aggressive attempts to develop a prophylactic vaccine against scrub typhus during the last several decades, all approaches have failed to generate long lasting immunity. In addition, little is known about the immunological pathogenesis of scrub typhus. To understand the pathogenic mechanisms of this infectious disease, we extensively analyzed peripheral leukocytes, especially T cells, in Korean scrub typhus patients and compared with healthy volunteers. We observed neutrophilia and CD4⁺/T lymphopenia in the acute phase of infection, followed by proliferation of CD8⁺ T cells during the convalescent phase. Massive T cell apoptosis was detected in the acute phase and a preferential increase of CD8⁺ T cells with activated phenotypes was observed in both acute and convalescent phases. The remarkable decrease of CD4⁺ T cells, including Treg cells, during the acute phase of infection may contribute to the loss of immunological memory and generate helpless but unregulated cytotoxic T cell responses observed in vaccine studies and recurrent human infection.

Host cell/Orientia tsutsugamushi interactions: evolution and expression of syndecan-4 in Asian rodents (Rodentia, Muridae)

Scrub typhus is an acute febrile zoonotic disease and worldwide more than a billion people may be at risk for infection. Orientia tsutsugamushi, the causative agent of scrub typhus, is an obligate intracellular bacterium. Rodents are reported to be the primary reservoir hosts of the disease and according to the most recent surveys, all species within the Rattus sensu lato complex of the tribe Rattini are carriers of scrub typhus. There is no evidence that any of mouse (Mus) species serves as the primary reservoir of the bacterium even when occurring in sympatry with wild infected rats. This contrast in the host/syndecan-4 interactions between Rattini and Asian Murini may be due to intrinsic (i.e., genetic) differences. Herein we compare the sequence and expression levels of syndecan-4 (the putative cell receptor of O. tsutsugamushi) between Rattini species that are known to be natural reservoirs for the typhus agents, and Murini species that are not. Although it was not possible to conclusively link the structural variations detected in syndecan-4 with carrier status in either Rattini and Murini, our findings indicate the absence of a strong Orientia-mediated selective regime acting on gene structure. In contrast, variable spleen-specific syndecan-4 expression levels show a strong correlation between under-expression of syndecan-4 in Murini and seropositive Rattini, compared to seronegative Rattini rodents. We postulate that two divergent responses may be at work in Murini and Rattini, both linked with differential expression of syndecan-4: (i) reduced syndecan-4 transcription in Murini decreases the likelihood that the host cells will become infected by the Orientia bacterium, while (ii) reduced syndecan-4 expression in seropositive Rattini limits the pathogenicity of Orientia and consequently improves the longevity of the rat hosts. These patterns may underpin the poor carrier status of wild mice on the one hand, and the effective role of wild rats as reservoir hosts on the other.

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.

Orientia tsutsugamushi induced endothelial cell activation via the NOD1-IL-32 pathway

Orientia tsutsugamushi (OT), the causative agent of scrub typhus, is an obligate intracellular bacterium. In order to verify the inflammatory responses involved in the pathogenesis of scrub typhus, we assessed the cytokine profile of the human endothelial cell line, ECV304, after OT infection. We noted that CCL5, CCL17, IL-1alpha, IL-6, IL-8, IL-10, IL-15, TNF-alpha and TNF-beta were strongly induced in response to OT. Additionally, IL-32, the candidate modulator for the induction of IL-6 and IL-8, was increased significantly with OT infection and these increases coincided with NOD1 pathway activation. Thus, we hypothesized that NOD1 pathway and IL-32 might act on cytokine release in endothelial cells as a modulator of the inflammation caused by OT infection. NOD1 siRNA resulted in a reduction in IL-32 levels, and also reduced IL-1beta, IL-6, IL-8, and ICAM-1 expression in OT-infected ECV304 cells. These changes in IL-1beta, IL-6, IL-8, and ICAM-1 induced by NOD1 knockdown were reversed as the result of IL-32 treatment. This indicated that OT infection activated the NOD1 pathway followed by IL-32 secretion, thus resulting in the production and expression of IL-1beta, IL-6, IL-8, and ICAM-1. Therefore, IL-32 might perform a role upstream of the inflammatory reaction in endothelial cells of OT infection.

Mitogen-activated protein kinases are involved in tumor necrosis factor alpha production in macrophages infected with Orientia tsutsugamushi

Orientia tsutsugamushi, an obligatory intracellular bacterium, is the causative agent of scrub typhus. Here the role of MAPK in TNF-alpha production in macrophages after infection with O. tsutsugamushi has been investigated. ERK1/2, JNK, and p38 MAPK became phosphorylated in Orientia-stimulated macrophages. Selective inhibitors of MAPK cascades could all significantly reduce Orientia-stimulated TNF-alpha production. Orientia-stimulated TNF-alpha production via p38 and JNK pathways was regulated by a post-transcriptional mechanism, whereas the ERK pathway mainly controlled the transcriptional step of TNF-alpha gene expression during infection. In conclusion, our data indicate that MAPK signaling is required to induce maximal TNF-alpha production in macrophages during Orientia infection.

Activation of mitogen-activated protein kinases is involved in the induction of interferon beta gene in macrophages infected with Orientia tsutsugamushi

We investigated the role of MAPK in IFN-beta gene expression in macrophages after infection with Orientia tsutsugamushi. ERK1/2 became phosphorylated in Orientia-stimulated macrophages. Selective inhibition of ERK1/2 and p38 MAPK could all significantly reduce Orientia-stimulated IFN-beta mRNA expression. Orientia inactivation by heat abolished IFN-beta mRNA induction only, whereas cytochalasin D treatment completely blocked both IFN-beta and chemokine expression, suggesting requirement of cellular internalization by viable bacteria for IFN-beta gene induction. In conclusion, our data indicate that MAPK pathways are required to induce maximal IFN-beta gene expression in macrophages during Orientia infection.

Orientia tsutsugamushi bacteremia and cytokine levels in Vietnamese scrub typhus patients

Scrub typhus, caused by the intracellular bacterium Orientia tsutsugamushi, is a major cause of febrile illness in the Asia/Pacific region. Here, we implemented a novel real-time PCR and determined the relation of DNA target gene concentration with serum cytokine levels. The limit of detection of the novel real-time PCR was 1,062 DNA copies per ml of EDTA whole blood. Specificity was excellent as determined on a panel of blood- and skin-borne bacteria, including Rickettsia spp. as well as healthy Vietnamese blood donors. Bacterial DNA concentrations after 9 to 12 days from symptoms onset were significantly higher than in earlier or later periods (P<0.05). Significantly higher concentrations of gamma interferon (IFN-gamma) and interleukin-10 (IL-10) occurred during the acute phase of disease (<10 days from onset) as opposed to the convalescent phase (P<0.05). No significant differences were observed between the acute and the convalescent phases for tumor necrosis factor alpha (TNF-alpha) and IL-1beta concentrations. Regression analysis of DNA concentrations and cytokine levels identified a significant positive relationship for IL-10 (P<0.0182) but not for IFN-gamma, TNF-alpha, and IL-1beta. In conclusion, proinflammatory cytokines and IL-10 were differentially related to human bacteremia. They may thus be induced by different constituents of O. tsutsugamushi. As a future prospect in a clinical diagnostic laboratory, quantitative real-time PCR may serve as a reliable tool to monitor therapy and to detect treatment failure.

Kinetics of inflammatory cytokines in patients with scrub typhus receiving doxycycline treatment

OBJECTIVES

Animal models have suggested that various cytokines and chemokines play an important role in host defense against Orientia tsutsugamushi, however, human data are limited. We investigated the kinetics of inflammatory responses in patients with scrub typhus receiving doxycycline.

METHODS

Amongst patients being treated for scrub typhus, serially collected sera were tested for TNF-alpha, IFN-gamma, IL-2, IL-4, IL-5, and IL-10 by immunoassay. The mRNAs encoding TNF-alpha, IL-1 beta, IL-6, IL-8, IFN-gamma, IL-12, IL-2, IL-4, IL-5, and IL-10 were measured by semiquantitative reverse transcription-PCR.

RESULTS

The concentrations of TNF-alpha, IFN-gamma, and IL-10 of patients prior to doxycycline treatment were significantly higher than those of healthy volunteers. They decreased markedly within 24h after starting doxycycline. The mRNAs for IL-1 beta, TNF-alpha, IL-6, IFN-gamma, and IL-10 were highly expressed. Expression of mRNAs for IL-1 beta, IFN-gamma, and IL-10 decreased at day 2-7 of doxycycline treatment.

CONCLUSIONS

Inflammatory cytokines including TNF-alpha, IL-1 beta, and IL-6 are markedly upregulated in patients with scrub typhus. Doxycycline treatment rapidly reduces the production of these cytokines, corresponding to the early defervescence after the start of the treatment. The profiles of T cell-derived cytokines in patients with scrub typhus do not follow typical Th1 or Th2 patterns.

Orientia tsutsugamushi inhibits tumor necrosis factor α production by inducing interleukin 10 secretion in murine macrophages

Orientia tsutsugamushi (OT) is the causative agent of scrub typhus or Tsutsugamushi disease. We have previously reported that OT suppresses the production of inflammatory cytokines in murine macrophages. In this study, we examined the mechanism of OT to suppress the tumor necrosis factor alpha (TNF-alpha) production. J774 macrophages were preinfected with OT for various times and then treated with lipopolysaccharide (LPS) for 24 h. Preinfection by OT inhibited LPS-induced production of TNF-alpha, but did not affect the activation of NF-kappaB. This suppression was also induced by the conditioned medium (CM) from OT-infected macrophages. Interestingly, the CM contained a potent interleukin-10 (IL-10)-inducing factor that is active on activated macrophages. Therefore, the IL-10-inducing factor might enhance the negative-feedback mechanism ascribed to IL-10, to allow bacterial survival in the hostile environment of macrophages.

Differential expression of interferon-gamma and interferon-gamma-inducing cytokines in Thai patients with scrub typhus or leptospirosis

Interferon (IFN)-gamma plays an important role in the induction of a type 1 immune response against intracellular pathogens. We compared the plasma levels of IFN-gamma and IFN-gamma-inducing cytokines in adult Thai patients with scrub typhus, caused by the obligate intracellular bacterium Orientia tsutsugamushi, and leptospirosis, caused by extracellular Leptospira interrogans. IFN-gamma, interleukin (IL)-18, and IL-15 levels were elevated only in patients with scrub typhus, whereas IL-12p40 and tumor necrosis factor-alpha concentrations were elevated in both patient groups, although more so in scrub typhus. These data suggest a role for a cell-mediated immune response in host defense against O. tsutsugamushi.