Imbalance of circulating monocyte subsets and PD-1 dysregulation in Q fever endocarditis: the role of IL-10 in PD-1 modulation

Q fever endocarditis, a severe complication of Q fever, is associated with a defective immune response, the mechanisms of which are poorly understood. We hypothesized that Q fever immune deficiency is related to altered distribution and activation of circulating monocyte subsets. Monocyte subsets were analyzed by flow cytometry in peripheral blood mononuclear cells from patients with Q fever endocarditis and controls. The proportion of classical monocytes (CD14(+)CD16(-) monocytes) was similar in patients and controls. In contrast, the patients with Q fever endocarditis exhibited a decrease in the non-classical and intermediate subsets of monocytes (CD16(+) monocytes). The altered distribution of monocyte subsets in Q fever endocarditis was associated with changes in their activation profile. Indeed, the expression of HLA-DR, a canonical activation molecule, and PD-1, a co-inhibitory molecule, was increased in intermediate monocytes. This profile was not restricted to CD16(+) monocytes because CD4(+) T cells also overexpressed PD-1. The mechanism leading to the overexpression of PD-1 did not require the LPS from C. burnetii but involved interleukin-10, an immunosuppressive cytokine. Indeed, the incubation of control monocytes with interleukin-10 led to a higher expression of PD-1 and neutralizing interleukin-10 prevented C. burnetii-stimulated PD-1 expression. Taken together, these results show that the immune suppression of Q fever endocarditis involves a cross-talk between monocytes and CD4(+) T cells expressing PD-1. The expression of PD-1 may be useful to assess chronic immune alterations in Q fever endocarditis.

Intracellular bacteria interfere with dendritic cell functions: role of the type I interferon pathway

Dendritic cells (DCs) orchestrate host defenses against microorganisms. In infectious diseases due to intracellular bacteria, the inefficiency of the immune system to eradicate microorganisms has been attributed to the hijacking of DC functions. In this study, we selected intracellular bacterial pathogens with distinct lifestyles and explored the responses of monocyte-derived DCs (moDCs). Using lipopolysaccharide as a control, we found that Orientia tsutsugamushi, the causative agent of scrub typhus that survives in the cytosol of target cells, induced moDC maturation, as assessed by decreased endocytosis activity, the ability to induce lymphocyte proliferation and the membrane expression of phenotypic markers. In contrast, Coxiella burnetii, the agent of Q fever, and Brucella abortus, the agent of brucellosis, both of which reside in vacuolar compartments, only partly induced the maturation of moDCs, as demonstrated by a phenotypic analysis. To analyze the mechanisms used by C. burnetii and B. abortus to alter moDC activation, we performed microarray and found that C. burnetii and B. abortus induced a specific signature consisting of TLR4, TLR3, STAT1 and interferon response genes. These genes were down-modulated in response to C. burnetii and B. abortus but up-modulated in moDCs activated by lipopolysaccharide and O. tsutsugamushi. This transcriptional alteration was associated with the defective interferon-β production. This study demonstrates that intracellular bacteria specifically affect moDC responses and emphasizes how C. burnetii and B. abortus interfere with moDC activation and the antimicrobial immune response. We believe that comparing infection by several bacterial species may be useful for defining new pathways and biomarkers and for developing new treatment strategies.

Persistence of Coxiella burnetii, the agent of Q fever, in murine adipose tissue

Coxiella burnetii, the agent of Q fever, is known to persist in humans and rodents but its cellular reservoir in hosts remains undetermined. We hypothesized that adipose tissue serves as a C. burnetii reservoir during bacterial latency. BALB/c and C57BL/6 mice were infected with C. burnetii by the intraperitoneal route or the intracheal route. Adipose tissue was tested for the presence of C. burnetii several months after infection. C. burnetii was detected in abdominal, inguinal and dorsal adipose tissue 4 months post-infection, when no bacteria were detected in blood, liver, lungs and spleen, regardless of the inoculation route and independently of mouse strain. The transfer of abdominal adipose tissue from convalescent BALB/c mice to naïve immunodeficient mice resulted in the infection of the recipient animals. It is likely that C. burnetii infects adipocytes in vivo because bacteria were found in adipocytes within adipose tissue and replicated within in vitro-differentiated adipocytes. In addition, C. burnetii induced a specific transcriptional program in in-vivo and in vitro-differentiated adipocytes, which was enriched in categories associated with inflammatory response, hormone response and cytoskeleton. These changes may account for bacterial replication in in-vitro and chronic infection in-vivo. Adipose tissue may be the reservoir in which C. burnetii persists for prolonged periods after apparent clinical cure. The mouse model of C. burnetii infection may be used to understand the relapses of Q fever and provide new perspectives to the follow-up of patients.

Early sex-specific modulation of the molecular clock in trauma

BACKGROUND

Immune system biology and most physiologic functions are tightly linked to circadian rhythms. Time of day-dependent variations in many biologic parameters also play a fundamental role in the disease process. We previously showed that the genes encoding the peripheral molecular clock were modulated in a sex-dependent manner in Q fever.

METHODS

Here, we examined severe trauma patients at admission to the intensive care unit. Using quantitative real-time polymerase chain reaction, the whole-blood expression of the molecular clock components ARNTL, CLOCK, and PER2 was assessed in male and female trauma patients. Healthy volunteers of both sexes were used as controls.

RESULTS

We observed a significant overexpression of both ARNTL and CLOCK in male trauma patients.

CONCLUSION

We report, for the first time, the sex-related modulation of the molecular clock genes in the blood following severe trauma. These results emphasize the role of circadian rhythms in the immune response in trauma patients.

LEVEL OF EVIDENCE

Epidemiologic study, level IV.

Whole-cell MALDI-TOF mass spectrometry is an accurate and rapid method to analyze different modes of macrophage activation

MALDI-TOF is an extensively used mass spectrometry technique in chemistry and biochemistry. It has been also applied in medicine to identify molecules and biomarkers. Recently, it has been used in microbiology for the routine identification of bacteria grown from clinical samples, without preparation or fractionation steps. We and others have applied this whole-cell MALDI-TOF mass spectrometry technique successfully to eukaryotic cells. Current applications range from cell type identification to quality control assessment of cell culture and diagnostic applications. Here, we describe its use to explore the various polarization phenotypes of macrophages in response to cytokines or heat-killed bacteria. It allowed the identification of macrophage-specific fingerprints that are representative of the diversity of proteomic responses of macrophages. This application illustrates the accuracy and simplicity of the method. The protocol we described here may be useful for studying the immune host response in pathological conditions or may be extended to wider diagnostic applications.

Whole-cell MALDI-TOF mass spectrometry: a tool for immune cell analysis and characterization

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is widely used in proteomics. It has been recently demonstrated that MALDI-TOF MS can be used to identify and classify numerous bacterial species or subspecies. We applied MALDI-TOF MS directly to intact mammalian cells, and we found that this method is valuable to identify human circulating cells and cells involved in the immune response including macrophages. As macrophages are characterized by a high degree of plasticity in response to their microenvironment, we stimulated human macrophages with cytokines, bacterial products, and a variety of bacteria. We found that MALDI-TOF MS discriminated unstimulated and stimulated macrophages, and also detected multifaceted activation of macrophages. We conclude that whole-cell MALDI-TOF MS is an accurate method to identify various cell types and to detect subtle modifications in cell activity.

Overexpression of the Per2 gene in male patients with acute Q fever

The prevalence of Q fever is higher in men than in women. Because the expression of circadian clock genes differs in male and female mice infected with Coxiella burnetii, we hypothesized that circadian genes are differently modulated in men and women with Q fever. The expression of the Per2 gene was significantly (P = .01) increased in males with acute Q fever compared with healthy volunteers. No significant difference was observed in females. We showed for the first time that gender altered the expression of a circadian gene, Per2, in an infectious disease.

Whole-cell MALDI-TOF MS: a new tool to assess the multifaceted activation of macrophages

Whole-cell MALDI-TOF MS is routinely used to identify bacterial species in clinical samples. This technique has also proven to allow identification of intact mammalian cells, including macrophages. Here, we wondered whether this approach enabled the assessment human macrophages plasticity. The whole-cell MALDI-TOF spectra of macrophages stimulated with IFN-γ and IL-4, two inducers of M1 and M2 macrophage polarisation, consisted of peaks ranging from 2 to 12 kDa. The spectra of unstimulated and stimulated macrophages were clearly different. The fingerprints induced by the M1 agonists, IFN-γ, TNF, LPS and LPS+IFN-γ, and the M2 agonists, IL-4, TGF-β1 and IL-10, were specific and readily identifiable. Thus, whole-cell MALDI-TOF MS was able to characterise M1 and M2 macrophage subtypes. In addition, the fingerprints induced by extracellular (group B Streptococcus, Staphylococcus aureus) or intracellular (BCG, Orientia tsutsugamushi, Coxiella burnetii) bacteria were bacterium-specific. The whole-cell MALDI-TOF MS fingerprints therefore revealed the multifaceted activation of human macrophages. This approach opened a new avenue of studies to assess the immune response in the clinical setting, by monitoring the various activation patterns of immune cells in pathological conditions.

Defective monocyte dynamics in Q fever granuloma deficiency

BACKGROUND

The outcome of Q fever, an infectious disease caused by Coxiella burnetii, is associated with granuloma formation. Granulomas are present in patients with resolutive Q fever but are lacking in patients with chronic Q fever.

METHODS

Study of granuloma formation requires invasive approaches. Here, we took advantage of a recently described method that enables in vitro generation of human granulomas specific for C. burnetii.

RESULTS

Circulating mononuclear cells progressively accumulated around beads coated with C. burnetii extracts, and complete granulomas were generated in 8 days. Granuloma cells consisted of macrophages, lymphocytes, and, to a lesser extent, epithelioid cells and multinucleated giant cells. Early events that govern granuloma formation were studied using live-imaging microscopy. Monocytes migrated toward C. burnetii-coated beads independently of the presence of T lymphocytes and then recruited T lymphocytes. About 90% of patients with chronic Q fever failed to form granulomas. This deficiency was associated with defective migration of monocytes toward coated beads.

CONCLUSIONS

Monocytes were involved in the early stages of granuloma formation and recruited T lymphocytes to complete granuloma formation. This article describes a direct relationship between defective granuloma formation and defective migration of monocytes.

The gene expression analysis of blood reveals S100A11 and AQP9 as potential biomarkers of infective endocarditis

BACKGROUND

The diagnostic and prognostic assessments of infective endocarditis (IE) are challenging. To investigate the host response during IE and to identify potential biomarkers, we determined the circulating gene expression profile using whole genome microarray analysis.

METHODS AND RESULTS

A transcriptomic case-control study was performed on blood samples from patients with native valve IE (n = 39), excluded IE after an initial suspicion (n = 10) at patient's admission, and age-matched healthy controls (n = 10). Whole genome microarray analysis showed that patients with IE exhibited a specific transcriptional program with a predominance of gene categories associated with cell activation as well as innate immune and inflammatory responses. Quantitative real-time RT-PCR performed on a selection of highly modulated genes showed that the expression of the gene encoding S100 calcium binding protein A11 (S100A11) was significantly increased in patients with IE in comparison with controls (P<0.001) and patients with excluded IE (P<0.05). Interestingly, the upregulated expression of the S100A11 gene was more pronounced in staphylococcal IE than in streptococcal IE (P<0.01). These results were confirmed by serum concentrations of the S100A11 protein. Finally, we showed that in patients with IE, the upregulation of the aquaporin-9 gene (AQP9) was significantly associated with the occurrence of acute heart failure (P = 0.02).

CONCLUSIONS

Using transcriptional signatures of blood samples, we identified S100A11 as a potential diagnostic marker of IE, and AQP9 as a potential prognostic factor.

Foxp3(+)CD4(+)CD25(+) regulatory T cells are increased in patients with Coxiella burnetii endocarditis

Chronic Q fever, which principally manifests as endocarditis, is characterized by Coxiella burnetii persistence and an impaired cell-mediated immune response. The long-term persistence of pathogens has been associated with the expansion of regulatory T cells (Tregs), the CD4(+) T-cell subset that is characterized by the expression of CD25 and Foxp3. We investigated the presence of Tregs in patients with acute Q fever (n = 17), known to exhibit an efficient immune response, patients with Q fever endocarditis (n = 54) and controls (n = 27) by flow cytometry. The proportion of CD3(+) , CD4(+) and CD8(+) T cells was similar in controls and patients with Q fever. The percentage of CD4(+) T cells that expressed CD25 was similar in controls and patients with Q fever. The population of CD4(+) T cells that expressed both CD25 and Foxp3 was significantly (P < 0.001) increased in patients with Q fever endocarditis compared with controls. Our data suggest that the expansion of Tregs may be critical for the chronic evolution of Q fever.

Orientia tsutsugamushi stimulates an original gene expression program in monocytes: relationship with gene expression in patients with scrub typhus

Orientia tsutsugamushi is the causal agent of scrub typhus, a public health problem in the Asia-Pacific region and a life-threatening disease. O. tsutsugamushi is an obligate intracellular bacterium that mainly infects endothelial cells. We demonstrated here that O. tsutsugamushi also replicated in monocytes isolated from healthy donors. In addition, O. tsutsugamushi altered the expression of more than 4,500 genes, as demonstrated by microarray analysis. The expression of type I interferon, interferon-stimulated genes and genes associated with the M1 polarization of macrophages was significantly upregulated. O. tsutsugamushi also induced the expression of apoptosis-related genes and promoted cell death in a small percentage of monocytes. Live organisms were indispensable to the type I interferon response and apoptosis and enhanced the expression of M1-associated cytokines. These data were related to the transcriptional changes detected in mononuclear cells isolated from patients with scrub typhus. Here, the microarray analyses revealed the upregulation of 613 genes, which included interferon-related genes, and some features of M1 polarization were observed in these patients, similar to what was observed in O. tsutsugamushi-stimulated monocytes in vitro. This is the first report demonstrating that monocytes are clearly polarized in vitro and ex vivo following exposure to O. tsutsugamushi. These results would improve our understanding of the pathogenesis of scrub typhus, during which interferon-mediated activation of monocytes and their subsequent polarization into an M1 phenotype appear critical. This study may give us a clue of new tools for the diagnosis of patients with scrub typhus.

Global analysis of circulating immune cells by matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Background

MALDI-TOF mass spectrometry is currently used in microbiological diagnosis to characterize bacterial populations. Our aim was to determine whether this technique could be applied to intact eukaryotic cells, and in particular, to cells involved in the immune response.

Methodology/Principal Findings

A comparison of frozen monocytes, T lymphocytes and polymorphonuclear leukocytes revealed specific peak profiles. We also found that twenty cell types had specific profiles, permitting the establishment of a cell database. The circulating immune cells, namely monocytes, T lymphocytes and polymorphonuclear cells, were distinct from tissue immune cells such as monocyte-derived macrophages and dendritic cells. In addition, MALDI-TOF mass spectrometry was valuable to easily identify the signatures of monocytes and T lymphocytes in peripheral mononuclear cells.

Conclusions/Significance

This method was rapid and easy to perform, and unlike flow cytometry, it did not require any additional components such as specific antibodies. The MALDI-TOF mass spectrometry approach could be extended to analyze the cell composition of tissues and the activation state of immune cells.

The transcriptional programme of human heart valves reveals the natural history of infective endocarditis

Infective endocarditis (IE) is an infectious disease that is mainly caused by Staphylococcus aureus and Streptococcus sp. It usually leads to valvular destruction and vegetation formation. Its pathophysiology is badly understood and likely involves immune and coagulation systems with close interactions with the microorganism. Our objective was to evaluate host response by comparing transcriptional profiles of cardiac valves from IE patients with controls. Hierarchical clustering revealed a signature of IE consisting of 146 genes. Among the 89 up-regulated genes, we identified two genes strongly associated with IE: metalloproteinase 12 (MMP-12) and aquaporin-9, a member of the aquaglyceroporin membrane channel family. The up-regulation of MMP-12 gene is strengthened by the down-modulation of the gene encoding its inhibitor TIMP3. In addition, MMP-12 was expressed in macrophages infiltrating EI valves. We also found that aquaporin-9 was expressed in endothelial cells lining neo-vessel lumen, suggesting that aquaporin-9 might be associated with neovascularization of infected valves leading to tissue oedema secondary to the inflammatory process. The Gene Ontology annotation and the resulting functional classification showed that most up-regulated genes account for recruitment of inflammatory cells in vegetations, angiogenesis and remodelling of endocardium tissue. A network analysis confirmed the involvement of molecules related to the remodelling of endocardium tissue and angiogenesis in IE. It also evidenced the role of caspases, especially that of caspase-9 and intrinsic apoptotic pathway in IE. Based on this study we propose a scenario for the natural history of IE in humans. Some parameters identified in this work could become tools for measuring the disease activity and should be tested as biomarkers for diagnosis or prognosis assessment in future studies.

Adipose tissue serves as a reservoir for recrudescent Rickettsia prowazekii infection in a mouse model

Brill-Zinsser disease, the relapsing form of epidemic typhus, typically occurs in a susceptible host years or decades after the primary infection; however, the mechanisms of reactivation and the cellular reservoir during latency are poorly understood. Herein we describe a murine model for Brill-Zinsser disease, and use PCR and cell culture to show transient rickettsemia in mice treated with dexamethasone >3 months after clinical recovery from the primary infection. Treatment of similarly infected mice with cyclosporine failed to produce recrudescent bacteremia. Therapy with doxycycline for the primary infection prevented recrudescent bacteremia in most of these mice following treatment with dexamethasone. Rickettsia prowazekii (the etiologic agent of epidemic typhus) was detected by PCR, cell culture, and immunostaining methods in murine adipose tissue, but not in liver, spleen, lung, or central nervous system tissues of mice 4 months after recovery from the primary infection. The lungs of dexamethasone-treated mice showed impaired expression of beta-defensin transcripts that may be involved in the pathogenesis of pulmonary lesions. In vitro, R. prowazekii rickettsiae infected and replicated in the murine adipocyte cell line 3T3-L1. Collectively these data suggest a role for adipose tissue as a potential reservoir for dormant infections with R. prowazekii.

Intracellular life of Coxiella burnetii in macrophages

Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that is considered a potential biological weapon of category B. C. burnetii survives within myeloid cells by subverting receptor-mediated phagocytosis and preventing phagosome maturation. The intracellular fate of C. burnetii also depends on the functional state of myeloid cells. This review describes the mechanisms used by C. burnetii to circumvent uptake and trafficking events, and the role of cytokines on C. burnetii survival in myeloid cells.

New microbicidal functions of tracheal glands: defective anti-infectious response to Pseudomonas aeruginosa in cystic fibrosis

Tracheal glands (TG) may play a specific role in the pathogenesis of cystic fibrosis (CF), a disease due to mutations in the cftr gene and characterized by airway inflammation and Pseudomonas aeruginosa infection. We compared the gene expression of wild-type TG cells and TG cells with the cftr DeltaF508 mutation (CF-TG cells) using microarrays covering the whole human genome. In the absence of infection, CF-TG cells constitutively exhibited an inflammatory signature, including genes that encode molecules such as IL-1alpha, IL-beta, IL-32, TNFSF14, LIF, CXCL1 and PLAU. In response to P. aeruginosa, genes associated with IFN-gamma response to infection (CXCL10, IL-24, IFNgammaR2) and other mediators of anti-infectious responses (CSF2, MMP1, MMP3, TLR2, S100 calcium-binding proteins A) were markedly up-regulated in wild-type TG cells. This microbicidal signature was silent in CF-TG cells. The deficiency of genes associated with IFN-gamma response was accompanied by the defective membrane expression of IFNgammaR2 and altered response of CF-TG cells to exogenous IFN-gamma. In addition, CF-TG cells were unable to secrete CXCL10, IL-24 and S100A8/S100A9 in response to P. aeruginosa. The differences between wild-type TG and CF-TG cells were due to the cftr mutation since gene expression was similar in wild-type TG cells and CF-TG cells transfected with a plasmid containing a functional cftr gene. Finally, we reported an altered sphingolipid metabolism in CF-TG cells, which may account for their inflammatory signature. This first comprehensive analysis of gene expression in TG cells proposes a protective role of wild-type TG against airborne pathogens and reveals an original program in which anti-infectious response was deficient in TG cells with a cftr mutation. This defective response may explain why host response does not contribute to protection against P. aeruginosa in CF.

Rickettsial diseases: from Rickettsia-arthropod relationships to pathophysiology and animal models

Rickettsiae cause spotted fevers and typhus-related diseases in humans. Some of these diseases occur worldwide and are life-threatening, for example, epidemic typhus is still a major health problem despite the apparent efficiency of antibiotic treatment. In addition, Rickettsia prowazekii, the agent of epidemic typhus, and R. rickettsii, the agent of Rocky Mountain spotted fever, are microorganisms that could potentially be used as bioweapons to induce panic in the population. Rickettsiae are obligate intracellular bacteria in both vertebrate and invertebrate hosts, but rickettsial species differ in terms of association with arthropods, behavior of the vector to infection, pathophysiology and outcome of the disease. Understanding the pathogenic steps of rickettsioses is essential to develop protective strategies against these bacteriological threats. Unfortunately, the mechanisms involved in the pathogenesis of many rickettsioses are poorly characterized, and protective immunity is incompletely understood, in part because accurate animal models that mimic human diseases are lacking. In the past, murine models have been of limited value because infection of mice was without effect or resulted in erratic mortality. Recent studies have reported that rickettsial infection can be established in mice, depending on the genetic background of mice, the type of rickettsial species and the route of inoculation. These models may be useful for analyzing the pathogenesis of rickettsioses, especially epidemic typhus, evaluating new therapeutic molecules and vaccine candidates, and preventing future outbreaks.

Ameobal pathogen mimivirus infects macrophages through phagocytosis

Mimivirus, or Acanthamoeba polyphaga mimivirus (APMV), a giant double-stranded DNA virus that grows in amoeba, was identified for the first time in 2003. Entry by phagocytosis within amoeba has been suggested but not demonstrated. We demonstrate here that APMV was internalized by macrophages but not by non-phagocytic cells, leading to productive APMV replication. Clathrin- and caveolin-mediated endocytosis pathways, as well as degradative endosome-mediated endocytosis, were not used by APMV to invade macrophages. Ultrastructural analysis showed that protrusions were formed around the entering virus, suggesting that macropinocytosis or phagocytosis was involved in APMV entry. Reorganization of the actin cytoskeleton and activation of phosphatidylinositol 3-kinases were required for APMV entry. Blocking macropinocytosis and the lack of APMV colocalization with rabankyrin-5 showed that macropinocytosis was not involved in viral entry. Overexpression of a dominant-negative form of dynamin-II, a regulator of phagocytosis, inhibited APMV entry. Altogether, our data demonstrated that APMV enters macrophages through phagocytosis, a new pathway for virus entry in cells. This reinforces the paradigm that intra-amoebal pathogens have the potential to infect macrophages.

The giant (750 nm) double-stranded DNA virus Acanthamoeba polyphaga mimivirus (APMV) is likely responsible for pneumonia. We demonstrate here that APMV was internalized by macrophages but not by non-phagocytic cells, leading to productive replication. We also show that APMV invaded macrophages through phagocytosis. This is the first evidence that a virus is internalized by macrophages via a mechanism normally used by bacteria and parasites. This finding adds a supplementary pathway to already known strategies used by viruses to enter cells. This underlines that intra-amoebal pathogens also infect macrophages. Finally, we can hypothesize that APMV replicates within alveolar macrophages, leading to human and murine pneumonia.

Persistent Coxiella burnetii infection in mice overexpressing IL-10: an efficient model for chronic Q fever pathogenesis

Interleukin (IL)-10 increases host susceptibility to microorganisms and is involved in intracellular persistence of bacterial pathogens. IL-10 is associated with chronic Q fever, an infectious disease due to the intracellular bacterium Coxiella burnetii. Nevertheless, accurate animal models of chronic C. burnetii infection are lacking. Transgenic mice constitutively expressing IL-10 in macrophages were infected with C. burnetti by intraperitoneal and intratracheal routes and infection was analyzed through real-time PCR and antibody production. Transgenic mice exhibited sustained tissue infection and strong antibody response in contrast to wild-type mice; thus, bacterial persistence was IL-10-dependent as in chronic Q fever. The number of granulomas was low in spleen and liver of transgenic mice infected through the intraperitoneal route, as in patients with chronic Q fever. Macrophages from transgenic mice were unable to kill C. burnetii. C. burnetii–stimulated macrophages were characterized by non-microbicidal transcriptional program consisting of increased expression of arginase-1, mannose receptor, and Ym1/2, in contrast to wild-type macrophages in which expression of inducible NO synthase and inflammatory cytokines was increased. In vivo results emphasized macrophage data. In spleen and liver of transgenic mice infected with C. burnetii by the intraperitoneal route, the expression of arginase-1 was increased while microbicidal pathway consisting of IL-12p40, IL-23p19, and inducible NO synthase was depressed. The overexpression of IL-10 in macrophages prevents anti-infectious competence of host, including the ability to mount granulomatous response and microbicidal pathway in tissues. To our knowledge, this is the first efficient model for chronic Q fever pathogenesis.

The interaction between immune system and invading bacteria is sufficient to eradicate microorganisms in the majority of bacterial infections, but the suppression of the microbicidal response leads to reactivation or chronic evolution of infections and to bacterial persistence. Coxiella burnetii, an obligate intracellular bacterium, is responsible for Q fever. This infectious disease is characterized by a primary infection that may become chronic as endocarditis in patients with valvular damage and immunocompromised patients. Clinical and in vitro studies have suggested a role for interleukin-10 in the chronic evolution of Q fever. However, an efficient mouse model for chronic Q fever pathogenesis, which could serve as a platform for anti–C. burnetii drug or immunotherapy development, is lacking. Here we use transgenic mice with constitutive overexpression of interleukin-10 in the macrophage lineage to study C. burnetii infection. We report an efficient mouse model for chronic Q fever pathogenesis, which associates high levels of specific antibodies, sustained tissue infection, and reduced granuloma formation, as in human Q fever. We also find an anti-inflammatory transcriptional program and altered expression of chemokines in infected tissues.

The uptake of apoptotic cells drives Coxiella burnetii replication and macrophage polarization: a model for Q fever endocarditis

Patients with valvulopathy have the highest risk to develop infective endocarditis (IE), although the relationship between valvulopathy and IE is not clearly understood. Q fever endocarditis, an IE due to Coxiella burnetii, is accompanied by immune impairment. Patients with valvulopathy exhibited increased levels of circulating apoptotic leukocytes, as determined by the measurement of active caspases and nucleosome determination. The binding of apoptotic cells to monocytes and macrophages, the hosts of C. burnetii, may be responsible for the immune impairment observed in Q fever endocarditis. Apoptotic lymphocytes (AL) increased C. burnetii replication in monocytes and monocyte-derived macrophages in a cell-contact dependent manner, as determined by quantitative PCR and immunofluorescence. AL binding induced a M2 program in monocytes and macrophages stimulated with C. burnetii as determined by a cDNA chip containing 440 arrayed sequences and functional tests, but this program was in part different in monocytes and macrophages. While monocytes that had bound AL released high levels of IL-10 and IL-6, low levels of TNF and increased CD14 expression, macrophages that had bound AL released high levels of TGF-beta1 and expressed mannose receptor. The neutralization of IL-10 and TGF-beta1 prevented the replication of C. burnetii due to the binding of AL, suggesting that they were critically involved in bacterial replication. In contrast, the binding of necrotic cells to monocytes and macrophages led to C. burnetii killing and typical M1 polarization. Finally, interferon-gamma corrected the immune deactivation induced by apoptotic cells: it prevented the replication of C. burnetii and re-directed monocytes and macrophages toward a M1 program, which was deleterious for C. burnetii. We suggest that leukocyte apoptosis associated with valvulopathy may be critical for the pathogenesis of Q fever endocarditis by deactivating immune cells and creating a favorable environment for bacterial persistence.

Monocyte deactivation in neutropenic acute respiratory distress syndrome patients treated with granulocyte colony-stimulating factor

INTRODUCTION

In severely neutropenic septic acute respiratory distress syndrome (ARDS) patients, macrophages and monocytes are the last potentially remaining innate immune cells. We have previously shown, however, a deactivation of the alveolar macrophage in neutropenic septic ARDS patients. In the present study, we tried to characterize in vitro monocyte baseline cytokine production and responsiveness to lipopolysaccharide exposure.

METHODS

Twenty-two consecutive patients with cancer were prospectively enrolled into a prospective observational study in an intensive care unit. All patients developed septic ARDS and were divided into two groups: neutropenic patients (n = 12) and non-neutropenic patients (n = 10). All of the neutropenic patients received granulocyte colony-stimulating factor whereas no patient in the non-neutropenic group received granulocyte colony-stimulating factor. We compared monocytes from neutropenic patients with septic ARDS with monocytes from non-neutropenic patients and healthy control individuals (n = 10). Peripheral blood monocytes were cultured, and cytokine levels (TNFalpha, IL-1beta, IL-6, IL-10, and IL-1 receptor antagonist) were assayed with and without lipopolysaccharide stimulation.

RESULTS

TNFalpha, IL-6, IL-10 and IL-1 receptor antagonist levels in unstimulated monocytes were lower in neutropenic patients compared with non-neutropenic patients. Values obtained in the healthy individuals were low as expected, comparable with neutropenic patients. In lipopolysaccharide-stimulated monocytes, both inflammatory and anti-inflammatory cytokine production were significantly lower in neutropenic patients compared with non-neutropenic patients and control individuals.

CONCLUSION

Consistent with previous results concerning alveolar macrophage deactivation, we observed a systemic deactivation of monocytes in septic neutropenic ARDS. This deactivation participates in the overall immunodeficiency and could be linked to sepsis, chemotherapy and/or the use of granulocyte colony-stimulating factor.

Coxiella burnetiiinfection in C57BL/6 mice aged 1 or 14 months

The objective of this study was to investigate the effects of age on infection with Coxiella burnetii, the agent of Q fever. Bacterial burden and granuloma number were increased in the spleens of 14-month-old as compared with 1-month-old mice. This increase was not the result of an anti-inflammatory macrophage response, because inflammatory and anti-inflammatory cytokines were induced in macrophages from young mice but were repressed in mature mice. In addition, macrophage microbicidal competence was similar in mature and young mice. These results suggest the importance of individual host factors in the pathophysiology of an infectious disease such as Q fever.

A murine model of infection with Rickettsia prowazekii: implications for pathogenesis of epidemic typhus

Epidemic typhus remains a major disease threat, furthermore, its etiologic agent, Rickettsia prowazekii, is classified as a bioterrorism agent. We describe here a murine model of epidemic typhus that reproduced some features of the human disease. When BALB/c mice were inoculated intravenously with R. prowazekii (Breinl strain), they survived but did not clear R. prowazekii infection. Immunohistological analysis of tissues and quantitative PCR showed that R. prowazekii was present in blood, liver, lungs and brain 1 day after infection and persisted for at least 9 days. Importantly, infected mice developed interstitial pneumonia, with consolidation of the alveoli, hemorrhages in lungs, multifocal granulomas in liver, and hemorrhages in brain, as seen in humans. Circulating antibodies directed against R. prowazekii were detected at day 4 post-infection and steadily increased for up to 21 days, demonstrating that R. prowazekii lesions were independent of humoral immune response. R. prowazekii-induced lesions were associated with inflammatory response, as demonstrated by elevated levels of inflammatory cytokines including interferon-gamma, tumor necrosis factor and the CC chemokine RANTES in the lesions. We concluded that the BALB/c mouse strain provides a useful model for studying the pathogenic mechanisms of epidemic typhus and its control by the immune system.

Coxiella burnetii stimulates production of RANTES and MCP-1 by mononuclear cells: modulation by adhesion to endothelial cells and its implication in Q fever

Q fever is an infectious disease caused by Coxiella burnetii, which may become chronic when cytokine network and cell-mediated immune responses are altered. Chemokines, such as Regulated upon Activation, Normal T cell Expressed and Secreted (RANTES, CCL5) and Monocyte Chemoattractant Protein-1 (MCP-1, CCL2), are specialized in the trafficing of peripheral blood mononuclear cells (PBMC), and are associated with T cell polarization that is essential for intracellular survival of C. burnetii. The present study investigated whether or not the infection status (no infection and acute or chronic infection with C. burnetii) of donors, affected the production of the two chemokines by PBMC with or without stimulation with virulent and avirulent C. burnetii. Our findings indicate that in vitro exposure to virulent or avirulent C. burnetii stimulated the production of RANTES and MCP-1 in PBMC obtained from healthy adults. The co-cultivation of endothelial cells and human PBMC resulted in an increased production of MCP-1 and the up-regulation of RANTES, which were contact-dependent. Unstimulated PBMC from patients with acute or chronic Q fever overproduced MCP-1. Interestingly, the addition of C. burnetii resulted in an increased production of RANTES and MCP-1 by PBMC obtained from patients with chronic Q fever, and the co-cultivation of PBMC with endothelial cells amplified increased production of chemokines. Circulating levels of RANTES and MCP-1 were also increased in chronic Q fever. We suggest that the overproduction of RANTES and MCP-1 secondary to the contact of PBMC with endothelium may perpetuate exaggerated inflammatory responses leading to inappropriate PBMC trafficking and to the pathogenesis of Q fever.

The two faces of interleukin 10 in human infectious diseases

Resolution of infections depends on the host's ability to mount a protective immune response. However, an exacerbated response to infections may result in deleterious lesions. Consequently, immunoregulatory mechanisms are needed to control immune response and prevent infection-associated lesions. Interleukin 10 may be a major regulator of innate and adaptive immunity in vitro and in animals, but its role in human infections is still unclear. Review of the published work reveals wide involvement of interleukin 10 in two major features of infectious diseases. On one hand, interleukin 10 prevents the development of immunopathological lesions that result from exacerbated protective immune response to acute and chronic infections. On the other hand, it is critically involved in persistence of bacteria and viruses by interfering with innate and adaptive protective immunity. Moreover, infections induce the expansion of interleukin-10-producing regulatory cells that are involved in protection against allergic diseases.

Deficient Transendothelial Migration of Leukocytes in Q Fever: The Role Played by Interleukin‐10

Chronic Q fever is characterized by deficient cell-mediated immune response, lack of granulomas, and dysregulation of the cytokine network. Altered transendothelial migration (TM) of peripheral-blood mononuclear cells might account for impaired immune response. TM of lymphocytes and monocytes was decreased in patients with Q fever endocarditis, compared with that in patients recovering from acute Q fever and in control subjects. This defect is related to interleukin (IL)-10, a cytokine involved in the chronic evolution of the disease; neutralizing anti-IL-10 antibodies corrected TM of mononuclear cells from patients with Q fever endocarditis. IL-10 may account for deficient protective immunity in patients with Q fever endocarditis by impairing TM.

Link between impaired maturation of phagosomes and defective Coxiella burnetii killing in patients with chronic Q fever

Q fever is caused by Coxiella burnetii, a bacterium that survives in monocytes/macrophages by resisting their natural microbicidal activity. Because the link between bacterial killing and phagosome maturation has yet to be demonstrated, we evaluated responses in monocytes from both immunologically naive control subjects and patients with various manifestations of Q fever. Monocytes from patients with chronic Q fever in evolution, who do not control the infection, exhibited defective phagosome maturation and impaired C. burnetii killing. Both responses were stimulated in patients recovering from Q fever. Phagosome maturation and C. burnetii killing were significantly correlated. Defective phagosome maturation and impaired C. burnetii killing were induced by adding interleukin (IL)-10 to monocytes from convalescent patients and were restored by IL-10 neutralization in chronic Q fever in evolution. We show that phagosome maturation and microbial killing are linked in Q fever and that IL-10 regulates both features of microbicidal activity.

Lipopolysaccharide fromCoxiella burnetiiIs Involved in Bacterial Phagocytosis, Filamentous Actin Reorganization, and Inflammatory Responses through Toll-Like Receptor 4

The role of Toll-like receptors (TLRs) in the recognition of extracellular and facultative intracellular bacteria by the innate immune system has been extensively studied, but their role in the recognition of obligate intracellular organisms remains unknown. Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that specifically inhabits monocytes/macrophages. We showed in this study that C. burnetii LPS is involved in the uptake of virulent organisms by macrophages but not in that of avirulent variants. The uptake of virulent organisms was dependent on TLR4 because it was reduced in macrophages from TLR4(-/-) mice. In addition, LPS was responsible for filamentous actin reorganization induced by virulent C. burnetii, which was prevented in TLR4(-/-) macrophages. In contrast, the intracellular fate of C. burnetii was not affected in TLR4(-/-) macrophages, suggesting that TLR4 does not control the maturation of C. burnetii phagosome and the microbicidal activity of macrophages. These results are consistent with in vivo experiments because the pattern of tissue infection and the clearance of C. burnetii were similar in wild-type and TLR4(-/-) mice. We also showed that the number of granulomas was decreased in the liver of infected TLR4(-/-) mice, and the formation of splenic granulomas was only transient. The impaired formation of granulomas was associated with decreased production of IFN-gamma and TNF. Taken together, these results demonstrate that TLR4 controls early events of C. burnetii infection such as macrophage phagocytosis, granuloma formation, and cytokine production.

Effect of sex on Coxiella burnetii infection: protective role of 17beta-estradiol

Q fever is a zoonosis caused by Coxiella burnetii and recently has been recognized as a potential agent of bioterrorism. In Q fever, men are symptomatic more often than women, despite equal seroprevalence. We hypothesized that sex hormones play a role in the pathogenesis of C. burnetii infection. When C57/BL6 mice were injected with C. burnetii, bacteria load and granuloma numbers were lower in females than in males. Ovarectomized mice showed increased bacteria load in the spleen and the liver, similar to that found in males. The granuloma number was also increased in ovarectomized mice and reached the levels found in males. Tissue infection and granulomatous response are largely under the control of estrogens: treatment of ovarectomized mice with 17beta-estradiol reduced both bacteria loads and granuloma numbers. These results show that sex hormones control host response to C. burnetii infection and may account for host-dependent clinical presentation of Q fever.

Interleukin-4 induces Coxiella burnetii replication in human monocytes but not in macrophages

Coxiella burnetii, an obligate intracellular bacterium, is the agent of Q fever. The chronic disease is characterized by impaired cell-mediated immune response and microbicidal activity of monocytes. We hypothesized that interleukin(IL)-4, a Th2 cytokine, interferes with the fate of C. burnetii inside monocytes. C. burnetii survived without multiplication in resting monocytes, but replicated in IL-4-treated monocytes. The effect of IL-4 is specific for monocytes since IL-4 did not stimulate C. burnetii replication in monocyte-derived macrophages. The effects of IL-4 on bacterial replication and on tumor necrosis factor (TNF) production in monocytes were apparently not related. Although IL-4 inhibited C. burnetii-stimulated release of TNF, the addition of recombinant TNF to IL-4-treated monocytes did not prevent the IL-4 effect. These results suggest that IL-4 enables monocytes to support C. burnetii replication and a Th2 polarization of immune response that may interfere with immune control of Q fever.

Coxiella burnetii avoids macrophage phagocytosis by interfering with spatial distribution of complement receptor 3

Phagocytosis is a highly localized event requiring the formation of spatially and temporally restricted signals. Numerous microorganisms have taken advantage of this property to invade host cells. Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that has developed a survival strategy in macrophages based on subversion of receptor-mediated phagocytosis. The uptake of C. burnetii is mediated by alpha(v)beta(3) integrin and is restricted by impaired cross-talk of alpha(v)beta(3) integrin and complement receptor 3 (CR3) (CD11b/CD18). In this study, we showed that CR3 molecules remained outside the pseudopodal extensions induced by C. burnetii in THP-1 monocytes, although alpha(v)beta(3) integrin was present in the pseudopods. Chemoattractants such as RANTES restored CR3 localization to the front of pseudopodal extensions and increased C. burnetii phagocytosis, demonstrating that the localization of CR3 is critical for bacterial uptake. In addition, monocyte activation due to the expression of HIV-1 Nef protein also restored CR3-mediated phagocytosis of C. burnetii by allowing CR3 redistribution toward bacterial-induced pseudopods. The redistribution of CR3 and increased C. burnetii phagocytosis in THP-1 cells stimulated by RANTES or expressing Nef were associated with the inhibition of intracellular replication of C. burnetii. Hence, the localization of CR3 is critical for bacterial phagocytosis and also for the control of bacterial replication. This study describes a nonpreviously reported strategy of phagocytosis subversion by intracellular pathogens based on altered localization of monocyte receptors.

Molecular adaptation to hibernation: the hemoglobin of Dryomys nitedula

The oxygen binding properties of Dryomys nitedula hemoglobin (Hb) were investigated as a function of pH both in the absence and in the presence of its physiological cofactors (i.e. chloride ions and 2,3-biphosphoglyceric acid) and at different temperatures. Moreover, the alpha- and beta-chains of the Dryomys Hb were partially sequenced. The results obtained show that the effects of Bohr protons, chloride ions, organic phosphates and temperature are significantly lower for Dryomys Hb than for human Hb. Thus, the increase in Hb oxygen affinity, resulting from the reduction of red cell organic phosphates and body temperature that occurs during hibernation, is advantageous for loading oxygen at the lung level without compromising oxygen release at the tissues, as could occur if Dryomys Hb had similar functional properties to those of other non-hibernating mammals. Furthermore, it is possible that the reduced Bohr effect may moderate the potential effects of increased CO(2) associated with prolonged apnea on the loading and unloading of oxygen. Moreover, the overall heat of oxygenation (Delta H) for Dryomys Hb is much less exothermic than that of the human Hb and it is completely independent of the 2,3-biphosphoglyceric acid concentration.

Dysregulation of cytokines in acute Q fever: role of interleukin-10 and tumor necrosis factor in chronic evolution of Q fever

Q fever manifests as primary infection or acute Q fever and may become chronic in patients with underlying valvulopathy. Because Coxiella burnetii infection depends on host response, we measured tumor necrosis factor (TNF), interleukin (IL)-6, IL-12, and IL-10 in patients with different clinical presentations of acute Q fever. Compared with control subjects, patients with uncomplicated acute Q fever exhibited increased release of the 4 cytokines. Their amounts were higher in patients with hepatitis than in patients with fever or pneumonia. In patients with valvulopathy, who exhibited the highest risk of chronic evolution, the amounts of TNF and IL-10 were higher than in patients without valvulopathy. TNF production was specifically enhanced in patients who developed Q fever endocarditis. These results show that acute Q fever is associated with cytokine overproduction. Persistent TNF amounts were associated with the occurrence of endocarditis in patients with valvulopathy, and that may be a marker of chronic evolution of Q fever.

Bartonella quintana bacteremia and overproduction of interleukin-10: model of bacterial persistence in homeless people

Chronic asymptomatic bacteremia caused by Bartonella quintana occurs in homeless people, but its pathophysiology is unknown. We investigated homeless people with bacteremia to determine whether the persistence of B. quintana is associated with a specific immune profile. Homeless people without B. quintana infection exhibited an inflammatory profile--levels of circulating markers of leukocyte activation (soluble interleukin [IL]-2 receptor and neopterin) and cytokines released by mononuclear cells (tumor necrosis factor, IL-1beta, IL-6, and IL-10) were significantly higher than levels in healthy control subjects. In contrast, homeless people with B. quintana bacteremia exhibited specific increases in IL-10 secretion by mononuclear cells. This overproduction of IL-10 was associated with an attenuated inflammatory profile. The depressed inflammatory response was specific of bacteremia, because patients with specific antibodies and without bacteremia had responses similar to those of homeless people. The overproduction of IL-10 and attenuated inflammatory response may account for the persistence of B. quintana in homeless people.

IFN-gamma-induced apoptosis and microbicidal activity in monocytes harboring the intracellular bacterium Coxiella burnetii require membrane TNF and homotypic cell adherence

IFN-gamma is critical for the protection against intracellular bacteria through activation of the antimicrobial machinery of phagocytes. Coxiella burnetii, the etiological agent of Q fever, is a strictly intracellular bacterium that inhabits monocytes/macrophages. We previously showed that IFN-gamma induced C. burnetii killing by promoting the apoptosis of infected monocytes. We show in this study that IFN-gamma-induced apoptosis of infected monocytes was characterized by a time- and dose-dependent activation of caspase-3. IFN-gamma-mediated caspase-3 activation and C. burnetii killing depend on the expression of membrane TNF. Indeed, TNF was transiently expressed on the cell surface of infected monocytes a few hours after IFN-gamma treatment. In addition, anti-TNF Abs inhibited IFN-gamma-mediated caspase-3 activation whereas soluble TNF had no effect on infected cells. Concomitantly, IFN-gamma induced homotypic adherence of C. burnetii-infected monocytes. The latter required the interaction of beta(2) integrins with CD54. When adherence was disrupted by pipetting, by a combination of Abs specific for CD11b, CD18, and CD54, or by an antisense oligonucleotide targeting CD18 mRNA, both cell apoptosis and bacterial killing induced by IFN-gamma were inhibited. Thus, adherence via CD54/beta(2) integrins together with membrane TNF are required to eliminate C. burnetii-infected cells through cell contact-dependent apoptosis. Our results reveal a new component of the antimicrobial arsenal mobilized by IFN-gamma against infection by intracellular bacteria.

Early postoperative compensatory anti-inflammatory response syndrome is associated with septic complications after major surgical trauma in patients with cancer

BACKGROUND

Patients who undergo major surgery for cancer are at high risk of postoperative infection. Postoperative immunosuppression may be due to dysregulation of cytokine production. The aim of this study was to investigate the association between changes in serum proinflammatory and anti-inflammatory cytokine concentrations and postoperative septic complications after major surgery.

METHODS

Serial blood samples were collected from 30 consecutive patients for determination of serum cytokine levels. Healthy volunteers were used as the control group.

RESULTS

Eleven patients developed no complications (group 1), 14 developed sepsis or severe sepsis (group 2), and five developed septic shock (group 3). On day 1 the patients in groups 2 and 3 had significantly higher levels of interleukin (IL) 6 than those in group 1. IL-6 levels remained high until day 5. Tumour necrosis factor (TNF), IL-1, interferon (IFN) gamma and IL-12 levels were not affected by surgical trauma or by the occurrence of septic complications. After operation the circulating IL-1 receptor antagonist (IL-1ra) concentration was increased in all groups, but patients in group 3 had significantly higher levels of IL-1ra than those in group 1. IL-1ra levels correlated with IL-6 levels. The pattern of IL-10 levels was similar to that of IL-1ra levels.

CONCLUSION

Serum concentrations of proinflammatory cytokines (TNF, IL-1, IFN-gamma and IL-12) were not affected by operation or the occurrence of septic complications. The postoperative increase in IL-6 concentration was associated with septic morbidity, while raised IL-1ra concentration was associated with postoperative septic shock.