Therapeutic modulation of V Set and Ig domain-containing 4 (VSIG4) signaling in immune and inflammatory diseases

Inflammation is the result of acute and chronic stresses, caused by emotional or physical trauma, or nutritional or environmental pollutants, and brings serious harm to human life and health. As an important cellular component of the innate immune barrier, the macrophage plays a key role in maintaining tissue homeostasis and promoting tissue repair by controlling infection and resolving inflammation. Several studies suggest that V Set and Ig domain-containing 4 is specifically expressed in tissue macrophages and is associated with a variety of inflammatory diseases. In this paper, we mainly summarize the recent research on V Set and Ig domain-containing 4 structures, functions, function and roles in acute and chronic inflammatory diseases, and provide a novel therapeutic avenue for the treatment of inflammatory diseases, including nervous system, urinary, respiratory and metabolic diseases.     

A mathematical model of pulmonary gas exchange under inflammatory stress

During a severe local or systemic inflammatory response, immune mediators target lung tissue. This process may lead to acute lung injury and impaired diffusion of gas molecules. Although several mathematical models of gas exchange have been described, none simulate acute lung injury following inflammatory stress. In view of recent laboratory and clinical progress in the understanding of the pathophysiology of acute lung injury, such a mathematical model would be useful. We first derived a partial differential equations model of gas exchange on a small physiological unit of the lung (≈25 alveoli), which we refer to as a respiratory unit (RU). We next developed a simple model of the acute inflammatory response and implemented its effects within a RU, creating a single RU model. Linking multiple RUs with various ventilation/perfusion ratios and taking into account pulmonary venous blood remixing yielded our lung-scale model. Using the lung-scale model, we explored the predicted effects of inflammation on ventilation/perfusion distribution and the resulting pulmonary venous partial pressure oxygen level during systemic inflammatory stresses. This model represents a first step towards the development of anatomically faithful models of gas exchange and ventilation under a broad range of local and systemic inflammatory stimuli resulting in acute lung injury, such as infection and mechanical strain of lung tissue.     

Hydrodynamic regulation of monocyte inflammatory response to an intracellular pathogen

Systemic bacterial infections elicit inflammatory response that promotes acute or chronic complications such as sepsis, arthritis or atherosclerosis. Of interest, cells in circulation experience hydrodynamic shear forces, which have been shown to be a potent regulator of cellular function in the vasculature and play an important role in maintaining tissue homeostasis. In this study, we have examined the effect of shear forces due to blood flow in modulating the inflammatory response of cells to infection. Using an in vitro model, we analyzed the effects of physiological levels of shear stress on the inflammatory response of monocytes infected with chlamydia, an intracellular pathogen which causes bronchitis and is implicated in the development of atherosclerosis. We found that chlamydial infection alters the morphology of monocytes and trigger the release of pro-inflammatory cytokines TNF-α, IL-8, IL-1β and IL-6. We also found that the exposure of chlamydia-infected monocytes to short durations of arterial shear stress significantly enhances the secretion of cytokines in a time-dependent manner and the expression of surface adhesion molecule ICAM-1. As a functional consequence, infection and shear stress increased monocyte adhesion to endothelial cells under flow and in the activation and aggregation of platelets. Overall, our study demonstrates that shear stress enhances the inflammatory response of monocytes to infection, suggesting that mechanical forces may contribute to disease pathophysiology. These results provide a novel perspective on our understanding of systemic infection and inflammation.     

A reduced mathematical model of the acute inflammatory response II. Capturing scenarios of repeated endotoxin administration

Bacterial lipopolysaccharide (LPS; endotoxin) is a potent immunostimulant that can induce an acute inflammatory response comparable to a bacterial infection. Experimental observations demonstrate that this biological response can be either blunted (tolerance) or augmented (potentiation) with repeated administration of endotoxin. Both phenomena are of clinical relevance. We show that a four-dimensional differential equation model of this response reproduces many scenarios involving repeated endotoxin administration. In particular, the model can display both tolerance and potentiation from a single parameter set, under different administration scenarios. The key determinants of the outcome of our simulations are the relative time-scales of model components. These findings support the hypothesis that endotoxin tolerance and other related phenomena can be considered as dynamic manifestations of a unified acute inflammatory response, and offer specific predictions related to the dynamics of this response to endotoxin.     

Hfe deficiency impairs pulmonary neutrophil recruitment in response to inflammation

Regulation of iron homeostasis and the inflammatory response are tightly linked to protect the host from infection. Here we investigate how imbalanced systemic iron homeostasis in a murine disease model of hereditary hemochromatosis (Hfe(-/-) mice) affects the inflammatory responses of the lung. We induced acute pulmonary inflammation in Hfe(-/-) and wild-type mice by intratracheal instillation of 20 μg of lipopolysaccharide (LPS) and analyzed local and systemic inflammatory responses and iron-related parameters. We show that in Hfe(-/-) mice neutrophil recruitment to the bronchoalveolar space is attenuated compared to wild-type mice although circulating neutrophil numbers in the bloodstream were elevated to similar levels in Hfe(-/-) and wild-type mice. The underlying molecular mechanisms are likely multifactorial and include elevated systemic iron levels, alveolar macrophage iron deficiency and/or hitherto unexplored functions of Hfe in resident pulmonary cell types. As a consequence, pulmonary cytokine expression is out of balance and neutrophils fail to be recruited efficiently to the bronchoalveolar compartment, a process required to protect the host from infections. In conclusion, our findings suggest a novel role for Hfe and/or imbalanced iron homeostasis in the regulation of the inflammatory response in the lung and hereditary hemochromatosis.     

Ablation of the complement C3a anaphylatoxin receptor causes enhanced killing of Pseudomonas aeruginosa in a mouse model of pneumonia

The C3a anaphylatoxin is a 77-amino acid peptide that is generated by enzymatic cleavage of C3 during activation of the complement system. C3a mediates numerous biological functions on binding its receptor (C3aR), which is present on both myeloid and nonmyeloid cells. To investigate the biological impact of C3a-mediated effects during acute pneumonia caused by Pseudomonas aeruginosa, we subjected C3aR-deficient mice and matched wild-type (WT) mice to P. aeruginosa pulmonary infection. C3aR-deficient mice exhibited increased killing of P. aeruginosa in the lungs, less dissemination of bacteria into the bloodstream, and a decreased inflammatory response to P. aeruginosa pulmonary infection compared with WT mice. To examine whether the absence of C3aR would impact the humoral immune response to P. aeruginosa, we immunized WT and C3aR-deficient mice via intraperitoneal injection with live P. aeruginosa. Both groups of mice developed similar levels of antibody specific to P. aeruginosa. Immunized C3aR-deficient and WT mice were subjected to P. aeruginosa pulmonary infection, and C3aR-deficient mice again displayed increased killing of P. aeruginosa in the lungs, less dissemination of bacteria into the bloodstream, and a decreased inflammatory response in the lungs. Collectively, these data demonstrate that independently of antibody production, absence of C3aR causes enhanced killing of P. aeruginosa despite a diminished inflammatory response in a mouse model of pneumonia.     

A simple model of pathogen-immune dynamics including specific and non-specific immunity

We present and analyze a model for the dynamics of the interactions between a pathogen and its host's immune response. The model consists of two differential equations, one for pathogen load, the other one for an index of specific immunity. Differently from other simple models in the literature, this model exhibits, according to the hosts' or pathogen's parameter values, or to the initial infection size, a rich repertoire of behaviours: immediate clearing of the pathogen through aspecific immune response; or acute infection followed by clearing of the pathogen through specific immune response; or uncontrolled infections; or acute infection followed by convergence to a stable state of chronic infection; or periodic solutions with intermittent acute infections. The model can also mimic some features of immune response after vaccination. This model could be a basis on which to build epidemic models including immunological features.     

TLR-2 and TLR-9 are sensors of apoptosis in a mouse model of doxorubicin-induced acute inflammation

Anthracycline antibiotics are inducers of an immunogenic form of apoptosis that has immunostimulatory properties because of the release of damage-associated molecular patterns. To study the mechanisms used by the innate immune system to sense this immunogenic form of cell death, we established an in vivo model of cell death induced by intraperitoneal injection of doxorubicin, a prototype of anthracyclines. The acute sterile inflammation in this model is characterized by rapid influx of neutrophils and increased levels of IL-6 and monocyte chemotactic protein-1. We demonstrate that acute inflammation induced by doxorubicin is associated with apoptosis of monocytes/macrophages and that it is specific for doxorubicin, an immunogenic chemotherapeutic. Further, the inflammatory response is significantly reduced in mice deficient in myeloid differentiation primary response gene 88 (MyD88), TLR-2 or TLR-9. Importantly, a TLR-9 antagonist reduces the recruitment of neutrophils induced by doxorubicin. By contrast, the acute inflammatory response is not affected in TRIF(Lps2) mutant mice and in TLR-3, TLR-4 and caspase-1 knockout mice, which shows that the inflammasome does not have a major role in doxorubicin-induced acute inflammation. Our findings provide important new insights into how the innate immune system senses immunogenic apoptotic cells and clearly demonstrate that the TLR-2/TLR-9-MyD88 signaling pathways have a central role in initiating the acute inflammatory response to this immunogenic form of apoptosis.     

Mast cells as sensors of cell injury through IL-33 recognition

In response to cell injury, caused, for example, by trauma, several processes must be initiated simultaneously to achieve an acute inflammatory response designed to prevent sustained tissue damage and infection and to restore and maintain tissue homeostasis. Detecting cell injury is facilitated by the fact that damaged cells release intracellular molecules not normally present in the extracellular space. However, potential underlying mechanisms for the recognition of endogenous danger signals released upon cell injury have yet to be elucidated. In this study, we demonstrate that mast cells, potent promoters of acute inflammation, play a key role in responding to cell injury by recognizing IL-33 released from necrotic structural cells. In an in vitro model of cell injury, this recognition was shown to involve the T1/ST2 receptor and result in the secretion of proinflammatory leukotrienes and cytokines by mouse mast cells. Remarkably, of all of the components released upon necrosis, our results show that IL-33 alone is a key component responsible for initiating proinflammatory responses in mast cells reacting to cell injury. Our findings identify IL-33 as a key danger signal released by necrotic structural cells capable of activating mast cells, thus providing novel insights concerning the role of mast cells as sensors of cell injury.     

A simple model of pathogen–immune dynamics including specific and non-specific immunity

We present and analyze a model for the dynamics of the interactions between a pathogen and its host’s immune response. The model consists of two differential equations, one for pathogen load, the other one for an index of specific immunity. Differently from other simple models in the literature, this model exhibits, according to the hosts’ or pathogen’s parameter values, or to the initial infection size, a rich repertoire of behaviours: immediate clearing of the pathogen through aspecific immune response; or acute infection followed by clearing of the pathogen through specific immune response; or uncontrolled infections; or acute infection followed by convergence to a stable state of chronic infection; or periodic solutions with intermittent acute infections. The model can also mimic some features of immune response after vaccination. This model could be a basis on which to build epidemic models including immunological features.     

Identification of Klebsiella pneumoniae virulence determinants using an intranasal infection model

Klebsiella pneumoniae is a Gram-negative enterobacterium that has historically been, and currently remains, a significant cause of human disease. It is a frequent cause of urinary tract infections and pneumonia, and subsequent systemic infections can have mortality rates as high as 60%. Despite its clinical significance, few virulence factors of K. pneumoniae have been identified or characterized. In this study we present a mouse model of acute K. pneumoniae respiratory infection using an intranasal inoculation method, and examine the progression of both pulmonary and systemic disease. Wild-type infection recapitulates many aspects of clinical disease, including significant bacterial growth in both the trachea and lungs, an inflammatory immune response characterized by dramatic neutrophil influx, and a steady progression to systemic disease with ensuing mortality. These observations are contrasted with an infection by an isogenic capsule-deficient strain that shows an inability to cause disease in either pulmonary or systemic tissues. The consistency and clinical accuracy of the intranasal mouse model proved to be a useful tool as we conducted a genetic screen to identify novel virulence factors of K. pneumoniae. A total of 4800 independent insertional mutants were evaluated using a signature-tagged mutagenesis protocol. A total of 106 independent mutants failed to be recovered from either the lungs or spleens of infected mice. Small scale independent infections proved to be helpful as a secondary screening method, as opposed to the more traditional competitive index assay. Those mutants showing verified attenuation contained insertions in loci with a variety of putative functions, including a large number of hypothetical open reading frames. Subsequent experiments support the premise that the central mechanism of K. pneumoniae pathogenesis is the production of a polysaccharide-rich cell surface that provides protection from the inflammatory response.     

A role for matrix metalloproteinase-9 in pathogenesis of urogenital Chlamydia muridarum infection in mice

Matrix metalloproteinases (MMPs) are a family of host-derived enzymes involved in the turnover of extracellular matrix (ECM) molecules and the processing of cytokines, chemokines and growth factors. We have previously reported that global inhibition of MMP in Chlamydia muridarum urogenital tract infection of susceptible strains of female mice impeded ascension of C. muridarum into the upper genital tract, blunted acute inflammatory responses and reduced the rate of formation of chronic disease. Because we have also observed that MMP-9 (also known as gelatinase B) is expressed in relatively large quantities in susceptible strains of mice in response to infection during acute phases of infection, we explored this further in a more selected fashion. We infected MMP-9 gene knockout mice and wild type controls intravaginally with C. muridarum. Both groups of mice had similar isolation rates from the lower urogenital tract but the absence of MMP-9 resulted in a slightly lower isolation rate in the upper genital tract, blunted acute inflammatory indices in the affected tissues and a reduced rate of formation of hydrosalpinx-a surrogate marker of infertility. These results imply that MMP-9 is involved in pathogenesis of chlamydial infection in this model possibly by amplifying inflammatory responses.     

Cellular Automata Modeling of Pulmonary Inflammation

Better understanding of the acute/chronic inflammation in airways is very important in order to avoid lung injuries for patients undergoing mechanical ventilation for treatment of respiratory problems. Local lung inflammation is triggered by many mechanisms within the lung, including pathogens. In this study, a cellular automata based model (CA) for pulmonary inflammation that incorporates biophysical processes during inflammatory responses was developed. The developed CA results in three possible outcomes related to homeostasis (healing), persistent infection, and resolved infection with high inflammation (inflamed state). The results from the model are validated qualitatively against other existing computational models. A sensitivity analysis was conducted on the model parameters and the outcomes were assessed. Overall, the model results showed possible outcomes that have been seen in clinical practice and animal models. The present model can be extended to include inflammation resulting from damage tissue and eventually to model inflammation resulting from acute lung injury and multiple organ dysfunction syndromes in critical illness and injury.     

Coordinated regulation of nutrient and inflammatory responses by STAMP2 is essential for metabolic homeostasis

Metabolic and inflammatory pathways crosstalk at many levels, and, while required for homeostasis, interaction between these pathways can also lead to metabolic dysregulation under conditions of chronic stress. Thus, we hypothesized that mechanisms might exist to prevent overt inflammatory responses during physiological fluctuations in nutrients or under nutrient-rich conditions, and we identified the six-transmembrane protein STAMP2 as a critical modulator of this integrated response system of inflammation and metabolism in adipocytes. Lack of STAMP2 in adipocytes results in aberrant inflammatory responses to both nutrients and acute inflammatory stimuli. Similarly, in whole animals, visceral adipose tissue of STAMP2(-/-) mice exhibits overt inflammation, and these mice develop spontaneous metabolic disease on a regular diet, manifesting insulin resistance, glucose intolerance, mild hyperglycemia, dyslipidemia, and fatty liver disease. We conclude that STAMP2 participates in integrating inflammatory and metabolic responses and thus plays a key role in systemic metabolic homeostasis.     

A mathematical model of parathyroid hormone response to acute changes in plasma ionized calcium concentration in humans

A complex bio-mechanism, commonly referred to as calcium homeostasis, regulates plasma ionized calcium (Ca²⁺) concentration in the human body within a narrow range which is crucial for maintaining normal physiology and metabolism. Taking a step towards creating a complete mathematical model of calcium homeostasis, we focus on the short-term dynamics of calcium homeostasis and consider the response of the parathyroid glands to acute changes in plasma Ca²⁺ concentration. We review available models, discuss their limitations, then present a two-pool, linear, time-varying model to describe the dynamics of this calcium homeostasis subsystem, the Ca-PTH axis. We propose that plasma PTH concentration and plasma Ca²⁺ concentration bear an asymmetric reverse sigmoid relation. The parameters of our model are successfully estimated based on clinical data corresponding to three healthy subjects that have undergone induced hypocalcemic clamp tests. In the first validation of this kind, with parameters estimated separately for each subject we test the model’s ability to predict the same subject’s induced hypercalcemic clamp test responses. Our results demonstrate that a two-pool, linear, time-varying model with an asymmetric reverse sigmoid relation characterizes the short-term dynamics of the Ca-PTH axis.     

A role for matrix metalloproteinase-9 in pathogenesis of urogenital Chlamydia muridarum infection in mice

Matrix metalloproteinases (MMPs) are a family of host-derived enzymes involved in the turnover of extracellular matrix (ECM) molecules and the processing of cytokines, chemokines and growth factors. We have previously reported that global inhibition of MMP in Chlamydia muridarum urogenital tract infection of susceptible strains of female mice impeded ascension of C. muridarum into the upper genital tract, blunted acute inflammatory responses and reduced the rate of formation of chronic disease. Because we have also observed that MMP-9 (also known as gelatinase B) is expressed in relatively large quantities in susceptible strains of mice in response to infection during acute phases of infection, we explored this further in a more selected fashion. We infected MMP-9 gene knockout mice and wild type controls intravaginally with C. muridarum. Both groups of mice had similar isolation rates from the lower urogenital tract but the absence of MMP-9 resulted in a slightly lower isolation rate in the upper genital tract, blunted acute inflammatory indices in the affected tissues and a reduced rate of formation of hydrosalpinx–a surrogate marker of infertility. These results imply that MMP-9 is involved in pathogenesis of chlamydial infection in this model possibly by amplifying inflammatory responses.     

Recognition of commensal microflora by toll-like receptors is required for intestinal homeostasis

Toll-like receptors (TLRs) play a crucial role in host defense against microbial infection. The microbial ligands recognized by TLRs are not unique to pathogens, however, and are produced by both pathogenic and commensal microorganisms. It is thought that an inflammatory response to commensal bacteria is avoided due to sequestration of microflora by surface epithelia. Here, we show that commensal bacteria are recognized by TLRs under normal steady-state conditions, and this interaction plays a crucial role in the maintenance of intestinal epithelial homeostasis. Furthermore, we find that activation of TLRs by commensal microflora is critical for the protection against gut injury and associated mortality. These findings reveal a novel function of TLRs-control of intestinal epithelial homeostasis and protection from injury-and provide a new perspective on the evolution of host-microbial interactions.     

3-Hydroxy kynurenine treatment controls T. cruzi replication and the inflammatory pathology preventing the clinical symptoms of chronic Chagas disease

Background

3-Hydroxy Kynurenine (3-HK) administration during the acute phase of Trypanosoma. cruzi infection decreases the parasitemia of lethally infected mice and improves their survival. However, due to the fact that the treatment with 3-HK is unable to eradicate the parasite, together with the known proapoptotic and immunoregulatory properties of 3-HK and their downstream catabolites, it is possible that the 3-HK treatment is effective during the acute phase of the infection by controlling the parasite replication, but at the same time suppressed the protective T cell response before pathogen clearance worsening the chronic phase of the infection. Therefore, in the present study, we investigated the effect of 3-HK treatment on the development of chronic Chagas’ disease.

Principal Findings

In the present study, we treated mice infected with T. cruzi with 3-HK at day five post infection during 5 consecutive days and investigated the effect of this treatment on the development of chronic Chagas disease. Cardiac functional (electrocardiogram) and histopathological studies were done at 60 dpi. 3-HK treatment markedly reduced the incidence and the severity of the electrocardiogram alterations and the inflammatory infiltrates and fibrosis in heart and skeletal muscle. 3-HK treatment modulated the immune response at the acute phase of the infection impairing the Th1- and Th2-type specific response and inducing TGF-β-secreting cells promoting the emergence of regulatory T cells and long-term specific IFN-γ secreting cells. 3-HK in vitro induced regulatory phenotype in T cells from T. cruzi acutely infected mice.

Conclusions

Our results show that the early 3-HK treatment was effective in reducing the cardiac lesions as well as altering the pattern of the immune response in experimental Chagas’ disease. Thus, we propose 3-HK as a novel therapeutic treatment able to control both the parasite replication and the inflammatory response.     

Quantitative Assessment of Human Neutrophil Migration Across a Cultured Bladder Epithelium

The recruitment of immune cells from the periphery to the site of inflammation is an essential step in the innate immune response at any mucosal surface. During infection of the urinary bladder, polymorphonuclear leukocytes (PMN; neutrophils) migrate from the bloodstream and traverse the bladder epithelium. Failure to resolve infection in the absence of a neutrophilic response demonstrates the importance of PMN in bladder defense. To facilitate colonization of the bladder epithelium, uropathogenic Escherichia coli (UPEC), the causative agent of the majority of urinary tract infections (UTIs), dampen the acute inflammatory response using a variety of partially defined mechanisms. To further investigate the interplay between host and bacterial pathogen, we developed an in vitro model of this aspect of the innate immune response to UPEC. In the transuroepithelial neutrophil migration assay, a variation on the Boyden chamber, cultured bladder epithelial cells are grown to confluence on the underside of a permeable support. PMN are isolated from human venous blood and are applied to the basolateral side of the bladder epithelial cell layers. PMN migration representing the physiologically relevant basolateral-to-apical direction in response to bacterial infection or chemoattractant molecules is enumerated using a hemocytometer. This model can be used to investigate interactions between UPEC and eukaryotic cells as well as to interrogate the molecular requirements for the traversal of bladder epithelia by PMN. The transuroepithelial neutrophil migration model will further our understanding of the initial inflammatory response to UPEC in the bladder.