Elastase release by transmigrating neutrophils deactivates endothelial-bound SDF-1alpha and attenuates subsequent T lymphocyte transendothelial migration

Tagetes erecta L.: A traditional medicine effective in inflammatory process treatment

ETHNOPHARMACOLOGICAL RELEVANCE

Tagetes erecta L. (Asteraceae), popularly known as Aztec Marigold, is used in folk medicine to treat several ailments including inflammatory processes. Despite its historical use, the specific mechanisms through which it may modulate inflammation, particularly its effects on neutrophils and macrophages activation, have not yet been completely investigated.

AIM OF THE STUDY

This study aimed to elucidate the anti-inflammatory mechanism of the hydroalcoholic extract obtained from T. erecta flowers, focusing on its role in the regulation of neutrophil and macrophage functions.

MATERIAL AND METHODS

The production of TNF, IL-6, CXCL-1, IL-1β, IL-10 (ELISA) and NO (Griess reaction), adhesion molecule expression (CD62L, CD49d and CD18, flow cytometry), and chemotaxis were analyzed in vitro using oyster glycogen-recruited peritoneal neutrophils or macrophages (RAW 264.7) stimulated with lipopolysaccharide (LPS) and treated with the extract (1, 10 or 100 μg/mL). The resolution of inflammation was accessed by efferocytosis assay. The in vivo anti-inflammatory activity was investigated using carrageenan-induced inflammation in the subcutaneous tissue of male Swiss mice orally treated with the T. erecta extract (30, 100 or 300 mg/kg). The leukocyte influx (optical microscopy), secretion of chemical mediators (TNF, IL-6 and IL-1β, ELISA) and protein exudation (Bradford reaction) were quantified in the inflamed exudate.

RESULTS

In vitro studies demonstrated that the extract inhibited neutrophil chemotaxis and reduced the production and/or release of cytokines (TNF, IL-1β, CXCL1, and IL-6) as well as nitric oxide (NO) by neutrophils and macrophages when stimulated with LPS. Neutrophils treated with LPS and incubated with the extract showed an increase in CD62L expression, which leads to the impairment of neutrophil adhesion. The extract also enhanced efferocytosis of apoptotic neutrophils by macrophages, which was accompanied by increased IL-10 secretion and decreased TNF levels. In vivo studies yielded similar results, showing reduction in neutrophil migration, protein exudation, and cytokine release (TNF, IL-6, and IL-1β).

CONCLUSIONS

Together, the data herein obtained shows that T. erecta flower extract has anti-inflammatory effects by regulating inflammatory mediators, limiting neutrophil migration, and promoting efferocytosis. The in vivo results suggest that an herbal medicine made with T. erecta could represent an interesting pharmacological tool for the treatment of acute inflammatory condition.

Abnormal adenosine metabolism of neutrophils inhibits airway inflammation and remodeling in asthma model induced by Aspergillus fumigatus

BACKGROUND

Neutrophils consume a large amount of energy when performing their functions. Compared with other white blood cells, neutrophils contain few mitochondria and mainly rely on glycolysis and gluconeogenesis to produce ATP. The inflammatory site is hypoxic and nutrient poor. Our aim is to study the role of abnormal adenosine metabolism of neutrophils in the asthmatic airway inflammation microenvironment.

METHOD

In this study, an asthma model was established by intratracheal instillation of Aspergillus fumigatus extract in Ecto-5'-Nucleotidase (CD73) gene-knockout and wild-type mice. Multiple analyses from bronchoalveolar lavage fluid (BALF) were used to determine the levels of cytokines and chemokines. Immunohistochemistry was used to detect subcutaneous fibrosis and inflammatory cell infiltration. Finally, adenosine 5'-(α, β-methylene) diphosphate (APCP), a CD73 inhibitor, was pumped subcutaneously before Aspergillus attack to observe the infiltration of inflammatory cells and subcutaneous fibrosis to clarify its therapeutic effect.

RESULT

PAS staining showed that CD73 knockout inhibited pulmonary epithelial cell proliferation and bronchial fibrosis induced by Aspergillus extract. The genetic knockdownof CD73 significantly reduced the production of Th2 cytokines, interleukin (IL)-4, IL-6, IL-13, chemokine (C-C motif) ligand 5 (CCL5), eosinophil chemokine, neutrophil IL-17, and granulocyte colony-stimulating factor (G-CSF). In addition, exogenous adenosine supplementation increased airway inflammation. Finally, the CD73 inhibitor APCP was administered to reduce inflammation and subcutaneous fibrosis.

CONCLUSION

Elevated adenosine metabolism plays an inflammatory role in asthma, and CD73 could be a potential therapeutic target for asthma.

Molecular Actors of Inflammation and Their Signaling Pathways: Mechanistic Insights from Zebrafish

Inflammation is a hallmark of the physiological response to aggressions. It is orchestrated by a plethora of molecules that detect the danger, signal intracellularly, and activate immune mechanisms to fight the threat. Understanding these processes at a level that allows to modulate their fate in a pathological context strongly relies on in vivo studies, as these can capture the complexity of the whole process and integrate the intricate interplay between the cellular and molecular actors of inflammation. Over the years, zebrafish has proven to be a well-recognized model to study immune responses linked to human physiopathology. We here provide a systematic review of the molecular effectors of inflammation known in this vertebrate and recapitulate their modes of action, as inferred from sterile or infection-based inflammatory models. We present a comprehensive analysis of their sequence, expression, and tissue distribution and summarize the tools that have been developed to study their function. We further highlight how these tools helped gain insights into the mechanisms of immune cell activation, induction, or resolution of inflammation, by uncovering downstream receptors and signaling pathways. These progresses pave the way for more refined models of inflammation, mimicking human diseases and enabling drug development using zebrafish models.

Highway to heal: Influence of altered extracellular matrix on infiltrating immune cells during acute and chronic lung diseases

Environmental insults including respiratory infections, in combination with genetic predisposition, may lead to lung diseases such as chronic obstructive pulmonary disease, lung fibrosis, asthma, and acute respiratory distress syndrome. Common characteristics of these diseases are infiltration and activation of inflammatory cells and abnormal extracellular matrix (ECM) turnover, leading to tissue damage and impairments in lung function. The ECM provides three-dimensional (3D) architectural support to the lung and crucial biochemical and biophysical cues to the cells, directing cellular processes. As immune cells travel to reach any site of injury, they encounter the composition and various mechanical features of the ECM. Emerging evidence demonstrates the crucial role played by the local environment in recruiting immune cells and their function in lung diseases. Moreover, recent developments in the field have elucidated considerable differences in responses of immune cells in two-dimensional versus 3D modeling systems. Examining the effect of individual parameters of the ECM to study their effect independently and collectively in a 3D microenvironment will help in better understanding disease pathobiology. In this article, we discuss the importance of investigating cellular migration and recent advances in this field. Moreover, we summarize changes in the ECM in lung diseases and the potential impacts on infiltrating immune cell migration in these diseases. There has been compelling progress in this field that encourages further developments, such as advanced in vitro 3D modeling using native ECM-based models, patient-derived materials, and bioprinting. We conclude with an overview of these state-of-the-art methodologies, followed by a discussion on developing novel and innovative models and the practical challenges envisaged in implementing and utilizing these systems.

Mechanisms Regulating T Cell-Endothelial Cell Interactions

T-cell interaction with the endothelial cells lining the vessel wall is a necessary step in the inflammatory response that allows T cells to extravasate from the circulation and migrate to sites of infectious or sterile inflammation. On one hand, the vascular endothelium is activated and, as a result, switches from an anti-adhesive to a pro-adhesive state, allowing adhesion of T cells and other leukocytes. On the other hand, T cells express ligands of endothelial adhesion molecules to sustain these interactions that eventually result in T-cell extravasation into sites of inflammation. A better understanding of the central players mediating these interactions may help develop novel therapeutics that modulate this process by preventing T-cell migration and inflammation. Here, I summarize current knowledge on the nature of these interactions in the context of inflammation and cancer immunotherapy.

Neutrophils in pregnancy: New insights into innate and adaptive immune regulation

The immunology of pregnancy has been the focus of many studies to better understand how the mother is able to tolerate the presence of a semi-allogeneic fetus. Far from the initial view of pregnancy as a state of immunosuppression, successful fetal development from implantation to birth is now known to be under the control of an intricate balance of immune cells. The balance between pro-inflammatory functions used to promote embryo implantation and placental development and immunosuppressive activity to maintain maternal tolerance of the fetus is an immunological phenotype unique to pregnancy, which is dependent on the time of gestation. Neutrophils are one of a host of innate immune cells detected at the maternal-fetal interface, but very little is known of their function. In this review, we explore the emerging functions of neutrophils during pregnancy and their interactions with and regulation of T cells, a key adaptive immune cell population essential for the establishment of fetal-maternal tolerance.

Neutrophil extracellular trap inhibition increases inflammation, bacteraemia and mortality in murine necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease affecting primarily premature infants. The disease is characterized by intestinal inflammation and leucocyte infiltration, often progressing to necrosis, perforation, systemic inflammatory response and death. Neutrophil extracellular traps (NETs), denoting nuclear DNA, histone and antimicrobial protein release, have been suggested to play a role in NEC. This study aimed to determine the role of NETs in NEC and explore the effect of chloramidine, a NET inhibitor, on a murine NEC-like intestinal injury model. Blood and intestinal tissues were collected from infants diagnosed with ≥ Stage II NEC, and levels of nucleosomes and NETs, respectively, were compared with those of case-matched controls. In mice, NEC was induced with dithizone/Klebsiella, and mice in the treatment group received 40 mg/kg chloramidine. Bacterial load, intestinal histology, plasma myeloperoxidase and cytokine levels, and immunofluorescent staining were compared with controls. Nucleosomes were significantly elevated in both human and mouse NEC plasma, whereas NET staining was only present in NEC tissue in both species. Chloramidine treatment increased systemic inflammation, bacterial load, organ injury and mortality in murine NEC. Taken together, our findings suggest that NETs are critical in the innate immune defence during NEC in preventing systemic bacteraemia.

The Neutrophil

Neutrophils are immune cells with unusual biological features that furnish potent antimicrobial properties. These cells phagocytose and subsequently kill prokaryotic and eukaryotic organisms very efficiently. Importantly, it is not only their ability to attack microbes within a constrained intracellular compartment that endows neutrophils with antimicrobial function. They can unleash their effectors into the extracellular space, where, even post-mortem, their killing machinery can endure and remain functional. The antimicrobial activity of neutrophils must not be misconstrued as being microbe specific and should be viewed more generally as biotoxic. Outside of fighting infections, neutrophils can harness their noxious machinery in other contexts, like cancer. Inappropriate or dysregulated neutrophil activation damages the host and contributes to autoimmune and inflammatory disease. Here we review a number of topics related to neutrophil biology based on contemporary findings.

Synergistic Roles of Macrophages and Neutrophils in Osteoarthritis Progression

OBJECTIVE

To evaluate the role of immune cells and their effector cytokines in the pathogenesis and progression of knee osteoarthritis (OA) in matched OA synovial fluid (SF) and synovial tissue samples.

METHODS

Cells from matched samples of synovial tissue and SF acquired from individuals undergoing total knee replacement for OA (n = 39) were characterized for immune cell-associated surface markers and intracellular cytokine expression using polychromatic flow cytometry. Additional individuals with radiographic knee OA (Kellgren/Lawrence severity grades ≥1) who had available etarfolatide (inflammatory cell) imaging (n = 26) or baseline and 3-year data on progression of radiographic knee OA (n = 85) were also assessed. SF cytokine concentrations in all cohorts were evaluated for associations with synovial tissue and SF cell phenotypes and severity of radiographic knee OA.

RESULTS

Macrophages (predominant in the synovial tissue, 53% of total cells) and neutrophils (predominant in the SF, 26% of total cells) were the major immune cell populations identified in the OA knee joints, exhibiting expression of or association with transforming growth factor β1 (TGFβ1) and elastase, respectively, in the SF. Expression levels of TGFβ1 and elastase were significantly associated with severity of radiographic knee OA. Baseline SF concentrations of TGFβ1 and elastase along with radiographic knee OA severity scores were predictive of knee OA progression, with areas under the receiver operating characteristic curves of 0.810 (for TGFβ1), 0.806 (for elastase), and 0.846 (for both TGFβ1 and elastase combined), with greater stability of prediction when both markers were utilized.

CONCLUSION

Our findings demonstrate the hitherto underappreciated role of neutrophils in the sterile inflammatory process and progression of OA. Two soluble mediators, SF elastase and TGFβ1, are strong predictors of knee OA progression, reflecting a synergistic role of neutrophil and macrophage populations in the pathogenesis and worsening of OA that could potentially be utilized to identify patients who may have a greater risk of more rapid disease progression.

Prognostic value of systemic inflammatory markers for oral cancer patients based on the 8th edition of AJCC staging system

It has been recognized that systemic inflammatory markers (SIMs) are associated with patient survival in various types of cancer. This study aimed to determine the optimal cut-off values, and to evaluate the prognostic performance of SIMs for oral squamous cell carcinoma (OSCC) within the framework of the American Joint Committee of Cancer (AJCC) cancer staging manual, 8th edition. Records were collected for a total 291 patients who had had a peripheral blood test within 1 week prior to surgery and had undergone the surgical resection of OSCC in a single institution between 2005 and 2018. The cut-off values of SIMs were obtained, and the survival analyses for overall survival (OS) and disease-free survival (DFS) were performed. Multivariate analyses incorporating other clinicopathologic factors were performed to verify the independent risk factors for survival. The cut-off values of neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) were 2.23, 135.14 for OS and 2.16, 131.07 for DFS, respectively, demonstrating a significant association for OS and DFS in OSCC. AJCC pathologic regional lymph node category (pN) (P < 0.001), perineural invasion (PNI) (P < 0.001) and NLR (P < 0.001) were independent predictors for OS. Meanwhile, for DFS, AJCC pN (P = 0.018) and NLR (P = 0.015) were shown to be independent predictors. Before the curative surgery, NLR and PLR could be auxiliary parameters for OS and DFS in OSCC. And based on the 8th edition of AJCC staging system, elevated NLR will be a potential indicator of the worse OS or DFS along with pN or PNI in OSCC.

Kunitz type protease inhibitor from the canine tapeworm as a potential therapeutic for melanoma

Modulating the tumor microenvironment to promote an effective immune response is critical in managing any type of tumor. Melanoma is an aggressive skin cancer and the incidence rate is increasing worldwide. Potent protease inhibitors have recently been extensively researched as potential therapeutic agents against various cancers. EgKI-1 is a potent Kunitz type protease inhibitor identified from the canine tapeworm Echinococcus granulosus that has shown anti-cancer activities in vivo. In this study we show that EgKI-1 significantly reduced the growth of melanoma in the B16-F0 mouse model and was not toxic to normal surrounding tissue. Moreover, EgKI-1 treatment significantly reduced survivin expression levels and increased the CD8+ T cell population in draining axillary lymph nodes. Therefore, EgKI-1 potentially reduces tumor growth by inducing apoptosis and modulating the tumor microenvironment, and has potential for development as an intra-lesional treatment for melanoma.

Sputum from chronic obstructive pulmonary disease patients inhibits T cell migration in a microfluidic device

Chronic obstructive pulmonary disease (COPD) is a common lung disease characterized by narrowed airways, resulting in serious breathing difficulty. Previous studies have demonstrated that inflammatory infiltration of leukocytes in the airway is associated with the pathogenesis of COPD. In the present study, we employed a microfluidic approach to assess the effect of COPD sputum on activated human peripheral blood T cell migration and chemotaxis under well-controlled gradient conditions. Our results showed considerable basal migration of T cells derived from peripheral blood of COPD patients and healthy controls in the medium control groups. By contrast, the migration of T cells from COPD patients and healthy controls was significantly inhibited in the presence of a gradient of sputum supernatant from COPD patients. Furthermore, chemotaxis of T cells from COPD patients or healthy subjects toward an SDF-1α gradient was clearly inhibited by sputum samples from the COPD patients. The inhibition effect revealed by the microfluidic cell migration experiments provides new information about the complex involvement of T cell trafficking in COPD.

Orchestration of Adaptive T Cell Responses by Neutrophil Granule Contents

Neutrophils are the most abundant leukocytes in peripheral blood and respond rapidly to danger, infiltrating tissues within minutes of infectious or sterile injury. Neutrophils were long thought of as simple killers, but now we recognise them as responsive cells able to adapt to inflammation and orchestrate subsequent events with some sophistication. Here, we discuss how these rapid responders release mediators which influence later adaptive T cell immunity through influences on DC priming and directly on the T cells themselves. We consider how the release of granule contents by neutrophils—through NETosis or degranulation—is one way in which the innate immune system directs the phenotype of the adaptive immune response.

Leukocytes Breach Endothelial Barriers by Insertion of Nuclear Lobes and Disassembly of Endothelial Actin Filaments

The endothelial cytoskeleton is a barrier for leukocyte transendothelial migration (TEM). Mononuclear and polymorphonuclear leukocytes generate gaps of similar micron-scale size when squeezing through inflamed endothelial barriers in vitro and in vivo. To elucidate how leukocytes squeeze through these barriers, we co-tracked the endothelial actin filaments and leukocyte nuclei in real time. Nuclear squeezing involved either preexistent or de novo-generated lobes inserted into the leukocyte lamellipodia. Leukocyte nuclei reversibly bent the endothelial actin stress fibers. Surprisingly, formation of both paracellular gaps and transcellular pores by squeezing leukocytes did not require Rho kinase or myosin II-mediated endothelial contractility. Electron-microscopic analysis suggested that nuclear squeezing displaced without condensing the endothelial actin filaments. Blocking endothelial actin turnover abolished leukocyte nuclear squeezing, whereas increasing actin filament density did not. We propose that leukocyte nuclei must disassemble the thin endothelial actin filaments interlaced between endothelial stress fibers in order to complete TEM.

Free circulating active elastase contributes to chronic inflammation in patients on hemodialysis

Atherosclerosis and cardiovascular complications are prevalent among patients undergoing chronic hemodialysis (HD). In this population, peripheral polymorphonuclear leukocytes (PMNLs) are primed, releasing proinflammatory mediators such as elastase. Elastase is normally inhibited by a specific inhibitor, avoiding undesirable degradation of cellular and extracellular components. This study tested the hypothesis that in states of noninfectious inflammation, elastase is released by PMNLs and acts in an uncontrolled manner to inflict vascular damage. Blood was collected from patients undergoing HD and healthy controls (HC). PMNL intracellular and surface expressions of elastase were determined by quantitative real-time PCR, Western blotting, and flow cytometry. The elastase activity was evaluated using a fluorescent substrate. The levels of serum α₁-antitrypsin (α₁-AT), the natural elastase inhibitor, were determined by Western blot. Free active elastase was elevated in HD sera, whereas the levels of α₁-AT were decreased compared with HC. The levels of the intracellular elastase enzyme and its activity were lower in HD PMNLs despite similar expression levels of elastase mRNA. Elastase binding to PMNL cell surface was higher in HD compared with HC. The increased circulating levels of free active elastase released from primed HD PMNLs together with the higher cell surface-bound enzymes and the lower levels of α₁-AT result in the higher elastase activity in HD sera. This exacerbated elastase activity could lead to the endothelial dysfunction, as hypothesized. In addition, it suggests that free circulating elastase can serve as a new biomarker and therapeutic target to reduce inflammation and vascular complications in patients on hemodialysis.

Defects in CD4+ T cell LFA-1 integrin-dependent adhesion and proliferation protect Cd47-/- mice from EAE

CD47 is known to play an important role in CD4⁺ T cell homeostasis. We recently reported a reduction in mice deficient in the Cd47 gene (Cd47^-/-) CD4⁺ T cell adhesion and transendothelial migration (TEM) in vivo and in vitro as a result of impaired expression of high-affinity forms of LFA-1 and VLA-4 integrins. A prior study concluded that Cd47^-/- mice were resistant to experimental autoimmune encephalomyelitis (EAE) as a result of complete failure in CD4⁺ T cell activation after myelin oligodendrocyte glycoprotein peptide 35-55 aa (MOG_35-55) immunization. As the prior EAE study was published before our report, authors could not have accounted for defects in T cell integrin function as a mechanism to protect Cd47^-/- in EAE. Thus, we hypothesized that failure of T cell activation involved defects in LFA-1 and VLA-4 integrins. We confirmed that Cd47^-/- mice were resistant to MOG_35-55-induced EAE. Our data, however, supported a different mechanism that was not a result of failure of CD4⁺ T cell activation. Instead, we found that CD4⁺ T cells in MOG_35-55-immunized Cd47^-/- mice were activated, but clonal expansion contracted within 72 h after immunization. We used TCR crosslinking and mitogen activation in vitro to investigate the underlying mechanism. We found that naïve Cd47^-/- CD4⁺ T cells exhibited a premature block in proliferation and survival because of impaired activation of LFA-1, despite effective TCR-induced activation. These results identify CD47 as an important regulator of LFA-1 and VLA-4 integrin-adhesive functions in T cell proliferation, as well as recruitment, and clarify the roles played by CD47 in MOG_35-55-induced EAE.

Endothelial-Mesenchymal Transition in Vascular Calcification of Ins2Akita/+ Mice

Endothelial-mesenchymal transition (EndMT) drives endothelium to contribute to normal development and disease processes. Here, we report that EndMTs occur in the diabetic endothelium of Ins2^Akita/wt mouse, and show that induction of sex determining region Y-box 2 (Sox2) is a mediator of excess BMP signaling that results in activation of EndMTs and increased vascular calcification. We also find an induction of a complex of serine proteases in the diabetic endothelium, required for the up-regulation of Sox2. Our results suggest that EndMTs contribute to vascular calcification in diabetic arteries.

Neutrophil plasticity enables the development of pathological microenvironments: implications for cystic fibrosis airway disease

INTRODUCTION

The pathological course of several chronic inflammatory diseases, including cystic fibrosis, chronic obstructive pulmonary disease, and rheumatoid arthritis, features an aberrant innate immune response dominated by neutrophils. In cystic fibrosis, neutrophil burden and activity of neutrophil elastase in the extracellular fluid have been identified as strong predictors of lung disease severity.

REVIEW

Although neutrophils are generally considered to be rigid, pre-programmed effector leukocytes, recent studies suggest extensive plasticity in how neutrophil functions unfold upon recruitment to peripheral tissues, and how they choose their ultimate fate. Indeed, upon migration to cystic fibrosis airways, neutrophils display dysregulated lifespan, metabolic activation, and altered effector and regulatory functions, consistent with profound adaptation and phenotypic reprogramming. Licensed by signals present in cystic fibrosis airway microenvironment to survive and develop these novel functions, neutrophils orchestrate, in partnership with the epithelium and with the resident microbiota, the evolution of a pathological microenvironment. This microenvironment is defined by altered proteolytic, redox, and metabolic balance and the presence of stable luminal structures in which neutrophils and microbes coexist.

CONCLUSIONS

The elucidation of molecular mechanisms driving neutrophil plasticity in vivo will open new treatment opportunities designed to modulate, rather than block, the crucial adaptive functions fulfilled by neutrophils. This review aims to outline emerging mechanisms of neutrophil plasticity and their participation in the building of pathological microenvironments in the context of cystic fibrosis and other diseases with similar features.

Crossing the Vascular Wall: Common and Unique Mechanisms Exploited by Different Leukocyte Subsets during Extravasation

Leukocyte extravasation is one of the essential and first steps during the initiation of inflammation. Therefore, a better understanding of the key molecules that regulate this process may help to develop novel therapeutics for treatment of inflammation-based diseases such as atherosclerosis or rheumatoid arthritis. The endothelial adhesion molecules ICAM-1 and VCAM-1 are known as the central mediators of leukocyte adhesion to and transmigration across the endothelium. Engagement of these molecules by their leukocyte integrin receptors initiates the activation of several signaling pathways within both leukocytes and endothelium. Several of such events have been described to occur during transendothelial migration of all leukocyte subsets, whereas other mechanisms are known only for a single leukocyte subset. Here, we summarize current knowledge on regulatory mechanisms of leukocyte extravasation from a leukocyte and endothelial point of view, respectively. Specifically, we will focus on highlighting common and unique mechanisms that specific leukocyte subsets exploit to succeed in crossing endothelial monolayers.

A lack of secretory leukocyte protease inhibitor (SLPI) causes defects in granulocytic differentiation

We identified diminished levels of the natural inhibitor of neutrophil elastase (NE), secretory leukocyte protease inhibitor (SLPI), in myeloid cells and plasma of patients with severe congenital neutropenia (CN). We further found that downregulation of SLPI in CD34(+) bone marrow (BM) hematopoietic progenitors from healthy individuals resulted in markedly reduced in vitro myeloid differentiation accompanied by cell-cycle arrest and elevated apoptosis. Reciprocal regulation of SLPI by NE is well documented, and we previously demonstrated diminished NE levels in CN patients. Here, we found that transduction of myeloid cells with wild-type NE or treatment with exogenous NE increased SLPI messenger RNA and protein levels, whereas transduction of mutant forms of NE or inhibition of NE resulted in downregulation of SLPI. An analysis of the mechanisms underlying the diminished myeloid differentiation caused by reduced SLPI levels revealed that downregulation of SLPI with short hairpin RNA (shRNA) upregulated nuclear factor κB levels and reduced phospho-extracellular signal-regulated kinase (ERK1/2)-mediated phosphorylation and activation of the transcription factor lymphoid enhancer-binding factor-1 (LEF-1). Notably, microarray analyses revealed severe defects in signaling cascades regulating the cell cycle, including c-Myc-downstream signaling, in myeloid cells transduced with SLPI shRNA. Taken together, these results indicate that SLPI controls the proliferation, differentiation, and cell cycle of myeloid cells.

Detection of alveolar fibrocytes in idiopathic pulmonary fibrosis and systemic sclerosis

Background

Fibrocytes are circulating precursors for fibroblasts. Blood fibrocytes are increased in patients with idiopathic pulmonary fibrosis (IPF). The aim of this study was to determine whether alveolar fibrocytes are detected in broncho-alveolar lavage (BAL), to identify their prognostic value, and their potential association with culture of fibroblasts from BAL.

Methods

We quantified fibrocytes in BAL from 26 patients with IPF, 9 patients with Systemic Sclerosis(SSc)-interstitial lung disease (ILD), and 11 controls. BAL cells were cultured to isolate alveolar fibroblasts.

Results

Fibrocytes were detected in BAL in 14/26 IPF (54%) and 5/9 SSc patients (55%), and never in controls. Fibrocytes were in median 2.5% [0.4–19.7] and 3.0% [2.7–3.7] of BAL cells in IPF and SSc-ILD patients respectively. In IPF patients, the number of alveolar fibrocytes was correlated with the number of alveolar macrophages and was associated with a less severe disease but not with a better outcome. Fibroblasts were cultured from BAL in 12/26 IPF (46%), 5/9 SSc-ILD (65%) and never in controls. The detection of BAL fibrocytes did not predict a positive culture of fibroblasts.

Conclusion

Fibrocytes were detected in BAL fluid in about half of the patients with IPF and SSc-ILD. Their number was associated with less severe disease in IPF patients and did not associate with the capacity to grow fibroblasts from BAL fluid.

Targeting stroma to treat cancers

All cancers depend on stroma for support of growth. Leukemias, solid tumors, cancer cells causing effusions, metastases as well as micro-disseminated cancer cells release factors that stimulate stromal cells, which in turn produce ligands that stimulate cancer cells. Therefore, elimination of stromal support by destroying the stromal cells or by inhibiting feedback stimulation of cancer growth is in the focus of many evolving therapies. A stringent evaluation of the efficacy of stromal targeting requires testing in animal models. Most current studies emphasize the successes of stromal targeting rather than deciphering its limitations. Here we show that many of the stromal targeting approaches, while often reducing tumor growth rates, are rarely curative. Therefore, we will also discuss conditions where stromal targeting can eradicate large established tumors. Finally, we will examine still unanswered questions of this promising and exciting area of cancer research.

Emergency granulopoiesis promotes neutrophil-dendritic cell encounters that prevent mouse lung allograft acceptance

The mechanisms by which innate immune signals regulate alloimmune responses remain poorly understood. In the present study, we show by intravital 2-photon microscopy direct interactions between graft-infiltrating neutrophils and donor CD11c(+) dendritic cells (DCs) within orthotopic lung allografts immediately after reperfusion. Neutrophils isolated from the airways of lung transplantation recipients stimulate donor DCs in a contact-dependent fashion to augment their production of IL-12 and expand alloantigen-specific IFN-γ(+) T cells. DC IL-12 expression is largely regulated by degranulation and induced by TNF-α associated with the neutrophil plasma membrane. Extended cold ischemic graft storage enhances G-CSF-mediated granulopoiesis and neutrophil graft infiltration, resulting in exacerbation of ischemia-reperfusion injury after lung transplantation. Ischemia reperfusion injury prevents immunosuppression-mediated acceptance of mouse lung allografts unless G-CSF-mediated granulopoiesis is inhibited. Our findings identify granulopoiesis-mediated augmentation of alloimmunity as a novel link between innate and adaptive immune responses after organ transplantation.

Emerging mechanisms of neutrophil recruitment across endothelium

Neutrophils are the all-terrain vehicle of the innate immune system because of their ability to gain entry into tissues and organs, and thus, play an essential role in host defense. Exactly how this marvel of nature works is still incompletely understood. In the past 2-3 years, new players and processes have been identified in the endothelial-leukocyte adhesion cascade. Novel signaling pathways have been discovered in both the endothelium and the neutrophils that regulate various steps in the recruitment process. This review focuses on these emerging pathways and the mechanisms that regulate neutrophil recruitment across endothelium.

Serotonin-mediated tuning of human helper T cell responsiveness to the chemokine CXCL12

In addition to its role as neurotransmitter, serotonin (5-HT) is an important modulator of inflammation and immunity. Here, we report novel findings suggesting a 5-HT involvement in T cell migration. In particular, we show that 5-HT tunes the responsiveness of human T lymphocytes to the broadly expressed chemokine CXCL12 in transwell migration assays. By real-time PCR, western blot analysis and electrophysiological patch clamp experiments, we demonstrate that the type 3 5-HT receptor (5-HT₃) is functionally expressed in human primary T cells. In addition, specific 5-HT₃ receptor agonists selectively decrease T cell migration towards gradients of CXCL12 but not of inflammatory chemokines, such as CCL2 and CCL5. In transmigration experiments, 5-HT₃ receptor stimulation reverts the inhibitory effect of endothelial-bound CXCL12 on T cell migration. Our data suggest that the reduced T cell responsiveness to CXCL12 induced by 5-HT may occur to facilitate T cell extravasation and migration into inflamed tissues.

Tailor-made inflammation: how neutrophil serine proteases modulate the inflammatory response

Neutrophil granulocytes are important mediators of innate immunity, but also participate in the pathogenesis of (auto)inflammatory diseases. Neutrophils express a specific set of proteolytic enzymes, the neutrophil serine proteases (NSPs), which are stored in cytoplasmic granules and can be secreted into the extra- and pericellular space upon cellular activation. These NSPs, namely cathepsin G (CG), neutrophil elastase (NE), and proteinase 3 (PR3), have early been implicated in bacterial defense. However, NSPs also regulate the inflammatory response by specifically altering the function of cytokines and chemokines. For instance, PR3 and NE both inactivate the anti-inflammatory mediator progranulin, which may play a role in chronic inflammation. Here, we provide a concise update on NSPs as modulators of inflammation and discuss the biological and pathological significance of this novel function of NSPs. Mounting evidence support an important proinflammatory function for PR3, which may have been underestimated in the past.

Neutrophil elastase is severely down-regulated in severe congenital neutropenia independent of ELA2 or HAX1 mutations but dependent on LEF-1

Severe congenital neutropenia (CN) is a heterogeneous disorder of myelopoiesis which follows an autosomal dominant or autosomal recessive pattern of inheritance. Genetic analyses indicate mutations in the ELA2 gene in most patients. We have identified LEF-1 as a decisive transcription factor in granulopoiesis controlling proliferation and granulocytic differentiation by direct activation of its target gene, C/EBPα. In patients with CN, the expression of LEF-1 and C/EBPα was abrogated in myeloid progenitors leading to maturation arrest of granulopoiesis. In the present study we demonstrated that ELA2 mRNA expression in myeloid progenitors and plasma protein levels of neutrophil elastase (NE) were markedly reduced in patients with CN harboring mutations in either ELA2 or HAX-1 genes. The ELA2 gene promoter is positively regulated by the direct binding of LEF-1 or C/EBPα, documenting the role of LEF1 in the diminished ELA2 expression. We found that transduction of hematopoietic cells with LEF-1 cDNA resulted in the up-regulation of ELA2/NE synthesis, whereas inhibition of LEF-1 by shRNA led to a marked reduction in the levels of ELA2/NE. LEF-1 rescue of CD34+ cells isolated from 2 patients with CN resulted in granulocytic differentiation of the cells which was in line with increased levels of functionally active ELA2/NE.

Neutrophil granule proteins tune monocytic cell function

Polymorphonuclear leukocytes (PMNs) release the contents of granules during their migration to inflammatory sites. On liberation from the first leukocyte to enter injured tissue, the granule proteins play a central role in the early inflammatory response. In particular, mononuclear phagocytes interact intimately with PMNs and their secretion products. PMN granule proteins enhance the adhesion of monocytes to the endothelium and stimulate subsequent extravasation of inflammatory monocytes. At the site of inflammation, PMN granule proteins activate macrophages to produce and release cytokines and to phagocytose IgG-opsonized bacteria. Furthermore, by direct cell-cell contacts, PMNs activate monocyte-derived dendritic cells, thereby enhancing antigen presentation. Efforts in this field might lead to the development of drugs for specific modulation of innate immune functions.

Mechanisms underlying neutrophil-mediated monocyte recruitment

Extravasation of polymorphonuclear leukocytes (PMNs) to the site of inflammation precedes a second wave of emigrating monocytes. That these events are causally connected has been established a long time ago. However, we are now just beginning to understand the molecular mechanisms underlying this cellular switch, which has become even more complex considering the emergence of monocyte subsets, which are affected differently by signals generated from PMNs. PMN granule proteins induce adhesion as well as emigration of inflammatory monocytes to the site of inflammation involving beta(2)-integrins and formyl-peptide receptors. Furthermore, modification of the chemokine network by PMNs and their granule proteins creates a milieu favoring extravasation of inflammatory monocytes. Finally, emigrated PMNs rapidly undergo apoptosis, leading to the discharge of lysophosphatidylcholine, which attracts monocytes via G2A receptors. The net effect of these mechanisms is the accumulation of inflammatory monocytes, thus promoting proinflammatory events, such as release of inflammation-sustaining cytokines and reactive oxygen species. As targeting PMNs without causing serious side effects seems futile, it may be more promising to aim at interfering with subsequent PMN-driven proinflammatory events.

Francisella tularensis directly interacts with the endothelium and recruits neutrophils with a blunted inflammatory phenotype

Francisella tularensis, the causative agent of tularemia, is a highly virulent organism, especially when exposure occurs by inhalation. Recent data suggest that Francisella interacts directly with alveolar epithelial cells. Although F. tularensis causes septicemia and can live extracellularly in a murine infection model, there is little information about the role of the vascular endothelium in the host response. We hypothesized that F. tularensis would interact with pulmonary endothelial cells as a prerequisite to the clinically observed recruitment of neutrophils to the lung. Using an in vitro Transwell model system, we studied interactions between F. tularensis live vaccine strain (Ft LVS) and a pulmonary microvascular endothelial cell (PMVEC) monolayer. Organisms invaded the endothelium and were visualized within individual endothelial cells by confocal microscopy. Although these bacteria-endothelial cell interactions did not elicit production of the proinflammatory chemokines, polymorphonuclear leukocytes (PMN) were stimulated to transmigrate across the endothelium in response to Ft LVS. Moreover, transendothelial migration altered the phenotype of recruited PMN; i.e., the capacity of these PMN to activate NADPH oxidase and release elastase in response to subsequent stimulation was reduced compared with PMN that traversed PMVEC in response to Streptococcus pneumoniae. The blunting of PMN responsiveness required PMN transendothelial migration but did not require PMN uptake of Ft LVS, was not dependent on the presence of serum-derived factors, and was not reproduced by Ft LVS-conditioned medium. We speculate that the capacity of Ft LVS-stimulated PMVEC to support transendothelial migration of PMN without triggering release of IL-8 and monocyte chemotactic protein-1 and to suppress the responsiveness of transmigrated PMN to subsequent stimulation could contribute to the dramatic virulence during inhalational challenge with Francisella.

Activation of critical, host-induced, metabolic and stress pathways marks neutrophil entry into cystic fibrosis lungs

Cystic fibrosis (CF) patients undergo progressive airway destruction caused in part by chronic neutrophilic inflammation. While opportunistic pathogens infecting CF airways can cause inflammation, we hypothesized that host-derived metabolic and stress signals would also play a role in this process. We show that neutrophils that have entered CF airways have increased phosphorylation of the eukaryotic initiation factor 4E and its partner the 4E-binding protein 1; 2 key effectors in the growth factor- and amino acid-regulated mammalian target of rapamycin (mTOR) pathway. Furthermore CF airway neutrophils display increased phosphorylation of the cAMP response element binding protein (CREB), a major transcriptional coactivator in stress signaling cascades. These active intracellular pathways are associated with increased surface expression of critical adaptor molecules, including the growth factor receptor CD114 and the receptor for advanced glycation end-products (RAGE), a CREB inducer and sensor for host-derived damage-associated molecular patterns (DAMPs). Most CF airway fluids lack any detectable soluble RAGE, an inhibitory decoy receptor for DAMPs. Concomitantly, CF airway fluids displayed high and consequently unopposed levels of S100A12; a potent mucosa- and neutrophil-derived DAMP. CF airway neutrophils also show increased surface levels of 2 critical CREB targets, the purine-recycling enzyme CD39 and the multifunctional, mTOR-inducing CXCR4 receptor. This coordinated set of events occurs in all patients, even in the context of minimal airway inflammation and well-preserved lung function. Taken together, our data demonstrate an early and sustained activation of host-responsive metabolic and stress pathways upon neutrophil entry into CF airways, suggesting potential targets for therapeutic modulation.

Endothelial CD47 interaction with SIRPgamma is required for human T-cell transendothelial migration under shear flow conditions in vitro

Leukocyte transendothelial migration (TEM) is a critical event during inflammation. CD47 has been implicated in myeloid cell migration across endothelium and epithelium. CD47 binds to signal regulatory protein (SIRP), SIRPalpha and SIRPgamma. So far, little is known about the role of endothelial CD47 in T-cell TEM in vivo or under flow conditions in vitro. Fluorescence-activated cell sorting and biochemical analysis show that CD3(+) T cells express SIRPgamma but not SIRPalpha, and fluorescence microscopy showed that CD47 was enriched at endothelial junctions. These expression patterns suggested that CD47 plays a role in T-cell TEM through binding interactions with SIRPgamma. We tested, therefore, whether CD47-SIRPgamma interactions affect T-cell transmigration using blocking mAb against CD47 or SIRPgamma in an in vitro flow model. These antibodies inhibited T-cell TEM by 70% plus or minus 6% and 82% plus or minus 1%, respectively, but had no effect on adhesion. In agreement with human mAb studies, transmigration of murine wild-type T helper type 1 cells across TNF-alpha-activated murine CD47(-/-) endothelium was reduced by 75% plus or minus 2% even though murine T cells appear to lack SIRPgamma. Nonetheless, these findings suggest endothelial cell CD47 interacting with T-cell ligands, such as SIRPgamma, play an important role in T-cell transendothelial migration.

Assays of transendothelial migration in vitro

The inflammatory response is critical for our ability to heal wounds and fight off foreign microorganisms. Uncontrolled inflammation is also at the root of most pathologic conditions. Recruitment of leukocytes to the site of inflammation plays a defining role in the inflammatory response, and migration of leukocytes across endothelium is arguably the point of no return of the inflammatory response. Assays to study the transmigration of leukocytes have and will continue to shed light on the regulation of this vital response. Assays of transendothelial migration in vitro allow the controlled observation of this phenomenon, as well as experiments to study its regulation. In this chapter, we describe in vitro assays of transendothelial migration that have been used successfully in the authors' laboratories for decades and have proven to be reproducible, reliable, and predictive of the behavior of leukocytes and endothelial cells in models of inflammation in vivo.

The multiple sclerosis degradome: enzymatic cascades in development and progression of central nervous system inflammatory disease

An array of studies implicate different classes of protease and their endogenous inhibitors in multiple sclerosis (MS) pathogenesis based on expression patterns in MS lesions, sera, and/or cerebrospinal fluid (CSF). Growing evidence exists regarding their mechanistic roles in inflammatory and neurodegenerative aspects of this disease. Proteolytic events participate in demyelination, axon injury, apoptosis, and development of the inflammatory response including immune cell activation and extravasation, cytokine and chemokine activation/inactivation, complement activation, and epitope spreading. The potential significance of proteolytic activity to MS therefore relates not only to their potential use as important biomarkers of disease activity, but additionally as prospective therapeutic targets. Experimental data indicate that understanding the net physiological consequence of altered protease levels in MS development and progression necessitates understanding protease activity in the context of substrates, endogenous inhibitors, and proteolytic cascade interactions, which together make up the MS degradome. This review will focus on evidence regarding the potential physiologic role of those protease families already identified as markers of disease activity in MS; that is, the metallo-, serine, and cysteine proteases.

Neutrophil serine proteases fine-tune the inflammatory response

Neutrophil serine proteases are granule-associated enzymes known mainly for their function in the intracellular killing of pathogens. Their extracellular release upon neutrophil activation is traditionally regarded as the primary reason for tissue damage at the sites of inflammation. However, studies over the past several years indicate that neutrophil serine proteases may also be key regulators of the inflammatory response. Neutrophil serine proteases specifically process and release chemokines, cytokines, and growth factors, thus modulating their biological activity. In addition, neutrophil serine proteases activate and shed specific cell surface receptors, which can ultimately prolong or terminate cytokine-induced responses. Moreover, it has been proposed that these proteases can impact cell viability through their caspase-like activity and initiate the adaptive immune response by directly activating lymphocytes. In summary, these studies point to neutrophil serine proteases as versatile mediators that fine-tune the local immune response and identify them as potential targets for therapeutic interventions.

Inhibitory control of endothelial galectin-1 on in vitro and in vivo lymphocyte trafficking

Galectin-1 (Gal-1) is a beta-galactoside-binding protein, the expression of which is increased in endothelial cells on exposure to proinflammatory stimuli. Through binding of several receptors (CD7, CD45, and CD43) Gal-1 is known to induce apoptosis of activated T lymphocytes, an effect thought to mediate the beneficial effects it exerts in various inflammatory models. The data presented here highlights another function for Gal-1, that of a negative regulator of T-cell recruitment to the endothelium under both physiological and pathophysiological conditions. We have shown, using siRNA to knockdown Gal-1 in endothelial cells, that endogenous Gal-1 limits T-cell capture, rolling, and adhesion to activated endothelial cells under flow. Furthermore, the reverse effect is observed when exogenous human recombinant Gal-1 is added to activated endothelial monolayers whereby a dramatic reduction in lymphocyte recruitment is seen. These findings are corroborated by studies in Gal-1 null mice in which homing of wild-type (WT) T lymphocytes is significantly increased to mesenteric lymph nodes and to the inflamed paw in a model of delayed-type hypersensitivity. In conclusion, mimicking endothelial Gal-1 actions would be a novel strategy for controlling aberrant T-cell trafficking, hence for the development of innovative anti-inflammatory therapeutics.

CD16+ monocytes produce IL-6, CCL2, and matrix metalloproteinase-9 upon interaction with CX3CL1-expressing endothelial cells

The CD16+ subset of peripheral blood monocytes (Mo) is expanded dramatically during inflammatory conditions including sepsis, HIV-1 infection, and cancer. CD16+ express high levels of CX3CR1, which mediates arrest onto CX3CL1-expressing endothelial cells (EC) under flow conditions. In contrast, attachment of CD16- Mo onto cytokine-activated EC is independent of CX3CL1. Here, we investigate the ability of CD16+ and CD16- Mo to produce proinflammatory cytokines upon interaction with CX3CL1-expressing HUVEC. We demonstrate that CD16+ but not CD16- Mo produce high levels of IL-6, CCL2, and matrix metalloproteinase (MMP)-9 when cocultured with TNF/IFN-gamma-activated HUVEC or nonactivated HUVEC expressing CX3CL1. Furthermore, supernatants from Mo cocultured with cytokine-activated HUVEC induce neuronal death in vitro. These results suggest that membrane-bound CX3CL1 stimulates production of IL-6, CCL2, and MMP-9 by CD16+ Mo, likely via engagement of CX3CR1. Thus, expansion of CD16+ Mo and their accumulation onto CX3CL1-expressing EC may result in recruitment of Mo and T cell subsets at sites of inflammation in response to CCL2, IL-6-induced cell activation and/or differentiation, and MMP-9-mediated vascular and tissue injury.

Dendritic cell expression of the transcription factor T-bet regulates mast cell progenitor homing to mucosal tissue

The transcription factor T-bet was identified in CD4⁺ T cells, and it controls interferon γ production and T helper type 1 cell differentiation. T-bet is expressed in certain other leukocytes, and we recently showed (Lord, G.M., R.M. Rao, H. Choe, B.M. Sullivan, A.H. Lichtman, F.W. Luscinskas, and L.H. Glimcher. 2005. Blood. 106:3432–3439) that it regulates T cell trafficking. We examined whether T-bet influences homing of mast cell progenitors (MCp) to peripheral tissues. Surprisingly, we found that MCp homing to the lung or small intestine in T-bet^−/− mice is reduced. This is reproduced in adhesion studies using bone marrow–derived MCs (BMMCs) from T-bet^−/− mice, which showed diminished adhesion to mucosal addresin cellular adhesion molecule–1 (MAdCAM-1) and vascular cell adhesion molecule–1 (VCAM-1), endothelial ligands required for MCp intestinal homing. MCp, their precursors, and BMMCs do not express T-bet, suggesting that T-bet plays an indirect role in homing. However, adoptive transfer experiments revealed that T-bet expression by BM cells is required for MCp homing to the intestine. Furthermore, transfer of WT BM-derived dendritic cells (DCs) to T-bet^−/− mice restores normal MCp intestinal homing in vivo and MCp adhesion to MAdCAM-1 and VCAM-1 in vitro. Nonetheless, T-bet^−/− mice respond vigorously to intestinal infection with Trichinella spiralis, eliminating a role for T-bet in MC recruitment to sites of infection and their activation and function. Therefore, remarkably, T-bet expression by DCs indirectly controls MCp homing to mucosal tissues.

Neutrophil serine proteases: specific regulators of inflammation

Neutrophils are essential for host defence against invading pathogens. They engulf and degrade microorganisms using an array of weapons that include reactive oxygen species, antimicrobial peptides, and proteases such as cathepsin G, neutrophil elastase and proteinase 3. As discussed in this Review, the generation of mice deficient in these proteases has established a role for these enzymes as intracellular microbicidal agents. However, I focus mainly on emerging data indicating that, after release, these proteases also contribute to the extracellular killing of microorganisms, and regulate non-infectious inflammatory processes by activating specific receptors and modulating the levels of cytokines.

Mechanisms of hematopoietic stem cell mobilization: When innate immunity assails the cells that make blood and bone

Mobilization is now used worldwide to collect large numbers of hematopoietic stem and progenitor cells (HSPCs) for transplantation. Although the first mobilizing agents were discovered largely by accident, discovery of more efficient mobilizing agents will require a better understanding of the molecular mechanisms responsible. During the past 5 years, a number of mechanisms have been identified, shedding new light on the dynamics of the hematopoietic system in vivo and on the intricate relationship between hematopoiesis, innate immunity, and bone. After briefly reviewing the mechanisms by which circulating HSPCs home into the bone marrow and what keeps them there, the current knowledge of mechanisms responsible for HSPC mobilization in response to hematopoietic growth factors such as granulocyte colony-stimulating factor, chemotherapy, chemokines, and polyanions will be discussed together with current strategies developed to further increase HSPC mobilization.

Chemoattractants, extracellular proteases, and the integrated host defense response

The host response to tissue injury and/or infection is dependent on the action of numerous extracellular proteases. Proteolytic cascades trigger blood clotting, fibrinolysis, and complement activation, while proteases released upon leukocyte degranulation are integral to the processes of inflammation and immunity. Modulation of effector protein activity by proteases provides a critical layer of posttranslational control that enables rapid enzymatic regulation of target proteins. This report reviews the emerging literature describing a novel class of proteolytic targets, leukocyte chemoattractants, and, in particular, chemerin, a dendritic cell and macrophage chemoattractant activated by serine proteases of the coagulation, fibrinolytic, and inflammatory cascades. As chemoattractants are critical for both systemic leukocyte positioning by triggering integrin activation and subsequent recruitment from circulation, and local intratissue leukocyte positioning via chemotaxis, modulation of attractant activities by proteases may have profound effects on the immune response.

Suppression of experimental autoimmune encephalomyelitis by extracellular adherence protein of Staphylococcus aureus

Multiple sclerosis (MS) is a devastating inflammatory disorder of the central nervous system (CNS). A major hallmark of MS is the infiltration of T cells reactive against myelin components. T cell infiltration is mediated by the interaction of integrins of the beta1 and beta2 family expressed by lymphocytes with their endothelial counter-receptors, vascular cell adhesion molecule 1 and intercellular adhesion molecule (ICAM)-1, respectively. We have reported previously that extracellular adherence protein (Eap) of Staphylococcus aureus exerts antiinflammatory activities by interacting with ICAM-1 and blocking beta2-integrin-dependent neutrophil recruitment. Here, we report that Eap inhibits experimental autoimmune encephalomyelitis (EAE) in mice. In vitro, Eap reduced adhesion of peripheral blood T cells to immobilized ICAM-1 as well as their adhesion and transmigration of TNF-activated human endothelium under static and shear flow conditions. These inhibitory effects were corroborated in two mouse models of inflammation. In a delayed-type hypersensitivity model, both T cell infiltration and the corresponding tissue edema were significantly reduced by Eap. In addition, Eap administration prevented the development of EAE and markedly decreased infiltration of inflammatory cells into the CNS. Strikingly, intervention with Eap after the onset of EAE suppressed the disease. Collectively, our findings indicate that Eap represents an attractive treatment for autoimmune neuroinflammatory disorders such as MS.

The etiology of sepsis: turned inside out

The sepsis syndrome is thought to occur when microbial products activate Toll-like receptors stimulating widespread inflammation, in turn causing organ failure, shock and death. However, recent discoveries reveal that: (i) not only microbial substances but also endogenous molecules can trigger Toll-like receptors; (ii) Toll-like receptor-4, the endotoxin receptor, is constitutively suppressed; and (iii) the first step in sepsis could be the release of Toll-like receptor-4 from suppression. These discoveries suggest that endotoxin might not always initiate the sepsis syndrome and they explain why anti-endotoxin therapies fail. The discoveries also suggest new therapeutic targets - endogenous agonists and Toll-like receptor regulators - for treatment of sepsis.