Sepsis lethality via exacerbated tissue infiltration and TLR-induced cytokine production by neutrophils is integrin α3β1-dependent

A synthetic bioactive peptide of the C-terminal fragment of adhesion protein Fibulin7 attenuates the inflammatory functions of innate immune cells in LPS-induced systemic inflammation

OBJECTIVE

Systemic inflammation is associated with improper localization of hyperactive neutrophils and monocytes in visceral organs. Previously, a C-terminal fragment of adhesion protein Fibulin7 (Fbln7-C) was shown to regulate innate immune functionality during inflammation. Recently, a shorter bioactive peptide of Fbln7-C, FC-10, via integrin binding was shown to reduce ocular angiogenesis. However, the role of FC-10 in regulating the neutrophils and monocyte functionality during systemic inflammatory conditions is unknown. The study sought to explore the role of FC-10 peptide on the functionality of innate immune cells during inflammation and endotoxemic mice.

METHODS

Neutrophils and monocytes were isolated from healthy donors and septic patient clinical samples and Cell adhesion assay was performed using a UV spectrophotometer. Gene expression studies were performed using qPCR. Protein level expression was measured using ELISA and flow cytometry. ROS assay, and activation markers analysis in vitro, and in vivo were done using flow cytometry.

TREATMENT

Cells were stimulated with LPS (100 ng/mL) and studied in the presence of peptides (10 μg, and 20 μg/mL) in vitro. In an in vivo study, mice were administered with LPS (36.8 mg/kg bw) and peptide (20 μg).

RESULTS

This study demonstrates that human neutrophils and monocytes adhere to FC-10 via integrin β1, inhibit spreading, ROS, surface activation markers (CD44, CD69), phosphorylated Src kinase, pro-inflammatory genes, and protein expression, compared to scrambled peptide in cells isolated from healthy donors and clinical sample. In line with the in vitro data, FC-10 (20 μg) administration significantly decreases innate cell infiltration at inflammatory sites, improves survival in endotoxemia animals & reduces the inflammatory properties of neutrophils and monocytes isolated from septic patients.

CONCLUSION

FC-10 peptide can regulate neutrophils and monocyte functions and has potential to be used as an immunomodulatory therapeutic in inflammatory diseases.

Early Diagnosis of Sepsis: The Role of Biomarkers and Rapid Microbiological Tests

Sepsis is a medical emergency resulting from a dysregulated response to an infection, causing preventable deaths and a high burden of morbidity. Protocolized and accurate interventions in sepsis are time-critical. Therefore, earlier recognition of cases allows for preventive interventions, early treatment, and improved outcomes. Clinical diagnosis of sepsis by clinical scores cannot be considered an early diagnosis, given that underlying molecular pathophysiological mechanisms have been activated in the preceding hour or days. There is a lack of a widely available tool enhancing preclinical diagnosis of sepsis. Sophisticated technologies for sepsis prediction have several limitations, including high costs. Novel technologies for fast molecular and microbiological diagnosis are focusing on bedside point-of-care combined testing to reach most settings where sepsis represents a challenge.

INHIBITION OF INTEGRIN VLA-3 AND TETRASPANIN CD151 PROTECTS AGAINST NEUTROPHIL-MEDIATED ENDOTHELIAL DAMAGE

ABSTRACT

Background: The recruitment of neutrophils to sites of localized injury or infection is initiated by changes on the surface of endothelial cells located in proximity to tissue damage. Inflammatory mediators, such as TNF-α, increase surface expression of adhesive ligands and receptors on the endothelial surface to which neutrophils tether and adhere. Neutrophils then transit through the activated endothelium to reach sites of tissue injury with little lasting vascular injury. However, in cases of sepsis, the interaction of endothelial cells with highly activated neutrophils can cause damage vascular damage. The identification of molecules that are essential for neutrophil diapedesis may reveal targets of therapeutic opportunity for preservation of endothelial function in the presence of critical illness. We tested the hypothesis that inhibition of neutrophil β1 integrin very late antigen-3 (VLA-3; α3β1) and/or inhibition of the tetraspanin (TM4) family member CD151 would protect against neutrophil-mediated loss of endothelial function. Methods: Blood was obtained from septic patients or healthy donors. Neutrophils were purified, and aliquots were treated with/without proinflammatory molecules. Confluent human umbilical vascular endothelial cells were activated with TNF-α. Electric cell impedance sensing was used to determine monolayer resistance over time after the addition of neutrophils that were treated with blocking antibodies against VLA-3 and/or CD151 or isotype controls. Groups (depending on relevancy) were analyzed by Mann-Whitney U test, Wilcoxon test, or repeated-measures one-way ANOVA. Results: Neutrophils from septic patients and neutrophils activated ex vivo reduced endothelial monolayer resistance to a greater extent than neutrophils from healthy donors. Antibody blockade of VLA-3 and/or CD151 significantly reduced activation-associated endothelial damage. Similar findings were demonstrated on fibronectin, collagen I, collagen IV, and laminin, suggesting that neutrophil surface VLA-3 and CD151 are responsible for endothelial damage regardless of substrata and are likely to be operative in all bodily tissues. Conclusion: This report identifies VLA-3 and CD151 on the activated human neutrophil, which are responsible for damage to endothelial function. Targeting these molecules in vivo may demonstrate preservation of organ function during critical illness.

S100A8/A9: An emerging player in sepsis and sepsis-induced organ injury

Sepsis, the foremost contributor to mortality in intensive care unit patients, arises from an uncontrolled systemic response to invading infections, resulting in extensive harm across multiple organs and systems. Recently, S100A8/A9 has emerged as a promising biomarker for sepsis and sepsis-induced organ injury, and targeting S100A8/A9 appeared to ameliorate inflammation-induced tissue damage and improve adverse outcomes. S100A8/A9, a calcium-binding heterodimer mainly found in neutrophils and monocytes, serves as a causative molecule with pro-inflammatory and immunosuppressive properties, which are vital in the pathogenesis of sepsis. Therefore, improving our comprehension of how S100A8/A9 acts as a pathological player in the development of sepsis is imperative for advancing research on sepsis. Our review is the first-to the best of our knowledge-to discuss the biology of S100A8/A9 and its release mechanisms, summarize recent advances concerning the vital roles of S100A8/A9 in sepsis and the consequential organ damage, and underscore its potential as a promising diagnostic biomarker and therapeutic target for sepsis.

Integrin α3 promotes TH17 cell polarization and extravasation during autoimmune neuroinflammation

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) caused by CNS-infiltrating leukocytes, including TH17 cells that are critical mediators of disease pathogenesis. Although targeting leukocyte trafficking is effective in treating autoimmunity, there are currently no therapeutic interventions that specifically block encephalitogenic TH17 cell migration. Here, we report integrin α3 as a TH17 cell-selective determinant of pathogenicity in experimental autoimmune encephalomyelitis. CNS-infiltrating TH17 cells express high integrin α3, and its deletion in CD4+ T cells or Il17a fate-mapped cells attenuated disease severity. Mechanistically, integrin α3 enhanced the immunological synapse formation to promote the polarization and proliferation of TH17 cells. Moreover, the transmigration of TH17 cells into the CNS was dependent on integrin α3, and integrin α3 deficiency enhanced the retention of CD4+ T cells in the perivascular space of the blood-brain barrier. Integrin α3-dependent interactions continuously maintain TH17 cell identity and effector function. The requirement of integrin α3 in TH17 cell pathogenicity suggests integrin α3 as a therapeutic target for MS treatment.

Sufu limits sepsis-induced lung inflammation via regulating phase separation of TRAF6

Rationale: Sepsis is a potentially life-threatening condition caused by the body's response to a severe infection. Although the identification of multiple pathways involved in inflammation, tissue damage and aberrant healing during sepsis, there remain unmet needs for the development of new therapeutic strategies essential to prevent the reoccurrence of infection and organ injuries. Methods: Expression of Suppressor of Fused (Sufu) was evaluated by qRT-PCR, western blotting, and immunofluorescence in murine lung and peritoneal macrophages. The significance of Sufu expression in prognosis was assessed by Kaplan-Meier survival analysis. The GFP-TRAF6-expressing stable cell line (GFP-TRAF6 Blue cells) were constructed to evaluate phase separation of TRAF6. Phase separation of TRAF6 and the roles of Sufu in repressing TRAF6 droplet aggregation were analyzed by co-immunoprecipitation, immunofluorescence, Native-PAGE, FRAP and in vitro assays using purified proteins. The effects of Sufu on sepsis-induced lung inflammation were evaluated by cell function assays, LPS-induced septic shock model and polymicrobial sepsis-CLP mice model. Results: We found that Sufu expression is reduced in early response to lipopolysaccharide (LPS)-induced acute inflammation in murine lung and peritoneal macrophages. Deletion of Sufu aggravated LPS-induced and CLP (cecal ligation puncture)-induced lung injury and lethality in mice, and augmented LPS-induced proinflammatory gene expression in cultured macrophages. In addition, we identified the role of Sufu as a negative regulator of the Toll-Like Receptor (TLR)-triggered inflammatory response. We further demonstrated that Sufu directly interacts with TRAF6, thereby preventing oligomerization and autoubiquitination of TRAF6. Importantly, TRAF6 underwent phase separation during LPS-induced inflammation, which is essential for subsequent ubiquitination activation and NF-κB activity. Sufu inhibits the phase-separated TRAF6 droplet formation, preventing NF-κB activation upon LPS stimulation. In a septic shock model, TRAF6 depletion rescued the augmented inflammatory phenotype in mice with myeloid cell-specific deletion of Sufu. Conclusions: These findings implicated Sufu as an important inhibitor of TRAF6 in sepsis and suggest that therapeutics targeting Sufu-TRAF6 may greatly benefit the treatment of sepsis.

NEUTROPHIL HETEROGENEITY IN SEPSIS: THE ROLE OF DAMAGE-ASSOCIATED MOLECULAR PATTERNS

ABSTRACT

Sepsis is a severe inflammatory disease syndrome caused by the dysregulated host response to infection. Neutrophils act as the first line of defense against pathogens by releasing effector molecules such as reactive oxygen species, myeloperoxidase, and neutrophil extracellular traps. However, uncontrolled activation of neutrophils and extensive release of effector molecules often cause a "friendly fire" to damage organ systems. Although neutrophils are considered a short-lived, terminally differentiated homogeneous population, recent studies have revealed its heterogeneity comprising different subsets or states implicated in sepsis pathophysiology. Besides the well-known N1 and N2 subsets of neutrophils, several new subsets including aged, antigen-presenting, reverse-migrated, intercellular adhesion molecule-1 + , low-density, olfactomedin 4 + , and Siglec-F + neutrophils have been reported. These neutrophils potentially contribute to the pathogenesis of sepsis based on their proinflammatory and immunosuppressive functions. Damage-associated molecular patterns (DAMPs) are endogenous molecules to induce inflammation by stimulating pattern recognition receptors on immune cells. Different kinds of DAMPs have been shown to contribute to sepsis pathophysiology, including extracellular cold-inducible RNA-binding protein, high-mobility group box 1, extracellular histones, and heat shock proteins. In this review, we summarize the different subsets of neutrophils and their association with sepsis and discuss the novel roles of DAMPs on neutrophil heterogeneity.

PD-L1 maintains neutrophil extracellular traps release by inhibiting neutrophil autophagy in endotoxin-induced lung injury

Programmed death ligand 1 (PD-L1) is not only an important molecule in mediating tumor immune escape, but also regulates inflammation development. Here we showed that PD-L1 was upregulated on neutrophils in lipopolysaccharide (LPS)-induced acute respiratory distress syndrome (ARDS). Neutrophil specific knockout of PD-L1 reduced lung injury in ARDS model induced by intratracheal LPS injection. The level of NET release was reduced and autophagy is elevated by PD-L1 knockout in ARDS neutrophils both in vivo and in vitro. Inhibition of autophagy could reverse the inhibitory effect of PD-L1 knockout on NET release. PD-L1 interacted with p85 subunit of PI3K at the endoplasmic reticulum (ER) in neutrophils from ARDS patients, activating the PI3K/Akt/mTOR pathway. An extrinsic neutralizing antibody against PD-L1 showed a protective effect against ARDS. Together, PD-L1 maintains the release of NETs by regulating autophagy through the PI3K/Akt/mTOR pathway in ARDS. Anti-PD-L1 therapy may be a promising measure in treating ARDS.

Neutrophil heterogeneity in complement C1q expression associated with sepsis mortality

Sepsis is a life-threatening systemic inflammatory condition causing approximately 11 million annual deaths worldwide. Although key hyperinflammation-based organ dysfunctions that drive disease pathology have been recognized, our understanding of the factors that predispose patients to septic mortality is limited. Due to the lack of reliable prognostic measures, the development of appropriate clinical management that improves patient survival remains challenging. Here, we discovered that a subpopulation of CD49chigh neutrophils with dramatic upregulation of the complement component 1q (C1q) gene expression arises during severe sepsis. We further found that deceased septic patients failed to maintain C1q protein expression in their neutrophils, whereas septic survivors expressed higher levels of C1q. In mouse sepsis models, blocking C1q with neutralizing antibodies or conditionally knocking out C1q in neutrophils led to a significant increase in septic mortality. Apoptotic neutrophils release C1q to control their own clearance in critically injured organs during sepsis; thus, treatment of septic mice with C1q drastically increased survival. These results suggest that neutrophil C1q is a reliable prognostic biomarker of septic mortality and a potential novel therapeutic target for the treatment of sepsis.

Lysophosphatidylcholine Alleviates Acute Lung Injury by Regulating Neutrophil Motility and Neutrophil Extracellular Trap Formation

Sepsis is predominantly initiated by bacterial infection and can cause systemic inflammation, which frequently leads to rapid death of the patient. However, this acute systemic inflammatory response requires further investigation from the perspectives of clinical judgment criteria and early treatment strategies for the relief of symptoms. Lysophosphatidylcholine (LPC) 18:0 may relieve septic symptoms, but the relevant mechanism is not clearly understood. Therefore, we aimed to assess the effectiveness of LPC as a therapeutic treatment for acute inflammation in the lung induced by lipopolysaccharide in mice. Systemic inflammation of mice was induced by lipopolysaccharide (LPS) inoculation to investigate the role of LPC in the migration and the immune response of neutrophils during acute lung injury. By employing two-photon intravital imaging of the LPS-stimulated LysM-GFP mice and other in vitro and in vivo assays, we examined whether LPC alleviates the inflammatory effect of sepsis. We also tested the effect of LPC to human neutrophils from healthy control and sepsis patients. Our data showed that LPC treatment reduced the infiltration of innate immune cells into the lung. Specifically, LPC altered neutrophil migratory patterns and enhanced phagocytic efficacy in the damaged lung. Moreover, LPC treatment reduced the release of neutrophil extracellular trap (NET), which can damage tissue in the inflamed organ and exacerbate disease. It also reduced human neutrophil migration under inflammatory environment. Our results suggest that LPC can alleviate sepsis-induced lung inflammation by regulating the function of neutrophils. These findings provide evidence for the beneficial application of LPC treatment as a potential therapeutic strategy for sepsis.

HS1 deficiency protects against sepsis by attenuating neutrophil-inflicted lung damage

Sepsis remains an important health problem worldwide due to inefficient treatments often resulting in multi-organ failure. Neutrophil recruitment is critical during sepsis. While neutrophils are required to combat invading bacteria, excessive neutrophil recruitment contributes to tissue damage due to their arsenal of molecular weapons that do not distinguish between host and pathogen. Thus, neutrophil recruitment needs to be fine-tuned to ensure bacterial killing, while avoiding neutrophil-inflicted tissue damage. We recently showed that the actin-binding protein HS1 promotes neutrophil extravasation; and hypothesized that HS1 is also a critical regulator of sepsis progression. We evaluated the role of HS1 in a model of lethal sepsis induced by cecal-ligation and puncture. We found that septic HS1-deficient mice had a better survival rate compared to WT mice due to absence of lung damage. Lungs of septic HS1-deficient mice showed less inflammation, fibrosis, and vascular congestion. Importantly, systemic CLP-induced neutrophil recruitment was attenuated in the lungs, the peritoneum and the cremaster in the absence of HS1. Lungs of HS1-deficient mice produced significantly more interleukin-10. Compared to WT neutrophils, those HS1-deficient neutrophils that reached the lungs had increased surface levels of Gr-1, ICAM-1, and L-selectin. Interestingly, HS1-deficient neutrophils had similar F-actin content and phagocytic activity, but they failed to polymerize actin and deform in response to CXCL-1 likely explaining the reduced systemic neutrophil recruitment in HS1-deficient mice. Our data show that HS1 deficiency protects against sepsis by attenuating neutrophil recruitment to amounts sufficient to combat bacterial infection, but insufficient to induce tissue damage.

Biomarkers for sepsis: more than just fever and leukocytosis-a narrative review

A biomarker describes a measurable indicator of a patient's clinical condition that can be measured accurately and reproducibly. Biomarkers offer utility for diagnosis, prognosis, early disease recognition, risk stratification, appropriate treatment (theranostics), and trial enrichment for patients with sepsis or suspected sepsis. In this narrative review, we aim to answer the question, "Do biomarkers in patients with sepsis or septic shock predict mortality, multiple organ dysfunction syndrome (MODS), or organ dysfunction?" We also discuss the role of pro- and anti-inflammatory biomarkers and biomarkers associated with intestinal permeability, endothelial injury, organ dysfunction, blood-brain barrier (BBB) breakdown, brain injury, and short and long-term mortality. For sepsis, a range of biomarkers is identified, including fluid phase pattern recognition molecules (PRMs), complement system, cytokines, chemokines, damage-associated molecular patterns (DAMPs), non-coding RNAs, miRNAs, cell membrane receptors, cell proteins, metabolites, and soluble receptors. We also provide an overview of immune response biomarkers that can help identify or differentiate between systemic inflammatory response syndrome (SIRS), sepsis, septic shock, and sepsis-associated encephalopathy. However, significant work is needed to identify the optimal combinations of biomarkers that can augment diagnosis, treatment, and good patient outcomes.

Inflammatory Monocytes and Subsets of Macrophages with Distinct Surface Phenotype Correlate with Specific Integrin Expression Profile during Murine Sepsis

Monocytes and macrophages participate in both pro- and anti-inflammatory responses during sepsis. Integrins are the cell adhesion receptors that mediate leukocyte migration and functions. To date, it is not known whether integrin profiles correlate with their trafficking, differentiation, and polarization during sepsis. In this study, using endotoxemia and cecal ligation and puncture model of murine sepsis, we have analyzed the role of surface integrins in tissue-specific infiltration, distribution of monocytes and macrophages, and their association with inflammation-induced phenotypic and functional alterations postinduction (p.i.) of sepsis. Our data show that Ly-6C^hi inflammatory monocytes infiltrated into the peritoneum from blood and bone marrow within a few hours p.i. of sepsis, with differential distribution of small (Ly-6C^loCD11b^loF4/80^lo) and large peritoneal macrophages (Ly-6C^loCD11b^hiF4/80^hi) in both models. The results from flow cytometry studies demonstrated a higher expression of integrin α₄β₁ on the Ly-6C^hi monocytes in different tissues, whereas macrophages in the peritoneum and lungs expressed higher levels of integrin α₅β₁ and α_vβ₃ in both models. Additionally, F4/80⁺ cells with CD206^hiMHCII^lo phenotype increased in the lungs of both models by six hours p.i. and expressed higher levels of integrin α_vβ₃ in both lungs and peritoneum. The presence of such cells correlated with higher levels of IL-10 and lower levels of IL-6 and IL-1β transcripts within six hours p.i. in the lungs compared with the mesentery. Furthermore, bioinformatic analysis with its experimental validation revealed an association of integrin α₄ and α₅ with inflammatory (e.g., p-SRC) and integrin α_v with regulatory molecules (e.g., TGFBR1) in macrophages during sepsis.

Integrin β3 Modulates TLR4-Mediated Inflammation by Regulation of CD14 Expression in Macrophages in Septic Condition

Sepsis is a major challenge in clinical practice and responsible for high mortality. Recent studies indicated that integrins participated in toll-like-receptor (TLR)-mediated innate immunity. In the present study, we investigated the mechanism of integrin β3 and TLR4 signaling using a cecal ligation and puncture (CLP)-induced sepsis and lipopolysaccharide (LPS)-treated macrophage cell model. In a lethal CLP model, the survival rate of integrin β3 mice was higher than that of wild-type mice. The levels of alanine aminotransferase, aspartate transaminase, creatinine, blood urea nitrogen , and lactate dehydrogenase in the serum and cluster of differentiation 14 (CD14) protein expression in the tissues were significantly decreased in integrin β3 mice. A similar effect with regard to CD14 down-regulation was observed in septic TLR4 mice. In wild-type macrophages, the inhibition of integrin β3 by P11 or with a specific antibody, inhibited TNF-α, and IL-6 release at the early time period of LPS stimulation. However, during the late periods of LPS stimulation this effect was not noted. CD14 expression levels had no change in such treatment. In contract, LPS-induced TNF-α and IL-6 release and LPS-induced CD14 expression were significantly decreased in integrin β3macrophages. The inhibition of the TLR4 pathway by TAK-242, or in TLR4 mutant macrophages abolished LPS-induced CD14 expression. Integrin β3 pathway activation by vitronectin exhibited no effect in CD14 expression. Furthermore, recombinant CD14 protein stimulation reversed integrin β3 deficiency and caused lower TNF-α and IL-6 release. Moreover, the molecular interaction of TLR4 and integrin β3 was significantly increased following LPS stimulation. In conclusion, integrin β3 positively regulated TLR4-mediated inflammatory responses via CD14 expression in macrophages in septic condition. Specifically targeting integrin β3/TLR4-CD14 signaling pathway may be a potential treatment strategy for polymicrobial sepsis.

ITGA3 Is Associated With Immune Cell Infiltration and Serves as a Favorable Prognostic Biomarker for Breast Cancer

Background

ITGA3 is a member of the integrin family, a cell surface adhesion molecule that can interact with extracellular matrix (ECM) proteins. The purpose of this study was to explore the significance of ITGA3 expression in the prognosis and clinical diagnosis of breast cancer patients.

Methods

Oncomine, the Human Protein Atlas (HPA) and UALCAN were used to analyze the expression of ITGA3 in various cancers. PrognoScan, GEPIA, Kaplan–Meier plotter and Easysurv were utilized to analyze the prognosis of ITGA3 in certain cancers. Based on TCGA data, a receiver operating characteristic (ROC) curve was used to evaluate the diagnostic performance of ITGA3 expression. cBio-Portal and MethSurv were used to evaluate the genomic mechanism. LinkedOmics, NetworkAnalyst and Metascape were used to build the signaling network. TIMER is a web server for comprehensive analysis of tumor infiltrating immune cells and tumor infiltrating lymphocytes (TILs).

Results

The expression of ITGA3 in normal breast tissues was greater than that in breast cancer tissues at both the mRNA and protein levels. High expression of ITGA3 was associated with better prognosis of breast cancer patients. ROC analysis indicated that ITGA3 had significant diagnostic value. Genomic analysis revealed that promoter methylation of ITGA3 leads to transcriptional silencing, which may be one of the mechanisms underlying ITGA3 downregulation in BRCA. Immune infiltration analysis showed that ITGA3 may be involved in the recruitment of immune cells.

Conclusions

This study identified ITGA3 as a novel biomarker to estimate the diagnosis and prognosis of breast cancer. In addition, ITGA3 is involved in ECM regulation and immune cell infiltration.

Upregulated PD-L1 delays human neutrophil apoptosis and promotes lung injury in an experimental animal model of sepsis

PD-L1 is a ligand for PD-1 and its expression has been shown to be upregulated in neutrophils harvested from septic patients. However, the effect of PD-L1 on neutrophil survival and sepsis-induced lung injury remains largely unknown. Here we show PD-L1 expression negatively correlates with rates of apoptosis in human neutrophils harvested from patients with sepsis. Using co-immunoprecipitation assays on control neutrophils challenged with IFN-γ and LPS, we show PD-L1 complexes with the p85 subunit of PI3-K to activate AKT-dependent survival signaling. Conditional CRE/LoxP deletion of neutrophil PD-L1 in vivo further protected against lung injury and reduced neutrophil lung infiltration in a cecal ligation and puncture (CLP) experimental sepsis animal model. Compared to wild-type animals, PD-L1-deficient animals presented lower plasma levels of plasma TNF-α and IL-6 and higher IL-10 following CLP, and reduced seven-day mortality in CLP PD-L1 knockout animals. Taken together, our data suggest that increased PD-L1 expression on human neutrophils delays cellular apoptosis by triggering PI-3K-dependent AKT phosphorylation to drive lung injury and increase mortality during clinical and experimental sepsis.

Neutrophil subtypes shape HIV-specific CD8 T-cell responses after vaccinia virus infection

Neutrophils are innate immune cells involved in the elimination of pathogens and can also induce adaptive immune responses. Nα and Nβ neutrophils have been described with distinct in vitro capacity to generate antigen-specific CD8 T-cell responses. However, how these cell types exert their role in vivo and how manipulation of Nβ/Nα ratio influences vaccine-mediated immune responses are not known. In this study, we find that these neutrophil subtypes show distinct migratory and motility patterns and different ability to interact with CD8 T cells in the spleen following vaccinia virus (VACV) infection. Moreover, after analysis of adhesion, inflammatory, and migration markers, we observe that Nβ neutrophils overexpress the α4β1 integrin compared to Nα. Finally, by inhibiting α4β1 integrin, we increase the Nβ/Nα ratio and enhance CD8 T-cell responses to HIV VACV-delivered antigens. These findings provide significant advancements in the comprehension of neutrophil-based control of adaptive immune system and their relevance in vaccine design.

A Bioinformatics Perspective on the Links Between Tetraspanin-Enriched Microdomains and Cardiovascular Pathophysiology

Background: Tetraspanins and integrins are integral membrane proteins. Tetraspanins interact with integrins to modulate the dynamics of adhesion, migration, proliferation, and signaling in the form of membrane domains called tetraspanin-enriched microdomains (TEMs). TEMs also contain other cell adhesion proteins like immunoglobulin superfamily (IgSF) proteins and claudins. Cardiovascular functions of these TEM proteins have emerged and remain to be further revealed. Objectives: The aims of this study are to explore the roles of these TEM proteins in the cardiovascular system using bioinformatics tools and databases and to highlight the TEM proteins that may functionally associate with cardiovascular physiology and pathology. Methods: For human samples, three databases-GTEx, NCBI-dbGaP, and NCBI-GEO-were used for the analyses. The dbGaP database was used for GWAS analysis to determine the association between target genes and human phenotypes. GEO is an NCBI public repository that archives genomics data. GTEx was used for the analyses of tissue-specific mRNA expression levels and eQTL. For murine samples, GeneNetwork was used to find gene-phenotype correlations and gene-gene correlations of expression levels in mice. The analysis of cardiovascular data was the focus of this study. Results: Some integrins and tetraspanins, such as ITGA8 and Cd151, are highly expressed in the human cardiovascular system. TEM components are associated with multiple cardiovascular pathophysiological events in humans. GWAS and GEO analyses showed that human Cd82 and ITGA9 are associated with blood pressure. Data from mice also suggest that various cardiovascular phenotypes are correlated with integrins and tetraspanins. For instance, Cd82 and ITGA9, again, have correlations with blood pressure in mice. Conclusion: ITGA9 is related to blood pressure in both species. KEGG analysis also linked ITGA9 to metabolism and MAPK signaling pathway. This work provides an example of using integrated bioinformatics approaches across different species to identify the connections of structurally and/or functionally related molecules to certain categories of diseases.

Functional and Therapeutic Relevance of Rho GTPases in Innate Immune Cell Migration and Function during Inflammation: An In Silico Perspective

Systematic regulation of leukocyte migration to the site of infection is a vital step during immunological responses. Improper migration and localization of immune cells could be associated with disease pathology as seen in systemic inflammation. Rho GTPases act as molecular switches during inflammatory cell migration by cycling between Rho-GDP (inactive) to Rho-GTP (active) forms and play an essential role in the precise regulation of actin cytoskeletal dynamics as well as other immunological functions of leukocytes. Available reports suggest that the dysregulation of Rho GTPase signaling is associated with various inflammatory diseases ranging from mild to life-threatening conditions. Therefore, it is crucial to understand the step-by-step activation and inactivation of GTPases and the functioning of different Guanine Nucleotide Exchange Factors (GEFs) and GTPase-Activating Proteins (GAPs) that regulate the conversion of GDP to GTP and GTP to GDP exchange reactions, respectively. Here, we describe the molecular organization and activation of various domains of crucial elements associated with the activation of Rho GTPases using solved PDB structures. We will also present the latest evidence available on the relevance of Rho GTPases in the migration and function of innate immune cells during inflammation. This knowledge will help scientists design promising drug candidates against the Rho-GTPase-centric regulatory molecules regulating inflammatory cell migration.

1- and 2-integrins: central players in regulating vascular permeability and leukocyte recruitment during acute inflammation

The integrin family, an indispensable part of cell-cell and cell-matrix interactions, consists of a group of heterodimeric adhesion receptors formed by α- and β-integrin subunits. Their wide expression and unique bidirectional signaling pathways allow them to play roles in a variety of biological activities including blood clot formation, cell attachment, and migration. Evidence suggests that integrins are essential regulators of the initiation of acute inflammation, especially two key aspects of this process i.e., vascular permeability and leukocyte recruitment. This mini-review discusses the importance of integrins at the onset of the acute inflammatory response and outlines research advances regarding the function of integrins and their modulators at different stages of this process. Insights into the fine-tuning of integrin signaling during acute inflammation may inspire the design of new drugs for inflammatory diseases.

Paracoccidioides brasiliensis downmodulates α3 integrin levels in human lung epithelial cells in a TLR2-dependent manner

Paracoccidioidomycosis (PCM) is the most prevalent systemic mycosis in Latin America and may be caused by the species Paracoccidioides brasiliensis. In the lungs, this fungus interacts with epithelial cells, activating host cell signalling pathways, resulting in the production of inflammatory mediators. This event may be initiated through the activation of Pattern-Recognition Receptors such as Toll-like Receptors (TLRs). By interacting with cell wall components, TLR2 is frequently related to fungal infections. In this work, we show that, after 24 h post-infection with P. brasiliensis, A549 lung epithelial cells presented higher TLR2 levels, which is important for IL-8 secretion. Besides, integrins may also participate in pathogen recognition by host cells. We verified that P. brasiliensis increased α3 integrin levels in A549 cells after 5 h of infection and promoted interaction between this receptor and TLR2. However, after 24 h, surprisingly, we verified a decrease of α3 integrin levels, which was dependent on direct contact between fungi and epithelial cells. Likewise, we observed that TLR2 is important to downmodulate α3 integrin levels after 24 h of infection. Thus, P. brasiliensis can modulate the host inflammatory response by exploiting host cell receptors and cell signalling pathways.

The Neutrophil: Constant Defender and First Responder

The role of polymorphonuclear neutrophils (PMNs) in biology is often recognized during pathogenesis associated with PMN hyper- or hypo-functionality in various disease states. However, in the vast majority of cases, PMNs contribute to resilience and tissue homeostasis, with continuous PMN-mediated actions required for the maintenance of health, particularly in mucosal tissues. PMNs are extraordinarily well-adapted to respond to and diminish the damaging effects of a vast repertoire of infectious agents and injurious processes that are encountered throughout life. The commensal biofilm, a symbiotic polymicrobial ecosystem that lines the mucosal surfaces, is the first line of defense against pathogenic strains that might otherwise dominate, and is therefore of critical importance for health. PMNs regularly interact with the commensal flora at the mucosal tissues in health and limit their growth without developing an overt inflammatory reaction to them. These PMNs exhibit what is called a para-inflammatory phenotype, and have reduced inflammatory output. When biofilm growth and makeup are disrupted (i.e., dysbiosis), clinical symptoms associated with acute and chronic inflammatory responses to these changes may include pain, erythema and swelling. However, in most cases, these responses indicate that the immune system is functioning properly to re-establish homeostasis and protect the status quo. Defects in this healthy everyday function occur as a result of PMN subversion by pathological microbial strains, genetic defects or crosstalk with other chronic inflammatory conditions, including cancer and rheumatic disease, and this can provide some avenues for therapeutic targeting of PMN function. In other cases, targeting PMN functions could worsen the disease state. Certain PMN-mediated responses to pathogens, for example Neutrophil Extracellular Traps (NETs), might lead to undesirable symptoms such as pain or swelling and tissue damage/fibrosis. Despite collateral damage, these PMN responses limit pathogen dissemination and more severe damage that would otherwise occur. New data suggests the existence of unique PMN subsets, commonly associated with functional diversification in response to particular inflammatory challenges. PMN-directed therapeutic approaches depend on a greater understanding of this diversity. Here we outline the current understanding of PMNs in health and disease, with an emphasis on the positive manifestations of tissue and organ-protective PMN-mediated inflammation.

Biomarkers and Associated Immune Mechanisms for Early Detection and Therapeutic Management of Sepsis

Sepsis is conceptually defined as life-threatening organ dysfunction that is caused by a dysregulated host response to infection. Although there has been significant advancement in recent decades in defining and understanding sepsis pathology, clinical management of sepsis is challenging due to difficulties in diagnosis, a lack of reliable prognostic biomarkers, and treatment options that are largely limited to antibiotic therapy and fundamental supportive measures. The lack of reliable diagnostic and prognostic tests makes it difficult to triage patients who are in need of more urgent care. Furthermore, while the acute inpatient treatment of sepsis warrants ongoing attention and investigation, efforts must also be directed toward longer term survival and outcomes. Sepsis survivors experience incomplete recovery, with long-term health impairments that may require both cognitive and physical treatment and rehabilitation. This review summarizes recent advances in sepsis prognosis research and discusses progress made in elucidating the underlying causes of prolonged health deficits experienced by patients surviving the early phases of sepsis.

A C-terminal fragment of adhesion protein Fibulin7 regulates neutrophil migration and functions and improves survival in LPS induced systemic inflammation

Accumulation of hyperactive neutrophils in the visceral organs was shown to be associated with sepsis-induced multi-organ failure. Recently, a C-terminal fragment of secreted glycoprotein Fibulin7 (Fbln7-C) was shown to inhibit angiogenesis and regulate monocyte functions in inflammatory conditions. However, its effects on neutrophil functions and systemic inflammation induced lethality remain unknown. In this study, we show that human peripheral blood neutrophils adhered to Fbln7-C in a dose-dependent manner via integrin β1. Moreover, the presence of Fbln7-C inhibited spreading, and fMLP mediated random migration of neutrophils on fibronectin. Significant reduction in ROS and inflammatory cytokine production (i.e., IL-6, IL-1β) was observed, including a reduction in ERK1⁄2 phosphorylation in neutrophils stimulated with LPS and fMLP in the presence of Fbln7-C compared to untreated controls. In an in vivo model of endotoxemia, the administration of Fbln7-C (10 μg/dose) significantly improved survival and reduced the infiltration of neutrophils to the site of inflammation. Additionally, neutrophils infiltrating into the inflamed peritoneum of Fbln7-C administered animals expressed lower levels CD11b marker, IL-6, and produced lower levels of ROS upon stimulation with PMA compared to untreated controls. In conclusion, our results show that Fbln7-C could bind to the integrin β1 on the neutrophil surface and regulate their inflammatory functions.

Investigation of Extracellular Matrix Protein Expression Dynamics Using Murine Models of Systemic Inflammation

Extracellular matrix (ECM) proteins form the structural support for migration of leukocytes and provide multiple signals to assist in their functions during inflammatory conditions. Presence of pro-inflammatory mediators in the tissues results in the remodelling of matrices which could modify the functions of extravasated leukocytes. Previous reports have shown changes in the expression of ECM proteins during local inflammatory responses. In this study, we have investigated the time- and tissue-specific expression profile of key ECM proteins in systemic inflammation using lipopolysaccharide (LPS)-induced endotoxemia and cecal ligation and puncture (CLP) mouse models. The results show that compared to naïve tissues, within 12 h following CLP surgery, a 20-30-fold increase was observed in the expression of collagen-IV (Col-IV) transcripts in the mesentery tissues with a 2.4-fold increase in the protein by 24 h. However, Western blot band intensities indicated that vimentin and fibrinogen were remarkably expressed in more quantity compared to Col-IV. Secondly, in CLP group of mice, fibrinogen showed 6-40-fold increase in mRNA level in various tissues with about 2-fold increase in the protein level compared to respective naïve tissues. Similar studies in the LPS-injected mice showed up to 2-3 fold increase in the expression of Col-IV, fibrinogen and vimentin at protein level in the lungs. In such animals, although similar pattern was observed for fibrinogen in kidney and liver tissues, the mesentery showed prominent changes in Col-IV and vimentin mRNA compared to CLP. Further, bioinformatics analysis showed multiple pathways which could be associated with vimentin, Col-IV and fibrinogen under inflammatory conditions both in human and mouse. The current study will help in better understanding of possible signalling from ECM proteins in inflammatory microenvironment and may contribute in development of cell adhesion-based therapeutics.

Molecular regulation of TLR signaling in health and disease: mechano-regulation of macrophages and TLR signaling

Immune cells encounter tissues with vastly different biochemical and physical characteristics. Much of the research emphasis has focused on the role of cytokines and chemokines in regulating immune cell function, but the role of the physical microenvironment has received considerably less attention. The tissue mechanics, or stiffness, of healthy tissues varies dramatically from soft adipose tissue and brain to stiff cartilage and bone. Tissue mechanics also change due to fibrosis and with diseases such as atherosclerosis or cancer. The process by which cells sense and respond to their physical microenvironment is called mechanotransduction. Here we review mechanotransduction in immunologically important diseases and how physical characteristics of tissues regulate immune cell function, with a specific emphasis on mechanoregulation of macrophages and TLR signaling.

Src family kinase-mediated vesicle trafficking is critical for neutrophil basement membrane penetration

Leukocyte recruitment into inflamed tissue is highly dependent on the activation and binding of integrins to their respective ligands, followed by the induction of various signaling events within the cell referred to as outside-in signaling. Src family kinases (SFK) are the central players in the outside-in signaling process, assigning them a critical role for proper immune cell function. Our study investigated the role of SFK on neutrophil recruitment in vivo using Hck^−/- Fgr^−/- Lyn^−/- mice, which lack SFK expressed in neutrophils. We show that loss of SFK strongly reduces neutrophil adhesion and post-arrest modifications in a shear force dependent manner. Additionally, we found that in the absence of SFK, neutrophils display impaired Rab27a-dependent surface mobilization of neutrophil elastase, VLA3 and VLA6 containing vesicles. This results in a defect in neutrophil vascular basement membrane penetration and thus strongly impaired extravasation. Taken together, we demonstrate that SFK play a role in neutrophil post-arrest modifications and extravasation during acute inflammation. These findings may support the current efforts to use SFK-inhibitors in inflammatory diseases with unwanted neutrophil recruitment.

Pathological alteration and therapeutic implications of sepsis-induced immune cell apoptosis

Sepsis is a life-threatening organ dysfunction syndrome caused by dysregulated host response to infection that leads to uncontrolled inflammatory response followed by immunosuppression. However, despite the high mortality rate, no specific treatment modality or drugs with high efficacy is available for sepsis to date. Although improved treatment strategies have increased the survival rate during the initial state of excessive inflammatory response, recent trends in sepsis show that mortality occurs at a period of continuous immunosuppressive state in which patients succumb to secondary infections within a few weeks or months due to post-sepsis “immune paralysis.” Immune cell alteration induced by uncontrolled apoptosis has been considered a major cause of significant immunosuppression. Particularly, apoptosis of lymphocytes, including innate immune cells and adaptive immune cells, is associated with a higher risk of secondary infections and poor outcomes. Multiple postmortem studies have confirmed that sepsis-induced immune cell apoptosis occurs in all age groups, including neonates, pediatric, and adult patients, and it is considered to be a primary contributing factor to the immunosuppressive pathophysiology of sepsis. Therapeutic perspectives targeting apoptosis through various strategies could improve survival in sepsis. In this review article, we will focus on describing the major apoptosis process of immune cells with respect to physiologic and molecular mechanisms. Further, advances in apoptosis-targeted treatment modalities for sepsis will also be discussed.

Endogenous Uteroglobin as Intrinsic Anti-inflammatory Signal Modulates Monocyte and Macrophage Subsets Distribution Upon Sepsis Induced Lung Injury

Sepsis is a serious clinical condition which can cause life-threatening organ dysfunction, and has limited therapeutic options. The paradigm of limiting excessive inflammation and promoting anti-inflammatory responses is a simplified concept. Yet, the absence of intrinsic anti-inflammatory signaling at the early stage of an infection can lead to an exaggerated activation of immune cells, including monocytes and macrophages. There is emerging evidence that endogenous molecules control those mechanisms. Here we aimed to identify and describe the dynamic changes in monocyte and macrophage subsets and lung damage in CL57BL/6N mice undergoing blunt chest trauma with subsequent cecal ligation and puncture. We showed that early an increase in systemic and activated Ly6C⁺CD11b⁺CD45⁺Ly6G^- monocytes was paralleled by their increased emigration into lungs. The ratio of pro-inflammatory Ly6C^highCD11b⁺CD45⁺Ly6G^- to patrolling Ly6C^lowCD11b⁺CD45⁺Ly6G^- monocytes significantly increased in blood, lungs and bronchoalveolar lavage fluid (BALF) suggesting an early transition to inflammatory phenotypes during early sepsis development. Similar to monocytes, the level of pro-inflammatory Ly6C^highCD45⁺F4/80⁺ macrophages increased in lungs and BALF, while tissue repairing Ly6C^lowCD45⁺F4/80⁺ macrophages declined in BALF. Levels of inflammatory mediators TNF-α and MCP-1 in blood and RAGE in lungs and BALF were elevated, and besides their boosting of inflammation via the recruitment of cells, they may promote monocyte and macrophage polarization, respectively, toward the pro-inflammatory phenotype. Neutralization of uteroglobin increased pro-inflammatory cytokine levels, activation of inflammatory phenotypes and their recruitment to lungs; concurrent with increased pulmonary damage in septic mice. In in vitro experiments, the influence of uteroglobin on monocyte functions including migratory behavior, TGF-β1 expression, cytotoxicity and viability were proven. These results highlight an important role of endogenous uteroglobin as intrinsic anti-inflammatory signal upon sepsis-induced early lung injury, which modules the early monocyte/macrophages driven inflammation.

Short Summary

Blunt chest injury is the third largest cause of death following major trauma, and ongoing excessive pro-inflammatory immune response entails high risk for the development of secondary complications, such as sepsis, with limited therapeutic options. In murine double hit trauma consisting of thoracic trauma and subsequent cecal ligation and puncture, we investigated the cytokine profile, pulmonary epithelial integrity and phenotypic shift of patrolling Ly6C^lowCD11b⁺CD45⁺Ly6G^- monocytes and Ly6C^lowCD45⁺F4/80⁺ macrophages to pro-inflammatory Ly6C^highCD11b⁺CD45⁺Ly6G^- monocytes and Ly6C^highCD45⁺F4/80⁺ cells in blood, lungs and bronchoalveolar lavage fluid (BALF). Pro-inflammatory mediators and phenotypes were elevated and uteroglobin neutralization led to further increase. Enhanced total protein levels in BALF suggests leakage of respiratory epithelium. In vitro, uteroglobin inhibited the migratory capacity of monocytes and the TGF-β1 expression without affecting the viability. These results highlight an important role of endogenous uteroglobin as an intrinsic anti-inflammatory signal upon sepsis-induced early lung injury, which modulates the early monocyte/macrophages driven inflammation.

Neutrophils homing into the retina trigger pathology in early age-related macular degeneration

Age-related macular degeneration (AMD) is an expanding problem as longevity increases worldwide. While inflammation clearly contributes to vision loss in AMD, the mechanism remains controversial. Here we show that neutrophils are important in this inflammatory process. In the retinas of both early AMD patients and in a mouse model with an early AMD-like phenotype, we show neutrophil infiltration. Such infiltration was confirmed experimentally using ribbon-scanning confocal microscopy (RSCM) and IFNλ- activated dye labeled normal neutrophils. With neutrophils lacking lipocalin-2 (LCN-2), infiltration was greatly reduced. Further, increased levels of IFNλ in early AMD trigger neutrophil activation and LCN-2 upregulation. LCN-2 promotes inflammation by modulating integrin β1 levels to stimulate adhesion and transmigration of activated neutrophils into the retina. We show that in the mouse model, inhibiting AKT2 neutralizes IFNλ inflammatory signals, reduces LCN-2-mediated neutrophil infiltration, and reverses early AMD-like phenotype changes. Thus, AKT2 inhibitors may have therapeutic potential in early, dry AMD.

LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) distinctly regulate neutrophil extravasation through hotspots I and II

Precise spatiotemporal regulation of leukocyte extravasation is key for generating an efficient immune response to injury or infection. The integrins LFA-1(CD11a/CD18) and Mac-1(CD11b/CD18) play overlapping roles in neutrophil migration because they bind the same as well as different ligands in response to extracellular signaling. Using two-photon intravital imaging and transmission electron microscopy, we observed the existence of preferred sites for neutrophil entrance into the endothelial cell monolayer and exit from the basement membrane and pericyte sheath during neutrophil extravasation, namely, hotspots I and II, by elucidating distinctive roles of LFA-1 and Mac-1. To penetrate the vascular endothelium, neutrophils must first penetrate the endothelial cell layer through hotspot I (i.e., the point of entry into the endothelium). Neutrophils frequently remain in the space between the endothelial cell layer and the basement membrane for a prolonged period (>20 min). Subsequently, neutrophils penetrate the basement membrane and pericyte sheath at hotspot II, which is the final stage of exiting the vascular endothelium. To further investigate the roles of LFA-1 and Mac-1, we newly generated LFA-1 FRET (CD11a-YFP/CD18-CFP) mice and Mac-1 FRET (CD11b-YFP/CD18-CFP) mice. Using both FRET mice, we were able to determine that LFA-1 and Mac-1 distinctly regulate the neutrophil extravasation cascade. Our data suggest that the vascular endothelium functions as a double-layered barrier in the steps of neutrophil extravasation. We propose that the harmonized regulation of neutrophil penetration through the endothelium via hotspots I and II may be critical for vascular homeostasis during inflammation.

A ligand-specific blockade of the integrin Mac-1 selectively targets pathologic inflammation while maintaining protective host-defense

Integrin-based therapeutics have garnered considerable interest in the medical treatment of inflammation. Integrins mediate the fast recruitment of monocytes and neutrophils to the site of inflammation, but are also required for host defense, limiting their therapeutic use. Here, we report a novel monoclonal antibody, anti-M7, that specifically blocks the interaction of the integrin Mac-1 with its pro-inflammatory ligand CD40L, while not interfering with alternative ligands. Anti-M7 selectively reduces leukocyte recruitment in vitro and in vivo. In contrast, conventional anti-Mac-1 therapy is not specific and blocks a broad repertoire of integrin functionality, inhibits phagocytosis, promotes apoptosis, and fuels a cytokine storm in vivo. Whereas conventional anti-integrin therapy potentiates bacterial sepsis, bacteremia, and mortality, a ligand-specific intervention with anti-M7 is protective. These findings deepen our understanding of ligand-specific integrin functions and open a path for a new field of ligand-targeted anti-integrin therapy to prevent inflammatory conditions.

Recombinant Human Vimentin Binds to P-Selectin and Blocks Neutrophil Capture and Rolling on Platelets and Endothelium

Leukocyte adhesion to vascular endothelium and platelets is an early step in the acute inflammatory response. The initial process is mediated through P-selectin glycoprotein ligand-1 (PSGL-1) on leukocytes binding to platelets adhered to endothelium and the endothelium itself via P-selectin. Although these interactions are generally beneficial, pathologic inflammation may occur in undesirable circumstances, such as in acute lung injury (ALI) and ischemia and reperfusion injury. Therefore, the development of novel therapies to attenuate inflammation may be beneficial. In this article, we describe the potential benefit of using a recombinant human vimentin (rhVim) on reducing human leukocyte adhesion to vascular endothelium and platelets under shear stress. The addition of rhVim to whole blood and isolated neutrophils decreased leukocyte adhesion to endothelial and platelet monolayers. Furthermore, rhVim blocked neutrophil adhesion to P-selectin-coated surfaces. Binding assays showed that rhVim binds specifically to P-selectin and not to its counterreceptor, PSGL-1. Finally, in an endotoxin model of ALI in C57BL/6J mice, treatment with rhVim significantly decreased histologic findings of ALI. These data suggest a potential role for rhVim in attenuating inflammation through blocking P-selectin-PSGL-1 interactions.

Potential Immunotherapeutics for Immunosuppression in Sepsis

Sepsis is a syndrome characterized by systemic inflammatory responses to a severe infection. Acute hyper-inflammatory reactions in the acute phase of sepsis have been considered as a primary reason for organ dysfunction and mortality, and advances in emergency intervention and improved intensive care management have reduced mortalities in the early phase. However it has been recognized that increased deaths in the late phase still maintain sepsis mortality high worldwide. Patients recovered from early severe illness are unable to control immune system with sepsis-induced immunosuppression such as immunological tolerance, exhaustion and apoptosis, which make them vulnerable to nosocomial and opportunistic infections ultimately leading to threat to life. Based on strategies to reverse immunosuppression, recent developments in sepsis therapy are focused on molecules having immune enhancing activities. These efforts are focused on defining and revising the immunocompromised status associated with long-term mortality.

Activated Protein C Attenuates Severe Inflammation by Targeting VLA-3high Neutrophil Subpopulation in Mice

The host injury involved in multiorgan system failure during severe inflammation is mediated, in part, by massive infiltration and sequestration of hyperactive neutrophils in the visceral organ. A recombinant form of human activated protein C (rhAPC) has shown cytoprotective and anti-inflammatory functions in some clinical and animal studies, but the direct mechanism is not fully understood. Recently, we reported that, during endotoxemia and severe polymicrobial peritonitis, integrin VLA-3 (CD49c/CD29) is specifically upregulated on hyperinflammatory neutrophils and that targeting the VLA-3high neutrophil subpopulation improved survival in mice. In this article, we report that rhAPC binds to human neutrophils via integrin VLA-3 (CD49c/CD29) with a higher affinity compared with other Arg-Gly-Asp binding integrins. Similarly, there is preferential binding of activated protein C (PC) to Gr1highCD11bhighVLA-3high cells isolated from the bone marrow of septic mice. Furthermore, specific binding of rhAPC to human neutrophils via VLA-3 was inhibited by an antagonistic peptide (LXY2). In addition, genetically modified mutant activated PC, with a high affinity for VLA-3, shows significantly improved binding to neutrophils compared with wild-type activated PC and significantly reduced neutrophil infiltration into the lungs of septic mice. These data indicate that variants of activated PC have a stronger affinity for integrin VLA-3, which reveals novel therapeutic possibilities.

The immune system's role in sepsis progression, resolution, and long-term outcome

Sepsis occurs when an infection exceeds local tissue containment and induces a series of dysregulated physiologic responses that result in organ dysfunction. A subset of patients with sepsis progress to septic shock, defined by profound circulatory, cellular, and metabolic abnormalities, and associated with a greater mortality. Historically, sepsis-induced organ dysfunction and lethality were attributed to the complex interplay between the initial inflammatory and later anti-inflammatory responses. With advances in intensive care medicine and goal-directed interventions, early 30-day sepsis mortality has diminished, only to steadily escalate long after "recovery" from acute events. As so many sepsis survivors succumb later to persistent, recurrent, nosocomial, and secondary infections, many investigators have turned their attention to the long-term sepsis-induced alterations in cellular immune function. Sepsis clearly alters the innate and adaptive immune responses for sustained periods of time after clinical recovery, with immune suppression, chronic inflammation, and persistence of bacterial representing such alterations. Understanding that sepsis-associated immune cell defects correlate with long-term mortality, more investigations have centered on the potential for immune modulatory therapy to improve long-term patient outcomes. These efforts are focused on more clearly defining and effectively reversing the persistent immune cell dysfunction associated with long-term sepsis mortality.

GEF-H1 is necessary for neutrophil shear stress-induced migration during inflammation

In their work, Fine et al. demonstrate that GEF-H1 is required for the spreading and crawling of neutrophils in response to intravascular blood flow. They uncover a novel mechanism that couples shear stress with Rho-dependent migratory behavior of neutrophils during inflammation.

Leukocyte crawling and transendothelial migration (TEM) are potentiated by shear stress caused by blood flow. The mechanism that couples shear stress to migration has not been fully elucidated. We found that mice lacking GEF-H1 (GEF-H1^−/−), a RhoA-specific guanine nucleotide exchange factor (GEF), displayed limited migration and recruitment of neutrophils into inflamed tissues. GEF-H1^−/− leukocytes were deficient in in vivo crawling and TEM in the postcapillary venules. We demonstrated that although GEF-H1 deficiency had little impact on the migratory properties of neutrophils under static conditions, shear stress triggered GEF-H1–dependent spreading and crawling of neutrophils and relocalization of GEF-H1 to flotillin-2–rich uropods. Our results identify GEF-H1 as a component of the shear stress response machinery in neutrophils required for a fully competent immune response to bacterial infection.

Peripheral blood AKAP7 expression as an early marker for lymphocyte-mediated post-stroke blood brain barrier disruption

Our group recently identified 16 genes whose peripheral blood expression levels are differentially regulated in acute ischemic stroke. The purpose of this study was to determine whether the early expression levels of any of these 16 genes are predictive for post-stroke blood brain barrier (BBB) disruption. Transcriptional expression levels of candidate genes were measured in peripheral blood sampled from ischemic stroke patients at emergency department admission, and BBB permeability was assessed at 24 hour follow up via perfusion-weighted imaging. Early heightened expression levels of AKAP7, a gene encoding a protein kinase A-binding scaffolding molecule, were significantly associated with BBB disruption 24 hours post-hospital admission. We then determined that AKAP7 is predominantly expressed by lymphocytes in peripheral blood, and strongly co-expressed with ITGA3, a gene encoding the adhesion molecule integrin alpha 3. Subsequent in vitro experiments revealed that heightened expression of AKAP7 and ITGA3 in primary human lymphocytes is associated with a highly adherent phenotype. Collectively, our results suggest that AKAP7 expression levels may have clinical utility as a prognostic biomarker for post-stroke BBB complications, and are likely elevated early in patients who later develop post-stroke BBB disruption due to the presence of an invasive lymphocyte population in the peripheral blood.

From leukocyte recruitment to resolution of inflammation: the cardinal role of integrins

Integrins constitute a large group of adhesion receptors that are formed as heterodimers of α and β subunits. Their presence and activation status on the surface of leukocytes modulate a broad spectrum of processes in inflammation and immunity. This mini review critically outlines research advances with regard to the function of leukocyte integrins in regulating and integrating the onset and resolution of acute inflammation. Specifically, we summarize and discuss relevant, current literature that supports the multifunctional role of integrins and their partners. The latter include molecules that physically associate with integrins or regulate their activity in the context of the following: 1) leukocyte recruitment to an inflamed tissue, 2) recognition and phagocytosis of apoptotic neutrophils (efferocytosis), and 3) egress of efferocytic macrophages from the inflamed site to lymphoid tissues. The understanding of the fine-tuning mechanisms of the aforementioned processes by integrins and their functional partners may enable the design of therapeutic tools to counteract destructive inflammation and promote more efficient resolution of inflammation.

Neutrophil Extravasation Cascade: What Can We Learn from Two-photon Intravital Imaging?

Immune cells (leukocytes or white blood cells) move actively and sensitively based on body conditions. Despite their important role as protectors inside the body, it is difficult to directly observe the spatiotemporal momentum of leukocytes. With advances in imaging technology, the introduction of two-photon microscopy has enabled researchers to look deeper inside tissues in a three-dimensional manner. In observations of immune cell movement along the blood vessel, vascular permeability and innate immune cell movements remain unclear. Here, we describe the neutrophil extravasation cascade, which were observed using a two-photon intravital imaging technique. We also provide evidence for novel mechanisms such as neutrophil body extension and microparticle formation as well as their biological roles during migration.

Integrin Cross-Talk Regulates the Human Neutrophil Response to Fungal β-Glucan in the Context of the Extracellular Matrix: A Prominent Role for VLA3 in the Antifungal Response

Candida albicans infection produces elongated hyphae resistant to phagocytic clearance compelling alternative neutrophil effector mechanisms to destroy these physically large microbial structures. Additionally, all tissue-based neutrophilic responses to fungal infections necessitate contact with the extracellular matrix (ECM). Neutrophils undergo a rapid, ECM-dependent mechanism of homotypic aggregation and NETosis in response to C. albicans mediated by the β₂ integrin, complement receptor 3 (CR3, CD11b/CD18, α_Mβ₂). Neither homotypic aggregation nor NETosis occurs when human neutrophils are exposed either to immobilized fungal β-glucan or to C. albicans hyphae without ECM. The current study provides a mechanistic basis to explain how matrix controls the antifungal effector functions of neutrophils under conditions that preclude phagocytosis. We show that CR3 ligation initiates a complex mechanism of integrin cross-talk resulting in differential regulation of the β₁ integrins VLA3 (α₃β₁) and VLA5 (α₅β₁). These β₁ integrins control distinct antifungal effector functions in response to either fungal β-glucan or C. albicans hyphae and fibronectin, with VLA3 inducing homotypic aggregation and VLA5 regulating NETosis. These integrin-dependent effector functions are controlled temporally whereby VLA5 and CR3 induce rapid, focal NETosis early after binding fibronectin and β-glucan. Within minutes, CR3 undergoes inside-out auto-activation that drives the downregulation of VLA5 and the upregulation of VLA3 to support neutrophil swarming and aggregation. Forcing VLA5 to remain in the activated state permits NETosis but prevents homotypic aggregation. Therefore, CR3 serves as a master regulator during the antifungal neutrophil response, controlling the affinity states of two different β₁ integrins, which in turn elicit distinct effector functions.

MST1-dependent vesicle trafficking regulates neutrophil transmigration through the vascular basement membrane

Neutrophils need to penetrate the perivascular basement membrane for successful extravasation into inflamed tissue, but this process is incompletely understood. Recent findings have associated mammalian sterile 20-like kinase 1 (MST1) loss of function with a human primary immunodeficiency disorder, suggesting that MST1 may be involved in immune cell migration. Here, we have shown that MST1 is a critical regulator of neutrophil extravasation during inflammation. Mst1-deficient (Mst1-/-) neutrophils were unable to migrate into inflamed murine cremaster muscle venules, instead persisting between the endothelium and the basement membrane. Mst1-/- neutrophils also failed to extravasate from gastric submucosal vessels in a murine model of Helicobacter pylori infection. Mechanistically, we observed defective translocation of VLA-3, VLA-6, and neutrophil elastase from intracellular vesicles to the surface of Mst1-/- neutrophils, indicating that MST1 is required for this crucial step in neutrophil transmigration. Furthermore, we found that MST1 associates with the Rab27 effector protein synaptotagmin-like protein 1 (JFC1, encoded by Sytl1 in mice), but not Munc13-4, thereby regulating the trafficking of Rab27-positive vesicles to the cellular membrane. Together, these findings highlight a role for MST1 in vesicle trafficking and extravasation in neutrophils, providing an additional mechanistic explanation for the severe immune defect observed in patients with MST1 deficiency.

Regulation of tissue infiltration by neutrophils: role of integrin α3β1 and other factors

PURPOSE OF REVIEW

Neutrophils have traditionally been viewed in the context of acute infection and inflammation forming the first line of defense against invading pathogens. Neutrophil trafficking to the site of inflammation requires adhesion and transmigration through blood vessels, which is orchestrated by adhesion molecules, such as β2 and β1-integrins, chemokines, and cytokines. The review focuses on recent advances in understanding the regulators of neutrophil recruitment during inflammation in both acute and chronic settings.

RECENT FINDINGS

Recent findings suggest that besides the established pathways of selectin or chemokine-mediated integrin activation, signaling by distinct Toll-like receptors (TLRs) (especially TLR2, TLR4, and TLR5) can activate integrin-dependent neutrophil adhesion. Moreover, the integrin α3β1 has been vitally implicated as a new player in neutrophil recruitment and TLR-mediated responses in septic inflammation. Furthermore, several endogenous inhibitory mechanisms of leukocyte recruitment have been identified, including the secreted molecules Del-1, PTX3, and GDF-15, which block distinct steps of the leukocyte adhesion cascade, as well as novel regulatory signaling pathways, involving the protein kinase AKT1 and IFN-λ2/IL-28A.

SUMMARY

The leukocyte adhesion cascade is a tightly regulated process, subjected to both positive and negative regulators. Dysregulation of this process and hence neutrophil recruitment can lead to the development of inflammatory and autoimmune diseases.

Role of cellular events in the pathophysiology of sepsis

INTRODUCTION

Sepsis is a dysregulated host immune response due to an uncontrolled infection. It is a leading cause of mortality in adult intensive care units globally. When the host immune response induced against a local infection fails to contain it locally, it progresses to sepsis, severe sepsis, septic shock and death.

METHOD

Literature survey was performed on the roles of different innate and adaptive immune cells in the development and progression of sepsis. Additionally, the effects of septic changes on reprogramming of different immune cells were also summarized to prepare the manuscript.

FINDINGS

Scientific evidences to date suggest that the loss of balance between inflammatory and anti-inflammatory responses results in reprogramming of immune cell activities that lead to irreversible tissue damaging events and multi-organ failure during sepsis. Many surface receptors expressed on immune cells at various stages of sepsis have been suggested as biomarkers for sepsis diagnosis. Various immunomodulatory therapeutics, which could improve the functions of immune cells during sepsis, were shown to restore immunological homeostasis and improve survival in animal models of sepsis.

CONCLUSION

In-depth and comprehensive knowledge on the immune cell activities and their correlation with severity of sepsis will help clinicians and scientists to design effective immunomodulatory therapeutics for treating sepsis.

WISP1-αvβ3 integrin signaling positively regulates TLR-triggered inflammation response in sepsis induced lung injury

We recently noted that the matricellular protein WISP1 contributes to sepsis induced acute lung injury (ALI) via integrin β6. In the current study, we pursued further aspects of WISP1 modulation of TLR signaling in lungs of mice after sepsis and TLR4 mediated release of TNF-α in macrophages. After confirming that TLR4 and CD14 are critical in transducing sepsis mediated ALI, we now demonstrate that intrapulmonary αvβ3 is increased by polymicrobrial sepsis in a TLR4, CD14 dependent fashion. Comparison of cultured macrophages revealed that WISP1 increased release of TNF-α from RAW264.7 cells with baseline expression of αvβ3, but primary cultures of peritoneal macrophages (PMø) required activation of TLR4 to induce de novo synthesis of αvβ3 enabling WISP1 to stimulate release of TNF-α. The specific requirement for β3 integrin was apparent when the effect of WISP1 was lost in PMø isolated from β3(-/-) mice. WISP1 enhanced TLR4 mediated ERK signaling and U0126 (an ERK inhibitor) blocked LPS induced β3 integrin expression and WISP1 enhanced TNF-α release. Collectively these data suggest that WISP1-αvβ3 integrin signaling is involved in TLR4 pathways in macrophages and may be an important contributor to TLR4/CD14 mediated inflammation in sepsis induced lung injury.

Diagnostic value of soluble triggering receptor expressed on myeloid cells in paediatric sepsis: a systematic review

Background

Differential diagnosis between sepsis and non-infectious inflammatory disorders demands improved biomarkers. Soluble Triggering Receptor Expression on Myeloid cells (sTREM-1) is an activating receptor whose role has been studied throughout the last decade. We performed a systematic review to evaluate the accuracy of plasma sTREM-1 levels in the diagnosis of sepsis in children with Systemic Inflammatory Response Syndrome (SIRS).

Methods

A literature search of PubMed, Cochrane Central Register of Controlled Trials, Cumulative Index to Nursing and Allied Health Literature (CINAHL) and ISI Web of Knowledge databases was performed using specific search terms. Studies were included if they assessed the diagnostic accuracy of plasma sTREM-1 for sepsis in paediatric patients with SIRS. Data on sensitivity, specificity, positive predictive value, negative predictive value, area under receiver operating characteristic curve were extracted. The methodological quality of each study was assessed using a checklist based on the Quality Assessment Tool for Diagnostic Accuracy Studies.

Results

Nine studies comprising 961 patients were included, four of which were in newborns, three in children and two in children with febrile neutropenia. Some data from single studies support a role of sTREM-1 as a diagnostic tool in pediatric sepsis, but cannot be considered conclusive, because a quantitative synthesis was not possible, due to heterogeneity in studies design.

Conclusions

This systematic review suggests that available data are insufficient to support a role for sTREM in the diagnosis and follow-up of paediatric sepsis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13052-016-0242-y) contains supplementary material, which is available to authorized users.

Histoplasma capsulatum-Induced Cytokine Secretion in Lung Epithelial Cells Is Dependent on Host Integrins, Src-Family Kinase Activation, and Membrane Raft Recruitment

Histoplasma capsulatum var. capsulatum is a dimorphic fungus that causes histoplasmosis, a human systemic mycosis with worldwide distribution. In the present work, we demonstrate that H. capsulatum yeasts are able to induce cytokine secretion by the human lung epithelial cell line A549 in integrin- and Src-family kinase (SFK)-dependent manners. This conclusion is supported by small interfering RNA (siRNA) directed to α3 and α5 integrins, and PP2, an inhibitor of SFK activation. siRNA and PP2 reduced IL-6 and IL-8 secretion in H. capsulatum-infected A549 cell cultures. In addition, α3 and α5 integrins from A549 cells were capable of associating with H. capsulatum yeasts, and this fungus promotes recruitment of these integrins and SFKs to A549 cell membrane rafts. Corroborating this finding, membrane raft disruption with the cholesterol-chelator methyl-β-cyclodextrin reduced the levels of integrins and SFKs in these cell membrane domains. Finally, pretreatment of A549 cells with the cholesterol-binding compound, and also a membrane raft disruptor, filipin, significantly reduced IL-6 and IL-8 levels in A549-H.capsulatum cultures. Taken together, these results indicate that H. capsulatum yeasts induce secretion of IL-6 and IL-8 in human lung epithelial cells by interacting with α3 and α5 integrins, recruiting these integrins to membrane rafts, and promoting SFK activation.

Immune and regulatory functions of neutrophils in inflammatory bone loss

Although historically viewed as merely anti-microbial effectors in acute infection or injury, neutrophils are now appreciated to be functionally versatile with critical roles also in chronic inflammation. Periodontitis, a chronic inflammatory disease that destroys the tooth-supporting gums and bone, is particularly affected by alterations in neutrophil numbers or function, as revealed by observations in monogenic disorders and relevant mouse models. Besides being a significant debilitating disease and health burden in its own right, periodontitis is thus an attractive model to dissect uncharted neutrophil-associated (patho)physiological pathways. Here, we summarize recent evidence that neutrophils can contribute to inflammatory bone loss not only through the typical bystander injury dogma but intriguingly also through their absence from the affected tissue, where they normally perform important immunomodulatory functions. Moreover, we discuss recent advances in the interactions of neutrophils with the vascular endothelium and - upon extravasation - with bacteria, and how the dysregulation of these interactions leads to inflammatory tissue damage. Overall, neutrophils have both protective and destructive roles in periodontitis, as they are involved in both the maintenance of periodontal tissue homeostasis and the induction of inflammatory bone loss. This highlights the importance of developing approaches that promote or sustain a fine balance between homeostatic immunity and inflammatory pathology.