Intraluminal crawling versus interstitial neutrophil migration during inflammation

Salivary calprotectin and neutrophils in inflammatory bowel disease in relation to oral diseases

OBJECTIVE

Calprotectin is elevated in saliva from inflammatory bowel disease (IBD) patients, but it is also affected by oral disease. We assessed the salivary concentration of calprotectin in IBD patients, in relation to intestinal and oral diseases. Furthermore, we investigated the phenotype of salivary neutrophils from IBD patients, and their ability to secrete calprotectin.

MATERIALS AND METHODS

Thirty IBD patients and 26 controls were orally examined and sampled for stimulated saliva. Twenty-five IBD patients provided fresh fecal samples. Calprotectin concentrations in saliva and feces were determined by an enzyme-linked immunosorbent assay. Expression of CD11b, CD15, and CD16 on oral neutrophils was assessed by flow cytometry. Secretion of calprotectin was evaluated in cultured oral neutrophils.

RESULTS

Calprotectin was significantly elevated in saliva of IBD patients compared to controls, particularly in Crohn's disease, irrespective of caries or periodontitis. Salivary calprotectin did not correlate to fecal calprotectin. CD11b expression was significantly reduced in salivary neutrophils from IBD patients. Salivary neutrophils from IBD patients tended to secrete more calprotectin than controls.

CONCLUSIONS

Salivary calprotectin is elevated in IBD regardless of oral diseases. Furthermore, salivary neutrophils secrete calprotectin, and display lower CD11b expression in IBD.

Neutrophil hitchhiking: Riding the drug delivery wave to treat diseases

Neutrophils are a crucial component of the innate immune system and play a pivotal role in various physiological processes. From a physical perspective, hitchhiking is considered a phenomenon of efficient transportation. The combination of neutrophils and hitchhikers has given rise to effective delivery systems both in vivo and in vitro, thus neutrophils hitchhiking become a novel approach to disease treatment. This article provides an overview of the innovative and feasible application of neutrophils as drug carriers. It explores the mechanisms underlying neutrophil function, elucidates the mechanism of drug delivery mediated by neutrophil-hitchhiking, and discusses the potential applications of this strategy in the treatment of cancer, immune diseases, inflammatory diseases, and other medical conditions.

Multifactorial assessment of neutrophil chemotaxis efficiency from a drop of blood

Following injury and infection, neutrophils are guided to the affected site by chemoattractants released from injured tissues and invading microbes. During this process (chemotaxis), neutrophils must integrate multiple chemical signals, while also responding to physical constraints and prioritizing their directional decisions to generate an efficient immune response. In some clinical conditions, human neutrophils appear to lose the ability to chemotax efficiently, which may contribute both directly and indirectly to disease pathology. Here, a range of microfluidic designs is utilized to test the sensitivity of chemotaxing neutrophils to various perturbations, including binary decision-making in the context of channels with different chemoattractant gradients, hydraulic resistance, and angle of approach. Neutrophil migration in long narrow channels and planar environments is measured. Conditions in which neutrophils are significantly more likely to choose paths with the steepest chemoattractant gradient and the most direct approach angle, and find that migration efficiency across planar chambers is inversely correlated with chamber diameter. By sequential measurement of neutrophil binary decision-making to different chemoattractant gradients, or chemotactic index in sequential planar environments, data supporting a model of biased random walk for neutrophil chemotaxis are presented.

Neutrophil activation and circulating neutrophil extracellular traps are increased in venous thromboembolism patients for at least one year after the clinical event

Neutrophil activation and neutrophil extracellular traps (NETs) have been associated with the pathogenesis of venous thromboembolism (VTE). Considering VTE-associated chronic sequelae, which suggest that some pathological mechanisms remain after the acute episode, we investigated whether neutrophil activation is increased in patients with a prior VTE at least one year before this investigation. Thirty-seven patients with prior VTE and 37 individuals with no history of VTE were included. Neutrophil activity was evaluated by the expression of the adhesive molecule activation-specific epitopes LFA-1 (CD11a) and MAC-1 (CD11b), chemotaxis, reactive oxygen species (ROS) and by MPO-DNA complexes as markers of NETs. The adhesive molecules sICAM-1 and sVCAM-1, involved in the cross talk between neutrophil and endothelial cells, were also evaluated. Patient neutrophils presented increased CD11a expression before and after TNF-α stimulus, whereas increased CD11b expression was observed only after TNF-α stimulus, as compared to controls. Neutrophil chemotaxis on both, basal state and after IL-8 stimulus, on circulating levels of sICAM-1 and sVCAM-1, and on MPO-DNA complexes were also increased in VTE patients. ROS release was similar between patients and controls. This is, to our knowledge, the first study to investigate neutrophil inflammatory activity in VTE patients a long period after an acute event (approximately 2 years). The results showed altered neutrophil activation patterns in these patients. While activated neutrophils can cause endothelial activation and injury, the activated endothelium can induce the release of NETs with consequent endothelial cytotoxicity, creating a vicious cycle of activation between neutrophils and endothelium that can lead to thrombosis.

Multiple pathophysiological roles of midkine in human disease

Midkine (MK) is a low molecular-weight protein that was first identified as the product of a retinoic acid-responsive gene involved in embryonic development. Recent studies have indicated that MK levels are related to various diseases, including cardiovascular disease (CVD), renal disease and autoimmune disease. MK is a growth factor involved in multiple pathophysiological processes, such as inflammation, the repair of damaged tissues and cancer. The pathophysiological roles of MK are diverse. MK enhances the recruitment and migration of inflammatory cells upon inflammation directly and also through induction of chemokines, and contributes to tissue damage. In lung endothelial cells, oxidative stress increased the expression of MK, which induced angiotensin-converting enzyme (ACE) expression and the consequent conversion from Ang I to Ang II, leading to further oxidative stress. MK inhibited cholesterol efflux from macrophages by reducing ATP-binding cassette transporter A1 (ABCA1) expression, which is involved in lipid metabolism, suggesting that MK is an important positive factor involved in inflammation, oxidative stress and lipid metabolism. Furthermore, MK can regulate the expansion, differentiation and activation of T cells as well as B-cell survival; mediate angiogenic and antibacterial activity; and possess anti-apoptotic activity. In this paper, we summarize the pathophysiological roles of MK in human disease.

Context-Dependent Role of Vinculin in Neutrophil Adhesion, Motility and Trafficking

Neutrophils are innate immune effector cells that traffic from the circulation to extravascular sites of inflammation. β2 integrins are important mediators of the processes involved in neutrophil recruitment. Although neutrophils express the cytoskeletal protein vinculin, they do not form mature focal adhesions. Here, we characterize the role of vinculin in β2 integrin-dependent neutrophil adhesion, migration, mechanosensing, and recruitment. We observe that knockout of vinculin attenuates, but does not completely abrogate, neutrophil adhesion, spreading, and crawling under static conditions. However, we also found that vinculin deficiency does not affect these behaviors in the presence of forces from fluid flow. In addition, we identify a role for vinculin in mechanosensing, as vinculin-deficient neutrophils exhibit attenuated spreading on stiff, but not soft, substrates. Consistent with these findings, we observe that in vivo neutrophil recruitment into the inflamed peritoneum of mice remains intact in the absence of vinculin. Together, these data suggest that while vinculin regulates some aspects of neutrophil adhesion and spreading, it may be dispensable for β2 integrin-dependent neutrophil recruitment in vivo.

How Glucocorticoids Affect the Neutrophil Life

Glucocorticoids are hormones that regulate several functions in living organisms and synthetic glucocorticoids are the most powerful anti-inflammatory pharmacological tool that is currently available. Although glucocorticoids have an immunosuppressive effect on immune cells, they exert multiple and sometimes contradictory effects on neutrophils. From being extremely sensitive to the anti-inflammatory effects of glucocorticoids to resisting glucocorticoid-induced apoptosis, neutrophils are proving to be more complex than they were earlier thought to be. The aim of this review is to explain these complex pathways by which neutrophils respond to endogenous or to exogenous glucocorticoids, both under physiological and pathological conditions.

The Role of Midkine in Arteriogenesis, Involving Mechanosensing, Endothelial Cell Proliferation, and Vasodilation

Mechanical forces in blood circulation such as shear stress play a predominant role in many physiological and pathophysiological processes related to vascular responses or vessel remodeling. Arteriogenesis, defined as the growth of pre-existing arterioles into functional collateral arteries compensating for stenosed or occluded arteries, is such a process. Midkine, a pleiotropic protein and growth factor, has originally been identified to orchestrate embryonic development. In the adult organism its expression is restricted to distinct tissues (including tumors), whereby midkine is strongly expressed in inflamed tissue and has been shown to promote inflammation. Recent investigations conferred midkine an important function in vascular remodeling and growth. In this review, we introduce the midkine gene and protein along with its cognate receptors, and highlight its role in inflammation and the vascular system with special emphasis on arteriogenesis, particularly focusing on shear stress-mediated vascular cell proliferation and vasodilatation.

The Role of TRP Channels in the Metastatic Cascade

A dysregulated cellular Ca2+ homeostasis is involved in multiple pathologies including cancer. Changes in Ca2+ signaling caused by altered fluxes through ion channels and transporters (the transportome) are involved in all steps of the metastatic cascade. Cancer cells thereby "re-program" and "misuse" the cellular transportome to regulate proliferation, apoptosis, metabolism, growth factor signaling, migration and invasion. Cancer cells use their transportome to cope with diverse environmental challenges during the metastatic cascade, like hypoxic, acidic and mechanical cues. Hence, ion channels and transporters are key modulators of cancer progression. This review focuses on the role of transient receptor potential (TRP) channels in the metastatic cascade. After briefly introducing the role of the transportome in cancer, we discuss TRP channel functions in cancer cell migration. We highlight the role of TRP channels in sensing and transmitting cues from the tumor microenvironment and discuss their role in cancer cell invasion. We identify open questions concerning the role of TRP channels in circulating tumor cells and in the processes of intra- and extravasation of tumor cells. We emphasize the importance of TRP channels in different steps of cancer metastasis and propose cancer-specific TRP channel blockade as a therapeutic option in cancer treatment.

Ligand-specific binding forces of LFA-1 and Mac-1 in neutrophil adhesion and crawling

The force spectra for various LFA-1/Mac-1–ligand bonds were compared and their functions tested in mediating PMN recruitment under flow. Multiple endothelial ligands present distinct bond rupture forces and lifetimes, which correlate well with their biological phenotypes. In addition to ICAM, JAM or RAGE is also crucial in cell adhesion and crawling.

Lymphocyte function–associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1) and their counterreceptors such as intercellular cell adhesion molecules (ICAM-1 and ICAM-2), junctional adhesion molecules (JAM-A, JAM-C), and receptors for advanced glycation end products (RAGE) are crucial for promoting polymorphonuclear leukocyte (neutrophil, PMN) recruitment. The underlying mechanisms of ligand-specific bindings in this cascade remain incompletely known. We compared the dynamic force spectra for various LFA-1/Mac-1–ligand bonds using single-molecule atomic force microscopy (AFM) and tested their functions in mediating PMN recruitment under in vitro shear flow. Distinct features of bond rupture forces and lifetimes were uncovered for these ligands, implying their diverse roles in regulating PMN adhesion on endothelium. LFA-1 dominates PMN adhesion on ICAM-1 and ICAM-2, while Mac-1 mediates PMN adhesion on RAGE, JAM-A, and JAM-C, which is consistent with their bond strength. All ligands can trigger PMN spreading and polarization, in which Mac-1 seems to induce outside-in signaling more effectively. LFA-1–ICAM-1 and LFA-1/Mac-1–JAM-C bonds can accelerate PMN crawling under high shear stress, presumably due to their high mechanical strength. This work provides new insight into basic molecular mechanisms of physiological ligands of β2 integrins in PMN recruitment.

KCa3.1 channel inhibition leads to an ICAM-1 dependent increase of cell-cell adhesion between A549 lung cancer and HMEC-1 endothelial cells

Early metastasis leads to poor prognosis of lung cancer patients, whose 5-year survival rate is only 15%. We could recently show that the Ca²⁺ sensitive K⁺ channel K_Ca3.1 promotes aggressive behavior of non-small cell lung cancer (NSCLC) cells and that it can serve as a prognostic marker in NSCLC. Since NSCLC patients die of metastases, we investigated whether K_Ca3.1 channels contribute to poor patient prognosis by regulating distinct steps of the metastatic cascade. We investigated the extravasation of NSCLC cells and focused on their adhesion to endothelial cells and on transendothelial migration. We quantified the adhesion forces between NSCLC cells and endothelial cells by applying single cell force spectroscopy, and we monitored transendothelial migration using live-cell imaging. Inhibition of K_Ca3.1 channels with senicapoc or K_Ca3.1 silencing increases the adhesion force of A549 lung cancer cells to human microvascular endothelial cells (HMEC-1). Western blotting, immunofluorescence staining and biotinylation assays indicate that the elevated adhesion force is due to increased expression of ICAM-1 in both cell lines when K_Ca3.1 channels are downregulated. Consistent with this interpretation, an anti-ICAM-1 blocking antibody abolishes the K_Ca3.1-dependent increase in adhesion. Senicapoc inhibits transendothelial migration of A549 cells by 50%. Selectively silencing K_Ca3.1 channels in either NSCLC or endothelial cells reveals that transendothelial migration depends predominantly on endothelial K_Ca3.1 channels.

In conclusion, our findings disclose a novel function of K_Ca3.1 channels in cancer. K_Ca3.1 channels regulate ICAM-1 dependent cell-cell adhesion between endothelial and cancer cells that affects the transmigration step of the metastatic cascade.

Misoprostol Inhibits Equine Neutrophil Adhesion, Migration, and Respiratory Burst in an In Vitro Model of Inflammation

In many equine inflammatory disease states, neutrophil activities, such as adhesion, migration, and reactive oxygen species (ROS) production become dysregulated. Dysregulated neutrophil activation causes tissue damage in horses with asthma, colitis, laminitis, and gastric glandular disease. Non-steroidal anti-inflammatory drugs do not adequately inhibit neutrophil inflammatory functions and can lead to dangerous adverse effects. Therefore, novel therapies that target mechanisms of neutrophil-mediated tissue damage are needed. One potential neutrophil-targeting therapeutic is the PGE₁ analog, misoprostol. Misoprostol is a gastroprotectant that induces intracellular formation of the secondary messenger molecule cyclic AMP (cAMP), which has been shown to have anti-inflammatory effects on neutrophils. Misoprostol is currently used in horses to treat NSAID-induced gastrointestinal injury; however, its effects on equine neutrophils have not been determined. We hypothesized that treatment of equine neutrophils with misoprostol would inhibit equine neutrophil adhesion, migration, and ROS production, in vitro. We tested this hypothesis using isolated equine peripheral blood neutrophils collected from 12 healthy adult teaching/research horses of mixed breed and gender. The effect of misoprostol treatment on adhesion, migration, and respiratory burst of equine neutrophils was evaluated via fluorescence-based adhesion and chemotaxis assays, and luminol-enhanced chemiluminescence, respectively. Neutrophils were pretreated with varying concentrations of misoprostol, vehicle, or appropriate functional inhibitory controls prior to stimulation with LTB₄, CXCL8, PAF, lipopolysaccharide (LPS) or immune complex (IC). This study revealed that misoprostol pretreatment significantly inhibited LTB₄-induced adhesion, LTB₄-, CXCL8-, and PAF-induced chemotaxis, and LPS-, IC-, and PMA-induced ROS production in a concentration-dependent manner. This data indicate that misoprostol-targeting of E-prostanoid (EP) receptors potently inhibits equine neutrophil effector functions in vitro. Additional studies are indicated to further elucidate the role of EP receptors in regulating neutrophil function. Overall, our results suggest misoprostol may hold promise as a novel anti-inflammatory therapeutic in the horse.

The Dual Role of Neutrophils in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis, are characterised by aberrant immunological responses leading to chronic inflammation without tissue regeneration. These two diseases are considered distinct entities, and there is some evidence that neutrophil behaviour, above all other aspects of immunity, clearly separate them. Neutrophils are the first immune cells recruited to the site of inflammation, and their action is crucial to limit invasion by microorganisms. Furthermore, they play an essential role in proper resolution of inflammation. When these processes are not tightly regulated, they can trigger positive feedback amplification loops that promote neutrophil activation, leading to significant tissue damage and evolution toward chronic disease. Defective chemotaxis, as observed in Crohn’s disease, can also contribute to the disease through impaired microbe elimination. In addition, through NET production, neutrophils may be involved in thrombo-embolic events frequently observed in IBD patients. While the role of neutrophils has been studied in different animal models of IBD for many years, their contribution to the pathogenesis of IBD remains poorly understood, and no molecules targeting neutrophils are used and validated for the treatment of these pathologies. Therefore, it is crucial to improve our understanding of their mode of action in these particular conditions in order to provide new therapeutic avenues for IBD.

Anti-inflammatory activity of aqueous extract and bioactive compounds identified from the fruits of Hancornia speciosa Gomes (Apocynaceae)

Background

Hancornia speciosa Gomes (Apocynaceae), popularly known as “mangabeira,” has been used in folk medicine to treat inflammatory disorders, hypertension, dermatitis, diabetes, liver diseases and gastric disorders. Although the ethnobotany indicates that its fruits can be used for the treatment of ulcers and inflammatory disorders, only few studies have been conducted to prove such biological activities. This study investigated the anti-inflammatory properties of the aqueous extract of the fruits of H. speciosa Gomes as well as its bioactive compounds using in vivo experimental models.

Methods

The bioactive compounds were identified by High Performance Liquid Chromatography coupled with diode array detector (HPLC-DAD) and Liquid Chromatography coupled with Mass Spectrometry (LC-MS). The anti-inflammatory properties were investigated through in vivo tests, which comprised xylene-induced ear edema, carrageenan-induced peritonitis and zymosan-induced air pouch. The levels of IL-1β, IL-6, IL-12 and TNF-α were determined using ELISA.

Results

Rutin and chlorogenic acid were identified in the extract as the main secondary metabolites. In addition, the extract as well as rutin and chlorogenic acid significantly inhibited the xilol-induced ear edema and also reduced the cell migration in both carrageenan-induced peritonitis and zymosan-induced air pouch models. Reduced levels of cytokines were also observed.

Conclusion

This is the first study that demonstrated the anti-inflammatory activity of the extract of H. speciosa fruits against different inflammatory agents in animal models, suggesting that its bioactive molecules, especially rutin and chlorogenic acid are, at least in part, responsible for such activity. These findings support the widespread use of Hancornia speciosa in popular medicine and demonstrate that its aqueous extract has therapeutical potential for the development of herbal drugs with anti-inflammatory properties.

Regulators and Effectors of Arf GTPases in Neutrophils

Polymorphonuclear neutrophils (PMNs) are key innate immune cells that represent the first line of defence against infection. They are the first leukocytes to migrate from the blood to injured or infected sites. This process involves molecular mechanisms that coordinate cell polarization, delivery of receptors, and activation of integrins at the leading edge of migrating PMNs. These phagocytes actively engulf microorganisms or form neutrophil extracellular traps (NETs) to trap and kill pathogens with bactericidal compounds. Association of the NADPH oxidase complex at the phagosomal membrane for production of reactive oxygen species (ROS) and delivery of proteolytic enzymes into the phagosome initiate pathogen killing and removal. G protein-dependent signalling pathways tightly control PMN functions. In this review, we will focus on the small monomeric GTPases of the Arf family and their guanine exchange factors (GEFs) and GTPase activating proteins (GAPs) as components of signalling cascades regulating PMN responses. GEFs and GAPs are multidomain proteins that control cellular events in time and space through interaction with other proteins and lipids inside the cells. The number of Arf GAPs identified in PMNs is expanding, and dissecting their functions will provide important insights into the role of these proteins in PMN physiology.

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.

The regulatory role of serum response factor pathway in neutrophil inflammatory response

PURPOSE OF REVIEW

Neutrophils rapidly migrate to sites of injury and infection. Egress of neutrophils from the circulation into tissues is a highly regulated process involving several distinct steps. Cell-cell interactions mediated by selectins and integrins and reorganization of the actin cytoskeleton are key mechanisms facilitating appropriate neutrophil recruitment. Neutrophil function is impaired in inherited and acquired disorders, such as leukocyte adhesion deficiency and myelodysplasia. Since the discovery that deletion of all or part of chromosome 5 is the most common genetic aberration in myelodysplasia, the roles of several of the deleted genes have been investigated in hematopoiesis. Several genes encoding proteins of the serum response factor (SRF) pathway are located on 5q. This review focuses, in particular, on the role of SRF in myeloid maturation and neutrophil function.

RECENT FINDINGS

SRF and its pathway fulfill multiple complex roles in the regulation of the innate and adaptive immune system. Loss of SRF leads to defects in B-cell and T-cell development. SRF-deficient macrophages fail to spread, transmigrate, and phagocytose bacteria, and SRF-deficient neutrophils show defective chemotaxis in vitro and in vivo with failure of inside-out activation and trafficking of the Mac1 integrin complex. Loss of the formin mammalian Diaphanous 1, a regulator of linear actin polymerization and mediator of Ras homolog family member A signaling to SRF, results in aberrant myeloid differentiation and hyperactivity of the immune system.

SUMMARY

SRF is an essential transcription factor in hematopoiesis and mature myeloid cell function. SRF regulates neutrophil migration, integrin activation, and trafficking. Disruption of the SRF pathway results in myelodysplasia and immune dysfunction.

Studies of the structure and functions of blood cells in senile patients with pneumonia on the biological model of hypoxia by scanning probe microscopy

Biological model of hypoxia can be used for the diagnosis of functional changes in human erythrocytes under the effect of the hypoxic factor. The use of this model together with modern methods of scanning probe microscopy for evaluation of the severity of pulmonological disease in senile patients will help to predict treatment efficiency and outcome.

Prenatal immunologic predictors of postpartum depressive symptoms: a prospective study for potential diagnostic markers

In postpartum depression (PPD), immunologic changes have been proposed to be involved in the disease pathology. The study evaluates the regulation of the innate and adaptive immune response over the course of late pregnancy and postpartum period and their association with the development of postpartum depressive symptoms. Furthermore, prenatal immunologic markers for a PPD were investigated. Hundred pregnant women were included. At 34th and 38th week of pregnancy as well as 2 days, 7 weeks and 6 months postpartum, immune parameters (neopterin, regulatory T cells, CXCR1, CCR2, MNP1 and CD11a) were measured by flow cytometry/ELISA, and the psychopathology was evaluated. We found that regulatory T cells were significantly increased prenatal (p=0.011) and postnatal (p=0.01) in mothers with postnatal depressive symptoms. The decrease in CXCR 1 after delivery was significantly higher in mother with postnatal depressive symptoms (p=0.032). Mothers with postnatal depressive symptoms showed already prenatal significantly elevated neopterin levels (p=0.049). Finally, regulatory T cells in pregnancy strongly predict postnatal depressive symptoms (p=0.004). The present study revealed that prenatal and postnatal immunologic parameters are associated with postpartum depressive symptoms in mothers. In addition, we found immune markers that could eventually be the base for a biomarker set that predicts postnatal depressive symptoms already during pregnancy.

SRF is required for neutrophil migration in response to inflammation

Serum response factor (SRF) is a ubiquitously expressed transcription factor and master regulator of the actin cytoskeleton. We have previously shown that SRF is essential for megakaryocyte maturation and platelet formation and function. Here we elucidate the role of SRF in neutrophils, the primary defense against infections. To study the effect of SRF loss in neutrophils, we crossed Srf(fl/fl) mice with select Cre-expressing mice and studied neutrophil function in vitro and in vivo. Despite normal neutrophil numbers, neutrophil function is severely impaired in Srf knockout (KO) neutrophils. Srf KO neutrophils fail to polymerize globular actin to filamentous actin in response to N-formyl-methionine-leucine-phenylalanine, resulting in significantly disrupted cytoskeletal remodeling. Srf KO neutrophils fail to migrate to sites of inflammation in vivo and along chemokine gradients in vitro. Polarization in response to cytokine stimuli is absent and Srf KO neutrophils show markedly reduced adhesion. Integrins play an essential role in cellular adhesion, and although integrin expression levels are maintained with loss of SRF, integrin activation and trafficking are disrupted. Migration and cellular adhesion are essential for normal cell function, but also for malignant processes such as metastasis, underscoring an essential function for SRF and its pathway in health and disease.

The cytokine midkine supports neutrophil trafficking during acute inflammation by promoting adhesion via β2 integrins (CD11/CD18)

Emerging evidence suggests a role of the cytokine midkine (MK) in inflammation. In this study, its functional relevance for recruitment of polymorphonuclear neutrophils (PMNs) during acute inflammation was investigated. Intravital microscopy and histologic analysis of tumor necrosis factor-α-stimulated cremaster muscle venules revealed severely compromised leukocyte adhesion and extravasation in MK(-/-) mice compared with MK(+/+) animals. Systemic administration of recombinant MK completely rescued the adhesion defect in MK(-/-) mice. In a hind limb ischemia model, leukocyte accumulation in MK(-/-) mice was significantly diminished compared with MK(+/+) animals. However, MK did not lead to an inflammatory activation of PMNs or endothelial cells suggesting that it does not serve as classical proinflammatory cytokine. Unexpectedly, immobilized MK mediated PMN adhesion under static and flow conditions, whereas PMN-derived MK was dispensable for the induction of adhesion. Furthermore, adhesion strengthening remained unaffected by MK. Flow cytometry revealed that immobilized, but not soluble MK, significantly promoted the high affinity conformation of β2 integrins of PMNs. Blocking studies of low-density lipoprotein receptor-related protein 1 (LRP1) suggested that LRP1 may act as a receptor for MK on PMNs. Thus, MK seems to support PMN adhesion by promoting the high affinity conformation of β2 integrins, thereby facilitating PMN trafficking during acute inflammation.

Update on selective treatments targeting neutrophilic inflammation in atherogenesis and atherothrombosis

Atherosclerosis is the most common pathological process underlying cardiovascular diseases. Current therapies are largely focused on alleviating hyperlipidaemia and preventing thrombotic complications, but do not completely eliminate risk of suffering recurrent acute ischaemic events. Specifically targeting the inflammatory processes may help to reduce this residual risk of major adverse cardiovascular events in atherosclerotic patients. The involvement of neutrophils in the pathophysiology of atherosclerosis is an emerging field, where evidence for their causal contribution during various stages of atherosclerosis is accumulating. Therefore, the identification of neutrophils as a potential therapeutic target may offer new therapeutic perspective to reduce the current atherosclerotic burden. This narrative review highlights the expanding role of neutrophils in atherogenesis and discusses on the potential treatment targeting neutrophil-related inflammation and associated atherosclerotic plaque vulnerability.

Neutrophil migration: moving from zebrafish models to human autoimmunity

There has been a resurgence of interest in the neutrophil's role in autoimmune disease. Classically considered an early responder that dies at the site of inflammation, new findings using live imaging of embryonic zebrafish and other modalities suggest that neutrophils can reverse migrate away from sites of inflammation. These 'inflammation-sensitized' neutrophils, as well as the neutrophil extracellular traps and other products made by neutrophils in general, may have many implications for autoimmunity. Here, we review what is known about the role of neutrophils in three different autoimmune diseases: rheumatoid arthritis, systemic lupus erythematosus, and small vessel vasculitis. We then highlight recent findings related to several cytoskeletal regulators that guide neutrophil recruitment including Lyn, Rac2, and SHIP. Finally, we discuss how our improved understanding of the molecules that control neutrophil chemotaxis may impact our knowledge of autoimmunity.

The multifaceted functions of neutrophils

Neutrophils and neutrophil-like cells are the major pathogen-fighting immune cells in organisms ranging from slime molds to mammals. Central to their function is their ability to be recruited to sites of infection, to recognize and phagocytose microbes, and then to kill pathogens through a combination of cytotoxic mechanisms. These include the production of reactive oxygen species, the release of antimicrobial peptides, and the recently discovered expulsion of their nuclear contents to form neutrophil extracellular traps. Here we discuss these primordial neutrophil functions, which also play key roles in tissue injury, by providing details of neutrophil cytotoxic functions and congenital disorders of neutrophils. In addition, we present more recent evidence that interactions between neutrophils and adaptive immune cells establish a feed-forward mechanism that amplifies pathologic inflammation. These newly appreciated contributions of neutrophils are described in the setting of several inflammatory and autoimmune diseases.

Identification of C-terminal phosphorylation sites of N-formyl peptide receptor-1 (FPR1) in human blood neutrophils

Accumulation, activation, and control of neutrophils at inflammation sites is partly driven by N-formyl peptide chemoattractant receptors (FPRs). Occupancy of these G-protein-coupled receptors by formyl peptides has been shown to induce regulatory phosphorylation of cytoplasmic serine/threonine amino acid residues in heterologously expressed recombinant receptors, but the biochemistry of these modifications in primary human neutrophils remains relatively unstudied. FPR1 and FPR2 were partially immunopurified using antibodies that recognize both receptors (NFPRa) or unphosphorylated FPR1 (NFPRb) in dodecylmaltoside extracts of unstimulated and N-formyl-Met-Leu-Phe (fMLF) + cytochalasin B-stimulated neutrophils or their membrane fractions. After deglycosylation and separation by SDS-PAGE, excised Coomassie Blue-staining bands (∼34,000 Mr) were tryptically digested, and FPR1, phospho-FPR1, and FPR2 content was confirmed by peptide mass spectrometry. C-terminal FPR1 peptides (Leu(312)-Arg(322) and Arg(323)-Lys(350)) and extracellular FPR1 peptide (Ile(191)-Arg(201)) as well as three similarly placed FPR2 peptides were identified in unstimulated and fMLF + cytochalasin B-stimulated samples. LC/MS/MS identified seven isoforms of Ala(323)-Lys(350) only in the fMLF + cytochalasin B-stimulated sample. These were individually phosphorylated at Thr(325), Ser(328), Thr(329), Thr(331), Ser(332), Thr(334), and Thr(339). No phospho-FPR2 peptides were detected. Cytochalasin B treatment of neutrophils decreased the sensitivity of fMLF-dependent NFPRb recognition 2-fold, from EC50 = 33 ± 8 to 74 ± 21 nM. Our results suggest that 1) partial immunopurification, deglycosylation, and SDS-PAGE separation of FPRs is sufficient to identify C-terminal FPR1 Ser/Thr phosphorylations by LC/MS/MS; 2) kinases/phosphatases activated in fMLF/cytochalasin B-stimulated neutrophils produce multiple C-terminal tail FPR1 Ser/Thr phosphorylations but have little effect on corresponding FPR2 sites; and 3) the extent of FPR1 phosphorylation can be monitored with C-terminal tail FPR1-phosphospecific antibodies.