Identification and characterization of specific receptors for monocyte-derived neutrophil chemotactic factor (MDNCF) on human neutrophils

Neutrophil diversity and function in health and disease

Neutrophils, the most abundant type of granulocyte, are widely recognized as one of the pivotal contributors to the acute inflammatory response. Initially, neutrophils were considered the mobile infantry of the innate immune system, tasked with the immediate response to invading pathogens. However, recent studies have demonstrated that neutrophils are versatile cells, capable of regulating various biological processes and impacting both human health and disease. Cytokines and other active mediators regulate the functional activity of neutrophils by activating multiple receptors on these cells, thereby initiating downstream signal transduction pathways. Dysfunctions in neutrophils and disruptions in neutrophil homeostasis have been implicated in the pathogenesis of numerous diseases, including cancer and inflammatory disorders, often due to aberrant intracellular signaling. This review provides a comprehensive synthesis of neutrophil biological functions, integrating recent advancements in this field. Moreover, it examines the biological roles of receptors on neutrophils and downstream signaling pathways involved in the regulation of neutrophil activity. The pathophysiology of neutrophils in numerous human diseases and emerging therapeutic approaches targeting them are also elaborated. This review also addresses the current limitations within the field of neutrophil research, highlighting critical gaps in knowledge that warrant further investigation. In summary, this review seeks to establish a comprehensive and multidimensional model of neutrophil regulation, providing new perspectives for potential clinical applications and further research.

A key regulator of tumor-associated neutrophils: the CXCR2 chemokine receptor

In recent years, with the advance of research, the role of tumor-associated neutrophils (TANs) in tumors has become a research hotspot. As important effector cells in the innate immune system, neutrophils play a key role in the immune and inflammatory responses of the body. As the first line of defense against bacterial and fungal infections, neutrophils have the ability to kill invading pathogens. In the pathological state of malignant tumors, the phenotype of neutrophils is altered and has an important regulatory function in tumor development. The C-X-C motif chemokine receptor 2(CXCR2) is a key molecule that mediates the migration and aggregation signaling pathway of immune cells, especially neutrophils. This review focuses on the regulation of CXCR2 on TANs in the process of tumorigenesis and development, and emphasizes the application significance of CXCR2 inhibitors in blocking the migration of TANs to tumors.

Detection and Localization of IL-8 and CXCR1 in Rainbow Trout Larvae in Response to Pseudomonas aeruginosa Lipopolysaccharide

The salmonid industry faces challenges due to the susceptibility of fish to opportunistic pathogens, particularly in early developmental stages. Understanding the immunological capacity during these stages is crucial for developing effective disease control strategies. IL-8R, a member of the G-protein-coupled receptor family, acts as a receptor for Interleukin 8 (IL-8). The binding of IL-8 to IL-8R plays a major role in the pathophysiology of a wide spectrum of inflammatory conditions. This study focused on the immune response capacity of rainbow trout (Oncorhynchus mykiss) larvae by analyzing IL-8/CXCR1 response to lipopolysaccharide (LPS) from Pseudomonas aeruginosa. Previous research demonstrated that LPS from P. aeruginosa acts as a potent immunostimulant in teleost, enhancing pro-inflammatory cytokines. The methodology included in silico analysis and the synthesis and characterization of an omCXCR1-derived epitope peptide, which was used to produce omCXCR1-specific anti98 serum in mice. The research revealed that rainbow trout larvae 19 days post-hatching (dph) exhibited pronounced immune responses post-stimulation with 1 µg/mL of LPS. This was evidenced by the upregulated protein expression of IL-8 and omCXCR1 in trout larvae 2 and 8 h after LPS challenge, as analyzed by ELISA and immunohistochemistry. Furthermore, fluorescence microscopy successfully revealed the colocalization of IL-8 and its receptor in cells from mucosal tissues after LPS challenge in larvae 19 dph. These findings underscore the efficacy of LPS immersion as a method to activate the innate immune system in trout larvae. Furthermore, we propose IL-8 and its receptor as molecular markers for evaluating immunostimulation in the early developmental stages of salmonids.

Expanding role of CXCR2 and therapeutic potential of CXCR2 antagonists in inflammatory diseases and cancers

C-X-C motif chemokine receptor 2 (CXCR2) is G protein-coupled receptor (GPCR) and plays important roles in various inflammatory diseases and cancers, including chronic obstructive pulmonary disease (COPD), atherosclerosis, asthma, and pancreatic cancer. Upregulation of CXCR2 is closely associated with the migration of neutrophils and monocytes. To date, many small-molecule CXCR2 antagonists have entered clinical trials, showing favorable safety and therapeutic effects. Hence, we provide an overview containing the discovery history, protein structure, signaling pathways, biological functions, structure-activity relationships and clinical significance of CXCR2 antagonists in inflammatory diseases and cancers. According to the latest development and recent clinical progress of CXCR2 small molecule antagonists, we speculated that CXCR2 can be used as a biomarker and a new target for diabetes and that CXCR2 antagonists may also attenuate lung injury in coronavirus disease 2019 (COVID-19).

Identification of key immune-related genes and immune infiltration in diabetic nephropathy based on machine learning algorithms

BACKGROUND

Diabetic nephropathy (DN) is a complication of diabetes. This study aimed to identify potential diagnostic markers of DN and explore the significance of immune cell infiltration in this pathology.

METHODS

The GSE30528, GSE96804, and GSE1009 datasets were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were identified by merging the GSE30528 and GSE96804 datasets. Enrichment analyses of the DEGs were performed. A LASSO regression model, support vector machine recursive feature elimination analysis and random forest analysis methods were performed to identify candidate biomarkers. The CIBERSORT algorithm was utilised to compare immune infiltration between DN and normal controls.

RESULTS

In total, 115 DEGs were obtained. The enrichment analysis showed that the DEGs were prominent in immune and inflammatory responses. The DEGs were closely related to kidney disease, urinary system disease, kidney cancer etc. CXCR2, DUSP1, and LPL were recognised as diagnostic markers of DN. The immune cell infiltration analysis indicated that DN patients contained a higher ratio of memory B cells, gamma delta T cells, M1 macrophages, M2 macrophages etc. cells than normal people.

CONCLUSION

Immune cell infiltration is important for the occurrence of DN. CXCR2, DUSP1, and LPL may become novel diagnostic markers of DN.

Construction of a prognostic classifier and prediction of the immune landscape and immunosuppressive molecules in gliomas based on combination of inflammatory response-related genes and angiogenesis-associated genes

Objective:We aimed to combine inflammatory response-related genes (IRRGs) and angiogenesis-associated genes (AAGs) to build a prognostic classifier and to predict immune landscapes and immunosuppressive molecules in gliomas.

Introduction: Gliomas, the commonest primary brain tumors, account for about 80% of cancerous tumors in the central nervous system (CNS), featuring rapid progression, high malignancy, and extremely poor prognosis. The induction of inflammatory responses and angiogenesis have been considered to be closely related to tumors. However, there are little publications systematically elaborating on their impacts on gliomas.

Methods: We downloaded the data of IRRGs and AAGs from The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) databases, and retrieved 68 differentially expressed genes (DEGs), of which 13 DEGs pertained to the prognosis of glioma cases. Next, 9 DEGs were screened from the 13 major DEGs with predictive significance and utilized to build a 9-gene signature as a prognostic risk score model (PRSM) with the aid of univariate Cox regression analyses (CRA) and least absolute shrinkage and selection operator (LASSO)-CRA. On this basis, glioma patients fell into high-risk (HR) group and low-risk (LR) group. Later, we implemented Gene Set Enrichment Analysis (GSEA, Gene Set: WP_ANGIOGENESIS) and calculate the scores of cell infiltration and immune-associated function by harnessing single-sample GSEA (ssGSEA).

Results: The prognosis was compared between the two groups by introducing Kaplan-Meier (KM) analysis, which yielded that HR group exhibited poorer prognosis. Additionally, the predictive capacity and independent characteristics were proven by the receiver operating characteristic curve (ROC) and multivariate CRA. Further, We took an evaluation of immune profiles, which unraveled that immunosuppressive cell count was distinctively larger in HS group. Finally, a protein-protein interaction (PPI) network of DEGs was built, and 10 hub genes were obtained, of which epidermal growth factor receptor (EGFR) was closely related to poor prognosis.

Conclusion: A 9-gene signature was established on the strength of IRRGs and AAGs for predicting glioma prognosis, tumor microenvironment (TME), immune landscapes and immunosuppressive molecules. However, the molecular mechanism developed by this signature to function in tumor immunity needs further experimental research in the future and is expected to be a research target for glioma immunotherapy strategies.

Targeting CXCR2 inhibits the progression of lung cancer and promotes therapeutic effect of cisplatin

Background

Drug-resistance and severe side effects of chemotherapeutic agents result in unsatisfied survival of patients with lung cancer. CXCLs/CXCR2 axis plays an important role in progression of cancer including lung cancer. However, the specific anti-cancer mechanism of targeting CXCR2 remains unclear.

Methods

Immunohistochemical analysis of CXCR2 was performed on the microarray of tumor tissues of clinical lung adenocarcinoma and lung squamous cell carcinoma patients. CCK8 test, TUNEL immunofluorescence staining, PI-Annexin V staining, β-galactosidase staining, and Western blot were used to verify the role of CXCR2 in vitro. Animal models of tail vein and subcutaneous injection were applied to investigate the therapeutic role of targeting CXCR2. Flow cytometry, qRT-PCR, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry analysis were performed for further mechanistic investigation.

Results

The expression of CXCR2 was elevated in both human lung cancer stroma and tumor cells, which was associated with patients’ prognosis. Inhibition of CXCR2 promoted apoptosis, senescence, epithelial-to-mesenchymal transition (EMT), and anti-proliferation of lung cancer cells. In vivo study showed that tumor-associated neutrophils (TANs) were significantly infiltrate into tumor tissues of mouse model, with up-regulated CXCLs/CXCR2 signaling and suppressive molecules, including Arg-1 and TGF-β. SB225002, a selective inhibitor of CXCR2 showed promising therapeutic effect, and significantly reduced infiltration of neutrophils and enhanced anti-tumor T cell activity via promoting CD8⁺ T cell activation. Meanwhile, blockade of CXCR2 could enhance therapeutic effect of cisplatin via regulation of neutrophils infiltration.

Conclusions

Our finds verify the therapeutic effects of targeting CXCR2 in lung cancer and uncover the potential mechanism for the increased sensitivity to chemotherapeutic agents by antagonists of CXCR2.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01355-1.

Roles of neutrophils in the regulation of the extent of human inflammation through delivery of IL-1 and clearance of chemokines

This study examined the establishment of neutrophilic inflammation in humans. We tested the hypotheses that neutrophil recruitment was associated with local CXCL8 production and that neutrophils themselves might contribute to the regulation of the size of the inflammatory response. Humans were challenged i.d. with endotoxin. Biopsies of these sites were examined for cytokine production and leukocyte recruitment by qPCR and IHC. Additional in vitro models of inflammation examined the ability of neutrophils to produce and sequester cytokines relevant to neutrophilic inflammation. i.d. challenge with 15 ng of a TLR4-selective endotoxin caused a local inflammatory response, in which 1% of the total biopsy area stained positive for neutrophils at 6 h, correlating with 100-fold up-regulation in local CXCL8 mRNA generation. Neutrophils themselves were the major source of the early cytokine IL-1β. In vitro, neutrophils mediated CXCL8 but not IL-1β clearance (>90% clearance of ≤2 nM CXCL8 over 24 h). CXCL8 clearance was at least partially receptor-dependent and modified by inflammatory context, preserved in models of viral infection but reduced in models of bacterial infection. In conclusion, in a human inflammatory model, neutrophils are rapidly recruited and may regulate the size and outcome of the inflammatory response through the uptake and release of cytokines and chemokines in patterns dependent on the underlying inflammatory stimulus.

Adaptive-control model for neutrophil orientation in the direction of chemical gradients

Neutrophils have a remarkable ability to detect the direction of chemoattractant gradients and move directionally in response to bacterial infections and tissue injuries. For their role in health and disease, neutrophils have been extensively studied, and many of the molecules involved in the signaling mechanisms of gradient detection and chemotaxis have been identified. However, the cellular-scale mechanisms of gradient sensing and directional neutrophil migration have been more elusive, and existent models provide only limited insight into these processes. Here, we propose a what we believe is a novel adaptive-control model for the initiation of cell polarization in response to gradients. In this model, the neutrophils first sample the environment by extending protrusions in random directions and subsequently adapt their sensitivity depending on localized, temporal changes in stimulation levels. Our results suggest that microtubules may play a critical role in integrating all the sensing events from the cellular periphery through their redistribution inside the neutrophils, and may also be involved in modulating local signaling. An unexpected finding was that model neutrophils exhibit significant randomness in timing and directionality of activation, comparable to our experimental observations in microfluidic devices. Moreover, their responses are robust against alterations of the rate and amplitude of the signaling reactions, and for a broad range in chemoattractant concentrations and spatial gradients.

Modeling the VEGF–Bcl-2–CXCL8 Pathway in Intratumoral Agiogenesis

Recent experiments show that vascular endothelial growth factor (VEGF) is the crucial mediator of downstream events that ultimately lead to enhanced endothelial cell survival and increased vascular density within many tumors. The newly discovered pathway involves up-regulation of the anti-apoptotic protein Bcl-2, which in turn leads to increased production of interleukin-8 (CXCL8). The VEGF-Bcl-2-CXCL8 pathway suggests new targets for the development of anti-angiogenic strategies including short interfering RNA (siRNA) that silence the CXCL8 gene and small molecule inhibitors of Bcl-2. In this paper, we present and validate a mathematical model designed to predict the effect of the therapeutic blockage of VEGF, CXCL8, and Bcl-2 at different stages of tumor progression. In agreement with experimental observations, the model predicts that curtailing the production of CXCL8 early in development can result in a delay in tumor growth and vascular development; however, it has little effect when applied at late stages of tumor progression. Numerical simulations also show that blocking Bcl-2 up-regulation, either at early stages or after the tumor has fully developed, ensures that both microvascular and tumor cell density stabilize at low values representing growth control. These results provide insight into those aspects of the VEGF-Bcl-2-CXCL8 pathway, which independently and in combination, are crucial mediators of tumor growth and vascular development. Continued quantitative modeling in this direction may have profound implications for the development of novel therapies directed against specific proteins and chemokines to alter tumor progression.

ELR+-CXC chemokines and their receptors in early metanephric development

Although originally identified as mediators of inflammation, it is now apparent that chemokines play a fundamental role in tissue development. In this study, ELR(+)-CXC chemokine family members CXCL2 and CXCL7, along with their preferred receptor CXCR2, were expressed at the earliest stages of metanephric development in the rat, and signaling through this receptor was required for the survival and maintenance of the undifferentiated metanephric mesenchyme (MM). A specific antagonist of the CXCR2 receptor SB225002 induced apoptosis in this population but did not affect more mature structures or cells in the ureteric bud. CXCL7 treatment of isolated MM elicited an angiogenic response by upregulation of matrix metalloprotease 9 and endothelial and mesangial markers (platelet-endothelial cell adhesion molecule, Megsin, Thy-1, PDGF receptor alpha, and vascular alpha-actin) and induced SB225002-sensitive cell invasion through a matrix. Because Wilms' tumor cells may similarly depend on CXCR2 signaling for survival, primary tumor samples were analyzed, and 15 of 16 Wilms' tumors were found to be CXCR2 positive, whereas grossly normal kidney tissues from tumor patients or renal cell carcinomas were CXCR2 negative. Furthermore, cell lines derived from Wilms' tumors but not those from renal cell carcinomas were sensitive to SB225002-induced apoptosis. These data provide evidence for a prosurvival and proangiogenic role of ELR(+)-CXC chemokines and their receptor CXCR2 during metanephric development and suggest a novel mechanism for chemotherapeutic intervention in Wilms' tumor.

High-resolution NMR spectroscopy of a GPCR in aligned bicelles

Solid-state NMR spectra with single-site resolution of CXCR1, a G protein-coupled receptor (GPCR), were obtained in magnetically aligned phospholipid bicelles. These results demonstrate that GPCRs in phospholipid bilayers are suitable samples for structure determination by solid-state NMR. The spectra also enable studies of drug-receptor interactions.

α-melanocyte-stimulating hormone down-regulates CXC receptors through activation of neutrophil elastase

Considering the role of interleukin-8 (IL-8) in a large number of acute and chronic inflammatory diseases, the regulation of IL-8-mediated biological responses is important. Alpha-melanocyte-stimulating hormone (alpha-MSH), a tridecapeptide, inhibits most forms of inflammation by an unknown mechanism. In the present study, we have found that alpha-MSH interacts predominantly with melanocortin-1 receptors and inhibits several IL-8-induced biological responses in macrophages and neutrophils. It down-regulated receptors for IL-8 but not for TNF, IL-4, IL-13 or TNF-related apoptosis-inducing ligand (TRAIL) in neutrophils. It down-regulated CXCR type 1 and 2 but not mRNA levels. alpha-MSH did not inhibit IL-8 binding in purified cell membrane or affinity-purified CXCR. IL-8 or anti-CXCR Ab protected against alpha-MSH-mediated inhibition of IL-8 binding. The level of neutrophil elastase, a specific serine protease, but not cathepsin G or proteinase 3 increased in alpha-MSH-treated cells, and restoration of CXCR by specific neutrophil elastase or serine protease inhibitors indicates the involvement of elastase in alpha-MSH-induced down-regulation of CXCR. These studies suggest that alpha-MSH inhibits IL-8-mediated biological responses by down-regulating CXCR through induction of serine protease and that alpha-MSH acts as a potent immunomodulator in neutrophil-driven inflammatory distress.

Synergy between IL-8 and GM-CSF in reproductive tract epithelial cell secretions promotes enhanced neutrophil chemotaxis

Neutrophils occur in tissues of the female reproductive tract (FRT) under non-infected conditions. These cells generally enter tissues under the influence of chemoattractants called chemokines. Primary epithelial cells (EC) from FRT were a potent source of chemokines, IL-8 being the chief neutrophil chemoattractant secreted. Blocking with neutralizing anti-IL-8 showed that IL-8 did not account for all of the chemoattraction observed. A mixture of 25 ng/mL rIL-8 and 1 ng/mL rGM-CSF mediated 2.7-fold more chemotaxis than that expected if the two agents were additive. We then found that GM-CSF was produced by EC in amounts that synergised strongly with IL-8 to enhance chemotaxis. Treatment of uterine EC conditioned medium with saturating doses of anti-IL-8 plus anti-GM-CSF antibodies produced an 84% inhibition of chemotaxis. These findings demonstrate that the majority of neutrophil chemoattractant activity produced by FRT EC results from the synergistic effects of IL-8 and GM-CSF.

Neutrophils are indispensable for hematopoietic stem cell mobilization induced by interleukin-8 in mice

The CXC chemokine interleukin-8 (IL-8/CXCL8) induces rapid mobilization of hematopoietic progenitor cells (HPCs). Previously we showed that mobilization could be prevented completely in mice by pretreatment with neutralizing antibodies against the beta2-integrin LFA-1 (CD11a). In addition, murine HPCs do not express LFA-1, indicating that mobilization requires a population of accessory cells. Here we show that polymorphonuclear cells (PMNs) serve as key regulators in IL-8-induced HPC mobilization. The role of PMNs was studied in mice rendered neutropenic by administration of a single injection of antineutrophil antibodies. Absolute neutropenia was observed up to 3-5 days with a rebound neutrophilia at day 7. The IL-8-induced mobilizing capacity was reduced significantly during the neutropenic phase, reappeared with recurrence of the PMNs, and was increased proportionally during the neutrophilic phase. In neutropenic mice, the IL-8-induced mobilizing capacity was restored by the infusion of purified PMNs but not by infusion of mononuclear cells. Circulating metalloproteinase gelatinase B (MMP-9) levels were detectable only in neutropenic animals treated with PMNs in combination with IL-8, showing that in vivo activated PMNs are required for the restoration of mobilization. However, IL-8-induced mobilization was not affected in MMP-9-deficient mice, indicating that MMP-9 is not indispensable for mobilization. These data demonstrate that IL-8-induced mobilization of HPCs requires the in vivo activation of circulating PMNs.

Chemokine receptors

Although chemokines were originally defined as host defense proteins it is now clear that their repertoire of functions extend well beyond this role. For example chemokines such as MGSA have growth regulatory properties while members of the CXC chemokine family can be mediators or inhibitors of angiogenesis and may be important targets for oncology. Recent work shows that the chemokine receptor CXCR4 and its cognate ligand SDF play important roles in the development of the immune, circulatory and central nervous systems. In addition, chemokine receptors play an important role in the pathogenesis of the AIDS virus, HIV-1. Taken together these findings expand the biological importance of chemokines from that of simple immune modulators to a much broader biological role than was at first appreciated and these and other properties of the chemokine receptor family are discussed in detail in this review.

Signal transduction by the chemokine receptor CXCR5: structural requirements for G protein activation analyzed by chimeric CXCR1/CXCR5 molecules

The human chemokine receptors CXCR5 and CXCR1 activate signaling pathways via pertussis toxin-sensitive as well as insensitive G proteins. CXCR5 induces Ca2+ signaling and chemotaxis independently of inhibitory G proteins, whereas the same signaling pathways are entirely dependent on inhibitory G proteins for CXCR1. In contrast, activation of the MAP kinase cascade via ERK1/2 is a pertussis toxin-sensitive signaling event for both receptors. Using chimeric CXCR1/CXCR5 receptors we investigated structural requirements for the activation of signal transduction pathways by CXCR5. Individual or multiple intracellular domains of CXCR1 were exchanged for the corresponding sequences of CXCR5, leading to receptors resembling CXCR5 at the cytoplasmic surface to a varying extent. Replacing the second intracellular domain of CXCR1 had a major influence on signaling mediated by inhibitory G proteins, whereas the exchange of the third or carboxy-terminal intracellular domain had only minor effects on signal transduction. Activation of the MAP kinase cascade via ERK1/2 and chemotaxis are largely reduced in chimeras comprising the second intracellular domain of CXCR5, although coupling to inhibitory G proteins is retained in all chimeric receptors. In summary, these data characterize the contribution of the intracellular domains of CXCR5 to receptor signaling, thereby disclosing unique structural requirements that modulate G protein coupling by the receptor.

Determination of Total Interleukin-8 in Whole Blood after Cell Lysis

Background: It has been shown that a high percentage of interleukin-8 (IL-8) in blood is cell associated. Recently, a simple method for determination of cell-associated IL-8 in whole blood after cell lysis has been described. The purpose of this study was to evaluate this method, to examine the influence of preanalytic sample handling, and to establish the concentration range of total IL-8 and its relation to age and sex in healthy subjects.

Methods: Total IL-8 content of whole blood was determined after lysing blood cells with Milenia® cell lysis solution. IL-8 in the resulting blood lysate was measured with the IMMULITE® IL-8 immunoassay.

Results: When freshly drawn blood was stored up to 48 h on ice, no significant changes in total IL-8 were measured in the subsequently prepared lysate, whereas with storage at room temperature, total IL-8 increased after 3 h from 94 ± 13 ng/L to 114 ± 16 ng/L (n = 10). In lysate stored for 48 h at 4 °C, marginal changes of the IL-8 concentration were noted, with storage at room temperature, only 76% ± 5% (n = 12) of initial concentration was recovered. From lysate frozen at −20 and −80 °C, respectively, 84% ± 4% and 93% ± 2% of initial IL-8 was recovered after 70 days (n = 10). IL-8 was measured with comparable precision in plasma (CV, 3.2–4.2%) and blood lysate (CV, 3.7–4.1%). When plasma was diluted with cell lysis solution, a slightly overestimated recovery (125% ± 3%) was observed; for lysate specimens with a cell lysis solution content ≥75%, the recovery after dilution was 98% ± 2%. In lysate prepared from 12 blood samples with exogenous IL-8 added, IL-8 recovery was 104% ± 2% (recovery from plasma <35%). The median total IL-8 in blood lysates from 103 healthy subjects (22–61 years) was 83 ng/L of blood (2.5–97.5 percentile range, 49–202 ng/L of blood). In females but not in males, total IL-8 increased significantly with advancing age (P <0.002). We found grossly increased total IL-8 in six pregnant women with amniotic infection syndrome.

Conclusions: The evaluated method allows the assessment of total IL-8 in blood with good performance when appropriate conditions of sample pretreatment are considered. The values in healthy volunteers all were above the detection limit of the IL-8 assay; therefore, slight changes of total IL-8 could be noted. Thus, the present method is a suitable tool to study the diagnostic relevance of total IL-8 in blood.

Chemokine receptors and their role in inflammation and infectious diseases

Chemokines are small peptides that are potent activators and chemoattractants for leukocyte subpopulations and some nonhemopoietic cells. Their actions are mediated by a family of 7-transmembrane G-protein–coupled receptors, the size of which has grown considerably in recent years and now includes 18 members. Chemokine receptor expression on different cell types and their binding and response to specific chemokines are highly variable. Significant advances have been made in understanding the regulation of chemokine receptor expression and the intracellular signaling mechanisms used in bringing about cell activation. Chemokine receptors have also recently been implicated in several disease states including allergy, psoriasis, atherosclerosis, and malaria. However, most fascinating has been the observation that some of these receptors are used by human immunodeficiency virus type 1 in gaining entry into permissive cells. This review will discuss structural and functional aspects of chemokine receptor biology and will consider the roles these receptors play in inflammation and in infectious diseases.

Chemokine receptors and their role in inflammation and infectious diseases

Chemokines are small peptides that are potent activators and chemoattractants for leukocyte subpopulations and some nonhemopoietic cells. Their actions are mediated by a family of 7-transmembrane G-protein–coupled receptors, the size of which has grown considerably in recent years and now includes 18 members. Chemokine receptor expression on different cell types and their binding and response to specific chemokines are highly variable. Significant advances have been made in understanding the regulation of chemokine receptor expression and the intracellular signaling mechanisms used in bringing about cell activation. Chemokine receptors have also recently been implicated in several disease states including allergy, psoriasis, atherosclerosis, and malaria. However, most fascinating has been the observation that some of these receptors are used by human immunodeficiency virus type 1 in gaining entry into permissive cells. This review will discuss structural and functional aspects of chemokine receptor biology and will consider the roles these receptors play in inflammation and in infectious diseases.

Metalloproteinases Are Involved in Lipopolysaccharide– and Tumor Necrosis Factor-–Mediated Regulation of CXCR1 and CXCR2 Chemokine Receptor Expression

The neutrophil-specific G-protein–coupled chemokine receptors, CXCR1 and CXCR2, bind with high affinity to the potent chemoattractant interleukin-8 (IL-8). The mechanisms of IL-8 receptor regulation are not well defined, although previous studies have suggested a process of ligand-promoted internalization as a putative regulatory pathway. Herein, we provide evidence for two distinct processes of CXCR1 and CXCR2 regulation. Confocal microscopy data showed a redistribution of CXCR1 expression from the cell surface of neutrophils to internal compartments after stimulation with IL-8, whereas stimulation with bacterial lipopolysaccharide (LPS) or tumor necrosis factor- (TNF-) did not induce CXCR1 internalization but instead mediated a significant loss of membrane-proximal CXCR1 staining intensity. To investigate whether proteolytic cleavage was the mechanism responsible for LPS- and TNF-–induced downmodulation of IL-8 receptors, we tested a panel of proteinase inhibitors. The downmodulation of CXCR1 and CXCR2 by LPS and TNF- was most dramatically inhibited by metalloproteinase inhibitors; 1,10-phenanthroline and EDTA significantly attenuated LPS- and TNF-–induced loss of CXCR1 and CXCR2 cell surface expression. Metalloproteinase inhibitors also blocked the release of CXCR1 cleavage fragments into the cell supernatants of LPS- and TNF-–stimulated neutrophils. In addition, while treatment of neutrophils with LPS and TNF- inhibited IL-8 receptor–mediated calcium mobilization and IL-8–directed neutrophil chemotaxis, both 1,10-phenanthroline and EDTA blocked these inhibitory processes. In contrast, metalloproteinase inhibitors did not affect IL-8–mediated downmodulation of CXCR1 and CXCR2 cell surface expression or receptor signaling. Thus, these findings may provide further insight into the mechanisms of leukocyte regulation during immunologic and inflammatory responses.

Metalloproteinases Are Involved in Lipopolysaccharide– and Tumor Necrosis Factor-–Mediated Regulation of CXCR1 and CXCR2 Chemokine Receptor Expression

The neutrophil-specific G-protein–coupled chemokine receptors, CXCR1 and CXCR2, bind with high affinity to the potent chemoattractant interleukin-8 (IL-8). The mechanisms of IL-8 receptor regulation are not well defined, although previous studies have suggested a process of ligand-promoted internalization as a putative regulatory pathway. Herein, we provide evidence for two distinct processes of CXCR1 and CXCR2 regulation. Confocal microscopy data showed a redistribution of CXCR1 expression from the cell surface of neutrophils to internal compartments after stimulation with IL-8, whereas stimulation with bacterial lipopolysaccharide (LPS) or tumor necrosis factor- (TNF-) did not induce CXCR1 internalization but instead mediated a significant loss of membrane-proximal CXCR1 staining intensity. To investigate whether proteolytic cleavage was the mechanism responsible for LPS- and TNF-–induced downmodulation of IL-8 receptors, we tested a panel of proteinase inhibitors. The downmodulation of CXCR1 and CXCR2 by LPS and TNF- was most dramatically inhibited by metalloproteinase inhibitors; 1,10-phenanthroline and EDTA significantly attenuated LPS- and TNF-–induced loss of CXCR1 and CXCR2 cell surface expression. Metalloproteinase inhibitors also blocked the release of CXCR1 cleavage fragments into the cell supernatants of LPS- and TNF-–stimulated neutrophils. In addition, while treatment of neutrophils with LPS and TNF- inhibited IL-8 receptor–mediated calcium mobilization and IL-8–directed neutrophil chemotaxis, both 1,10-phenanthroline and EDTA blocked these inhibitory processes. In contrast, metalloproteinase inhibitors did not affect IL-8–mediated downmodulation of CXCR1 and CXCR2 cell surface expression or receptor signaling. Thus, these findings may provide further insight into the mechanisms of leukocyte regulation during immunologic and inflammatory responses.

Expression and Function of the Chemokine Receptors CXCR1 and CXCR2 in Sepsis

Neutrophils (polymorphonuclear neutrophils; PMN) and a redundant system of chemotactic cytokines (chemokines) have been implicated in the pathogenesis of the acute respiratory distress syndrome in patients with sepsis. PMN express two cell surface receptors for the CXC chemokines, CXCR1 and CXCR2. We investigated the expression and function of these receptors in patients with severe sepsis. Compared with normal donors, CXCR2 surface expression was down-regulated by 50% on PMN from septic patients (p < 0.005), while CXCR1 expression persisted. In vitro migratory responses to the CXCR1 ligand, IL-8, were similar in PMN from septic patients and normal donors. By contrast, the migratory response to the CXCR2 ligands, epithelial cell-derived neutrophil activator (ENA-78) and the growth-related oncogene proteins, was markedly suppressed in PMN from septic patients (p < 0.05). Ab specific for CXCR1 blocked in vitro migration of PMN from septic patients to IL-8 (p < 0.05), but not to FMLP. Thus, functionally significant down-regulation of CXCR2 occurs on PMN in septic patients. We conclude that in a complex milieu of multiple CXC chemokines, CXCR1 functions as the single dominant CXC chemokine receptor in patients with sepsis. These observations offer a potential strategy for attenuating adverse inflammation in sepsis while preserving host defenses mediated by bacteria-derived peptides such as FMLP.

Expression and Functional Activity of the IL-8 Receptor Type CXCR1 and CXCR2 on Human Mast Cells

To further elucidate mechanisms involved in mast cell accumulation at sites of cutaneous inflammation, we have studied the ability of human leukemic mast cells (HMC-1 cells) to express functionally active IL-8 receptors. Expression of mRNA for both types of IL-8 receptors (CXCR1 and CXCR2) was demonstrated by PCR and of both proteins by flow cytometry. Binding and competition studies with 125I-labeled IL-8 and its homologue melanoma growth stimulating activity (125I-labeled MGSA) revealed two specific binding sites for IL-8, K1 = 1.1 × 1011 M−1 and K2 = 5 × 107 M−1; and for MGSA, K1 = 2.8 × 1010 M−1 and K2 = 5 × 107 M−1. This finding was supported by a dose-dependent rise of cytosolic free calcium concentration ([Ca2+]i) induced by both chemokines and to a lesser extent by the homologue neutrophil-activating peptide-2 (NAP-2). A significant migratory response of human leukemic mast cells (HMC-1) was observed with all three chemokines at a range from 10−8 M to 10−9 M. Moreover, the formation of cellular F-actin was induced in a rapid, dose-dependent fashion, with a maximally 1.7-fold increase at 10−7 M. Using postembedding immunoelectron microscopy, we could show the expression of CXCR1 on the cytoplasmatic membrane of isolated human skin mast cells whereas CXCR2 was located in mast cell-specific granules. These findings demonstrate for the first time the functional expression of both types of IL-8 receptors on human mast cells, suggesting a role for their ligands during mast cell activation and recruitment.

Importance of the carboxy-terminus of the CXCR2 for signal transduction

The CXCR2 is phosphorylated at the C-terminal intracytoplasmic portion within 15 sec following the addition of IL-8 or MGSA. Cells transfected with a truncated form of the receptor missing the last 12 amino acids (T3) showed normal binding affinity, but were no longer phosphorylated; individual alanine replacement indicated that Ser346 and 348 were the primary sites of phosphorylation. In studies of the importance of phosphorylation in CXCR2 desensitization, cells expressing wild type CXCR2 lost GTP gamma S binding above basal rate after the first exposure to IL-8, while cells with the T3 mutant retained 60% of their capacity to induce GTP gamma S exchange upon a second exposure to IL-8. In contrast, receptor internalization was not affected by the loss of phosphorylation of the T3 mutant. Further receptor truncation led to decreasing binding affinities for IL-8 and MGSA and a decreased rate of GTP gamma S exchange following addition of excess ligand which suggests involvement of this region in G-protein coupling.

Identification and characterization of receptor for cytokine-induced neutrophil chemoattractant-3 on rat neutrophils

Cytokine-induced neutrophil chemoattractants (CINCs), members of alpha-chemokines, are considered to be major neutrophil chemotactic factors in rats. Recombinant CINC-3/rat macrophage inflammatory protein-2 (MIP-2) having an additional tyrosine residue at the carboxyl terminus (CINC-3-Tyr) was constructed, purified, radiolabeled with 125I, and used for binding studies. The specific binding of 125I-labeled CINC-3-Tyr (125I-CINC-3-Tyr) to rat neutrophils reached a plateau after approximately 60 min at 4 degrees C. This binding of 125I-CINC-3-Tyr could be reversed by adding an excess amount of unlabeled CINC-3-Tyr. Scatchard analysis revealed approximately 12,000 binding sites per cell on rat neutrophils with an apparent Kd value of 120 pM. Chemical cross-linking experiments suggested that the rat neutrophil CINC-3 receptor is a mass of approximately 69 kDa. Taken together, our results strongly suggest that rat neutrophils express a high affinity receptor for CINC-3.

Presence of high levels of leukocyte-associated interleukin-8 upon cell activation and in patients with sepsis syndrome

In inflammatory and infectious diseases, the presence of circulating cytokines in plasma strongly suggests, following their exacerbated production, that saturation of specific binding sites has occurred or that an equilibrium between receptor-bound and free cytokines has been reached. In this report, we demonstrate that in addition to circulating interleukin-8 (IL-8), high levels of cell-associated IL-8 were detected in blood samples from patients with sepsis syndrome. The following analysis will reveal that in addition to erythrocytes, which have been dubbed a "sink" for IL-8, peripheral blood mononuclear cells (PBMC) and polymorphonuclear cells (PMN) contributed to the detection of cell-associated IL-8. On a per cell basis, 2,000 to 7,000 times the amount of IL-8 was found associated with PMN than with erythrocytes. In addition, circulating cells may well be the source of the leukocyte-associated form of IL-8. Similarly, in vitro experiments, such as whole-blood stimulation assays or the addition of exogenous IL-8 in blood samples, demonstrated that a large proportion of the IL-8 was associated with leukocytes. This suggests that the trapping of free cytokines onto the cell surface and the internalization of the IL-8 bound to its receptor, occurring both in vitro and in vivo, allows the detection of this cell-associated form. This analysis of cell-associated cytokines was extended to IL-1ra, another component of the inflammatory response, which, in contrast to IL-8, has been demonstrated to exist as an intracellular form. Indeed, cell-associated IL-1ra was also detected in septic patients. The measurement of cell-associated proinflammatory and anti-inflammatory cytokines in patients is clearly a more reliable reflection of their production than is the simple measurement in plasma and may provide useful indication to further understand the inflammatory process.

Relationship between interleukin-8 levels and myeloperoxidase activity in human gastric mucosa

Although interleukin (IL)-8 is well known as a chemotactic agent for neutrophil migration in vitro, the relationship between IL-8 activity and the degree of neutrophil infiltration in gastric mucosa is still unclear. In the present study, we investigated IL-8 and myeloperoxidase activity, a marker of neutrophil infiltration, in gastric antral mucosa using biopsy samples in 23 patients with no gastric lesions. The results indicate that there is a good correlation between IL-8 and myeloperoxidase activity (y = 0.173x + 13.9; r = 0.49, P < 0.01). Furthermore, IL-8 and myeloperoxidase activity are significantly higher in Helicobacter pylori-positive patients than in H. pylori-negative patients. In conclusion, an increase of IL-8 activity in the gastric mucosa causes increased neutrophil infiltration in human gastric mucosa and H. pylori infection accelerates these reactions in the mucosa.

Interleukin-8 regulation of the Ras/Raf/mitogen-activated protein kinase pathway in human neutrophils

Interleukin-8 (IL-8), the prototypic member of the CXC subfamily of chemokines, induces in neutrophils chemotaxis, the respiratory burst, granule release, and increased cell adhesion. The IL-8 receptor is a seven-transmembrane spanning receptor coupled to specific heterotrimeric G proteins including Gi and G16. IL-8 stimulation of its receptor on neutrophils activates Ras GTP loading and the mitogen-activated protein kinase (MAPK) pathway including Raf-1 and B-Raf. The properties of IL-8 stimulation of the MAPK pathway differ from those observed for chemoattractants such as C5a. Even though Ras GTP loading is similar for IL-8 and C5a, the maximal activation of Raf-1 and B-Raf is approximately 2-fold and 3-7-fold, respectively, less for IL-8 than that observed for C5a. Raf-1 activation is rapid but transient, returning to near basal levels by 10 min. B-Raf activation is slower in onset and does not return to basal levels for nearly 30 min. IL-8 activation of MAPK follows a time course suggesting an involvement of both Raf-1 and B-Raf. Surprisingly, wortmannin, at low concentrations, inhibits Raf-1, B-Raf, and MAPK activation in response to IL-8 and C5a demonstrating a role for phosphatidylinositol 3-kinase in the activation of Raf kinases in G protein-coupled receptor systems in human neutrophils. Furthermore, wortmannin inhibits IL-8 stimulated granule release and neutrophil adherence. These findings demonstrate the control of Raf kinases, the MAPK pathway and specific neutrophil functions by phosphatidylinositol 3-kinase enzymes.

Dansyl cadaverine regulates ligand induced endocytosis of interleukin-8 receptor in human polymorphonuclear neutrophils

Interleukin-8 (IL-8), a neutrophil chemotactic agent, acts as a key mediator in a large number of acute and chronic inflammatory diseases. At 37 degrees C, the receptor for IL-8 is rapidly internalized with its ligand. But no specific inhibitor of this ligand induced internalization of the receptor has been reported so far. We have found that monodansyl cadaverine (MDC) inhibited about 70% of IL-8 induced endocytosis and caused 70% and 66% inhibition of IL-8 mediated chemotaxis and respiratory burst response, respectively, in neutrophils. The uninternalized receptor was detected by anti IL-8R antibody in MDC treated cells. The endocytosis of IL-8R was strongly inhibited under Ca2+ depleted conditions which was restored on addition of 1 mM CaCl2 indicating the critical involvement of a Ca2+ ion in the process. Absence of receptor internalisation makes the MDC treated neutrophils suitable for studying the interaction of IL-8R with potential therapeutic agents e.g. for in vitro screening of anti-inflammatory agents.

Granulocyte-colony stimulating factor and lipopolysaccharide regulate the expression of interleukin 8 receptors on polymorphonuclear leukocytes

Interleukin 8 (IL-8) is a potent chemoattractant and activating factor for human polymorphonuclear leukocytes (PMN) and hence plays a critical role in the pathogenesis of acute inflammation. Two unique but homologous receptors for IL-8 have been cloned (IL-8RA and -B), each of which binds the IL-8 ligand with high affinity. PMN stimulated by cytokines or lipopolysaccharide (LPS) exhibit changes in IL-8R mRNA and 125I-IL-8 binding. Granulocyte-colony stimulating factor (G-CSF) treatment of PMN enhances, and LPS inhibits, IL-8R mRNA expression. Similarly, 125I-IL-8 ligand binding to PMN is increased by G-CSF and decreased by LPS treatment. The stimulatory effect of G-CSF on IL-8R expression is transcriptional as it is inhibited by actinomycin D and is evident in nuclear run-on analyses. In contrast, LPS down-regulates IL-8R by both transcriptional and post-transcriptional mechanisms. The alterations in IL-8R expression are associated with similar changes in the IL-8-induced chemotactic responses of PMN. In conclusion, the two types of IL-8 receptor differ in their cellular distribution and are regulated in response to cytokines and LPS. Regulation of IL-8R expression by endogenous and exogenous immunomodulators may be important in the in vivo control of PMN effector functions in inflammation.

Regulation of interleukin-8 receptor expression in human polymorphonuclear neutrophils

Interleukin-8, a neutrophil chemotactic agent, is known to have an active role in the induction of inflammatory response in a number of diseases. Although the activity of IL-8 is known to be through a receptor (IL-8R) on the surface of neutrophils, no information is available regarding the regulation of the IL-8R expression. The present study demonstrates that serum activated LPS at a concentration of 10 ng/ml induces expression of functionally active IL-8R by 120% within 30 min through de novo protein synthesis. The upregulated receptors could be detected by anti-IL-8R antibody and could also be demonstrated by autoradiography with crosslinking 125I IL-8. The serum-activated LPS-stimulated neutrophils migrated faster and showed higher Ca2+ flux over the unstimulated cells. The LPS-induced receptors were downregulated rapidly, about 85% of the receptor activity being lost within 90 min of incubation at 37 degrees C. The downregulation could be partially prevented by treatment with a cocktail of protease inhibitors, suggesting the possible involvement of protease(s) in this process. Both EDTA (100 microM) and bestatin (40 microM) afforded almost complete protection of the receptor from proteolytic cleavage indicating that the enzyme involved is a metalloprotease, possibly an aminopeptidase. The study shows that stimulation of PMNs with LPS leads to induction of IL-8R expression enhancing the IL-8-mediated biological responses and also provides evidence for post-stimulatory restoration of receptor level on the neutrophil surface by proteolytic cleavage of the amino-terminal end of the receptor.

Upregulation of interleukin-8 receptor in human polymorphonuclear neutrophils by formyl peptide and lipopolysaccharide

Interleukin-8 (IL-8) is implicated in the pathogenesis of a large number of neutrophil-driven inflammatory diseases. Although the cytokine activates neutrophils through a receptor, no information is available regarding the regulation of IL-8 receptor (IL-8R) expression. The present study shows that, compared to control, the bacterial products--formylpeptide and LPS (serum-activated) upregulate IL-8 receptor by 54% and 115%, respectively, the former by degranulation of the secretory vesicle and the latter by de novo protein synthesis. The newly expressed IL-8R could be demonstrated with anti-IL-8R-antibody and by autoradiogram of the receptor crosslinked with [125I]IL-8. The study may be useful for understanding the potential role of IL-8 during neutrophil mediated inflammatory response.

An anti-interleukin 8 monoclonal antibody that interferes with the binding of interleukin 8 to cellular receptors and the activation of human blood neutrophils

Interleukin 8 (IL-8) is a proinflammatory cytokine produced by a wide variety of cells. Interleukin 8 acts as a neutrophil activator and chemotactic factor. In the current studies, we examined the properties of a monoclonal antibody against human IL-8. The estimated affinity of the antibody was 1.74 x 10(7) liters/mol. The antibody interfered with the binding of radiolabeled recombinant human IL-8 (rhIL-8) to human blood neutrophils (IC50 = 3 x 10(-7) M, at an IL-8 concentration of 2.4 nM). Neutrophil degranulation elicited by 5 x 10(-6)-4 x 10(-8) M rhIL-8 was blocked by the antibody at three-fold molar excess. However, a higher concentration of anti-IL-8 antibody was needed to suppress the chemotactic activity of rhIL-8. The inhibition of neutrophil chemotaxis triggered by 2 x 10(-7)-2 x 10(-9) M rhIL-8 required 6 x 10(-5) M antibody. Similarly, a 300-fold molar excess of anti-IL-8 antibody [10(-5) M] was necessary to abrogate the increase in cytosolic free calcium in neutrophils stimulated with 4 x 10(-8) M rhIL-8. In addition, epitope analysis using synthetic peptides corresponding to different regions of the IL-8 molecule showed that peptide consisting of residues 44-72 (corresponding to the C-terminal of the IL-8 molecule) competed with the antibody for binding to rhIL-8. Because IL-8 is an important inflammatory mediator in several human diseases, anti-IL-8 antibodies may have pharmacological potential.

Cytokine-stimulated chemotaxis of human neutrophils in a 3-D conjoined fibrin gel assay

The ability of neutrophils to migrate through three-dimensional (3-D) tissues in response to chemical stimuli is critical to their host defense function. However, studies characterizing stimulated migration in vitro have been largely limited to two-dimensional (2-D) surfaces. In this study, we have employed direct observation methods to quantify human neutrophil migration in 3-D fibrin gel using time-lapse video microscopy and automated cell tracking methods. A novel 3-D conjoined gel assay was developed to establish experimentally quantifiable and theoretically predictable diffusion gradients of chemotactic factors. This assay was used to measure objective migration parameters, namely the random motility and chemotaxis coefficients, in response to the cytokine, interleukin-8 (IL-8). The random motility coefficient, mu, showed a biphasic dependence on IL-8 concentration with a maximum of 1.1 x 10(-8) cm2/s at 5 x 10(-8) M IL-8; no significant motility was observed in the absence of IL-8. We further established the dependence of cell orientation bias, phi, on the concentration and gradient steepness (i.e., specific gradient, SG) of IL-8. Results indicate that phi increases with increasing SG, provided the concentration is maintained sufficiently low, which we conjecture to result from minimizing IL-8 receptor down-regulation. The chemotaxis coefficient, chi, was maximum at an intermediate SG for both IL-8 concentrations studied. We also examined the applicability of this assay to estimate mu and chi from indirect measurements of chemotaxis, namely the simpler measurement of cell redistribution after a prescribed incubation time, as opposed to direct cell tracking measurements. By virtue of measuring chi, this is the first quantitatively objective study of mammalian cell chemotaxis in a physiologically relevant 3-D gel and, in particular, of neutrophil chemotaxis on any substratum in response to the physiologically relevant chemotactic factor, IL-8.

A fluorescent interleukin-8 receptor probe produced by targetted labelling at the amino terminus

Interleukin-8 is the most extensively characterised member of the structurally related chemotactic and pro-inflammatory proteins collectively called chemokines. It binds to two closely related members of the seven transmembrane chemokine receptor family found on a variety of leukocyte cell types. In order to study the interaction of interleukin-8 with its receptors, and their distribution, we have produced a fluorescently labelled protein as an alternative to the radioactive 125I-interleukin-8 ligand. Interleukin-8 is naturally produced as two forms, a 72-residue polypeptide by monocytes and a 77-residue form produced by endothelial cells which has an extension of five amino acids at the amino terminal. Both forms are active at nanomolar concentrations, implying that chemical modification to the amino terminus of the 72-residue form will not destroy activity. The 72-residue interleukin-8 sequence starts with a serine residue, which can be oxidised under mild conditions to give a reactive glyoxylyl function which is then reacted with a nucleophilic fluorescein derivative. The site-specifically labelled protein was easily isolated by reverse-phase HPLC. The dissociation constant of the fluorescently labelled interleukin-8 from its receptors on neutrophils was measured by displacement of 125I-interleukin-8 and found to be 10 nM compared to 1 nM for the unmodified protein. The modified protein is highly active in in vitro bioassays using human neutrophils, giving an EC50 of 7 nM in chemotaxis and an EC50 of 0.62 nM for shape change. The binding of the fluorescent protein to neutrophils can also be measured by fluorescent automatic cell sorter (FACS) analysis, and can be competed by unlabelled interleukin-8. The amino-terminal modification of interleukin-8 has produced a reagent which is useful for the quantification of interleukin-8 receptor expression, and will also be useful in monitoring the fate of the ligand after receptor binding.

Interleukin-8 induces motile behavior and loss of focal adhesions in primary fibroblasts

Interleukin-8 (IL-8) is a proinflammatory cytokine that promotes neutrophil migration. Although fibroblasts are known to secrete IL-8, the actions of this cytokine on fibroblasts have not been previously reported. We have found that in subconfluent populations of cultured primary fibroblasts, IL-8 causes an increase in the percentage of cells lacking focal adhesions. Most of the IL-8-stimulated cells not only exhibit a lack of focal adhesions but also have a migratory phenotype that includes a protrusive leading edge and trailing tail. In addition, IL-8 was found to promote primary fibroblast chemotaxis in modified Boyden chambers as well as chemokinesis on serum-coated coverslips. Human primary fibroblasts were also found to specifically bind to IL-8 with high affinity. We have previously shown that a lack of focal structures in primary fibroblasts can be used as an index of chemokinetic locomotion and have fully characterized this system using newborn rat heart conditioned medium. The main stimulus in heart conditioned medium that is responsible for the lack of focal adhesions in the majority of cells can be immunoprecipitated using a polyclonal antibody against recombinant human IL-8. Additionally, video microscopy assays using heart conditioned medium depleted with the IL-8 antibody show an increase in the percentage of stationary cells, a consequent decrease in the percentage of migrating cells, and a twofold increase in the mitotic rate. Interleukin-1 alpha and tumor necrosis factor-alpha, which are early inflammatory cytokines, have been previously shown to stimulate IL-8 production in macrophages, fibroblasts, endothelial and epithelial cells. Our findings indicate that these two cytokines also cause an increase in the percentage of fibroblasts without focal adhesions. Additionally, this increase in cells lacking focal structures can be largely attributed to the production and subsequent autocrine action of a factor immunoprecipitated with an IL-8 antibody. Conversely, GRO-alpha, which has a high homology with IL-8, does not cause a similar increase in the percentage of cells lacking focal adhesions, but was not antagonistic to the effects of IL-8.

Staurosporine restores signaling and inhibits interleukin-8-induced chemotactic desensitization

Interleukin 8 (IL-8) is a chemotactic cytokine (chemokine) that plays a key role in the accumulation and activation of neutrophils at inflammatory sites. In this report we demonstrate that homologous chemotactic desensitization occurs upon pretreatment of neutrophils with IL-8 or N-formyl-methionyl-leucyl-phenylalanine (FMLP) and results in the inhibition of neutrophil chemotaxis upon subsequent challenge with the same ligand. This homologous chemotactic desensitization could be prevented by pretreating the neutrophils with the protein kinase inhibitor staurosporine, indicating that protein kinases may play an essential role. The attenuation of homologous desensitization by staurosporine restored chemotaxis but was not associated with a change in IL-8 receptor expression, affinity or the rate of ligand internalization, indicating that homologous desensitization does not alter ligand-receptor interaction. Using two-dimensional analysis we have shown that IL-8 induced a rapid serine/threonine phosphorylation of a number of neutrophil substrates the most prominent being phosphoprotein 39 (pp39), extracellular signal-related kinase-1, pp55 and pp66. Prior desensitization of neutrophils with IL-8 blocked all subsequent phosphorylation upon rechallenge with IL-8. However, the desensitization was specific for IL-8 since normal phosphorylation of identical substrates was observed in response to FMLP. When neutrophils were pretreated with staurosporine, prior to desensitization, phosphorylation of pp39 was observed upon restimulation with IL-8. Further study revealed that pp55 and pp66 were not phosphorylated in the presence of staurosporine. Thus, homologous desensitization of neutrophils in response to IL-8 does not result from changes in receptor expression, but rather from a staurosporine-sensitive inactivation of subsequent signal transduction. This desensitization is selective since the cells are able to respond to other ligands.

Isolation and characterization of an interleukin-8-like peptide in the bovine species

Human interleukin-8 (IL-8) is a biologically active peptide which displays chemo-attractive activity for neutrophils and T-cells. The molecule is produced by a variety of cell types upon exposure to lipopolysaccharide, interleukin-1 and tumor necrosis factor. Recombinant human IL-8 also stimulates chemotaxis of bovine cells in a dose dependent manner. The purpose of this series of studies was to investigate the ability of bovine cells to produce an active IL-8-like molecule and to determine if bovine cells respond to human recombinant IL-8. Stimulation of purified peripheral blood mononuclear cells results in the time dependent production of an IL-8-like molecule as determined using an anti-human IL-8 ELISA assay and a bovine neutrophil chemotactic assay. Physical characterization indicates that the biological activity of the molecule was significantly reduced by heat inactivation at 56 degrees C for 30 min or exposure to extreme acidic or basic conditions. The peptide was affinity purified using an anti-human IL-8 antibody produced from ATCC hybridoma HB9647. SDS-PAGE analysis yields a distinct band at 7.8 kDa. The isoelectric point of the purified protein was determined to be 8.65. Biological activity of the purified protein was confirmed and the anti-human IL-8 antibody was capable of partially neutralizing the chemotactic activity.

Analysis of cytokine receptor messenger RNA expression in human glioblastoma cells and normal astrocytes by reverse-transcription polymerase chain reaction

To elucidate which cytokine receptors may be expressed by human glioblastoma and normal astrocytic cells, the presence of messenger ribonucleic acid (RNA) for a number of cytokine receptors was examined in 16 glioblastoma cell lines and adult and fetal astrocytes. A complementary deoxyribonucleic acid copy of total RNA was synthesized and amplified with specific primers using the polymerase chain reaction method. The receptors studied were interleukin (IL)-1 receptor type I (IL-1RI) and type II (IL-1RII), p75 and p55 tumor necrosis factor (TNF) receptors (p75TNFR and p55TNFR), interferon (IFN)-alpha/beta and -gamma receptors (IFN-alpha/beta R and IFN-gamma R), granulocyte-macrophage (GM) colony-stimulating factors receptor alpha subunit (GM-CSFR), G-CSF receptor (G-CSFR), M-CSF receptor (c-fms, M-CSFR), stem cell factor receptor (c-kit, SCFR), IL-6 receptor (IL-6R), and IL-8 receptor (IL-8R). Transcripts for IL-1RI, p55TNFR, IFN-alpha/beta R, and IFN-gamma R were present in all cell lines. The presence of IL-1RII, p75TNFR, GM-CSFR, M-CSFR, SCFR, IL-6R, and IL-8R was identified in 13, eight, seven, eight, 14, three, and one cell lines, respectively. Normal astrocytes were positive for IL-1RI, p75TNFR, p55TNFR, IFN-alpha/beta R, IFN-gamma R, M-CSFR, and SCFR, showing a similarity to glioblastoma cells. Expression of IL-1RII was observed in adult astrocytes but not in fetal astrocytes. Furthermore, gene expression was assessed in normal brain tissue and 11 glioblastoma tissue specimens. The normal brain tissue expressed IL-1RI, IL-1RII, IFN-alpha/beta R, M-CSFR, and SCFR. Of the 11 glioblastoma tissue specimens, IL-1RI was positive in 11, IL-1RII in 10, p75TNFR in nine, p55TNFR in nine, IFN-alpha/beta R in 10, IFN-gamma R in 10, GM-CSFR in two, G-CSFR in three, IL-8R in eight, and M-CSFR and SCFR in 11. These expressions were consistent with those in the cell lines, except for IL-8R. It is concluded that glioblastoma cells and normal astrocytes express a similar set of cytokine receptor genes in vitro and in vivo. Possible autocrine loops are suggested for IL-1 alpha/IL-1RI, TNF-alpha/p55TNFR, IFN-beta/IFN-alpha/beta R, M-CSF/M-CSFR, and SCF/SCFR in glioblastomas.

Biological activity of the growth factor-induced cytokine N51: structure-function analysis using N51/Interleukin-8 chimeric molecules

The immediate-early gene N51/KC encodes a protein which following expression in the baculovirus system and purification to apparent homogeneity is able to induce chemotaxis and intracellular Ca2+ flux, to compete for 125I-labeled interleukin-8 (IL-8) binding, and upon iodination, to bind specifically to human neutrophils. The activity of N51/KC can be distinguished from that of IL-8 by a number of criteria. First, at equivalent concentrations, the specific binding of [125I]N51/KC to human neutrophils is about 10 times less than that of [125I]IL-8. Second, the competition studies of [125I]IL-8 with IL-8 define a single class of high-affinity receptors, while the presence of both a high- and a low-affinity class of receptors is defined by N51/KC. Third, although the changes in intracellular Ca2+ of fura-2/AM-preloaded human neutrophils elicited by N51/KC and IL-8 are similar, pretreatment of the cells with N51/KC did not result in a loss of response to a subsequent treatment with IL-8; in contrast, treatment with IL-8 did result in the subsequent desensitization to N51/KC. To further characterize N51/KC, mutants and hybrids of N51/KC and IL-8 were produced and analyzed for the ability to compete for [125I]IL-8 binding and elicit intracellular Ca2+ changes in human neutrophils. Two important observations came from these studies. First, the N51/IL-8I hybrid in which the N51/KC sequence between cysteines 2 and 3 (or first disulfide bond) is replaced by the corresponding sequence in IL-8 shows IL-8-like properties, indicating that this region is important for specific receptor recognition. Second, the N51 delta III and IL-8 delta III C-terminus deletion mutants were biologically inactive, but the hybrid molecules N51/IL-8III and IL-8/N51III, in which the C termini were exchanged, had biological activities similar to that of the wild-type molecules, demonstrating that the presence of the C terminus is essential for the biological activity of these chemokines but does not confer receptor specificity.

Cloning of a cDNA encoding a mouse homolog of the interleukin-8 receptor

A mouse cDNA library was screened using a DNA fragment generated by polymerase chain reaction (PCR) with oligodeoxyribonucleotide primers which were derived from the conserved sequences in cDNAs encoding the human and rabbit interleukin-8 receptors (hIL-8R and rIL-8R). A novel cDNA was obtained encoding 359 amino acids (aa) with seven putative transmembrane portions similar to hIL-8R and rIL-8R. Its aa sequence shows 64 and 69% homology to those of type-1 and type-2 hIL-8R, respectively. COS-7 cells transfected with the isolated cDNA in a mammalian expression vector bind IL-8, but do not bind a related protein, monocyte chemotactic and activating factor, suggesting that the isolated cDNA encodes the mouse homolog of IL-8R. Northern blot analysis showed that mRNA of this clone was highly expressed in mouse peritoneal neutrophils, and the single band was observed in Southern blotting analysis on mouse genomic DNA digested with HindIII or KpnI, suggesting that this is a single-copy gene.

Molecular properties of the chemokine receptor family

Chemokine receptors play a major role in the mobilization and activation of the cells of the immune system, and are discussed in this review by Richard Horuk. Six receptors that bind chemokines with high affinity have been cloned and all belong to the superfamily of G protein-coupled receptors. Chemokine receptors are mainly expressed in immune cells, which are their major target cells. However, two of the cloned receptors are expressed by viruses and may play a role in protecting the virus from immune surveillance. In addition, a novel chemokine receptor that is expressed in human erythrocytes not only binds CC and CXC chemokines with high affinity but is also a receptor for the malarial parasite Plasmodium vivax.