De novo isolation of antibodies with pH-dependent binding properties

pH-dependent antibodies are engineered to release their target at a slightly acidic pH, a property making them suitable for clinical as well as biotechnological applications. Such antibodies were previously obtained by histidine scanning of pre-existing antibodies, a labor-intensive strategy resulting in antibodies that displayed residual binding to their target at pH 6.0. We report here the de novo isolation of pH-dependent antibodies selected by phage display from libraries enriched in histidines. Strongly pH-dependent clones with various affinity profiles against CXCL10 were isolated by this method. Our best candidate has nanomolar affinity for CXCL10 at pH 7.2, but no residual binding was detected at pH 6.0. We therefore propose that this new process is an efficient strategy to generate pH-dependent antibodies.

Cellular assays of chemokine receptor activation

This unit describes procedures for measuring the activation of chemokine receptors by their ligands. Chemokines are chemoattractant proteins and two assays are described for analyzing the chemoattractant properties (chemotaxis) of these proteins. Chemokine receptors are coupled to G proteins, and activation of the receptors results in the mobilization of intracellular Ca²⁺ stores. Two assays for the measurement of this activity are described which employ calcium-sensitive dyes, one for adherent and one for non-adherent cells. In addition, an assay for quantitating chemokine receptor downmodulation and subsequent recycling events is described. The assays are applicable to both purified leukocytes and stably expressed recombinant chemokine receptors.This unit describes procedures for measuring the activation of chemokine receptors by their ligands.

Regulation of protein function by glycosaminoglycans--as exemplified by chemokines

Immune modulators such as cytokines and growth factors exert their biological activity through high-affinity interactions with cell-surface receptors, thereby activating specific signaling pathways. However, many of these molecules also participate in low-affinity interactions with another class of molecules, referred to as proteoglycans. Proteoglycans consist of a protein core to which glycosaminoglycan (GAG) chains are attached. The GAGs are long, linear, sulfated, and highly charged heterogeneous polysaccharides that are expressed throughout the body in different forms, depending on the developmental or pathological state of the organ/organism. They participate in many biological functions, including organogenesis and growth control, cell adhesion, signaling, inflammation, tumorigenesis, and interactions with pathogens. Recently, it was demonstrated that certain chemokines require interactions with GAGs for their in vivo function. The GAG interaction is thought to provide a mechanism for retaining chemokines on cell surfaces, facilitating the formation of chemokine gradients. These gradients serve as directional cues to guide the migration of the appropriate cells in the context of their inflammatory, developmental, and homeostatic functions. In this review, we discuss GAGs and their interaction with proteins, with a special emphasis on the chemokine system.

Interaction of chemokines and glycosaminoglycans: a new twist in the regulation of chemokine function with opportunities for therapeutic intervention

Despite their key role in inflammation, the apparent redundancy in the chemokine system is often cited as an argument against probing chemokines as therapeutic targets for inflammation. However, this in vitro redundancy frequently does not translate to the in vivo situation, as exemplified by the use of specific receptor antagonists, ligand neutralizing or receptor blocking antibodies and gene-deleted mice in models of human disease. Specificity may be conferred onto the chemokine system by fine-tuning of responses both temporally and spatially through their highly specific interactions with glycosaminoglycans (GAGs). In this survey, we present evidence for specificity in the interaction and introduce emerging technologies that enable detailed assessment of protein-GAG interactions. Finally, we address the issue of exploitation of this interaction for therapeutic advantage.

Chemokine receptors--the next therapeutic target for HIV?

To date, the available therapies for the treatment of HIV infection are targeted against proteins encoded by the virus itself. Thus, combination drug therapies for HIV with reverse transciptase and protease inhibitors have resulted in spectacular reductions of viraemia, often leading to a remarkable improvement in symptoms and recovery from disease in infected people. There is still however, a great need for improved therapies since many patients are unable to take these drugs, either for reasons of intolerance, strain resistance, complexity of regimen or prohibitive cost. Multiple therapies aimed at different events in the HIV life cycle will ensure switching of treatments to combat resistant viruses, and also allow treatment flexibility if patients are unable to tolerate particular therapies. One event that could provide a key to reducing or even eliminating viral infection would be to prevent the virus from entering the host cell. Intense efforts are now underway to produce drugs that target chemokine receptors, one of the essential components for HIV cell entry. HIV needs two receptors on the host cell surface for efficient attachment and infection. The first is CD4 and the second, identified in 1996, is a member of the family of chemokine receptors, members of the G-protein coupled 7TM superfamily, which are involved in the trafficking of leukocytes in immune surveillance and inflammation. Many small, orally bioavailable molecules that block various 7TM receptors are used to treat a panoply of diseases including ulcers, allergies, migraines, and schizophrenia. These molecules are the cornerstone of the pharmaceutical industry's contribution to the fight against so many diseases. Small molecule inhibitors of the HIV-coreceptors are now entering the first stages of clinical trials as new therapeutics for the fight against AIDS.

Macrophage inflammatory protein-1alpha uses a novel receptor for primitive hemopoietic cell inhibition

Macrophage inflammatory protein-1alpha (MIP-1alpha) is a member of the chemokine family of proinflammatory mediators. In addition to its inflammatory roles, MIP-1alpha has been shown to be active as an inhibitor of primitive hemopoietic cell proliferation. Indeed, a dysfunction in this inhibitory process has been postulated to contribute to leukemogenesis. Research has been aimed at characterizing the receptor involved in cellular inhibition by MIP-1alpha. This study demonstrates that of all the beta-chemokines tested, only MIP-1alpha is capable of inhibiting primitive hemopoietic cell proliferation. Because no MIP-1alpha-specific receptors have been identified, this suggests that inhibition is mediated by an uncharacterized receptor. Further evidence for the involvement of a novel receptor in this process is the equivalent potencies of MIP-1alphaS and MIP-1alphaP variants of human MIP-1alpha and the fact that primitive cells from bone marrow derived from individual MIP-1alpha receptor null mice display a full response to MIP-1alpha inhibition.

CC chemokine receptor (CCR)4 and the CCR10 ligand cutaneous T cell-attracting chemokine (CTACK) in lymphocyte trafficking to inflamed skin

The chemokine thymus and activation-regulated chemokine (TARC; CCL17) is displayed by cutaneous (but not intestinal) venules, and is thought to trigger vascular arrest of circulating skin homing memory T cells, which uniformly express the TARC receptor CC chemokine receptor (CCR)4. Cutaneous T cell-attracting chemokine (CTACK; CCL27), expressed by skin keratinocytes, also attracts cutaneous memory T cells, and is hypothesized to assist in lymphocyte recruitment to skin as well. Here we show that chronic cutaneous inflammation induces CD4 T cells expressing E-selectin binding activity (a marker of skin homing memory cells) in draining lymph node, and that these E-selectin ligand+ T cells migrate efficiently to TARC and to CTACK. In 24 h in vivo homing assays, stimulated lymph node T cells from wild-type mice or, surprisingly, from CCR4-deficient donors migrate efficiently to inflamed skin; and an inhibitory anti-CTACK antibody has no effect on wild-type lymphocyte recruitment. However, inhibition with anti-CTACK monoclonal antibody abrogates skin recruitment of CCR4-deficient T cells. We conclude that CTACK and CCR4 can both support homing of T cells to skin, and that either one or the other is required for lymphocyte recruitment in cutaneous delayed type hypersensitivity.

Characterization of chemokine receptors

This unit describes the procedures for measuring binding of a radiolabeled chemokine to chemokine receptors in cells or cell membranes. The whole-cell binding assay can be used for both purified leukocytes as well as transfected cell lines expressing chemokine receptors. Two basic protocols are described. The first is applicable to all cells expressing chemokine receptors, both primary cultures as well as recombinantly transfected cell lines expressing a single chemokine receptor. The second is used principally for transfected cell lines and measures chemokine binding to cell membranes using scintillation proximity assay (SPA) methodology, but does not require washing steps and thus is applicable to automated high-throughput screening strategies. An alternative procedure is also described which also uses SPA methodology to measure GTP-gamma-S binding to chemokine receptors in cell membranes. The two basic protocols can be used to determine the binding of compounds to chemokine receptors, while the alternate protocol determines the effects of compounds on the chemokine-stimulated activation of the receptor.

IL-3 induces down-regulation of CCR3 protein and mRNA in human eosinophils

Cytokines and chemokines are responsible for the attraction and activation of eosinophils in allergic and inflammatory diseases. Whereas cytokines such as IL-3, IL-5, and GM-CSF activate eosinophils via heterodimeric receptors containing a distinct alpha-chain (binding domain) and a common beta-chain (signaling domain), chemokines such as eotaxin activate eosinophils via seven-transmembrane G(i) protein-coupled CCRs. Recent studies have demonstrated the importance of CCR3 on human eosinophils that undergo receptor recycling after chemokine activation, but the modulation of this receptor by cytokines has not yet been addressed. In this study, we demonstrate that IL-3 induces a dose- and time-dependent down-regulation of CCR3 from the surface of human eosinophils comparable to the CCR3-specific ligand eotaxin, whereas IL-5, GM-CSF, IL-4, IL-10, IL-13, IFN-gamma, and TNF-alpha had no effect. Maximal down-regulation of CCR3 in response to IL-3 was reached at 24 h. Reduction of CCR3 surface protein in response to IL-3 could be prevented by an anti-IL-3 mAb and was neither due to the release of CC chemokines nor to nonspecific binding of IL-3 to CCR3. Moreover, down-regulation was prevented by phenylarsine oxide, a nonspecific inhibitor of receptor internalization. After 24 h, IL-3-induced decrease of CCR3 surface expression correlated with diminished mRNA expression, suggesting a transcriptional regulation mechanism. Since wortmannin partially inhibited IL-3- but not eotaxin-induced CCR3 down-regulation, receptor down-modulation seems to underlie different signaling events. Therefore, these data suggest a novel role for the cytokine IL-3 in the activation process of eosinophils and its predominant chemokine receptor CCR3.

The chemokine system: novel broad-spectrum therapeutic targets

Chemokines are cytokines that specifically direct the trafficking of immune cells in the body. They offer a novel point of therapeutic intervention, as inhibiting specific chemokines and receptors could prevent the excessive recruitment of leukocytes to sites of inflammation. This approach could be considered to act upstream of the therapies used today which, for the most part, act on the cells already at the site of inflammation. The receptors for chemokines are G-protein-coupled seven-transmembrane receptors, which are particularly tractable for the pharmaceutical industry. The search for small-molecule inhibitors of these receptors has been fruitful and the numbers of patents and, more recently, peer-reviewed publications are growing rapidly. The first clinical trial was initiated this year, so although it is too soon to be able to report these results we hope to see the outcome of this research in the near future.

Selective recruitment of Th2-type cells and evasion from a cytotoxic immune response mediated by viral macrophage inhibitory protein-II

The viral CC chemokine macrophage inhibitory protein-II (vMIP-II) encoded by human herpes virus 8 (HHV-8) binds to multiple chemokine receptors, however, its ability to control the initial recruitment of specific leukocyte subtypes from the peripheral circulation has not been fully clarified. Here we show that vMIP-II blocks the firm arrest and transmigration of monocytes or Th1-like T lymphocytes triggered by RANTES immobilized on activated human microvascular endothelium (HMVEC) under flow conditions. The internalization of the receptors CCR1 and CCR5 that mediate arrest and transmigration of these cells in response to RANTES was prevented by vMIP-II, supporting its role as an antagonist of CCR1 and CCR5. In contrast, vMIP-II triggered the firm arrest of eosinophils and Th2-like T cells by engaging CCR3, as confirmed by its down-regulation. Immunohistochemical analysis of HHV-8-associated Kaposi's sarcoma lesions marked by vMIP-II expression and mononuclear cell infiltration revealed a predominance of Th2-type CCR3(+) lymphocytes over Th1-type CXCR3(+)/CCR5(+) leukocytes, indicating that as a CCR3 agonist vMIP-II can drive a Th2-type immune response in vivo. Thus, our data provide evidence for a immunomodulatory role of vMIP-II in directing inflammatory cell recruitment away from a Th1-type towards a Th2-type response and thereby facilitating evasion from cytotoxic reactions.

Regulation of dendritic cell recruitment into resting and inflamed airway epithelium: use of alternative chemokine receptors as a function of inducing stimulus

Dendritic cells (DC) were purified by flow cytometry from rat tracheal mucosa; they exhibited the phenotypic characteristics of immature DC including high endocytic activity, low CD80/86 expression, and in vitro responsiveness to a broad range of CC chemokines. Daily treatment of adult rats with the selective CCR1 and CCR5 antagonist Met-RANTES reduced baseline numbers of tracheal intraepithelial DC by 50-60%, and pretreatment of animals with Met-RANTES before inhalation of aerosol containing heat-killed bacteria abolished the rapid DC influx into the epithelium that occurred in untreated controls, implicating CCR1 and CCR5 and their ligands in recruitment of immature DC precursors into resting airway tissues and during acute bacterial-induced inflammation. Comparable levels of DC recruitment were observed during airway mucosal Sendai virus infection and after aerosol challenge of sensitized animals with the soluble recall Ag OVA. However, Met-RANTES did not affect these latter responses, indicating the use of alternative chemokine receptors/ligands for DC recruitment, or possibly attraction of different DC subsets, depending on the nature of the eliciting stimulus.

A chimeric MIP-1alpha/RANTES protein demonstrates the use of different regions of the RANTES protein to bind and activate its receptors

Human RANTES (CCL5) and MIP-1alpha (CCL3) bind and activate several CC chemokine receptors. RANTES is a high-affinity ligand for CCR1 and CCR5, and it binds CCR3 with moderate affinity and CCR4 with low affinity. MIP-1alpha has similar binding characteristics to RANTES except that it does not bind to CCR3. Here we have generated a chimera of human MIP-1alpha and RANTES, called MIP/RANTES, consisting of the eight amino terminal residues of MIP-1alpha preceding the CC motif, and the remainder of the sequence is RANTES. The chimera is able to induce chemotaxis of human monocytes. MIP/RANTES has >100-fold reduction in binding to CCR1 and does not bind to CCR3 but retains full, functional binding to CCR5. It has equivalent affinity for CCR5 to MIP-1alpha and RANTES, binding with an IC(50) of 1.12 nM, and is able to mobilize calcium and induce endocytosis of CCR5 in PBMC in a manner equi-potent to RANTES. It also retains the ability to inhibit R5 using HIV-1 strains. Therefore, we conclude that the amino terminus of RANTES is not involved in CCR5 binding, but it is essential for CCR1 and CCR3.

The BBXB motif of RANTES is the principal site for heparin binding and controls receptor selectivity

The chemokine RANTES (regulated on activation normal T cell expressed and secreted; CCL5) binds selectively to glycosaminoglycans (GAGs) such as heparin, chondroitin sulfate, and dermatan sulfate. The primary sequence of RANTES contains two clusters of basic residues, (44)RKNR(47) and (55)KKWVR(59). The first is a BBXB motif common in heparin-binding proteins, and the second is located in the loop directly preceding the C-terminal helix. We have mutated these residues to alanine, both as point mutations as well as triple mutations of the 40s and 50s clusters. Using a binding assay to heparin beads with radiolabeled proteins, the (44)AANA(47) mutant demonstrated an 80% reduction in its capacity to bind heparin, whereas the (55)AAWVA(59) mutant retained full binding capacity. Mutation of the (44)RKNR(47) site reduced the selectivity of RANTES binding to different GAGs. The mutants were tested for their integrity by receptor binding assays on CCR1 and CCR5 as well as their ability to induce chemotaxis in vitro. In all assays the single point mutations and the triple 50s cluster mutation caused no significant difference in activity compared with the wild type sequence. However, the triple 40s mutant showed a 80-fold reduction in affinity for CCR1, despite normal binding to CCR5. It was only able to induce monocyte chemotaxis at micromolar concentrations. The triple 40s mutant was also able to inhibit HIV-1 infectivity, but consistent with its abrogated GAG binding capacity, it no longer induced enhanced infectivity at high concentrations.

Rantes activates Jak2 and Jak3 to regulate engagement of multiple signaling pathways in T cells

The chemokine RANTES (regulated on activation normal T cell expressed and secreted) and its cognate receptor CC chemokine receptor 5 (CCR5) have been implicated in regulating immune cell function. Previously we reported that in T cells, RANTES activation of CCR5 results in Stat1 and Stat3 phosphorylation-activation, leading to Stat1:1 and Stat1:3 dimers that exhibit DNA binding activity and the transcriptional induction of a Stat-inducible gene, c-fos. Given that RANTES and CCR5 have been implicated in T cell activation, we have studied RANTES-induced signaling events in a CCR5-expressing T cell line, PM1. RANTES treatment of PM1 T cells results in the rapid phosphorylation-activation of CCR5, Jak2, and Jak3. RANTES-inducible Jak phosphorylation is insensitive to pertussis toxin inhibition, indicating that RANTES-CCR5-mediated tyrosine phosphorylation events are not coupled directly to Galpha(i) protein-mediated events. In addition to Jaks, several other proteins are rapidly phosphorylated on tyrosine residues in a RANTES-dependent manner, including the Src kinase p56(lck), which associates with Jak3. Additionally our data confirm that the amino-terminally modified RANTES proteins, aminooxypentane-RANTES and Met-RANTES, are agonists for CCR5 and induce early tyrosine phosphorylation events that are indistinguishable from those inducible by RANTES with similar kinetics. Our data also demonstrate that RANTES activates the p38 mitogen-activated protein (MAP) kinase pathway. This is evidenced by the rapid RANTES-dependent phosphorylation and activation of p38 MAP kinase as well as the activation of the downstream effector of p38, MAP kinase-activated protein (MAPKAP) kinase-2. Pharmacological inhibition of RANTES-dependent p38 MAP kinase activation blocks MAPKAP kinase-2 activity. Thus, activation of Jak kinases and p38 MAP kinase by RANTES regulates the engagement of multiple signaling pathways.

RANTES deposition by platelets triggers monocyte arrest on inflamed and atherosclerotic endothelium

BACKGROUND

Circulating platelets and chemoattractant proteins, such as the CC chemokine RANTES, contribute to the activation and interaction of monocytes and endothelium and may thereby play a pivotal role in the pathogenesis of inflammatory and atherosclerotic disease.

METHODS AND RESULTS

The binding of RANTES to human endothelial cells was detected by ELISA or immunofluorescence after perfusion with platelets or exposure to their supernatants. Monocyte arrest on endothelial monolayers or surface-adherent platelets was studied with a parallel-wall flow chamber and video microscopy. We show that RANTES secreted by thrombin-stimulated platelets is immobilized on the surface of inflamed microvascular or aortic endothelium and triggers shear-resistant monocyte arrest under flow conditions, as shown by inhibition with the RANTES receptor antagonist Met-RANTES or a blocking RANTES antibody. Deposition of RANTES and its effects requires endothelial activation, eg, by interleukin-1beta, and is not supported by venous endothelium or adherent platelets. Immunohistochemistry revealed that RANTES is present on the luminal surface of carotid arteries of apolipoprotein E-deficient mice with early atherosclerotic lesions after wire-induced injury or cytokine exposure. In a mechanistic model of atherogenesis, monocyte adherence on endothelium covering such lesions was studied in murine carotid arteries perfused ex vivo, showing that the accumulation of monocytic cells in these carotid arteries involved RANTES receptors.

CONCLUSIONS

The deposition of RANTES by platelets triggers shear-resistant monocyte arrest on inflamed or atherosclerotic endothelium. Delivery of RANTES by platelets may epitomize a novel principle relevant to inflammatory or atherogenic monocyte recruitment from the circulation.

Expression and characterization of the chemokine receptors CCR2 and CCR5 in mice

The chemokine receptors CCR2 and CCR5 play important roles in the recruitment of monocytes/macrophages and T cells. To better understand the role of both receptors in murine models of inflammatory diseases and to recognize potential problems when correlating these data to humans, we have generated mAbs against murine CCR2 and CCR5. In mice CCR2 is homogeneously expressed on monocytes and on 2--15% of T cells, closely resembling the expression pattern in humans. In contrast to humans, murine NK cells are highly CCR5 positive. In addition, CCR5 is expressed on 3--10% of CD4 and 10--40% of CD8-positive T cells and is weakly detectable on monocytes. Using a model of immune complex nephritis, we examined the effects of inflammation on chemokine receptor expression and found a 10-fold enrichment of CCR5(+) and CCR2(+) T cells in the inflamed kidneys. The activity of various chemokines and the antagonistic properties of the mAbs were measured by ligand-induced internalization of CCR2 and CCR5 on primary leukocytes. The Ab MC-21 (anti-CCR2) reduced the activity of murine monocyte chemotactic protein 1 by 95%, whereas the Ab MC-68 (anti-CCR5) blocked over 99% of the macrophage-inflammatory protein 1alpha and RANTES activity. MC-21 and MC-68 efficiently blocked the ligand binding to CCR2 and CCR5 with an IC(50) of 0.09 and 0.6--1.0 microg/ml, respectively. In good correlation to these in vitro data, MC-21 almost completely prevented the influx of monocytes in thioglycollate-induced peritonitis. Therefore, both Abs appear as useful reagents to further study the role of CCR2 and CCR5 in murine disease models.

Aminooxypentane-RANTES induces CCR3 activation and internalization of CCR3 from the surface of human eosinophils

Eosinophils are predominant effector cells in allergic diseases attracted by several CC chemokines into the inflammatory tissue. According to their important role in attracting leukocytes, several kinds of chemokine receptor antagonists have been developed. Therefore, the aim of this study was to investigate the effect of aminooxypentane (AOP)-RANTES on the activation of the CC chemokine receptor 3, CCR3, exemplary on human eosinophils, because they represent the dominant CCR3+ cell type. AOP-RANTES dose-dependently induced an increase of intracellular calcium concentration ([Ca(2+)](i)) and a release of reactive oxygen species, which could be inhibited by pertussis toxin, in human eosinophils from normal nonatopic donors. AOP-RANTES was as effective as RANTES but less effective than eotaxin and eotaxin-2 in the activation of the respiratory burst. Flow-cytometric analyses revealed that eosinophils constitutively expressed the CC chemokine receptors CCR1 and CCR3, whereas CCR5 was not expressed. AOP-RANTES, RANTES, eotaxin and eotaxin-2, but not Met-RANTES, induced a downregulation of CCR3 at 37 degrees C. Reexpression of CCR3 on eosinophils was observed within 120 min. Whereas no differences of CCR3 downregulation and recycling after stimulation with AOP-RANTES, RANTES, eotaxin and eotaxin-2 were found there exists a distinct profile of activity with respect to the activation of the respiratory burst in human eosinophils.

The chemokine RANTES is a crucial mediator of the progression from acute to chronic colitis in the rat

Chemokines have well characterized proinflammatory actions, including the ability to induce extravasation of leukocytes that participate in chronic inflammation. In this study, we evaluated the role of a C-C chemokine, RANTES, in the chronic phase of a rat model of colitis. Colitis was induced by intracolonic administration of trinitrobenzene sulfonic acid. At various timepoints thereafter (2 h to 14 days), colonic tissue levels of several chemokines were measured. Unlike the expression of monocyte chemoattractant protein-1, macrophage inflammatory protein-2, and cytokine-induced neutrophil chemoattractant, the expression of RANTES was significantly elevated during the chronic phase of colitis (> or =7 days after induction). Colonic RANTES mRNA expression was also significantly elevated during the chronic phase of colitis. The numbers of macrophages and monocytes in the colonic mucosa increased substantially during the chronic phase, as did expression of two of the receptors (CCR1 and CCR5) to which RANTES is known to bind. Administration on days 7 through 14 after trinitrobenzene sulfonic acid administration of a CCR1/CCR5 receptor antagonist, Met-RANTES, resulted in a significant reduction of both macroscopic and microscopic colonic damage, as well as reducing the recruitment into the colon of monocytes, mast cells, and neutrophils. In some rats, treatment with Met-RANTES resulted in a near-complete resolution of colonic damage and inflammation. These results suggest a crucial role of RANTES in the progression from acute to chronic inflammation in a rat model of colitis.

Functional expression of CCR1, CCR3, CCR4, and CXCR4 chemokine receptors on human platelets

Platelets are known to contain platelet factor 4 and beta-thromboglobulin, alpha-chemokines containing the CXC motif, but recent studies extended the range to the beta-family characterized by the CC motif, including RANTES and Gro-alpha. There is also evidence for expression of chemokine receptors CCR4 and CXCR4 in platelets. This study shows that platelets have functional CCR1, CCR3, CCR4, and CXCR4 chemokine receptors. Polymerase chain reaction detected chemokine receptor messenger RNA in platelet RNA. CCR1, CCR3, and especially CCR4 gave strong signals; CXCR1 and CXCR4 were weakly positive. Flow cytometry with specific antibodies showed the presence of a clear signal for CXCR4 and weak signals for CCR1 and CCR3, whereas CXCR1, CXCR2, CXCR3, and CCR5 were all negative. Immunoprecipitation and Western blotting with polyclonal antibodies to cytoplasmic peptides clearly showed the presence of CCR1 and CCR4 in platelets in amounts comparable to monocytes and CCR4 transfected cells, respectively. Chemokines specific for these receptors, including monocyte chemotactic protein 1, macrophage inflammatory peptide 1alpha, eotaxin, RANTES, TARC, macrophage-derived chemokine, and stromal cell-derived factor 1, activate platelets to give Ca(++) signals, aggregation, and release of granule contents. Platelet aggregation was dependent on release of adenosine diphosphate (ADP) and its interaction with platelet ADP receptors. Part, but not all, of the Ca(++) signal was due to ADP release feeding back to its receptors. Platelet activation also involved heparan or chondroitin sulfate associated with the platelet surface and was inhibited by cleavage of these glycosaminoglycans or by heparin or low molecular weight heparin. These platelet receptors may be involved in inflammatory or allergic responses or in platelet activation in human immunodeficiency virus infection.

Lymph-borne chemokines and other low molecular weight molecules reach high endothelial venules via specialized conduits while a functional barrier limits access to the lymphocyte microenvironments in lymph node cortex

Lymph-borne, soluble factors (e.g., chemokines and others) influence lymphocyte recirculation and endothelial phenotype at high endothelial venules (HEVs) in lymph node cortex. Yet the route lymph-borne soluble molecules travel from the subcapsular sinus to the HEVs is unclear. Therefore, we injected subcutaneously into mice and rats a wide variety of fluorophore-labeled, soluble molecules and examined their distribution in the draining lymph nodes. Rather than percolating throughout the draining lymph node, all molecules, including microbial lipopolysaccharide, were very visible in the subcapsular and medullary sinuses but were largely excluded from the cortical lymphocyte microenvironments. Exclusion prevailed even during the acute lymph node enlargement accompanying viral infection. However, low molecular mass (MW) molecules, including chemokines, did gain entry into the cortex, but in a very defined manner. Low MW, fluorophore-labeled molecules highlighted the subcapsular sinus, the reticular fibers, and the abluminal and luminal surfaces of the associated HEVs. These low MW molecules were in the fibers of the reticular network, a meshwork of collagen fibers ensheathed by fibroblastic reticular cells that connects the subcapsular sinus floor and the HEVs by intertwining with their basement membranes. Thus, low MW, lymph-borne molecules, including chemokines, traveled rapidly from the subcapsular sinus to the HEVs using the reticular network as a conduit.

The strategy of blocking the chemokine system to combat disease

One of the key characteristics of inflammation is the recruitment of leukocytes to the site of inflammation. Most anti-inflammatory strategies act intracellularly on the target cells, but after the cells have migrated to the site. We therefore propose that the prevention of cellular recruitment by blockade of the relevant chemokine receptor/ligand pair would present a novel therapy in that it would act upstream of the therapies currently in use. The chemokine system is a complex family of over 40 ligands and 18 receptors and as such may appear difficult to inhibit selectively. In the first part of the article we discuss the specificity mechanisms that are beginning to be unraveled which we believe occur at multiple levels. These levels of control of specificity include the temporal regulation of both the ligands and their receptors, which are under the control of pro-inflammatory cytokines; the localization of chemokines on cell surfaces through their interactions with glycosaminoglycans; differential receptor/ligand interactions; and different patterns of receptor trafficking, to name but a few. The chemokine system has been validated as providing good therapeutic targets by several approaches. In our laboratory, we have used a chemokine receptor antagonist in models of inflammation in vivo to demonstrate that this approach is successful in reducing inflammation. Chemokine receptors belong to the class of seven transmembrane spanning receptors, which have proven to be excellent targets by the pharmaceutical industry for many diseases. The number of small molecule inhibitors of chemokine receptors is rapidly growing in the patent literature, and reports both in the literature as well as conferences in the field have shown them to be effective in inflammatory disease models, as well as inhibiting HIV-1 infection. Since clinical trials will begin this year with some of these molecules, hopefully we will fairly soon have the answer of the efficacy of this therapeutic approach.

Co-receptor use by HIV and inhibition of HIV infection by chemokine receptor ligands

Human and simian immunodeficiency viruses (HIV and SIV) require a seven transmembrane chemokine (7TM) receptor in addition to CD4 for efficient entry into cells. CCR5 and CXCR4 act as major co-receptors for non-syncytium-inducing and syncytium-inducing strains respectively. We have examined the co-receptor requirement for HIV-1 infection of cells of macrophage lineage. Both CCR5 and CXCR4 can operate as functional co-receptors for infection in these cell types. Other co-receptors utilised by multi-co-receptor-using strains of HIV-1, including CCR3 and STRL33, were not used for macrophage infection. HIV-2 and SIV strains, however, can replicate in both peripheral blood mononuclear cells (PBMCs) and other primary cell types such as fibroblasts independently of CCR5 or CXCR4. HIV co-receptors, particularly CCR5, will be major targets for new therapeutics in this decade. We have therefore investigated different chemokines and derivatives that bind co-receptors for their capacity to inhibit HIV infection. These included derivatives of a CCR5 ligand, RANTES, with modified N-termini as well as Kaposi's sarcoma-associated herpesvirus-encoded chemokines that bind a wide range of co-receptors, including CCR5, CXCR4, CCR3 and CCR8, as well as the orphan 7TM receptors GPR1 and STRL33. One compound, aminooxypentane or AOP-RANTES, was a particularly potent inhibitor of HIV infection on PBMCs, macrophages and CCR5+ cell lines and demonstrated the great promise of therapeutic strategies aimed at CCR5.

A key role for CC chemokine receptor 4 in lipopolysaccharide-induced endotoxic shock

CC chemokine receptor (CCR)4, a high affinity receptor for the CC chemokines thymus and activation-regulated chemokine (TARC) and macrophage-derived chemokine (MDC), is expressed in the thymus and spleen, and also by peripheral blood T cells, macrophages, platelets, and basophils. Recent studies have shown that CCR4 is the major chemokine receptor expressed by T helper type 2 (Th2) polarized cells. To study the in vivo role of CCR4, we have generated CCR4-deficient (CCR4(-/-)) mice by gene targeting. CCR4(-/-) mice developed normally. Splenocytes and thymocytes isolated from the CCR4(-/-) mice failed to respond to the CCR4 ligands TARC and MDC, as expected, but also surprisingly did not undergo chemotaxis in vitro in response to macrophage inflammatory protein (MIP)-1alpha. The CCR4 deletion had no effect on Th2 differentiation in vitro or in a Th2-dependent model of allergic airway inflammation. However, CCR4(-/-) mice exhibited significantly decreased mortality on administration of high or low dose bacterial lipopolysaccharide (LPS) compared with CCR4(+/+) mice. After high dose LPS treatment, serum levels of tumor necrosis factor alpha, interleukin 1beta, and MIP-1alpha were reduced in CCR4(-/-) mice, and decreased expression of MDC and MIP-2 mRNA was detected in peritoneal exudate cells. Analysis of peritoneal lavage cells from CCR4(-/)- mice by flow cytometry also revealed a significant decrease in the F4/80(+) cell population. This may reflect a defect in the ability of the CCR4(-/-) macrophages to be retained in the peritoneal cavity. Taken together, our data reveal an unexpected role for CCR4 in the inflammatory response leading to LPS-induced lethality.

Differential activation of CC chemokine receptors by AOP-RANTES

RANTES (regulated on activation normal T cell expressed) has been found at elevated levels in biological fluids from patients with a wide range of allergic and autoimmune diseases and is able to attract several subtypes of leukocytes including eosinophils and monocytes into inflamed tissue. Amino-terminal modifications of RANTES produce receptor antagonists which are candidates for blocking this cellular recruitment. Met-RANTES has been shown to modulate inflammation in vivo, while AOP-RANTES is a potent inhibitor of R5 human immunodeficiency virus type 1 (HIV-1) strains and has been shown to down-modulate CCR5 and prevent recycling of the receptor. We have studied the effect of AOP-RANTES in eosinophil activation and have found that it is able to efficiently elicit eosinophil effector functions through CCR3, as measured by the release of reactive oxygen species and calcium mobilization, whereas Met-RANTES is inactive in these assays. AOP-RANTES is found to inhibit CCR3-mediated HIV-1 infection with moderate potency, in contrast to its potent inhibition of CCR5-mediated HIV-1 infection. Furthermore, we have investigated the abilities of these modified proteins to down-modulate CCR1 and CCR3 from the surface of monocytes and eosinophils. We show here that AOP-RANTES is much less effective than RANTES in down-modulation of CCR1. Surprisingly, recycling of CCR1 was minimal after incubation with RANTES while there was complete recycling with AOP-RANTES. In the case of CCR3, no significant difference was found between RANTES and AOP-RANTES in down-modulation and recycling. It therefore appears that trafficking of RANTES receptors follows different patterns, which opens up potential new targets for therapeutic intervention.

[Reduction of acute kidney transplantation rejection by the chemokine receptor antagonist Met-RANTES]

Chemokines contribute to the mononuclear cell infiltrate in vessels and interstitium which is characteristic of renal transplant rejection. By employing the chemokine receptor blocker Met-RANTES it was shown that recruitment of inflammatory cells into renal allografts could be significantly suppressed. In a renal transplant model (Fisher RT1(1v1) rat kidney into Lewis RT1(1) rat) Met-RANTES-treated animals showed a significant reduction in vascular injury score (16.10 +/- 5.20 vs. 62.67 +/- 18.64) and tubular damage score (15.70 +/- 5.22 vs. 33.00 +/- 6.44) relative to untreated animals. In a severe rejection model (Brown-Norway RT1n rat kidney into Lewis RT1(1) rat), Met-RANTES significantly augmented low-dose cyclosporin A treatment to reduce all aspects of renal injury including interstitial inflammation (score 71.00 +/- 6.10 vs. 157.30 +/- 21.30). In a monocyte attachment assay on microvascular endothelium under physiological flow conditions exposure of microvascular endothelium to RANTES resulted in RANTES immobilization and RANTES-induced firm adhesion of monocytes only after prestimulation of the endothelium with IL-1 beta. Met-RANTES completely inhibited this RANTES-mediated arrest. Thus, Met-RANTES can reduce acute rejection by impeding leukocyte arrest to inflamed endothelium.

C-C chemokine receptor 3 antagonism by the beta-chemokine macrophage inflammatory protein 4, a property strongly enhanced by an amino-terminal alanine-methionine swap

Allergic reactions are characterized by the infiltration of tissues by activated eosinophils, Th2 lymphocytes, and basophils. The beta-chemokine receptor CCR3, which recognizes the ligands eotaxin, eotaxin-2, monocyte chemotactic protein (MCP) 3, MCP4, and RANTES, plays a central role in this process, and antagonists to this receptor could have potential therapeutic use in the treatment of allergy. We describe here a potent and specific CCR3 antagonist, called Met-chemokine beta 7 (Ckbeta7), that prevents signaling through this receptor and, at concentrations as low as 1 nM, can block eosinophil chemotaxis induced by the most potent CCR3 ligands. Met-Ckbeta7 is a more potent CCR3 antagonist than Met- and aminooxypentane (AOP)-RANTES and, unlike these proteins, exhibits no partial agonist activity and is highly specific for CCR3. Thus, this antagonist may be of use in ameliorating leukocyte infiltration associated with allergic inflammation. Met-Ckbeta7 is a modified form of the beta-chemokine macrophage inflammatory protein (MIP) 4 (alternatively called pulmonary and activation-regulated chemokine (PARC), alternative macrophage activation-associated C-C chemokine (AMAC) 1, or dendritic cell-derived C-C chemokine (DCCK) 1). Surprisingly, the unmodified MIP4 protein, which is known to act as a T cell chemoattractant, also exhibits this CCR3 antagonistic activity, although to a lesser extent than Met-Ckbeta7, but to a level that may be of physiological relevance. MIP4 may therefore use chemokine receptor agonism and antagonism to control leukocyte movement in vivo. The enhanced activity of Met-Ckbeta7 is due to the alteration of the extreme N-terminal residue from an alanine to a methionine.

Amino-terminally modified RANTES analogues demonstrate differential effects on RANTES receptors

Modification of the amino terminus of regulated on activated normal T-cell expressed (RANTES) has been shown to have a significant effect on biological activity and produces proteins with antagonist properties. Two amino-terminally modified RANTES proteins, Met-RANTES and aminooxypentane-RANTES (AOP-RANTES), exhibit differential inhibitory properties on both monocyte and eosinophil chemotaxis. We have investigated their binding properties as well as their ability to activate the RANTES receptors CCR1, CCR3, and CCR5 in cell lines overexpressing these receptors. We show that Met-RANTES has weak activity in eliciting a calcium response in Chinese hamster ovary cells expressing CCR1, CCR3, and CCR5, whereas AOP-RANTES has full agonist activity on CCR5 but is less effective on CCR3 and CCR1. Their ability to induce chemotaxis of the murine pre-B lymphoma cell line, L1.2, transfected with the same receptors, consolidates these results. Monocytes have detectable mRNA for CCR1, CCR2, CCR3, CCR4, and CCR5, and they respond to the ligands for these receptors in chemotaxis but not always in calcium mobilization. AOP-RANTES does not induce calcium mobilization in circulating monocytes but is able to do so as these cells acquire the macrophage phenotype, which coincides with a concomitant up-regulation of CCR5. We have also tested the ability of both modified proteins to induce chemotaxis of freshly isolated monocytes and eosinophils. Cells from most donors do not respond, but occasionally cells from a particular donor do respond, particularly to AOP-RANTES. We therefore hypothesize that the occasional activity of AOP-RANTES to induce leukocyte chemotaxis is due to donor to donor variation of receptor expression.

Glycosaminoglycans interact selectively with chemokines and modulate receptor binding and cellular responses

Chemokines selectively recruit and activate a variety of cells during inflammation. Interactions between cell surface glycosaminoglycans (GAGs) and chemokines drive the formation of haptotactic or immobilized gradients of chemokines at the site of inflammation, directing this recruitment. Chemokines bind to glycosaminoglycans on human umbilical vein endothelial cells (HUVECs) with affinities in the micromolar range: RANTES > MCP-1 > IL-8 > MIP-1alpha. This binding can be competed with by soluble glycosaminoglycans: heparin, heparin sulfate, chondroitin sulfate, and dermatan sulfate. RANTES binding showed the widest discrimination between glycosaminoglycans (700-fold), whereas MIP-1alpha was the least selective. Almost identical results were obtained in an assay using heparin sulfate beads as the source of immobilized glycosaminoglycan. The binding of chemokines to glycosaminoglycan fragments has a strong length dependence, and optimally requires both N- and O-sulfation. Isothermal titration calorimetry data confirm these results; IL-8 binds heparin fragments with a K(d) of 0.39-2.63 microM, and requires five saccharide units to bind each monomer of chemokine. In membranes from cells expressing the G-protein-coupled chemokine receptors CXCR1, CXCR2, and CCR1, soluble GAGs inhibit the binding of chemokine ligands to their receptors. Consistent with this, heparin and heparin sulfate could inhibit IL-8-induced neutrophil calcium flux. Chemokines can therefore form complexes with both cell surface and soluble GAGs; these interactions have different functions. Soluble GAG chemokines complexes are unable to bind the receptor, resulting in a block of the biological activity. Previously, we have shown that cell surface GAGs present chemokines to the G-protein-coupled receptors, by increasing the local concentration of protein. A model is presented which brings together all of these data. The selectivity in the chemokine-GAG interaction suggests selective disruption of the haptotactic gradient may be an achievable therapeutic approach in inflammatory disease.

The CC-chemokine RANTES increases the attachment of human immunodeficiency virus type 1 to target cells via glycosaminoglycans and also activates a signal transduction pathway that enhances viral infectivity

We have studied the mechanisms by which the CC-chemokine RANTES can enhance the infectivities of human immunodeficiency virus type 1 (HIV-1) and other enveloped viruses, when present at concentrations in excess of 500 ng/ml in vitro. Understanding the underlying mechanisms might throw light on fundamental processes of viral infection, in particular for HIV-1. Our principal findings are twofold: firstly, that oligomers of RANTES can cross-link enveloped viruses, including HIV-1, to cells via glycosaminoglycans (GAGs) present on the membranes of both virions and cells; secondly, that oligomers of RANTES interact with cell-surface GAGs to transduce a herbimycin A-sensitive signal which, over a period of several hours, renders the cells more permissive to infection by several viruses, including HIV-1. The enhancement mechanisms require that RANTES oligomerize either in solution or following binding to GAGs, since no viral infectivity enhancement is observed with a mutant form of the RANTES molecule that contains a single-amino-acid change (glutamic acid to serine at position 66) which abrogates oligomerization.

Coreceptor ligand inhibition of fetal brain cell infection by HIV type 1

The capacity of a panel of HIV-1 isolates to infect primary mixed fetal brain cell cultures was estimated and their sensitivity to inhibition by a range of coreceptor ligands assessed. Our results show that (1) HIV-1 strains that predominantly use CCR5 or only CXCR4 are able to infect microglia in primary brain cell cultures, and (2) ligands to these two coreceptors can inhibit brain cell infection. CCR5 ligands (including AOP-RANTES, a potent inhibitor of CCR5-dependent infection), however, blocked infection only weakly, raising the possibility that alternative unidentified coreceptors are also used. Interestingly, vMIP-II, a chemokine encoded by the Kaposi sarcoma-associated herpes virus (KSHV), reduced brain cell infection by all HIV-1 strains tested, including both R5 and X4 viruses. Our results therefore indicate that novel drugs targeted to the major HIV-1 coreceptors will influence HIV replication in the brain, if they cross the blood-brain barrier.

Mouse monocyte-derived chemokine is involved in airway hyperreactivity and lung inflammation

The cloning, expression, and function of the murine (m) homologue of human (h) monocyte-derived chemokine (MDC) is reported here. Like hMDC, mMDC is able to elicit the chemotactic migration in vitro of activated lymphocytes and monocytes. Among activated lymphocytes, Th2 cells were induced to migrate most efficiently. mMDC mRNA and protein expression is modulated during the course of an allergic reaction in the lung. Neutralization of mMDC with specific Abs in a model of lung inflammation resulted in prevention of airway hyperreactivity and significant reduction of eosinophils in the lung interstitium but not in the airway lumen. These data suggest that mMDC is essential in the transit/retention of leukocytes in the lung tissue rather than in their extravasation from the blood vessel or during their transepithelial migration into the airways. These results also highlight the relevance of factors, such as mMDC, that regulate the migration and accumulation of leukocytes within the tissue during the development of the key physiological endpoint of asthma, airway hyperreactivity.

Chemokine receptors and their antagonists in allergic lung disease

The trafficking and homing of leukocytes in normal homeostasis and in disease is under the control of a variety of cytokine and lipid mediators. One family of small cytokines particularly involved in inflammation which has been identified is the chemokine family. Their action is mediated by a large superfamily of seven transmembrane spanning G-protein coupled receptors. One of the hopes in this field has been there may be selectivity in terms of which cells are recruited to sites of inflammation by virtue of their chemokine receptor expression pattern. This means that it may be possible to find antagonists of chemokine receptors that can selectively down regulate certain cell type recruitment, without provoking a generalized immunosuppression. In this review, we discuss the current state of understanding of the chemokine receptor field. The therapeutic potential of this field can be judged from recent data on the use of protein chemokine antagonists in allergic disease. The data so far obtained in animal studies point to the potential clinical uses of this emerging class of therapeutic agents.

Differential effects of CC chemokines on CC chemokine receptor 5 (CCR5) phosphorylation and identification of phosphorylation sites on the CCR5 carboxyl terminus

The binding of CC chemokines to CC chemokine receptor 5 (CCR5) triggers cellular responses that, generally, are only transient in nature. To explore the potential role of G protein-coupled receptor kinases (GRKs) in the regulation of CCR5, we performed phosphorylation experiments in a rat basophilic leukemia cell line stably expressing CCR5. The ability of various CCR5 ligands to stimulate calcium mobilization in these cells correlated with their ability to induce receptor phosphorylation, desensitization, internalization, and GRK association with the receptor. Aminooxypentane-RANTES, a potent inhibitor of human immunodeficiency virus infection, has been proposed to act through enhanced CCR5 internalization and inhibition of receptor recycling. Aminooxypentane-RANTES profoundly induced CCR5 phosphorylation, but had no effect on CCR1. In permeabilized rat basophilic leukemia CCR5 cells, monoclonal antibodies with specificity for GRK2/3 inhibited RANTES-induced receptor phosphorylation. Consistent with a role for these kinases in CCR5 regulation, 1-2 x 10(5) copies of GRK2 or GRK3 were found to be expressed in peripheral blood leukocytes. Phosphoamino acid analysis revealed that RANTES-induced CCR5 phosphorylation selectively occurs on serine residues. Our findings with receptor mutants indicate that serine residues at positions 336, 337, 342, and 349 represent GRK phosphorylation sites on CCR5. This study demonstrates that chemokines differ in their ability to induce CCR5 phosphorylation and desensitization and provides a molecular mechanism for the agonist-induced attenuation of CCR5 signaling.

Chemokine-induced phosphorylation of CC chemokine receptor 5 (CCR5)

The CC-chemokine receptor 5 (CCR5) mediates activation of T lymphocytes and macrophages by chemokines and is a major co-receptor for macrophage-tropic HIV-1 strains. Recently, it was shown that the natural CCR5 ligands RANTES, macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and amino-terminal modifications of RANTES (Met-RANTES, AOP-RANTES) significantly differ in their abilities to induce sequestration of CCR5 from cellular surfaces. It was hypothesized that these findings may account for the observed differences between these molecules to inhibit HIV infectivity in vitro. Herein we review our work on early regulatory mechanisms that are initiated by ligand binding to CCR5 and that, conceptually, are involved in receptor endocytosis. A better understanding of these mechanisms may provide new therapeutic strategies to prevent HIV infection.

Chemokine receptors--future therapeutic targets for HIV?

To date, triple drug therapies for HIV have resulted in spectacular reductions in the number of virus particles and often remarkable recovery from disease in infected people. There is still, however, a great need for improved therapies. A battery of drugs aimed at different stages in the life cycle of HIV will enable switching of treatments if resistant viruses emerge or if patients are unable to tolerate particular therapies. Intense efforts are now underway to produce drugs that target chemokine receptors used by HIV to gain entry into cells. HIV needs two receptors on the host cell surface for efficient attachment and infection. HIV first interacts with CD4 but requires a coreceptor to penetrate the cell membrane. The first coreceptor, identified in 1996, is a member of the family of chemokine receptors, members of the G-protein coupled 7TM superfamily, which are involved in the trafficking of leukocytes in immune surveillance and inflammation. Such a therapeutic approach would differ from those used successfully to date, which focus largely on proteins coded by the HIV virus itself, and which are required for the replicative cycle of the virus. Many small, orally bioavailable molecules that block various 7TM receptors are used to treat a panoply of diseases including ulcers, allergies, migraines, and schizophrenia. These molecules are the cornerstone of the pharmaceutical industry's contribution to the fight against so many diseases, and it is hoped that a small molecule inhibitor of coreceptors can be developed that will become an invaluable drug in the fight against AIDS.

Similarities and differences in RANTES- and (AOP)-RANTES-triggered signals: implications for chemotaxis

Chemokines are a family of proinflammatory cytokines that attract and activate specific types of leukocytes. Chemokines mediate their effects via interaction with seven transmembrane G protein-coupled receptors (GPCR). Using CCR5-transfected HEK-293 cells, we show that both the CCR5 ligand, RANTES, as well as its derivative, aminooxypentane (AOP)- RANTES, trigger immediate responses such as Ca2+ influx, receptor dimerization, tyrosine phosphorylation, and Galphai as well as JAK/STAT association to the receptor. In contrast to RANTES, (AOP)-RANTES is unable to trigger late responses, as measured by the association of focal adhesion kinase (FAK) to the chemokine receptor complex, impaired cell polarization required for migration, or chemotaxis. The results are discussed in the context of the dissociation of the late signals, provoked by the chemokines required for cell migration, from early signals.

The CC chemokine receptor antagonist met-RANTES inhibits eosinophil effector functions

Eosinophils play an important role in allergic diseases such as allergic asthma, rhinoconjunctivitis and atopic dermatitis. Recruitement of eosinophils to the side of inflammation, the release of reactive oxygen species, leading to tissue damage, and the propagation of the inflammatory response are mediated by chemokines. Thus, the applicability of agents able to inhibit or antagonize chemokine-induced eosinophil activation seems to be of interest in the treatment of allergic diseases. Therefore, the effect of the CC chemokine antagonist, Met-RANTES, on its effect on human eosinophil effector functions in response to RANTES, MCP-3 and eotaxin was investigated. Met-RANTES had no intrinsic activity on [Ca2+]i transients in eosinophils and was able to dose-dependently inhibit [Ca2+]i transients in eosinophils following stimulation with RANTES, MCP-3 and eotaxin. Besides its effect on [Ca2+]i transients, Met-RANTES dose-dependently inhibited actin polymerization in eosinophils and the release of reactive oxygen species following stimulation with RANTES, MCP-3 and eotaxin. The results of this study lead to the conclusion that Met-RANTES is an effective and powerful compound to antagonize effector functions of human eosinophils following stimulation with RANTES, MCP-3 and eotaxin and is therefore a promising therapeutic approach to prevent the invasion and destructive power of eosinophils in allergic diseases.

Enhancement of human immunodeficiency virus type 1 infection by the CC-chemokine RANTES is independent of the mechanism of virus-cell fusion

We have studied the effects of CC-chemokines on human immunodeficiency virus type 1 (HIV-1) infection, focusing on the infectivity enhancement caused by RANTES. High RANTES concentrations increase the infectivity of HIV-1 isolates that use CXC-chemokine receptor 4 for entry. However, RANTES can have a similar enhancing effect on macrophagetropic viruses that enter via CC-chemokine receptor 5 (CCR5), despite binding to the same receptor as the virus. Furthermore, RANTES enhances the infectivity of HIV-1 pseudotyped with the envelope glycoprotein of murine leukemia virus or vesicular stomatitis virus, showing that the mechanism of enhancement is independent of the route of virus-cell fusion. The enhancing effects of RANTES are not mediated via CCR5 or other known chemokine receptors and are not mimicked by MIP-1alpha or MIP-1beta. The N-terminally modified derivative aminooxypentane RANTES (AOP-RANTES) efficiently inhibits HIV-1 infection via CCR5 but otherwise mimics RANTES by enhancing viral infectivity. There are two mechanisms of enhancement: one apparent when target cells are pretreated with RANTES (or AOP-RANTES) for several hours, and the other apparent when RANTES (or AOP-RANTES) is added during virus-cell absorption. We believe that the first mechanism is related to cellular activation by RANTES, whereas the second is an increase in virion attachment to target cells.

Chemokine receptors and their role in leukocyte activation

Chemokines were originally isolated based on their abilities to selectively attract and recruit leukocyte populations. Over the last few years there has been an explosion in the number of new chemokines identified, and as a result many receptors previously considered to be orphans have now been paired up with their ligands. Here we review some of the latest results in this area, illustrating with data from our laboratory. The central question from a drug discovery perspective, is to show whether inhibiting chemokine receptors leads to a change in disease status. Although we are still a long way from having candidate molecules to take into the clinic, a flavour of what may be possible can be inferred from mutant chemokines with antagonistic properties. We discuss recent data using two of these proteins, Met-RANTES which has anti-inflammatory properties, and AOP-RANTES which has been shown to prevent infection of macrophages and T-cells by M-tropic HIV strains.

HIV-1 Tat protein mimicry of chemokines

The HIV-1 Tat protein is a potent chemoattractant for monocytes. We observed that Tat shows conserved amino acids corresponding to critical sequences of the chemokines, a family of molecules known for their potent ability to attract monocytes. Synthetic Tat and a peptide (CysL24-51) encompassing the "chemokine-like" region of Tat induced a rapid and transient Ca2+ influx in monocytes and macrophages, analogous to beta-chemokines. Both monocyte migration and Ca2+ mobilization were pertussis toxin sensitive and cholera toxin insensitive. Cross-desensitization studies indicated that Tat shares receptors with MCP-1, MCP-3, and eotaxin. Tat was able to displace binding of beta-chemokines from the beta-chemokine receptors CCR2 and CCR3, but not CCR1, CCR4, and CCR5. Direct receptor binding experiments with the CysL24-51 peptide confirmed binding to cells transfected with CCR2 and CCR3. HIV-1 Tat appears to mimic beta-chemokine features, which may serve to locally recruit chemokine receptor-expressing monocytes/macrophages toward HIV producing cells and facilitate activation and infection.

CXCR4 as a functional coreceptor for human immunodeficiency virus type 1 infection of primary macrophages

The coreceptors used by primary syncytium-inducing (SI) human immunodeficiency virus type 1 isolates for infection of primary macrophages were investigated. SI strains using only CXCR4 replicated equally well in macrophages with or without CCR5 and were inhibited by several different ligands for CXCR4 including SDF-1 and bicyclam derivative AMD3100. SI strains that used a broad range of coreceptors including CCR3, CCR5, CCR8, CXCR4, and BONZO infected CCR5-deficient macrophages about 10-fold less efficiently than CCR5(+) macrophages. Moreover, AMD3100 blocked infection of CCR5-negative macrophages by these strains. Our results therefore demonstrate that CXCR4, as well as CCR5, is used for infection of primary macrophages but provide no evidence for the use of alternative coreceptors.

Definition, function and pathophysiological significance of chemokine receptors

Chemokines and their receptors are at the core of many processes in biology, from routine immunosurveillance and the inflammatory process, through to the infection of cells by HIV. In the past two years, various bioinformatic and cloning strategies have led to an explosion in the number of chemokines and receptors that have been identified. Although the picture is far from complete, several themes are emerging. In particular, there are important differences between observations in vitro, where there appears to be much redundancy, and studies in vivo, where distinct roles are clearer. In this review, Timothy Wells, Christine Power and Amanda Proudfoot discuss the chemokines and their receptors and recent data from immunological and virology studies, and speculate on the potential of interfering with the chemokine network as a useful approach to ameliorating disease.

Identification of a glycosaminoglycan binding surface on human interleukin-8

The activation of leukocytes by chemokines is believed to be mediated via binding of chemokines to glycosaminoglycan chains of the extracellular matrix. The binding site on the chemokine interleukin-8 (IL-8) for the glycosaminoglycan heparin has been characterized using a systematic series of site-directed mutants of IL-8 in which the basic residues of the protein have been replaced by alanine. Mutation of K64 and R68 caused the largest decrease in affinity for a heparin Sepharose matrix, with smaller effects seen with mutations of K20, R60, and K67. Heparin-derived disaccharides that could disrupt the IL-8-heparin Sepharose interaction were identified by a competitive binding assay. Heteronuclear NMR spectroscopic titration of 15N-labeled IL-8 with a trisulfated disaccharide revealed a cluster of residues on IL-8 which were perturbed by disaccharide binding. These data identify a heparin-binding surface on IL-8 that includes the C-terminal alpha-helix and the proximal loop around residues 18-23. The heparin-binding site is spatially distinct from the residues involved in receptor binding.

A broad range of chemokine receptors are used by primary isolates of human immunodeficiency virus type 2 as coreceptors with CD4

Like human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), HIV-2 requires a coreceptor in addition to CD4 for entry into cells. HIV and SIV coreceptor molecules belong to a family of seven-transmembrane-domain G-protein-coupled receptors. Here we show that primary HIV-2 isolates can use a broad range of coreceptor molecules, including CCR1, CCR2b, CCR3, CCR4, CCR5, and CXCR4. Despite broad coreceptor use, the chemokine ligand SDF-1 substantially blocked HIV-2 infectivity of peripheral blood mononuclear cells, indicating that its receptor, CXCR4, was the predominant coreceptor for infection of these cells. However, expression of CXCR4 together with CD4 on some cell types did not confer susceptibility to infection by all CXCR4-using virus isolates. These data therefore indicate that another factor(s) influences the ability of HIV-2 to replicate in human cell types that express the appropriate receptors for virus entry.

Aminooxypentane-RANTES induces CCR5 internalization but inhibits recycling: a novel inhibitory mechanism of HIV infectivity

CCR5, a chemokine receptor expressed on T cells and macrophages, is the principal coreceptor for M-tropic HIV-1 strains. Recently, we described an NH2-terminal modification of the CCR5 ligand regulated on activation, normal T cell expressed and secreted (RANTES), aminooxypentane-RANTES (AOP-RANTES), that showed potent inhibition of macrophage infection by HIV-1 under conditions where RANTES was barely effective. To investigate the mechanism of AOP-RANTES inhibition of HIV infectivity we examined the surface expression of CCR5 using a monoclonal anti-CCR5 antibody, MC-1. We demonstrate that AOP-RANTES rapidly caused >90% decrease in cell surface expression of CCR5 on lymphocytes, monocytes/ macrophages, and CCR5 transfected Chinese hamster ovary (CHO) cells. RANTES also caused a loss of cell surface CCR5, although its effect was less than with AOP-RANTES. Significantly, AOP-RANTES inhibited recycling of internalized CCR5 to the cell surface, whereas RANTES did not. When peripheral blood mononuclear cells are cultured for prolonged periods of time in the presence of RANTES, CCR5 expression is comparable to that seen on cells treated with control medium, whereas there is no CCR5 surface expression on cells cultured in the presence of AOP-RANTES. Immunofluorescence indicated that both AOP-RANTES and RANTES induced downmodulation of cell surface CCR5, and that the receptor was redistributed into endocytic organelles containing the transferrin receptor. When RANTES was removed, the internalized receptor was recycled to the cell surface; however, the receptor internalized in the presence of AOP-RANTES was retained in endosomes. Using human osteosarcoma (GHOST) 34/CCR5 cells, the potency of AOP-RANTES and RANTES to inhibit infection by the M-tropic HIV-1 strain, SF 162, correlated with the degree of downregulation of CCR5 induced by the two chemokines. These differences between AOP-RANTES and RANTES in their effect on receptor downregulation and recycling suggest a mechanism for the potent inhibition of HIV infection by AOP-RANTES. Moreover, these results support the notion that receptor internalization and inhibition of receptor recycling present new targets for therapeutic agents to prevent HIV infection.