Assignment of the human CC chemokine gene TARC (SCYA17) to chromosome 16q13

CC Chemokine Family Members' Modulation as a Novel Approach for Treating Central Nervous System and Peripheral Nervous System Injury-A Review of Clinical and Experimental Findings

Despite significant progress in modern medicine and pharmacology, damage to the nervous system with various etiologies still poses a challenge to doctors and scientists. Injuries lead to neuroimmunological changes in the central nervous system (CNS), which may result in both secondary damage and the development of tactile and thermal hypersensitivity. In our review, based on the analysis of many experimental and clinical studies, we indicate that the mechanisms occurring both at the level of the brain after direct damage and at the level of the spinal cord after peripheral nerve damage have a common immunological basis. This suggests that there are opportunities for similar pharmacological therapeutic interventions in the damage of various etiologies. Experimental data indicate that after CNS/PNS damage, the levels of 16 among the 28 CC-family chemokines, i.e., CCL1, CCL2, CCL3, CCL4, CCL5, CCL6, CCL7, CCL8, CCL9, CCL11, CCL12, CCL17, CCL19, CCL20, CCL21, and CCL22, increase in the brain and/or spinal cord and have strong proinflammatory and/or pronociceptive effects. According to the available literature data, further investigation is still needed for understanding the role of the remaining chemokines, especially six of them which were found in humans but not in mice/rats, i.e., CCL13, CCL14, CCL15, CCL16, CCL18, and CCL23. Over the past several years, the results of studies in which available pharmacological tools were used indicated that blocking individual receptors, e.g., CCR1 (J113863 and BX513), CCR2 (RS504393, CCX872, INCB3344, and AZ889), CCR3 (SB328437), CCR4 (C021 and AZD-2098), and CCR5 (maraviroc, AZD-5672, and TAK-220), has beneficial effects after damage to both the CNS and PNS. Recently, experimental data have proved that blockades exerted by double antagonists CCR1/3 (UCB 35625) and CCR2/5 (cenicriviroc) have very good anti-inflammatory and antinociceptive effects. In addition, both single (J113863, RS504393, SB328437, C021, and maraviroc) and dual (cenicriviroc) chemokine receptor antagonists enhanced the analgesic effect of opioid drugs. This review will display the evidence that a multidirectional strategy based on the modulation of neuronal-glial-immune interactions can significantly improve the health of patients after CNS and PNS damage by changing the activity of chemokines belonging to the CC family. Moreover, in the case of pain, the combined administration of such antagonists with opioid drugs could reduce therapeutic doses and minimize the risk of complications.

CC Chemokine Receptor 4 (CCR4) as a Possible New Target for Therapy

Chemokines and their receptors participate in many biological processes, including the modulation of neuroimmune interactions. Approximately fifty chemokines are distinguished in humans, which are classified into four subfamilies based on the N-terminal conserved cysteine motifs: CXC, CC, C, and CX3C. Chemokines activate specific receptors localized on the surface of various immune and nervous cells. Approximately twenty chemokine receptors have been identified, and each of these receptors is a seven-transmembrane G-protein coupled receptor. Recent studies provide new evidence that CC chemokine receptor 4 (CCR4) is important in the pathogenesis of many diseases, such as diabetes, multiple sclerosis, asthma, dermatitis, and cancer. This review briefly characterizes CCR4 and its ligands (CCL17, CCL22, and CCL2), and their contributions to immunological and neoplastic diseases. The review notes a significant role of CCR4 in nociceptive transmission, especially in painful neuropathy, which accompanies many diseases. The pharmacological blockade of CCR4 seems beneficial because of its pain-relieving effects and its influence on opioid efficacy. The possibilities of using the CCL2/CCL17/CCL22/CCR4 axis as a target in new therapies for many diseases are also discussed.

CCR4 as a Therapeutic Target for Cancer Immunotherapy

Simple Summary

CCR4 is a chemokine receptor selectively expressed on normal T cell subsets such as type 2 helper T cells, skin-homing T cells and regulatory T cells, and on skin-associated T cell malignancies such as adult T cell leukemia/lymphoma (ATLL), which is etiologically associated with human T lymphocyte virus type 1 (HTLV-1), and cutaneous T cell lymphomas (CTCLs). Mogamulizumab is a fully humanized and glyco-engineered monoclonal anti-CCR4 antibody used for the treatment of refractory/relapsed ATLL and CTCLs, often resulting in complete remission. The clinical applications of Mogamulizumab are now being extended to solid tumors, exploring the therapeutic effect of regulatory T cell depletion. This review overviews the expression of CCR4 in various T cell subsets, HTLV-1-infected T cells, ATLL and CTCLs, and the clinical applications of Mogamulizumab.

Abstract

CCR4 is a chemokine receptor mainly expressed by T cells. It is the receptor for two CC chemokine ligands, CCL17 and CCL22. Originally, the expression of CCR4 was described as highly selective for helper T type 2 (Th2) cells. Later, its expression was extended to other T cell subsets such as regulatory T (Treg) cells and Th17 cells. CCR4 has long been regarded as a potential therapeutic target for allergic diseases such as atopic dermatitis and bronchial asthma. Furthermore, the findings showing that CCR4 is strongly expressed by T cell malignancies such as adult T cell leukemia/lymphoma (ATLL) and cutaneous T cell lymphomas (CTCLs) have led to the development and clinical application of the fully humanized and glyco-engineered monoclonal anti-CCR4 Mogamulizumab in refractory/relapsed ATLL and CTCLs with remarkable successes. However, Mogamulizumab often induces severe adverse events in the skin possibly because of its efficient depletion of Treg cells. In particular, treatment with Mogamulizumab prior to allogenic hematopoietic stem cell transplantation (allo-HSCT), the only curative option of these T cell malignancies, often leads to severe glucocorticoid-refractory graft-versus-host diseases. The efficient depletion of Treg cells by Mogamulizumab has also led to its clinical trials in advanced solid tumors singly or in combination with immune checkpoint inhibitors. The main focus of this review is CCR4; its expression on normal and malignant T cells and its significance as a therapeutic target in cancer immunotherapy.

What does elevated TARC/CCL17 expression tell us about eosinophilic disorders?

Eosinophilic disorders encompass a large spectrum of heterogeneous diseases sharing the presence of elevated numbers of eosinophils in blood and/or tissues. Among these disorders, the role of eosinophils can vary widely, ranging from a modest participation in the disease process to the predominant perpetrator of tissue damage. In many cases, eosinophilic expansion is polyclonal, driven by enhanced production of interleukin-5, mainly by type 2 helper cells (Th2 cells) with a possible contribution of type 2 innate lymphoid cells (ILC2s). Among the key steps implicated in the establishment of type 2 immune responses, leukocyte recruitment toward inflamed tissues is particularly relevant. Herein, the contribution of the chemo-attractant molecule thymus and activation-regulated chemokine (TARC/CCL17) to type 2 immunity will be reviewed. The clinical relevance of this chemokine and its target, C-C chemokine receptor 4 (CCR4), will be illustrated in the setting of various eosinophilic disorders. Special emphasis will be put on the potential diagnostic, prognostic, and therapeutic implications related to activation of the TARC/CCL17-CCR4 axis.

Blockade of CCR4 Diminishes Hypersensitivity and Enhances Opioid Analgesia - Evidence from a Mouse Model of Diabetic Neuropathy

Chemokine signaling has been implicated in the pathogenesis of diabetic neuropathy; however, the role of chemokine CC motif receptor 4 (CCR4) remains unknown. The goal was to examine the function of CCR4 in hypersensitivity development and opioid effectiveness in diabetic neuropathy. Streptozotocin (STZ; 200 mg/kg, intraperitoneally administered)-induced mouse model of diabetic neuropathy were used. An analysis of the mRNA/protein expression of CCR4 and its ligands was performed by qRT-PCR, microarray and/or Western blot methods. C021 (CCR4 antagonist), morphine and buprenorphine were injected intrathecally or intraperitoneally, and pain-related behavior was evaluated by the von Frey, cold plate and rotarod tests. We observed that on day 7 after STZ administration, the blood glucose level was increased, and as a consequence, hypersensitivity to tactile and thermal stimuli developed. In addition, we observed an increase in the mRNA level of CCL2 but not CCL17/CCL22. The microarray technique showed that the CCL2 protein level was also upregulated. In naive mice, the pronociceptive effect of intrathecally injected CCL2 was blocked by C021, suggesting that this chemokine acts through CCR4. Importantly, our results provide the first evidence that in a mouse model of diabetic neuropathy, single intrathecal and intraperitoneal injections of C021 diminished neuropathic pain-related behavior in a dose-dependent manner and improved motor functions. Moreover, both single intrathecal and intraperitoneal injections of C021 enhanced morphine and buprenorphine effectiveness. These results reveal that pharmacological modulation of CCR4 may be a good potential therapeutic target for the treatment of diabetic neuropathy and may enhance the effectiveness of opioids.

CCR4 antagonist (C021) influences the level of nociceptive factors and enhances the analgesic potency of morphine in a rat model of neuropathic pain

Neuropathic pain is a chronic condition which significantly reduces the quality of life and serious clinical issue that is in general resistant to available therapies. Therefore looking for new analgesics is still critical issue. Recent, studies have indicated that chemokine signaling pathways are crucial for the development of neuropathy; however, the role of CC chemokine receptor 4 (CCR4) in this process has not yet been studied. Therefore, the aim of our research was to investigate the influence of C021 (a CCR4 antagonist) and CCR4 CC chemokine ligands 17 and 22 (CCL17 and CCL22) on the development of hypersensitivity and the effectiveness of morphine induced analgesia in naive animals and/or animals exposed to chronic constriction injury (CCI) of the sciatic nerve. Firstly, we demonstrated that the intrathecal administration of CCL17 and CCL22 induced pain-related behavior in naive mice. Secondly, we revealed that the intrathecal injection of C021 significantly reduced CCI-induced hypersensitivity after nerve injury. In parallel, C021 reduced microglia/macrophages activation and the level of some pronociceptive interleukins (IL-1beta; IL-18) in the spinal cord 8 days after CCI. Moreover, C021 not only attenuated mechanical and thermal hypersensitivity but also enhanced the analgesic properties of morphine. Our research indicates that CCR4 ligands might be important factors in the early stages of neuropathy, when we observe intense microglia/macrophages activation. Moreover, pharmacological blockade of CCR4 may serve as a potential new target for better understanding the mechanisms of neuropathic pain development.

Association between a Single Donor TARC/CCL17 Promotor Polymorphism and Obstructive Chronic Lung Allograft Dysfunction after Lung Transplantation

Lung transplantation (LTx) outcome is hampered by development of chronic rejection, often manifested as the bronchiolitis obliterans syndrome (BOS). Low serum levels of thymus and activation-regulated chemokine (TARC/CCL17), a chemoattractant, measured during the first month post-LTx are predictive for BOS development. Since TARC/CCL17 promotor polymorphisms correlate with serum TARC/CCL17 levels, we investigated seven single-nucleotide polymorphisms (SNPs) within this region and their potential association with LTx outcome. We analyzed donor and patient SNP configurations and haplotypes and observed a trend between a donor SNP (rs223899) configuration and patient TARC/CCL17 serum levels post-LTx (p = 0.066). Interestingly, this SNP configuration in patients did not show any correlation with pre-LTx TARC/CCL17 serum levels (p = 0.776). Survival analysis showed that receiving a graft from a donor heterozygous for rs223899 has a disadvantageous impact on transplantation outcome. When stratified per donor SNP genotype, patients receiving a transplant from a heterozygous donor showed a lower BOS-free survival (p = 0.023) and survival rate (p = 0.0079). Since rs223899 is located within a NFκB binding site, heterozygosity at this position could result in a reduced TARC/CCL17 expression. Our data indicate that a single TARC/CCL17 promotor SNP in the donor correlates with lower serum TARC/CCL17 levels measured 1 month after LTx and affects clinical outcome after LTx.

Natural history of the scuttle fly, Megaselia scalaris

The larvae of Megaselia scalaris (Diptera: Phoridae) exploit a broad spectrum of larval pabula. Consequently, the species features in a range of situations that affect the resources or well-being of humans. Furthermore, M. scalaris is readily cultured in the laboratory and is therefore favored as an experimental species for genetic, developmental, and bioassay studies. However, the extensive but widely scattered literature, reviewed herein, is frequently ignored by specialists, which gives rise to the unwitting repetition of previous work as well as insupportable proposals.

IL-4 induces expression of TARC/CCL17 via two STAT6 binding sites

A cardinal feature of allergic disorders and immune responses is enhanced leukocyte trafficking. This is largely orchestrated by chemokines. The CC chemokine thymus- and activation-regulated chemokine (TARC/CCL17) selectively attracts Th2 cells via the G protein-coupled chemokine receptor CCR4. We show here that TARC/CCL17 is expressed by human T cells upon stimulation with IL-4. Mapping of the transcriptional start site revealed the presence of two putative STAT6 binding motifs in proximity to the start position. EMSA and chromatin immunoprecipitation experiments demonstrated that STAT6 was able to bind to both motifs. A fragment of the TARC/CCL17 promoter containing both sites was tested in reporter gene assays for IL-4 inducibility. The promoter was inducible in a STAT6-deficient cell line only after introduction of functional STAT6. When mutations were inserted into one of the STAT6 motifs, IL-4-induced promoter activation was reduced. With both sites mutated, inducibility was completely abrogated. These data demonstrate collectively that T cells serve as a source of TARC/CCL17 when stimulated with IL-4 and that STAT6 is essential for this.

The -431C>T polymorphism of thymus and activation-regulated chemokine increases the promoter activity but is not associated with susceptibility to atopic dermatitis in Japanese patients

BACKGROUND

Thymus and activation-regulated chemokine (TARC) plays an important role in the pathogenesis of atopic dermatitis (AD). We recently detected the single nucleotide polymorphism (SNP) (-431C>T) in the 5'-flanking region of TARC gene.

OBJECTIVES

To examine whether the -431C>T SNP of the TARC gene is associated with susceptibility to AD and whether it affects the promoter activity of the TARC gene.

METHODS

We investigated the genotype and allele frequencies of the SNP in 193 AD patients and 158 healthy controls by polymerase chain reaction-restriction fragment length polymorphism method. We compared the promoter activities between TARC promoter carrying 431C and that carrying -431T by transient-transfection assay in DJM-1 cell line.

RESULTS

There were no significant differences in genotype or allele frequencies between AD patients and controls (genotype: P = 0.38, allele: P = 0.22). Luciferase activity was higher in -431T constructs than in -431C constructs (2.3-fold, P = 9.5 x 10(-6)).

CONCLUSION

These results suggest that the -431C>T SNP of the TARC gene enhances the promoter activity of TARC gene but is not associated with susceptibility to AD in Japanese population.

Plasma concentration of thymus and activation-regulated chemokine is elevated in childhood asthma

BACKGROUND

Thymus and activation-regulated chemokine (TARC) is responsible for the trafficking of T(H)2 lymphocytes into sites of allergic inflammation. Serum TARC levels correlate with the severity of atopic dermatitis. The relationship between this marker and the occurrence and severity of asthma has not been evaluated.

OBJECTIVE

We tested whether plasma TARC level is a useful marker for asthma and atopy in children.

METHODS

Plasma total IgE levels were measured by means of microparticle immunoassay, and specific IgE levels to common aeroallergens were measured by using a fluorescent enzyme immunoassay. We used a sandwich enzyme immunoassay to measure plasma TARC concentrations.

RESULTS

Sixty asthmatic children and 28 age- and sex-matched control subjects were recruited, with mean logarithmic plasma total IgE levels of 2.66 +/- 0.60 kIU/L and 1.74 +/- 0.58 kIU/L, respectively (P <.0001). The median plasma TARC concentration was higher in asthmatic patients without inhaled corticosteroid treatment (131.0 pg/mL) compared with those seen in steroid-treated patients (97.5 pg/mL) and control subjects (76.0 pg/mL; P =.01 and P <.0001, respectively). Plasma TARC concentration was found to correlate with total IgE level in plasma (r = 0.219, P =.04). This marker was also increased in subjects who were sensitized to cat allergen (P =.001) but not in subjects sensitized to other aeroallergens. Disease severity score, FEV(1) value, and atopy were not associated with increased plasma TARC levels.

CONCLUSION

Our results suggest that plasma TARC concentrations are elevated in childhood asthma. This marker is also linked to plasma total IgE levels and cat allergen sensitization.

Chemokines in immunity

Chemokines are a superfamily of small, heparin-binding cytokines that induce directed migration of various types of leukocytes through interactions with a group of seven-transmembrane G protein-coupled receptors. At present, over 40 members have been identified in humans. Until a few years ago, chemokines were mainly known as potent attractants for leukocytes such as neutrophils and monocytes, and were thus mostly regarded as the mediators of acute and chronic inflammatory responses. They had highly complex ligand-receptor relationships and their genes were regularly mapped on chromosomes 4 and 17 in humans. Recently, novel chemokines have been identified in rapid succession, mostly through application of bioinformatics on expressed sequence tag databases. A number of surprises have followed the identification of novel chemokines. They are constitutively expressed in lymphoid and other tissues with individually characteristic patterns. Most of them turned out to be highly specific for lymphocytes and dendritic cells. They have much simpler ligand-receptor relationships, and their genes are mapped to chromosomal loci different from the traditional chemokine gene clusters. Thus, the emerging chemokines are functionally and genetically quite different from the classical "inflammatory chemokines" and may be classified as "immune (system) chemokines" because of their profound importance in the genesis, homeostasis and function of the immune system. The emergence of immune chemokines has brought about a great deal of impact on the current immunological research, leading us to a better understanding on the fine traffic regulation of lymphocytes and dendritic cells. The immune chemokines and their receptors are also likely to be important future targets for therapeutic intervention of our immune responses.

Genomic organization of the CC chemokine mip-3alpha/CCL20/larc/exodus/SCYA20, showing gene structure, splice variants, and chromosome localization

We describe the genomic organization of a recently identified CC chemokine, MIP3alpha/CCL20 (HGMW-approved symbol SCYA20). The MIP-3alpha/CCL20 gene was cloned and sequenced, revealing a four exon, three intron structure, and was localized by FISH analysis to 2q35-q36. Two distinct cDNAs were identified, encoding two forms of MIP-3alpha/CCL20, Ala MIP-3alpha/CCL20 and Ser MIP-3alpha/CCL20, that differ by one amino acid at the predicted signal peptide cleavage site. Examination of the sequence around the boundary of intron 1 and exon 2 showed that use of alternative splice acceptor sites could give rise to Ala MIP-3alpha/CCL20 or Ser MIP-3alpha/CCL20. Both forms of MIP-3alpha/CCL20 were chemically synthesized and tested for biological activity. Both flu antigen plus IL-2-activated CD4(+) and CD8(+) T lymphoblasts and cord blood-derived dendritic cells responded to Ser and Ala MIP-3alpha/CCL20. T lymphocytes exposed only to IL-2 responded inconsistently, while no response was detected in naive T lymphocytes, monocytes, or neutrophils. The biological activity of Ser MIP-3alpha/CCL20 and Ala MIP-3alpha/CCL20 and the tissue-specific preference of different splice acceptor sites are not yet known.

Chemokines and atherosclerosis

Chemokines or chemotactic cytokines represent an expanding family of structurally related small molecular weight proteins, recognised as being responsible for leukocyte trafficking and activation. Soon after the discovery of this class of cytokines, about a decade ago, monocyte chemoattractant protein-1 (MCP-1) was found to be highly expressed in human atherosclerotic lesions and postulated to be central in monocyte recruitment into the arterial wall and developing lesions. In this review, we will discuss our present knowledge about MCP-1 and its receptor CCR2 and their role in atherogenesis. Although less well established, other chemokines such as RANTES, MIP-1alpha and MIP-1beta have also been implicated in atherosclerotic lesion formation as are a number of more recently discovered chemokines like MCP-4, ELC and PARC. The role of these chemokines in the progression of atherosclerosis will be discussed as well as the emerging role of IL-8, mostly know for its effects on neutrophils. Particular attention will be given not only to the involvement of chemokines in the inflammatory recruitment of monocytes/macrophages, but also to their role in the related local immune responses and vascular remodelling which occur during the formation of unstable atherosclerotic plaques.

Overproduction of Th2-specific chemokines in NC/Nga mice exhibiting atopic dermatitis-like lesions

We have examined the expression of chemokines and their receptors in the atopic dermatitis-like (AD-like) lesions of NC/Nga mice. Such lesions develop when the mice are kept in conventional conditions, but not when they are kept isolated from specific pathogens. The thymus- and activation-regulated chemokine TARC is unexpectedly highly expressed in the basal epidermis of 14-week-old mice with lesions, whereas it is not expressed in the skin without lesions. Production of TARC by keratinocytes was confirmed by culturing murine keratinocytic cell line cells (PAM212) with TNF-alpha, IFN-gamma, or IL-1beta. Expression of another Th2 chemokine, macrophage-derived chemokine (MDC), was observed in the skin from mice kept in both conventional and pathogen-free conditions, but expression of MDC was increased severalfold in the skin with lesions. The cellular origin of MDC was identified to be dermal dendritic cells. Infiltration of the skin by IL-4-producing T cells and mast cells, and the increase of CCR4 mRNA in the skin, coincided with the development of AD lesions. These observations indicate that TARC and MDC actively participate in the pathogenesis of AD-like lesions in NC/Nga mice and that these Th2 chemokines could be novel targets for intervention therapy of AD in humans.

Genomic organization and biological characterization of the novel human CC chemokine DC-CK-1/PARC/MIP-4/SCYA18

The chemokines are a group of chemotactic molecules that appear to regulate the directed movement of white blood cells in vitro and in vivo and may therefore play important roles in inflammation and immunity. The genes encoding the chemokines are clustered in close physical proximity to each other. A large cluster of human CC chemokine genes resides on chromosome 17. We have used this information in a positional cloning approach to identify novel chemokine genes within this cluster. We constructed a YAC contig encompassing the MIP-1alpha (HGMW-approved symbol SCYA3) gene region and used exon trapping and sequence analysis to isolate novel chemokine genes. Using this approach, a gene encoding a chemokine named MIP-4, based on its homology with MIP-1alpha (49.5% identity at the nucleotide level and 59.6% at the predicted amino acid level), was found. The MIP-4 gene (HGMW-approved symbol SCYA18) consists of three exons spread over 7.1 kb and is separated from the MIP-1alpha gene by 16 kb. The MIP-4 gene encodes a 750-bp mRNA that is expressed in lung and macrophages but not in brain or muscle. The mRNA encodes an 89-amino-acid protein and includes a predicted signal peptide of 21 amino acids. Recombinant or synthetic MIP-4 induced calcium mobilization in naive and activated T lymphocyte subpopulations in vitro. Injection of synthetic MIP-4 into the peritoneal cavity of mice led to the accumulation of both CD4(+) and CD8(+) T lymphocytes, but not monocytes or granulocytes. These observations provide new information concerning the arrangement of the CC chemokine gene cluster on human chromosome 17 and indicate that the MIP-4 gene product is chemotactic in vivo for both CD4(+) and CD8(+) T lymphocytes and may therefore be implicated in both humoral and cell-mediated immunity.

The MCP/eotaxin subfamily of CC chemokines

Migration of leukocytes from the bone marrow to the circulation, the primary lymphoid organs and inflammatory sites is directed by chemokines and specific receptor interactions. Besides the role of this group of low molecular weight cytokines in leukocyte attraction and activation, anti-HIV and hematopoietic activities were also attributed to chemokines. On the basis of the number and arrangement of the conserved cysteines, chemokines are subdivided in two multi-member families, namely the CXC and CC chemokines, whereas fractalkine (CX3C) and lymphotactin (C) are unique relatives. The CC chemokines possess four cysteines of which the first two are adjacent. Functionally, they form a rather heterogeneous family. Here, the focus is on the monocyte chemotactic proteins and eotaxin which, on a structural basis, can be considered as a CC chemokine subfamily. Not only the protein sequences, but also the gene structures, chromosomal location, biological activities and receptor usage exhibit considerable similarities. The review is complemented with a comparison of the biological functions of the MCP/eotaxin-subfamily in physiology and pathology.

Opportunities for novel therapeutic agents acting at chemokine receptors

Chemokines are proinflammatory mediators that primarily control leukocyte migration into selected tissues and upregulation of adhesion receptors. They also have a role in pathological conditions that require neovascularization and are implicated in the suppression of viral replication. By interaction with their respective G-protein-coupled receptor, chemokines have a profound influence over the selective recruitment of specific cell types in acute inflammatory disease and, hence, inhibition of their action should be of therapeutic benefit. Only now are small molecule inhibitors becoming available to validate this speculation. In this review, without seeking to be comprehensive, the authors provide an introduction to chemokines, their receptors and their role in certain disease processes. Also, recent disclosures claiming novel nonpeptide ligands for chemokine receptors are summarized.

Chemokines: understanding their role in T-lymphocyte biology

The chemokines are a complex superfamily of small, secreted proteins that were initially characterized through their chemotactic effects on a variety of leucocytes. The superfamily is divided into families based on structural and genetic considerations and have been termed the CXC, CC, C and CX3C families. Chemokines from these families have a key role in the recruitment and function of T lymphocytes. Moreover, T lymphocytes have also been identified as a source of a number of chemokines. T lymphocytes also express most of the known CXC and CC chemokine receptors to an extent that depends on their state of activation/differentiation and/or the activating stimuli. The expression of two chemokine receptors, namely CXCR4 and CCR5, together with the regulated production of their respective ligands, appears to be extremely important in determining sensitivity of T cells to HIV-1 infection. The intracellular events which mediate the effects of chemokines, particularly those elicited by the CC chemokine RANTES, include activation of both G-protein- and protein tyrosine kinase-coupled signalling pathways. The present review describes our current understanding of the structure and expression of chemokines and their receptors, the effects of chemokines on T-cell function(s), the intracellular signalling pathways activated by chemokines and the role of certain chemokines and chemokine receptors in determining sensitivity to HIV-1 infection.

CKβ-11/Macrophage Inflammatory Protein-3β/EBI1-Ligand Chemokine Is an Efficacious Chemoattractant for T and B Cells

We examined the functional properties of CKβ-11/MIP-3β/ELC, a recently reported CC chemokine that specifically binds to a chemokine receptor, EBI1/BLR2/CCR7. CKβ-11/MIP-3β/ELC is distantly related to other CC and CXC chemokines in primary amino acid sequence structure. Recombinant human CKβ-11/MIP-3β/ELC expressed from a mammalian cell system showed potent chemotactic activity for T cells and B cells but not for granulocytes and monocytes. An optimal concentration of CKβ-11/MIP-3β/ELC attracted most input T cells within 3 h, a chemotactic activity comparable with that of stromal cell derived factor 1 (SDF-1), a highly efficacious CXC chemokine. CKβ-11/MIP-3β/ELC equally attracted naive CD45RA+ and memory type CD45RO+ T cells. CKβ-11/MIP-3β/ELC also strongly attracted both CD4+ and CD8+ T cells, but the attraction for CD4+ T cells was greater. CKβ-11/MIP-3β/ELC was also a more efficacious chemoattractant for B cells than MIP-1α, a known B cell chemoattractant. CKβ-11/MIP-3β/ELC induced actin polymerization in lymphocytes, and chemotaxis was completely blocked by pertussis toxin showing its receptor, most likely EBI1/BLR2/CCR7, is coupled to a Gαi protein. CKβ-11/MIP-3β/ELC induced calcium mobilization in lymphocytes, which could be desensitized by SDF-1, suggesting possible cross-regulation in their signaling. Human CKβ-11/MIP-3β/ELC attracted murine splenocytes suggesting functional conservation of CKβ-11/MIP-3β/ELC between human and mouse. The efficacy of chemoattraction by CKβ-11/MIP-3β/ELC and tissue expression of its mRNA suggest that CKβ-11/MIP-3β/ELC may be important in trafficking of T cells in thymus, and T cell and B cell migration to secondary lymphoid organs.

Macrophage-derived chemokine is a functional ligand for the CC chemokine receptor 4

Macrophage-derived chemokine (MDC) is a recently identified member of the CC chemokine family. MDC is not closely related to other chemokines, sharing most similarity with thymus- and activation-regulated chemokine (TARC), which contains 37% identical amino acids. Both chemokines are highly expressed in the thymus, with little expression seen in other tissues. In addition, the genes for MDC and TARC are encoded by human chromosome 16. To explore this relationship in greater detail, we have more precisely localized the MDC gene to chromosome 16q13, the same position reported for the TARC gene. We have also examined the interaction of MDC with CC chemokine receptor 4 (CCR4), recently shown to be a receptor for TARC. Using a fusion protein of MDC with secreted alkaline phosphatase, we observed high affinity binding of MDC-secreted alkaline phosphatase to CCR4-transfected L1.2 cells (Kd = 0.18 nM). MDC and TARC competed for binding to CCR4, while no binding competition was observed for six other chemokines (MCP-1, MCP-3, MCP-4, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein-1 alpha, macrophage inflammatory protein-1 beta). MDC was tested for calcium mobilization in L1.2 cells tranfected with seven different CC chemokine receptors. MDC induced a calcium flux in CCR4-transfected cells, but other receptors did not respond to MDC. TARC, which also induced calcium mobilization in CCR4 transfectants, was unable to desensitize the response to MDC. In contrast, MDC fully desensitized a subsequent response to TARC. Both MDC and TARC functioned as chemoattractants for CCR4 transfectants, confirming that MDC is also a functional ligand for CCR4. Since MDC and TARC are both expressed in the thymus, one role for these chemokines may be to attract CCR4-bearing thymocytes in the process of T cell education and differentiation.

Localization of the human CXC chemokine subfamily on the long arm of chromosome 4 using radiation hybrids

All 12 of the human CXC chemokine genes were physically mapped using gene-specific PCR primers and the GenBridge 4 radiation hybrid panel. Nine genes, PF4, PF4V1, GRO1, GCP2, PPBP, IL8, GRO2, GRO3, and SCYB5, were assigned within a 1.8-cR interval of one another on 4q. Two additional genes, MIG and INP10, map within 0.5 cR of each another and 6 cR distal to the above-mentioned group. The final gene, SDF1, is localized on 10q. Phylogenetic analyses of amino acid sequences revealed that SDF1 is the most divergent member and that the physically separated MIG-INP10 pair constitutes a distinct evolutionary lineage.

Molecular cloning of a novel human CC chemokine secondary lymphoid-tissue chemokine that is a potent chemoattractant for lymphocytes and mapped to chromosome 9p13

By searching the Expressed Sequence Tag (EST) data base, we identified partial cDNA sequences potentially encoding a novel human CC chemokine. We determined the entire cDNA sequence which encodes a highly basic polypeptide of 134 amino acids total with a putative signal peptide of 23 amino acids. The predicted mature protein of 111 amino acids has the four canonical cysteine residues and shows 21-33% identity to other human CC chemokines, but has a unique carboxyl-terminal extension of about 30 amino acids which contains two extra cysteine residues. The mRNA was expressed strongly in tissues such as the lymph nodes, Appendix, and spleen. The recombinant protein, which was produced by the baculovirus system and purified to homogeneity, was a highly efficient chemoattractant for certain human T cell lines and a highly potent one for freshly isolated peripheral blood lymphocytes and cultured normal T cells expanded by phytohemagglutinin and interleukin 2. Unlike most other CC chemokines, however, this novel chemokine was not chemotactic for monocytes or neutrophils, suggesting that it is specific for lymphocytes. From these results, we designated this novel CC chemokine as SLC from secondary lymphoid-tissue chemokine. SLC fused with the secreted form of alkaline phosphatase (SLC-SEAP) was used to characterize the SLC receptor. Binding of SLC-SEAP to freshly isolated lymphocytes was blocked by SLC (IC50, 0.12 nM) but not by any other CC chemokine so far tested, suggesting that resting lymphocytes express a class of receptors highly specific for SLC. By using somatic cell hybrids, radiation hybrids, and selected yeast and bacterial artificial chromosome clones, we mapped the SLC gene (SCYA21) at chromosome 9p13 and between chromosomal markers, D9S1978(WI-8765) and AFM326vd1, where the gene for another novel CC chemokine termed ELC from EBI1-ligand chemokine (SCYA19) also exists. Collectively, SLC is a novel CC chemokine specific for lymphocytes and, together with ELC, constitutes a new group of chemokines localized at chromosome 9p13.

The T cell-directed CC chemokine TARC is a highly specific biological ligand for CC chemokine receptor 4

Thymus and activation-regulated chemokine (TARC) is a recently identified CC chemokine that is expressed constitutively in thymus and transiently in stimulated peripheral blood mononuclear cells. TARC functions as a selective chemoattractant for T cells that express a class of receptors binding TARC with high affinity and specificity. To identify the receptor for TARC, we produced TARC as a fusion protein with secreted alkaline phosphatase (SEAP) and used it for specific binding. By stably transfecting five orphan receptors and five known CC chemokine receptors (CCR1 to -5) into K562 cells, we found that TARC-SEAP bound selectively to cells expressing CCR4. TARC-SEAP also bound to K562 cells stably expressing CCR4 with a high affinity (Kd = 0.5 nM). Only TARC and not five other CC chemokines (MCP-1 (monocyte chemoattractant protein-1), RANTES (regulated upon activation, normal T cells expressed and secreted), MIP-1alpha (macrophage inflammatory protein-1alpha), MIP-1beta, and LARC (liver and activation-regulated chemokine)) competed with TARC-SEAP for binding to CCR4. TARC but not RANTES or MIP-1alpha induced migration and calcium mobilization in 293/EBNA-1 cells stably expressing CCR4. K562 cells stably expressing CCR4 also responded to TARC in a calcium mobilization assay. Northern blot analysis revealed that CCR4 mRNA was expressed strongly in human T cell lines and peripheral blood T cells but not in B cells, natural killer cells, monocytes, or granulocytes. Taken together, TARC is a specific functional ligand for CCR4, and CCR4 is the specific receptor for TARC selectively expressed on T cells.

Identification of CCR6, the specific receptor for a novel lymphocyte-directed CC chemokine LARC

Liver and activation-regulated chemokine (LARC) is a recently identified CC chemokine that is expressed mainly in the liver. LARC functions as a selective chemoattractant for lymphocytes that express a class of receptors specifically binding to LARC with high affinity. To identifiy the receptor for LARC, we examined LARC-induced calcium mobilization in cells stably expressing five CC chemokine receptors (CCR1-CCR5) and five orphan seven-transmembrane receptors. LARC specifically induced calcium flux in K562 cells as well as 293/EBNA-1 cells stably expressing an orphan receptor GPR-CY4. LARC induced migration in 293/EBNA-1 cells stably expressing GPR-CY4 with a bi-modal dose-response curve. LARC fused with secreted alkaline phosphatase (LARC-SEAP) bound specifically to Raji cells stably expressing GPR-CY4 with a Kd of 0.9 nM. Only LARC but not five other CC chemokines (MCP-1, RANTES, MIP-1alpha, MIP-1beta, and TARC) competed with LARC-SEAP for binding to GPR-CY4. By Northern blot analysis, GPR-CY4 mRNA was expressed mainly in spleen, lymph nodes, Appendix, and fetal liver among various human tissues. Among various leukocyte subsets, GPR-CY4 mRNA was detected in lymphocytes (CD4(+) and CD8(+) T cells and B cells) but not in natural killer cells, monocytes, or granulocytes. Expression of GPR-CY4 mRNA in CD4(+) and CD8(+) T cells was strongly up-regulated by IL-2. Taken together, GPR-CY4 is the specific receptor for LARC expressed selectively on lymphocytes, and LARC is a unique functional ligand for GPR-CY4. We propose GPR-CY4 to be designated as CCR6.

Molecular cloning of a novel human CC chemokine EBI1-ligand chemokine that is a specific functional ligand for EBI1, CCR7

By searching the expressed sequence tag (EST) data base, we identified partial cDNA sequences encoding a novel human CC chemokine. We determined the complete cDNA sequence that encodes a highly basic polypeptide of a total 98 amino acids with 20 to 30% identity to other human CC chemokines. We termed this novel chemokine from EBI1-Ligand Chemokine as ELC (see below). The ELC mRNA was most strongly expressed in the thymus and lymph nodes. Recombinant ELC protein was expressed as a fusion protein with the Flag tag (ELC-Flag). For receptor-binding assays, recombinant ELC protein fused with the secreted form of alkaline phosphatase (SEAP) was used. By stably expressing five CC chemokine receptors (CCR1 to 5) and five orphan receptors, ELC-SEAP was found to bind specifically to an orphan receptor EBI1. Only ELC-Flag, but not MCP-1, MCP-2, MCP-3, eotaxin, MIP-1alpha, MIP-1beta, RANTES (regulated on activation normal T cell expressed and secreted), thymus and activation-regulated chemokine (TARC), or liver and activation-regulated chemokine (LARC), competed with ELC-SEAP for EBI1. ELC-Flag-induced transient calcium mobilization and chemotactic responses in EBI1-transfected cells. ELC-Flag also induced chemotaxis in HUT78 cells expressing endogenous EBI1 at high levels. By somatic hybrid and radiation hybrid analyses, the gene for ELC (SCYA19) was mapped to chromosome 9p13 instead of chromosome 17q11.2 where the genes for CC chemokines are clustered. Taken together, ELC is a highly specific ligand for EBI1, which is known to be expressed in activated B and T lymphocytes and strongly up-regulated in B cells infected with Epstein-Barr virus and T cells infected with herpesvirus 6 or 7. ELC and EBI1 may thus play roles in migration and homing of normal lymphocytes, as well as in pathophysiology of lymphocytes infected with these herpesviruses. We propose EBI1 to be designated as CCR7.

Human macrophage-derived chemokine (MDC), a novel chemoattractant for monocytes, monocyte-derived dendritic cells, and natural killer cells

A cDNA encoding a novel human chemokine was isolated by random sequencing of cDNA clones from human monocyte-derived macrophages. This protein has been termed macrophage-derived chemokine (MDC) because it appears to be synthesized specifically by cells of the macrophage lineage. MDC has the four-cysteine motif and other highly conserved residues characteristic of CC chemokines, but it shares <35% identity with any of the known chemokines. Recombinant MDC was expressed in Chinese hamster ovary cells and purified by heparin-Sepharose chromatography. NH2-terminal sequencing and mass spectrophotometry were used to verify the NH2 terminus and molecular mass of recombinant MDC (8,081 dalton). In microchamber migration assays, monocyte-derived dendritic cells and IL-2-activated natural killer cells migrated to MDC in a dose-dependent manner, with a maximal chemotactic response at 1 ng/ml. Freshly isolated monocytes also migrated toward MDC, but with a peak response at 100 ng/ml MDC. Northern analyses indicated MDC is highly expressed in macrophages and in monocyte-derived dendritic cells, but not in monocytes, natural killer cells, or several cell lines of epithelial, endothelial, or fibroblast origin. High expression was also detected in normal thymus and less expression in lung and spleen. Unlike most other CC chemokines, MDC is encoded on human chromosome 16. MDC is thus a unique member of the CC chemokine family that may play a fundamental role in the function of dendritic cells, natural killer cells, and monocytes.