Showing papers on "Chemokine receptor published in 1998"

Function of the chemokine receptor CXCR4 in haematopoiesis and in cerebellar development

Abstract: Chemokines and their receptors are important in cell migration during inflammation, in the establishment of functional lymphoid microenvironments, and in organogenesis. The chemokine receptor CXCR4 is broadly expressed in cells of both the immune and the central nervous systems and can mediate migration of resting leukocytes and haematopoietic progenitors in response to its ligand, SDF-1. CXCR4 is also a major receptor for strains of human immunodeficiency virus-1 (HIV-1) that arise during progression to immunodeficiency and AIDS dementia. Here we show that mice lacking CXCR4 exhibit haematopoietic and cardiac defects identical to those of SDF-1-deficient mice, indicating that CXCR4 may be the only receptor for SDF-1. Furthermore, fetal cerebellar development in mutant animals is markedly different from that in wild-type animals, with many proliferating granule cells invading the cerebellar anlage. This is, to our knowledge, the first demonstration of the involvement of a G-protein-coupled chemokine receptor in neuronal cell migration and patterning in the central nervous system. These results may be important for designing strategies to block HIV entry into cells and for understanding mechanisms of pathogenesis in AIDS dementia.

Differential Expression of Chemokine Receptors and Chemotactic Responsiveness of Type 1 T Helper Cells (Th1s) and Th2s

Abstract: T helper cells type 1 (Th1s) that produce interferon-γ predominantly mediate cellular immune responses and are involved in the development of chronic inflammatory conditions, whereas Th2s which produce large amounts of IL-4 and IL-5 upregulate IgE production and are prominent in the pathogenesis of allergic diseases. The precise factors determining whether Th1- or Th2-mediated immune responses preferentially occur at a peripheral site of antigen exposure are largely unknown. Chemokines, a superfamily of polypeptide mediators, are a key component of the leukocyte recruitment process. Here we report that among four CXC (CXCR1-4) and five CC (CCR1-5) chemokine receptors analyzed, CXCR3 and CCR5 are preferentially expressed in human Th1s. In contrast, Th2s preferentially express CCR4 and, to a lesser extent, CCR3. In agreement with the differential chemokine receptor expression, Th1s and Th2s selectively migrate in response to the corresponding chemokines. The differential expression of chemokine receptors may dictate, to a large extent, the migration and tissue homing of Th1s and Th2s. It may also determine different susceptibility of Th1s and Th2s to human immunodeficiency virus strains using different fusion coreceptors.

Decreased lesion formation in CCR2 −/− mice reveals a role for chemokines in the initiation of atherosclerosis

Abstract: Chemokines are proinflammatory cytokines that function in leukocyte chemoattraction and activation and have recently been shown to block the HIV-1 infection of target cells through interactions with chemokine receptors. In addition to their function in viral disease, chemokines have been implicated in the pathogenesis of atherosclerosis. Expression of the CC chemokine monocyte chemoattractant protein-1 (MCP-1) is upregulated in human atherosclerotic plaques, in arteries of primates on a hypercholesterolaemic diet; and in vascular endothelial and smooth muscle cells exposed to minimally modified lipids. To determine whether MCP-1 is causally related to the development of atherosclerosis, we generated mice that lack CCR2, the receptor for MCP-1 (ref. 7), and crossed them with apolipoprotein (apo) E-null mice which develop severe atherosclerosis. Here we show that the selective absence of CCR2 decreases lesion formation markedly in apoE-/- mice but has no effect on plasma lipid or lipoprotein concentrations. These data reveal a role for MCP-1 in the development of early atherosclerotic lesions and suggest that upregulation of this chemokine by minimally oxidized lipids is an important link between hyperlipidaemia and fatty streak formation.

Flexible programs of chemokine receptor expression on human polarized T helper 1 and 2 lymphocytes.

Abstract: Chemokines and their receptors are important elements for the selective attraction of various subsets of leukocytes. To better understand the selective migration of functional subsets of T cells, chemokine receptor expression was analyzed using monoclonal antibodies, RNase protection assays, and the response to distinct chemokines. Naive T cells expressed only CXC chemokine receptor (CXCR)4, whereas the majority of memory/activated T cells expressed CXCR3, and a small proportion expressed CC chemokine receptor (CCR)3 and CCR5. When polarized T cell lines were analyzed, CXCR3 was found to be expressed at high levels on T helper cell (Th)0s and Th1s and at low levels on Th2s. In contrast, CCR3 and CCR4 were found on Th2s. This was confirmed by functional responses: only Th2s responded with an increase in [Ca2+]i to the CCR3 and CCR4 agonists eotaxin and thymus and activation regulated chemokine (TARC), whereas only Th0s and Th1s responded to low concentrations of the CXCR3 agonists IFN-γ–inducible protein 10 (IP-10) and monokine induced by IFN-γ (Mig). Although CCR5 was expressed on both Th1 and Th2 lines, it was absent in several Th2 clones and its expression was markedly influenced by interleukin 2. Chemokine receptor expression and association with Th1 and Th2 phenotypes was affected by other cytokines present during polarization. Transforming growth factor β inhibited CCR3, but enhanced CCR4 and CCR7 expression, whereas interferon α inhibited CCR3 but upregulated CXCR3 and CCR1. These results demonstrate that chemokine receptors are markers of naive and polarized T cell subsets and suggest that flexible programs of chemokine receptor gene expression may control tissue-specific migration of effector T cells.

The chemokine receptor CXCR4 is essential for vascularization of the gastrointestinal tract.

Abstract: Vascularization of organs generally occurs by remodelling of the preexisting vascular system during their differentiation and growth to enable them to perform their specific functions during development. The molecules required by early vascular systems, many of which are receptor tyrosine kinases and their ligands, have been defined by analysis of mutant mice. As most of these mice die during early gestation before many of their organs have developed, the molecules responsible for vascularization during organogenesis have not been identified. The cell-surface receptor CXCR4 is a seven-transmembrane-spanning, G-protein-coupled receptor for the CXC chemokine PBSF/SDF-1 (for pre-B-cell growth-stimulating factor/stromal-cell-derived factor), which is responsible for B-cell lymphopoiesis, bone-marrow myelopoiesis and cardiac ventricular septum formation. CXCR4 also functions as a co-receptor for T-cell-line tropic human immunodeficiency virus HIV-1. Here we report that CXCR4 is expressed in developing vascular endothelial cells, and that mice lacking CXCR4 or PBSF/SDF-1 have defective formation of the large vessels supplying the gastrointestinal tract. In addition, mice lacking CXCR4 die in utero and are defective in vascular development, haematopoiesis and cardiogenesis, like mice lacking PBSF/SDF-1, indicating that CXCR4 is a primary physiological receptor for PBSF/SDF-1. We conclude that PBSF/SDF-1 and CXCR4 define a new signalling system for organ vascularization.

Rapid and coordinated switch in chemokine receptor expression during dendritic cell maturation

Abstract: Dendritic cells (DC) migrate into inflamed peripheral tissues where they capture antigens and, following maturation, to lymph nodes where they stimulate T cells. To gain insight into this process we compared chemokine receptor expression in immature and mature DC. Immature DC expressed CCR1, CCR2, CCR5 and CXCR1 and responded to their respective ligands, which are chemokines produced at inflammatory sites. Following stimulation with LPS or TNF-alpha maturing DC expressed high levels of CCR7 mRNA and acquired responsiveness to the CCR7 ligand EBI1 ligand chemokine (ELC), a chemokine produced in lymphoid organs. Maturation also resulted in up-regulation of CXCR4 and down-regulation of CXCR1 mRNA, while CCR1 and CCR5 mRNA were only marginally affected for up to 40 h. However, CCR1 and CCR5 were lost from the cell surface within 3 h, due to receptor down-regulation mediated by chemokines produced by maturing DC. A complete down-regulation of CCR1 and CCR5 mRNA was observed only after stimulation with CD40 ligand of DC induced to mature by LPS treatment. These different patterns of chemokine receptors are consistent with "inflammatory" and "primary response" phases of DC function.

A Conserved HIV gp120 Glycoprotein Structure Involved in Chemokine Receptor Binding

Abstract: The entry of primate immunodeficiency viruses into target cells depends on a sequential interaction of the gp120 envelope glycoprotein with the cellular receptors, CD4 and members of the chemokine receptor family. The gp120 third variable (V3) loop has been implicated in chemokine receptor binding, but the use of the CCR5 chemokine receptor by diverse primate immunodeficiency viruses suggests the involvement of an additional, conserved gp120 element. Through the use of gp120 mutants, a highly conserved gp120 structure was shown to be critical for CCR5 binding. This structure is located adjacent to the V3 loop and contains neutralization epitopes induced by CD4 binding. This conserved element may be a useful target for pharmacologic or prophylactic intervention in human immunodeficiency virus (HIV) infections.

CCR5 is characteristic of Th1 lymphocytes

Abstract: CD4+ lymphocytes can be assigned to two subsets1 Th1 lymphocytes secrete interferon gamma (IFNγ) and lymphotoxin, promoting cell-mediated immunity to intracellular pathogens; and Th2 lymphocytes secrete interleukins 4 and 5 (IL-4 and IL-5), which function in allergy and humoral immunity to parasites Th2 lymphocytes preferentially express the chemokine receptor CCR3 (23) We have studied the occurrence of two additional chemokine receptors, CCR5 and CXCR3, in human, antigen-specific CD4+ Th1 and Th2 cell clones4

B Cell–attracting Chemokine 1, a Human CXC Chemokine Expressed in Lymphoid Tissues, Selectively Attracts B Lymphocytes via BLR1/CXCR5

Abstract: Although most leukocytes, T lymphocytes in particular, respond to several different chemokines, there is virtually no information on chemokine activities and chemokine receptors in B lymphocytes. A putative chemokine receptor, BLR1, that is expressed in Burkitt's lymphoma cells and B lymphocytes was cloned a few years ago. Deletion of the gene for BLR1 yielded mice with abnormal primary follicles and germinal centers of the spleen and Peyer's patches, reflecting the inability of B lymphocytes to migrate into B cell areas. By screening expressed sequence tag DNA sequences, we have identified a CXC chemokine, termed B cell–attracting chemokine 1 (BCA-1), that is chemotactic for human B lymphocytes. BCA-1 cDNA encodes a protein of 109 amino acids with a leader sequence of 22 residues. The mature protein shares 23–34% identical amino acids with known CXC chemokines and is constitutively expressed in secondary lymphoid organs. BCA-1 was chemically synthesized and tested for activity on murine pre–B cells 300-19 transfected with BLR1 and on human blood B lymphocytes. In transfected cells, BCA-1 induced chemotaxis and Ca2+ mobilization demonstrating that it acts via BLR1. Under the same conditions, no activity was obtained with 10 CXC and 19 CC chemokines, lymphotactin, neurotactin/fractalkine and several other peptide ligands. BCA-1 was also a highly effective attractant for human blood B lymphocytes (which express BLR1), but was inactive on freshly isolated or IL-2–stimulated T lymphocytes, monocytes, and neutrophils. In agreement with the nomenclature rules for chemokine receptors, we propose the term CXCR5 for BLR1. Together with the observed disturbance of B cell colonization in BLR1/ CXCR5-deficient mice, the present results indicate that chemotactic recruitment by locally produced BCA-1 is important for the development of B cell areas of secondary lymphoid tissues.

Genetic Restriction of AIDS Pathogenesis by an SDF-1 Chemokine Gene Variant

Abstract: Stromal-derived factor (SDF-1) is the principal ligand for CXCR4, a coreceptor with CD4 for T lymphocyte cell line-tropic human immunodeficiency virus-type 1 (HIV-1). A common polymorphism, SDF1-3'A, was identified in an evolutionarily conserved segment of the 3' untranslated region of the SDF-1 structural gene transcript. In the homozygous state, SDF1-3'A/3'A delays the onset of acquired immunodeficiency syndrome (AIDS), according to a genetic association analysis of 2857 patients enrolled in five AIDS cohort studies. The recessive protective effect of SDF1-3'A was increasingly pronounced in individuals infected with HIV-1 for longer periods, was twice as strong as the dominant genetic restriction of AIDS conferred by CCR5 and CCR2 chemokine receptor variants in these populations, and was complementary with these mutations in delaying the onset of AIDS.

Differential regulation of chemokine receptors during dendritic cell maturation: a model for their trafficking properties.

Abstract: Upon exposure to immune or inflammatory stimuli, dendritic cells (DC) migrate from peripheral tissues to lymphoid organs, where they present Ag CC chemokines induce chemotactic and transendothelial migration of immature DC, in vitro Maturation of DC by CD40L, or by LPS, IL-1, and TNF, induces down-regulation of the two main CC chemokine receptors expressed by these cells, CCR1 and CCRS, and abrogates chemotaxis to their ligands Inhibition was rapid (<1 h) and included the unrelated agent FMLP Concomitantly, the expression of CCR7 and the migration to its ligand EBI1 ligand chemokine (ELC)/macrophage inflammatory protein (MIP)-3beta, a chemokine expressed in lymphoid organs, were strongly up-regulated, though with slower kinetics (24-48 h) Rapid inhibition of responsiveness to chemoattractants present at sites of inflammation and immune reaction may be permissive for leaving peripheral tissues Conversely, the slower acquisition of responsiveness to ELC/MIP-3beta may guide subsequent localization of DC in lymphoid organs

Chemokines regulate hippocampal neuronal signaling and gp120 neurotoxicity

Abstract: The HIV-1 envelope protein gp120 induces apoptosis in hippocampal neurons. Because chemokine receptors act as cellular receptors for HIV-1, we examined rat hippocampal neurons for the presence of functional chemokine receptors. Fura-2-based Ca imaging showed that numerous chemokines, including SDF-1α, RANTES, and fractalkine, affect neuronal Ca signaling, suggesting that hippocampal neurons possess a wide variety of chemokine receptors. Chemokines also blocked the frequency of spontaneous glutamatergic excitatory postsynaptic currents recorded from these neurons and reduced voltage-dependent Ca currents in the same neurons. Reverse transcription–PCR demonstrated the expression of CCR1, CCR4, CCR5, CCR9/10, CXCR2, CXCR4, and CX3CR1, as well as the chemokine fractalkine in these neurons. Both fractalkine and macrophage-derived chemokine (MDC) produced a time-dependent activation of extracellular response kinases (ERK)-1/2, whereas no activation of c-JUN NH2-terminal protein kinase (JNK)/stress-activated protein kinase, or p38 was evident. Furthermore, these two chemokines, as well as SDF-1α, activated the Ca- and cAMP-dependent transcription factor CREB. Several chemokines were able also to block gp120-induced apoptosis of hippocampal neurons, both in the presence and absence of the glial feeder layer. These data suggest that chemokine receptors may directly mediate gp120 neurotoxicity.

Selective up-regulation of chemokine receptors CCR4 and CCR8 upon activation of polarized human type 2 Th cells

Abstract: Polarized Th1 and Th2 cells differentially express adhesion molecules and chemokine receptors, endowing these cells with distinct tissue homing capabilities. Here we report that, in contrast to other chemokine receptors, the expression of CCR4 and CCR8 on Th2 cells is transiently increased following TCR and CD28 engagement. IL-4 is not required for this activation-induced up-regulation of CCR4 and CCR8. In accordance with receptor expression, the response of Th2 cells to I-309 (CCR8 ligand) and thymus- and activation-regulated chemokine (CCR4 and CCR8 ligand) is enhanced upon activation. Moreover, activated Th1 cells up-regulate CCR4 expression and functional responsiveness to thymus- and activation-regulated chemokine. Analysis of polarized subsets of CD8+ T cells reveals a similar pattern of chemokine receptor expression and modulation of responsiveness. Taken together, these findings suggest that an up-regulation of CCR4 and CCR8 following Ag encounter may contribute to the proper positioning of activated T cells within sites of antigenic challenge and/or specialized areas of lymphoid tissues.

A chemokine receptor CCR2 allele delays HIV-1 disease progression and is associated with a CCR5 promoter mutation.

Abstract: Viral and host factors influence the rate of HIV-1 disease progression. For HIV-1 to fuse, a CD4+ cell must express a co-receptor that the virus can use. The chemokine receptors CCR5 and CXCR4 are used by R5 and X4 viruses, respectively. Most new infections involve transmission of R5 viruses, but variants can arise later that also use CXCR4 (R5-X4 or X4 viruses). This is associated with an increased rate of CD4+ T-cell loss and poor prognosis. The ability of host cells to support HIV-1 entry also influences progression. The absence of CCR5 in approximately 1% of the Caucasian population, due to homozygosity for a 32-nucleotide deletion in the coding region (delta32-CCR5 allele), very strongly protects against HIV-1 transmission. Heterozygosity for the delta32-CCR5 allele delays progression typically by 2 years. A recent study showed that a conservative substitution (V64I) in the coding region of CCR2 also has a significant impact on disease progression, but not on HIV-1 transmission. This was unexpected, since CCR2 is rarely used as a co-receptor in vitro and the V64I change is in a transmembrane region. Because a subsequent study did not confirm this effect on progression to disease, we analyzed CCR2-V64I using subjects in the Chicago MACS. We show that CCR2-V64I is indeed protective against disease progression and go on to show that the CCR2-V64I allele is in complete linkage disequilibrium with a point mutation in the CCR5 regulatory region.

The chemokine receptor CCR8 is preferentially expressed in Th2 but not Th1 cells.

Abstract: In this paper we report on the cloning and characterization of mouse CCR8. Like its human homologue, it is predominantly expressed in the thymus. In the periphery, murine CCR8 mRNA was found most abundantly expressed in activated Th2-polarized cells and in NK1.1+ CD4+ T cells. Human CCR8 is also preferentially expressed in human Th2-polarized cells and clones. This pattern of expression suggests that CCR8 is part of a Th2-specific gene expression program. The CCR8 ligands I-309 and its mouse homologue T cell activation gene 3 (TCA-3) are potent chemoattractants for Th2-polarized cells. Taken together, these observations strongly suggest that CCR8 plays a role in the control of Th2 responses, and may represent a potential target for treatment of allergic diseases.

EBI1/CCR7 Is a New Member of Dendritic Cell Chemokine Receptor That Is Up-Regulated upon Maturation

Abstract: Dendritic cells (DC) that are stimulated with inflammatory mediators can maturate and migrate from nonlymphoid tissues to lymphoid organs to initiate T cell-mediated immune responses. This migratory step is closely related to the maturation of the DC. In an attempt to identify chemokine receptors that might influence migration and are selectively expressed in mature DC, we have discovered that the chemokine receptor, EBI1/CCR7, is strikingly up-regulated upon maturation in three distinct culture systems: 1) mouse bone marrow-derived DC, 2) mouse epidermal Langerhans cells, and 3) human monocyte-derived DC. The EBI1/CCR7 expressed in mature DC is functional because ELC/MIP-3β, recently identified as a ligand of EBI1/CCR7, induces a rise in intracellular free calcium concentrations and directional migration of human monocyte-derived mature DC (HLA-DRhigh, CD1alow, CD14−, CD25+, CD83+, and CD86high) in a dose-dependent manner, but not of immature DC (HLA-DRlow, CD1ahigh, CD14−, CD25−, CD83−, and CD86−). In contrast, macrophage inflammatory protein-1α (MIP-1α), monocyte chemotactic protein-3 (MCP-3), and RANTES are active on immature DC but not on mature DC. Thus, it seems likely that MIP-1α, MCP-3, and RANTES can mediate the migration of immature DC located in peripheral sites, whereas ELC/MIP-3β can direct the migration of Ag-carrying DC from peripheral inflammatory sites, where DC are stimulated to up-regulate the expression of EBI1/CCR7, to lymphoid organs. It is postulated that different chemokines and chemokine receptors are involved in DC migration in vivo, depending on the maturation state of DC.

Genealogy of the CCR5 locus and chemokine system gene variants associated with altered rates of HIV-1 disease progression

Abstract: Allelic variants for the HIV-1 co-receptors chemokine receptor 5 (CCR5) and CCR2, as well as the ligand for the co-receptor CXCR4, stromal-derived factor (SDF-1), have been associated with a delay in disease progression. We began this study to test whether polymorphisms in the CCR5 regulatory regions influence the course of HIV-1 disease, as well as to examine the role of the previously identified allelic variants in 1,090 HIV-1 infected individuals. Here we describe the evolutionary relationships between the phenotypically important CCR5 alleles, define precisely the CCR5 regulatory sequences that are linked to the CCR5-delta32 and CCR2-641 polymorphisms, and identify genotypes associated with altered rates of HIV-1 disease progression. The disease-retarding effects of the CCR2-641 allele were found in African Americans but not in Caucasians, and the SDF1-3'A/3'A genotype was associated with an accelerated progression to death. In contrast, the CCR5-delta32 allele and a CCR5 promoter mutation with which it is tightly linked were associated with limited disease-retarding effects. Collectively, these findings draw attention to a complex array of genetic determinants in the HIV-host interplay.

CD4-Induced Conformational Changes in the Human Immunodeficiency Virus Type 1 gp120 Glycoprotein: Consequences for Virus Entry and Neutralization

Abstract: Human immunodeficiency virus type 1 (HIV-1) entry into target cells involves sequential binding of the gp120 exterior envelope glycoprotein to CD4 and to specific chemokine receptors. Soluble CD4 (sCD4) is thought to mimic membrane-anchored CD4, and its binding alters the conformation of the HIV-1 envelope glycoproteins. Two cross-competing monoclonal antibodies, 17b and CG10, that recognize CD4-inducible gp120 epitopes and that block gp120-chemokine receptor binding were used to investigate the nature and functional significance of gp120 conformational changes initiated by CD4 binding. Envelope glycoproteins derived from both T-cell line-adapted and primary HIV-1 isolates exhibited increased binding of the 17b antibody in the presence of sCD4. CD4-induced exposure of the 17b epitope on the oligomeric envelope glycoprotein complex occurred over a wide range of temperatures and involved movement of the gp120 V1/V2 variable loops. Amino acid changes that reduced the efficiency of 17b epitope exposure following CD4 binding invariably compromised the ability of the HIV-1 envelope glycoproteins to form syncytia or to support virus entry. Comparison of the CD4 dependence and neutralization efficiencies of the 17b and CG10 antibodies suggested that the epitopes for these antibodies are minimally accessible following attachment of gp120 to cell surface CD4. These results underscore the functional importance of these CD4-induced changes in gp120 conformation and illustrate viral strategies for sequestering chemokine receptor-binding regions from the humoral immune response.

Chemokine Sequestration by Viral Chemoreceptors as a Novel Viral Escape Strategy: Withdrawal of Chemokines from the Environment of Cytomegalovirus-infected Cells

Abstract: Human cytomegalovirus (HCMV), a betaherpesvirus, has developed several ways to evade the immune system, notably downregulation of cell surface expression of major histocompatibility complex class I heavy chains. Here we report that HCMV has devised another means to compromise immune surveillance mechanisms. Extracellular accumulation of both constitutively produced monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor–superinduced RANTES (regulated on activation, normal T cell expressed and secreted) was downregulated in HCMV-infected fibroblasts in the absence of transcriptional repression or the expression of polyadenylated RNA for the cellular chemokine receptors CCR-1, CCR-3, and CCR-5. Competitive binding experiments demonstrated that HCMV-infected cells bind RANTES, MCP-1, macrophage inflammatory protein (MIP)-1β, and MCP-3, but not MCP-2, to the same receptor as does MIP-1α, which is not expressed in uninfected cells. HCMV encodes three proteins with homology to CC chemokine receptors: US27, US28, and UL33. Cells infected with HCMV mutants deleted of US28, or both US27 and US28 genes, failed to downregulate extracellular accumulation of either RANTES or MCP-1. In contrast, cells infected with a mutant deleted of US27 continues to bind and downregulate those chemokines. Depletion of chemokines from the culture medium was at least partially due to continuous internalization of extracellular chemokine, since exogenously added, biotinylated RANTES accumulated in HCMV-infected cells. Thus, HCMV can modify the chemokine environment of infected cells through intense sequestering of CC chemokines, mediated principally by expression of the US28-encoded chemokine receptor.

Blockade of Chemokine Activity by a Soluble Chemokine Binding Protein from Vaccinia Virus

Abstract: Chemokines direct migration of immune cells into sites of inflammation and infection. Chemokine receptors are seven-transmembrane domain proteins that, in contrast to other cytokine receptors, cannot be easily engineered as soluble chemokine inhibitors. Poxviruses encode several soluble cytokine receptors to evade immune surveillance, providing new strategies for immune modulation. Here we show that vaccinia virus and other orthopoxviruses (cowpox and camelpox) express a secreted 35-kDa chemokine binding protein (vCKBP) with no sequence similarity to known cellular chemokine receptors. The vCKBP binds CC, but not CXC or C, chemokines with high affinity ( K d = 0.1–15 nM for different CC chemokines), blocks the interaction of chemokines with cellular receptors, and inhibits chemokine-induced elevation of intracellular calcium levels and cell migration in vitro, thus representing a soluble inhibitor that binds and sequesters chemokines. The potential of vCKBP as a therapeutic agent in vivo was illustrated in a guinea pig skin model by the blockade of eotaxin-induced eosinophil infiltration, a feature of allergic inflammatory reactions. Furthermore, vCKBP may enable the rational design of antagonists to neutralize pathogens that use chemokine receptors to initiate infection, such as HIV or the malarial parasite.

Intracellular and Surface Expression of the HIV-1 Coreceptor CXCR4/Fusin on Various Leukocyte Subsets: Rapid Internalization and Recycling Upon Activation

Abstract: We describe the expression and regulation of the HIV-1 coreceptor CXCR4/fusin Using anti-CXCR4 mAb, we demonstrate that this chemokine receptor is highly expressed on neutrophils, monocytes, B cells, and naive T cells among peripheral blood cells In secondary lymphoid organs CXCR4 was found to be expressed on B cells However, individual variations with regard to surface expression could be observed on T cells Expression of the receptor is not confined to the cell surface, as large amounts of intracellular stores can be found on various leukocytes Upon activation with phorbol esters the amount of cell surface-expressed CXCR4 on lymphocytes increases twofold within 30 s before it is completely down-regulated within the next 2 min Incubation of leukocytes with stroma derived factor-1α, the natural ligand for CXCR4, induces down-regulation of up to 60% of surface-expressed receptors in a pertussis toxin-insensitive manner Interestingly, receptor cross-linking caused by incubation of cells with anti-CXCR4 mAb triggers receptor trafficking, in that the receptor is rapidly internalized and recycled to the cell surface Therefore, receptor internalization and recycling may regulate the functional interaction of the receptor with envelope proteins during an initial step of HIV-1 infection

ChemR23, a putative chemoattractant receptor, is expressed in monocyte-derived dendritic cells and macrophages and is a coreceptor for SIV and some primary HIV-1 strains.

Abstract: Leukocyte chemoattractants act through a rapidly growing subfamily of G protein-coupled receptors. We report the cloning of a novel human gene encoding an orphan receptor (ChemR23) related to the C3a, C5a and formyl Met-Leu-Phe receptors, and more distantly to the subfamilies of chemokine receptors. ChemR23 transcripts were found to be abundant in monocyte-derived dendritic cells and macrophages, treated or not with LPS. Low expression could also be detected by reverse transcription-PCR in CD4+ T lymphocytes. The gene encoding ChemR23 was assigned by radiation hybrid mapping to the q21.2-21.3 region of human chromosome 12, outside the gene clusters identified so far for chemoattractant receptors. Given the increasing number of chemoattractant receptors used by HIV-1, HIV-2 and SIV as coreceptors, ChemR23 was tested in fusion assays for potential coreceptor activity by a range of viral strains. None of the tested HIV-2 strains made use of ChemR23 as a coreceptor, but several SIV strains (SIVmac316, SIVmac239, SIVmacl7E-Fr and SIVsm62A), as well as a primary HIV-1 strain (92UG024-2) used it efficiently. ChemR23 therefore appears as a coreceptor for immunodeficiency viruses that does not belong to the chemokine receptor family. It is also a putative chemoattractant receptor relatively specific for antigen-presenting cells, and it could play an important role in the recruitment or trafficking of these cell populations. Future work will be required to identify the ligand(s) of this new G protein-coupled receptor and to define its precise role in the physiology of dendritic cells and macrophages.

Immunohistochemical Study of the β-Chemokine Receptors CCR3 and CCR5 and Their Ligands in Normal and Alzheimer's Disease Brains

Abstract: Chemokines belong to an expanding family of cytokines the primary function of which is recruitment of leukocytes to inflammatory sites. Recent evidence has shown their presence in the central nervous system. Because inflammatory responses have been implicated in the pathogenesis of Alzheimer's disease (AD), we studied the expression of CCR3, CCR5, and their ligands in normal and AD brains by immunohistochemistry. CCR3 and CCR5 are present on microglia of both control and AD brains, with increased expression on some reactive microglia in AD. Immunohistochemistry for MIP-1β, MIP-1α, RANTES, eotaxin, and MCP-3 (ligands for CCR5 and/or CCR3) revealed the presence of MIP-1β predominantly in a subpopulation of reactive astrocytes, which were more widespread in AD than control brains, and MIP-1α predominantly in neurons and weakly in some microglia in both AD and controls. Many of the CCR3 + or CCR5 + reactive microglia and MIP-1β + reactive astrocytes were found associated with amyloid deposits. Immunoreactivity for eotaxin, RANTES, and MCP-3 were not detected. Detection of these β-chemokine receptors on microglia and some of their ligands in reactive astrocytes and neurons as well as microglia suggests a role for this system in glial-glial and glial-neuronal interactions, potentially influencing the progression of AD.