Polymorphism in the 5' regulatory region of the B-lymphocyte activating factor gene is associated with the Ro/La autoantibody response and serum BAFF levels in primary Sjogren's syndrome

OBJECTIVE

To investigate the association between haplotypes in the 5' regulatory region of the B-lymphocyte activating factor (BAFF) gene, disease susceptibility and serum BAFF (s-BAFF) levels in Caucasian primary SS (pSS) patients.

METHODS

Case-control study in an established pSS cohort with PCR-RFLP genotyping for four SNPs (-2841 T-->C, -2704 T-->C, -2701 T-->A, -871 C-->T), which tag a haplotype block in the 5' regulatory region of the BAFF gene and s-BAFF determination by ELISA.

RESULTS

s-BAFF levels were elevated in Ro/La-positive pSS patients (n = 85, 1770 pg/ml) compared with both Ro/La-negative pSS patients (n = 27, 1193 pg/ml) and controls (n = 59, 1171 pg/ml), P < 0.001. s-BAFF increased with diversification of the anti-Ro/La antibody response, but was not correlated with age, RF or immunoglobulin G levels. There were four common BAFF haplotypes. While the CTAT haplotype was associated with Ro/La-positive pSS [odds ratio (OR) 2.6; 95% CI 1.7, 4.1; P = 0.00004], the TTTT haplotype was associated with elevated s-BAFF in autoantibody-positive pSS (n = 85; 88% females; P = 0.008). The shared -871 T allele had no independent contribution to disease susceptibility or s-BAFF.

CONCLUSIONS

Disease susceptibility for Ro/La-positive pSS is increased with the CTAT haplotype, but not associated with high s-BAFF levels. Elevated s-BAFF levels in pSS are associated with the TTTT haplotype and may be a secondary phenomenon in Ro/La-positive pSS. While both haplotypes carry the -871 T allele, this allele is not independently associated with disease susceptibility.

Overlapping gene expression profiles in rheumatoid fibroblast-like synoviocytes induced by the proinflammatory cytokines interleukin-1 ? and tumor necrosis factor

OBJECTIVE AND DESIGN

The development of therapies directed against TNF alpha and IL-1 beta has underscored the importance of these cytokines in rheumatoid arthritis (RA). In this study, oligonucleotide microarrays were used to identify novel transcriptional events mediated by TNF alpha and IL-1 beta.

METHODS

In this study we have used Affymetrix U95A GeneChips representing 12,600 full-length human genes to identify transcriptional events mediated by these cytokines. Fibroblast-like synoviocytes were cultured from rheumatoid synovium from RA patients and stimulated with TNF alpha and IL-1 beta. Gene transcript levels were determined using Affymetrix U95A GeneChips representing 12,600 full-length human genes.

RESULTS

A large number of differentially regulated genes were identified (1.7% of array-displayed genes for TNF alpha and 2.4% for IL-1 beta), and the validity of the array protocol was subsequently confirmed using real-time PCR. The majority of the differentially expressed genes were regulated by both TNF alpha and IL-1 beta, reflecting the distal signaling pathways shared by these cytokines. A large number of novel TNF alpha and IL-1 beta-regulated genes were identified.

CONCLUSIONS

A panel of novel TNF alpha- and IL-1 beta-regulated genes was identified, and these are promising candidates for further study in relation to RA and other inflammatory diseases.

Levels of BAFF in serum in primary biliary cirrhosis and autoimmune diabetes

Levels of the B-cell activating cytokine BAFF are increased in serum in various autoimmune disease, and particularly Sjögren's syndrome in which there is evident B-lymphocyte proliferation. Studies in two autoimmune disease in which B-cell proliferation is less evident, primary biliary cirrhosis (PBC), and adult-onset Type 1 diabetes, showed serum levels of BAFF to be mostly in the normal range. A single raised level among eight sera tested in one patient studied with autoimmune hepatitis (AH) coincided with a relapse of the disease. Increased levels of BAFF in human sera, indexing a potent antigenic drive on B-cell production and survival in some autoimmune diseases, may mark only particular stages in the evolution of such diseases.

Gene microarrays reveal extensive differential gene expression in both CD4(+) and CD8(+) type 1 and type 2 T cells

An important subdivision of effector T cells can be made based on patterns of cytokine production and functional programs. Type 1 T cells produce IFN-gamma and protect against viral pathogens, whereas type 2 cells produce cytokines such as IL-4 and IL-5 and protect against large extracellular parasites. Both CD4(+) and CD8(+) T cells can be polarized into type 1 or type 2 cytokine-secreting cells, suggesting that both populations play a regulatory role in immune responses. In this study, we used high-density oligonucleotide arrays to produce a comprehensive picture of gene expression in murine CD4(+) Th1 and Th2 cells, as well as CD8(+) type 1 and type 2 T cells. Polarized type 1 and 2 cells transcribed mRNA for an unexpectedly large number of genes, most of which were expressed in a similar fashion between type 1 and type 2 cells. However, >100 differentially expressed genes were identified for both the CD4(+) and CD8(+) type 1 and 2 subsets, many of which have not been associated with T cell polarization. These genes included cytokines, transcription factors, molecules involved in cell migration, as well as genes with unknown function. The program for type 1 or type 2 polarization was similar for CD4(+) and CD8(+) cells, since gene expression patterns were roughly the same. The expression of select genes was confirmed using real-time PCR. The identification of genes associated with T cell polarization may give important insights into functional and phenotypic differences between effector T cell subsets and their role in normal responses and inflammatory disease.

Monocyte chemotactic protein-1, -2, and -3 are distinctively expressed in portal tracts and granulomata in primary biliary cirrhosis: implications for pathogenesis

The monocyte chemotactic proteins (MCPs) form a distinct structurally related subclass of C-C chemokines. MCPs select specific target cells due to binding to a distinct set of chemokine receptors and because of their effects on monocytes, and may participate in the process of granuloma formation during bacterial and/or mycobacterial infections. The aetiology of primary biliary cirrhosis (PBC) is still unclear, although bacterial infection and autoimmune processes have been implicated. In this study, the expression of three of the most potent monocyte chemoattractants, MCP-1, -2, and -3, was examined in patients with PBC and the data were compared with results for other liver diseases including primary sclerosing cholangitis (PSC), chronic viral hepatitis C, hepatic sarcoidosis, and normal liver. MCP-1 was expressed mainly in biliary epithelial cells of all liver specimens, irrespective of the cause of disease. Some mononuclear leukocytes in the portal tract expressed MCP-1 in all the disease groups examined and there were no significant differences in frequency between these groups. In contrast, more than 80% of PBC livers showed MCP-2- and MCP-3-positive mononuclear leukocyte infiltration in portal tracts, particularly around the bile ducts, whereas such cells were far less frequent in the other disease groups or in normal livers. Epithelioid granulomata of PBC patients contained MCP-2- and MCP-3-positive cells at their edge. In double staining experiments, more than 60% of the MCP-positive mononuclear cells co-expressed CD68, suggesting that a proportion of MCP-2- and MCP-3-positive cells are derived from monocytes. These monocytes expressing MCP-2 and MCP-3 may be responsible for the chemotactic activity of more monocytes. Such an expression pattern of MCP-1, -2 and -3 in portal tracts seems to be distinctive for PBC. This pattern underlines the importance of MCP-1, -2, and -3 in the recruitment of monocytes and possibly T lymphocytes into portal tracts, around the injured bile ducts, and into epithelioid granulomata in PBC. The data further implicate bacterial materials derived from bile in the overall pathogenesis of PBC.

Chemokines: immunology's high impact factors

Chemokines facilitate leukocyte migration and positioning as well as other processes such as angiogenesis and leukocyte degranulation. The burgeoning knowledge on chemokines and their receptors has influenced many aspects of immunology, in part because cell migration is intimately related to leukocyte function. This overview assesses the impact that chemokines have had on our understanding of immunology and infectious diseases. These include the role of chemokines in leukocyte-endothelial cell interactions; dendritic cell function; T cell differentiation and function; inflammatory diseases; mucosal and subcutaneous immunity; and subversion of immune responses by viruses, including HIV-1. This knowledge heralds new opportunities for the manipulation of immune responses and the development of new anti-inflammatory therapies. It has also provided a new perspective on the functioning of the immune system.

Monocyte chemotactic protein-1, -2, and -3 are distinctively expressed in portal tracts and granulomata in primary biliary cirrhosis: implications for pathogenesis

The monocyte chemotactic proteins (MCPs) form a distinct structurally related subclass of C-C chemokines. MCPs select specific target cells due to binding to a distinct set of chemokine receptors and because of their effects on monocytes, and may participate in the process of granuloma formation during bacterial and/or mycobacterial infections. The aetiology of primary biliary cirrhosis (PBC) is still unclear, although bacterial infection and autoimmune processes have been implicated. In this study, the expression of three of the most potent monocyte chemoattractants, MCP-1, -2, and -3, was examined in patients with PBC and the data were compared with results for other liver diseases including primary sclerosing cholangitis (PSC), chronic viral hepatitis C, hepatic sarcoidosis, and normal liver. MCP-1 was expressed mainly in biliary epithelial cells of all liver specimens, irrespective of the cause of disease. Some mononuclear leukocytes in the portal tract expressed MCP-1 in all the disease groups examined and there were no significant differences in frequency between these groups. In contrast, more than 80% of PBC livers showed MCP-2- and MCP-3-positive mononuclear leukocyte infiltration in portal tracts, particularly around the bile ducts, whereas such cells were far less frequent in the other disease groups or in normal livers. Epithelioid granulomata of PBC patients contained MCP-2- and MCP-3-positive cells at their edge. In double staining experiments, more than 60% of the MCP-positive mononuclear cells co-expressed CD68, suggesting that a proportion of MCP-2- and MCP-3-positive cells are derived from monocytes. These monocytes expressing MCP-2 and MCP-3 may be responsible for the chemotactic activity of more monocytes. Such an expression pattern of MCP-1, -2 and -3 in portal tracts seems to be distinctive for PBC. This pattern underlines the importance of MCP-1, -2, and -3 in the recruitment of monocytes and possibly T lymphocytes into portal tracts, around the injured bile ducts, and into epithelioid granulomata in PBC. The data further implicate bacterial materials derived from bile in the overall pathogenesis of PBC.

Enhanced levels of functional HIV-1 co-receptors on human mucosal T cells demonstrated using intestinal biopsy tissue

OBJECTIVE

To examine compartmental differences in co-receptor expression on CD4 lymphocytes between blood and gut using endoscopic biopsies.

DESIGN

Mucosal and peripheral CD4 T cells from healthy controls were compared for co-receptor expression and vulnerability to infection by HIV-1.

METHODS

Expression of CCR5 and CXCR4 was quantified by flow cytometry on isolated mucosal CD4 lymphocytes obtained from endoscopic biopsies and blood from healthy controls. Vulnerability to in vitro infection by both R5 and X4 strains was assessed by measuring p24.

RESULTS

Biopsies yielded sufficient lymphocytes for flow cytometric characterization and infectivity studies. The percentage of mucosal CD4 T lymphocytes that expressed CCR5 and the per cell expression of CCR5 were both significantly increased compared with that in peripheral blood CD4 T lymphocytes. CXCR4 was expressed on the majority of CD4 lymphocytes in both compartments. In vitro infection of mucosal mononuclear cells supported greater viral replication of both R5 and X4 strains than peripheral blood mononuclear cells.

CONCLUSIONS

Enhanced expression of CXCR4 and CCR5 on CD4 lymphocytes in normal intestinal mucosa predicts increased vulnerability to infection by both R5 and X4 HIV-1. Endoscopic biopsies provide a useful mucosal tissue sampling technique to identify compartmental immunologic differences that may be exploited by HIV-1 in establishing initial mucosal infection.

The role of chemokine receptors in primary, effector, and memory immune responses

The immune system is composed of single cells, and its function is entirely dependent on the capacity of these cells to traffic, localize within tissues, and interact with each other in a precisely coordinated fashion. There is growing evidence that the large families of chemokines and chemokine receptors provide a flexible code for regulating cell traffic and positioning in both homeostatic and inflammatory conditions. The regulation of chemokine receptor expression during development and following cell activation explains the complex migratory pathways taken by dendritic cells, T and B lymphocytes, providing new insights into the mechanisms that control priming, effector function, and memory responses.

Monoclonal antibody screening of a phage-displayed random peptide library reveals mimotopes of chemokine receptor CCR5: implications for the tertiary structure of the receptor and for an N-terminal binding site for HIV-1 gp120

The chemokine receptor CCR5 contains seven transmembrane-spanning domains. It binds chemokines and acts as co-receptor for macrophage (m)-tropic (or R5) strains of HIV-1. Monoclonal antibodies (mAb) to CCR5, 3A9 and 5C7, were used for biopanning a nonapeptide cysteine (C)-constrained phage-displayed random peptide library to ascertain contact residues and define tertiary structures of possible epitopes on CCR5. Reactivity of antibodies with phagotopes was established by enzyme-linked immunosorbent assay (ELISA). mAb 3A9 identified a phagotope C-HASIYDFGS-C (3A9 / 1), and 5C7 most frequently identified C-PHWLRDLRV-C (5C7 / 1). Corresponding peptides were synthesized. Phagotopes and synthetic peptides reacted in ELISA with corresponding antibodies and synthetic peptides inhibited antibody binding to the phagotopes. Reactivity by immunofluorescence of 3A9 with CCR5 was strongly inhibited by the corresponding peptide. Both mAb 3A9 and 5C7 reacted similarly with phagotopes and the corresponding peptide selected by the alternative mAb. The sequences of peptide inserts of phagotopes could be aligned as mimotopes of the sequence of CCR5. For phage 3A9 / 1, the motif SIYD aligned to residues at the N terminus and FG to residues on the first extracellular loop; for 5C7 / 1, residues at the N terminus, first extracellular loop, and possibly the third extracellular loop could be aligned and so would contribute to the mimotope. The synthetic peptides corresponding to the isolated phagotopes showed a CD4-dependent reactivity with gp120 of a primary, m-tropic HIV-1 isolate. Thus reactivity of antibodies raised to CCR5 against phage-displayed peptides defined mimotopes that reflect binding sites for these antibodies and reveal a part of the gp120 binding sites on CCR5.

HIV-1 infectability of CD4+ lymphocytes with relation to beta-chemokines and the CCR5 coreceptor

CD4+ lymphocytes exhibit variable permissiveness to the replication of HIV-1. A cohort of sexually-exposed-yet-uninfected individuals were previously shown to have CD4+ lymphocytes refractory for M-tropic viral replication. In particular, two individuals from this population whose CD4+ lymphocytes exhibited complete resistance to M-tropic viral replication were later shown to be homozygous for a 32bp (delta32) deletion in the gene encoding for CCR5. In screening diverse populations, HIV-1 infected individuals heterozygous for the delta32 allele were statistically favored in their disease course to harbor lower viral loads and exhibit slower rates of CD4+ cell loss when compared to control CCR5 wild-type individuals. Further comparative analysis between individuals in the exposed but uninfected cohort who demonstrated intermediate levels of in vitro viral replication and CD4+ lymphocytes isolated from uninfected delta32 heterozygous individuals indicate that reduced levels of in vitro M-tropic replication are a CCR5-related phenomenon: CD4+ lymphocytes from these individuals were more sensitive to the HIV-1 blocking effects of recombinant chemokines, displayed lower CCR5 cell surface expression levels and a proportionate increase in the production of RANTES when compared to CD4+ lymphocytes from control individuals. These results suggest that the CCR5 phenotype is important in determining the replicative capacity of M-tropic HIV-1 in vitro. The implications of these results with relation to HIV-1 transmission and disease progression are discussed.

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

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.

Immunohistochemical study of the beta-chemokine receptors CCR3 and CCR5 and their ligands in normal and Alzheimer's disease brains

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-1beta, MIP-1alpha, RANTES, eotaxin, and MCP-3 (ligands for CCR5 and/or CCR3) revealed the presence of MIP-1beta predominantly in a subpopulation of reactive astrocytes, which were more widespread in AD than control brains, and MIP-1alpha predominantly in neurons and weakly in some microglia in both AD and controls. Many of the CCR3+ or CCR5+ reactive microglia and MIP-1beta+ reactive astrocytes were found associated with amyloid deposits. Immunoreactivity for eotaxin, RANTES, and MCP-3 were not detected. Detection of these beta-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.

The C-C chemokine receptor CCR3 participates in stimulation of eosinophil arrest on inflammatory endothelium in shear flow

Chemokines are widely hypothesized to stimulate firm adhesion of leukocytes on endothelium in shear flow. Thus far, this has been demonstrated experimentally for exogenously added chemoattractants, but not for those released by endothelium. We found that human umbilical cord endothelial cells (HUVEC) stimulated with TNF-alpha and IFN-gamma secreted eosinophil chemoattractants into the culture supernatant. This material induced transendothelial chemotaxis, stimulated eosinophil binding to purified intercellular adhesion molecule 1, and augmented binding to purified vascular cell adhesion molecule 1 in a 3-min static assay. Chemotaxis and stimulation of adhesion were abrogated completely by the pretreatment of eosinophils with an mAb to the C-C chemokine receptor 3 (CCR3). Eosinophils accumulated efficiently on HUVEC stimulated with TNF-alpha and IFN-gamma in shear flow at 1.5 dyn/cm2. CCR3 mAb slightly but significantly reduced eosinophil arrest and accumulation, by preventing development of firm adhesion by some of the tethered eosinophils, so that they detached within 30 s after the initial tethering. In the presence of mAb to the alpha4 integrin subunit, the effect of CCR3 mAb was more prominent, and approximately half of eosinophil arrest and accumulation was abolished. Inhibition by CCR3 mAb in the presence of beta2 integrin mAb was similar to that in control eosinophils. This is the first evidence that endothelial cell-derived chemokines can activate firm adhesion through alpha4 and beta2 integrins even in the presence of shear flow.

Reduced HIV-1 infectability of CD4+ lymphocytes from exposed-uninfected individuals: association with low expression of CCR5 and high production of beta-chemokines

We examined the human immunodeficiency virus type 1 infectability of CD4+ lymphocytes isolated from CCR5 wild-type individuals, individuals heterozygous for the delta32 allele of CCR5, and HIV-1-exposed but uninfected (EU) individuals who had CD4+ lymphocytes refractory to M-tropic viral replication. None of the EU individuals were found to be heterozygous for the delta32 allele. The CD4+ lymphocytes isolated from CCR5/delta32 and EU individuals were less infectable with an M-tropic viral isolate of HIV-1 than CCR5/CCR5 control individuals but were equally as infectable with a T-tropic viral isolate. The restriction to M-tropic viral isolate replication did not associate with any profound genotypic change in the CCR5 gene. CD4+ lymphocytes from CCR5/delta32 and CCR5/CCR5 EU individuals were more sensitive to the HIV-inhibitory effects of the recombinant beta-chemokines RANTES, MIP-1alpha, and MIP-1beta than were CD4+ lymphocytes from CCR5/CCR5 control individuals. CD4+ lymphocytes from EU individuals also showed increased sensitivity to recombinant beta-chemokines and low surface expression of CCR5. A phenotype of low CCR5 expression and high secretion of beta-chemokines is associated with reduced infectability of cells by M-tropic HIV-1. This phenotype may also be associated with protection against sexual transmission of HIV-1.

Role of the beta-chemokine receptors CCR3 and CCR5 in human immunodeficiency virus type 1 infection of monocytes and microglia

Human immunodeficiency virus type 1 (HIV-1) infection in mononuclear phagocyte lineage cells (monocytes, macrophages, and microglia) is a critical component in the pathogenesis of viral infection. Viral replication in macrophages serves as a reservoir, a site of dissemination, and an instigator for neurological sequelae during HIV-1 disease. Recent studies demonstrated that chemokine receptors are necessary coreceptors for HIV-1 entry which determine viral tropism for different cell types. To investigate the relative contribution of the beta-chemokine receptors CCR3 and CCR5 to viral infection of mononuclear phagocytes we utilized a panel of macrophage-tropic HIV-1 strains (from blood and brain tissue) to infect highly purified populations of monocytes and microglia. Antibodies to CD4 (OKT4A) abrogated HIV-1 infection. The beta chemokines and antibodies to CCR3 failed to affect viral infection of both macrophage cell types. Antibodies to CCR5 (3A9) prevented monocyte infection but only slowed HIV replication in microglia. Thus, CCR5, not CCR3, is an essential receptor for HIV-1 infection of monocytes. Microglia express both CCR5 and CCR3, but antibodies to them fail to inhibit viral entry, suggesting the presence of other chemokine receptors for infection of these cells. These studies demonstrate the importance of mononuclear phagocyte heterogeneity in establishing HIV-1 infection and persistence.

Human eotaxin induces alpha 4 and beta 2 integrin-dependent eosinophil accumulation in rat skin in vivo: delayed generation of eotaxin in response to IL-4

The CC chemokine eotaxin, originally purified from bronchoalveolar lavage fluid of sensitized guinea pigs following allergen challenge, is a potent eosinophil-selective chemoattractant. In the present study, we have used (111)In-eosinophils and human eotaxin to characterize the profile of chemokine-induced eosinophil accumulation in vivo in rat skin. Intradermally injected eotaxin caused a dose-dependent accumulation of (111)In-eosinophils. Time course studies indicated that the response was rapid, since all the accumulation occurred within the first 1 to 2 h of eotaxin injection. The i.v. administration of anti-intercellular adhesion molecule-1, anti-vascular cell adhesion molecule-1, or anti-alpha4 integrin mAbs significantly inhibited the eosinophil accumulation induced by 100 pmol of human eotaxin by 73, 43, and 67%, respectively. Further, when (111)In-eosinophils were pretreated in vitro with anti-alpha4 integrin or anti-beta2 integrin mAbs, or with a combination of both mAbs, eotaxin-induced responses in vivo were reduced by 52, 49, and 68%, respectively. Eosinophil accumulation induced by intradermal IL-4, but not that induced by TNF-alpha or leukotriene B4, appeared to be mediated in part by endogenously generated eotaxin. Anti-eotaxin Abs significantly inhibited (54%) the later phases (24-28 h) but not the early phase (0-4 h) of the response to IL-4. This was consistent with eotaxin mRNA expression peaking at 18 h after IL-4 injection. Our findings show that human eotaxin is a potent inducer of eosinophil accumulation in vivo, this response being dependent on alpha4 integrin/vascular cell adhesion molecule-1 and beta2 integrin/intercellular adhesion molecule-1 adhesion pathways. Further, the eosinophil accumulation in response to IL-4 is partly mediated by endogenously generated eotaxin.

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

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-gamma-inducible protein 10 (IP-10) and monokine induced by IFN-gamma (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 beta inhibited CCR3, but enhanced CCR4 and CCR7 expression, whereas interferon alpha 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 CXCR3 mediates rapid and shear-resistant adhesion-induction of effector T lymphocytes by the chemokines IP10 and Mig

Integrin-mediated adhesion to the vascular endothelium is an essential step in leukocyte diapedesis. We show that the chemokines 10-kDa inflammatory protein (IP10) and monokine induced by IFN (Mig) induce rapid and transient adhesion of human IL-2-stimulated T lymphocytes (IL-2 T cells) to immobilized integrin ligands through their receptor CXCR3, which is selectively expressed on activated T cells. Induction of adhesion by IP10 and Mig was already observed at subnanomolar concentrations and was maximal at 5-10 nM, resulting in three- to sixfold increase in adhesion of IL-2 T cells over background. No effect was seen with resting naive/memory T cells which lack CXCR3 and migration responses to IP10 and Mig. Both chemokines are produced in human umbilical vein endothelial cells (HUVEC) upon stimulation with IFN-gamma and TNF-alpha. These chemokines induce IL-2 T cell adhesion also when captured on the surface of endothelial cells. Under conditions of flow, IL-2 T cells roll and rapidly adhere to IP10/Mig-expressing HUVEC, and anti-CXCR3 mAb treatment reduces arrest and firm adhesion. This is the first study that shows chemokine-induced adhesion in activated memory/effector T cells which represent the fraction of T cells that are selectively mobilized in inflammation. The critical role of IFN-gamma as inducer of IP10/Mig production in HUVEC indicates that these chemokines are essential mediators of effector T cell recruitment to IFN-gamma-dependent pathologies.

Mature dendritic cells respond to SDF-1, but not to several beta-chemokines

Immature dendritic cells (DCs) are highly motile, but after differentiation they stop migration. Chemokines are chemotactic cytokines that direct leukocyte trafficking, therefore we looked for the expression and function of chemokine receptors in immature and mature DCs. As a model, we used the human DCs that develop from CD14+ peripheral blood monocytes cultured with GM-CSF and IL-4. After 6-7 days in culture, these cells have the characteristics of immature DCs, but can be induced to mature further by inflammatory stimuli or by monocyte conditioned medium (MCM). Immature DCs express mRNA for CXCR4, CCR3 and CCR5. The receptors are expressed on the cell surface, as assessed with monoclonal antibodies, and are functional (with the exception of CCR3) as assessed by CA++ mobilization in response to specific chemokines. Further differentiation and maturation of DC in MCM causes a downregulation of expression and function of the beta-chemokine receptors, while CXCR4 still remains, and signals a calcium flux on mature DCs. We argue that the downregulation of beta-chemokine receptors during maturation helps to stop DC movement after T cells have been identified in lymphoid organs or at sites of delayed-type hypersensitivity.

The chemokine receptors CXCR3 and CCR5 mark subsets of T cells associated with certain inflammatory reactions

T cells infiltrating inflammatory sites are usually of the activated/memory type. The precise mechanism for the positioning of these cells within tissues is unclear. Adhesion molecules certainly play a role; however, the intricate control of cell migration appears to be mediated by numerous chemokines and their receptors. Particularly important chemokines for activated/memory T cells are the CXCR3 ligands IP-10 and Mig and the CCR5 ligands RANTES, macrophage inflammatory protein-1alpha, and macrophage inflammatory protein-1beta. We raised anti-CXCR3 mAbs and were able to detect high levels of CXCR3 expression on activated T cells. Surprisingly, a proportion of circulating blood T cells, B cells, and natural killer cells also expressed CXCR3. CCR5 showed a similar expression pattern as CXCR3, but was expressed on fewer circulating T cells. Blood T cells expressing CXCR3 (and CCR5) were mostly CD45RO+, and generally expressed high levels of beta1 integrins. This phenotype resembled that of T cells infiltrating inflammatory lesions. Immunostaining of T cells in rheumatoid arthritis synovial fluid confirmed that virtually all such T cells expressed CXCR3 and approximately 80% expressed CCR5, representing high enrichment over levels of CXCR3+ and CCR5+ T cells in blood, 35 and 15%, respectively. Analysis by immunohistochemistry of various inflamed tissues gave comparable findings in that virtually all T cells within the lesions expressed CXCR3, particularly in perivascular regions, whereas far fewer T cells within normal lymph nodes expressed CXCR3 or CCR5. These results demonstrate that the chemokine receptor CXCR3 and CCR5 are markers for T cells associated with certain inflammatory reactions, particularly TH-1 type reactions. Moreover, CXCR3 and CCR5 appear to identify subsets of T cells in blood with a predilection for homing to these sites.

Amino-terminal substitutions in the CCR5 coreceptor impair gp120 binding and human immunodeficiency virus type 1 entry

The CC-chemokine receptor CCR5 is required for the efficient fusion of macrophage (M)-tropic human immunodeficiency virus type 1 (HIV-1) strains with the plasma membrane of CD4+ cells and interacts directly with the viral surface glycoprotein gp120. Although receptor chimera studies have provided useful information, the domains of CCR5 that function for HIV-1 entry, including the site of gp120 interaction, have not been unambiguously identified. Here, we use site-directed, alanine-scanning mutagenesis of CCR5 to show that substitutions of the negatively charged aspartic acid residues at positions 2 and 11 (D2A and D11A) and a glutamic acid residue at position 18 (E18A), individually or in combination, impair or abolish CCR5-mediated HIV-1 entry for the ADA and JR-FL M-tropic strains and the DH123 dual-tropic strain. These mutations also impair Env-mediated membrane fusion and the gp120-CCR5 interaction. Of these three residues, only D11 is necessary for CC-chemokine-mediated inhibition of HIV-1 entry, which is, however, also dependent on other extracellular CCR5 residues. Thus, the gp120 and CC-chemokine binding sites on CCR5 are only partially overlapping, and the former site requires negatively charged residues in the amino-terminal CCR5 domain.

Genetic subtype-independent inhibition of human immunodeficiency virus type 1 replication by CC and CXC chemokines

We have studied the breadth and potency of the inhibitory actions of the CC chemokines macrophage inhibitory protein 1alpha (MIP-1alpha), MIP-1beta, and RANTES against macrophage-tropic (M-tropic) primary isolates of human immunodeficiency virus type 1 (HIV-1) and of the CXC chemokine stromal cell-derived factor 1alpha against T-cell-tropic (T-tropic) isolates, using mitogen-stimulated primary CD4+ T cells as targets. There was considerable interisolate variation in the sensitivity of HIV-1 to chemokine inhibition, which was especially pronounced for the CC chemokines and M-tropic strains. However, this variation was not obviously dependent on the genetic subtype (A through F) of the virus isolates. Peripheral blood mononuclear cell donor-dependent variation in chemokine inhibition potency was also observed. Among the CC chemokines, the rank order for potency (from most to least potent) was RANTES, MIP-1beta, MIP-1alpha. Some M-tropic isolates, unexpectedly, were much more sensitive to RANTES than to MIP-1beta, whereas other isolates showed sensitivities comparable to those of these two chemokines. Down-regulation of the CCR5 and CXCR4 receptors occurred in cells treated with the cognate chemokines and probably contributes to anti-HIV-1 activity. Thus, for CCR5, the rank order for down-regulation was also RANTES, MIP-1beta, MIP-1alpha.

Enhanced expression of eotaxin and CCR3 mRNA and protein in atopic asthma. Association with airway hyperresponsiveness and predominant co-localization of eotaxin mRNA to bronchial epithelial and endothelial cells

Eotaxin is a newly discovered C-C chemokine which preferentially attracts and activates eosinophil leukocytes by acting specifically on its receptor CCR3. The airway inflammation characteristic of asthma is believed to be, at least in part, the result of eosinophil-dependent tissue injury. This study was designed to determine whether there is increased expression of eotaxin and CCR3 in the bronchial mucosa of asthmatics and whether this is associated with disease severity. The major sources of eotaxin and CCR3 mRNA were determined by co-localization experiments. Bronchial mucosal biopsy samples were obtained from atopic asthmatics and normal non-atopic controls. Eotaxin and CCR3 mRNA were identified in tissue sections by in situ hybridization (ISH) using radiolabeled riboprobes and their protein product visualized by immunohistochemistry (IHC). Co-localization experiments were performed by double ISH/IHC. Eotaxin and CCR3 (mRNA and protein) were significantly elevated in atopic asthmatics compared with normal controls. In the asthmatics there was a highly significant inverse correlation between eotaxin mRNA+ cells and the histamine provocative concentration causing a 20% fall in FEV1 (PC20). Cytokeratin-positive epithelial cells and CD31+ endothelial cells were the major source of eotaxin mRNA whereas CCR3 co-localized predominantly to eosinophils. These data are consistent with the hypothesis that damage to the bronchial mucosa in asthma involves secretion of eotaxin by epithelial and endothelial cells resulting in eosinophil infiltration mediated via CCR3. Since selective (eotaxin) and non-selective C-C chemokines such as RANTES, MCP-3 and MCP-4 all stimulate eosinophils via CCR3, this receptor is potentially a prime therapeutic target in the spectrum of diseases involving eosinophil-mediated tissue damage.

Functional expression of the eotaxin receptor CCR3 in T lymphocytes co-localizing with eosinophils

BACKGROUND

The chemokine eotaxin is produced at sites of allergic inflammation, binds selectively to the chemokine receptor CCR3 and attracts eosinophil and basophil leukocytes, which express high numbers of this receptor. Responses of T lymphocytes to eotaxin have not been reported so far. We have investigated the expression of CCR3 in T lymphocytes and analysed the properties and in vivo distribution of T lymphocytes expressing this receptor.

RESULTS

In search of chemokine receptors with selective expression in T lymphocytes, we have isolated multiple complementary DNAs (cDNAs) encoding CCR3 from a human CD4+ T-cell cDNA library. T-lymphocyte clones with selectivities for protein and non-protein antigens were analysed for expression of CCR3 and production of Th1- and Th2-type cytokines. Of 13 clones with surface CCR3, nine secreted enhanced levels of interleukin-4 and/or interleukin-5, indicating that CCR3 predominates in Th2-type lymphocytes. CCR3+ T lymphocytes readily migrated in response to eotaxin, and showed the characteristic changes in cytosolic free calcium. Immunostaining of contact dermatitis, nasal polyp and ulcerative colitis tissue showed that CCR3+ T lymphocytes are recruited together with eosinophils and, as assessed by flow cytometry, a large proportion of CD3+ cells extracted from the inflamed skin tissue were CCR3+. By contrast, CCR3+ T lymphocytes were absent from tissues that lack eosinophils, as demonstrated for normal skin and rheumatoid arthritis synovium.

CONCLUSIONS

We show that T lymphocytes co-localizing with eosinophils at sites of allergic inflammation express CCR3, suggesting that eotaxin/CCR3 represents a novel mechanism of T-lymphocyte recruitment. These cells are essential in allergic inflammation, as mice lacking mature T lymphocytes were insensitive to allergen challenge. Surface CCR3 may mark a subset of T lymphocytes that induce eosinophil mobilization and activation through local production of Th2-type cytokines.

Cellular localization of the chemokine receptor CCR5. Correlation to cellular targets of HIV-1 infection

The chemokine receptor CCR5 has recently been described as a co-receptor for macrophage-tropic strains of human immunodeficiency virus (HIV)-1. In this study, using a panel of monoclonal antibodies specific for human CCR5, we show by immunohistochemistry and flow cytometry that CCR5 is expressed by bone-marrow-derived cells known to be targets for HIV-1 infection, including a subpopulation of lymphocytes and monocyte/macrophages in blood, primary and secondary lymphoid organs, and noninflamed tissues. In the central nervous system, CCR5 is expressed on neurons, astrocytes, and microglia. In other tissues, CCR5 is expressed on epithelium, endothelium, vascular smooth muscle, and fibroblasts. Chronically inflamed tissues contain an increased number of CCR5+ mononuclear cells, and the number of immunoreactive cells is directly associated with a histopathological correlate of inflammatory severity. Collectively, these results suggest that CCR5+ cells are recruited to inflammatory sites and, as such, may facilitate transmission of macrophage-tropic strains of HIV-1.

Interaction of chemokine receptor CCR5 with its ligands: multiple domains for HIV-1 gp120 binding and a single domain for chemokine binding

CCR5 is a chemokine receptor expressed by T cells and macrophages, which also functions as the principal coreceptor for macrophage (M)-tropic strains of HIV-1. To understand the molecular basis of the binding of chemokines and HIV-1 to CCR5, we developed a number of mAbs that inhibit the various interactions of CCR5, and mapped the binding sites of these mAbs using a panel of CCR5/CCR2b chimeras. One mAb termed 2D7 completely blocked the binding and chemotaxis of the three natural chemokine ligands of CCR5, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta, to CCR5 transfectants. This mAb was a genuine antagonist of CCR5, since it failed to stimulate an increase in intracellular calcium concentration in the CCR5 transfectants, but blocked calcium responses elicited by RANTES, MIP-1alpha, or MIP-1beta. This mAb inhibited most of the RANTES and MIP-1alpha chemotactic responses of activated T cells, but not of monocytes, suggesting differential usage of chemokine receptors by these two cell types. The 2D7 binding site mapped to the second extracellular loop of CCR5, whereas a group of mAbs that failed to block chemokine binding all mapped to the NH2-terminal region of CCR5. Efficient inhibition of an M-tropic HIV-1-derived envelope glycoprotein gp120 binding to CCR5 could be achieved with mAbs recognizing either the second extracellular loop or the NH2-terminal region, although the former showed superior inhibition. Additionally, 2D7 efficiently blocked the infectivity of several M-tropic and dual-tropic HIV-1 strains in vitro. These results suggest a complicated pattern of HIV-1 gp120 binding to different regions of CCR5, but a relatively simple pattern for chemokine binding. We conclude that the second extracellular loop of CCR5 is an ideal target site for the development of inhibitors of either chemokine or HIV-1 binding to CCR5.

Selective expression of the eotaxin receptor CCR3 by human T helper 2 cells

There is growing evidence that T helper cell subsets (TH1 and TH2) can be differentially recruited to promote different types of inflammatory reactions. Murine TH1 but not TH2 cells are recruited through P- and E-selectin into inflamed tissues, where they induce delayed-type hypersensitivity reactions. The human eotaxin-receptor CCR3, originally described on eosinophils and basophils, was also found to be expressed by TH2 cells. An antibody to CCR3 was used to isolate T cells from peripheral blood that give rise to TH2-polarized cell lines and to identify TH2 cells derived from naïve T cells in vitro. Eotaxin stimulated increases in intracellular calcium and chemotaxis of CCR3(+) T cells. The attraction of TH2 cells by eotaxin could represent a key mechanism in allergic reactions, because it promotes the allergen-driven production of interleukin-4 and interleukin-5 necessary to activate basophils and eosinophils.

High expression of the chemokine receptor CCR3 in human blood basophils. Role in activation by eotaxin, MCP-4, and other chemokines

Eosinophil leukocytes express high numbers of the chemokine receptor CCR3 which binds eotaxin, monocyte chemotactic protein (MCP)-4, and some other CC chemokines. In this paper we show that CCR3 is also highly expressed on human blood basophils, as indicated by Northern blotting and flow cytometry, and mediates mainly chemotaxis. Eotaxin and MCP-4 elicited basophil migration in vitro with similar efficacy as regulated upon activation normal T cells expressed and secreted (RANTES) and MCP-3. They also induced the release of histamine and leukotrienes in IL-3-primed basophils, but their efficacy was lower than that of MCP-1 and MCP-3, which were the most potent stimuli of exocytosis. Pretreatment of the basophils with a CCR3-blocking antibody abrogated the migration induced by eotaxin, RANTES, and by low to optimal concentrations of MCP-4, but decreased only minimally the response to MCP-3. The CCR3-blocking antibody also affected exocytosis: it abrogated histamine and leukotriene release induced by eotaxin, and partially inhibited the response to RANTES and MCP-4. In contrast, the antibody did not affect the responses induced by MCP-1, MCP-3, and macrophage inflammatory protein-1alpha, which may depend on CCR1 and CCR2, two additional receptors detected by Northern blotting with basophil RNA. This study demonstrates that CCR3 is the major receptor for eotaxin, RANTES, and MCP-4 in human basophils, and suggests that basophils and eosinophils, which are the characteristic effector cells of allergic inflammation, depend largely on CCR3 for migration towards different chemokines into inflamed tissues.

Human mucosal addressin cell adhesion molecule-1 is preferentially expressed in intestinal tract and associated lymphoid tissue

Lymphocyte homing to normal tissues and recruitment to inflammatory tissue sites are controlled, in part, by the selective expression of chemokines, pro-inflammatory cytokines and mediators, and various adhesion proteins and molecules. In the mouse, mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is selectively expressed on endothelium of high endothelial venules in gut and gut-associated lymphoid tissue. By interaction with its integrin ligand, alpha 4 beta 7, lymphocytes presumed to be involved in mucosal immunity are selectively recruited to these intestinal sites. After generating monoclonal antibodies against a murine cell line expressing recombinant human MAdCAM-1, we qualitatively and semiquantitatively assessed MAdCAM-1 expression in human tissue sections from various normal and inflammatory disorders. We found that human MAdCAM-1, as in the mouse, is expressed in a tissue-selective manner. In normal tissues, MAdCAM-1 is constitutively expressed to endothelium of venules of intestinal lamina propria. Interestingly, using computer-assisted morphometric analysis, the proportion of venular endothelium within lamina propria that expresses MAdCAM-1 is increased, compared with normal tissues, at inflammatory foci associated with ulcerative colitis and Crohn's disease. Moreover, for the most part, MAdCAM-1 is not detected in the majority of normal or inflamed extra-intestinal tissues, including those with mucosal surfaces. These results are consistent with a role, as originally defined in the mouse, for human MAdCAM-1 in the localization of alpha 4 beta 7+ lymphocytes in the gastrointestinal tract and associated lymphoid tissue. As such, the pathway defined by MAdCAM-1/alpha 4 beta 7 may be a relevant tissue-specific therapeutic target for the modulation of inflammatory bowel disease activity.

Chemokines: what chemokine is that?

The discovery of a new and unusual member of the chemokine family illustrates the importance of chemoattractant diversity in the regulation of leukocyte movement through the body. The chemokines are now divisible into four clearly defined subgroups on the basis of structural and functional properties.

CCR5 levels and expression pattern correlate with infectability by macrophage-tropic HIV-1, in vitro

Chemokine receptors serve as coreceptors for HIV entry into CD4+ cells. Their expression is thought to determine the tropism of viral strains for different cell types, and also to influence susceptibility to infection and rates of disease progression. Of the chemokine receptors, CCR5 is the most important for viral transmission, since CCR5 is the principal receptor for primary, macrophage-tropic viruses, and individuals homozygous for a defective CCR5 allele (delta32/delta32) are highly resistant to infection with HIV-1. In this study, CCR5-specific mAbs were generated using transfectants expressing high levels of CCR5. The specificity of these mAbs was confirmed using a broad panel of chemokine receptor transfectants, and by their non-reactivity with T cells from delta32/delta32 individuals. CCR5 showed a distinct pattern of expression, being abundant on long-term activated, IL-2-stimulated T cells, on a subset of effector/memory T cells in blood, and on tissue macrophages. A comparison of normal and CCR5 delta32 heterozygotes revealed markedly reduced expression of CCR5 on T cells from the heterozygotes. There was considerable individual to individual variability in the expression of CCR5 on blood T cells, that related to factors other than CCR5 genotype. Low expression of CCR5 correlated with the reduced infectability of T cells with macrophage-tropic HIV-1, in vitro. Anti-CCR5 mAbs inhibited the infection of PBMC by macrophage-tropic HIV-1 in vitro, but did not inhibit infection by T cell-tropic virus. Anti-CCR5 mAbs were poor inhibitors of chemokine binding, indicating that HIV-1 and ligands bind to separate, but overlapping regions of CCR5. These results illustrate many of the important biological features of CCR5, and demonstrate the feasibility of blocking macrophage-tropic HIV-1 entry into cells with an anti-CCR5 reagent.

HIV-1 entry and macrophage inflammatory protein-1beta-mediated signaling are independent functions of the chemokine receptor CCR5

The human immunodeficiency virus type 1 (HIV-1) requires the presence of specific chemokine receptors in addition to CD4 to enter its target cell. The chemokine receptor CCR5 is used by macrophage-tropic strains of HIV-1, which predominate during the asymptomatic stages of infection. Here we investigate whether the ability of CCR5 to signal in response to its beta-chemokine ligands is necessary or sufficient for viral entry. Three CCR5 mutants with little or no ability to mobilize calcium in response to macrophage inflammatory protein-1beta could nonetheless support HIV-1 entry and the early steps in the virus life cycle with efficiencies comparable with those of wild-type CCR5. Conversely, a chimeric receptor with the N terminus of CCR2 replacing that of CCR5 responded to macrophage inflammatory protein-1beta and MCP-1 but did not efficiently support viral entry. These results demonstrate that chemokine signaling and HIV-1 entry are separable functions of CCR5 and that only viral entry requires the N-terminal domain of CCR5.

The HIV coreceptors CXCR4 and CCR5 are differentially expressed and regulated on human T lymphocytes

The chemokine receptors CXCR4 and CCR5 function as coreceptors for HIV-1 entry into CD4+ cells. During the early stages of HIV infection, viral isolates tend to use CCR5 for viral entry, while later isolates tend to use CXCR4. The pattern of expression of these chemokine receptors on T cell subsets and their regulation has important implications for AIDS pathogenesis and lymphocyte recirculation. A mAb to CXCR4, 12G5, showed partial inhibition of chemotaxis and calcium influx induced by SDF-1, the natural ligand of CXCR4. 12G5 stained predominantly the naive, unactivated CD26(low) CD45RA+ CD45R0- T lymphocyte subset of peripheral blood lymphocytes. In contrast, a mAb specific for CCR5, 5C7, stained CD26(high) CD45RA(low) CD45R0+ T lymphocytes, a subset thought to represent previously activated/memory cells. CXCR4 expression was rapidly up-regulated on peripheral blood mononuclear cells during phytohemagglutinin stimulation and interleukin 2 priming, and responsiveness to SDF-1 increased simultaneously. CCR5 expression, however, showed only a gradual increase over 12 days of culture with interleukin 2, while T cell activation with phytohemagglutinin was ineffective. Taken together, the data suggest distinct functions for the two receptors and their ligands in the migration of lymphocyte subsets through lymphoid and nonlymphoid tissues. Furthermore, the largely reciprocal expression of CXCR4 and CCR5 among peripheral blood T cells implies distinct susceptibility of T cell subsets to viral entry by T cell line-tropic versus macrophage-tropic strains during the course of HIV infection.

CCR3 and CCR5 are co-receptors for HIV-1 infection of microglia

Several members of the chemokine receptor family are used together with CD4 for HIV-1 entry into target cells. T cell line-tropic (T-tropic) HIV-1 viruses use the chemokine receptor CXCR4 as a co-receptor, whereas macrophage-tropic (M-tropic) primary viruses use CCR5 (refs 2-6). Individuals with defective CCR5 alleles exhibit resistance to HIV-1 infection, suggesting that CCR5 has an important role in vivo in HIV-1 replication. A subset of primary viruses can use CCR3 as well as CCR5 as a co-receptor, but the in vivo contribution of CCR3 to HIV-1 infection and pathogenesis is unknown. HIV-1 infects the central nervous system (CNS) and causes the dementia associated with AIDS. Here we report that the major target cells for HIV-1 infection in the CNS, the microglia, express both CCR3 and CCR5. The CCR3 ligand, eotaxin, and an anti-CCR3 antibody inhibited HIV-1 infection of microglia, as did MIP-1beta, which is a CCR5 ligand. Our results suggest that both CCR3 and CCR5 promote efficient infection of the CNS by HIV-1.

Chemokine receptor usage by human eosinophils. The importance of CCR3 demonstrated using an antagonistic monoclonal antibody

Chemokines bind and signal through G-protein coupled seven transmembrane receptors. Various chemokine receptors are expressed on leukocytes, and these may impart selective homing of leukocyte subsets to sites of inflammation. Human eosinophils express the eotaxin receptor, CCR3, but respond to a variety of CC chemokines apart from eotaxin, including RANTES, monocyte chemotactic protein (MCP)-2, MCP-3, and MCP-4. Here we describe a mAb, 7B11, that is selective for CCR3 and has the properties of a true receptor antagonist. 7B11 blocked binding of various radiolabeled chemokines to either CCR3 transfectants, or eosinophils. Pretreatment of eosinophils with this mAb blocked chemotaxis and calcium flux induced by all CCR3 ligands. In all individuals examined, including allergic and eosinophilic donors, > 95% of the response of eosinophils to eotaxin, RANTES, MCP-2, MCP-3, and MCP-4 was shown to be mediated through CCR3. The IL-8 receptors, particularly CXCR2, were induced on IL-5 primed eosinophils, however these eosinophils responded to CC chemokines in the same manner as unprimed eosinophils. These results demonstrate the importance of CCR3 for eosinophil responses, and the feasibility of completely antagonizing this receptor.

Discrete steps in binding and signaling of interleukin-8 with its receptor

The mechanisms by which chemokines bind and signal through their receptors are complex and poorly understood. In the present study, we sought to dissect these processes and to map important functional domains of the two CXC chemokine (interleukin-8) receptors, CXCR1 (formally IL-8RA) and CXCR2 (formally IL-8RB), using blocking monoclonal antibodies (mAbs) to the receptors and a series of chimeras between CXCR1 and CXCR2. A panel of specific mAbs against CXCR1 or CXCR2, generated by immunizing mice with transfectants expressing either receptor, were shown to effectively block IL-8- and/or growth-related oncogene alpha (GROalpha) -mediated ligand binding, chemotaxis, elastase release, and VCAM-1 binding in CXCR1 and CXCR2 transfectants and/or human neutrophils. Of particular interest was an anti-CXCR1 mAb, 7D9, that inhibited chemotaxis, elastase release, and VCAM-1 binding but had no detectable effects on ligand binding. The epitopes of these blocking mAbs were mapped by using a series of CXCR1/2 chimera transfectants and synthetic peptides. Most of the anti-CXCR1 antibodies, except 7D9, mapped to the amino acid sequence WDFDDL (CXCR1 residues 10-15), and all the anti-CXCR2 antibodies mapped to the amino acid sequence FEDFW (CXCR2 residues 6-10). The epitope of mAb 7D9 mainly involved a region within the first 45 residues of CXCR1, and it appeared to be conformation-sensitive. These results support a model in which the binding and signaling of IL-8 with its receptor occur in at least two discrete steps involving distinct domains of the receptor. This model is consistent with the notion that discrete conformational changes of the receptor secondary to ligand binding are required to trigger various biological responses. Moreover, the ligand binding and chemotaxis properties of each CXCR1/2 chimeric receptor to IL-8 and GROalpha were determined. It was found that each is distinct in its ability to confer ligand binding and chemotactic response to IL-8 and GROalpha, and two conclusions could be made. 1) The N-terminal segment of CXCR1 is a dominant determinant of receptor subtype selectivity, consistent with previous studies using rabbit/human CXCR1/2 chimeras; and 2) the specificity determinant for GROalpha binding in CXCR2 involves sequences in the N terminus, distal to the first 15 residues, as well as other parts of the receptor.

Rapid resolution of chronic colitis in the cotton-top tamarin with an antibody to a gut-homing integrin alpha 4 beta 7

BACKGROUND & AIMS

Integrins play diverse roles in cellular actions and signalling in the immune system. In the context of mucosal immune responses, the integrin alpha 4 beta 7 has received particular attention because of its intimate involvement in lymphocyte recruitment to normal gastrointestinal mucosa and associated lymphoid tissue. The aim of this study was to determine the functional relevance of alpha 4 beta 7 in the pathogenesis of colonic inflammatory disease using the colitic cotton-top tamarin, an animal model of human ulcerative colitis.

METHODS

Chronically colitic cotton-top tamarins were given either a cross-reactive monoclonal antibody to human alpha 4 beta 7 or an irrelevant control monoclonal antibody. The animals were then evaluated clinically and mucosal biopsy specimens assessed by histological and quantitative morphometric analysis.

RESULTS

A blocking monoclonal antibody to alpha 4 beta 7 integrin ameliorated inflammatory activity and rapidly improved stool consistency when administered to chronically colitic animals. Furthermore, using morphometric analysis of biopsy specimens, antibody therapy reduced the mucosal density of alpha 4 beta 7+ lymphocytes and alpha 4 beta 7 neutrophils and macrophages.

CONCLUSIONS

These results suggest that the alpha 4 beta 7 integrin represents a novel, potentially organ-specific therapeutic target for the treatment of inflammatory bowel disease.

Chemokine expression in simian immunodeficiency virus-induced AIDS encephalitis

The pathogenesis of neurological dysfunction associated with human immunodeficiency (HIV)-1 infection is uncertain. However, the presence of macrophage infiltrates in the central nervous system is a key feature of HIV encephalitis and is correlated with HIV-associated dementia. Moreover, it has been demonstrated that HIV-infected monocyte/macrophages can produce toxic substances that may play a critical role in the development of HIV-associated dementia. However, the exact mechanisms responsible for HIV infection and leukocyte recruitment to the central nervous system remain speculative. Similar to HIV-infected patients, simian immunodeficiency virus (SIV)-infected macaque monkeys develop immunosuppression and acquired immune deficiency syndrome (AIDS)-related inflammatory disorders, including AIDS encephalitis. In this study, we demonstrate that encephalitic brain from SIV-infected animals has elevated immunohistochemical expression of the C-C chemokines, macrophage inflammatory protein-1 alpha and -beta, RANTES, and monocyte chemotactic protein-3, and the C-X-C chemokine interferon-inducible protein-10. These findings suggest that one or all of of these chemokines could be involved in leukocyte recruitment to the brain in SIV-infected macaque monkeys.

Phenotype, and migration properties of three major subsets of tissue homing T cells in sheep

T cells show a bias in their migration pathways: some T cells preferentially migrate to peripheral lymph nodes (LN), some to mucosal tissues, and some to peripheral tissues such as skin. These recirculation pathways were examined in sheep by collecting lymph draining into and out of peripheral and intestinal LN, and using fluorescent dyes to trace the recirculation of the lymph cells. Monoclonal antibodies (mAb) to alpha 4, beta 1, and beta 7 integrins, and L-selectin, were used to define three major populations of recirculating T cells. Naive-type T cells (L-selectin+, alpha 4 beta 1lo beta 7lo) migrated preferentially through peripheral LN. Two memory populations could be defined: alpha 4 beta 1hi beta 7- and alpha 4 beta 7hi beta 1lo. alpha 4 beta 1hi beta 7- T cells were present in lymph draining from the skin. T cells migrating preferentially through intestinal LN were alpha 4 beta 7hi beta 1lo. Consistent with this migration pattern, the endothelial receptor for alpha 4 beta 7, mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was detected on high endothelial venules within intestinal LN and Peyer's patches, but only weakly on high endothelial venules within peripheral LN. Thus, there are at least three easily definable subsets of T cells, based on integrin expression, which show distinct migration preferences.

Characterisation of leucocytic somatic cells in bovine milk

The mammary gland is of cutaneous origin with stromal leucocytic infiltrates and it excretes leucocytes in the milk. Milk T lymphocytes are highly enriched by sedimenting milk somatic cells in a 43 per cent preformed Percoll gradient. Thirty to 54 per cent of leucocytes, harvested from the upper Percoll band, belong to CD2+ CD3+ T lymphocytes. These milk T lymphocytes are mature CD4+, or CD8+ single positive T cells, expressing CD44, CD26, and beta 1 integrin, but not Lam-1. Milk T lymphocyte subsets may play an important role in regional immunosurveillance of the mammary epithelia and stroma. Selective mechanisms may account for the trafficking of this activated, memory T lymphocyte subset in the gland.

Biology of chemokine and classical chemoattractant receptors: differential requirements for adhesion-triggering versus chemotactic responses in lymphoid cells

Several chemoattractant receptors can support agonist-induced, integrin-dependent arrest of rolling neutrophils in inflamed venules in vivo, as well as subsequent crawling into tissues. It has been hypothesized that receptors of the Galpha(i)-linked chemoattractant subfamilies, especially receptors for chemokines, may mediate parallel activation-dependent arrest of homing lymphocyte subsets. However, although several chemokines can attract subsets of B or T cells, robust chemoattractant triggering of resting lymphocyte adhesion to vascular ligands has not been observed. To study the biology of individual leukocyte chemoattractant receptors in a defined lymphoid environment, mouse L1/2 pre-B cells and/or human Jurkat T cells were transfected with alpha (IL-8 receptor A) or beta (MIP-1alpha/CC-CKR-1) chemokine receptors, or with the classical chemoattractant C5a (C5aR) or formyl peptide receptors (fPR). All receptors supported robust agonist-dependent alpha4beta1 integrin-mediated adhesion of lymphocytes to VCAM-1. L1/2 cells cotransfected with fPR and beta7 integrin were also induced to bind MAdCAM-1, suggesting common mechanisms coupling chemoattractant receptors to activation of distinct integrins. Adhesion was rapid but transient, with spontaneous reversion to unstimulated levels within 5 min after peak binding. When observed under flow conditions, alpha4beta1-mediated arrest occurred within seconds after initiation of contact and rolling of IL-8RA transfectants on VCAM-1/IL-8 co-coated surface; and arrest reversed spontaneously after a mean of 5 min with a return to rolling behavior. Each of the receptors also conferred agonist-specific chemotaxis; however, whereas strong adhesion required simultaneous occupancy of many receptors with maximal responses above the Kd, chemotaxis in each case was suppressed at high agonist concentrations. The findings indicate that alpha and beta chemokine as well as classical chemoattractant receptors can trigger robust adhesion as well as directed migration of lymphoid cells, but that the requirements for and kinetics of adhesion triggering and chemotaxis are distinct, thus permitting their independent regulation. They suggest that the discordance between proadhesive and chemoattractant responses of circulating lymphocytes to many chemokines may reflect quantitative aspects of receptor expression and/or coupling rather than qualitative differences in receptor signaling.

The beta-chemokine receptors CCR3 and CCR5 facilitate infection by primary HIV-1 isolates

We examined the ability of chemokine receptors and related G protein-coupled receptors to facilitate infection by primary, clinical HIV-1 isolates. CCR5, when expressed along with CD4, the HIV-1 receptor, allowed cell lines resistant to most primary HIV-1 isolates to be infected. CCR3 facilitated infection by a more restricted subset of primary viruses, and binding of the CCR3 ligand, eotaxin, inhibited infection by these isolates. Utilization of CCR3 and CCR5 on the target cell depended upon the sequence of the third variable (V3) region of the HIV-1 gp120 exterior envelope glycoprotein. The ability of various members of the chemokine receptor family to support the early stages of HIV-1 infection helps to explain viral tropism and beta-chemokine inhibition of primary HIV-1 isolates.