Chemokines: a new classification system and their role in immunity

Role of RANTES in experimental cardiac allograft rejection

The host response to alloantigen results in upregulation of Class II MHC antigens and associated cytokine production (especially IL-2 and interferon-gamma (IFN-gamma)) as well as lymphocytic infiltration and cellular activation which leads to graft damage/destruction. RANTES (Regulated upon Activation, Normal T-cell Expressed and presumably Secreted) is a member of the beta subfamily (CC) of chemokines and has been shown to function as a lymphocyte chemoattractant. We now describe the requirement for RANTES in cardiac heterotopic allograft (brown Norway into Lewis rats) rejection in rats. By Northern blot analysis, mRNA could be detected in allografts at 6 and 8 days post-transplantation but not in isogenic (Lewis) grafts. RANTES protein could be demonstrated by Western blot analysis in homogenates from allografts at day 8 but not at day 0 and could not be identified in isogenic cardiac transplants. By immunostaining, RANTES protein was present in mononuclear cells of allografts at day 6 but was absent in the isogenic transplants. When rats were treated with anti-RANTES serum, there was a significant delay in rejection time (cessation of beating) of the allografts. These data demonstrate that expression of RANTES in rat cardiac allografts is linked to the rejection phenomenon.

The role of macrophage inflammatory protein-1 alpha/CCL3 in regulation of T cell-mediated immunity to Cryptococcus neoformans infection

Macrophage inflammatory protein-1alpha (MIP-1alpha/CCL3) is a CC chemokine required for optimal recruitment of leukocytes in response to cryptococcal Ags. MIP-1alpha is expressed in the lungs by day 6 post Cryptococcus neoformans infection and could play a role in the development of cell-mediated immunity. To address this possibility, wild-type (MIP-1alpha(+/+)) mice and MIP-1alpha knockout (MIP-1alpha(-/-)) mice were infected intratracheally with a highly virulent strain of C. neoformans (145A). MIP-1alpha message was detected in the lungs on days 3, 7, and 14 in MIP-1alpha(+/+) mice, but it was undetectable in MIP-1alpha(-/-) mice. On day 16, MIP-1alpha(-/-) mice had a 7-fold increase in C. neoformans burden in the lungs, but no decrease in pulmonary leukocyte recruitment. MIP-1alpha(+/+) and MIP-1alpha(-/-) mice had similar numbers of recruited lymphocytes and monocytes/macrophages. Notably, MIP-1alpha(-/-) mice had a significantly greater number of eosinophils. MIP-1alpha(-/-) mice had extremely high levels of serum IgE. This switch of immune response to a T(2) phenotype was associated with enhanced IL-4 and IL-13 expression in the lungs of MIP-1alpha(-/-) mice compared with MIP-1alpha (+/+) mice. Progression of pulmonary cryptococcosis in the presence of nonprotective T(2) immunity resulted in profound lung damage in MIP-1alpha(-/-) mice (eosinophilic crystal deposition, destruction of lung parenchyma, and pulmonary hemorrhage). Twelve-week survival was dramatically decreased in MIP-1alpha(-/-) mice. These studies, together with our previous studies, demonstrate that MIP-1alpha plays a role in both the afferent (T(1)/T(2) development) and efferent (T(1)-mediated leukocyte recruitment) phases of cell-mediated immunity to C. neoformans.

The leukotriene C(4) transporter MRP1 regulates CCL19 (MIP-3beta, ELC)-dependent mobilization of dendritic cells to lymph nodes

Adaptive immune responses begin after antigen-bearing dendritic cells (DCs) traffic from peripheral tissues to lymph nodes. Here, we show that DC migration from skin to lymph nodes utilizes the leukotriene C(4) (LTC(4)) transporter multidrug resistance-associated protein 1 (MRP1). DC mobilization from the epidermis and trafficking into lymphatic vessels was greatly reduced in MRP1(-/-) mice, but migration was restored by exogenous cysteinyl leukotrienes LTC(4) or LTD(4). In vitro, these cysteinyl leukotrienes promoted optimal chemotaxis to the chemokine CCL19, but not to other related chemokines. Antagonism of CCL19 in vivo prevented DC migration out of the epidermis. Thus, MRP-1 regulates DC migration to lymph nodes, apparently by transporting LTC(4), which in turn promotes chemotaxis to CCL19 and mobilization of DCs from the epidermis.

Requirement of the chemokine receptor CXCR3 for acute allograft rejection

Chemokines provide signals for activation and recruitment of effector cells into sites of inflammation, acting via specific G protein-coupled receptors. However, in vitro data demonstrating the presence of multiple ligands for a given chemokine receptor, and often multiple receptors for a given chemokine, have led to concerns of biologic redundancy. Here we show that acute cardiac allograft rejection is accompanied by progressive intragraft production of the chemokines interferon (IFN)-gamma-inducible protein of 10 kD (IP-10), monokine induced by IFN-gamma (Mig), and IFN-inducible T cell alpha chemoattractant (I-TAC), and by infiltration of activated T cells bearing the corresponding chemokine receptor, CXCR3. We used three in vivo models to demonstrate a role for CXCR3 in the development of transplant rejection. First, CXCR3-deficient (CXCR3(-/)-) mice showed profound resistance to development of acute allograft rejection. Second, CXCR3(-/)- allograft recipients treated with a brief, subtherapeutic course of cyclosporin A maintained their allografts permanently and without evidence of chronic rejection. Third, CXCR(+/+) mice treated with an anti-CXCR3 monoclonal antibody showed prolongation of allograft survival, even if begun after the onset of rejection. Taken in conjunction with our findings of CXCR3 expression in rejecting human cardiac allografts, we conclude that CXCR3 plays a key role in T cell activation, recruitment, and allograft destruction.

Mast cells control neutrophil recruitment during T cell-mediated delayed-type hypersensitivity reactions through tumor necrosis factor and macrophage inflammatory protein 2

Polymorphonuclear leukocytes (PMNs) characterize the pathology of T cell-mediated autoimmune diseases and delayed-type hypersensitivity reactions (DTHRs) in the skin, joints, and gut, but are absent in T cell-mediated autoimmune diseases of the brain or pancreas. All of these reactions are mediated by interferon gamma-producing type 1 T cells and produce a similar pattern of cytokines. Thus, the cells and mediators responsible for the PMN recruitment into skin, joints, or gut during DTHRs remain unknown. Analyzing hapten-induced DTHRs of the skin, we found that mast cells determine the T cell-dependent PMN recruitment through two mediators, tumor necrosis factor (TNF) and the CXC chemokine macrophage inflammatory protein 2 (MIP-2), the functional analogue of human interleukin 8. Extractable MIP-2 protein was abundant during DTHRs in and around mast cells of wild-type (WT) mice but absent in mast cell-deficient WBB6F(1)-Kit(W)/Kit(W-)(v) (Kit(W)/Kit(W)(-v)) mice. T cell-dependent PMN recruitment was reduced >60% by anti-MIP-2 antibodies and >80% in mast cell-deficient Kit(W)/Kit(W)(-v) mice. Mast cells from WT mice efficiently restored DTHRs and MIP-2-dependent PMN recruitment in Kit(W)/Kit(W)-(v) mice, whereas mast cells from TNF(-/)- mice did not. Thus, mast cell-derived TNF and MIP-2 ultimately determine the pattern of infiltrating cells during T cell-mediated DTHRs.

Murine eotaxin-2: a constitutive eosinophil chemokine induced by allergen challenge and IL-4 overexpression

The generation of tissue eosinophilia is governed in part by chemokines; initial investigation has identified three chemokines in the human genome with eosinophil selectivity, referred to as eotaxin-1, -2, and -3. Elucidation of the role of these chemokines is dependent in part upon analysis of murine homologues; however, only one murine homologue, eotaxin-1, has been identified. We now report the characterization of the murine eotaxin-2 cDNA, gene and protein. The eotaxin-2 cDNA contains an open reading frame that encodes for a 119-amino acid protein. The mature protein, which is predicted to contain 93 amino acids, is most homologous to human eotaxin-2 (59.1% identity), but is only 38.9% identical with murine eotaxin-1. Northern blot analysis reveals three predominant mRNA species and highest constitutive expression in the jejunum and spleen. Additionally, allergen challenge in the lung with Aspergillus fumigatus or OVA revealed marked induction of eotaxin-2 mRNA. Furthermore, eotaxin-2 mRNA was strongly induced by both transgenic over-expression of IL-4 in the lung and administration of intranasal IL-4. Analysis of eotaxin-2 mRNA expression in mice transgenic for IL-4 but genetically deficient in STAT-6 revealed that the IL-4-induced expression was STAT-6 dependent. Recombinant eotaxin-2 protein induced dose-dependent chemotactic responses on murine eosinophils at concentrations between 1-1000 ng/ml, whereas no activity was displayed on murine macrophages or neutrophils. Functional analysis of recombinant protein variants revealed a critical role for the amino terminus. Thus, murine eotaxin-2 is a constitutively expressed eosinophil chemokine likely to be involved in homeostatic, allergen-induced, and IL-4-associated immune responses.

Coexpression of the chemokines ELC and SLC by T zone stromal cells and deletion of the ELC gene in the plt/plt mouse

The spontaneous mutant mouse strain, plt/plt, lacks the secondary lymphoid organ chemokine (SLC)-ser gene and has disrupted trafficking of T cells and dendritic cells (DCs) to lymphoid tissues. We demonstrate here that the gene for the related chemokine, Epstein-Barr virus-induced molecule-1 ligand chemokine (ELC), is also deleted in this immunodeficient mouse strain. Using a combination of approaches, including bone marrow reconstitution and double in situ hybridization, we show in wild-type mice that ELC is expressed by T zone stromal cells that also make SLC. Smaller amounts of ELC are made by DCs, predominantly of the CD8(+) phenotype. We propose that ELC- and SLC-expressing T zone stromal cells play a central role in bringing naive T cells and DCs together for the initiation of immune responses.

CXCR4 and CCR5 expression by H9 T-cells is downregulated by a peptide-nucleic acid immunomodulator

Product R (Reticulose(TM)) is a peptide-nucleic acid immunomodulator with broad-spectrum antiviral activity that was recently shown to increase expression of mRNAs encoding the proinflammatory cytokines, IFN-gamma, IL-1beta, IL-6 and TNF-alpha. Since these cytokines induce expression of the chemokines, MIP-1alpha, MIP-1beta, RANTES, and SDF-1, all of which inhibit viral infectivity, we were interested to determine if Product R also alters chemokine expression. In addition, the finding, that Product R decreases HIV-1 RNA and extracellular p24 antigen in H9 T-lymphoma cells, suggested to us that this drug may block viral infection by reducing the expression of chemokine receptors on target cells. We have therefore utilized H9 cells to test the effects of Product R on expression of mRNAs encoding the chemokine receptors, CD4, CXCR4 and CCR5, as well as their ligands, IL-16, SDF-1, MIP-1alpha, MIP-1beta, and RANTES, by RT-PCR. We also assayed the effect of Product R on surface receptor expression by flow cytometry, and on the chemotactic activity of these cells towards the CXCR4 ligand, SDF-1, and the CCR5 ligands, MIP-1alpha and RANTES. H9 cells were cultured for 3-21 days in medium containing 5% or 10% Product R, or 5% or 10% PBS. We found that, compared to control cultures, cells cultured in media containing Product R expressed lower amounts of CXCR4 and CCR5 mRNA and surface antigen at all time points. Culture for 3 days in media containing Product R also reduced the ability of cells to migrate towards 10-20 ng/ml SDF-1 and 100-250 ng/ml RANTES. In contrast, Product R had no effect on the expression of CD4 mRNA and receptor protein, or on expression of IL-16 mRNA. These findings suggest that Product R may have clinical efficacy in HIV-1-infected patients by downregulating viral coreceptors on target T-cells.

Astrocytes express functional chemokine receptors

Multiple lines of evidence are presented characterizing the functional expression of chemokine receptors CXCR4, CCR1, CCR5, and CX3CR1 on astrocytes. Most of these receptors are expressed at low levels and may only be detectable on a subset of cells during disease or following cytokine induction. The expression of CXCR2, CCR2, CCR3, CCR10, CCR11, and several orphan receptors associated with HIV-1 infection has also been proposed. The appearance of several chemokine receptors implies a wider role for chemokines in the regulation of central nervous system functions. Available evidence indicates that selected chemokines induce further chemokine synthesis in astrocytes providing a mechanism to amplify inflammatory responses in the central nervous system.

The role of thymus-expressed chemokine and its receptor CCR9 on lymphocytes in the regional specialization of the mucosal immune system

Chemokines play an important role in the migration of leukocytes at sites of inflammation, and some constitutively expressed chemokines may direct lymphocyte trafficking within lymphoid organs and peripheral tissues. Thymus-expressed chemokine (TECK or Ckbeta-15/CCL25), which signals through the chemokine receptor CCR9, is constitutively expressed in the thymus and small intestine but not colon, and chemoattracts a small fraction of PBLs that coexpress the integrin alpha(4)beta(7). Here we show that TECK is expressed in the human small bowel but not colon by endothelial cells and a subset of cells in intestinal crypts and lamina propria. CCR9 is expressed in the majority of freshly isolated small bowel lamina propria mononuclear cells (LPMC) and at significantly higher levels compared with colonic LPMC or PBL. TECK was selectively chemotactic for small bowel but not colonic LPMC in vitro. The TECK-induced chemotaxis was sensitive to pertussis toxin and partially inhibited by Abs to CCR9. TECK attracts predominantly the T cell fraction of small bowel LPMC, whereas sorted CD3(+)CCR9(+) and CD3(+)CCR9(-) lymphocytes produce similar Th1 or Th2 cytokines at the single cell level. Collectively, our data suggest that the selective expression of TECK in the small bowel underlie the homing of CCR9(+) intestinal memory T cells to the small bowel rather than to the colon. This regional specialization implies a segregation of small intestinal from colonic immune responses.

Uncoupling of inflammatory chemokine receptors by IL-10: generation of functional decoys

As originally demonstrated for the interleukin 1 (IL-1) type II receptor, some primary proinflammatory cytokines from the IL-1 and tumor necrosis factor families are regulated by decoy receptors that are structurally incapable of signaling. Here we report that concomitant exposure to proinflammatory signals and IL-10 generates functional decoy receptors in the chemokine system. Inflammatory signals, which cause dendritic cell (DC) maturation and migration to lymphoid organs, induce a chemokine receptor switch, with down-regulation of inflammatory receptors (such as CCR1, CCR2, CCR5) and induction of CCR7. Concomitant exposure to lipopolysaccharide (LPS) and IL-10 blocks the chemokine receptor switch associated with DC maturation. LPS + IL-10-treated DCs showed low expression of CCR7 and high expression of CCR1, CCR2 and CCR5. These receptors were unable to elicit migration. We provide evidence that uncoupled receptors, expressed on LPS + IL-10-treated cells, sequester and scavenge inflammatory chemokines. Similar results were obtained for monocytes exposed to activating signals and IL-10. Thus, in an inflammatory environment, IL-10 generates functional decoy receptors on DC and monocytes, which act as molecular sinks and scavengers for inflammatory chemokines.

Road signs guiding leukocytes along the inflammation superhighway

The term inflammation is used to describe the localized tissue changes, including leukocyte extravasation, that occur as part of the response to tissue damage, infection, or other immunologic responses. This carefully orchestrated series of events requires the existence of highly specific, regulated mechanisms for control of leukocyte recruitment and is dependent on both the inciting event and organ involved. This review summarizes recent developments in our understanding of how adhesion molecules and chemokines interact to facilitate tissue-specific and leukocyte subtype-specific influx during inflammation. Novel mechanisms believed to be responsible for capture and compartmentalization of B and T lymphocytes within lymph nodes are discussed, along with a description of adhesion molecule- and chemokine-mediated pathways that are believed to be involved in selective recruitment of lymphocytes and eosinophils to a variety of tissues, including the skin, gut, and lung. This growing knowledge and its potential importance provide enthusiasm for future anti-inflammatory therapies that target these recruitment pathways.

Micronutrients and host resistance to viral infection

Previous work in our laboratory demonstrated that a virus could undergo rapid mutation in a host deficient in Se, leading to a normally avirulent virus acquiring virulence due to genome changes. Once these mutations occur, even a host with adequate Se-nutriture is susceptible to the newly virulent virus. What influence does the deficiency in Se have on the immune response of the host? Infection with myocarditic strains of coxsackievirus induces an inflammatory response in the cardiac tissue. It is this immune response that induces the heart damage, rather than direct viral effects on the heart tissue. Chemokines are chemo-attractant molecules that are secreted during an infection in order to attract immune cells to the site of the injury, and have been found to be important for the development of coxsackievirus-induced myocarditis. We found that a deficiency in Se influences the expression of mRNA for the chemokine monocyte chemo-attractant protein-1, which may have implications for the development of myocarditis in the Se-deficient host. Expression of mRNA for interferon-gamma was also greatly decreased in the Se-deficient animal. Thus, a deficiency in Se can have profound effects on the host as well as on the virus itself. How the alteration of the immune response of the Se-deficient animal affects the development of the virulent genotype remains to be answered.

Isolation and characterization of a new chemokine receptor gene, the putative chicken CXCR1

This study delineates the isolation and characterization of a novel chemokine receptor gene, the putative chicken CXC receptor 1 (cCXCR1). Using a human CXCR1 probe, we isolated several positive clones from a chicken genomic library. One of the clones contained a fragment of approximately 5000bp that hybridized strongly with the hCXCR1 probe. This fragment was sequenced and subjected to a variety of computer analyses. The open reading frame for this gene predicts a seven transmembrane domain protein with all the characteristics of a chemokine receptor and with 67% sequence homology to hCXCR1, 65% to hCXCR2 and also with considerable sequence homology to other human chemokine receptors such as hCXCR4 (50%), hCCR2 (49%) and hCCR1 (49%). However, the homology to a previously isolated potential G-protein-coupled receptor for chickens (AvCRL1) is only 47%. Using 5' RACE, two transcription initiation sites were identified suggesting the potential for the expression of two protein isoforms (I and II) in vivo. The promoter for the putative cCXCR1 contains a variety of consensus transcription factor binding elements that can potentially be involved in the expression of this chicken receptor upon stimulation by stress-inducing agents. RT-PCR analysis was used to determine the pattern of expression of the larger isoform (I) of this receptor in a variety of tissues. This form of the receptor is expressed primarily in the organs of the gastrointestinal tract, tissues that are frequently exposed to stress-inducing agents, but not in the central nervous system, tissues that are protected from insult by the blood barrier. Using the same RT-PCR approach we show that stress-inducing agents, such as 'first-hand' and 'second-hand' cigarette smoke components, tumor promoters and thrombin, differentially stimulate the expression of the isoform I in primary fibroblasts. Thrombin is an enzyme that plays many important roles in thrombosis, angiogenesis and wound healing and exposure to both cigarette smokes and/or to tumor promoters can lead to tumorigenesis. Therefore, upregulation of chemokines and their receptors by stress-inducing agents can confer highly regulated modulation of cellular responses to traumatic and pathological situations.

Macrophage-derived dendritic cells have strong Th1-polarizing potential mediated by beta-chemokines rather than IL-12

Monocyte-derived dendritic cells (MDDCs) activate naive T lymphocytes to induce adaptive immunity, effecting Th1 polarization through IL-12. However, little is known about other potential DC Th1 polarizing mechanisms, or how T cell polarization may be affected by DCs differentiating in, or exposed to, a proinflammatory environment. Macrophages (MPhis) are DC precursors abundant in inflamed tissues, lymph nodes, and tumors. Thus we studied the T cell-activating and -polarizing properties of MPhi-derived DCs (PhiDCs). Monocytes were cultured in MPhi-CSF (M-CSF) to produce MPhis, which were then differentiated into DCs following culture with GM-CSF plus IL-4. PhiDCs activated a significant allogeneic MLR and were significantly better than MDDCs in activating T cells with superantigen. Most strikingly, PhiDCs elicited up to 9-fold more IFN-gamma from naive or Ag-specific T cells compared with MDDCs (with equivalent IL-4 secretion), despite producing up to 9-fold less IL-12. Neutralization of MDDC, but not PhiDC IL-12 significantly inhibited T cell IFN-gamma induction. PhiDCs produced up to 12-fold more beta-chemokines (macrophage-inflammatory protein-1alpha, -1beta, and RANTES) than MDDCs. Ab blockade of CCR5, but not CXC chemokine receptor 4, inhibited T cell IFN-gamma induction by PhiDCs significantly greater than by MDDCs. Thus DCs differentiating from MPhis induce T cell IFN-gamma through beta-chemokines with little or no requirement for IL-12. Myeloid DCs arising from distinct precursor cells may have differing properties, including different mechanisms of Th1 polarization. These data are the first reports of IFN-gamma induction through chemokines by DCs.

Regulated production and molecular diversity of human liver and activation-regulated chemokine/macrophage inflammatory protein-3 alpha from normal and transformed cells

Liver and activation-regulated chemokine (LARC), also designated macrophage inflammatory protein-3alpha (MIP-3alpha), Exodus, or CCL20, is a C-C chemokine that attracts immature dendritic cells and memory T lymphocytes, both expressing CCR6. Depending on the cell type, this chemokine was found to be inducible by cytokines (IL-1beta) and by bacterial, viral, or plant products (including LPS, dsRNA, and PMA) as measured by a specific ELISA. Although coinduced with monocyte chemotactic protein-1 (MCP-1) and IL-8 by dsRNA, measles virus, and IL-1beta in diploid fibroblasts, leukocytes produced LARC/MIP-3alpha only in response to LPS. However, in myelomonocytic THP-1 cells LARC/MIP-3alpha was better induced by phorbol ester, whereas in HEp-2 epidermal carcinoma cells IL-1beta was the superior inducer. The production levels of LARC/MIP-3alpha (1-10 ng/ml) were, on the average, 10- to 100-fold lower than those of IL-8 and MCP-1, but were comparable to those of other less abundantly secreted chemokines. Natural LARC/MIP-3alpha protein isolated from stimulated leukocytes or tumor cell lines showed molecular diversity, in that NH(2)- and COOH-terminally truncated forms were purified and identified by amino acid sequence analysis and mass spectrometry. In contrast to other chemokines, including MCP-1 and IL-8, the natural processing did not affect the calcium-mobilizing capacity of LARC/MIP-3alpha through its receptor CCR6. Furthermore, truncated natural LARC/MIP-3alpha isoforms were equally chemotactic for lymphocytes as intact rLARC/MIP-3alpha. It is concluded that in addition to its role in homeostatic trafficking of leukocytes, LARC/MIP-3alpha can function as an inflammatory chemokine during host defense.

Modulation of experimental autoimmune encephalomyelitis: effect of altered peptide ligand on chemokine and chemokine receptor expression

Experimental autoimmune encephalomyelitis (EAE) is a T helper 1 (Th1) cell mediated demyelinating disease and the principal animal model for multiple sclerosis. Spinal cords from SJL mice primed with proteolipid protein peptide 139-151 (pPLP) expressed the chemokines RANTES, MCP-1, MIP-2, KC, MIP-1alpha, MIP-1beta, Mig, and fractalkine. We also identified IP-10 in these samples and described a sequence polymorphism in this transcript. Chemokine expression was specific for tissues of the central nervous system. MCP-1, IP-10, and MIP-2 RNA expression significantly correlated with clinical score. Chemokine receptor expression generally correlated with ligand expression. pPLP-primed mice expressed the Th1-associated markers CCR5 and CXCR3 on mononuclear cells. In addition, cells expressing CCR1, CCR2, CCR3, CCR4, CCR8, and CXCR2 were detected. Here we demonstrate that altered peptide ligand (APL)-induced protection from EAE was accompanied by modulation of chemokine and chemokine receptor expression. Spinal cord tissue sections from APL-protected mice showed greatly reduced levels of all chemokines and of CCR1, CCR5, CCR8, CXCR2 and CXCR3. The Th2-associated chemokine receptors CCR3 and CCR4 were found in protected mice, supporting the hypothesis that Th1 but not Th2 cells are down-regulated by APL treatment. This report concludes that chemokines and chemokine receptors can be useful tools to follow modulation of autoimmune disease.

Interferon-gamma stimulates the expression of CX3CL1/fractalkine in cultured human endothelial cells

CX3CL1/Fractalkine, a CX3C chemokine, is a potent agonist for the chemotaxis and adhesion of monocytes and lymphocytes. It was first identified as a membrane protein in endothelial cells activated with IL-1 or TNF-alpha. We have found the enhanced expression of fractalkine in human umbilical vein endothelial cells stimulated with interferon-gamma (IFN-gamma). Pretreatment of the cells with cycloheximide did not inhibit the expression of fractalkine mRNA. The majority of fractalkine protein was found in the cell lysate, and an antibody-blocking experiment disclosed that fractalkine contributes to the adhesion of mononuclear cells to endothelial monolayers stimulated with IFN-gamma. Vascular endothelial cells produce fractalkine in response to IFN-gamma, and this may play an important role in immune responses by eliciting a traffic of mononuclear cells through the vascular wall.

A transmembrane CXC chemokine is a ligand for HIV-coreceptor Bonzo

We describe a protein with the hallmarks of a chemokine, designated CXCL16, that is made by dendritic cells (DCs) in lymphoid organ T cell zones and by cells in the splenic red pulp. CXCL16 contains a transmembrane domain and both membrane-bound and soluble forms are produced. Naïve CD8 T cells, natural killer T cells and a subset of memory CD4 T cells bind CXCL16, and activated T cells migrated chemotactically to the soluble chemokine. By expression cloning, Bonzo (also known as STRL33 and TYMSTR) was identified as a CXCL16 receptor. CXCL16 may function in promoting interactions between DCs and CD8 T cells and in guiding T cell movements in the splenic red pulp. CXCL16 was also found in the thymic medulla and in some nonlymphoid tissues, indicating roles in thymocyte development and effector T cell trafficking.

Macrophage inflammatory protein-2 and KC induce chemokine production by mouse astrocytes

Astrocytes are specialized cells of the CNS that are implicated in the pathogenesis of multiple sclerosis and experimental allergic encephalomyelitis. In acute and relapsing-remitting experimental allergic encephalomyelitis, the neutrophil chemoattractant CXC chemokines macrophage-inflammatory protein (MIP)-2 and KC are associated with reactive astrocytes in the parenchyma. In vitro treatment of primary astrocyte cultures with nanomolar concentrations of MIP-2 or KC markedly up-regulated expression of the monocyte/T cell chemoattractants monocyte chemoattractant protein-1, inflammatory protein-10, and RANTES by a mechanism that includes stabilization of mRNA. Production of TNF-alpha and IL-6 transcripts were also noted, as was autocrine induction of MIP-2 and KC message. In addition, low levels of MIP-1alpha and MIP-1beta were induced following treatment with MIP-2 or KC. These effects are specific to astrocytes as MIP-2 treatment of microglial cells failed to elicit chemokine production. The astrocyte chemokine receptor for MIP-2 has 2.5 nM affinity for ligand. Astrocytes from CXCR2-deficient mice still respond to KC and MIP-2, indicating the presence of an alternative or novel high affinity receptor for these ligands. We propose that this KC/MIP-2 chemokine cascade may contribute to the persistence of mononuclear cell infiltration in demyelinating autoimmune diseases.

Chemokines and their receptors in allograft rejection

Despite current recognition of over 40 chemokines and more than 18 chemokine receptors, understanding of their role in transplant immunobiology and transplant rejection is extremely limited and fragmentary. Recent literature has demonstrated the presence of chemokines and their receptors in transplants and some studies demonstrate important functional roles.

T-lymphocyte-epithelial-cell interactions: integrin alpha(E)(CD103)beta(7), LEEP-CAM and chemokines

The epithelia are the avascular layers of cells that cover the environment-exposed surfaces of the body. It appears that T cells localize to selected sites in or adjacent to epithelia via the selective expression of adhesion molecules and chemokine receptors on T cells. These bind to counter-receptors and to chemokines expressed by epithelial cells. Recently, there has been an advance in our understanding of the interaction of the alpha(Ebeta7) integrin with its epithelial cell ligand, E-cadherin. In addition, a new adhesion molecule has been identified on non-intestinal epithelial cells, termed lymphocyte-endothelial-epithelial-cell adhesion molecule (LEEP-CAM). Finally, there have been advances in our understanding of the role of skin- or gut-epithelia-derived chemokines in regulating activated T cell homing to these sites.

Cell migration and the anatomic control of thymocyte precursor differentiation

The thymus performs several essential functions during the steady-state production of T lymphocytes in adults, including expansion of the precursor pool, differentiation into multiple lineages and screening for TCRs with restricted specificities. Other than those functions attributed to the TCR, most of the factors that control these processes remain undefined. One potential mechanism for such control may be related to the movement of precursor cells between distinct anatomical compartments in the thymus. Histological studies show that the majority of CD4- CD8- cells are found in the subcapsular region. However; vascular tissues that support the migration of precursor cells into the thymus (postcapillary venules) are located deep in the tissue, near the cortico-medullary junction. This implies that blood-borne cells entering the thymus must transit outward across the cortex in order to accumulate in the SCR. Differentiation of DN cells into the CD4+ 8+ stage correlates with a reversal in polarity and migration inward, while mature cells ultimately transit the CMJ in the opposite direction of cells first entering the organ. Here we review evidence for a model in which differentiation is induced and proliferation is controlled by this progressive translocation of immature precursors through discrete stromal compartments. In addition, we attempt to summarize what is known about the molecular mechanisms that may support polarized migration of early CD4- 8- thymocytes in the adult, as well as how and where the relevant differentiative and/or proliferative signals may be compartmentalized.

Role of chemokines in thymocyte development

As they mature, thymocytes migrate to specific regions of the thymus, interact with different types of stromal cells, and thereby receive signals for survival, differentiation, or death. Despite its importance, the molecular control of thymocyte trafficking remains poorly understood. Chemokines and their receptors probably control the homing of T cell progenitors to the thymus, their intrathymic migration, and exit to the periphery. Certain chemokines are abundant in the thymus, and their receptors are expressed during distinct developmental stages. Below, we discuss recent studies of chemokines and their receptors in the thymus, speculating on their function in the frame work of thymocyte trafficking.

CC chemokine receptor 2 is critical for induction of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a CD4(+) T lymphocyte-mediated disease of the central nervous system (CNS) characterized by mononuclear cell infiltration, demyelination, and paralysis. We previously demonstrated a role for chemokines in acute and relapsing EAE pathogenesis. Presently, we investigated the role of CC chemokine receptor 2 (CCR2) in acute EAE. CCR2(-/-) mice did not develop clinical EAE or CNS histopathology, and showed a significant reduction in T cell- and CNS-infiltrating CD45(high)F4/80(+) monocyte subpopulations. Peripheral lymphocytes from CCR2(-/-) mice produced comparable levels of interferon-gamma (IFN-gamma) and interleukin (IL)-2 in response to antigen-specific restimulation when compared with control mice. Adoptively transferred myelin oligodendrocyte glycoprotein 35-55-specific T cells lacking expression of CCR2 were able to induce EAE, whereas CCR2(-/-) recipients of wild-type T cells failed to develop disease. These results suggest that CCR2 expression on host-derived mononuclear cells is critical for disease induction.

Lymphocyte CC chemokine receptor 9 and epithelial thymus-expressed chemokine (TECK) expression distinguish the small intestinal immune compartment: Epithelial expression of tissue-specific chemokines as an organizing principle in regional immunity

The immune system has evolved specialized cellular and molecular mechanisms for targeting and regulating immune responses at epithelial surfaces. Here we show that small intestinal intraepithelial lymphocytes and lamina propria lymphocytes migrate to thymus-expressed chemokine (TECK). This attraction is mediated by CC chemokine receptor (CCR)9, a chemoattractant receptor expressed at high levels by essentially all CD4(+) and CD8(+) T lymphocytes in the small intestine. Only a small subset of lymphocytes in the colon are CCR9(+), and lymphocytes from other tissues including tonsils, lung, inflamed liver, normal or inflamed skin, inflamed synovium and synovial fluid, breast milk, and seminal fluid are universally CCR9(-). TECK expression is also restricted to the small intestine: immunohistochemistry reveals that intense anti-TECK reactivity characterizes crypt epithelium in the jejunum and ileum, but not in other epithelia of the digestive tract (including stomach and colon), skin, lung, or salivary gland. These results imply a restricted role for lymphocyte CCR9 and its ligand TECK in the small intestine, and provide the first evidence for distinctive mechanisms of lymphocyte recruitment that may permit functional specialization of immune responses in different segments of the gastrointestinal tract. Selective expression of chemokines by differentiated epithelium may represent an important mechanism for targeting and specialization of immune responses.

Roles of phospholipid signaling in chemoattractant-induced responses

Chemoattractants, including chemokines, play a central role in regulation of inflammatory reactions by attracting and activating leukocytes. These molecules have been found to regulate metabolism of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) via phospholipase C (PLC) and phosphoinositide 3-kinase (PI3K). Recent studies of mouse lines that lack PLC-(beta)2, PLC-(beta)3, or PI3K(gamma) demonstrate that chemoattractants act through PLC-(beta)2 and PLC-(beta)3 to hydrolyze PtdIns(4,5)P(2) and through PI3K(gamma) to phosphorylate PtdIns(4,5)P(2) in mouse neutrophils. These studies also confirmed the importance and revealed new roles of these signaling pathways in chemoattractant-induced responses.

Antigen presentation in extracellular matrix: interactions of T cells with dendritic cells are dynamic, short lived, and sequential

Cognate interactions of naive T cells with antigen-presenting dendritic cells require physical cell-cell contacts leading to signal induction and T cell activation. Using a three-dimensional collagen matrix videomicroscopy model for ovalbumin peptide-specific activation of murine and oxidative mitogenesis of human T cells, we show that T cells maintain vigorous migration upon cognate interactions to DC (dendritic cell), continuously crawl across the DC surface, and rapidly detach (median within 6-12 min). These dynamic and short-lived encounters favor sequential contacts with the same or other DC and trigger calcium influx, upregulation of activation markers, T blast formation, and proliferation. We conclude that a tissue environment supports the accumulation of sequential signals, implicating a numeric or "digital" control mechanism for an ongoing primary immune response.

Identification of a novel chemokine (CCL28), which binds CCR10 (GPR2)

We report the identification and characterization of a novel CC chemokine designated CCL28 and its receptor CCR10, known previously as orphan G-protein-coupled receptor GPR2. Human and mouse CCL28 share 83% identity at the amino acid and 76% at the nucleic acid levels. We also identified the mouse homologues of CCL28 and of CCR10, which map to mouse chromosomes 13 and 11, respectively. CCL28 is expressed in a variety of human and mouse tissues, and it appears to be predominantly produced by epithelial cells. Both human and mouse CCL28 induce calcium mobilization in human and mouse CCR10-expressing transfectants. CCL28 desensitized the calcium mobilization induced in CCR10 transfectants by CCL27, indicating that these chemokines share this new chemokine receptor. In vitro, recombinant human CCL28 displays chemotactic activity for resting CD4 or CD8 T cells.

MIP-1alpha induces binding of nuclear factors to the kappaB DNA element in human B cells

The chemokine macrophage inflammatory protein-1 alpha (MIP-1alpha) stimulates migration of B cells through an unknown mechanism. Furthermore, little is known about signal transduction mechanisms through which MIP-1alpha might signal phenotypic changes in B cells. We are investigating the role of MIP-1alpha in B cell signaling. Here we report that stimulation of the Ramos B cell line or tonsil B or peripheral blood-B (PBL-B) cells with MIP-1alpha caused the transcription factor NF-kappaB to bind to DNA. NF-kappaB induction was dose dependent, and was transient, with peak induction occurring at 30 min. MIP-1alpha treatment stimulated the degradation of IkappaBalpha, a cytoplasmic inhibitor of NF-kappaB. The biological significance of NF-kappaB activation by MIP-1alpha is currently unknown, but it is known that NF-kappaB modulates expression of genes involved in many inflammatory and immune responses. Here we show that NF-kappaB activation is a target of signals sent into B cells by MIP-1alpha.

Respiratory syncytial virus G and/or SH glycoproteins modify CC and CXC chemokine mRNA expression in the BALB/c mouse

Chemokine mRNA expression by pulmonary leukocytes following infection of BALB/c mice with two strains of respiratory syncytial virus (RSV) and one strain of parainfluenza virus type 3 (PIV-3) was determined. The results suggest that RSV G and/or SH proteins inhibit early MIP-1alpha, MIP-1beta, MIP-2, MCP-1, and IP-10 mRNA expression. TCA-3 mRNA expression was found to be increased during PIV-3 infection.

Up-regulation of macrophage inflammatory protein-3 alpha/CCL20 and CC chemokine receptor 6 in psoriasis

Autoimmunity plays a key role in the immunopathogenesis of psoriasis; however, little is known about the recruitment of pathogenic cells to skin lesions. We report here that the CC chemokine, macrophage inflammatory protein-3 alpha, recently renamed CCL20, and its receptor CCR6 are markedly up-regulated in psoriasis. CCL20-expressing keratinocytes colocalize with skin-infiltrating T cells in lesional psoriatic skin. PBMCs derived from psoriatic patients show significantly increased CCR6 mRNA levels. Moreover, skin-homing CLA+ memory T cells express high levels of surface CCR6. Furthermore, the expression of CCR6 mRNA is 100- to 1000-fold higher on sorted CLA+ memory T cells than other chemokine receptors, including CXCR1, CXCR2, CXCR3, CCR2, CCR3, and CCR5. In vitro, CCL20 attracted skin-homing CLA+ T cells of both normal and psoriatic donors; however, psoriatic lymphocytes responded to lower concentrations of chemokine and showed higher chemotactic responses. Using ELISA as well as real-time quantitative PCR, we show that cultured primary keratinocytes, dermal fibroblasts, and dermal microvascular endothelial and dendritic cells are major sources of CCL20, and that the expression of this chemokine can be induced by proinflammatory mediators such as TNF-alpha/IL-1 beta, CD40 ligand, IFN-gamma, or IL-17. Taken together, these findings strongly suggest that CCL20/CCR6 may play a role in the recruitment of T cells to lesional psoriatic skin.

CCR6 mediates dendritic cell localization, lymphocyte homeostasis, and immune responses in mucosal tissue

Chemokine-directed migration of leukocyte subsets may contribute to the qualitative differences between systemic and mucosal immunity. Here, we demonstrate that in mice lacking the chemokine receptor CCR6, dendritic cells expressing CD11c and CD11b are absent from the subepithelial dome of Peyer's patches. These mice also have an impaired humoral immune response to orally administered antigen and to the enteropathic virus rotavirus. In addition, CCR6(-/-) mice have a 2-fold to 15-fold increase in cells of select T lymphocyte populations within the mucosa, including CD4+ and CD8+ alphabeta-TCR T cells. By contrast, systemic immune responses to subcutaneous antigens in CCR6(-/-) mice are normal. These findings demonstrate that CCR6 is a mucosa-specific regulator of humoral immunity and lymphocyte homeostasis in the intestinal mucosa.

Cutting edge: the orphan chemokine receptor G protein-coupled receptor-2 (GPR-2, CCR10) binds the skin-associated chemokine CCL27 (CTACK/ALP/ILC)

We recently reported the identification of a chemokine (CTACK), which has been renamed CCL27 according to a new systematic chemokine nomenclature. We report that CCL27 binds the previously orphan chemokine receptor GPR-2, as detected by calcium flux and chemotactic responses of GPR-2 transfectants. We renamed this receptor CCR10. Because of the skin-associated expression pattern of CCL27, we focused on the expression of CCL27 and CCR10 in normal skin compared with inflammatory and autoimmune skin diseases. CCL27 is constitutively produced by keratinocytes but can also be induced upon stimulation with TNF-alpha and IL-1beta. CCR10 is not expressed by keratinocytes and is instead expressed by melanocytes, dermal fibroblasts, and dermal microvascular endothelial cells. CCR10 was also detected in T cells as well as in skin-derived Langerhans cells. Taken together, these observations suggest a role for this novel ligand/receptor pair in both skin homeostasis as well as a potential role in inflammatory responses.