Impaired host defense, hematopoiesis, granulomatous inflammation and type 1-type 2 cytokine balance in mice lacking CC chemokine receptor 1

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.

Cleavage by CD26/dipeptidyl peptidase IV converts the chemokine LD78β into a most efficient monocyte attractant and CCR1 agonist

Chemokines are proinflammatory cytokines that play a role in leukocyte migration and activation. Recent reports showed that RANTES (regulated on activation normal T-cell expressed and secreted chemokine), eotaxin, macrophage-derived chemokine (MDC), and stromal cell–derived factor-1 (SDF-1) are NH2-terminally truncated by the lymphocyte surface glycoprotein and protease CD26/dipeptidyl peptidase IV (CD26/DPP IV). Removal of the NH2-terminal dipeptide resulted in impaired inflammatory properties of RANTES, eotaxin, MDC, and SDF-1. The potential CD26/DPP IV substrate macrophage inflammatory protein–1β (MIP-1β) and the related chemokine, LD78α (ie, one of the MIP-1α isoforms), were not affected by this protease. However, CD26/DPP IV cleaved LD78β, a most potent CCR5 binding chemokine and inhibitor of macrophage tropic human immunodeficiency virus–1 (HIV-1) infection, into LD78β(3-70). Naturally truncated LD78β(3-70), but not truncated MIP-1β, was recovered as an abundant chemokine form from peripheral blood mononuclear cells. In contrast to all other chemokines processed by CD26/DPP IV, LD78β(3-70) had increased chemotactic activity in comparison to intact LD78β. With a minimal effective concentration of 30 pmol/L, LD78β(3-70) became the most efficient monocyte chemoattractant. LD78β(3-70) retained its high capacity to induce an intracellular calcium increase in CCR5-transfected cells. Moreover, on CCR1 transfectants, truncated LD78β(3-70) was 30-fold more potent than intact LD78β. Thus, CD26/DPP IV can exert not only a negative but also a positive feedback during inflammation by increasing the specific activity of LD78β. CD26/DPP IV–cleaved LD78β(3-70) is the most potent CCR1 and CCR5 agonist that retains strong anti–HIV-1 activity, indicating the importance of the chemokine-protease interaction in normal and pathologic conditions.

Cleavage by CD26/dipeptidyl peptidase IV converts the chemokine LD78β into a most efficient monocyte attractant and CCR1 agonist

Chemokines are proinflammatory cytokines that play a role in leukocyte migration and activation. Recent reports showed that RANTES (regulated on activation normal T-cell expressed and secreted chemokine), eotaxin, macrophage-derived chemokine (MDC), and stromal cell–derived factor-1 (SDF-1) are NH2-terminally truncated by the lymphocyte surface glycoprotein and protease CD26/dipeptidyl peptidase IV (CD26/DPP IV). Removal of the NH2-terminal dipeptide resulted in impaired inflammatory properties of RANTES, eotaxin, MDC, and SDF-1. The potential CD26/DPP IV substrate macrophage inflammatory protein–1β (MIP-1β) and the related chemokine, LD78α (ie, one of the MIP-1α isoforms), were not affected by this protease. However, CD26/DPP IV cleaved LD78β, a most potent CCR5 binding chemokine and inhibitor of macrophage tropic human immunodeficiency virus–1 (HIV-1) infection, into LD78β(3-70). Naturally truncated LD78β(3-70), but not truncated MIP-1β, was recovered as an abundant chemokine form from peripheral blood mononuclear cells. In contrast to all other chemokines processed by CD26/DPP IV, LD78β(3-70) had increased chemotactic activity in comparison to intact LD78β. With a minimal effective concentration of 30 pmol/L, LD78β(3-70) became the most efficient monocyte chemoattractant. LD78β(3-70) retained its high capacity to induce an intracellular calcium increase in CCR5-transfected cells. Moreover, on CCR1 transfectants, truncated LD78β(3-70) was 30-fold more potent than intact LD78β. Thus, CD26/DPP IV can exert not only a negative but also a positive feedback during inflammation by increasing the specific activity of LD78β. CD26/DPP IV–cleaved LD78β(3-70) is the most potent CCR1 and CCR5 agonist that retains strong anti–HIV-1 activity, indicating the importance of the chemokine-protease interaction in normal and pathologic conditions.

The chemokine macrophage-inflammatory protein-1 alpha and its receptor CCR1 control pulmonary inflammation and antiviral host defense in paramyxovirus infection

In this work, we explore the responses of specific gene-deleted mice to infection with the paramyxovirus pneumonia virus of mice (PVM). We have shown previously that infection of wild type mice with PVM results in pulmonary neutrophilia and eosinophilia accompanied by local production of macrophage-inflammatory protein-1 alpha (MIP-1 alpha). Here we examine the role of MIP-1 alpha in the pathogenesis of this disease using mice deficient in MIP-1 alpha or its receptor, CCR1. The inflammatory response to PVM in MIP-1 alpha-deficient mice was minimal, with approximately 10-60 neutrophils/ml and no eosinophils detected in bronchoalveolar lavage fluid. Higher levels of infectious virus were recovered from lung tissue excised from MIP-1 alpha-deficient than from fully competent mice, suggesting that the inflammatory response limits the rate of virus replication in vivo. PVM infection of CCR1-deficient mice was also associated with attenuated inflammation, with enhanced recovery of infectious virus, and with accelerated mortality. These results suggest that the MIP-1 alpha/CCR1-mediated acute inflammatory response protects mice by delaying the lethal sequelae of infection.

Enhanced pulmonary allergic responses to Aspergillus in CCR2-/- mice

Allergic responses to Aspergillus species exacerbate asthma and cystic fibrosis. The natural defense against live Aspergillus fumigatus spores or conidia depends on the recruitment and activation of mononuclear and polymorphonuclear leukocytes, events that are dependent on chemotactic cytokines. In this study, we explored the relative contribution of the monocyte chemoattractant protein-1 receptor, CCR2, in the pulmonary response to A. fumigatus conidia. Following sensitization to soluble A. fumigatus Ags, mice lacking CCR2 due to targeted deletion were markedly more susceptible to the injurious effects of an intrapulmonary challenge with live conidia compared with mice that expressed CCR2 or CCR2+/+. CCR2-/- mice exhibited a major defect in the recruitment of polymorphonuclear cells, but these mice also had significantly more eosinophils and lymphocytes in bronchoalveolar lavage samples. CCR2-/- mice also had significant increases in serum levels of total IgE and whole lung levels of IL-5, IL-13, eotaxin, and RANTES compared with CCR2+/+ mice. Airway inflammation, hyper-responsiveness to spasmogens, and subepithelial fibrosis were significantly enhanced in CCR2-/- mice compared with CCR2+/+ mice after the conidia challenge. Thus, these findings demonstrate that CCR2 plays an important role in the immune response against A. fumigatus, thereby limiting the allergic airway inflammatory and remodeling responses to this fungus.

Airway remodeling is absent in CCR1-/- mice during chronic fungal allergic airway disease

Asthmatic-like reactions characterized by elevated IgE, Th2 cytokines, C-C chemokines, eosinophilic inflammation, and persistent airway hyperresponsiveness follow pulmonary exposure to the spores or conidia from Aspergillus fumigatus fungus in sensitized individuals. In addition to these features, subepithelial fibrosis and goblet cell hyperplasia characterizes fungal-induced allergic airway disease in mice. Because lung concentrations of macrophage inflammatory protein-1alpha and RANTES were significantly elevated after A. fumigatus-sensitized mice received an intrapulmonary challenge with A. fumigatus spores or conidia, the present study addressed the role of their receptor, C-C chemokine receptor 1 (CCR1), in this model. A. fumigatus-sensitized CCR1 wild-type (+/+) and CCR1 knockout (-/-) mice exhibited similar increases in serum IgE and polymorphonuclear leukocyte numbers in the bronchoalveolar lavage. Airway hyperresponsiveness was prominent in both groups of mice at 30 days after an intrapulmonary challenge with A. fumigatus spores or conidia. However, whole lung levels of IFN-gamma were significantly higher whereas IL-4, IL-13, and Th2-inducible chemokines such as C10, eotaxin, and macrophage-derived chemokine were significantly lower in whole lung samples from CCR1-/- mice compared with CCR1+/+ mice at 30 days after the conidia challenge. Likewise, significantly fewer goblet cells and less subepithelial fibrosis were observed around large airways in CCR1-/- mice at the same time after the conidia challenge. Thus, these findings demonstrate that CCR1 is a major contributor to the airway remodeling responses that arise from A. fumigatus-induced allergic airway disease.

The chemokine/chemokine-receptor family: potential and progress for therapeutic intervention

The chemokines are a large superfamily of chemotactic cytokines that are utilized to direct the trafficking and migration of leukocytes within the immune system. The chemokines mediate their activity through a large family of G-protein-coupled receptors, and thus are highly tractable as therapeutic targets. Exciting advances have been made in the field within the past year, not the least of which is the disclosure of potent antagonists of several chemokine receptors. Several CCR5 antagonists have demonstrated potent antiviral activity and may represent novel therapeutic agents for the treatment of AIDS. In addition, new biological insights have been gained from the demonstration that the targeting of cells to inflammatory sites is tissue specific, such that different chemokine/chemokine-receptor pairs are utilized in recruitment of T-lymphocytes to the skin and to the intestine. Also, utilization of neutralizing antibodies to the CXCR3 ligand Mig in murine allograft transplantation models has demonstrated the importance of CXCR3 in orchestrating T-cell-mediated tissue rejection.

Macrophage inflammatory protein-1 alpha is a critical mediator of host defense against invasive pulmonary aspergillosis in neutropenic hosts

Invasive pulmonary aspergillosis is a devastating complication of immunosuppression that usually occurs in neutropenic patients. In this setting, augmentation of the antifungal activity of available immune cells may improve the outcome of the infection. Macrophage inflammatory protein-1 alpha (MIP-1 alpha) is a CC chemokine with potent chemotactic activity for various subsets of mononuclear leukocytes. We therefore tested the hypothesis that the influx of mononuclear cells into the lung in invasive pulmonary aspergillosis is in part mediated by MIP-1 alpha, and the manipulation of this ligand alters the outcome of the infection. We found that in both immunocompetent and neutropenic mice, MIP-1 alpha was induced in the lungs in response to intratracheal administration of Aspergillus fumigatus conidia. In neutrophil-depleted mice challenged with intratracheal conidia, there was evidence of invasive fungal pneumonia associated with a predominantly mononuclear leukocyte infiltrate. Ab-mediated depletion of MIP-1 alpha resulted in a 6-fold increase in mortality in neutropenic mice, which was associated with a 12-fold increase in lung fungal burden. Studies of single-cell suspensions of whole lungs revealed a 36% decrease in total lung leukocyte infiltration as a result of MIP-1 alpha neutralization. Flow cytometry on whole lung suspensions showed a 41% reduction in lung monocyte/macrophages as a result of MIP-1 alpha neutralization, but no difference in other lung leukocyte subsets. These studies indicate that MIP-1 alpha is a critical mediator of host defense against A. fumigatus in the setting of neutropenia and may be an important target in devising future therapeutic strategies against invasive aspergillosis.

Mice with a selective deletion of the CC chemokine receptors 5 or 2 are protected from dextran sodium sulfate-mediated colitis: lack of CC chemokine receptor 5 expression results in a NK1.1+ lymphocyte-associated Th2-type immune response in the intestine

The chemokine receptors CCR2 and CCR5 and their respective ligands regulate leukocyte chemotaxis and activation. To determine the role of these chemokine receptors in the regulation of the intestinal immune response, we induced colitis in CCR2- and CCR5-deficient mice by continuous oral administration of dextran sodium sulfate (DSS). Both CCR2- and CCR5-deficient mice were susceptible to DSS-induced intestinal inflammation. The lack of CCR2 or CCR5 did not reduce the DSS-induced migration of macrophages into the colonic lamina propria. However, both CCR5-deficient mice and, to a lesser degree, CCR2-deficient mice were protected from DSS-induced intestinal adhesions and mucosal ulcerations. CCR5-deficient mice were characterized by a greater relative infiltration of CD4+ and NK1.1+ lymphocyte in the colonic lamina propria when compared to wild-type and CCR2-deficient mice. In CCR5-deficient mice, mucosal mRNA expression of IL-4, IL-5, and IL-10 was increased, whereas that of IFN-gamma was decreased, corresponding to a Th2 pattern of T cell activation. In CCR2-deficient mice, the infiltration of Th2-type T cells in the lamina propria was absent, but increased levels of IL-10 and decreased levels of IFN-gamma may have down regulated mucosal inflammation. Our data indicate that CCR5 may be critical for the promotion of intestinal Th1-type immune responses in mice.

Immunolocalization of macrophage adhesion molecule-1 and macrophage inflammatory protein-1 in schistosomal soluble egg antigen-induced granulomatous hyporesponsiveness

This work studied the histopathological changes and the changes in the expression of macrophage adhesion molecule-1 (Mac-1) and macrophage inflammatory protein-1alpha (MIP-1alpha) in a murine model of soluble egg antigen (SEA) - induced granulomatous hyporesponsiveness. Histopathological results of hepatic sections in an SEA group showed early acceleration of ova destruction and markedly diminished granuloma cellularity with eosinophils and macrophages still being the predominant cells. Later, giant cells and pigmented macrophages that were scattered among granuloma cells and in intimate contact with the deposited eggs were more predominant in the SEA group than in the infected control group. Concurrently, the counts of Mac-1 positive cells were significantly increased in liver sections of the SEA group than the infected control group during the course of infection. MIP-1alpha showed early higher counts followed by lower counts in the later stages of infection on granuloma cells in the SEA group than the infected control group. During the course of infection, similar distribution of Mac-1 and MIP-1alpha was present in both groups. This study suggests that sensitization with SEA probably leads to enhancement of phagocytic activity of macrophages via increasing expression of Mac-1 and hence engulfment of ic3b coated schistosomal products such as ova. It leads to rapid destruction of ova and hence decreases the host inflammatory response to infection and amelioration of hepatic pathology which would be a promising approach in reduction of host morbidity and mortality.

Are chemokines essential or secondary participants in allergic responses?

OBJECTIVES

This review will provide a concise and critical overview of the rapidly evolving concepts in chemokine biology with a special relevance to allergic responses. The article is intended for clinicians with little or no expertise in chemokine biology.

DATA SOURCES

A detailed literature search was performed through MEDLINE (PubMed). Those reports considered important and relevant to the topic were critically reviewed and their conclusions included.

RESULTS

Chemokines are a group of structurally related small proteins with a common biological activity of inducing directional migration (chemotaxis) of various cell types. Chemokines such as eotaxins and MCP-4 play a key role in selective eosinophil recruitment to sites of inflammation in allergies and asthma. Several other chemokine activities relevant to allergic responses are: activation of basophils and eosinophils to release inflammatory mediators, regulation of IgE responses, and Th1/Th2-type cytokine balance. A number of therapeutic strategies aimed at inhibiting chemokine function are being tested in animal models of allergies and asthma.

CONCLUSIONS

Chemokines have been widely viewed as pathogenic mediators of acute and chronic inflammation and tissue damage in allergies and asthma. On the other hand, recent evidence suggests that endogenous production of certain chemokines might be beneficial to the host in preventing allergic response. Met-RANTES, a modified antagonist of RANTES, and eotaxin receptor (CCR3) antagonists, represent promising novel therapeutic agents potentially useful in atopic disorders. Thus, suppression of chemokines may interrupt the sequence of signals culminating in an allergic response. Whether chemokines are actually essential for an allergic response awaits confirmation with gene knockout animal experiments.

Enhanced hematopoietic activity accompanies parasite expansion in the spleen and bone marrow of mice infected with Leishmania donovani

In this study, we have analyzed hematopoietic activity in the spleen, bone marrow, and blood of BALB/c and scid mice infected with Leishmania donovani. Our analysis demonstrates that infection induces a rapid but transient mobilization of progenitor cells into the circulation, associated with elevated levels of granulocyte/macrophage colony-stimulating factor (GM-CSF) and MIP-1alpha. From 14 to 28 days postinfection, when parasite expansion begins in the spleen and bone marrow, both the frequency and cell cycle activity of hematopoietic progenitors, particulary CFU-granulocyte, monocyte, are dramatically increased in these organs. This is associated with increased accumulation of mRNA for GM-CSF, M-CSF, and G-CSF, but not interleukin-3. Our data also illustrate that hematopoietic activity, as assessed by changes in the frequency of progenitor cell populations and their levels of cell cycle activity, can be regulated in both a T-cell-independent and T-cell-dependent, as well as in an organ-specific, manner. Collectively, these data add to our knowledge of the long-term changes which occur in organs in which L. donovani is able to persist.

Chemokine signaling in inflammation

The events that lead to an inflammatory response are characterized by recognition of the site of injury by inflammatory cells, specific recruitment of subpopulations of leukocytes into tissue, removal of the offending agent and "debridement" of the injured cells/tissue, and repair of the site of injury with attempts to reestablish normal parenchymal, stromal, and extracellular matrix relationship. The molecular regulation of this complex physiologic process involves the interaction between cell surface, extracellular matrix, and soluble mediators, such as chemokines. Chemokine activities are mediated through G-protein coupled receptors. This is the largest known family of cell-surface receptors, which mediate transmission of stimuli as diverse as hormones, peptides, glycopeptides, and chemokines. In this review, we will focus on the signaling pathways involved in the production and function of chemokines as they relate to the inflammatory response.

Cutaneous injection of human subjects with macrophage inflammatory protein-1 alpha induces significant recruitment of neutrophils and monocytes

Macrophage inflammatory protein (MIP-1 alpha), a member of the CC chemokine subfamily, has been shown to attract T cells and monocytes in vitro and to be expressed at sites of inflammation. Although the in vitro activities of MIP-1 alpha have been well documented, the in vivo biological activities of MIP-1 alpha in humans have not been studied. To address this, we challenged human subjects by intradermal injection with up to 1000 pmol of MIP-1 alpha and performed biopsies 2, 10, and 24 h later. Although no acute cutaneous or systemic reactions were noted, endothelial cell activation, as indicated by the expression of E-selectin, was observed. In agreement with its in vitro activity, monocyte, lymphocyte, and, to a lesser degree, eosinophil infiltration was observed, peaking at 10-24 h. Surprisingly, in contrast to its reported lack of in vitro neutrophil-stimulating activity, a rapid infiltration of neutrophils was observed in vivo. This neutrophil infiltration occurred as early as 2 h, preceding the appearance of other cells, and peaked at 10 h. Interestingly, we found that neutrophils in whole blood, but not after isolation, expressed CCR1 on their cell surface. This CCR1 was thought to be functional as assessed by neutrophil CD11b up-regulation following whole-blood MIP-1 alpha stimulation. These studies substantiate the biological effects of MIP-1 alpha on monocytes and lymphocytes and uncover the previously unrecognized activity of MIP-1 alpha to induce neutrophil infiltration and endothelial cell activation, underscoring the need to evaluate chemokines in vivo in humans.

Chemokines fail to up-regulate beta 1 integrin-dependent adhesion in human Th2 T lymphocytes

Th1 and Th2 cells are functionally distinct subsets of CD4+ T lymphocytes whose tissue-specific homing to sites of inflammation is regulated in part by the differential expression of P- and E-selectin ligands and selected chemokine receptors. Here we investigated the expression and function of beta 1 integrins in Th1 and Th2 cells polarized in vitro. Th1 lymphocytes adhere transiently to the extracellular matrix ligands laminin 1 and fibronectin in response to chemokines such as RANTES and stromal cell-derived factor-1, and this process is paralleled by the activation of the Rac1 GTPase and by a rapid burst of actin polymerization. Selective inhibitors of phosphoinositide-3 kinase prevent efficiently all of the above processes, whereas the protein kinase C inhibitor bisindolylmaleimide prevents chemokine-induced adhesion without affecting Rac1 activation and actin polymerization. Notably, chemokine-induced adhesion to beta 1 integrin ligands is markedly reduced in Th2 cells. Such a defect cannot be explained by a reduced sensitivity to chemokine stimulation in this T cell subset, nor by a defective activation of the signaling cascade involving phosphoinositide-3 kinase, Rac1, and actin turnover, as all these processes are activated at comparable levels by chemokines in the two subsets. We propose that reduced beta 1 integrin-mediated adhesion in Th2 cells may restrain their ability to invade and/or reside in sites of chronic inflammation, which are characterized by thickening of basement membranes and extensive fibrosis, requiring efficient interaction with organized extracellular matrices.

Pivotal role of CCR1-positive leukocytes in bleomycin-induced lung fibrosis in mice

We have investigated the involvement of chemokine receptor CCR1-positive cells in bleomycin-induced lung injury, a model of pulmonary fibrosis. After bleomycin challenge in C57BL/6J mice, the expression of CCR1 mRNA increased and peaked at day 7, which paralleled to the expression of its ligands, macrophage-inflammatory protein-1 alpha and RANTES. Immunohistochemical study showed that CCR1-positive cells accumulated in the interstitial inflammatory site. Furthermore, the treatment of anti-CCR1 Ab significantly reduced the accumulation of inflammatory cells and collagen deposition, resulting in dramatic improvement of survival. These results suggest that CCR1-positive cells play significant roles in the pathogenesis of pulmonary fibrosis subsequent to bleomycin-induced lung injury, and that CCR1 could be a novel molecular target for intervention therapy against pulmonary fibrosis.

Chronic airway hyperreactivity, goblet cell hyperplasia, and peribronchial fibrosis during allergic airway disease induced by Aspergillus fumigatus

Clinical allergic airway disease is associated with persistent airway hyperreactivity and remodeling, but little is known about the mechanisms leading to these alterations. This paucity of information is related in part to the absence of chronic models of allergic airway disease. Herein we describe a model of persistent airway hyperreactivity, goblet cell hyperplasia, and subepithelial fibrosis that is initiated by the intratracheal introduction of Aspergillus fumigatus spores or conidia into the airways of mice previously sensitized to A. fumigatus. Similar persistent airway alterations were not observed in nonsensitized mice challenged with A. fumigatus conidia alone. A. fumigatus-sensitized mice exhibited significantly enhanced airway hyperresponsiveness to a methacholine challenge that was still present at 30 days after the conidia challenge. Eosinophils and lymphocytes were present in bronchoalveolar lavage (BAL) samples from A. fumigatus-sensitized mice at all times after conidia challenge. Compared with levels measured in A. fumigatus-sensitized mice immediately before conidia, significantly elevated interferon-gamma (IFN-gamma) and transforming growth factor (TGF-beta) levels were present in whole lung homogenates up to 7 days after the conidia challenge. At day 30 after conidia challenge, significantly elevated levels of interleukin-4 (IL-4) and IL-13 were present in the A. fumigatus-sensitized mice. Histological analysis revealed profound goblet cell hyperplasia and airway fibrosis at days 30 after conidia, and the latter finding was confirmed by hydroxyproline measurements. Thus the introduction of A. fumigatus conidia into A. fumigatus-sensitized mice results in persistent airway hyperresponsiveness, fibrosis, and goblet cell hyperplasia.

Granulocyte macrophage colony-stimulating factor and interleukin-3 regulate chemokine and chemokine receptor expression in bone marrow macrophages

The beta-chemokine macrophage inflammatory protein-1 alpha (MIP-1alpha) and its associated receptors are involved in the regulation of pro-inflammatory and haemopoietic processes. This study was designed to investigate regulation of expression MIP-1alpha and its receptors by other haemopoietic cytokines. Murine bone marrow macrophages (BMM) were treated with or without GM-CSF or IL-3 and expression of MIP-1alpha, other chemokines and their receptors examined by Northern blotting. Receptor levels were also examined using Scatchard analysis and functional tests. Treatment of BMM with GM-CSF revealed a striking increase in MIP-1alpha mRNA levels, relative to untreated cells with a corresponding increase in MIP-1alpha protein. A similar increase in mRNA levels was found when BMM were treated with IL-3. An increase in the expression of three other beta-chemokines namely MIP-1beta, MCP-1 and MCP-3, was also found following treatment with GM-CSF or IL-3. We have additionally examined the expression of the known beta-chemokine receptors in BMM and observed an increase in CCR1 mRNA levels following treatment with GM-CSF and IL-3, but no change was seen in the level of CCR5 expression. The increase in CCR1 expression was reflected in an increase in the number of cell surface receptors for MIP-1alpha on the GM-CSF treated BMM and in an enhanced response of the GM-CSF treated BMM to CCR1 ligands. These data suggest that GM-CSF and IL-3 may be involved in mechanisms regulating expression levels of MIP-1alpha and its receptors.

Lack of chemokine receptor CCR1 enhances Th1 responses and glomerular injury during nephrotoxic nephritis

During the development of nephrotoxic nephritis (NTN) in the mouse, we find that a variety of chemokines and chemokine receptors are induced: CCR1 (RANTES, MIP-1alpha), CCR2 (MCP-1), CCR5 (RANTES, MIP-1alpha, MIP-1beta), CXCR2 (MIP-2), and CXCR3 (IP-10). Their timing of expression indicated that CXCR2 and CCR1 are probably important in the neutrophil-dependent heterologous phase of the disease, whereas CCR1, CCR2, CCR5, and CXCR3 accompany the subsequent mononuclear cell infiltration characteristic of autologous disease. We therefore assessed the role of CCR1 in NTN using CCR1(-/-) mice. We found that neutrophil accumulation in CCR1(-/-) mice was comparable to that in wild-type animals but that renal recruitment of CD4(+) and CD8(+) T cells and macrophages increased significantly. Moreover, CCR1(-/-) mice developed more severe glomerulonephritis than did controls, with greater proteinuria and blood urea nitrogen, as well as a higher frequency of crescent formation. In addition, CCR1(-/-) mice showed enhanced Th1 immune responses, including titers of antigen-specific IgG2a antibody, delayed-type hypersensitivity responses, and production of IFN-gamma and TNF-alpha. Lastly, using recombinant proteins and transfected cells that overexpressed CCR1, we demonstrated that MIP-1alpha, but not RANTES, bound CCR1 and induced cell chemotaxis. Thus, rather than simply promoting leukocyte recruitment during NTN, CCR1 expression profoundly alters the effector phase of glomerulonephritis. Therapeutic targeting of chemokine receptors may, on occasion, exacerbate underlying disease.

Differentiation Stage–Specific Regulation of Primitive Human Hematopoietic Progenitor Cycling by Exogenous and Endogenous Inhibitors in an In Vivo Model

Nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice transplanted with human cord blood or adult marrow cells and injected 6 weeks posttransplant with 2 daily doses of transforming growth factor-β1 (TGF-β1), monocyte chemoattractant protein-1 (MCP-1), or a nonaggregating form of macrophage inflammatory protein-1 (MIP-1) showed unique patterns of inhibition of human progenitor proliferation 1 day later. TGF-β1 was active on long-term culture initiating cells (LTC-IC) and on primitive erythroid and granulopoietic colony-forming cells (HPP-CFC), but had no effect on mature CFC. MCP-1 inhibited the cycling of both types of HPP-CFC but not LTC-IC. MIP-1 did not inhibit either LTC-IC or granulopoietic HPP-CFC but was active on erythroid HPP-CFC and mature granulopoietic CFC. All of these responses were independent of the source of human cells transplanted. LTC-IC of either human cord blood or adult marrow origin continue to proliferate in NOD/SCID mice for many weeks, although the turnover of all types of human CFC in mice transplanted with adult human marrow (but not cord blood) is downregulated after 6 weeks. Interestingly, administration of either MIP-1β, an antagonist of both MIP-1 and MCP-1 or MCP-1(9-76), an antagonist of MCP-1 (and MCP-2 and MCP-3), into mice in which human marrow-derived CFC had become quiescent, caused the rapid reactivation of these progenitors in vivo. These results provide the first definition of stage-specific inhibitors of human hematopoietic progenitor cell cycling in vivo. In addition they show that endogenous chemokines can contribute to late graft failure, which can be reversed by the administration of specific antagonists.

CXC Chemokine Receptor-2 Ligands Are Necessary Components of Neutrophil-Mediated Host Defense in Invasive Pulmonary Aspergillosis

Invasive pulmonary aspergillosis is a devastating complication of immunosuppression, which occurs in association with neutrophil dysfunction or deficiency. ELR+ CXC chemokines are a subfamily of chemokines that play a critical role in neutrophil chemotaxis and activation both in vitro and in vivo. We hypothesized that interaction of these ligands with CXC chemokine receptor-2 (CXCR2), their sole murine receptor, is a major component of neutrophil-dependent pulmonary host defense against Aspergillus fumigatus. In immunocompetent animals, neutrophils were recruited to the lung in response to intratracheally administered A. fumigatus conidia. In a model of transient in vivo depletion of neutrophils, animals developed invasive pulmonary aspergillosis, associated with delayed influx of neutrophils into the lung. In both normal and neutrophil-depleted animals, the ELR+ CXC chemokines MIP-2 and KC were induced in response to intratracheal administration of conidia. Ab-mediated neutralization of the common ELR+ CXC chemokine receptor, CXCR2, resulted in development of invasive disease indistinguishable from the disease in neutrophil-depleted animals, while control animals were highly resistant to the development of infection. CXCR2 neutralization was associated with reduced lung neutrophil influx and resulted in a marked increase in mortality compared with controls. In contrast, animals with constitutive lung-specific transgenic expression of KC were resistant to the organism, with reduced mortality and lower lung burden of fungus. We conclude that CXCR2 ligands are essential mediators of host defense against A. fumigatus, and may be important targets in devising future therapeutic strategies in this disease.

Differentiation Stage–Specific Regulation of Primitive Human Hematopoietic Progenitor Cycling by Exogenous and Endogenous Inhibitors in an In Vivo Model

Nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice transplanted with human cord blood or adult marrow cells and injected 6 weeks posttransplant with 2 daily doses of transforming growth factor-β1 (TGF-β1), monocyte chemoattractant protein-1 (MCP-1), or a nonaggregating form of macrophage inflammatory protein-1 (MIP-1) showed unique patterns of inhibition of human progenitor proliferation 1 day later. TGF-β1 was active on long-term culture initiating cells (LTC-IC) and on primitive erythroid and granulopoietic colony-forming cells (HPP-CFC), but had no effect on mature CFC. MCP-1 inhibited the cycling of both types of HPP-CFC but not LTC-IC. MIP-1 did not inhibit either LTC-IC or granulopoietic HPP-CFC but was active on erythroid HPP-CFC and mature granulopoietic CFC. All of these responses were independent of the source of human cells transplanted. LTC-IC of either human cord blood or adult marrow origin continue to proliferate in NOD/SCID mice for many weeks, although the turnover of all types of human CFC in mice transplanted with adult human marrow (but not cord blood) is downregulated after 6 weeks. Interestingly, administration of either MIP-1β, an antagonist of both MIP-1 and MCP-1 or MCP-1(9-76), an antagonist of MCP-1 (and MCP-2 and MCP-3), into mice in which human marrow-derived CFC had become quiescent, caused the rapid reactivation of these progenitors in vivo. These results provide the first definition of stage-specific inhibitors of human hematopoietic progenitor cell cycling in vivo. In addition they show that endogenous chemokines can contribute to late graft failure, which can be reversed by the administration of specific antagonists.

Defects in the Generation of IFN-γ Are Overcome to Control Infection with Leishmania donovani in CC Chemokine Receptor (CCR) 5-, Macrophage Inflammatory Protein-1α-, or CCR2-Deficient Mice

We investigated the immune responses in mice lacking CCR2, CCR5, or macrophage inflammatory protein-1α (MIP-1α), a ligand for CCR5, in two situations: following T cell stimulation or after challenge with Leishmania donovani, an intracellular microbe whose control is dependent on a Th1 immune response. Mice deficient in CCR5, MIP-1α, or CCR2 had reduced IFN-γ responses following ligation of the TCR. Reduced IFN-γ responses following PMA and ionomycin were also observed in CD8+ T cells of CCR5−/− and CCR2−/− mice. During the early phases of infection, all three knockout mice had low Ag-specific IFN-γ responses. However, this reduced IFN-γ response was overcome during a state of persistent Ag stimulation (chronic infection), and was not associated with an adverse parasitologic outcome in any of the gene-targeted mouse strains. To the contrary, during the late phase of infection, an exaggerated Ag-specific IFN-γ response was evident in CCR5−/− and MIP-1α−/− mice, and this correlated with an enhanced control of parasite replication. Although granuloma formation was abnormal in each of the knockout mice, there was no correlation between the number or architecture of the granulomas and parasite burden. Collectively, these findings indicate an important role for CCR5, MIP-1α, and CCR2 in granulomatous inflammation, and that CCR5 and MIP-1α, possibly acting through CCR5, might play a deleterious role in the outcome of chronic L. donovani infection. Our data also suggest that there might be cross-talk between TCR and chemokine receptor signaling pathways.

SDF-1 Responsiveness Does Not Correlate With CXCR4 Expression Levels of Developing Human Bone Marrow B Cells

Chemokines and their receptors are broadly expressed in different tissues and are involved in diverse biologic processes. Gene inactivation studies have shown that both stromal cell derived factor-1 (SDF-1) and chemokine receptor 4 (CXCR4) are essential for B lymphopoiesis. However, it is not yet clear by which mechanisms B lymphopoiesis is affected. In the present study, we have examined CXCR4 expression and function on primary B cells representing sequential stages of development (eg, pro-B, pre-B, immature, and mature B cells) in fetal and adult bone marrow. The expression of CXCR4 was observed to be sinusoidal. Expression was highest on pre-B cells, decreased as cells developed into immature B cells, and then increased again upon transition to the mature B-cell stage. The corresponding ligand SDF-1 was shown to trigger vigorous cell signaling and migration responses, which are restricted to early lineage B cells. The responsiveness to SDF-1 was markedly decreased for immature and mature B cells despite relatively high levels of CXCR4 expression. Thus, the diminished responsiveness to SDF-1 by more mature B cells was determined to be disproportionate to the level of CXCR4 expression. These findings raise the possibility that CXCR4 function is differentially controlled during B lymphopoiesis and may be relevant to the compartmentalization of B-cell precursors in the bone marrow.

SDF-1 Responsiveness Does Not Correlate With CXCR4 Expression Levels of Developing Human Bone Marrow B Cells

Chemokines and their receptors are broadly expressed in different tissues and are involved in diverse biologic processes. Gene inactivation studies have shown that both stromal cell derived factor-1 (SDF-1) and chemokine receptor 4 (CXCR4) are essential for B lymphopoiesis. However, it is not yet clear by which mechanisms B lymphopoiesis is affected. In the present study, we have examined CXCR4 expression and function on primary B cells representing sequential stages of development (eg, pro-B, pre-B, immature, and mature B cells) in fetal and adult bone marrow. The expression of CXCR4 was observed to be sinusoidal. Expression was highest on pre-B cells, decreased as cells developed into immature B cells, and then increased again upon transition to the mature B-cell stage. The corresponding ligand SDF-1 was shown to trigger vigorous cell signaling and migration responses, which are restricted to early lineage B cells. The responsiveness to SDF-1 was markedly decreased for immature and mature B cells despite relatively high levels of CXCR4 expression. Thus, the diminished responsiveness to SDF-1 by more mature B cells was determined to be disproportionate to the level of CXCR4 expression. These findings raise the possibility that CXCR4 function is differentially controlled during B lymphopoiesis and may be relevant to the compartmentalization of B-cell precursors in the bone marrow.

Cutting Edge: Role of C-C Chemokine Receptor 5 in Organ-Specific and Innate Immunity to Cryptococcus neoformans

After intratracheal inoculation of the AIDS-associated pathogen Cryptococcus neoformans, 12-wk survival was >90% for CCR5+/+ mice but <25% for CCR5−/− mice. There were no defects in lung leukocyte recruitment (wk 5), pulmonary clearance, or delayed-type hypersensitivity in CCR5−/− mice. However, CCR5−/− mice had defects in leukocyte recruitment into the brain and, strikingly, in elimination of cryptococcal polysaccharide from the brain. In nonimmune CCR5−/− mice, there was a significant defect in macrophage recruitment after challenge with shed cryptococcal products (C. neoformans filtrate Ag) but not other nonspecific stimuli. Thus, CCR5 plays specific roles in innate immunity and organ-specific leukocyte trafficking during host defense against C. neoformans.

Integrating conflicting chemotactic signals. The role of memory in leukocyte navigation

Leukocytes navigate through complex chemoattractant arrays, and in so doing, they must migrate from one chemoattractant source to another. By evaluating directional persistence and chemotaxis during neutrophil migration under agarose, we show that cells migrating away from a local chemoattractant, against a gradient, display true chemotaxis to distant agonists, often behaving as if the local gradient were without effect. We describe two interrelated properties of migrating cells that allow this to occur. First, migrating leukocytes can integrate competing chemoattractant signals, responding as if to the vector sum of the orienting signals present. Second, migrating cells display memory of their recent environment: cells' perception of the relative strength of orienting signals is influenced by their history, so that cells prioritize newly arising or newly encountered attractants. We propose that this cellular memory, by promoting sequential chemotaxis to one attractant after another, is in fact responsible for the integration of competitive orienting signals over time, and allows combinations of chemoattractants to guide leukocytes in a step-by-step fashion to their destinations within tissues.

Chemokines in the CNS: plurifunctional mediators in diverse states

The past decade has witnessed the remarkable ascendance of chemokines as pivotal regulatory molecules in cellular communication and trafficking. Evidence increasingly implicates chemokines and chemokine receptors as plurifunctional molecules that have a significant impact on the CNS. Initially, these molecules were found to be involved in the pathogenesis of many important neuroinflammatory diseases that range from multiple sclerosis and stroke to HIV encephalopathy. However, more-recent studies have fuelled the realization that, in addition to their role in pathological states, chemokines and their receptors have an important role in cellular communication in the developing and the normal adult CNS. For example, stromal-cell-derived factor 1, which is synthesized constitutively in the developing brain, has an obligate role in neurone migration during the formation of the granule-cell layer of the cerebellum. Many chemokines are capable of directly regulating signal-transduction pathways that are involved in a variety of cellular functions, which range from synaptic transmission to growth. Clearly, the potential use of chemokines and their receptors as targets for therapeutic intervention in CNS disease might now have to be considered in the context of the broader physiological functions of these molecules.

Rat macrophage inflammatory protein-1alpha, a CC chemokine, acts as a neutrophil chemoattractant in vitro and in vivo

Recombinant rat macrophage inflammatory protein-1alpha (rMIP-1alpha) at a concentration of 3x10(-8) M had strong neutrophil chemotactic activity, though the potency of rMIP-1alpha was less than that of cytokine-induced neutrophil chemoattractant (CINC)-1 at lower concentrations. In addition, rMIP-1alpha induced neutrophil chemotaxis in vivo when rMIP-1alpha was injected into the preformed air-pouch on the back of rats. The adhesion of rMIP-1alpha-treated neutrophils to fibrinogen significantly increased, reaching a maximum adhesion at 10(-8) M. Stimulation of neutrophils with rMIP-1alpha induced a transient increase in intracellular free [Ca2+] dose-dependently. rMIP-1alpha still induced an increase in the intracellular [Ca2+] of rat neutrophils stimulated first with CINC-1, CINC-3 or C5a, suggesting that rat neutrophils have a specific receptor for rMIP-1alpha. Supporting these findings, an additive increase in chemotactic potency was found when both rMIP-1alpha and CINC-were added to the lower wells of Boyden chamber in vitro. In addition, high levels of rMIP-1alpha were detected in the inflammatory site of air-pouch/carrageenan-induced inflammation in rats. Our results suggest that rMIP-1alpha acts as a neutrophil chemoattractant and, together with CINCs, plays an important role in infiltration of neutrophils into inflammatory sites in rats.

Experimental liver injury induced by Propionibacterium acnes and lipopolysaccharide in macrophage colony stimulating factor-deficient osteopetrotic (op/op) mice

To clarify the involvement of growth and differentiation of liver macrophages mediated by macrophage colony-stimulating factor (M-CSF) in the liver injury induced by Propionibacterium acnes (P. acnes) and lipopolysaccharide (LPS), we used M-CSF-deficient osteopetrotic (op/op) mice. Seven days after injection of P. acnes, granulomas as well as the numbers of Thy-1.2-, Mac-1-, and ERMP-20-positive cells and F4/80-positive areas in the liver were significantly reduced in the op/op mice compared to the normal littermates. After injection of LPS, serum levels of alanine aminotransferase as well as concentrations of IL-1beta and TNF-alpha in the serum and liver were significantly lower in the op/op mice than in the normal littermates, whereas the concentrations of IL-1beta and TNF-alpha in the spleen were similar in op/op mice and normal littermates. These results suggest that M-CSF plays a partial but highly significant role in the development of liver injury induced by P. acnes and LPS via an intrahepatic increase of primed macrophages including those in granulomas, in response to P. acnes, which produce proinflammatory cytokines such as IL-1beta and TNF-alpha.

Chemokines and allergic disease

Understanding the chemokine network has become one of the great challenges for researchers interested in inflammatory mechanisms and inflammation-based diseases. The complexity and diversity of the system provide not only a daunting task for its comprehension but also numerous opportunities for development of new, targeted therapies. It is now certain that chemokines are involved as important mediators of allergic inflammation; the fine details and scope of their roles are now under investigation. Presumably, because of distinct pressures on the immune systems of people living in different geographic regions, genetic variation of ligands, receptors, and regulatory regions in the network have emerged. Establishing the roles of these polymorphisms in determining disease susceptibility or progression among individuals and in distinct ethnic groups will provide a basis for improved understanding and treatment of allergic diseases.

beta-Chemokines enhance parasite uptake and promote nitric oxide-dependent microbiostatic activity in murine inflammatory macrophages infected with Trypanosoma cruzi

In the present study, we describe the ability of Trypanosoma cruzi trypomastigotes to stimulate the synthesis of beta-chemokines by macrophages. In vivo infection with T. cruzi led to MIP-1alpha, RANTES, and JE/MCP1 mRNA expression by cells from peritoneal inflammatory exudate. In addition, in vitro infection with T. cruzi resulted in expression of beta-chemokine MIP-1alpha, MIP-1beta, RANTES, and JE mRNA by macrophages. The expression of the beta-chemokine MIP-1alpha, MIP-1beta, RANTES, and JE proteins by murine macrophages cultured with trypomastigote forms of T. cruzi was confirmed by immunocytochemistry. Interestingly, macrophage infection with T. cruzi also resulted in NO production, which we found to be mediated mainly by beta-chemokines. Hence, treatment with anti-beta-chemokine-specific neutralizing antibodies partially inhibited NO release by macrophages incubated with T. cruzi parasites. Further, the addition of the exogenous beta-chemokines MIP-1alpha, MIP-1beta, RANTES, and JE/MCP-1 induced an increased T. cruzi uptake, leading to enhanced NO production and control of parasite replication in a dose-dependent manner. L-NMMA, a specific inhibitor of the L-arginine-NO pathway, caused a decrease in NO production and parasite killing when added to cultures of macrophages stimulated with beta-chemokines. Among the beta-chemokines tested, JE was more potent in inhibiting parasite growth, although it was much less efficient than gamma interferon (IFN-gamma). Nevertheless, JE potentiates parasite killing by macrophages incubated with low doses of IFN-gamma. Together, these results suggest that in addition to their chemotactic activity, murine beta-chemokines may also contribute to enhancing parasite uptake and promoting control of parasite replication in macrophages and may play a role in resistance to T. cruzi infection.

Role of cytokines in pulmonary antimicrobial host defense

Host defense of the lung is characterized by a fine balance between the generation of a vigorous inflammatory response to clear pathogens and maintenance of the integrity of the alveolar gas-exchange surface. The magnitude of the inflammatory response is therefore tightly regulated by pro- and anti-inflammatory cytokine mediators. This article summarizes current information on the roles of specific cytokines in pneumonia, with particular emphasis on ongoing investigations into the role of innate immunity in bacterial and fungal pneumonia.

Key role of chemokines and chemokine receptors in inflammation, immunity, neoplasia, and infectious disease

Leukocyte homing is a complex, multistep process involving the coordinated expression of adhesion molecules and certain chemotactic cytokines, termed chemokines. Although chemokines initially burst into the literature as potent inflammatory mediators, it is now clear that they are involved in a variety of processes including lymphocyte maturation, angiogenesis, and tumor growth. Furthermore, a variety of important pathogens manipulate various chemokine/receptor pathways to infect the host and evade the immune system.

Inhibition of Murine Neutrophil Recruitment In Vivo by CXC Chemokine Receptor Antagonists

In this study, we have examined the ability of chemokine receptor antagonists to prevent neutrophil extravasation in the mouse. Two murine CXC chemokines, macrophage-inflammatory protein (MIP)-2 and KC, stimulated the accumulation of leukocytes into s.c. air pouches, although MIP-2 was considerably more potent. The leukocyte infiltrate was almost exclusively neutrophilic in nature. A human CXC chemokine antagonist, growth-related oncogene (GRO)-α(8–73), inhibited calcium mobilization induced by MIP-2, but not by platelet-activating factor in leukocytes isolated from the bone marrow, indicating that this antagonist inhibits MIP-2 activity toward murine leukocytes. Pretreatment of mice with GROα(8–73) inhibited, in a dose-dependent manner, the MIP-2-induced influx of neutrophils to levels that were not significantly different from control values. Moreover, this antagonist was also effective in inhibiting the leukocyte recruitment induced by TNF-α, LPS, and IL-1β. Leukocyte infiltration into the peritoneal cavity in response to MIP-2 was also inhibited by prior treatment of mice with GROα(8–73) or the analogue of platelet factor 4, PF4(9–70). The results of this study indicate 1) that the murine receptor for MIP-2 and KC, muCXCR2, plays a major role in neutrophil recruitment to s.c. tissue and the peritoneal cavity in response to proinflammatory agents and 2) that CXCR2 receptor antagonists prevent acute inflammation in vivo.

Chemokines and chemokine receptors: their role in allergic airway disease

One of the hallmarks of allergic pulmonary disorders is the accumulation of an abnormally large number of leukocytes including eosinophils, neutrophils, lymphocytes, basophils, and macrophages in the lung. There is now substantial evidence that eosinophils, under the control of T lymphocytes, are major effector cells in the pathogenesis of asthma. Therefore, understanding the mechanisms by which eosinophils accumulate and are activated in tissues is a fundamental question very relevant to allergic diseases. Another characteristic of allergic inflammation is the activation of leukocytes resulting in the release of biologically active mediators, such as histamine from mast cells and basophils. It is now apparent that chemokines are potent leukocyte chemoattractants, cellular activating factors, histamine releasing factors, and regulators of homeostatic immunity, making them particularly important in the pathogenesis of airway inflammation in asthma. In this regard, chemokines are attractive new therapeutic targets for the treatment of allergic disease. This article focuses on recently emerging data on the importance of chemokines and their receptors in allergic airway inflammation.

Contrasting roles for RANTES and macrophage inflammatory protein-1 alpha (MIP-1 alpha) in a murine model of allergic peritonitis

Cell accumulation and CC chemokine production were assessed in the peritoneal cavity of ovalbumin (OVA)-sensitized mice following antigen challenge. Intraperitoneal challenge with OVA induced a significant eosinophil influx from 6 h post-challenge with increased numbers persisting at 24 h. At 6 h there was also a marked presence of neutrophils. Messenger RNA expression and protein levels for the chemokines RANTES and MIP-1 alpha were measured in the cell pellets and supernatants, respectively, from peritoneal washes following OVA challenge. RANTES mRNA was detected from 2 h to 4 h following OVA injection, whereas mRNA for MIP-1 alpha was only detectable at 4 h. RANTES protein was first detected from 4 h after OVA injection and by 24 h the protein levels had increased further. Basal levels of MIP-1 alpha were detected in peritoneal washes. These levels peaked at 2 h after OVA challenge and rapidly declined to basal levels by 6 h. A functional role for the chemokines was assessed using neutralizing polyclonal antibodies. Co-injection of OVA with anti-RANTES antibodies resulted in a significant inhibition of eosinophil infiltration into the cavity at 6 h and 24 h (63% and 52% inhibition, respectively) without significantly influencing the number of neutrophils present. In contrast, injection of anti-MIP-1 alpha antibodies only inhibited neutrophil migration at the 6 h time point by 44% without significantly affecting the accumulation of eosinophils. These results demonstrate an important role for RANTES in mediating eosinophil influx in allergic inflammation and a contrasting role for MIP-1 alpha in mediating neutrophil recruitment.

Interfering with chemokine networks--the hope for new therapeutics

Chemokines are a large family of cytokines with a wide variety of biological actions. Originally, they were identified as controllers of the routine trafficking of immune cells, and directed migration of cells during inflammatory response - from which they get their name, a contraction of chemotactic cytokines. They are now also known to be active in angiogenesis, embryonic development and infection by viruses such as HIV-1. Studies with antibodies, modified chemokine and transgenic mice suggest that chemokine receptor antagonists may be selective anti-inflammatory, antiviral or immunomodulatory agents. Small-molecule antagonists of seven of the receptors have been reported, some with potency in the low nanomolar range. These compounds are shown to be active in cell biology assays; the next step will be to determine their efficacy in animal models of disease.

Regulation of hematopoiesis in a sea of chemokine family members with a plethora of redundant activities

The field of chemokine biology is a rapidly advancing one, with over 50 chemokines identified that mediate their effects through one or more of 16 different chemokine receptors. Chemokines, originally identified as chemotactic cytokines, manifest a number of functions, including modulation of blood cell production at the level of hematopoietic stem/progenitor cells and the directed movement of these early blood cells. This report reviews chemokines and chemokine/receptor activities mainly in the context of hematopoietic cell regulation and the numerous chemokines that manifest suppressive activity on proliferation of stem/progenitor cells. This is contrasted with the specificity of only a few chemokines for the chemotaxis of these early cells. The large number of chemokines with suppressive activity is hypothesized to reflect the different cell, tissue, and organ sites of production of these chemokines and the need to control stem/progenitor cell proliferation in different organ sites throughout the body.

Dominant myelopoietic effector functions mediated by chemokine receptor CCR1

Macrophage inflammatory protein (MIP)-1alpha, a CC chemokine, enhances proliferation of mature subsets of myeloid progenitor cells (MPCs), suppresses proliferation of immature MPCs, and mobilizes mature and immature MPCs to the blood. MIP-1alpha binds at least three chemokine receptors. To determine if CCR1 was dominantly mediating the above activities of MIP-1alpha, CCR1-deficient (-/-) mice, produced by targeted gene disruption, were used. MIP-1alpha enhanced colony formation of marrow granulocyte/macrophage colony-forming units (CFU-GM), responsive to stimulation by granulocyte/macrophage colony-stimulating factor (GM-CSF), and CFU-M, responsive to stimulation by M-CSF, from littermate control CCR1(+/+) but not CCR1(-/-) mice. Moreover, MIP-1alpha did not mobilize MPCs to the blood or synergize with G-CSF in this effect in CCR1(-/-) mice. However, CCR1(-/-) mice were increased in sensitivity to MPC mobilizing effects of G-CSF. Multi-growth factor-stimulated MPCs in CCR1(-/-) and CCR1(+/+) marrow were equally sensitive to inhibition by MIP-1alpha. These results implicate CCR1 as a dominant receptor for MIP-1alpha enhancement of proliferation of lineage-committed MPCs and for mobilization of MPCs to the blood. CCR1 is not a dominant receptor for MIP-1alpha suppression of MPC proliferation, but it does negatively impact G-CSF-induced MPC mobilization.

The chemokine system: redundancy for robust outputs

Chemokines are redundant in their action on target cells and promiscuous in receptor usage. Moreover, certain cells concomitantly produce several chemokines with an overlapping spectrum of action. Here, Alberto Mantovani argues that such robustness provides a conceptual framework to understand these intriguing aspects of the chemokine system.

Upon dendritic cell (DC) activation chemokines and chemokine receptor expression are rapidly regulated for recruitment and maintenance of DC at the inflammatory site

Dendritic cells (DC) are highly motile antigen-presenting cells that are recruited to sites of infection and inflammation to antigen uptake and processing. Then, to initiate T cell-dependent immune responses, they migrate from non-lymphoid organs to lymph nodes and the spleen. Since chemokines have been involved in human DC recruitment, we investigated the role of chemokines on mouse DC migration using the mouse growth factor-dependent immature DC line (D1). In this study, we characterized receptor expression, responsiveness to chemoattractants and chemokine expression of D1 cells during the maturation process induced by lipopolysaccharide (LPS). MIP-1alpha and MIP-5 were found to be the most effective chemoattractants, CCR1 was the main receptor expressed and modulated during LPS treatment, and MIP-2, RANTES, IP-10 and MCP-1 were the chemokines modulated during DC maturation. Thus, murine DC respond to a unique set of CC and CXC chemokines, and the maturational stage determines the program of chemokine receptors and chemokines that are expressed. Since CCR1 is modulated during the early phases of DC maturation, our results indicate that the CCR1 receptor may participate in the recruitment and maintenance of DC at the inflammatory site.

Differential Effects of Leukotactin-1 and Macrophage Inflammatory Protein-1α on Neutrophils Mediated by CCR1

The human CC chemokine leukotactin-1 (Lkn-1) is both a strong chemoattractant for neutrophils, monocytes, and lymphocytes and a potent agonist for CCR1 and CCR3. However, human neutrophils do not migrate when the cells are stimulated with other human CC chemokines, such as human macrophage inflammatory protein-1α (hMIP-1α) and eotaxin, which also use the CCR1 and CCR3 as their receptors. In this report, we demonstrate that while hMIP-1α induced a negligible level of calcium flux and chemotaxis, Lkn-1 produced a high level of calcium flux and chemotaxis in human neutrophils. Lkn-1 cross-desensitized hMIP-1α-induced calcium flux, but hMIP-1α had little effect on the Lkn-1-induced response in human neutrophils. The same pattern was observed in peritoneal neutrophils from wild-type mice, whereas neutrophils from CCR1−/− mice failed to respond to either MIP-1α or Lkn-1. Scatchard analysis revealed a single class of receptor for both hMIP-1α and Lkn-1 on human neutrophils with dissociation constants (Kd) of 3.2 nM and 1.1 nM, respectively. We conclude that CCR1 is a receptor mediating responses to both MIP-1α and Lkn-1 on neutrophils and produces different biological responses depending on the ligand bound.

On the edge: the physiological and pathophysiological role of chemokines during inflammatory and immunological responses

Most, if not all, chemokines bind to seven transmembrane spanning G protein-coupled receptors and activate cellular migration. Stimulated chemokine expression is essential for directing leukocyte emigration from the circulation into sites of inflammation and tissue damage. In contrast, constitutive chemokine expression plays a role in the development of lymphoid cells, organs, and tissues. The present review examines rheumatoid arthritis and transplantation rejection as two examples of pathological conditions where chemokine directed leukocyte infiltration aids in the pathogenesis of the disease. We further discuss insights into leukocyte trafficking gained by chemokine and chemokine receptor transgenic and null mutant mice.