Myelopoietic enhancing effects of murine macrophage inflammatory proteins 1 and 2 on colony formation in vitro by murine and human bone marrow granulocyte/macrophage progenitor cells

Predictive nonlinear modeling of malignant myelopoiesis and tyrosine kinase inhibitor therapy

Chronic myeloid leukemia (CML) is a blood cancer characterized by dysregulated production of maturing myeloid cells driven by the product of the Philadelphia chromosome, the BCR-ABL1 tyrosine kinase. Tyrosine kinase inhibitors (TKIs) have proved effective in treating CML, but there is still a cohort of patients who do not respond to TKI therapy even in the absence of mutations in the BCR-ABL1 kinase domain that mediate drug resistance. To discover novel strategies to improve TKI therapy in CML, we developed a nonlinear mathematical model of CML hematopoiesis that incorporates feedback control and lineage branching. Cell-cell interactions were constrained using an automated model selection method together with previous observations and new in vivo data from a chimeric BCR-ABL1 transgenic mouse model of CML. The resulting quantitative model captures the dynamics of normal and CML cells at various stages of the disease and exhibits variable responses to TKI treatment, consistent with those of CML patients. The model predicts that an increase in the proportion of CML stem cells in the bone marrow would decrease the tendency of the disease to respond to TKI therapy, in concordance with clinical data and confirmed experimentally in mice. The model further suggests that, under our assumed similarities between normal and leukemic cells, a key predictor of refractory response to TKI treatment is an increased maximum probability of self-renewal of normal hematopoietic stem cells. We use these insights to develop a clinical prognostic criterion to predict the efficacy of TKI treatment and design strategies to improve treatment response. The model predicts that stimulating the differentiation of leukemic stem cells while applying TKI therapy can significantly improve treatment outcomes.

Neutrophil-Dependent Immunity During Pulmonary Infections and Inflammations

Rapid recruitment of neutrophils to an inflamed site is one of the hallmarks of an effective host defense mechanism. The main pathway through which this happens is by the innate immune response. Neutrophils, which play an important part in innate immune defense, migrate into lungs through the modulation actions of chemokines to execute a variety of pro-inflammatory functions. Despite the importance of chemokines in host immunity, little has been discussed on their roles in host immunity. A holistic understanding of neutrophil recruitment, pattern recognition pathways, the roles of chemokines and the pathophysiological roles of neutrophils in host immunity may allow for new approaches in the treatment of infectious and inflammatory disease of the lung. Herein, this review aims at highlighting some of the developments in lung neutrophil-immunity by focusing on the functions and roles of CXC/CC chemokines and pattern recognition receptors in neutrophil immunity during pulmonary inflammations. The pathophysiological roles of neutrophils in COVID-19 and thromboembolism have also been summarized. We finally summarized various neutrophil biomarkers that can be utilized as prognostic molecules in pulmonary inflammations and discussed various neutrophil-targeted therapies for neutrophil-driven pulmonary inflammatory diseases.

Regulation of hematopoiesis by the chemokine system

Although chemokines are best known for their role in directing cell migration, accumulating evidence indicate their involvement in many other processes. This review focus on the role of chemokines in hematopoiesis with an emphasis on myelopoiesis. Indeed, many chemokine family members are an important component of the cytokine network present in the bone marrow that controls proliferation, retention, and mobilization of hematopoietic progenitors.

The Chemokine CCL3 Regulates Myeloid Differentiation and Hematopoietic Stem Cell Numbers

The chemokine CCL3 is frequently overexpressed in malignancies and overexpression leads to microenvironmental dysfunction. In murine models of chronic myelogenous leukemia (CML), CCL3 is critical for the maintenance of a leukemia stem cell population, and leukemia progression. With CCL3 implicated as a potentially viable therapeutic target, it is important to carefully characterize its role in normal hematopoietic homeostasis. CCL3^−/− mice were used to evaluate the role of CCL3 in regulating hematopoietic stem and progenitor cell (HSPC) populations. CCL3^−/− mice had loss of mature myeloid populations, while myeloid progenitors and HSPCs were increased, and microenvironmental populations were unchanged. These data show that CCL3 promotes myeloid lineage differentiation and the size of the HSPC pool independent of the supportive bone marrow microenvironment. Our results demonstrate a previously unrecognized role of CCL3 in the maintenance of homeostatic hematopoiesis that should be evaluated when targeting CCL3 signaling for the treatment of hematologic malignancy.

Chemokines as adjuvants for immunotherapy: implications for immune activation with CCL3

INTRODUCTION

Immunotherapy embodies any approach that manipulates the immune system for therapeutic benefit. In this regard, various clinical trials have employed direct vaccination with patient-specific dendritic cells or adoptive T cell therapy to target highly aggressive tumors. Both modalities have demonstrated great specificity, an advantage that is unmatched by other treatment strategies. However, their full potential has yet to be realized. Areas covered: In this review, we provide an overview of chemokines in pathogen and anti-tumor immune responses and discuss further improving immunotherapies by arming particular chemokine axes. Expert commentary: The chemokine macrophage inflammatory protein-1 alpha (MIP-1α, CCL3) has emerged as a potent activator of both innate and adaptive responses. Specifically, CCL3 plays a critical role in recruiting distinct immune phenotypes to intratumoral sites, is a pivotal player in regulating lymph node homing of dendritic cell subsets, and induces antigen-specific T cell responses. The recent breadth of literature outlines the various interactions of CCL3 with these cellular subsets, which have now served as a basis for immunotherapeutic translation.

Chemokines as a Conductor of Bone Marrow Microenvironment in Chronic Myeloid Leukemia

All blood lineage cells are generated from hematopoietic stem cells (HSCs), which reside in bone marrow after birth. HSCs self-renew, proliferate, and differentiate into mature progeny under the control of local microenvironments including hematopoietic niche, which can deliver regulatory signals in the form of bound or secreted molecules and from physical cues such as oxygen tension and shear stress. Among these mediators, accumulating evidence indicates the potential involvement of several chemokines, particularly CXCL12, in the interaction between HSCs and bone marrow microenvironments. Fusion between breakpoint cluster region (BCR) and Abelson murine leukemia viral oncogene homolog (ABL)-1 gene gives rise to BCR-ABL protein with a constitutive tyrosine kinase activity and transforms HSCs and/or hematopoietic progenitor cells (HPCs) into disease-propagating leukemia stem cells (LSCs) in chronic myeloid leukemia (CML). LSCs can self-renew, proliferate, and differentiate under the influence of the signals delivered by bone marrow microenvironments including niche, as HSCs can. Thus, the interaction with bone marrow microenvironments is indispensable for the initiation, maintenance, and progression of CML. Moreover, the crosstalk between LSCs and bone marrow microenvironments can contribute to some instances of therapeutic resistance. Furthermore, evidence is accumulating to indicate the important roles of bone marrow microenvironment-derived chemokines. Hence, we will herein discuss the roles of chemokines in CML with a focus on bone marrow microenvironments.

Modulation of Hematopoietic Chemokine Effects In Vitro and In Vivo by DPP-4/CD26

Dipeptidyl peptidase 4 (DPP4)/CD26 truncates certain proteins, and this posttranslational modification can influence their activity. Truncated (T) colony-stimulating factors (CSFs) are decreased in potency for stimulating proliferation of hematopoietic progenitor cells (HPCs). T-CXCL12, a modified chemokine, is inactive as an HPC chemotactic, survival, and enhancing factor for replating or ex-vivo expansion of HPCs. Moreover, T-CSFs and T-CXCL12 specifically downmodulates the positively acting effects of their own full-length molecule. Other chemokines have DPP4 truncation sites. In the present study, we evaluated effects of DPP4 inhibition (by Diprotin A) or gene deletion of HPC on chemokine inhibition of multicytokine-stimulated HPC, and on chemokine-enhancing effects on single CSF-stimulated HPC proliferation, as well as effects of DPP4 treatment of a number of chemokines. Myelosuppressive effects of chemokines with, but not without, a DPP4 truncation site were greatly enhanced in inhibitory potency by pretreating target bone marrow (BM) cells with Diprotin A, or by assaying their activity on dpp4/cd26(-/-) BM cells. DPP4 treatment of myelosuppressive chemokines containing a DPP4 truncation site produced a nonmyelosuppressive molecule, but one which had the capacity to block suppression by that unmodified chemokine both in vitro and in vivo. Additionally, DPP4 treatment ablated the single cytokine-stimulated HPC-enhancing activity of CCL3/MIP-1α and CCL4/MIP-1β, and blocked the enhancing activity of each unmodified molecule, in vitro and in vivo. These results highlight the functional posttranslational modulating effects of DPP4 on chemokine activities, and information offering additional biological insight into chemokine regulation of hematopoiesis.

Chemokines and immunity

Chemokines are a large family of small cytokines and generally have low molecular weight ranging from 7 to 15kDa. Chemokines and their receptors are able to control the migration and residence of all immune cells. Some chemokines are considered pro-inflammatory, and their release can be induced during an immune response at a site of infection, while others are considered homeostatic and are involved in controlling of cells migration during tissue development or maintenance. The physiologic importance of this family of mediators is resulting from their specificity − members of the chemokine family induce recruitment of well-defined leukocyte subsets. There are two major chemokine sub-families based upon cysteine residues position: CXC and CC. As a general rule, members of the CXC chemokines are chemotactic for neutrophils, and CC chemokines are chemotactic for monocytes and sub-set of lymphocytes, although there are some exceptions. This review discusses the potential role of chemokines in inflammation focusing on the two best-characterized chemokines: monocyte chemoattractant protein-1, a CC chemokine, and interleukin-8, a member of the CXC chemokine sub-family.

Role of macrophage inflammatory protein (MIP)-1α/CCL3 in leukemogenesis

The biologic function of the CC chemokine macrophage inflammatory protein-1α (MIP-1α/CCL3) has been extensively studied since its initial identification as a macrophage-derived inflammatory mediator. In addition to its proinflammatory activities, CCL3 negatively regulates the proliferation of hematopoietic stem/progenitor cells (HSPCs). On the basis of this unique function, CCL3 is alternatively referred to as a stem cell inhibitor. This property has prompted many researchers to investigate the effects of CCL3 on normal physiologic hematopoiesis and pathophysiologic processes of hematopoietic malignancies. Consequently, there is accumulating evidence supporting a crucial involvement of CCL3 in the pathophysiology of several types of leukemia arising from neoplastic transformation of HSPCs. In this review we discuss the roles of CCL3 in leukemogenesis and its potential value as a target in a novel therapeutic strategy for the treatment of leukemia.

Innate signaling in otitis media: pathogenesis and recovery

Otitis media (OM) is the most prevalent childhood disease in developed countries. Involvement of innate immunity mediated by Toll-like receptors (TLRs) in OM has been implicated primarily in cell lines and by association studies of innate immune gene polymorphisms with OM prevalence. However, the precise role of innate immunity in OM is incompletely understood. We review recent research that has advanced our understanding of how innate immunity in the middle ear is mediated by the interaction of pathogen molecules with receptors such as the TLRs, leading to the activation of adaptor molecules and production of proinflammatory cytokines. TLR genes and signaling molecules are upregulated in OM in a murine model. Deletion of several key innate immune genes results in persistent OM in mice, coupled with an inability to clear bacterial infection from the middle ear. It is concluded that an intact innate immune signaling system is critical to recovery from bacterial OM.

CC chemokine ligand 3 overcomes the bacteriocidal and phagocytic defect of macrophages and hastens recovery from experimental otitis media in TNF-/- mice

Innate immune mechanisms are crucial in defense against bacterial illnesses in humans, as evidenced by abnormal antibacterial responses due to defects in TLR signaling, seen in children with MyD88 or IL-1R-associated kinase 4 deficiency. Otitis media (OM) is the most common disease of childhood, and the role of innate immune molecules in this disorder remains unclear. In a murine model of OM, we show that, in the absence of TNF, a key effector of innate immunity, this disease is prolonged after middle ear infection with nontypeable Haemophilus influenzae (NTHi). In the absence of TNF, mice fail to upregulate both TLRs and downstream genes and proteins, such as CCL3, resulting in defects in both inflammatory cell recruitment and macrophage function. Peritoneal macrophages of mice lacking TNF have a diminished ability to phagocytose and kill NTHi, and this defect is partially corrected in vitro by exogenous rTNF. Addition of rCCL3 alone or in combination with rTNF restores phagocytosis and killing by TNF-deficient macrophages to that of unstimulated wild-type macrophages. In vivo administration of rCCL3 to animals deficient in TNF fully restores the ability to control OM due to NTHi, whereas a CCL3-blocking Ab impaired the ability of wild-type mice to recover from OM. Thus, CCL3 is a potent downstream effector of TNF-mediated inflammation in vitro and in vivo. Manipulation of CCL3 and/or TNF may prove to be effective therapeutic approaches in OM or other conditions associated with defective TNF generation.

The granulopoietic cytokine response and enhancement of granulopoiesis in mice during endotoxemia

In response to bacterial infection, the production of neutrophils by the bone marrow is accelerated. This study investigated the granulopoietic cytokine response and granulopoiesis during endotoxemia. Male Balb/c mice were intravenously challenged with lipopolysaccharide (LPS, 20 microg in 100 microL of saline per mouse). Control animals received saline alone. In a separate set of experiments, i.v. murine granulocyte colony-stimulating factor (G-CSF; 20 microg/kg) or vehicle (5% dextrose) was administered to mice. Endotoxemia caused a marked increase in G-CSF, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) in the plasma and bone marrow between 1 and 4 h after the challenge. G-CSF, KC, and MIP-2 mRNA expression was also upregulated in the lung, liver, spleen, and bone marrow between 1 and 4 h after i.v. LPS. Intravenous administration of G-CSF caused a significant increase in G-CSF concentration in the plasma and bone marrow without upregulating G-CSF mRNA expression in the bone marrow. The levels of phospho-signal transducers and activators of transcription 3 and phospho-p44/42 mitogen-activated protein kinase were elevated in bone marrow cells at 30 min and 4 h after i.v. G-CSF and LPS, respectively. Granulocyte-macrophage colony-forming unit counts were significantly increased in the bone marrow, spleen, and blood at 48 h post-i.v. LPS or G-CSF. These data show that extramedullary organs produce granulopoietic cytokines in response to LPS. Because the tissue mass in extramedullary organs far exceeds that in the bone marrow, extramedullary production of these cytokines likely play a critical role in the regulation of the host's granulopoietic response to endotoxemia.

Escherichia coli pneumonia enhances granulopoiesis and the mobilization of myeloid progenitor cells into the systemic circulation

OBJECTIVE

The process by which hematopoietic tissues respond to a pulmonary infection remains poorly understood. This study investigated the potential role of lung-derived granulopoietic cytokines in facilitating this response.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

SUBJECTS

Male Balb/c mice.

INTERVENTIONS

Mice were challenged with intratracheal Escherichia coli or granulocyte colony-stimulating factor (G-CSF). Bone marrow cells were isolated from normal mice and treated in vitro with G-CSF.

MEASUREMENTS AND MAIN RESULTS

Bronchoalveolar lavage fluid concentrations of G-CSF, macrophage inflammatory protein-2, and keratinocyte-derived chemokine were elevated 3 and 6 hrs after intratracheal E. coli. The increases in intrapulmonary G-CSF and keratinocyte-derived chemokine were associated with increases of their concentrations in the plasma. The numbers of granulocyte-macrophage colony forming units in bone marrow, spleen, and blood were increased 48 hrs after intratracheal E. coli or G-CSF. In addition, plasma G-CSF and the number of progenitor cells (lin-ckit+Sca-1(-)) in the blood were increased at 30 mins and 48 hrs, respectively, following intratracheal G-CSF. Signal transducer and activator of transcription-3 in bone marrow cells was activated following intratracheal E. coli or G-CSF in addition to activation by in vitro G-CSF stimulation.

CONCLUSIONS

During pulmonary infection, locally produced cytokines enter the circulation and may play an important role in initiating a granulopoietic response.

Epstein-Barr virus nuclear antigen leader protein induces expression of thymus- and activation-regulated chemokine in B cells

Epstein-Barr virus (EBV) nuclear antigen leader protein (EBNA-LP) plays a critical role in transformation of primary B lymphocytes to continuously proliferating lymphoblastoid cell lines (LCLs). To identify cellular genes in B cells whose expression is regulated by EBNA-LP, we performed microarray expression profiling on an EBV-negative human B-cell line, BJAB cells, that were transduced by a retroviral vector expressing the EBV EBNA-LP (BJAB-LP cells) and on BJAB cells that were transduced with a control vector (BJAB-vec cells). Microarray analysis led to the identification of a cellular gene encoding the CC chemokine TARC as a novel target gene that was induced by EBNA-LP. The levels of TARC mRNA expression and TARC secretion were significantly up-regulated in BJAB-LP compared with BJAB-vec cells. Induction of TARC was also observed when a subline of BJAB cells was converted by a recombinant EBV. Among the EBV-infected B-cell lines with the latency III phenotype that were tested, the LCLs especially secreted significantly high levels of TARC. The level of TARC secretion appeared to correlate with the level of full-length EBNA-LP expression. These results indicate that EBV infection induces TARC expression in B cells and that EBNA-LP is one of the viral gene products responsible for the induction.

Molecular cloning and characterization of a novel rat CXC chemokine, rPBP, the homologue of human and mouse PBP

We have previously cloned the mouse platelet basic protein (mPBP), a homologue of human PBP, from mouse thymic stromal cells. Using EST alignment and RT-PCR, the rat homologue of human and mouse PBP was cloned from lung and named as rPBP. The complete open reading frame and part of the 3'- and 5'-non-coding regions were obtained through rapid amplification of cDNA ends. The rPBP cDNA encodes a protein of 111 amino acids containing a signal peptide of 37 amino acids at the N-terminus, with the mature protein of 74 amino acids. The rPBP is a new member of ELR+CXC chemokines. The mature protein of rPBP shares 69% and 45% homology with mouse and human PBP, respectively. In situ hybridization assay revealed rPBP to be predominantly localized in the pulmonary vascular endothelial cells. The eukaryotic expression vector pCDNA3-rPBP was constructed and transiently transfected into COS-7 cells. In the in vitro chemotaxis assay, the polymorphonuclear leukocytes (PMNs) were chemoattracted to the supernatants from transfected COS-7 cells in a dose-dependent manner. The implication of rPBP found in rat lung is that this chemokine may have the function to recruit PMNs to fight against pulmonary infection.

CAL72: a human osteosarcoma cell line with unique effects on hematopoietic cells

Permanent osteoblastic cell lines are potential tools to study the interactions between osteoblastic and hematopoietic cells in the bone marrow cavity. In a recent work we have shown that the osteosarcoma cell line CAL72 may be more closely related to normal osteoblasts than the osteosarcoma cells previously described. In the present work we continued the characterisation of the CAL72 cell line with regard to its effects on various hematopoietic cells, in coculture experiments. We show here that CAL72 cells, in contrast to MG-63 or SaOS-2 osteosarcoma cell lines, do not inhibit hematopoietic colony formation and sustain the limited expansion of hematopoietic progenitors in a similar way to that described for normal osteoblasts. We also demonstrate that CAL72 cells induce the monocytic differentiation of the promyelocytic HL-60 cell line like MG-63 and SaOS-2, but support a better maturation and a longer survival of the differentiated cells than the two other osteosarcoma cell lines. In order to better understand the differential effects observed between CAL72 and MG-63 or SaOS-2, we analysed the cytokine and chemokine mRNA expression of these cells using the RNase protection quantitative assay. We show here that the expression profile of CAL72 is clearly different from that of MG-63 or SaOS-2 and may explain, at least in part, its specific effects on hematopoietic cells. Taken together these experiments confirm that CAL72 has particular properties and is an interesting tool to study the role of osteoblastic cells in hematopoietic cell growth and differentiation.

Effect of monocyte chemoattractant protein-1 on murine bone marrow cells: proliferation, colony-forming ability and signal transduction pathway involved

Monocyte chemoattractant protein-1 (MCP-1) plays a crucial role in the migration and activation of leukocytes in both physiological and pathological contexts. In this paper, we report the in vitro effect of MCP-1 on myeloid haematopoiesis. MCP-1-treated murine nonadherent bone marrow cells (NABMCs) were assayed for in vitro proliferation and colony forming ability. It is observed that MCP-1 treatment in vitro caused an enhancement in the proliferation and colony forming ability of the murine NABMCs as compared to the untreated cells. This response was concentration-dependent and most effective at a dose of 100ng/ml MCP-1. In the presence of MCSF (200U/ml), GCSF (200U/ml), GMCSF (200U/ml) or IL-3 (200U/ml), the MCP-1-induced colony forming ability of the NABMCs was significantly augmented, indicating a synergistic effect of MCP-1 with these CSFs. However, irrespective of the CSFs used, MCP-1 stimulated the lineage-restricted differentiation of the murine BMCs into predominantly the granulocytic lineage. NABMCs cultured in medium alone formed minimal colonies. The probable signal transduction mechanism responsible for the MCP-1-induced NABMC proliferation/differentiation was also investigated. The results of the colony forming assay indicate that the protein kinase inhibitors, genistein (10&mgr;g/ml), chelenthryin chloride (10&mgr;M), wortmannin (200nM) and PD98059 (10&mgr;M) significantly blocked the in vitro colony forming ability of the MCP-1-treated NABMCs, while the phosphatase inhibitors, okadaic acid (10nM) and sodium orthovanadate (10&mgr;M) caused an increase in the BMC colony forming ability in response to MCP-1. These data suggests the involvement of the respective protein kinases and phosphatases in the above process. Correlating with this, the role of several signaling molecules likes Lyn, p42/44MAPK, PI3K and STAT5 has also been implicated in the signal cascade of murine NABMC proliferation/differentiation following MCP-1 treatment.

Impaired T cell function in RANTES-deficient mice

The chemokine RANTES is a chemoattractant for monocytes and T cells and is postulated to participate in many aspects of the immune response. To evaluate the biological roles of RANTES in vivo, we generated RANTES-deficient (-/-) mice and characterized their T cell function. In cutaneous delayed-type hypersensitivity assays, a 50% reduction in ear and footpad swelling was seen in -/- mice compared to +/+ mice. In vitro, polyclonal and antigen-specific T cell proliferation was decreased. Quantitative analysis using the fluorescent dye carboxy-fluorescein succinimidyl ester revealed that this proliferative defect was due both to fewer antigen-reactive T cells and to a reduction in the capacity of these cells to proliferate. In addition, IFN-gamma and IL-2 production by the -/- T cells was dramatically decreased. Together, these data suggest that RANTES is required for normal T cell functions as well as for recruiting monocytes and T cells to sites of inflammation.

Expression of beta-chemokines and chemokine receptors in human fetal astrocyte and microglial co-cultures: potential role of chemokines in the developing CNS

Chemokines play specific roles in directing the recruitment of leukocyte subsets into inflammatory foci within the central nervous system (CNS). The involvement of these cytokines as mediators of inflammation is widely accepted. Recently, it has become evident that cells of the CNS (astrocytes, microglia, and neurons) not only synthesize, but also respond functionally or chemotactically to chemokines. We previously reported developmental events associated with colonization of the human fetal CNS by mononuclear phagocytes (microglial precursors), which essentially takes place within the first two trimesters of life. As part of the array of signals driving colonization, we noted specific anatomical distribution of chemokines and chemokine receptors expressed during this period. In order to further characterize expression of these molecules, we have isolated and cultured material from human fetal CNS. We demonstrate that unstimulated subconfluent human fetal glial cultures express high levels of CCR2 and CXCR4 receptors in cytoplasmic vesicles. Type I astrocytes, and associated ameboid microglia in particular, express high levels of surface and cytoplasmic CXCR4. Of the chemokines tested (MIP-1alpha, MIP-1beta, MCP-1, MCP-3, RANTES, SDF-1, IL-8, IP-10), only MIP-1alpha, detected specifically on microglia, was expressed both constitutively and consistently. Low variable levels of MCP-1, MIP-1alpha, and RANTES were also noted in unstimulated glial cultures. Recombinant human chemokines rhMCP-1 and rhMIP-1alpha also displayed proliferative effects on glial cultures at [10 ng/ml], but displayed variable effects on CCR2 levels on these cells. rhMCP-1 specifically upregulated CCR2 expression on cultured glia at [50 ng/ml]. It is gradually becoming evident that chemokines are important in embryonic development. The observation that human fetal glial cells and their progenitors express specific receptors for chemokines and can be stimulated to produce MCP-1, as well as proliferate in response to chemokines, supports a role for these cytokines as regulatory factors during development.

Macrophage inflammatory protein 1alpha/CCL3 is required for clearance of an acute Klebsiella pneumoniae pulmonary infection

The objective of these studies was to determine the role of macrophage inflammatory protein 1alpha/CCL3 in pulmonary host defense during Klebsiella pneumoniae infection. Following intratracheal inoculation, 7-day survival of CCL3(-/-) mice was less than 10%, compared to 60% for CCL3(+/+) mice. Survival of CCR5(-/-) mice was equivalent to that of controls, indicating that the enhanced susceptibility of CCL3(-/-) mice to K. pneumoniae is mediated via another CCL3 receptor, presumably CCR1. At day 3, CFU burden in the lungs of CCL3(-/-) mice was 800-fold higher than in CCL3(+/+) mice, demonstrating that CCL3 is critical for control of bacterial growth in the lung. Surprisingly, CCL3(-/-) mice had no differences in the recruitment of monocytes/macrophages and even showed enhanced neutrophil recruitment at days 1, 2, and 3 postinfection, compared to CCL3(+/+) mice. Therefore, the defect in clearance was not due to insufficient recruitment of leukocytes. No significant differences in cytokine levels of monocyte chemoattractant protein 1 (MCP-1), interleukin 12, gamma interferon, or tumor necrosis factor alpha in lung lavages were found between CCL3(+/+) and CCL3(-/-) mice. CCL3(-/-) alveolar macrophages were found to have significantly lower phagocytic activity toward K. pneumoniae than CCL3(+/+) alveolar macrophages. These findings demonstrate that CCL3 production is critical for activation of alveolar macrophages to control the pulmonary growth of the gram-negative bacterium K. pneumoniae.

Regulation of hematopoiesis by chemokine family members

Chemokines, originally designated as chemoattractant cytokines, comprise a large family of molecules that have been implicated in a number of different functions mediated through chemokine receptors. Among these functions are regulatory roles in hematopoiesis that encompass effects on the proliferation, survival, and homing/migration of myeloid progenitor cells. This article reviews the field of chemokine regulation of hematopoiesis at the level of myeloid progenitor cells.

Growth Factors: Production of Monocyte Chemotactic Protein-1 (MCP-1/JE) by Bone Marrow Stromal Cells: Effect on the Migration and Proliferation of Hematopoietic Progenitor Cells

Recombinant chemotactic cytokines (chemokines) have been shown to modulate in vitro proliferation of hematopoietic progenitor cells. Whether bone marrow stromal cells produce chemokines and the physiological role they may have in the regulation of hematopoiesis has largely remained unexamined. We have examined the expression of monocyte chemoattractant protein-1 (MCP-1/JE) in bone marrow stromal cells and its effect on the migration and proliferation of murine hematopoietic progenitor cells. Freshly derived murine bone marrow stromal cells were found to secrete abundant amounts of MCP-1/JE, which was further increased upon stimulation of stromal cells with pro-inflammatory agents LPS, IL1-alpha, IFN-gamma, or TNF-alpha. Although culture supernatant conditioned by stromal cells exhibited chemotactic activity toward hematopoietic progenitor cells, the chemotactic activity was not due to MCP-1/JE. Furthermore, rMCP-1/JE also failed to induce migration of progenitor cells. MCP-1/JE, however, caused 20 to 30% increase in the clonal expansion of progenitor cells. Thus, although MCP-1/JE does not chemoattract hematopoietic progenitor cells it may have a role in their proliferation and clonal expansion.

Cyclophosphamide Induces the Development of Early Myeloid Cells Suppressing Tumor Cell Growth by a Nitric Oxide-Dependent Mechanism

Adoptive immunotherapy with cyclophosphamide (Cy) increases the host resistance against tumor growth. The precise mechanism(s) by which this therapy enhances tumor suppression is unclear. Cy induces the development of early myeloid cells that may be strongly antiproliferative through NO production. These cells are similar to the natural suppressor cells found in normal bone marrow with a potential antitumor effect. Here we have addressed whether the development of NO-producing cells may be involved in this tumor resistance in Cy-treated mice. The results show a synergism between Cy treatment and tumor-specific lymphocytes transferred systemically (i.v.) or locally (Winn's assay) that results in a strong tumor suppression. Inhibition of NO production by N(G)-monomethyl-L-arginine at the site of tumor inoculation results in a loss of the protection achieved by the combined therapy. Cy-treated mice develop splenic early myeloid (CD11b, Gr-1, CD31 (ER-MP12), ER-MP20, ER-MP54) cells producing large amounts of NO upon T cell-derived signals (IFN-gamma plus CD40 ligation) able to inhibit tumor cell growth in vitro. Early myeloid cells (ER-MP54(+)) and cells expressing inducible NO synthase are increased at the site of tumor challenge in mice treated with the combined therapy, but not in those treated with Cy or immune cell transfer alone. Thus, Cy induces the expansion of early myeloid cells, inhibiting tumor cell growth by a mechanism involving NO. Both the recruitment and the activation of these myeloid cells at the site of tumor challenge appear to be dependent on the presence of tumor-specific lymphocytes.

Molecular cloning and characterization of a novel CXC chemokine macrophage inflammatory protein-2 gamma chemoattractant for human neutrophils and dendritic cells

Chemokines play important roles in leukocyte trafficking as well as function regulation. In this study, we described the identification and characterization of a novel CXC chemokine from a human dendritic cell (DC) cDNA library, the full-length cDNA of which contains an open reading frame encoding 111 aa with a putative signal peptide of 34 aa. This CXC chemokine shares greatest homology with macrophage inflammatory protein (MIP)-2alphabeta, hence is designated as MIP-2gamma. Mouse MIP-2gamma was identified by electrocloning and is highly homologous to human MIP-2gamma. Northern blotting revealed that MIP-2gamma was constitutively and widely expressed in most normal tissues with the greatest expression in kidney, but undetectable in most tumor cell lines except THP-1 cells. In situ hybridization analysis demonstrated that MIP-2gamma was mainly expressed by the epithelium of tubules in the kidney and hepatocytes in the liver. Although no detectable expression was observed in freshly isolated or PMA-treated monocytes, RT-PCR analysis revealed MIP-2gamma expression by monocyte-derived DC. Recombinant MIP-2gamma from 293 cells is about 9.5 kDa in size and specifically detectable by its polyclonal Ab developed by the immunization with its 6His-tagged fusion protein. The eukaryotically expressed MIP-2gamma is a potent chemoattractant for neutrophils, and weaker for DC, but inactive to monocytes, NK cells, and T and B lymphocytes. Receptor binding assays showed that MIP-2gamma does not bind to CXCR2. This implies that DC might contribute to the innate immunity through the production of neutrophil-attracting chemokines and extends the knowledge about the regulation of DC migration.

Identification of unique truncated KC/GRO beta chemokines with potent hematopoietic and anti-infective activities

SK&F 107647, a previously described synthetic immunomodulatory peptide, indirectly stimulates bone marrow progenitor cells and phagocytic cells, and enhances host defense effector mechanisms in bacterial and fungal infection models in vivo. In vitro, SK&F 107647 induces the production of a soluble mediator that augments colony forming cell (CFU-GM) formation in the presence of CSFs. In this paper we purified and sequenced the stromal cell-derived hematopoietic synergistic factors (HSF) secreted from both murine and human cell lines stimulated with SK&F 107647. Murine HSF is an N-terminal 4-aa truncated form of the CXC chemokine, KC, while human HSF was identified as an N-terminal 4-aa truncated form of the CXC chemokine, GRO beta. In comparison to their full-length forms, truncated KC and truncated GRO beta were 10 million times more potent as synergistic growth stimulants for CFU-GM. Enhanced potency of these novel truncated chemokines relative to their full-length forms was also demonstrated in respiratory burst assays, CD11b Ag expression, and intracellular killing of the opportunistic pathogen, Candida albicans. Administration of truncated KC significantly enhanced survival of mice lethally infected with C. albicans. The results reported herein delineate the biological mechanism of action of SK&F 107647, which functions via the induction of unique specific truncated forms of the chemokines KC and GRO beta. To our knowledge, this represents the first example where any form of KC or GRO beta were purified from marrow stromal cells. Additionally, this is the first demonstration of in vivo efficacy of a CXC chemokine in an animal infectious fungal disease model.

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.

Effects of CC, CXC, C, and CX3C chemokines on proliferation of myeloid progenitor cells, and insights into SDF-1-induced chemotaxis of progenitors

Chemokines have been implicated in the regulation of stem/progenitor cell proliferation and movement. The purpose of the present study was to assess a number of new chemokines for suppressive activity and to delve further into SDF-1-mediated chemotaxis of progenitor cells. This report extends the list of chemokines that have suppressive activity against immature subsets of myeloid progenitors stimulated to proliferate by multiple growth factors to include: MCP-4/CK beta-10, MIP-4/CK beta-7, I-309, TECK, GCP-2, MIG and lymphotactin. The suppressive activity of a number of other chemokines was confirmed. Additionally, pretreatment of the active chemokines with an acetylnitrile solution enhanced specific activity of a number of these chemokines. The new chemokines found to be lacking suppressive activity include: MCP-2, MCP-3, eotaxin-1, MCIF/HCC-1/CK beta-1, TARC, MDC, MPIF-2/eotaxin-2/CK beta-6, SDF-1 and fractalkine/neurotactin. Overall, 19 chemokines, crossing the CC, CXC, and C subgroups, have now been found to be myelosuppressive, and 14 chemokines crossing the CC, CXC and CX3C subgroups have been found to lack myelosuppressive activity under the culture conditions of our assays. Because of the redundancy in chemokine/chemokine receptor interactions, it is not yet clear through which chemokine receptors many of these chemokines signal to elicit suppressive activities. It was also found that SDF-1-induced chemotaxis of progenitors can occur in the presence of fibronectin (FN) and extracellular matrix components and that FN effects involve activation of beta 1-, and possibly alpha 4-, integrins.

Solution structure of murine macrophage inflammatory protein-2

The solution structure of murine macrophage inflammatory protein-2 (MIP-2), a heparin-binding chemokine that is secreted in response to inflammatory stimuli, has been determined using two-dimensional homonuclear and heteronuclear NMR spectroscopy. Structure calculations were carried out by means of torsion-angle molecular dynamics using the program X-PLOR. The structure is based on a total of 2390 experimental restraints, comprising 2246 NOE-derived distance restraints, 44 distance restraints for 22 hydrogen bonds, and 100 torsion angle restraints. The structure is well-defined, with the backbone (N, Calpha, C) and heavy atom atomic rms distribution about the mean coordinates for residues 9-69 of the dimer being 0.57 +/- 0.16 A and 0.96 +/- 0.12 A, respectively. The N- and C-terminal residues (1-8 and 70-73, respectively) are disordered. The overall structure of the MIP-2 dimer is similar to that reported previously for the NMR structures of MGSA and IL-8 and consists of a six-stranded antiparallel beta-sheet (residue 25-29, 39-44, and 48-52) packed against two C-terminal antiparallel alpha-helices. A best fit superposition of the NMR structure of MIP-2 on the structures of MGSA, NAP-2, and the NMR and X-ray structures of IL-8 are 1.11, 1.02, 1.27, and 1.19 A, respectively, for the monomers, and 1.28, 1.10, 1.55, and 1.36 A, respectively, for the dimers (IL-8 residues 7-14 and 16-67, NAP-2 residues 25-84). At the tertiary level, the main differences between the MIP-2 solution structure and the IL-8, MGSA, and NAP-2 structures involve the N-terminal loop between residues 9-23 and the loops formed by residues 30-38 and residues 53-58. At the quaternary level, the difference between MIP-2 and IL-8, MGSA, or NAP-2 results from differing interhelical angles and separations.

The growth inhibitory role and potential clinical value of macrophage inflammatory protein 1 alpha in myeloid leukaemias

The control of primitive haemopoietic progenitor cell proliferation in vitro can be achieved with combinations of growth stimulatory cytokines. Acting in apparent opposition to these growth stimulators are growth inhibitory substances, including prostaglandins, cytokines and chemokines which bind to specific cognate cell surface receptors and promote signal transduction events that interfere with cellular proliferation. Within the bone marrow microenvironment, significant quantities of both growth inhibitors and growth promoters can be detected. The ratio of their concentrations within microenvironmental niches of the marrow may regulate primitive blood cell production. The potential exists, therefore, for the disregulation of haemopoiesis via the disruption of the balance between positive and negative regulators of haemopoietic progenitor proliferation. In one particular disease, chronic myeloid leukaemia (CML), there is a lack of response of leukaemic cells to the chemokine growth inhibitor, Macrophage Inflammatory Protein-1alpha (MIP-1alpha). The role of MIP-1alpha in regulation of haemopoiesis, the response of CML progenitor cells and other myeloid leukaemic cells to this chemokine, and the reasons for lack of response to MIP-1alpha in leukaemic cells are reviewed.

The Chemotactic Cytokine Eotaxin Acts as a Granulocyte-Macrophage Colony-Stimulating Factor During Lung Inflammation

During inflammatory processes, inflamed tissues signal the bone marrow (BM) to produce more mature leukocytes in ways that are not yet understood. We report here that, during the development of lung allergic inflammation, the administration of neutralizing antibodies to the chemotactic cytokine, Eotaxin, prevented the increase in the number of myeloid progenitors produced in the BM, therefore reducing the output of mature myeloid cells from BM. Conversely, the in vivo administration of Eotaxin increased the number of myeloid progenitors present in the BM. Furthermore, we found that, in vitro, Eotaxin is a colony-stimulating factor for granulocytes and macrophages. Eotaxin activity synergized with stem cell factor but not with interleukin-3 or granulocyte-macrophage colony-stimulating factor and was inhibited bypertussis toxin. We report also that CCR-3, the receptor for Eotaxin, was expressed by hematopoietic progenitors (HP). Thus, during inflammation, Eotaxin acts in a paracrine way to shift the differentiation of BM HP towards the myeloid lineage.

The Chemotactic Cytokine Eotaxin Acts as a Granulocyte-Macrophage Colony-Stimulating Factor During Lung Inflammation

During inflammatory processes, inflamed tissues signal the bone marrow (BM) to produce more mature leukocytes in ways that are not yet understood. We report here that, during the development of lung allergic inflammation, the administration of neutralizing antibodies to the chemotactic cytokine, Eotaxin, prevented the increase in the number of myeloid progenitors produced in the BM, therefore reducing the output of mature myeloid cells from BM. Conversely, the in vivo administration of Eotaxin increased the number of myeloid progenitors present in the BM. Furthermore, we found that, in vitro, Eotaxin is a colony-stimulating factor for granulocytes and macrophages. Eotaxin activity synergized with stem cell factor but not with interleukin-3 or granulocyte-macrophage colony-stimulating factor and was inhibited bypertussis toxin. We report also that CCR-3, the receptor for Eotaxin, was expressed by hematopoietic progenitors (HP). Thus, during inflammation, Eotaxin acts in a paracrine way to shift the differentiation of BM HP towards the myeloid lineage.

Myeloid progenitor cell proliferation and mobilization effects of BB10010, a genetically engineered variant of human macrophage inflammatory protein-1alpha, in a phase I clinical trial in patients with relapsed/refractory breast cancer

Macrophage Inflammatory Protein (MIP)-1alpha is myelosuppressive in vitro and in vivo for hematopoietic stem and immature subsets of myeloid progenitor cells, demonstrates some myeloprotective effects in mice treated with Ara-C and hydroxyurea, and has stem/progenitor cell mobilizing activity in mice. Based on these observations, BB10010, a genetic variant of MIP-1alpha, was assessed for effects on marrow and blood myeloid progenitor cells in patients with relapsed/refractory breast cancer. MIP-1alpha readily polymerizes, whereas BB10010 has a reduced tendency to form large polymers at physiological pH and ionic strength and retains biological activity. Patients were injected with 5, 10, 30 or 100 microg/kg BB10010 s.c. daily for 3 days. BB10010 significantly reduced the cycling status of marrow myeloid progenitors from pretreatment levels of 39-58% to 0 - 11% one day after the third and last injection of BB10010. This was associated with significant decreases in frequency of marrow progenitors (number of colonies formed per number of cells plated) and percent biopsied marrow CD34+ cells. The suppressive effects were reversible in patients and the rapidity of this reversal demonstrated in mouse studies. BB10010 had no effect on nucleated cellularity or on the proliferation of nucleated cells as assessed in marrow biopsies from the patients. These latter effects may in part reflect the noted decreased apoptosis of nucleated cells by BB10010. BB10010 also demonstrated significant but modest myeloid progenitor cell mobilizing capacity. Blood progenitors were in a slow or non-cycling state prior to treatment and this did not change after administration of BB10010. The above effects of BB10010 were similar at the four different dosage levels assessed. These results demonstrate in humans the suppressive and mobilizing effects of MIP-1alpha and BB10010 previously noted in vivo in mice.

Identification of the CC chemokines TARC and macrophage inflammatory protein-1 beta as novel functional ligands for the CCR8 receptor

Chemokines are key molecules in directing leukocyte migration toward sites of inflammation. We have previously cloned a putative CC chemokine receptor gene, TER1, whose expression is restricted to lymphoid tissues and cell lines. Recently, this receptor has been shown to signal in response to the human CC chemokine I-309 and thus it has been renamed CCR8 according to the current nomenclature. In the present study, we report the identification of the CC chemokines thymus and activation-regulated cytokine (TARC) and macrophage inflammatory protein-1 beta (MIP-1 beta) as CCR8 ligands, as they induce chemotaxis in CCR8 Jurkat stable transfectants. Furthermore, we have generated a polyclonal antiserum that is able to recognize the CCR8 molecule in transfectant lysates. The pattern of CCR8 mRNA expression and the functional effects exerted by its ligand suggest that the triggering of this receptor may regulate multiple functions including activation, migration and proliferation of lymphoid cells.

Chemokines, lymphocytes, and HIV

Chemokines are members of a family of more than 30 human cytokines whose best-described activities are as chemotactic factors for leukocytes and that are presumed to be important in leukocyte recruitment and trafficking. While many chemokines can act on lymphocytes, the roles of chemokines and their receptors in lymphocyte biology are poorly understood. The recent discoveries that chemokines can suppress infection by HIV-1 and that chemokine receptors serve, along with CD4, as obligate co-receptors for HIV-1 entry have lent urgency to studies on the relationships between chemokines and lymphocytes. My laboratory has characterized Mig and Crg-2/IP-10, chemokines that are induced by IFN-gamma and that specifically target lymphocytes, particularly activated T cells. We have demonstrated that the genes for these chemokines are widely expressed during experimental infections in mice with protozoan and viral pathogens, but that the patterns of mig and crg-2 expression differed, suggesting non-redundant roles in vivo. Our related studies to identify new chemokine receptors from activated lymphocytes resulted in the cloning of STRL22 and STRL33. We and others have shown that STRL22 is a receptor for the CC chemokine MIP-3 alpha, and STRL22 has been renamed CCR6. Although STRL33 remains an orphan receptor, we have shown that it can function as a co-receptor for HIV-1 envelope glycoproteins, and that it is active with a broader range of HIV-1 envelope glycoproteins than the major co-receptors described to date. The ability of STRL33 to function with a wide variety of envelope glycoproteins may become particularly important if therapies are instituted to block other specific co-receptors. We presume that investigations into the roles of chemokines and their receptors in lymphocyte biology will provide information important for understanding the pathogenesis of AIDS and for manipulating immune and inflammatory responses for clinical benefit.

Growth factors and hematopoietic stem cells

The hematopoietic system is mediated in part by cell-to-cell interactions and soluble mediators or growth factors (cytokines). A large number of cytokines directly and potently control hematopoietic stem and precursor cell proliferation and differentiation. This review focuses on the recent studies devoted to the role of cytokines in the ex vivo expansion and differentiation of hematopoietic stem and precursor cells.

The chemokine SDF-1, stromal cell-derived factor 1, attracts early stage B cell precursors via the chemokine receptor CXCR4

In the bone marrow, progenitor (pro-) and precursor (pre-) B cells depend on close contact with stromal cells for growth and maturation. Stromal cell-derived factor 1 (SDF-1), also known as pre-B cell growth-stimulating factor, is produced by bone marrow stromal cells and was reported to act together with interleukin-7 as co-mitogen for pre-B cells. SDF-1 was recently shown to be a chemokine which is chemotactic for different types of leukocytes and acts via the chemokine receptor CXCR4. Using sorted B220+ bone marrow cells and several B cell lines characteristic for different stages of B lymphopoiesis, we now show that SDF-1 is a potent attractant for pro- and pre-B cells, but is inactive on B cells at later stages of development. In early B cell precursors, SDF-1 induced intracellular Ca2+ mobilization and in vitro migration with a potency and efficacy similar to that observed for chemokines acting on blood leukocytes. These responses were mediated via CXCR4 as they could be inhibited by an antireceptor antibody. SDF-1 is the first chemokine shown to act on early-stage B cell precursors. Mice lacking SDF-1 die perinatally and show a severe deficiency in B lymphopoiesis. We propose that SDF-1 released from the stromal cells exerts its critical hematopoietic function by selectively attracting and confining early B cell precursors within the bone marrow microenvironment that provides the necessary factors for growth and differentiation.

Modulation of macrophage inflammatory protein-1alpha and its receptors in human B-cell lines derived from patients with acquired immunodeficiency syndrome and Burkitt's lymphoma

Macrophage inflammatory protein-1 alpha (MIP-1alpha) is a member of the -C-C- family of low-molecular weight chemokines. MIP-1alpha is involved in the homeostatic control of stem cell proliferation, in inducing chemotaxis, and also in inflammatory responses in mature cell types. In order to observe modulations of MIP-1alpha secretion and expression along with MIP-1alpha receptor (MIP-1alpha-R) expression for a possible autocrine role in AIDS associated B-cell lines, we studied a wide panel of human B-cell lines. Previous work by us has shown that HIV-1 tat down modulates MIP-1alpha by inducing a novel transcription factor MNP. Our data in this report suggest that HIV down modulates MIP-1alpha as a mechanism to evade suppression by this chemokine in human B-cells. Furthermore, our results strongly suggest MIP-1alpha autocrine loops in a majority of tumor B-cells as evident by MIP-1alpha-R expression, and also secretion of MIP-1alpha.

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

CC chemokine receptor 1 (CCR1) is expressed in neutrophils, monocytes, lymphocytes, and eosinophils, and binds the leukocyte chemoattractant and hematopoiesis regulator macrophage inflammatory protein (MIP)-1alpha, as well as several related CC chemokines. Four other CCR subtypes are known; their leukocyte and chemokine specificities overlap with, but are not identical to, CCR1, suggesting that CCR1 has both redundant and specific biologic roles. To test this, we have developed CCR1-deficient mice (-/-) by targeted gene disruption. Although the distribution of mature leukocytes was normal, steady state and induced trafficking and proliferation of myeloid progenitor cells were disordered in -/- mice. Moreover, mature neutrophils from -/- mice failed to chemotax in vitro and failed to mobilize into peripheral blood in vivo in response to MIP-1alpha. Consistent with this, -/- mice had accelerated mortality when challenged with Aspergillus fumigatus, a fungus controlled principally by neutrophils. To test the role of CCR1 in granuloma formation, we injected Schistosoma mansoni eggs intravenously, and observed a 40% reduction in the size of lung granulomas in -/- mice compared to +/+ littermates. This was associated with increased interferon-gamma and decreased interleukin-4 production in -/- versus +/+ lung lymph node cells stimulated with egg-specific antigen, suggesting that CCR1 influences the inflammatory response not only through direct effects on leukocyte chemotaxis, but also through effects on the type 1-type 2 cytokine balance. Thus CCR1 has nonredundant functions in hematopoiesis, host defense, and inflammation.

The chemokine SDF-1 is a chemoattractant for human CD34+ hematopoietic progenitor cells and provides a new mechanism to explain the mobilization of CD34+ progenitors to peripheral blood

Hematopoietic progenitor cells migrate in vitro and in vivo towards a gradient of the chemotactic factor stromal cell-derived factor-1 (SDF-1) produced by stromal cells. This is the first chemoattractant reported for human CD34+ progenitor cells. Concentrations of SDF-1 that elicit chemotaxis also induce a transient elevation of cytoplasmic calcium in CD34+ cells. SDF-1-induced chemotaxis is inhibited by pertussis toxin, suggesting that its signaling in CD34+ cells is mediated by seven transmembrane receptors coupled to Gi proteins. CD34+ cells migrating to SDF-1 include cells with a more primitive (CD34+/CD38- or CD34+/DR-) phenotype as well as CD34+ cells phenotypically committed to the erythroid, lymphoid and myeloid lineages, including functional BFU-E, CFU-GM, and CFU-MIX progenitors. Chemotaxis of CD34+ cells in response to SDF-1 is increased by IL-3 in vitro and is lower in CD34+ progenitors from peripheral blood than in CD34+ progenitors from bone marrow, suggesting that an altered response to SDF-1 may be associated with CD34 progenitor mobilization.

Human chemokines: an update

Interleukin 8, the first chemokine to be characterized, was discovered nearly ten years ago. Today, more than 30 human chemokines are known. They are often upregulated in inflammation and act mainly on leukocytes inducing migration and release responses. The present review deals largely with the new developments of the last three years. Several structural studies have shown that most chemokines form dimers. The dimers, however, dissociate upon dilution, and the monomers constitute the biologically active form. Chemokine activities are mediated by seven-transmembrane-domain, G protein coupled receptors, five of which were discovered in the past three years. The primary receptor-binding domain of all chemokines is near the NH2 terminus, and antagonists can be obtained by truncation or substitutions in this region. Major progress has been made in the understanding of chemokine actions on T lymphocytes that respond to several CC chemokines but also to IP10 and Mig, two CXC chemokines that selectively attract T cells via a novel receptor. Effects of chemokines on angiogenesis and tumor growth have been reported, but the data are still contradictory and the mechanisms unknown. Of considerable interest is the recent discovery that some chemokines function as HIV-suppressive factors by interacting with chemokine receptors which, together with CD4, were recognized as the binding sites for HIV-1.

Leukocyte migration and activation by murine chemokines

Chemokines are a family of chemotactic cytokines which attract different types of leukocytes. This property, combined with some additional inflammatory and growth-regulatory activities, demonstrate their crucial role in the immune system. Chemokines are low molecular weight proteins and possess a typical positioning of four conserved cysteines. This family is further subdivided in two subfamilies depending on whether the first two cysteines are adjacent or not (CC and CXC chemokines, respectively). The CXC chemokines (including interleukin-8) predominantly attract neutrophils, whereas CC chemokines induce migration of monocytes, as well as other leukocyte cell types. In this article, the general characteristics of chemokines are reviewed. Furthermore, the murine CC chemokines, JE/MCP-1, MCP-3/MARC, MIP-1 alpha, MIP-1 beta, RANTES, TCA3, C10/MRP-1, MRP-2, and eotaxin, are discussed more in detail.

Molecular cloning of a novel T cell-directed CC chemokine expressed in thymus by signal sequence trap using Epstein-Barr virus vector

Precursors of most secreted and cell surface molecules carry signal sequences at their amino termini. Here we describe an efficient signal sequence trap method and isolation of a novel CC chemokine. An expression library was constructed by inserting 5' portion-enriched cDNAs from phytohemagglutinin-stimulated peripheral blood mononuclear cells into upstream of signal sequence-deleted CD4 cDNA in an Epstein-Barr virus shuttle vector. After electroporation into Raji cells, CD4 antigen-positive cells were enriched by repeated cell sorting and plasmids were recovered in Escherichia coli. Out of 100 plasmid clones examined, 42 clones directed expression of CD4 antigen on the cell surface. Among them were signal sequences of CD6, beta2-microglobulin, MGC-24, and T cell receptor epsilon-chain, and at least four novel potential signal sequences. A cDNA clone encoding a novel CC chemokine was isolated by using one of the trapped fragments. The gene designated as TARC from Thymus and Activation-Regulated Chemokine was expressed transiently in phytohemagglutinin-stimulated peripheral blood mononuclear cells and constitutively in thymus. Radiolabeled recombinant TARC specifically bound to T cell lines and peripheral T cells but not to monocytes or granulocytes. The binding of radiolabeled TARC to the high-affinity receptor (Kd, 2.1 nM) on Jurkat was displaced by TARC but not by interleukin-8, MIP-1alpha, RANTES, or MCP-1. TARC also bound to the promiscuous chemokine receptor on erythrocytes (Kd, 17 nM). TARC induced chemotaxis in T cell lines Hut78 and Hut102. Pretreatment of Hut78 with pertussis toxin abolished the TARC-induced cell migration. Collectively, T cells express a highly selective receptor for TARC that is coupled to pertussis toxin-sensitive G-protein. TARC may a factor playing important roles in T cell development in thymus as well as in trafficking and activation of mature T cells.

Molecular expression of the alpha-chemokine rabbit GRO in Escherichia coli and characterization of its production by lung cells in vitro and in vivo

GRO proteins are alpha-chemokine cytokines that attract neutrophils and stimulate the growth of a variety of cells. Previously, we observed that rabbit alveolar macrophages transcribe the genes for at least two GRO homologues. In order to study the role of GRO cytokines in lung inflammation, we cloned the predominant rabbit GRO cDNA (RabGRO) from alveolar macrophages, expressed bioactive recombinant protein (rRabGRO) in Escherichia coli, and developed a sensitive and specific enzyme-linked immunosorbent assay for RabGRO protein. We found that rabbit AM express and secrete GRO in vitro in response to both exogenous (e.g. lipopolysaccharide, heat-killed Staphylococcus aureus, and crystalline silica) and endogenous inflammatory stimuli (e.g. tumor necrosis factor-alpha) as determined by both radioimmunoprecipitation and enzyme-linked immunosorbent assay. Biologically significant amounts of GRO are present in vivo in the bronchoalveolar lavage fluid of rabbits with E. coli pneumonia; by in situ hybridization, GRO mRNA is detectable in infiltrating pulmonary leukocytes and bronchial epithelial cells. These results indicate that GRO chemokines are likely to be important mediators of the inflammatory response that accompanies acute infectious processes in the lungs.