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Bone marrow-derived fibrocytes review as key cellular players in the promotion of the pathogenesis of variety of fibroproliferative disorders, including pulmonary fibrosis. Pulmonary fibrosis is associated with a number of disorders that affect the lung. Although there are several cellular types that are involved in the pathogenesis pulmonary fibrosis, the resident lung fibroblast has been viewed traditionally as the primary cell involved in promoting the deposition of ECM that culminates in pulmonary fibrosis. However, recent findings demonstrate that a circulating cell (i.e., the fibrocyte) can contribute to the evolution of pulmonary fibrosis. Fibrocytes are bone marrow-derived mesenchymal progenitor cells that express a variety of cell-surface markers related to leukocytes, hematopoietic progenitor cells, and fibroblasts. Fibrocytes are unique in that they are capable of differentiating into fibroblasts and myofibroblasts, as well as adipocytes. In this review, we present data supporting the critical role these cells play in the pathogenesis of pulmonary fibrosis.

Fibrocytes were first described over a decade ago as a population of cells in circulation with fibroblast-like properties, which were involved in tissue repair. Since that time, we have learned a significant amount about these bone marrow-derived cells, which contribute to wound healing and fibrosis. Fibrocytes express leukocyte markers such as CD34, CD45, and CD13 and also express mesenchymal markers such as pro-collagens I and III, vimentin, and fibronectin. In addition, they have been shown to express the chemokine receptors CXCR4 and CCR7, which appear to be important in cellular trafficking from the vascular to the extravascular compartment. Fibrocytes have been shown to contribute to a number of fibrotic disorders, and here, we review their involvement in lung diseases including pulmonary fibrosis, asthma, and vascular remodeling.

CXC chemokines, which induce angiogenesis, haveglutamine-leucine-arginine amino acid residues (ELR motif) in the aminoterminus and bind CXCR2 and the Duffy antigen chemokine-bindingprotein. Duffy, a seven transmembrane protein that binds CXC and CCchemokines, has not been shown to couple to trimeric G proteins or totransduce intracellular signals, although it is highly expressed on redblood cells, endothelial cells undergoing neovascularization, andneuronal cells. The binding of chemokines by Duffy could modulatechemokine responses positively or negatively. Positive regulation couldcome through the presentation of chemokine to functional receptors, andnegative regulation could come through Duffy competition withfunctional chemokine receptors for chemokine binding, thus serving as adecoy receptor. To determine whether Duffy has a role in angiogenesisand/or maintenance of homeostasis, we developed transgenic miceexpressing mDuffy under the control of the preproendothelinpromoter/enhancer (PPEP), which directs expression of the transgeneto the endothelium. Two PPEP-mDuffy-transgenic founders wereidentified, and expression of the transgene in the endothelium wasverified by Northern blot, RT-PCR, and immunostaining of tissues. Thephenotype of the mice carrying the transgene appeared normal by allvisual parameters. However, careful comparison of transgenic andnontransgenic mice revealed two phenotypic differences:mDuffy-transgenic mice exhibited a diminished angiogenic response to MIP-2 in the corneal micropocket assay, and mDuffy-transgenic miceexhibited enhanced hepatocellular toxicity and necrosis as comparedwith nontransgenic littermates in response to overdose of acetaminophen(APAP; 400 mg/kg body weight). Morover, APAP treatment was lethal in50% of the mDuffy-transgenic mice 24 h post challenge, and 100%of the nontransgenic littermates survived this treatment at the 24 h time point. Our data suggest that enhanced expression of mDuffy onendothelial cells can lead to impaired angiogenic response tochemokines and impaired maintenance of homeostasis in response to toxicstresses.

A variety of factors have been identified that regulate angiogenesis, including the CXC chemokine family. The CXC chemokines are a unique family of cytokines for their ability to behave in a disparate manner in the regulation of angiogenesis. CXC chemokines have four highly conserved cysteine amino acid residues, with the first two cysteine amino acid residues separated by one non-conserved amino acid residue (i.e., CXC). A second structural domain within this family determines their angiogenic potential. The NH2 terminus of the majority of the CXC chemokines contains three amino acid residues (Glu-Leu-Arg: the ELR motif), which precedes the first cysteine amino acid residue of the primary structure of these cytokines. Members that contain the ELR motif (ELR+) are potent promoters of angiogenesis. In contrast, members that are inducible by interferons and lack the ELR motif (ELR−) are potent inhibitors of angiogenesis. This difference in angiogenic activity may impact on the pathogenesis of a variety of disorders.

Continuous expression of the MGSA/GROα, β, or γ chemokine bestows tumor-forming capacity to the immortalized murine melanocyte cell line, melan-a. The mechanism for this transformation is unclear, although both autocrine and paracrine processes are possible because melan-a cells as well as endothelial cells express a low level of the receptor for this ligand. To further define the role of MGSA/GRO proteins in melanocyte transformation, two types of experiments were designed to neutralize the biological effects of MGSA/GRO in the transfected melan-a clones: (1) the effect of neutralizing antiserum to MGSA/GRO proteins on melan-a tumor growth was assessed; (2) the tumor-forming capacity of melan-a clones expressing ELR motif-mutated forms of MGSA/GRO with compromised receptor affinity was compared to the tumor-forming capacity of clones expressing wild-type MGSA/GRO. These experiments revealed that SCID mice inoculated with MGSA/GROα- or γ-expressing melan-a cells and subsequently treated with antiserum to the respective chemokine exhibited decreased tumor growth. This reduction in tumor growth was accompanied by declining angiogenic activity in MGSA/GROγ-expressing tumors. Moreover, athymic nude mice injected with melan-a cells expressing ELR-mutant forms of MGSA/GROα exhibited markedly impaired tumor-forming capacity compared with those mice injected with melan-a clones expressing wild-type MGSA/GRO. These data suggest that continuous expression of MGSA/GRO proteins may facilitate tumor growth by stimulating the growth of microvessels into the tumor (paracrine) and by affecting melanocyte growth (autocrine). J. Leukoc. Biol. 67: 53–62; 2000.

This study examined the cell-to-cell interaction between fibroblasts and macrophages as a possible contributor to the chronic inflammatory state. In a coculture system, consisting of macrophages layered over confluent fibroblasts, there was a significant increase in macrophage inflammatory protein 1α (MIP-1α) compared with control cultures. ICAM-1 adhesion was identified as an important stimulus of MIP-1α production by using ICAM-1-specific monoclonal antibodies. Furthermore, fibroblasts from ICAM-1 knockout mice induced significantly less MIP-1α production from peritoneal macrophages when compared to control fibroblasts. In addition, it appeared that oxygen radicals functioned as activating molecules during cellular interaction and production of MIP-1α, as the addition of the antioxidant N-acetylcysteine (NAC) prevented MIP-1α secretion. Thus, the ICAM-1 and oxygen radical-mediated induction of MIP-1α associated with a macrophage/fibroblast coculture system provides one possible mechanism by which immune/inflammatory cell interactions may augment chemokine production and exacerbate chronic inflammatory diseases. J. Leukoc. Biol. 64: 636–641; 1998.

Although many studies have characterized soluble factors that stimulate or inhibit chemokine secretion, in this review we focus on the event of cellular adhesion as a novel mechanism for stimulating chemokine expression. Recent work has demonstrated chemokine expression following cell-to-cell and cell-to-matrix adhesion. The specificity of this finding was demonstrated utilizing various techniques that illustrate that adhesion, and not a soluble stimulus, is in some cases responsible for initiating or augmenting chemokine expression. For example, co-cultures of peripheral blood monocytes and endothelial cells secreted elevated levels of IL-8 and MCP-1 compared with either cell type alone. When co-cultured in transwells, this effect was significantly attenuated. In other experiments, neutralizing monoclonal antibodies to various adhesion molecules inhibited chemokine expression. The effects of adhesion were not limited to leukocytes. Both immune and non-immune cell types were evaluated as potential sources of adhesion-mediated chemokine expression. Not suprisingly, expression of some chemokines was associated with adhesion, whereas others were not, supporting the notion that adhesion differentially signals chemokine secretion during the inflammatory response. We hypothesize that as a recruited leukocyte encounters different adhesion substrates such as endothelial cells, basement membrane, extracellular matrix, and fibroblasts, the expression of chemokines from both the leukocyte and the substrate may be initiated, inhibited, or augmented. Careful characterization of the contribution of adhesion to regulation of chemokine expression will provide insight into the pathogenesis of many human diseases where chemokines have a central role.

The production of eosinophil-specific chemotactic factors during allergic airway responses may be a pivotal event resulting in eosinophil accumulation, activation, and airway damage. Recent studies have identified specific chemokines that may play crucial roles in recruitment of eosinophils to the site of allergic reactions. In this study we have utilized an established model of schistosome egg antigen (SEA)-mediated allergic responses to examine the role of specific C-C chemokines [macrophage inflammatory protein-1α (MIP-1α), RANTES, and monocyte chemoattractant protein-1 (MCP-1)] in eosinophil recruitment. We have previously identified a role for MIP-1α in eosinophil accumulation in the lung and airway during allergic airway inflammation. We extend those studies using in vitro eosinophil chemotaxis to establish that both MIP-1α and RANTES are potent eosinophil chemotactic factors in lungs during allergic airway responses. Morphometric analysis demonstrated a peribronchial accumulation of eosinophils within the lungs beginning at 8 h, peaking at 24 h, and plateauing at 48–96 h after allergen (SEA) challenge. Utilizing whole-lung homogenates from allergen-challenged mice, in vitro eosinophil chemotactic assays demonstrated significant increases in eosinophil chemotactic activity with 8-h lung homogenates and peak activity with samples from 24-h lung homogenates. These data correlated with the morphometric analysis of peribronchial eosinophil accumulation in situ. When lung homogenates from allergen-challenged mice were preincubated in vitro with antibodies specific for MIP-1α, RANTES, or MCP-1, a significant reduction in eosinophil chemotaxis was observed with only MIP-1α and RANTES neutralization. Altogether, these studies indicate that RANTES and MIP-1α are major eosinophil chemotactic factors produced during allergic airway responses.

Effective host defense against bacterial invasion is characterized by the vigorous recruitment and activation of inflammatory cells, which is dependent on the coordinated expression of both pro-and anti-inflammatory cytokines. In this review, we present evidence indicating that both C-X-C and C-C chemokines are integral components of antibacterial host defense. Specifically, in vitro studies indicate that C-X-C chemokines [interleukin-8 (IL-8) and macrophage inflammatory protein 2 (MIP-2)] and the C-C chemokine macrophage inflammatory protein 1 alpha (MIP-1α) augment the ability of polymorphonuclear leukocytes (PMNs) and alveolar macrophages, respectively, to phagocytose and kill Escherichia coli. In addition, the intratracheal instillation of Klebsiella pneumoniae in CD-I mice results in time-dependent production of MIP-2 and MIP-1α, and the inhibition of MIP-2 bioactivity in vivo results in decreases in lung PMN influx, impaired bacterial clearance, and early mortality. Finally, the anti-inflammatory cytokine interleukin-10 (IL-10) is also expressed within the lung during the evolution of Klebsiella pneumonia, and neutralization of IL-10 in vivo results in enhanced proinflammatory cytokine production, bacterial clearance, and increases in both short- and long-term survival. In conclusion, our studies indicate that specific chemokines are important mediators of leukocyte recruitment and/or activation in bacterial pneumonia and that the expression of these chemokines is regulated by endogenously produced IL-10.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by the elicitation and activation of a number of leukocyte populations within both the synovial space and joint tissue. The recruited leukocytes subsequently play an instrumental role in synovial cell proliferation, pannus formation, and bone erosion. Although it is known that leukocytes are important participants in the evolving joint pathology, the mechanism responsible for the successful elicitation of cells to the joint is not clear. A number of studies have identified an association of specific cytokines, including chemokines, with active arthritis, but longitudinal analyses of cytokine expression and the causal role of these mediators have not been defined. Animal models and cell culture systems have proved useful in identifying the expression of various cytokines during the maintenance of chronic joint inflammation. In addition, animal models have provided important information regarding the kinetic production and contribution of specific mediators to the development of experimental arthritis. These studies provide insight into the potential mechanisms for leukocyte involvement in inflammatory joint disease.

The two chemotactic cytokines interleukin-8 (IL-8) and epithelial neutrophil activating protein 78 (ENA-78) were recently shown to be potent chemoattractants and activators of neutrophil function and to be present in certain inflammatory diseases. We have studied the effects of recombinant and natural interferon-α (IFN-α) and of recombinant interferon gamma (rIFN-γ) on the production of EL-8 and ENA-78 in lipopolysaccharide- and interleukin-1–stimulated human monocytes. Both types of interferons showed a strong, concentration-dependent inhibition of neutrophil-stimulating bioactivity. Similarly, the secretion of IL-8 and ENA-78 was also inhibited by up to 73%. Northern blot experiments demonstrated that IFN-α decreases the steady-state levels of IL-8 and ENA-78 mRNA in monocytes, suggesting that IFN-α as well as IFN-γ may control the expression of neutrophil chemotactic cytokines at the mRNA level. J. Leukoc. Biol. 57: 929–935; 1995.

Pulmonary fibrosis is the end point of a chronic inflammatory process characterized by leukocyte recruitment and activation, fibroblast proliferation, and increased extracellular matrix production. Previous studies of models of pulmonary fibrosis have investigated the role of cytokines in the evolution of the fibrotic response. The involvement of tumor necrosis factor and interleukin-1 in bleomycin-induced lung injury, a model of idiopathic pulmonary fibrosis, has been well established, suggesting that cytokines mediate the initiation and maintenance of chronic inflammatory lesions. However, the aforementioned cytokines alone cannot account for the recruitment and activation of specific leukocyte populations found in the bleomycin model. Recently, a family of novel proinflammatory cytokines (chemokines) was cloned and characterized, yielding many putative mediators of leukocyte functions. Macrophage inflammatory protein-1α (MIP-1α) and monocyte chemoattractant protein-1 (MCP-1) belong to the C-C chemotactic cytokine family, a group of low-molecular-weight peptides. These molecules modulate chemotaxis, proliferation, and cytokine expression in leukocyte subsets. Our group has investigated the roles of MCP-1 and MIP-1α in the bleomycin model. Both MCP-1 and MIP-1α are expressed in a time-dependent manner after bleomycin challenge, and passive immunization of these animals with either anti-MIP-1α or anti-MCP-1 antibodies attenuated leukocyte accumulation. In addition, we have identified specific cell types expressing MCP-1 or MIP-1α by in situ hybridization and immunohistochemical localization, respectively. Furthermore, our results indicate that MIP-1α expression is mediated by alveolar macrophage-derived tumor necrosis factor, identifying an important cytokine pathway in the initiation of pulmonary fibrosis. Finally, anti-MIP-1α therapy attenuated fibrosis, providing direct evidence for its involvement in fibrotic pathology. Our work has clearly established that the C-C chemokines MCP-1 and MIP-1α are expressed and contribute to the initiation and maintenance of the bleomycin-induced pulmonary lesion. J. Leukoc. Biol. 57: 782–787; 1995.

The accumulation of polymorphonuclear cells (PMN) in tissue is an essential element of the inflammatory response that is important in host defense. Adherence to endothelium constitutes the first step in PMN migration from the vascular compartment to the interstitium. We demonstrate that human peripheral blood mononuclear cells (PBMC) adherent to plastic can result in expression of interleukin-8 (IL-8), a potent PMN chemoattractant and activating cytokine. Northern blot analyses showed PBMC adherent to plastic expressed IL-8 steady-state mRNA levels by 30 min, peaked at 8 h, and then decreased over the next 16 h. In contrast, nonadherent PBMC (cultured in teflon chambers) expressed less than 25% of the maximal IL-8 steady-state mRNA levels as compared with adherent PBMC. Adherent PBMC-associated IL-8 determined by immunohistochemistry, supernatant chemotactic bioactivity, and extracellular antigenic IL-8 paralleled IL-8 mRNA expression. Antigenic and bioactive IL-8 were significantly apparent by 4–8 h, respectively, and increased significantly to maximal levels by 24 h. Furthermore, adherent PBMC IL-8 gene expression was suppressed by either concomitant treatment with actinomycin-D or cycloheximide, yet specific neutralizing antibodies directed against either IL-1β or tumor necrosis factor (TNF)-α failed to alter adherence-induced steady-state IL-8 mRNA levels. These data support the hypothesis that PBMC adherence is an important signal for the production of IL-8, and may be essential to the development of the inflammatory response through the elicrtation of PMN.

CD14 is a myeloid receptor for bacterial cell membrane/wall components, for which we previously showed a strong induction in cerebrospinal fluid (CSF) during meningitis. Here, we studied CD14 function in murine Streptococcus pneumoniae meningitis by using wild-type (WT), CD14−/− mice, and WT mice pretreated with neutralizing anti-CD14 antibodies. Early polymorphonuclear leukocytes (PMN) immigration was more pronounced in CSF of CD14−/− than of WT mice. This was not a result of altered adherence molecule expression in blood and CSF PMN or brain endothelial cells. Macrophage inflammatory protein-2 (MIP-2) and keratinocyte-derived chemokine levels were similar in CSF in both strains, but MIP-2 was higher in infected brain and in brain-derived endothelial cells infected in vitro in CD14−/− than in WT mice. CD14−/− PMN demonstrated increased expression of CXC chemokine receptor 2 (CXCR2) after infection and stronger in vitro chemotaxis than WT PMN toward CSF from WT or CD14−/− mice and toward MIP-2. Excess PMN migration in CD14−/− mice did not result in improved bacterial clearing but in increased tumor necrosis factor in CSF, higher disease severity, and earlier death. Pretreatment with anti-CXCR2 reduced PMN infiltration into CSF and brain MIP-2 production and abolished earlier mortality in CD14−/− mice. In conclusion, CD14 plays a protective role in pneumococcal meningitis by slowing PMN migration via MIP-2 and CXCR2 modulation.

CXC chemokines, which induce angiogenesis, have glutamine-leucine-arginine amino acid residues (ELR motif) in the amino terminus and bind CXCR2 and the Duffy antigen chemokine-binding protein. Duffy, a seven transmembrane protein that binds CXC and CC chemokines, has not been shown to couple to trimeric G proteins or to transduce intracellular signals, although it is highly expressed on red blood cells, endothelial cells undergoing neovascularization, and neuronal cells. The binding of chemokines by Duffy could modulate chemokine responses positively or negatively. Positive regulation could come through the presentation of chemokine to functional receptors, and negative regulation could come through Duffy competition with functional chemokine receptors for chemokine binding, thus serving as a decoy receptor. To determine whether Duffy has a role in angiogenesis and/or maintenance of homeostasis, we developed transgenic mice expressing mDuffy under the control of the preproendothelin promoter/enhancer (PPEP), which directs expression of the transgene to the endothelium. Two PPEP-mDuffy-transgenic founders were identified, and expression of the transgene in the endothelium was verified by Northern blot, RT-PCR, and immunostaining of tissues. The phenotype of the mice carrying the transgene appeared normal by all visual parameters. However, careful comparison of transgenic and nontransgenic mice revealed two phenotypic differences: mDuffy-transgenic mice exhibited a diminished angiogenic response to MIP-2 in the corneal micropocket assay, and mDuffy-transgenic mice exhibited enhanced hepatocellular toxicity and necrosis as compared with nontransgenic littermates in response to overdose of acetaminophen (APAP; 400 mg/kg body weight). Morover, APAP treatment was lethal in 50% of the mDuffy-transgenic mice 24 h post challenge, and 100% of the nontransgenic litter-mates survived this treatment at the 24 h time point. Our data suggest that enhanced expression of mDuffy on endothelial cells can lead to impaired angiogenic response to chemokines and impaired maintenance of homeostasis in response to toxic stresses.

The inflammatory response during allergic airway inflammation involves the recruitment of multiple leukocyte populations, including neutrophils, monocytes, lymphocytes, and eosinophils. All of these populations likely contribute to the pathology observed during repeated episodes of allergic airway inflammation. We have examined the role of a human neutrophil-specific chemokine (C-x-C), ENA-78, in a model of allergic airway responses and identified murine mast cells as a cellular source of an ENA-78-like molecule. Within this allergic airway model, neutrophil infiltration into the airway occurs within 4–8 h post-allergen challenge, persists within the airway until 24 h, and resolves by 48 h post-challenge. Neutrophil influx precedes the eosinophil infiltration, which peaks in the airway at 48 h post-allergen challenge. In this study the production of ENA-78 from challenged lungs demonstrated a significant increase in the allergen-, but not vehicle-, challenged lungs. In vivo neutralization of ENA-78 by passive immunization demonstrated a significant decrease in peak neutrophil infiltration at 8 h, with no effect on the eosinophil infiltration at 48 h post-challenge. Because ENA-78 has been shown to be chemotactic for neutrophils and given the involvement of mast cell degranulation in allergic responses, we examined mast cells for the presence of ENA-78. Cultured mast cells spontaneously released ENA-78, but on activation with IgE + antigen, NG-L-arginine methyl ester or compound 48/80 produced significantly increased levels of ENA-78. Supernatants from sonicated MC-9 mast cells induced an overwhelming influx of neutrophils into the BAL by 4 h post-intratracheal injection into mice, suggesting that the mast cell is a significant source of neutrophil chemotactic factors. Mast cell supernatant-mediated neutrophil infiltration was substantially decreased by preincubation of the supernatant with antibodies specific for ENA-78. These data indicate a major neutrophil chemotactic protein produced by mast cells during allergic responses may be mast cell-derived ENA-78.

By reverse transcriptase-polymerase chain reaction, enzymelinked immunosorbent assay, and immunohistochemistry, MGSA-α, -β, -γ, and CXCR2 mRNA expression and proteins are detected in 7 out of 10 human melanoma lesions. The biological consequence of constitutive expression of the MGSA/GRO chemokine in immortalized melanocytes was tested in SCID and nude mouse models. Continuous expression of MGSA/GRO-α, -β, or -γ in immortalized melan-a mouse melanocytes results in nearly 100% tumor formation for each of the clones tested, whereas clones expressing only the neomycin resistance vector form tumors

Angiogenesis is a critical component of tumor biology. In recent years newer techniques of cell and molecular biology have led to important advances in our understanding of this process. The regulation of angiogenesis depends on a balance between the activity of local factors that promote (angiogenic factors) or inhibit (angiostatic factors) neovascularization. Nowhere is this paradigm of a balance more apparent than in the study of tumor-associated angiogenesis. Tumors promote angiogenesis through a combination of overexpression of angiogenic factors and local inhibition of angiostatic factors. This strategy leads to an angiogenic environment that promotes tumor growth and metastases. Our laboratory has focused studies on the role of the CXC chemokine family in the regulation of angiogenesis by non-small cell lung cancer (NSCLC). In this article, we review our findings that the CXC chemokine family is composed of members that are either angiogenic or angiostatic. We have found that in NSCLC an imbalance exists in the expression of these factors that favors tumor-derived angiogenesis, and therefore tumor growth and metastases. Furthermore, when this imbalance is corrected to reduce the presence of angiogenic factors or increase the presence of angiostatic factors, tumor growth and metastases are reduced.

Chronic hyperglycemia is thought to be important in the development of diabetic neovascularization but the mechanisms involved remain poorly understood. Interleukin-8 (IL-8) is a leukocyte chemokine and activating agent with angiogenic properties that is present in diabetic vitreous and may play a role in diabetic vasculopathy. We studied IL-8 and monocyte chemotactic protein-1 (MCP-1) production by human retinal pigment epithelial (hRPE) cells exposed to glycated human serum albumin (GHSA). Enzyme-linked immunoassay GHSA (500 μg/mL)-treated hRPE cells secreted levels of IL-8 and MCP-1 detectable within 4 h and reached 26.0 ± 1.3 and 42.2 ± 0.4 ng/106 cells/mL after 24 h, respectively. Induction of IL-8 and MCP-1 by GHSA at concentrations ranging from 62.5 to 3,000 μg/mL exhibited dose-dependent kinetics. The GHSA-induced chemokine secretion by hRPE was almost completely inhibited by actinomycin D and cycloheximide, suggesting that de novo mRNA and protein synthesis are necessary for the GHSA-induced IL-8 and MCP-1 production. Northern blot analysis of GHSA-induced hRPE IL-8 and MCP-1 mRNA expression corresponded to the time- and dose-dependent increases measured by enzyme-linked immunosorbent assay. High concentrations of glucose (20 mM; 360 mg/dl) increased GHSA-induced hRPE IL-8 and MCP-1 secretion, whereas added insulin (0.5 ng/mL) inhibited IL-8 but not MCP-1 protein secretion and mRNA expression. GHSA also induced hRPE to secrete GRO-α, RAN-TES, and NAP-2 chemokines. GHSA induction of hRPE chemokines further suggests a role for the hRPE in leukocyte infiltration, vascular injury, and neovascularization.

This study examined the effects of endogenous urokinase (uPA) on lipopolysaccharide (LPS)-stimulated tumor necrosis factor α (TNF-α) secretion in THP-1 mononuclear phagocytes. Anti-uPA monoclonal antibody (mAb) suppressed LPS-driven TNF-α secretion by 61.6 ± 5.9% (P < .001), and PAI-1, a uPA inhibitor, suppressed it to 53.1 ± 8.2% of the control value (P < .001). Up-regulation of TNF-α mRNA was suppressed in parallel with secreted TNF-α protein. TNF-α secretion was unaffected by depleting plasminogen or by aprotinin, a plasmin inhibitor. When endogenous uPA was displaced from the cell, exogenous high-molecular-weight (intact) uPA augmented LPS-driven TNF-α secretion. By contrast, a uPA fragment containing the catalytic domain was inhibitory, and the uPA receptor-binding domain had no effect. We conclude that endogenous uPA amplifies TNF-α neosynthesis of UPS-stimulated THP-1 mononuclear phagocytes. The effect requires intact uPA and is independent of plasmin activity. This represents a novel mechanism by which a mononuclear phagocyte–derived protease contributes to generating proinflammatory signals.

Lung cancer is the leading cause of malignancy-related mortality in the U.S. and is predicted to increase over the remainder of this decade. Despite attempts to advance early diagnosis and use combination therapies, the clinical response of this cancer yields an overall 5-year survival rate of less than 15%. Clearly, new strategies for therapy are indicated. Although carcinogenesis is complex, tumor growth beyond 1–2 mm3 is dependent on angiogenesis. One of the potential mechanisms that allows for tumorigenesis is dysregulation of the balance of angiogenic and angiostatic factors that favors net neovascularization within the primary tumor. Numerous studies have investigated the role of a variety of molecules in the regulation of angiogenesis. Recently, interleukin-8 (IL-8), a member of the C-X-C chemokine family, has been found to be an angiogenic factor. In contrast, platelet factor 4 (PF4), another C-X-C chemokine, has been shown to have angiostatic properties. It is interesting that the major structural difference between IL-8 and PF4 is the presence of the NH2-terminal ELR (Glu-Leu-Arg) motif that precedes the first cysteine amino acid residue of IL-8 and is important in ligand/receptor interactions. We hypothesize that angiogenesis associated with tumorigenesis is dependent on members of the C-X-C chemokine family acting as either angiogenic or angiostatic factors. This paradigm predicts that the biological balance in the expression of these C-X-C chemokines dictates whether the neoplasm grows and develops metastatic potential or regresses. In this review we discuss our recent laboratory findings that support this contention and suggest that further elucidation of the biology of C-X-C chemokines in the context of neovascularization of nonsmall cell lung cancer will permit novel targeted therapy aimed specifically at attenuating tumor growth and metastasis. J. Leukoc. Biol. 57: 752–762; 1995.