Transgenic expression of the chemokine receptor encoded by human herpesvirus 8 induces an angioproliferative disease resembling Kaposi's sarcoma.

Human herpesvirus 8 (HHV8, also known as Kaposi's sarcoma [KS]-associated herpesvirus) has been implicated as an etiologic agent for KS, an angiogenic tumor composed of endothelial, inflammatory, and spindle cells. Here, we report that transgenic mice expressing the HHV8-encoded chemokine receptor (viral G protein-coupled receptor) within hematopoietic cells develop angioproliferative lesions in multiple organs that morphologically resemble KS lesions. These lesions are characterized by a spectrum of changes ranging from erythematous maculae to vascular tumors, by the presence of spindle and inflammatory cells, and by expression of vGPCR, CD34, and vascular endothelial growth factor. We conclude that vGPCR contributes to the development of the angioproliferative lesions observed in these mice and suggest that this chemokine receptor may play a role in the pathogenesis of KS in humans.

Tumorigenesis induced by the HHV8-encoded chemokine receptor requires ligand modulation of high constitutive activity.

ORF74 (or KSHV-vGPCR) is a highly constitutively active G protein-coupled receptor encoded by HHV8 that is regulated both positively and negatively by endogenous chemokines. When expressed in transgenic mice, this chemokine receptor induces an angioproliferative disease closely resembling Kaposi sarcoma (KS). Here we demonstrate that several lines of mice carrying mutated receptors deficient in either constitutive activity or chemokine regulation fail to develop KS-like disease. In addition, animals expressing a receptor that preserves chemokine binding and constitutive activity but that does not respond to agonist stimulation have a much lower incidence of angiogenic lesions and tumors. These results indicate that induction of the KS-like disease in transgenic mice by ORF74 requires not only high constitutive signaling activity but also modulation of this activity by endogenous chemokines.

Generation and analysis of mice lacking the chemokine fractalkine.

Fractalkine (CX(3)CL1) is the first described chemokine that can exist either as a soluble protein or as a membrane-bound molecule. Both forms of fractalkine can mediate adhesion of cells expressing its receptor, CX(3)CR1. This activity, together with its expression on endothelial cells, suggests that fractalkine might mediate adhesion of leukocytes to the endothelium during inflammation. Fractalkine is also highly expressed in neurons, and its receptor, CX(3)CR1, is expressed on glial cells. To determine the biologic role of fractalkine, we used targeted gene disruption to generate fractalkine-deficient mice. These mice did not exhibit overt behavioral abnormalities, and histologic analysis of their brains did not reveal any gross changes compared to wild-type mice. In addition, these mice had normal hematologic profiles except for a decrease in the number of blood leukocytes expressing the cell surface marker F4/80. The cellular composition of their lymph nodes did not differ significantly from that of wild-type mice. Similarly, the responses of fractalkine(-/-) mice to a variety of inflammatory stimuli were indistinguishable from those of wild-type mice.

Elevated levels of NO in both unchallenged and LPS-challenged C. parvum-primed mice are attributable to the activity of a cytokine-inducible isoform of iNOS.

Elevated levels of nitric oxide (NO2-/NO3-) were detected in the serum of mice 3-7 days after priming with Corynebacterium parvum (Propionibacterium acnes). The serum NO2-/NO3- response was completely inhibited when C. parvum-primed (C. parrum) mice were treated with N(G)-monomethyl-L-arginine (L-NMMA) or aminoguanidine (AG) on days 6 and 7 post priming. The response was also inhibited when the mice were treated with interleukin-10 (IL-10) and the cytokine was most effective when given in multiple doses beginning on the day of priming. In contrast to L-NMMA and AG, IL-10 had no effect on the serum NO2-/NO3- response when administered to the mice on days 6 and 7 post priming. The inducible isoform of NOS (iNOS) appeared to be responsible for the elevated NO2-/NO3- response in C. parvum mice because iNOS transcripts were readily detected in their livers. Moreover, these transcripts as well as the circulating levels of NO2-/NO3- were dramatically reduced when the mice were treated with anti-tumor necrosis factor alpha (anti-TNF-alpha) or anti-interferon-gamma (anti-IFN-gamma) monoclonal antibodies (mAbs) during the priming interval. There was a modest increase (less than twofold) in the serum NO2-/NO3- response following a lipopolysaccharide (LPS) challenge to C. parvum mice (C. parvum/LPS mice). LPS had a more dramatic stimulatory effect if the levels of NO2-/NO3- preexisting in C. parvum/LPS mice were reduced by treatment with L-NMMA, AG, or IL-10 before the challenge. Thus the levels of NO2-/NO3- that preexisted in C. parvum/LPS mice appeared to influence their ability to mount a NO2-/NO3- response subsequent to the LPS challenge. The NO2-/NO3- response did not contribute to lethality in C. parvum/LPS mice because anti-TNF-alpha and anti-IFN-gamma mAbs were protective but had no effect on serum NO2-/NO3- levels when administered to mice 24 h before the LPS challenge.

Expression and purification of two recombinant sterol-carrier proteins: SCPX and SCP2.

We report the cloning, expression, and purification of the rat sterol carrier proteins SCPX and SCP2. The cDNA's encoding rat SCPX and SCP2 were isolated from a lambda gt11 rat liver cDNA library. To maximize expression and to facilitate the purification of the recombinant proteins, the SCPX and SCP2 proteins were expressed as carboxy-terminal fusion proteins to the glutathione S-transferase (GST). The GST-SCPX and GST-SCP2 fusion proteins contained a thrombin recognition site between the GST and SCPX or SCP2 polypeptides. The expression of the fusion proteins was controlled by the inducible tac promoter. Under optimal conditions, the approximately 85-kDa GST-SCPX and the approximately 41-kDa GST-SCP2 proteins represented approximately 1-2% of the total cell lysate. Both fusion proteins were easily purified under nondenaturing conditions from the soluble fraction of total cell lysate by glutathione-Sepharose 4B affinity chromatography. Thrombin cleavage resulted in the release of the SCPX and SCP2 proteins from the GST-SCPX and GST-SCP2 fusions, respectively. Amino terminal protein sequencing confirmed the authenticity of the recombinant proteins. Furthermore, functional assay revealed that recombinant SCP2 is highly active in facilitating the conversion of 7-dehydrocholesterol to cholesterol. Recombinant SCPX is also active in this assay but only 50% as active as SCP2. We anticipate that the preparation and purification techniques described in this study will facilitate further biochemical characterization of these proteins.

Endogenous mouse interleukin-10 is up-regulated by exogenously administered recombinant human interleukin-10, but does not contribute to the efficacy of the human protein in mouse models of endotoxemia.

In murine models of experimental endotoxemia, inflammatory cytokines as well as antiinflammatory interleukin-10 (IL-10) appear in the circulation after the injection of lipopolysaccharide (LPS). There is considerable experimental evidence to suggest that the major function of endogenously produced IL-10 is to down-regulate inflammatory cytokine production. Indeed, the protective effects of exogenously administered IL-10 against murine endotoxin lethality have been shown to correlate with its ability to inhibit the LPS-induced production of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). While mouse IL-10 (mIL-10) has been used in the majority of studies in murine endotoxemia, we have found the human homolog to be equally effective in suppressing inflammatory cytokine production and in protecting mice from endotoxin lethality. However, we have recently observed that the LPS-induced endogenous IL-10 response is enhanced when mice are treated with recombinant human IL-10 (rhuIL-10). The upregulation of endogenous IL-10 by exogenously administered rhuIL-10 is particularly evident in mice that are primed with Corynebacterium partum (Proprionibacterium acnes). In the present study, we have examined the potential contributions of the increased circulating levels of mouse IL-10 to the inhibitory effects seen with rhuIL-10 on inflammatory cytokine production and endotoxin lethality. We show that pretreatment with a neutralizing anti-mouse IL-10 monoclonal antibody (mAb) has no effect on the ability of rhuIL-10 to suppress an LPS-induced inflammatory cytokine response in these mice. In contrast, the suppressive effects of the human protein on inflammatory cytokine responses are blocked completely by pretreating the animals with an anti-huIL-10 mAb. These data show that despite the up-regulated endogenous IL-10 response, it is the exogenously administered rhuIL-10 that is directly responsible for the suppressed inflammatory cytokine responses that are observed when the human protein is given to endotoxemic mice.

Regulatory effects of interleukin-4 and interleukin-10 on human neutrophil function ex vivo and on neutrophil influx in a rat model of arthritis.

OBJECTIVE: To assess the capacity of interleukin-4 (IL-4) and IL-10 to block polymorphonuclear neutrophil (PMN) activation in an ex vivo human model system, and to confirm their effect on neutrophil function in an animal model of arthritis. METHODS: The ex vivo phagocytic capacity of cytokine-activated human PMNs was assessed by use of assays for measuring the ingestion of heat-killed yeast and by subsequent hexose-monophosphate shunt activation using nitroblue tetrazolium reduction. The in vivo activity of IL-4 and IL-10 was measured using a rat adjuvant arthritis model in which the mycobacterial antigen concentration was titrated to modify disease intensity. RESULTS: IL-4 and IL-10 suppressed the ex vivo activation state of interferon-gamma- and tumor necrosis factor alpha-activated human neutrophils. In the rat adjuvant arthritis model, treatment with systemic murine IL-10 (mIL-10) effectively suppressed all disease parameters in rats that received the lower concentrations of mycobacteria, whereas systemic mIL-4 was effective against even the most severe disease. Both cytokines were effective in lowering the absolute PMN cell number recovered and the PMN activation state in the joint synovia. We also observed lower levels of the messenger RNA transcript for CINC protein (cytokine-induced neutrophil chemoattractant; a rat homolog for human IL-8) in the synovia. CONCLUSION: IL-10 is an effective antiarthritic agent and has a major effect on the presence and function of PMNs in the joint synovia when disease intensity is not severe. IL-4 has an inhibitory profile that is similar to that of IL-10, but is effective in modifying even the most severe disease. Both cytokines reduced the phagocytic activation of human PMNs in response to proinflammatory cytokines. These data demonstrate that IL-4 and IL-10 can exert powerful regulatory effects on neutrophil function that translate into a therapeutic response in a disease model of arthritis. Treatment with these cytokines alone or in combination may therefore be very useful in the management of patients with rheumatoid arthritis.

Role of nitric oxide on eosinophilic lung inflammation in allergic mice.

Nitric oxide (NO) is an important mediator of inflammatory reactions and may contribute to the lung inflammation in allergic pulmonary diseases. To assess the role of NO in pulmonary inflammation, we studied the effect of four nitric oxide synthase (NOS) inhibitors, N-nitro-L-arginine methyl ester (L-NAME), aminoguanidine, N(G)-monomethyl-L-arginine (NMMA) and L-N6-(1-Iminoethyl) lysine (L-NIL), on the influx of eosinophils into the bronchoalveolar lavage (BAL) fluid and lung tissue of antigen-challenged allergic mice. We also analyzed lung tissues for the presence of steady state mRNA for inducible nitric oxide synthase (iNOS) and iNOS protein. Furthermore, BAL fluid and serum were analyzed for their nitrite content. B6D2F1/J mice were sensitized to ovalbumin (OVA) and challenged with aerosolized OVA. The NOS inhibitors were given 0.5 h before and 4 h after the antigen challenge. OVA challenge induced a marked eosinophilia in the BAL fluid and lung tissue 24 h after challenge. The OVA-induced pulmonary eosinophilia was significantly reduced by L-NAME (10 and 50 mg/kg, intraperitoneally [i.p.]). The inactive isomer, D-NAME (50 mg/kg, i.p.) had no effect. When mice were treated with L-NAME (20 mg/kg, i.p.) and an excess of NOS substrate, L-arginine (200 mg/kg, i.p.), the OVA-induced pulmonary eosinophilia was restored. Treatment with aminoguanidine (0.4-50 mg/kg, i.p.) also reduced the pulmonary eosinophilia. Treatment with NMMA (2-50 mg/kg, i.p.) partially reduced the eosinophilia, but L-NIL (10-50 mg/kg, i.p.), a selective iNOS inhibitor, had no effect. L-NAME had no effect on the reduction of eosinophils in the bone marrow following OVA challenge to sensitized mice. OVA challenge to sensitized mice had no effect on iNOS protein expression or iNOS mRNA in the lungs or on the levels of nitrite in the BAL fluid. These results suggest that NO is involved in the development of pulmonary eosinophilia in allergic mice. The NO contributing to the eosinophilia is not generated through the activity of iNOS nor does NO contribute to the efflux of eosinophils from the bone marrow in response to antigen challenge. It is speculated that after antigen challenge, the localized production of NO, possibly from pulmonary vascular endothelial cells, is involved in the extravasation of eosinophils from the circulation into the lung tissue.

Leukocytes expressing green fluorescent protein as novel reagents for adoptive cell transfer and bone marrow transplantation studies.

Transgenic mice expressing green fluorescent protein (GFP) were generated to provide a source of labeled leukocytes for cell transfer studies. The transgene comprises the GFP coding region under the transcriptional control of the chicken ss-actin promoter and human cytomegalovirus enhancer. Mice expressing this GFP transgene were generated in the B6D2 and in the 129SvEv backgrounds. Flow cytometric analysis of cells from the blood, spleen, and bone marrow of these transgenic mice revealed that most leukocytes, including dendritic cells and memory T cells, express GFP. In allogeneic cell transfers, donor GFP+ splenocytes were detected in the spleen and mesenteric lymph nodes of recipient mice within 2 hours after transfer and for at least 9 days thereafter. In syngeneic experiments using 129-derived GFP+ donor splenocytes, donor cells were detected in multiple tissues of 129 recipients from 2 hours to 3 weeks after transfer. In bone-marrow transplantation experiments using irradiated allogeneic recipients, the percent of GFP+ donor cells in recipients at 3 weeks was comparable to that seen in similar tissues of GFP+ donor mice. These data demonstrate that GFP+ transgenic mice provide a ready source of GFP-expressing primary cells that can be easily monitored after their transfer to recipient animals.

Impaired pulmonary host defense in mice lacking expression of the CXC chemokine lungkine.

Lungkine (CXCL15) is a novel CXC chemokine that is highly expressed in the adult mouse lung. To determine the biologic function of Lungkine, we generated Lungkine null mice by targeted gene disruption. These mice did not differ from wild-type mice in their hematocrits or in the relative number of cells in leukocyte populations of peripheral blood or other tissues, including lung and bone marrow. However, Lungkine null mice were more susceptible to Klebsiella pneumonia infection, with a decreased survival and increased lung bacterial burden compared with infected wild-type mice. Histologic analysis of the lung and assessment of leukocytes in the bronchioalveolar lavage revealed that neutrophil numbers were normal in the lung parenchyma, but reduced in the airspace. The production of other neutrophil chemoattractants in the Lungkine null mice did not differ from that in wild-type mice, and neutrophil migration into other tissues was normal. Taken together, these findings demonstrate that Lungkine is an important mediator of neutrophil migration from the lung parenchyma into the airspace.

Disruption of neutrophil migration in a conditional transgenic model: evidence for CXCR2 desensitization in vivo.

We developed transgenic mice conditionally expressing the neutrophil chemoattracting chemokine KC and the beta-galactosidase gene in multiple tissues. In these transgenic mice, doxycycline treatment induced a strong up-regulation in the expression of KC in several tissues, including heart, liver, kidney, skin, and skeletal muscle. Expression of KC within these tissues led to a rapid and substantial increase in the serum levels of KC (serum KC levels were higher than 200 ng/ml 24 h after treatment). Accordingly, beta-galactosidase expression was also detected after injection of doxycycline and was highest in skeletal muscle, pancreas, and liver. Surprisingly, despite expression of KC in multiple tissues, no neutrophil infiltration was observed in any of the tissues examined, including skin. Doxycycline treatment of nontransgenic mice grafted with transgenic skin caused dense neutrophilic infiltration of the grafts, but not the surrounding host skin, indicating that the KC produced in transgenic tissues was biologically active. In separate experiments, neutrophil migration toward a localized source of recombinant KC was impaired in animals overexpressing KC but was normal in response to other neutrophil chemoattractants. Analysis of transgenic neutrophils revealed that high concentrations of KC in transgenic blood had no influence on L-selectin cell surface expression but caused desensitization of the receptor for KC, CXCR2. These results confirm the neutrophil chemoattractant properties of KC and provide a mechanistic explanation for the paradoxical lack of leukocyte infiltration observed in the presence of elevated concentrations of this chemokine.

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

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