Critical role of interleukin 5 and eosinophils in concanavalin A-induced hepatitis in mice

BACKGROUND & AIMS: Eosinophils are observed in several liver diseases, but their contribution in the pathogenesis of these disorders remains poorly investigated. Concanavalin A (Con A)-induced hepatitis is an experimental model of immune-mediated liver injury in which natural killer T (NKT) cells play a critical role through the production of interleukin (IL)-4 and the expression of Fas ligand (FasL). Because activated NKT cells also produce IL-5, a critical cytokine for eosinophil maturation and function, the role of IL-5 was investigated in this model. METHODS: IL-5-deficient mice, eosinophil depletion in wild-type (WT) mice, and NKT cell transfer from WT- or IL-5-deficient mice into NKT cell-deficient mice were used to assess the role of IL-5 and eosinophils. RESULTS: Liver eosinophil infiltrate and IL-5 production were observed after Con A challenge. Liver injury was dramatically reduced in IL-5-deficient or eosinophil-depleted mice. In addition, residual hepatitis observed in Fas-deficient mice was abolished after IL-5 neutralization. Finally, we showed that NKT cells constituted a critical source of IL-5. Indeed, transfer of WT NKT cells to mice lacking NKT cells restored liver injury, whereas transfer of IL-5-deficient NKT cells did not. CONCLUSIONS: These observations highlight the pathologic role of IL-5 and eosinophils in experimental immune-mediated hepatitis.     

Effects of CH-100, a chinese herbal medicine, on acute concanavalin A-mediated hepatitis in control and alcohol-fed rats

BACKGROUND: Administration of concanavalin A (Con A) leads to acute hepatitis that involves T-cell activation and inflammatory mediator production in mice and rats. We examined the role of CH-100, a Chinese herbal medicine previously trialed in human hepatitis C, in the prevention of Con A-related, T-cell-mediated, acute liver injury in rats. METHODS: Female Wistar rats were fed 40% ethanol, 2% sucrose, or isocaloric sucrose for 8 weeks. At the same time, these animals were fed either the Chinese herbal medicine CH-100 (4 tablets/kg body weight/ day) or placebo in chow daily. Blood from the tail vein was collected for endotoxin (lipopolysaccharide) assay at 0, 4, and 8 weeks of ethanol consumption. Twenty-four hours after injection of Con A (20 mg/kg body weight) or phosphate-buffered saline, blood from the tail vein was collected for alanine aminotransferase and tumor necrosis factor (TNF)-alpha assays. Liver-associated CD4+ T cells were isolated from liver perfusates and then cultured with Con A (5 microg/ml) at 37 degrees C for 24 hr. Supernatants were harvested for TNF-alpha assay. The proportion of CD4+ T cells in blood and liver perfusates was measured. Liver samples were collected for histopathological analysis. RESULTS: Lipopolysaccharide levels were significantly reduced in CH-100-treated ethanol-fed rats compared with placebo-treated rats. After Con A injection, alanine aminotransferase levels were lower at 12 and 24 hr in herb-treated rats compared with placebo-treated rats. Furthermore, serum TNF-alpha levels were lower in ethanol-fed rats on herbal treatment. A significant decrease in TNF-alpha production by liver-associated CD4+ T cells in culture was observed in CH-100-treated ethanol-fed rats. CH-100 treatment was associated with a decreased percentage of CD4+ cells in both blood and liver perfusate in all groups. Herb-treated rats displayed markedly less hepatic necrosis and a reduced CD4+ T-cell infiltrate in portal areas than did placebo-fed rats. CONCLUSIONS: The results demonstrate that CH-100 modified the T-cell response to Con A injection. The effect was more marked in ethanol-fed rats, which suggests a possible role for CH-100 in treating alcoholic liver disease.     

Hepatic macrophage migration and differentiation critical for liver fibrosis is mediated by the chemokine receptor C-C motif chemokine receptor 8 in mice

Chemokines critically control the infiltration of immune cells upon liver injury, thereby promoting hepatic inflammation and fibrosis. The chemokine receptor CCR8 can affect trafficking of monocytes/macrophages, monocyte-derived dendritic cells (DCs) and T-helper cell (Th) subsets, but its role in liver diseases is currently unknown. To investigate the functional role of CCR8 in liver diseases, ccr8(-/-) and wild-type (WT) mice were subjected to chronic experimental injury models of carbon tetrachloride (CCl(4) ) administration and surgical bile duct ligation (BDL). CCR8 was strongly up-regulated in the injured liver. Ccr8(-/-) mice displayed attenuated liver damage (e.g., ALT, histology, and TUNEL) compared to WT mice and were also protected from liver fibrosis in two independent injury models. Flow cytometry revealed reduced infiltrates of liver macrophages, neutrophils and natural killer cells, whereas hepatic CD4(+) T cells increased. The main CCR8-expressing cells in the liver were hepatic macrophages, and CCR8 was functionally necessary for CCL1-directed migration of inflammatory but not for nonclassical monocytes into the liver. Moreover, the phenotype of liver macrophages from injured ccr8(-/-) animals was altered with increased expression of DC markers and enhanced expression of T-cell-attracting chemokine macrophage inflammatory protein 1-alpha (MIP-1α/CCL3). Correspondingly, hepatic CD4(+) T cells showed increased Th1 polarization and reduced Th2 cells in CCR8-deficient animals. Liver fibrosis progression, but also subsequent T-cell alterations, could be restored by adoptively transferring CCR8-expressing monocytes/macrophages into ccr8(-/-) mice during experimental injury. CONCLUSIONS: CCR8 critically mediates hepatic macrophage recruitment upon injury, which subsequently shapes the inflammatory response in the injured liver, affecting macrophage/DC and Th differentiation. CCR8 deficiency protects the liver against injury, ameliorating initial inflammatory responses and hepatic fibrogenesis. Inhibition of CCR8 or its ligand, CCL1, might represent a successful therapeutic target to limit liver inflammation and fibrosis progression.     

A key pathogenic role for the STAT1/T-bet signaling pathway in T-cell-mediated liver inflammation

TH1 cytokines have been suggested to contribute to the pathogenesis of T-cell-mediated liver injury and inflammation. However, the molecular signaling pathways involved in such injury are still poorly understood. In the present study, we investigated the role of the STAT1/T-bet signaling pathway in a murine model of T-cell-mediated liver inflammation induced by the application of concanavalin A (Con A) using newly created STAT1 transgenic mice as well as STAT1- and T-bet-deficient mice. Liver injury induced by Con A was associated with an increase of both pSTAT1 and T-bet levels in the liver. Furthermore, functional studies suggested a pathogenic role for STAT1 in Con A-induced liver injury, because transgenic mice overexpressing STAT1 under the control of the CD2 promoter/enhancer construct showed elevated interferon gamma (IFN-gamma) and IRF-1 levels as well as significantly augmented liver injury following administration of Con A. Consistently, we observed that both STAT1-deficient and T-bet-deficient mice were protected from such T-cell-dependent liver injury. In conclusion, these findings suggest a key pathogenic role for the STAT1/T-bet signaling pathway for T-cell activation in the Con A model of T-cell-mediated liver pathology.     

Interleukin-15 prevents concanavalin A-induced liver injury in mice via NKT cell-dependent mechanism

Administration of concanavalin A (Con A) induces a rapid and severe liver injury in mice. Natural killer T (NKT) cells are recognized to be the key effector cells, and a variety of cytokines [e.g., interleukin 4 (IL-4), IL-5, interferon gamma (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha)] have been shown to play vital roles in Con A-induced liver injury, whereas the role of IL-15, a critical cytokine in the development and homeostasis of NKT cells, remains obscure. In this study, pretreatment with IL-15 prevented mice from Con A-induced mortality, elevation of serum transaminase, liver necrosis, and hepatocyte apoptosis. Depletion of NKT cells abolished Con A-induced liver injury, which could be restored by adoptive transfer of purified NKT cells but not by that of in vivo or in vitro IL-15-treated hepatic NKT cells. Furthermore, transfer of wild-type NKT cells to CD1d-/- mice restored liver injury, whereas transfer of IL-15-treated NKT cells did not. IL-15 pretreatment decreased the NKT-derived IL-4, IL-5, and TNF-alpha production, thereby resulting in less infiltration of eosinophils, which play a critical role in Con A-induced liver injury. In conclusion, IL-15 protects against Con A-induced liver injury via an NKT cell-dependent mechanism by reducing their production of IL-4, IL-5, and infiltration of eosinophils. These findings suggest that IL-15 may be of therapeutic relevance in human autoimmune-related hepatitis.     

Baicalin protects mouse from Concanavalin A-induced liver injury through inhibition of cytokine production and hepatocyte apoptosis.

BACKGROUND: Baicalin (BA) exhibits an anti-inflammatory effect in vivo and in vitro and is used to treat chronic hepatitis. However, the mechanism by which BA exerts the liver-protective effect remains largely unknown. AIMS: The present study reports that BA inhibits cytokine production and hepatocyte apoptosis to protect mice from liver injury induced by concanavalin A (Con A), a T-cell-dependent liver injury model. RESULTS: Con A injection of mice induced severe immune responses and extensive hepatocellular apoptosis within 24 h. Pretreatment of 200 or 100 mg/kg BA markedly reduced serum aminotransferase activities, protected hepatoycte apoptosis and reduced the increase of plasma cytokine levels, including tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and interleukin-6 (IL-6). Furthermore, BA pretreatment decreased tissue myeloperoxidase activity and lipid peroxidation, but increased the superoxide dismutase level. In vitro studies indicated that the beneficial effect of BA was associated with reduced cytokine production from lymphocytes and reduced TNF-alpha-induced hepatocyte apoptosis. CONCLUSION: These results suggest that BA has therapeutic potential for T-cell-mediated liver injury.     

Galectin-3 deficiency prevents concanavalin A-induced hepatitis in mice

We used concanavalin A (Con A)-induced liver injury to study the role of galectin-3 (Gal-3) in the induction of inflammatory pathology and hepatocellular damage. We tested susceptibility to Con A-induced hepatitis in galectin-3-deficient (Gal-3(-/-)) mice and analyzed the effects of pretreatment with a selective inhibitor of Gal-3 (TD139) in wild-type (WT) C57BL/6 mice, as evaluated by a liver enzyme test, quantitative histology, mononuclear cell (MNC) infiltration, cytokine production, intracellular staining of immune cells, and percentage of apoptotic MNCs in the liver. Gal-3(-/-) mice were less sensitive to Con A-induced hepatitis and had a significantly lower number of activated lymphoid and dendritic cells (DCs) in the liver. The level of tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), and interleukin (IL)-17 and -4 in the sera and the number of TNFα-, IFNγ-, and IL-17- and -4-producing cluster of differentiation (CD)4(+) cells as well as IL-12-producing CD11c(+) DCs were lower, whereas the number of IL-10-producing CD4(+) T cells and F4/80(+) macrophages were significantly higher in livers of Gal-3(-/-) mice. Significantly higher percentages of late apoptotic Annexin V(+) propidium-idodide(+) liver-infiltrating MNCs and splenocytes were observed in Gal-3(-/-) mice, compared to WT mice. Pretreatment of WT C57BL/6 mice with TD139 led to the attenuation of liver injury and milder infiltration of IFNγ- and IL-17- and -4-producing CD4(+) T cells, as well as an increase in the total number of IL-10-producing CD4(+) T cells and F4/80(+) CD206(+) alternatively activated macrophages and prevented the apoptosis of liver-infiltrating MNCs. CONCLUSIONS: Gal-3 plays an important proinflammatory role in Con A-induced hepatitis by promoting the activation of T lymphocytes and natural killer T cells, maturation of DCs, secretion of proinflammatory cytokines, down-regulation of M2 macrophage polarization, and apoptosis of MNCs in the liver.     

Repeated administrations of concanavalin A induce Th1 to Th2 cytokine shift and tolerance against liver injury in mice.

The intravenous injection of concanavalin A (Con A) activates T cells and induces cytokine dependent liver injury in mice. However, the effect of repeated administrations of Con A has not been fully investigated. Female BALB/c mice were intravenously injected with Con A (20mg/kg) or saline once a week for six times. Mice were rechallenged with Con A 17 days after repeated administrations of Con A. Repeated Con A administrations elicited a sustained inhibition of rechallenged-Con A-induced liver injury. Plasma TNF-alpha and IFN-gamma levels after rechallenge of Con A were decreased compared with that of repeated saline treatments. By contrast, plasma IL-4 and IL-10 levels after rechallenge of Con A were increased. In spleen cells prepared from repeated Con A treated mice, the production of TNF-alpha and IFN-gamma 24h after co-incubation with Con A decreased, and that of IL-4 and IL-10 increased. In naive mice, plasma ALT level after Con A injection was decreased by the transfer of spleen cells prepared from the repeated Con A treated mice. The repeated administrations of Con A elicited Th1 to Th2 cytokine shift and the tolerant state against the Con A-induced liver injury in mice.     

Lack of macrophage migration inhibitory factor protects mice against concanavalin A-induced liver injury.

BACKGROUND: Macrophage migration inhibitory factor (MIF) is involved in inflammatory and immune-mediated diseases but the role of MIF in liver injury has not yet been elucidated. METHODS: We investigated biochemically, histologically and immunologically the character of MIF in concanavalin A (Con A)-induced T-cell-mediated liver injury using MIF knockout (KO) mice and wild-type (WT) mice. RESULTS: MIF KO mice showed significantly decreased serum alanine aminotransferase values and suppressed histological change with massive necrosis of the hepatic parenchymal cells and infiltration of inflammatory cells compared with their WT counterparts. This protection was not mediated by either tumor necrosis factor-alpha or interferon-gamma, which are critical mediators of Con A-induced liver injury, as their serum concentrations were shown to be similar in MIF KO and WT mice. On the other hand, a flow cytometric analysis demonstrated that the number of activated hepatic leukocytes decreased more in the MIF KO mice than in the WT mice. CONCLUSIONS: A lack of MIF protected the mice from Con A-induced liver injury. Controlling the MIF activity may be a useful therapeutic strategy for treating such T-cell activation-associated liver diseases as autoimmune hepatitis and viral hepatitis.     

Inhibition of concanavalin A-induced acute T cell dependent hepatic damage in mice by hypothyroidism.

AIMS/BACKGROUND: Concanavalin A (Con A) activates T lymphocytes and causes acute T-cell-mediated hepatic injury in mice. Decreased thyroid hormonal production is associated with a variety of immunological manifestations, including inactivation of macrophages with reduced TNF production and reduced soluble IL-2 receptors in the serum. We have recently shown that hypothyroidism prevents the development of cirrhosis and also minimizes hepatic damage in rats with fulminant hepatic failure. In the present study we examined the effects of hypothyroidism on a mouse model of Con A induced T cell-mediated acute hepatitis. METHODS: Hypothyroidism was induced both medically (MMI, PTU) and surgically. Eight groups of 10 mice each were studied: euthyroid controls (2 groups: water, Con A) and hypothyroid (6 groups: MMI, PTU, Surgical, MMI-Con A, PTU-Con A, Surgical-Con A). RESULTS: Hepatic inflammation was significantly decreased in each of the Con A treated hypothyroid groups of mice. The serum transaminases, TNF-alpha and IL-6 levels were significantly elevated in the Con A treated group while near normal levels were found in the hypothyroid Con A treated groups (mean+/-SE AST: 1499+/-18 vs 78+/-10 IU/l, p<0.001; TNF: 2500+/-250 vs 135+/-15 pg/ml, p<0.001, IL-6: 12,200+/-300 vs 1260+/-140 pg/ml, p<0.001, respectively). CONCLUSIONS: Hypothyroidism, independent of the mode of induction, can effectively inhibit the development of acute T cell-mediated liver damage in mice. These results suggest that some decrease in thyroid function might have a role in the prevention of immune mediated liver diseases.     

CCL16 activates an angiogenic program in vascular endothelial cells

Besides regulating leukocyte trafficking in normal and injured tissues, several chemokines may positively or negatively regulate angiogenesis. Here we report that CCL16 activates an angiogenic program in vascular endothelial cells by activating CCR1. CCL16 induces dose-dependent random and directional migration of endothelial cells isolated from large vessels and liver capillaries without inducing their proliferation. It also promotes endothelial differentiation into capillary-like structures in an in vitro assay and is angiogenic in the chick chorionallantoic membrane. These angiogenic activities are neutralized by a specific antibody against CCL16. The direct angiogenic activity of CCL16 is further amplified by its ability to prime endothelium to a mitogen signal induced by vascular endothelial growth factor A and to raise their basal production of CXCL8 and CCL2, 2 other angiogenic chemokines. BX471 (R-N-[5-chloro-2-[2-[4(4-fluorophenyl) methyl]-2-methyl-1-piperazinyl]-2-oxoethoxy]phenyl] urea hydrochloric acid salt), a CCR1 antagonist, inhibits angiogenic properties of CCL16, whereas blocking of CCR8 or desensitizing CCR2, which are both well known receptors for CCL16, did not abolish endothelial activation. CCL16 may be specifically cross-linked to CCR1 expressed on endothelial cells. The largely restricted CCL16 expression in the liver suggests that this chemokine may play a role in hepatic vascular formation during development and in angiogenesis associated to hepatic diseases.     

Glycyrrhizin enhances interleukin-10 production by liver dendritic cells in mice with hepatitis

Background Glycyrrhizin (GL), an aqueous extract of licorice root, is known to have various immune-modulating and biological response-modifier activities. GL is used in patients with hepatitis to reduce the activity of liver inflammation; however, the mechanism underlying the anti-inflammatory activity of GL is poorly understood. As antigen-presenting dendritic cells (DC) in the tissue play a major role in the regulation of the inflammatory mucosal milieu during tissue inflammation, we studied whether the function of liver DC was altered by GL therapy in a murine model of concanavalin-A (Con A)-induced hepatitis.Methods Liver DC were propagated from control mice or mice with Con-A-induced hepatitis, and the effect of GL on liver DC was evaluated in vivo and in vitro.Results The levels of interleukin (IL)-10 produced by liver DC were significantly lower in mice with Con-A-induced hepatitis compared with control mice. However, treatment with GL caused increased production of IL-10 in mice with Con A-induced hepatitis. The increased production of IL-10 by mice with Con A-induced hepatitis was also confirmed in vitro by culturing liver DC with GL.Conclusions This study indicates that increased production of IL-10 by liver DC due to GL administration may be involved in downregulation of the levels of liver inflammation in mice with Con A-induced hepatitis.     

Galectin-1 exerts immunomodulatory and protective effects on concanavalin A-induced hepatitis in mice

Galectin-1, an endogenous lectin with immunomodulatory activities, induces selective, Fas-independent apoptosis of activated T cells. The aim of the present study was to evaluate the effect galectin-1 exerts on concanavalin A (Con A)-induced hepatitis, a T-cell-dependent model of liver injury. Con A administration resulted in liver injury, as shown by the increased transaminase plasma levels and liver DNA fragmentation, and caused spleen T-cell activation, which was associated with a strong increment in liver infiltrating T helper cells. Moreover, Con A injection leads to a marked increase in plasma tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) levels. Galectin-1 pretreatment dose-dependently prevented both liver injury and T-helper cell liver infiltration induced by Con A. In vivo and in vitro experiments indicated that the protective effects of galectin-1 depend on the selective elimination of Con A-activated T cells. In addition, galectin-1 almost completely prevented the Con A-induced increase in plasma TNF-alpha and IFN-gamma, an effect that was, at least in part, independent on the elimination of activated T helper cells, because galectin-1 prevented lipopolysaccharide (LPS)-induced release of TNF-alpha and IFN-gamma also from macrophages in vitro, without affecting their viability. The present study suggests that galectin-1 is potentially useful in the treatment of T-cell-mediated human liver disorders.     

The role of CCR5/CXCR3 expressing CD8+ cells in liver damage and viral control during persistent hepatitis C virus infection

BACKGROUND/AIMS: CXCR3 and CCR5 play a major role in recruiting cytotoxic T cells (Tc) and secreting secondary type 1 cytokines (Tc1) in the liver. HCV could impair their expression as a survival mechanism. The role of these chemokine receptors on CD8+ cells in chronic hepatitis C is analysed. METHODS: Serum, chemokines, peripheral blood and intrahepatic lymphocytes from chronic hepatitis C patients were studied. CXCR3/CCR5 expressing CD8+ cells were quantified by flow-cytometry. Serum chemokines concentration (CXCL10/CCL3) was measured by ELISA. Basal data were correlated with liver inflammation. Longitudinal data were obtained during treatment and correlated with virologic response. RESULTS: CCR5/CXCR3 expressing CD8+ cells were enriched in the liver and correlated with inflammation. Chronic HCV patients presented the same frequency of CCR5(high)/CXCR3(high) expressing CD8+ cells in peripheral blood as in healthy controls but higher serum concentration of CXCL10/CCL3. Treatment with PEG-interferon alpha-2b plus ribavirin increased CCR5(high)/CXCR3(high) expressing CD8+ cells frequency in peripheral blood and decreased CXCL10/CCL3 serum concentration. Increase in CXCR3(high) expressing CD8+ cells after 24 weeks of treatment was correlated with SVR. CONCLUSIONS: In chronic hepatitis C, anti-viral treatment induces an increase in CD8+ cells expressing chemokine receptors associated with Tc1 response and a reduction in their ligands. Achievement of viral control is associated with an increase in CXCR3(high) expressing CD8+ cells during treatment.     

Gene expression changes in foam cells and the role of chemokine receptor CCR7 during atherosclerosis regression in ApoE-deficient mice

Atherosclerosis regression is an important clinical goal. In previous studies of regression in mice, the rapid loss of plaque foam cells was explained by emigration to lymph nodes, a process reminiscent of dendritic cells. In the present study, plaque-containing arterial segments from apoE-/- mice were transplanted into WT recipient normolipidemic mice or apoE-/- mice. Three days after transplant, in the WT regression environment, plaque size decreased by approximately 40%, and foam cell content by approximately 75%. In contrast, both parameters increased in apoE-/- recipients. Foam cells were isolated by laser capture microdissection. In WT recipients, there were 3- to 6-fold increases in foam cells of mRNA for liver X receptor alpha and cholesterol efflux factors ABCA1 and SR-BI. Although liver X receptor alpha was induced, there was no detectable expression of its putative activator, peroxisome proliferator-activated receptor gamma. Expression levels of VCAM or MCP-1 were reduced to 25% of levels in pretransplant or apoE-/- recipient samples, but there was induction at the mRNA and protein levels of chemokine receptor CCR7, an essential factor for dendritic cell migration. Remarkably, when CCR7 function was abrogated in vivo by treatment of WT recipients with antibodies to CCR7 ligands CCL19 and CCL21, lesion size and foam cell content were substantially preserved. In summary, in foam cells during atherosclerosis regression, there is induction of CCR7 and a requirement for its function. Taken with the other gene expression data, these results in vivo point to complex relationships among the immune system, nuclear hormone receptors, and inflammation during regression.     

Ethanol-Altered Liver-Associated T Cells Mediate Liver Injury in Rats Administered Concanavalin A (Con A) or Lipopolysaccharide (LPS)

BACKGROUND: Recent work from our laboratory implicates T cells in the pathogenesis of alcoholic liver disease. We have studied the role of liver-associated T cells in acute hepatitis produced in control rats administered Concanavalin A (Con A) after adoptive transfer of T cells from alcohol-consuming animals. METHODS: Liver-associated T cells from ethanol-consuming rats were transferred via tail vein to nonethanol-consuming rats. They then received Con A (20 mg/kg body weight) intravenously. This produced a severe hepatitis. Serum was collected for the assay of alanine aminotransferase (ALT) and cytokines. RESULTS: Hepatic necrosis was accompanied by an increase in plasma levels of ALT, interleukin-6, and tumor necrosis factor-alpha. These increases correlated with increased production of interleukin-6 and tumor necrosis factor-alpha in culture of liver-associated T cells stimulated or unstimulated with Con A. Immunohistology staining showed increased infiltration of inflammatory cells comprised of neutrophils and mononuclear cells, which included greater numbers of CD4+ T cells in the portal tract areas and around the central vein. Focal and lobular necrosis was seen with inflammatory cells in the necrotic area. Hepatocytes isolated from the liver showed increased apoptosis compared with rats that received liver-associated T cells from nonethanol-consuming rats. Injection of endotoxin LPS, in the same model, was associated with less hepatocyte injury indicating a distinct role for T cells as opposed to Kupffer cells in this model of liver disease. CONCLUSIONS: Chronic ethanol consumption induces a lesion in a pool of liver-associated T cells which can mediate liver injury after polyclonal mitogen activation.     

Crucial role of the CCL2/CCR2 axis in neointimal hyperplasia after arterial injury in hyperlipidemic mice involves early monocyte recruitment and CCL2 presentation on platelets

Monocyte chemoattractant protein-1 (also known as CC chemokine ligand 2 [CCL2]) and its receptor CC chemokine receptor 2 (CCR2) play a central role in the inflammatory response and neointimal formation after vascular injury. In the context of hyperlipidemia, this appears to involve neointimal monocyte infiltration. Hence, we investigated the function of the CCL2/CCR2 axis in early monocyte recruitment to injured arteries. Wire-induced injury of the carotid artery in apoE-/- mice caused a rapid increase of JE/CCL2 protein in the vessel wall peaking at 24 hours after injury, whereas serum JE/CCL2 was increased solely at 6 hours and blood cell-associated levels were unaltered, as demonstrated by enzyme-linked immunosorbent assay. Immunohistochemistry revealed intense staining for JE/CCL2 in smooth muscle cells (SMCs) and in association with platelets adherent to the denuded vessel wall 24 hours after injury. In vitro, exogenous or SMC-derived JE/CCL2 binds to the platelet surface and triggers monocyte arrest on adherent platelets but not on SMCs in flow assays. Accordingly, monocyte arrest in ex vivo perfused apoE-/- carotid arteries isolated 24 hours after injury was profoundly inhibited by pretreatment with a JE/CCL2 antibody. In CCR2-/-/apoE-/- mice, neointimal plaque area was reduced by 47% compared with CCR2+/+/apoE-/- mice. Moreover, CCR2 deletion markedly decreased neointimal macrophage content while expanding SMC content. Vascular JE/CCL2 expressed by SMCs and immobilized by adherent platelets after endothelial denudation is crucial for mediating early monocyte recruitment to injured arteries in hyperlipidemic mice. This mechanism may explain reduced neointimal macrophage infiltration and lesion formation in CCR2-deficient apoE-/- mice.     

CCR5 is involved in resolution of inflammation in proteoglycan‐induced arthritis

Objective

CCR5 and its ligands (CCL3, CCL4, and CCL5) may play a role in inflammatory cell recruitment into the joint. However, it was recently reported that CCR5 on T cells and neutrophils acts as a decoy receptor for CCL3 and CCL5 to assist in the resolution of inflammation. The aim of this study was to determine whether CCR5 functions as a proinflammatory or antiinflammatory mediator in arthritis, by examining the role of CCR5 in proteoglycan (PG)–induced arthritis (PGIA).

Methods

Arthritis was induced by immunizing wild‐type (WT) and CCR5‐deficient (CCR5^−/−) BALB/c mice with human PG in adjuvant. The onset and severity of PGIA were monitored over time. Met‐RANTES was used to block CCR5 in vivo. Arthritis was transferred to SCID mice, using spleen cells from arthritic WT and CCR5^−/− mice. The expression of cytokines and chemokines was measured by enzyme‐linked immunosorbent assay.

Results

In CCR5^−/− mice and WT mice treated with the CCR5 inhibitor Met‐RANTES, exacerbated arthritis developed late in the disease course. The increase in arthritis severity in CCR5^−/− mice correlated with elevated serum levels of CCL5. However, exacerbated arthritis was not intrinsic to the CCR5^−/− lymphoid cells, because the arthritis that developed in SCID mouse recipients was similar to that in WT and CCR5^−/− mice. CCR5 expression in the SCID mouse was sufficient to clear CCL5, because serum levels of CCL5 were the same in SCID mouse recipients receiving cells from either WT or CCR5^−/− mice.

Conclusion

These data demonstrate that CCR5 is a key player in controlling the resolution of inflammation in experimental arthritis.