Comment on "Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake".

Zhang et al. (Research Articles, 11 November 2005, p. 996) reported that obestatin, a peptide derived from the ghrelin precursor, activated the orphan G protein-coupled receptor GPR39. However, we found that I125-obestatin does not bind GPR39 and observed no effects of obestatin on GPR39-transfected cells in various functional assays (cyclic adenosine monophosphate production, calcium mobilization, and GPR39 internalization). Our results indicate that obestatin is not the cognate ligand for GPR39.

IL-6 switches the differentiation of monocytes from dendritic cells to macrophages.

Monocytes can give rise to either antigen presenting dendritic cells (DCs) or scavenging macrophages. This differentiation is initiated when monocytes cross the endothelium. But the regulation of DC and macrophage differentiation in tissues remains elusive. When stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4), monocytes yield DCs. However, we show here that the addition of fibroblasts switches differentiation to macrophages. On contact with monocytes, fibroblasts release IL-6, which up-regulates the expression of functional M-CSF receptors on monocytes. This allows the monocytes to consume their autocrine M-CSF. Thus, the interplay between IL-6 and M-CSF switches monocyte differentiation to macrophages rather than DCs, and IL-6 is an essential factor in the molecular control of antigen presenting cell development.

In breast carcinoma tissue, immature dendritic cells reside within the tumor, whereas mature dendritic cells are located in peritumoral areas.

We have analyzed the presence of immature and mature dendritic cells (DCs) within adenocarcinoma of the breast using immunohistochemistry. Immature DCs were defined by expression of CD1a-, Langerin-, and intracellular major histocompatibility complex class II-rich vesicles. Mature DCs were defined by expression of CD83 and DC-Lamp. Breast carcinoma cells were defined by morphology and/or cytokeratin expression. We demonstrate two levels of heterogeneity of DCs infiltrating breast carcinoma tissue: (a) immature CD1a(+) DCs, mostly of the Langerhans cell type (Langerin(+)), were retained within the tumor bed in 32/32 samples and (b) mature DCs, CD83(+)DC-Lamp(+), present in 20/32 samples, are confined to peritumoral areas. The high numbers of immature DCs found in the tumor may be best explained by high levels of macrophage inflammatory protein 3alpha expression by virtually all tumor cells. Confirming the immature/mature DC compartmentalization pattern, in vitro-generated immature DCs adhere to the tumor cells, whereas mature DCs adhere selectively to peritumoral areas. In some cases, T cells are clustering around the mature DCs in peritumoral areas, thus resembling the DC-T cell clusters of secondary lymphoid organs, which are characteristic of ongoing immune reactions.

Hepatitis B virus-induced liver injury and altered expression of carcinogen metabolising enzymes: the role of the HBx protein.

Hepatitis B virus (HBV) and aflatoxins are major risk factors for hepatocellular carcinoma (HCC) exhibiting a synergistic interaction in the development of this disease. The molecular mechanisms of this interaction remain to be elucidated but an altered carcinogen metabolism in the presence of hepatitis-induced liver injury is one hypothesis. The availability of biomarkers of aflatoxin exposure and metabolism permits this hypothesis to be examined in human populations whilst animal models, such as HBV transgenic mice permit parallel studies in an experimental setting. The hepatitis B virus X protein (HBx) is suspected to play a role in the hepatocarcinogenic process by virtue of its capacity to transactivate oncogenes and several other cellular genes via cis-acting elements. In previous studies in HBV transgenic mice expressing the HB surface antigen and X genes we observed a marked induction of specific cytochrome P450s (CYP) (Kirby et al., 1994a). In the current study we investigated the status of CYP, glutathione S-transferases (GST) and antioxidant enzymes in mice carrying only the X gene under the control of the alpha-1 antitrypsin regulatory elements (ATX mice). Livers of ATX mice showed no major pathological alterations compared to age-matched non-transgenic control mice. Immunohistochemical staining for CYP1A, 2A5 and GST expression and determination of related enzymatic activities (7-ethoxyresorufin O-deethylation, 7-methoxyresorufin O-deethylation, coumarin 7-hydroxylation and GST activities) revealed no differences between control and ATX mice. In addition, no differences in antioxidant enzymes were observed. Overall, these results support the conclusion that HBx expression alone is insufficient to induce transactivation of CYP and GST genes or to alter the antioxidant system and that the induction in other HBV models is a result of inflammatory injury in the liver, a feature absent in ATX mice. These data are compared to biomarker studies of enzyme activities in aflatoxin-exposed human populations with and without HBV infection.

Distinct time courses of increase in cytochromes P450 1A2, 2A5 and glutathione S-transferases during the progressive hepatitis associated with Helicobacter hepaticus.

Mice naturally infected by Helicobacter hepaticus develop a chronic active hepatitis leading to hepatocellular carcinoma. This mouse model of liver cancer was used to examine the impact of bacterial infection on the hepatic expression and activity of enzymes involved in carcinogen bioactivation (phase I enzymes) and detoxification (phase II enzymes). No major differences in total cytochrome P450 (CYP) content were found between control and infected mice during the course of the study. The most striking modulations of individual isoenzymes were the increases in immunohistochemical staining observed for CYP1A and CYP2A5 in relation to increasing age and liver lesions. The increase in CYP2A5 in mice aged over 12 months was confirmed by the observed increases in coumarin 7-hydroxylation (CYP2A5 substrate) in vitro and CYP2A5 mRNA levels by Northern blot analysis. Immunoblotting confirmed the specific induction of CYP1A2 in infected mice 12 and 18 months of age. Perfusion of liver with nitroblue tetrazolium, an indicator for superoxide formation, demonstrated that in livers of infected mice, hepatocytes often co-expressed CYP2A5 and formazan deposition. Concerning phase II enzymes, an enhancement of glutathione S-transferase (GST) activities, related to the disease process, was observed in infected mice. An age-specific increase of GSTpi and A4.4 (early stage of disease) and GST YaYa (>9 months) expression was also demonstrated by immunohistochemical staining. In contrast, catalase and glutathione-peroxidase activities, as well as reduced glutathione content were decreased in the early stages of disease (3-9 months) in infected mice compared to age-matched control mice. Overall, these results suggest that alterations in CYP and GST expression may contribute to the aetiology of tumour incidence due to H. hepaticus infection via production of reactive oxygen species.

Increased oxidative DNA damage and hepatocyte overexpression of specific cytochrome P450 isoforms in hepatitis of mice infected with Helicobacter hepaticus.

A recently discovered bacterium, Helicobacter hepaticus, infects the intrahepatic bile canaliculi of mice, causing a severe chronic hepatitis culminating in liver cancer. Thus, it affords an animal model for study of bacteria-associated tumorigenesis including H. pylori-related gastric cancer. Reactive oxygen species are often postulated to contribute to this process. We now report that hepatitis of male mice infected with H. hepaticus show significant increases in the oxidatively damaged DNA deoxynucleoside 8-hydroxydeoxyguanosine, with the degree of damage increasing with progression of the disease. Perfusion of infected livers with nitro blue tetrazolium revealed that superoxide was produced in the cytoplasm of hepatocytes, especially in association with plasmacytic infiltrates near portal triads. Contrary to expectations, Kupffer cells, macrophages, and neutrophils were rarely involved. However, levels of cytochrome P450 (CYP) isoforms 1A2 and 2A5 in hepatocytes appeared to be greatly increased, as indicated by the number of cells positive in immunohistochemistry and the intensity of staining in many cells, concomitant with severe hepatitis. The CYP2A5 immunohistochemical staining co-localized with formazan deposits resulting from nitro blue tetrazolium reduction and occurred in nuclei as well as cytoplasm. These findings suggest that CYP2A5 contributes to the superoxide production and 8-hydroxydeoxyguanosine formation, although reactive oxygen species from an unknown source in the hepatocytes leading to CYP2A5 induction or coincidental occurrence of these events are also possibilities. Three glutathione S-transferase isoforms, mGSTP1-1 (pi), mGSTA1-1 (YaYa), and mGSTA4-4, also showed striking increases evidencing major oxidative stress in these livers.

An update on interleukin-4 and its receptor.

Interleukin-4 (IL-4) exhibits many biological and immunoregulatory functions on B lymphocytes, monocytes, dendritic cells and fibroblasts. The IL-4 gene is located on chromosome 5 and displays several cell-specific regulatory sequences in its promoter, which explain its restricted secretion pattern to activated T cells and mast cells. The IL-4 receptor is multimeric and is constituted by at least IL-4Ralpha, a chain common to other cytokine receptors. Two types of IL-4 receptors have been defined: one constituted by the IL-4Ralpha and the gamma(c) chain, and a second constituted by the IL-4Ralpha and the IL-13Ralpha, which is able to transduce both IL-4 and IL-13 signals. Major events of IL-4 transducing signal have now been elucidated and are known to be mediated through JAK/IRS-2 and STAT6 pathways. Numerous studies have also demonstrated the key regulatory role of IL-4 in allergic responses as well as its anti-tumor and anti-inflammatory effects.

The functional CD40 antigen of fibroblasts may contribute to the proliferation of rheumatoid synovium.

This paper demonstrates that CD40 is expressed on rheumatoid synovial pannus and primary fibroblast cell lines established from rheumatoid and osteoarthritic synovium as well as normal skin. Among various tested cytokines, interferon-gamma (IFN-gamma) and to a lower extent, tumour necrosis factor-alpha (TNF-alpha) were found to upregulate CD40 expression on fibroblasts. Synovial and skin fibroblasts cultured over CD40 Ligand transfected L cells (L-CD40 L) demonstrate a CD40 specific increase of DNA synthesis as measured by tritiated thymidine incorporation. Cell-cycle analysis and enumeration of viable cells further show that CD40 induced fibroblast proliferation. Costimulation with L-CD40 L and IFN-gamma resulted in maximal proliferation. Engagement of fibroblasts CD40 increased the IL-1-induced production of granulocyte macrophage-colony stimulating factor and macrophage inflammatory protein-1 alpha MIP-1 alpha. CD40 L activated fibroblasts showed decreased levels of CD40, but only marginal alterations of other cell-surface antigens. Taken together, the present results indicate that fibroblasts express functional CD40 and suggest a possible role of CD40 L expressing cells, such as activated T cells and mast cells, in the development of synovium hyperplasia.

T cell interleukin-17 induces stromal cells to produce proinflammatory and hematopoietic cytokines.

Analysis of the cDNA encoding murine interleukin (IL) 17 (cytotoxic T lymphocyte associated antigen 8) predicted a secreted protein sharing 57% amino acid identity with the protein predicted from ORF13, an open reading frame of Herpesvirus saimiri. Here we report on the cloning of human IL-17 (hIL-17), the human counterpart of murine IL-17. hIL-17 is a glycoprotein of 155 amino acids secreted as an homodimer by activated memory CD4+ T cells. Although devoid of direct effects on cells of hematopoietic origin, hIL-17 and the product of its viral counterpart, ORF13, stimulate epithelial, endothelial, and fibroblastic cells to secrete cytokines such as IL-6, IL-8, and granulocyte-colony-stimulating factor, as well as prostaglandin E2. Furthermore, when cultured in the presence of hIL-17, fibroblasts could sustain the proliferation of CD34+ hematopoietic progenitors and their preferential maturation into neutrophils. These observations suggest that hIL-17 may constitute (a) an early initiator of the T cell-dependent inflammmatory reaction; and (b) an element of the cytokine network that bridges the immune system to hematopoiesis.

Contribution of IL-1, CD14, and CD13 in the increased IL-6 production induced by in vitro monocyte-synoviocyte interactions.

Rheumatoid synovitis is characterized by an infiltration of mononuclear cells and by the proliferation of synoviocytes. Monocytes and synoviocytes are major producers of cytokines, growth factors, and enzymes that contribute to the rheumatoid arthritis (RA) process. Since they are in close contact in vivo, we engaged in an in vitro study of the functional consequences of their interactions. Coculture of unstimulated elutriated normal blood monocytes over RA synoviocytes resulted in a synergistic increase of the production of IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), leukemia inhibitory factor (LIF), and IL-8, when compared with their respective production in culture alone. In contrast, cytokines such as IL-10, IL-1 beta, IL-1 alpha, and TNF-alpha could not be detected. The IL-6 production in coculture was further increased by the addition of IL-1 beta, GM-CSF, IFN-gamma, or TNF-alpha, but was inhibited by the addition of IL-10, IL-4, IL-13, or IL-1Ra, an effect reverted by the addition of IL-1 beta. Moreover, an inhibition was also observed with anti-CD14 mAb and newly raised mAbs directed against RA synoviocytes. Under reducing conditions, the mAb SY12 precipitated a 150-kDa surface membrane protein, identified as amino-peptidase N (CD13/AP-N). Collectively, these results indicate that 1) monocytes and synoviocytes interact with each other to produce proinflammatory cytokines, 2) pro- and antiinflammatory cytokines have opposite effects on IL-6 production, and 3) molecules such as IL-1, CD14, and CD13 are involved.

Differential effects of interleukins 10 and 4 on the production of interleukin-6 by blood and synovium monocytes in rheumatoid arthritis.

OBJECTIVE: To determine how the antiinflammatory cytokines interleukin-10 (IL-10) and IL-4 affect the production of IL-6 in rheumatoid arthritis (RA) and to assess the contribution of IL-10 production. METHODS: IL-6 production was measured by enzyme-linked immunosorbent assay (ELISA) in the supernatants of cultured RA synovium pieces (from 23 patients), purified RA synovial tissue monocyte/macrophages, and RA blood monocytes, in the presence of IL-10 and IL-4. IL-10 was also detected by ELISA in culture supernatants and in RA sera. RESULTS: The production of IL-6 by RA synovium was strongly inhibited by IL-4 (46.6%; P = 0.0001) and was inhibited to a lower extent by IL-10 (25.3%; P = 0.03). Likewise, the spontaneous production of IL-6 by RA synovial tissue monocyte/macrophages was decreased by the addition of IL-4 (48.8%) and IL-10 (23.7%). This inhibition of IL-6 production was significantly lower (P < 0.03) than that observed with RA blood monocytes (83.0% for IL-10 and 85.2% for IL-4). Interestingly, and in contrast to RA blood monocytes, RA synovial tissue monocyte/macrophages produced spontaneously high levels of IL-10, which were inhibited by IL-4 and interferon-gamma. CONCLUSION: The ability of IL-10 and IL-4 to suppress IL-6 production was dependent on 1) differences in the state of differentiation of blood and synovial tissue monocytes, and 2) local production of cytokine inside the synovium.

Balance of IL-1 receptor antagonist/IL-1 beta in rheumatoid synovium and its regulation by IL-4 and IL-10.

The spontaneous production of IL-1 beta (IL-1 beta) and IL-1 receptor antagonist (IL-1Ra) by rheumatoid arthritis (RA) synovium, and the regulation of their production by IL-4 and IL-10, were studied. Supernatants from cultured synovium pieces from 19 RA patients were assayed for IL-1 beta and IL-1Ra production using ELISA and RIA, respectively. After 10 days of culture, spontaneous production of IL-1Ra was 1.42 +/- 0.43 ng/ml/100 mg of synovium whereas spontaneous production of IL-1 beta was 4.03 +/- 0.90 ng/ml/100 mg of synovium (n = 19). The addition of IL-4 reduced IL-1 beta production by 2.3-fold (p = 0.001) and increased that of IL-1Ra by 2.8-fold (p = 0.003). IL-10 had no significant effect on IL-1Ra production and suppressed IL-1 beta production (primarily in samples producing high levels of IL-1 beta). However, IL-10 was less potent than IL-4 in suppressing IL-1 beta production. IL-1Ra was mainly produced by rheumatoid synovial monocytes/macrophages. IL-4 was more potent than IL-10 in inducing IL-1Ra production by monocytes/macrophages purified from RA synovium, as well as from RA blood. Thus, RA synovium is characterized by an imbalance between IL-1Ra and IL-1 beta production, in favor of the latter. IL-4, and to a lesser extent IL-10, shift this balance in favor of an anti-inflammatory situation.

Interleukin-4 inhibits bone resorption through an effect on osteoclasts and proinflammatory cytokines in an ex vivo model of bone resorption in rheumatoid arthritis.

OBJECTIVE: To assess local bone resorption in the context of rheumatoid synovitis and its modulation by interleukin-4 (IL-4). METHODS: We developed an ex vivo model of bone resorption using juxtaarticular samples of bone obtained during joint surgery. We studied the histomorphometric parameters of bone resorption and the regulation of the production of IL-6, leukemia inhibitory factor (LIF), and the collagen cross-link pyridinoline, which is released during bone resorption in vivo. RESULTS: This was a sensitive and dynamic model of bone resorption. The bone samples produced high levels of pyridinoline and as much cytokine as synovium pieces obtained from the same joint. IL-4 induced a 70% reduction of IL-6 and LIF production by bone pieces and reduced pyridinoline levels. Histomorphometric studies performed on bone samples indicated a 35% increase in the mean total bone area after 7 days of treatment with IL-4. More importantly, with IL-4, osteoclasts were not detectable in the bone sections. CONCLUSION: The inhibitory effect of IL-4 on bone resorption extends our knowledge of its antiinflammatory properties and suggests that the inflammatory cytokine imbalance in rheumatoid synovium also contributes to defects in bone resorption in RA.

Interleukin-4 but not interleukin-10 inhibits the production of leukemia inhibitory factor by rheumatoid synovium and synoviocytes.

The expression of the proinflammatory cytokine leukemia inhibitory factor (LIF) has been reported in the cartilage and synovium of rheumatoid arthritis (RA) patients. Here, we show that high levels of LIF were constitutively produced by cultures of synovium pieces. Low levels of LIF were produced spontaneously by isolated synoviocytes, but interleukin (IL)-1 beta caused a fourfold enhancement of this secretion. The anti-inflammatory cytokine IL-4 reduced the production of LIF by synovium pieces by 75%, as observed earlier with IL-6, IL-1 beta and tumor necrosis factor (TNF)-alpha. IL-4 had a direct effect since it inhibited LIF production by unstimulated and IL-1 beta- or TNF-alpha-stimulated synoviocytes. Conversely, IL-4 enhanced the production of IL-6, which shares with LIF biological activities and receptor components. The inhibitory effect of IL-4 was dose dependent and was reversed using a blocking anti-IL-4 receptor antibody. Similar inhibitory action of IL-4 on LIF production was observed on synovium pieces from patients with osteoarthritis and on normal synoviocytes. IL-10, another anti-inflammatory cytokine acting on monocytes, had no effect on LIF production by either synovium pieces or isolated synoviocytes. Thus, the production of LIF by synovium tissue was inhibited by IL-4 through both a direct effect on synoviocytes and an indirect effect by inhibition of the production of LIF-inducing cytokines.

Interferon gamma inhibits interleukin 10 production by monocytes.

Interleukin 10 (IL-10) was first described for its ability to inhibit interferon gamma (IFN-gamma) production. Herein, we studied the balance between IFN-gamma and IL-10 production by human peripheral blood mononuclear cells (PBMC) in response to Staphylococcus aureus Cowan (SAC) or lipopolysaccharide (LPS). Monocyte depletion reduced IL-10 production by 90% and resulted in an increased IFN-gamma production. Addition of anti-IL-10 antibody to PBMC cultures also strongly increased IFN-gamma production. In contrast, among various cytokines, only IFN-gamma strongly reduced IL-10 synthesis by SAC- or LPS-activated PBMC and monocytes. Thus, IFN-gamma has proinflammatory effects through the combination of two mechanisms: (a) induction of early tumor necrosis factor alpha (TNF-alpha) and IL-1 beta synthesis; and (b) inhibition of the delayed production of IL-10, an inhibitor of TNF-alpha and IL-1 beta synthesis. Taken together, the present data indicate that IFN-gamma and IL-10 antagonize each other's production and function.