Presentation of IFN-gamma to nitric oxide-producing cells: a novel function for mast cells

Glycosaminoglycans and Proteoglycans: Overlooked Entities?

♦ Background

By virtue of their high net negative charge, glycosaminoglycans and proteoglycans play pivotal roles in biologic processes such as cell–cell and cell–matrix interactions, sequestration of growth factors, activation of chemokines and cytokines, and permselectivity of basement membranes.

♦ Methods

The present article reviews the putative roles of glycosaminoglycans and proteoglycans in the peritoneal cavity during normal peritoneal homeostasis and chronic inflammation, the latter induced by constant exposure of the peritoneum to non-physiologic peritoneal dialysis (PD) solutions.

♦ Results

Glycosaminoglycans have been identified in the mesothelial glycocalyx, a slippery, non-adhesive layer that protects the peritoneal membrane from abrasion and infection. Dermatan sulfate proteoglycans can neutralize the activity of transforming growth factor β1 and can thus play an essential role in modulating peritoneal fibrosis. Heparan sulfate proteoglycans play a crucial role in the sequestration of growth factors; they also modulate selective permeability of proteins across the peritoneal cavity. Reduced expression of perlecan, a heparan sulfate proteoglycan of the basement membrane, is observed in peritoneal biopsies obtained from established PD patients, consequent to prolonged exposure to the elevated glucose concentrations in conventional PD solutions. Supplementation of PD fluids with glycosaminoglycans has been shown to be beneficial to both the structural and functional integrity of the peritoneum.

♦ Conclusions

Recent advances in the field of glycobiology have revealed a multitude of biologic processes that are controlled or influenced by glycosaminoglycans and proteoglycans. Altered synthesis of these macromolecules during PD has serious implications for the peritoneal transport of proteins, host defense, wound healing, inflammation, and fibrosis.

Galactosaminoglycans: Medical Applications and Drawbacks

Galactosaminoglycans (GalAGs) are sulfated glycans composed of alternating N-acetylgalactosamine and uronic acid units. Uronic acid epimerization, sulfation patterns and fucosylation are modifications observed on these molecules. GalAGs have been extensively studied and exploited because of their multiple biomedical functions. Chondroitin sulfates (CSs), the main representative family of GalAGs, have been used in alternative therapy of joint pain/inflammation and osteoarthritis. The relatively novel fucosylated chondroitin sulfate (FCS), commonly found in sea cucumbers, has been screened in multiple systems in addition to its widely studied anticoagulant action. Biomedical properties of GalAGs are directly dependent on the sugar composition, presence or lack of fucose branches, as well as sulfation patterns. Although research interest in GalAGs has increased considerably over the three last decades, perhaps motivated by the parallel progress of glycomics, serious questions concerning the effectiveness and potential side effects of GalAGs have recently been raised. Doubts have centered particularly on the beneficial functions of CS-based therapeutic supplements and the potential harmful effects of FCS as similarly observed for oversulfated chondroitin sulfate, as a contaminant of heparin. Unexpected components were also detected in CS-based pharmaceutical preparations. This review therefore aims to offer a discussion on (1) the current and potential therapeutic applications of GalAGs, including those of unique features extracted from marine sources, and (2) the potential drawbacks of this class of molecules when applied to medicine.

Catch and Release of Cytokines Mediated by Tumor Phosphatidylserine Converts Transient Exposure into Long-Lived Inflammation

Immune cells constantly survey the host for pathogens or tumors and secrete cytokines to alert surrounding cells of these threats. In vivo, activated immune cells secrete cytokines for several hours, yet an acute immune reaction occurs over days. Given these divergent timescales, we addressed how cytokine-responsive cells translate brief cytokine exposure into phenotypic changes that persist over long timescales. We studied melanoma cell responses to transient exposure to the cytokine interferon γ (IFNγ) by combining a systems-scale analysis of gene expression dynamics with computational modeling and experiments. We discovered that IFNγ is captured by phosphatidylserine (PS) on the surface of viable cells both in vitro and in vivo then slowly released to drive long-term transcription of cytokine-response genes. This mechanism introduces an additional function for PS in dynamically regulating inflammation across diverse cancer and primary cell types and has potential to usher in new immunotherapies targeting PS and inflammatory pathways.

E3 ubiquitin ligase NKLAM ubiquitinates STAT1 and positively regulates STAT1-mediated transcriptional activity

Signal transducer and activator of transcription 1 (STAT1) is critically important for the transcription of a large number of immunologically relevant genes. In macrophages, interferon gamma (IFNγ) signal transduction occurs via the JAK/STAT pathway and ends with the transcription of a number of genes necessary for a successful host immune response. The predominant mechanism of regulation of STAT1 is phosphorylation; however, there is a growing body of evidence that demonstrates STAT1 is also regulated by ubiquitination. In this report we show that JAK1 and STAT1 in macrophages deficient in an E3 ubiquitin ligase termed Natural Killer Lytic-Associated Molecule (NKLAM) are hyperphosphorylated following IFNγ stimulation. We found NKLAM was transiently localized to the IFNγ receptor complex during stimulation with IFNγ, where it bound to and mediated K63-linked ubiquitination of STAT1. In vitro nucleofection studies demonstrated that STAT1-mediated transcription was significantly reduced in NKLAM-KO macrophages. There was no obvious defect in STAT1 nuclear translocation; however, STAT1 from NKLAM-KO macrophages had a reduced ability to bind a functional gamma activation DNA sequence. There was also less mRNA expression of STAT1-mediated genes in NKLAM-KO macrophages treated with IFNγ. Our results demonstrate for the first time that NKLAM is a positive regulator of STAT1-mediated transcriptional activity and is an important component of the innate immune response.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Decorin mimic regulates platelet-derived growth factor and interferon-γ stimulation of vascular smooth muscle cells

Following balloon injury, smooth muscle cells (SMCs) serve as targets for many of the pro-inflammatory and pro-fibrotic factors, including platelet-derived growth factor (PDGF) and interferon-γ (IFN-γ) released from activated inflammatory cells and platelets. Previously, our lab designed a mimic of the proteoglycan decorin, termed DS-SILY20, that suppressed vascular SMC proliferation, migration, and protein synthesis in vitro, and injured vessels treated with DS-SILY20 demonstrated reduced hyperplasia in vivo. Here we characterize the effects of DS-SILY20 on modulating PDGF and IFN-γ stimulation in both proliferative and quiescent human SMCs to further evaluate the potential impact of DS-SILY20-SMC interaction on restenosis. Nanomolar dissociation constants were observed between DS-SILY20 and both PDGF and IFN-γ. PDGF significantly increased migration, proliferation, and protein and cytokine expression, as well as increased ERK-1/2 and p38 MAPK phosphorylation in both quiescent and proliferative cultures. However, DS-SILY20 inhibited these increases, presumably through sequestration of the PDGF. Consistent with the complex responses seen with IFN-γ in SMC physiology in the literature, the response of SMC cultures to IFN-γ was variable and complex. However, where increased activity was seen with IFN-γ, DS-SILY20 attenuated this activity. Overall, the results suggest that DS-SILY20 would be an ideal alternative to traditional therapeutics used and may be an effective therapy for the prevention of intimal hyperplasia after balloon angioplasty.

Insights into the mechanism by which interferon-γ basic amino acid clusters mediate protein binding to heparan sulfate

The extensive functional repertoire of heparin and heparan sulfate, which relies on their ability to interact with a large number of proteins, has recently emerged. To understand the forces that drive such interactions the binding of heparin to interferon-γ (IFNγ), used as a model system, was investigated. NMR-based titration experiments demonstrated the involvement of two adjacent cationic domains (D1: KTGKRKR and D2: RGRR), both of which are present within the carboxy-terminal sequence of the cytokine. Kinetic analysis showed that these two domains contribute differently to the interaction: D1 is required to form a complex and constitutes the actual binding site, whereas D2, although unable to associate with heparin by itself, increased the association rate of the binding. These data are consistent with the view that D2, through nonspecific electrostatic forces, places the two molecules in favorable orientations for productive binding within the encounter complex. This mechanism was supported by electrostatic potential analysis and thermodynamic investigations. They showed that D1 association to heparin is driven by both favorable enthalpic and entropic contributions, as expected for a binding sequence, but that D2 gives rise to entropic penalty, which opposes binding in a thermodynamic sense. The binding mechanism described herein, by which the D2 domain kinetically drives the interaction, has important functional consequences and gives a structural framework to better understand how specific are the interactions between proteins and heparin.

Decorin potentiates interferon-γ activity in a model of allergic inflammation

The proteoglycan decorin modulates leukocyte recruitment during delayed-type hypersensitivity responses. Decorin-deficient (Dcn(-/-)) mice show reduced edema formation during the first 24 h with a concurrent attenuated recruitment of CD8(+) leukocytes in the inflamed Dcn(-/-) ears. The aim of this study was to elucidate the molecular pathways affected by the loss of decorin. In vivo, reduced numbers of CD8(+) cells in Dcn(-/-) ears correlated with a reduced interferon-γ (Ifn-γ) and CXCL-10 expression. In vitro, Dcn(-/-) lymphocytes displayed an increased adhesion to brain microvascular (bEnd.3) endothelial cells. Decorin treatment of bEnd.3 increased Icam1 and down-regulated Vcam1 expression after TNF-α stimulation. However, Dcn(-/-) and wild-type lymphocytes produced IFN-γ after activation with CD3ε. Upon incubation with decorin, endothelial cells and fibroblasts responded differently to IFN-γ and TNF-α; CCL2 in bEnd.3 cells was more prominently up-regulated by TNF-α compared with IFN-γ. Notably, both factors were more potent in the presence of decorin. Compared with TNF-α, IFN-γ treatment induced significantly more CXCL-10, and both factors increased synthesis of CXCL-10 in the presence of decorin. The response to IFN-γ was similar in Dcn(-/-) and wild-type fibroblasts, an additional source of CXCL-10. However, addition of decorin yielded significantly more CXCL-10. Notably, decorin increased the stability of IFN-γ in vitro and potentiated IFN-γ-induced activation of STAT-1. Furthermore, only dermatan sulfate influenced IFN-γ signaling by significantly increasing CXCL-10 expression in contrast to decorin protein core alone. Our data demonstrate that decorin modulates delayed-type hypersensitivity responses by augmenting the induction of downstream effector cytokines of IFN-γ and TNF-α, thereby influencing the recruitment of CD8(+) lymphocytes into the inflamed tissue.

Characterization of cis-regulatory elements conferring mercury-induced interleukin-4 gene expression in rat mast cells: a role for signal transducer and activator of transcription 6 and TATA box binding sites

We have previously shown that oxidative stress is involved in the pathogenesis of a mercuric chloride (HgCl(2))-induced, T helper type 2 (Th2)-driven autoimmune syndrome in Brown Norway (BN) rats. In the context of the syndrome, the oxidative stress-induced mast cell response seems to determine the development of the early phase of vasculitis, while oxidative stress-mediated interleukin (IL)-4 production may contribute to the subsequent Th2-driven autoimmune response. However, the molecular basis of IL-4 gene transcription induced by HgCl(2) in mast cells remains unknown. In the present study, we dissect the critical regulatory mechanisms in the IL-4 gene promoter in the rat mast cell line RBL-2H3. Immunoprecipitation provided evidence that treatment with HgCl(2) increased phosphorylation of signal transducer and activator of transcription 6 (STAT6). Transient transfection reporter analyses with a series of 5' end deletions of the IL-4 promoter produced evidence that STAT6 and TATA box binding sites are important in HgCl(2)-induced IL-4 gene expression. Subsequent elimination of one or both sites by site-directed mutagenesis significantly inhibited IL-4 promoter activity. Our results provide evidence that STAT6 and TATA box regulatory elements play an important role in HgCl(2)-induced IL-4 transcription in rat mast cells.

CD4+ T cell-specific deletion of IL-4 receptor alpha prevents ovalbumin-induced anaphylaxis by an IFN-gamma-dependent mechanism

IL-4Ralpha-mediated STAT6 activation serves an essential role in various animal models of allergy and asthma at both the sensitization and effector phases. IL-4 and IL-13 signaling via the IL-4Ralpha chain exacerbates murine anaphylaxis, but the cell-specific requirements for IL-4Ralpha expression are unclear. The purpose of this study was to elucidate the mechanisms of systemic anaphylaxis to OVA in gene-targeted mice with a deletion of the IL-4Ralpha chain in the macrophage/neutrophil or CD4+ T lymphocyte population. Results demonstrated that anaphylaxis in this model was entirely dependent upon the FcgammaRII/III and was associated with mast cell degranulation. Expression of the IL-4Ralpha on CD4+ T cells, but not macrophages or neutrophils, was critical for severe anaphylaxis, characterized by diarrhea, hypothermia, and death. Ab depletion experiments demonstrated that IFN-gamma protected against mortality and severe intestinal pathology despite the presence of Ag and specific Ab. This protection was associated with reduced levels of mast cell protease, a marker of mast cell degranulation, suggesting that IFN-gamma may inhibit mast cell degranulation in vivo. These data suggest that it may be possible to limit the severity of anaphylaxis using rational therapies designed to increase numbers of IFN-gamma-producing cells by targeting IL-4Ralpha signaling in CD4+ T lymphocytes.

Presence of SNAP-23 and syntaxin 4 in mouse and hamster peritoneal mast cells

Mast cells (MCs) play a crucial role in inflammatory reactions. Their presence and number in the peritoneal cavity is important to overcome and enhance resistance to peritoneal infection. When MCs are activated they release a variety of biological mediators from their granules, such as histamine, that contribute to the appropriate and rapid local immune response. Granular content is released using a process of compound exocytosis, also termed degranulation. SNAP-23 and syntaxin 4 are plasma membrane proteins involved in degranulation of rat MCs. Their presence, however, has not been studied in MCs of other rodent species. The aim of the present study was to investigate using immunocytochemistry whether SNAP-23 and syntaxin 4 are present in peritoneal MCs of the mouse and hamster. In addition, the diameter, percentage and histamine content of these cells were also analyzed. Our results demonstrate that SNAP-23 and syntaxin 4 are present in the mouse and hamster peritoneal MCs, suggesting that proteins involved in the secretory process in MCs are conserved among species. Likewise, we conclude that peritoneal MCs of mouse and hamster are heterogeneous in size, percentage and histamine content.

Effects of cigarette smoke on degranulation and NO production by mast cells and epithelial cells

Exhaled nitric oxide (eNO) is decreased by cigarette smoking. The hypothesis that oxides of nitrogen (NO_X) in cigarette smoke solution (CSS) may exert a negative feedback mechanism upon NO release from epithelial (AEC, A549, and NHTBE) and basophilic cells (RBL-2H3) was tested in vitro. CSS inhibited both NO production and degranulation (measured as release of beta-hexosaminidase) in a dose-dependent manner from RBL-2H3 cells. Inhibition of NO production by CSS in AEC, A549, and NHTBE cells was also dose-dependent. In addition, CSS decreased expression of NOS mRNA and protein expression. The addition of NO inhibitors and scavengers did not, however, reverse the effects of CSS, nor did a NO donor (SNP) or nicotine mimic CSS. N-acetyl-cysteine, partially reversed the inhibition of beta-hexosaminidase release suggesting CSS may act via oxidative free radicals. Thus, some of the inhibitory effects of CSS appear to be via oxidative free radicals rather than a NO_X -related negative feedback.

Endocan or endothelial cell specific molecule-1 (ESM-1): a potential novel endothelial cell marker and a new target for cancer therapy

Endocan, previously called endothelial cell specific molecule-1, is a soluble proteoglycan of 50 kDa, constituted of a mature polypeptide of 165 amino acids and a single dermatan sulphate chain covalently linked to the serine residue at position 137. This dermatan sulphate proteoglycan, which is expressed by the vascular endothelium, has been found freely circulating in the bloodstream of healthy subjects. Experimental evidence is accumulating that implicates endocan as a key player in the regulation of major processes such as cell adhesion, in inflammatory disorders and tumor progression. Inflammatory cytokines such as TNF-alpha, and pro-angiogenic growth factors such as VEGF, FGF-2 and HGF/SF, strongly increased the expression, synthesis or the secretion of endocan by human endothelial cells. Endocan is clearly overexpressed in human tumors, with elevated serum levels being observed in late-stage lung cancer patients, as measured by enzyme-linked immunoassay, and with its overexpression in experimental tumors being evident by immunohistochemistry. Recently, the mRNA levels of endocan have also been recognized as being one of the most significant molecular signatures of a bad prognosis in several types of cancer including lung cancer. Overexpression of this dermatan sulphate proteoglycan has also been shown to be directly involved in tumor progression as observed in mouse models of human tumor xenografts. Collectively, these results suggest that endocan could be a biomarker for both inflammatory disorders and tumor progression as well as a validated therapeutic target in cancer. On the basis of the recent successes of immunotherapeutic approaches in cancer, the preclinical data on endocan suggests that an antibody raised against the protein core of endocan could be a promising cancer therapy.

Nitric Oxide Inhibits IgE-Dependent Cytokine Production and Fos and Jun Activation in Mast Cells

NO is a cell-derived radical reported to inhibit mast cell degranulation and subsequent allergic inflammation, although whether its action is nonspecific or occurs via specific molecular mechanisms remains unknown. To examine this question, we set out to determine whether NO inhibits mast cell cytokine production, and, if so, whether it also alters FcepsilonRI-dependent signal transduction. As hypothesized, the radical inhibited IgE/Ag-induced IL-4, IL-6, and TNF production. Although NO did not influence phosphorylated JNK, p38 MAPK, or p44/42 MAPK, it did inhibit phosphorylation of phospholipase Cgamma1 and the AP-1 transcription factor protein c-Jun, but not NF-kappaB or CREB. NO further completely abrogated IgE/Ag-induced DNA-binding activity of the nuclear AP-1 proteins Fos and Jun. These results show that NO is capable of inhibiting FcepsilonRI-dependent mast cell cytokine production at the level of gene regulation, and suggest too that NO may contribute to resolution of allergic inflammation.

Rodent and human mast cells produce functionally significant intracellular reactive oxygen species but not nitric oxide

In immunity, reactive oxygen species (ROS) and nitric oxide (NO) are important antimicrobial agents and regulators of cell signaling and activation pathways. However, the cellular sources of ROS and NO are much debated. Particularly, there is contention over whether mast cells, key secretory cells in allergy and immunity, can generate these chemical species, and if so, whether they are of functional significance. We therefore examined directly by flow cytometry the capacity of mast cells to generate intracellular ROS and NO using the respective cell-permeable fluorescent probes dichlorodihydrofluorescein and diaminofluorescein and evaluated the effects of inhibitors of ROS and NO synthesis on cell degranulation. For each of three mast cell types (rat peritoneal mast cells, mouse bone marrow-derived mast cells, and human blood-derived mast cells), degranulation stimulated by IgE/antigen was accompanied by production of intracellular ROS but not NO. Inhibition of ROS production led to reduced degranulation, indicating a facilitatory role for ROS, whereas NO synthase inhibitors were without effect. Likewise, bacterial lipopolysaccharide and interferon-gamma over a wide range of conditions failed to generate intracellular NO in mast cells, whereas these agents readily induced intracellular NO in macrophages. NO synthase protein, as assessed by Western blotting, was readily induced in macrophages but not mast cells. We conclude that rodent and human mast cells generate intracellular ROS but not NO and that intracellular ROS but not intracellular NO are functionally linked to mast cell degranulation.

Mouse mast cell protease-1 is required for the enteropathy induced by gastrointestinal helminth infection in the mouse

BACKGROUND & AIMS

The relationship between intestinal pathology and immune expulsion of gastrointestinal nematodes remains controversial. Immune expulsion of gastrointestinal helminth parasites is usually associated with Th2 responses, but the effector mechanisms directly responsible for parasite loss have not been elucidated. Mast cell hyperplasia is a hallmark of infection with gastrointestinal nematodes, in particular Trichinella spiralis. Although the precise mechanism by which mast cells induce expulsion of these parasites has not been elucidated, it has been proposed that mast cell mediators, including cytokines and granule chymases, act to create an environment inhospitable to the parasite, part of this being the induction of intestinal inflammation. Therefore, the aims of this study were to dissect the role of mast cells and mast cell proteases in the induction of parasite-induced enteropathy.

METHODS

Mast cell-deficient W/Wv and mouse mast cell protease-1 (mMCP-1)-deficient mice were infected with T. spiralis, and parasite expulsion, enteropathy, and Th2 responses were determined.

RESULTS

Expulsion of the parasite was delayed in both strains of mice compared with wild-type controls; additionally, in both cases, the enteropathy was significantly ameliorated. Although Th2 responses were significantly reduced in mast cell-deficient W/Wv mice, those from mMCP-1-deficient mice were similar to wild-type mice. Additionally, levels of TNF-alpha and nitric oxide were significantly reduced in both W/Wv and mMCP-1 deficient mice.

CONCLUSIONS

These results imply that mast cells may contribute to the induction of protective Th2 responses and, importantly, that the intestinal inflammation associated with gastrointestinal helminths is partly mediated by mMCP-1.

Benzylpenicillin differentially conjugates to IFN-gamma, TNF-alpha, IL-1beta, IL-4 and IL-13 but selectively reduces IFN-gamma activity

It is known that beta-lactam antibiotics can conjugate to lysine and histidine residues on proteins via the carbonyl group of the opened beta-lactam ring. However, it is not known which proteins these drugs target and there is little work addressing whether conjugation is preferential for some proteins over others or if conjugation has functional consequences for the protein. We have previously shown that the beta-lactam antibiotic benzylpenicillin (BP) conjugates to IFN-gamma and reduces its activity. This interaction demonstrates selectivity, as BP does not bind to IL-4. Here, we extend our study to include other Th1 and Th2 cell-associated cytokines and two cytokines associated with inflammatory responses. We demonstrate by Western blotting that BP also conjugates to IL-1beta, IL-2, IL-5, IL-13 and TNF-alpha but not to IL-10. Densitometric analysis of leading cytokine bands on blots revealed that IFN-gamma always gave more intense BP-positive bands than any other cytokine analysed. Cytokines pre-incubated with BP at 37 degrees C in a protein-containing, serum-free medium were assayed for their biological activity. By in vitro bioassay, BP inhibited the ability of IFN-gamma but not IL-1beta or TNF-alpha to induce CD54 expression on epithelial cells. In addition, BP did not affect IL-4 or IL-13 inhibition of mast cell proliferation. When the pre-incubation temperature was reduced to 4 degrees C, BP did not conjugate to IFN-gamma or modulate its activity. BP retained its inhibitory effect on IFN-gamma activity when 20% FCS was added to the pre-incubation medium. In conclusion, BP conjugates to some cytokines but not others and this does not appear to be related to primary protein structure. Furthermore, of the cytokines studied, conjugation only to IFN-gamma is accompanied by inhibition of activity. This phenomenon is temperature dependent and occurs in the presence of serum. These findings provide further evidence for differential, direct drug-cytokine interactions. Such interactions may have therapeutic implications in terms of targeting cytokines to regulate their activity.

A comparison of reactive oxygen species generation by rat peritoneal macrophages and mast cells using the highly sensitive real-time chemiluminescent probe pholasin: inhibition of antigen-induced mast cell degranulation by macrophage-derived hydrogen peroxide

Mast cells and macrophages live in close proximity in vivo and reciprocally regulate one another's function in various ways. Although activated macrophages possess a powerful reactive oxygen species (ROS) generating system, there is conflicting evidence regarding whether mast cells can produce ROS. We used the highly sensitive real-time chemiluminescent probe Pholasin to examine ROS release by peritoneal macrophages and mast cells isolated from OVA-sensitized rats. Macrophages stimulated with PMA (0.8 microM) or ionomycin (1 microM), but not OVA (1 microg/ml), released high-level ROS, levels of which peaked after 3-7 min and declined to baseline levels within 1 h. Superoxide was identified as the major ROS species induced by PMA but not by ionomycin. In contrast, purified mast cells stimulated with PMA released low-level ROS, which was entirely due to the contaminating (2%) macrophages, and did not release any detectable ROS in response to ionomycin or OVA at concentrations that induced degranulation. Stimulation of mixed cell populations with PMA to induce macrophage ROS release led to 50% inhibition of serotonin release from mast cells stimulated 5 min later with OVA. The PMA-induced inhibitory factor was identified as hydrogen peroxide. In conclusion, activated rat peritoneal macrophages but not mast cells produce ROS, and macrophage-derived hydrogen peroxide inhibits mast cell degranulation. The latter could be an important mechanism whereby phagocytic cells regulate mast cell activation and promote resolution of IgE-mediated inflammation.

Tumour necrosis factor-alpha interacts with biglycan and decorin

Several interactions of cytokines with extracellular matrix molecules are mediated by proteoglycans, such as biglycan and decorin. Using surface plasmon resonance, we show for the first time that tumour necrosis factor-alpha (TNF-alpha) binds to both biglycan and decorin with K(d)s of 0.81 microM and 1.23 microM respectively, a binding that was confirmed by Scatchard plots using a solid phase assay. Binding occurs preferentially via the core protein, shown by lower K(d)s, 0.26 microM and 0.81 microM for biglycan and decorin respectively. There was also binding to dermatan sulphate, with a K(d) of 10.53 microM. The function of this interaction between TNF-alpha and biglycan and decorin is not known, but we suggest that the differential localisation of the proteoglycans enables the cytokines to be immobilised in different environments.

Dermatan sulfate: new functions from an old glycosaminoglycan

Glycosaminoglycans constitute a considerable fraction of the glycoconjugates found on cellular membranes and in the extracellular matrix of virtually all mammalian tissues. Their ability to bind and alter protein-protein interactions or enzymatic activity has identified them as important determinants of cellular responsiveness in development, homeostasis, and disease. Although heparan sulfate tends to be emphasized as the most biologically active glycosaminoglycan, dermatan sulfate is a particularly attractive subject for further study because it is expressed in many mammalian tissues and it is the predominant glycan present in skin. Dermatan and dermatan sulfate proteoglycans have also been implicated in cardiovascular disease, tumorigenesis, infection, wound repair, and fibrosis. Growing evidence suggests that this glycosaminoglycan, like the better studied heparin and heparan sulfate, is an important cofactor in a variety of cell behaviors.

Number, distribution pattern, and identification of macrophages in the testes of infertile men

OBJECTIVE

To investigate the number, location, and secretory products of macrophages in human testes showing normal and abnormal spermatogenesis.

DESIGN

Evaluation of testicular biopsies with the use of immunohistochemistry, laser capture microdissection, and reverse transcriptase polymerase chain reaction.

SETTING

University research and clinical institutes.

PATIENT(S)

Infertile men with germ cell arrest (n = 10), Sertoli cell only (n = 8), or mixed atrophy (n = 7) syndromes, and with cases of idiopathic infertility showing normal spermatogenesis (n = 8).

INTERVENTION(S)

Diagnostic testicular biopsy was performed on participants.

MAIN OUTCOME MEASURE(S)

We recorded the location, number, distribution, and cytokine expression of human testicular macrophages.

RESULT(S)

CD68-positive macrophages were found in the testes of all groups analyzed. These macrophages expressed the genes for interleukin 1 and tumor necrosis factor-alpha, and were located in the interstitium, tubular wall, and tubular lumen. In Sertoli cell only and germ cell arrest syndromes, the overall macrophage number was increased over twofold. In all pathologic states, there was a significant shift of these cells from the interstitium to the tubules.

CONCLUSION(S)

Our study suggests that increased numbers of CD68-positive macrophages directly (via phagocytosis) or indirectly (via paracrine actions exerted through their secretory products) are involved in the regulation of steroidogenesis, Sertoli cell activity, germ cell survival, and, in consequence, in the pathogenesis or maintenance of infertility states in the human testes.

Nitric oxide: a regulator of mast cell activation and mast cell-mediated inflammation

Nitric oxide (NO) plays diverse roles in physiological and pathological processes. During immune and inflammatory responses, for example in asthma, NO is generated at relatively high and sustained levels by the inducible form of nitric oxide synthase (NOS-2). NOS-2 derived NO regulates the function, growth, death and survival of many immune and inflammatory cell types. In the case of mast cells, NO suppresses antigen-induced degranulation, mediator release, and cytokine expression. The action of NO on mast cells is time dependent, requiring several hours, and noncGMP mediated, most probably involving chemical modification of proteins. NO inhibits a number of mast cell-dependent inflammatory processes in vivo, including histamine mediated vasodilatation, vasopermeation and leucocyte-endothelial cell attachment. In human asthma and animal models of lung inflammation the role of NO is harder to define. However, although there are conflicting data, the balance of evidence favours a predominantly protective role for NO. Mimicking or targeting NO dependent pathways may prove to be a valuable therapeutic approach to mast cell mediated diseases.

Antioxidants inhibit mercuric chloride-induced early vasculitis

In the Brown Norway (BN) rat, mercuric chloride (HgCl(2)) induces a T(h)2-dominated autoimmune syndrome which includes an early phase of mast cell-dependent vasculitis. We have shown in vitro that oxidative stress up-regulates IL-4 in mast cells and predisposes to degranulation. The aim of this study was to determine whether administration of antioxidants inhibits HgCl(2)-induced early vasculitis in vivo, and, if so, to examine whether modulation of the oxidative/antioxidative balance influences IgE and IL-4 expression by mast cells in situ. Groups of rats were given HgCl(2) + saline, HgCl(2) + N-acetyl-L-cysteine (NAC), saline + saline or saline + NAC respectively and blood was taken and animals killed 48 h later. NAC significantly reduced both HgCl2-induced early vasculitis and HgCl(2)-enhanced IgE expression on mast cells with a trend to a decrease in HgCl(2)-enhanced IL-4 expression in these cells. In addition, there was an increased rat mast cell protease (RMCP) II concentration in the serum after HgCl(2) injection and the elevated levels of RMCP II stimulated by HgCl(2) were totally abolished by the administration NAC in the HgCl(2) + NAC group. However, there was no significant change in serum total IgE concentrations between the HgCl(2) + saline group and the HgCl(2) + NAC group. The non-sulphydryl-containing antioxidants desferrioxamine and pyruvate demonstrated a similar effect in inhibiting HgCl(2)-induced early vasculitis. Our data show that administration of an antioxidant to BN rats reduces HgCl(2)-induced early vasculitis, suggesting that oxidative stress plays a role in the pathogenesis of HgCl(2)-induced early vasculitis. This finding may have implications for the understanding of the initiation in this experimental model of T(h)2 cell-driven autoimmunity and possibly of analogous human diseases.

Mast cells as a source and target for nitric oxide

Mast cells (MC), which are tissue-resident cells found widely distributed in the body, are derived from primitive hematopoietic cells. MC produce a variety of biologically active substances such as histamine, proteases, lipid derivatives and numerous cytokines and chemokines in response to immunologic or non-immunologic stimuli. Of interest, it has been reported that rodent MC can also be a source of nitric oxide (NO) derivatives, that they synthesize spontaneously, or only after activation, depending on their subtype. This synthesis appears to be under the control of the expression of the inducible isoform of the nitric oxide synthase (iNOS) and of the constitutive neuronal NOS (nNOS). MC might thus be able to influence the survival and functions of other types of NO-sensitive cells in close vicinity. Apart from being a source of NO, MC can also be the target for NO and its derivatives. Indeed, survival and reactivity of rodent MC is influenced by NO derivatives produced by MC themselves or by other cellular elements in close contact with the MC in tissues. By contrast, the existence of such mechanisms of cross-talk between MC and NO remains poorly documented in humans. If evidence are supplied in favor of such relationship, pharmacological modulation by agents acting at the level of the NO pathway might be of interest in order to regulate the functions of MC in immunologic, neoplastic, inflammatory and other conditions.

The role of NO in contact hypersensitivity

Contact dermatitis or contact hypersensitivity (CHS) is a common T lymphocyte-mediated allergic disease characterized by local inflammatory skin reactions following contact with small reactive compounds called haptens. In common with other allergic processes, the development of contact dermatitis proceeds in two phases: a sensitization phase which occurs on first exposure to allergen, and an elicitation phase which occurs on subsequent exposure when the clinical manifestations of the disease are observed. This process is hapten-specific. While the pathophysiology of the sensitization phase is well characterized, our understanding of the elicitation phase is still incomplete, including the relative contribution of the different effector cells and mediators involved. Here we summarize current knowledge of the contribution of nitric oxide (NO) to skin inflammation with special focus on CHS. A number of inflammatory stimuli trigger expression of NO in human and animal skin, and topical application of an NO-releasing cream results in inflammation. Moreover, expression of the inducible isoform of nitric oxide synthase (iNOS) is induced in CHS and iNOS inhibitors injected intradermally suppress CHS responses. However, iNOS-deficient mice develop an aggravated CHS response late in the elicitation phase, suggesting that NO is involved in downregulation of CHS. Based on these data, we propose a comprehensive model of the role of NO in CHS.