Subfornical organ mediates sympathetic and hemodynamic responses to blood-borne proinflammatory cytokines

Proinflammatory cytokines play an important role in regulating autonomic and cardiovascular function in hypertension and heart failure. Peripherally administered proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), act on the brain to increase blood pressure, heart rate, and sympathetic nerve activity. These molecules are too large to penetrate the blood-brain barrier, and so the mechanisms by which they elicit these responses remain unknown. We tested the hypothesis that the subfornical organ (SFO), a forebrain circumventricular organ that lacks a blood-brain barrier, plays a major role in mediating the sympathetic and hemodynamic responses to circulating proinflammatory cytokines. Intracarotid artery injection of TNF-α (200 ng) or IL-1β (200 ng) dramatically increased mean blood pressure, heart rate, and renal sympathetic nerve activity in rats with sham lesions of the SFO (SFO-s). These excitatory responses to intracarotid artery TNF-α and IL-1β were significantly attenuated in SFO-lesioned (SFO-x) rats. Similarly, the increases in mean blood pressure, heart rate, and renal sympathetic nerve activity in response to intravenous injections of TNF-α (500 ng) or IL-1β (500 ng) in SFO-s rats were significantly reduced in the SFO-x rats. Immunofluorescent staining revealed a dense distribution of the p55 TNF-α receptor and the IL-1 receptor accessory protein, a subunit of the IL-1 receptor, in the SFO. These data suggest that SFO is a predominant site in the brain at which circulating proinflammatory cytokines act to elicit cardiovascular and sympathetic responses.

BRET Biosensor Analysis of Receptor Tyrosine Kinase Functionality

Bioluminescence resonance energy transfer (BRET) is an improved version of earlier resonance energy transfer technologies used for the analysis of biomolecular protein interaction. BRET analysis can be applied to many transmembrane receptor classes, however the majority of the early published literature on BRET has focused on G protein-coupled receptor (GPCR) research. In contrast, there is limited scientific literature using BRET to investigate receptor tyrosine kinase (RTK) activity. This limited investigation is surprising as RTKs often employ dimerization as a key factor in their activation, as well as being important therapeutic targets in medicine, especially in the cases of cancer, diabetes, neurodegenerative, and respiratory conditions. In this review, we consider an array of studies pertinent to RTKs and other non-GPCR receptor protein-protein signaling interactions; more specifically we discuss receptor-protein interactions involved in the transmission of signaling communication. We have provided an overview of functional BRET studies associated with the RTK superfamily involving: neurotrophic receptors [e.g., tropomyosin-related kinase (Trk) and p75 neurotrophin receptor (p75NTR)]; insulinotropic receptors [e.g., insulin receptor (IR) and insulin-like growth factor receptor (IGFR)] and growth factor receptors [e.g., ErbB receptors including the EGFR, the fibroblast growth factor receptor (FGFR), the vascular endothelial growth factor receptor (VEGFR) and the c-kit and platelet-derived growth factor receptor (PDGFR)]. In addition, we review BRET-mediated studies of other tyrosine kinase-associated receptors including cytokine receptors, i.e., leptin receptor (OB-R) and the growth hormone receptor (GHR). It is clear even from the relatively sparse experimental RTK BRET evidence that there is tremendous potential for this technological application for the functional investigation of RTK biology.

Type III IFNs are produced by and stimulate human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDC) are rare cells found in peripheral blood and lymphoid tissues. pDC are considered to be "professional" type I IFN-producing cells and produce 10- to 100-fold more IFN-α than other cell types in response to enveloped viruses or synthetic TLR7 and TLR9 agonists. In this study, purified pDC were found to express high levels of IFN-λ receptor mRNA, as well as cell-surface IFN-λ receptor. We have developed intracellular flow cytometry assays using Abs to IFN-λ1/3 or -λ2 to assess the expression of IFN-λ proteins by pDC. We observed that a subset of human pDC expresses only intracellular IFN-α, whereas another subset produces both IFN-α and IFN-λ after stimulation with virus or the TLR9 agonist, CpG A; the cells that coexpressed IFN-α and IFN-λ were the cells with the highest levels of IFN-α expression. Ab cross-linking of CD4 or CD303 molecules on pDC inhibited both HSV-induced IFN-λ and IFN-α production. Like the production of IFN-α, the HSV-induced IFN-λ production in pDC was mediated through TLR9 and independent of virus replication. Exogenous IFN-λ treatment of pDC resulted in increased virus-induced expression of both IFN-α and IFN-λ. In addition, both exogenous IFN-λ and -α inhibited dexamethasone-induced apoptosis of pDC. We conclude that pDC are major producers of IFN-λ1 and -λ2 in response to viral stimulation and also express functional receptors for this cytokine. Thus, IFN-λ can serve as an autocrine signal to strengthen the antiviral response of pDC by increasing IFN-α and IFN-λ production, resulting in prolonged pDC survival.

Once a killer, always a killer: from cytotoxic T cell to memory cell

The control of the differentiation pathways followed by responding CD8(+) T cells to produce protective memory cells has been intensely studied. Recent developments have identified heterogeneity at the effector cytotoxic T-lymphocyte level within which a bona fide memory cell precursor has emerged. The challenge now is to identify the cellular and molecular factors that control this developmental pathway. This review considers aspects of the regulation of the induction of effectors, the transition of effectors to memory cells, and the dynamics of the memory population.

Type I interferons are not critical for skin allograft rejection or the generation of donor-specific CD8+ memory T cells

Type I interferons (IFN-I) link innate to adaptive immunity in microbial infection, autoimmune disease and tumor immunity. It is not known whether IFN-I have an equally central role in alloimmunity. Here we tested this possibility by studying skin allograft survival and donor-specific CD8+ T-cell responses in mice that lack the IFN-I receptor (IFN-IR-/-). We found that IFN-IR-/- mice reject fully allogeneic wild-type skin grafts at the same rate as wild-type recipients. Similarly, allograft rejection was not delayed if IFN-IR-/- male skin was transplanted to syngeneic IFN-IR-/- female mice. Quantitation of the male (H-Y)-specific CD8+ T-cell response in these mice revealed normal generation of donor-specific CD8+ effector T cells but fourfold reduction in CD8+ memory T cells. Memory CD8+ T cells generated in the absence of IFN-IR had normal phenotype and recall function, assessed by ex vivo cytokine production and the ability of IFN-IR-/- mice to mount second set rejection. Finally, these memory T cells were maintained at a constant number despite their inability to respond to IFN-1. Our findings indicate that IFN-I cytokines are not critical for acute allograft rejection or for the expansion and differentiation of donor-specific CD8+ T cells into long-lived, functional memory T cells.

Human interleukin 10 receptor 1/IgG1-Fc fusion proteins: immunoadhesins for human IL-10 with therapeutic potential

Interleukin 10 (IL-10) is produced by various types of human cancer, including malignant melanoma, and plays an important role in negative regulation of cell-mediated immune responses against tumors. We have developed chimeric molecules (immunoadhesins), combining the extracellular domain of human interleukin 10 receptor 1 (IL-10R1) with the Fc regions of human IgG1 heavy chain and investigated their capability of blocking the biological activities of human IL-10. Monomeric and dimeric immunoadhesins (IL-10R1/IgG1) constructs were tested for capturing human IL-10 and blocking its biological activities. Plasmid vectors that contained the IL-10 immunoadhesin constructs were directly transfected into human melanoma cell lines. Transfection of plasmid vectors into melanoma cell lines resulted in capturing of exogenously added as well as endogeneously produced IL-10. The supernatants obtained from an IL-10 non-producing melanoma cell line transfected with monomeric IL-10 immunoadhesin plasmids most efficiently captured exogenously added IL-10, compared to those obtained with the dimeric IL-10R1/IgG1 plasmid vector. Transfection of IL-10-producing melanoma cells with the monomeric IL-10 immunoadhesin plasmids totally captured endogenously produced IL-10 and enhanced T cell responses against allogeneic melanoma cells. Furthermore, purified monomeric IL-10 immunoadhesin protein showed IL-10 capturing efficacy compatible with that of IL-10-specific monoclonal antibodies. Collectively, these studies indicate that IL-10 immunoadhesins, especially in monomeric form, are potent inhibitors of biological activities of IL-10 and suggest that these molecules, alone or in conjunctions with other immunotherapeutic approaches, can be utilized for the immuno-targeting of IL-10 producing tumors.

Down modulation of IFN-gamma signaling in alveolar macrophages isolated from smokers

The master cytokine, IFN-gamma possesses a wide spectrum of biological effects and is crucial for development of the highly activated macrophage phenotype characteristically found during inflammation. However, no data exists regarding the potential influence of cigarette smoke on the status of the expression of the cell surface receptor for IFN-gamma (IFN-gammaR) on alveolar macrophages (AM) of smokers. Here in, we report reduction in the expression of the IFN-gammaR alpha-chain on AM of cigarette smokers, when compared with non-smokers. Ensuing from the loss of receptor expression on the AM of smokers there was a decrease in IFN-gamma-mediated cell signaling. This included a decrease in the phosphorylation of signal transducer and activator of transcription (STAT)-1 and induction of interferon regulatory factor (IRF)-1. Further, diminished activation/induction of transcription factors did not appear to result from induction of known members of the 'suppressors of cytokine signaling (SOCS)' family. Decreased IFN-gamma signal transduction in AM from smokers may have an important implication regarding the use of therapeutic IFN-gamma in the lungs of patients that develop respiratory disorders as a result of tobacco use.

IFN-gamma dictates allograft fate via opposing effects on the graft and on recipient CD8 T cell responses

CD8 T cells are necessary for costimulation blockade-resistant rejection. However, the mechanism by which CD8 T cells mediate rejection in the absence of major costimulatory signals is poorly understood. IFN-gamma promotes CD8 T cell-mediated immune responses, but IFN-gamma-deficient mice show early graft loss despite costimulation blockade. In contrast, we found that IFN-gamma receptor knockout mice show dramatically prolonged graft survival under costimulation blockade. To investigate this paradox, we addressed the effects of IFN-gamma on T cell alloresponses in vivo independent of the effects of IFN-gamma on graft survival. We identified a donor-specific CD8 T cell breakthrough response temporally correlated with costimulation blockade-resistant rejection. Neither IFN-gamma receptor knockout recipients nor IFN-gamma-deficient recipients showed a CD8 breakthrough response. Graft death on IFN-gamma-deficient recipients despite costimulation blockade could be explained by the lack of IFN-gamma available to act on the graft. Indeed, the presence of IFN-gamma was necessary for graft survival on IFN-gamma receptor knockout recipients, as either IFN-gamma neutralization or the lack of the IFN-gamma receptor on the graft precipitated early graft loss. Thus, IFN-gamma is required both for the recipient to mount a donor-specific CD8 T cell response under costimulation blockade as well as for the graft to survive after allotransplantation.

Cord blood hemopoietic progenitor profiles predict acute respiratory symptoms in infancy

Atopy is characterized by eosinophilic inflammation associated with recruitment of eosinophil/basophil (Eo/B) progenitors. We have previously shown that Eo/B progenitor phenotypes are altered in cord blood (CB) in infants at high risk of atopy/asthma, and respond to maternal dietary intervention during pregnancy. As respiratory tract viral infections have been shown to induce wheeze in infancy, we investigated the relationship between CB progenitor function and phenotype and acute respiratory illness (ARI), specifically wheeze and fever. CB from 39 high-risk infants was studied by flow cytometry for CD34(+) progenitor phenotype and by ex vivo Eo/B-colony forming unit (CFU) responses to cytokine stimulation in relation to ARI in the first year of life. A consistent relationship was observed between increased numbers of granulocyte/macrophage (GM)-colony-stimulating factor (CSF)- and IL-3-responsive Eo/B-CFU in CB and the frequency/characteristics of ARI during infancy. Comparable associations were found between ARI and CB IL-3R(+) and GM-CSFR(+)CD34(+) cell numbers. Conversely, a reciprocal decrease in the proportion of CB IL-5R(+) cells was found in relation to the clinical outcomes. The elevation of IL-3/GM-CSF-responsive Eo/B progenitors in high-risk infants in relation to ARI outcomes suggests a mechanism for the increased severity of inflammatory responses in these subjects following viral infection.

Clathrin-independent endocytosis used by the IL-2 receptor is regulated by Rac1, Pak1 and Pak2

There are several endocytic pathways, which are either dependent on or independent of clathrin. This study focuses on a poorly characterized mechanism-clathrin- and caveolae-independent endocytosis-used by the interleukin-2 receptor beta (IL-2R beta). We address the question of its regulation in comparison with the clathrin-dependent pathway. First, we show that Ras-related C3 botulinum toxin substrate 1 (Rac1) is specifically required for IL-2R beta entry, and we identify p21-activated kinases (Paks) as downstream targets. By RNA interference, we show that Pak1 and Pak2 are both necessary for IL-2R beta uptake, in contrast to the clathrin-dependent route. We observe that cortactin, a partner of actin and dynamin-two essential endocytic factors-is required for IL-2R beta uptake. Furthermore, we find that cortactin acts downstream from Paks, suggesting control of its function by these kinases. Thus, we describe a cascade composed of Rac1, Paks and cortactin specifically regulating IL-2R beta internalization. This study indicates Paks as the first specific regulators of the clathrin-independent endocytosis pathway.

Retinal degeneration in experimental coronavirus retinopathy (ECOR) is associated with increased TNF-alpha, soluble TNFR2 and altered TNF-alpha signaling

Experimental coronavirus retinopathy (ECOR) is a virally triggered model of retinal degeneration composed of both genetic and autoimmune components. Since TNF-alpha plays a role in immune-mediated processes we evaluated the levels of TNF-alpha/TNF-alpha receptors and the downstream signaling molecule nitric oxide (NO) during disease in both retinal degeneration susceptible BALB/c and degeneration resistant CD-1 mice. Following coronavirus injection, TNF-alpha mRNA was detected at higher levels within the retinas, and concentrations of TNF-alpha (p<0.005) and sTNFR1 (p<0.0005) proteins were increased within the sera of BALB/c but not CD-1 mice. While concentrations of sTNFR2 proteins were elevated in both BALB/c (p<0.00005) and CD-1 (p<0.005) mice compared to controls, concentrations were higher in BALB/c mice (p<0.0005). Gene expression of iNOS while initially high in BALB/c mice decreased during the acute phase of infection, while it increased in CD-1 mice. These trends are attributable to differences in monocyte TNFR2 release (p<0.0005) between the strains since sTNFR2 decreased (p<0.01) levels of NO production. These studies demonstrate that retinal degeneration following viral infection is associated with increased release of TNF-alpha/TNF receptors combined with a down-regulation of NO. Furthermore they suggest that these molecules are involved in alterations in immune response leading to autoimmune reactivity.

Profile of soluble cytokine receptors in Crohn's disease

INTRODUCTION

Soluble cytokine receptors (sCRs) modulate the in vivo activity of cytokines. Deficient sCR production could participate in the pathogenesis and course of Crohn's disease (CD). The aim of the study was to examine the profile of sCRs in CD patients and their modulation by infliximab and corticosteroids.

METHODS

We prospectively examined active CD patients (aCD) treated with either infliximab (n = 21) or corticosteroids (n = 9), CD patients in clinical remission (rCD, n = 20), ulcerative colitis patients (UC, n = 24), and healthy subjects (HS, n = 15). Cultures of colonic biopsies were also examined from CD inflamed (n = 8), CD non-inflamed (n = 7), and healthy mucosa (n = 8). Levels of tumour necrosis factor alpha (TNF-alpha), soluble TNF receptor I (sTNFRI), soluble TNF receptor II (sTNFRII), interleukin 1beta (IL-1beta), soluble IL-1 receptor I (sIL-1RI), soluble IL-1 receptor II (sIL-1RII), IL-6, soluble IL-6 receptor (sIL-6R), and sgp130 were measured using ELISA.

RESULTS

Higher levels of sTNFRI (p<0.05, p<0.01), sTNFRII (p<0.01, p<0.01), sIL-1RI (p<0.05, NS), IL-6 (p<0.01, p<0.01), and sIL-6R (p<0.05, NS) were observed in aCD compared with rCD and HS. Interestingly, sIL-1RII (p<0.05, p<0.01) and sgp130 (p<0.01, p<0.01) were profoundly decreased in aCD compared with rCD and HS, and were negatively correlated with CRP. Deficient production of sIL-1RII was specific to CD (not observed in ulcerative colitis), and was further confirmed at the mucosal level. Infliximab decreased sTNFRII at one and four weeks (p<0.05) and enhanced sIL-6R levels at one week (p<0.05). Corticosteroids increased sIL-1RII levels at one week (p<0.05).

CONCLUSION

CD is associated with dysregulated production of sCRs. Deficiency in sIL-1RII and sgp130 may be essential to CD pathogenesis. Their replacement through the use of fusion proteins could represent future alternative therapeutic strategies for CD.

Imbalance between interleukin-1 agonists and antagonists: relationship to severity of inflammatory bowel disease

Interleukin (IL)-1 is a key mediator in the pathogenesis of inflammatory bowel disease (IBD). Naturally occurring IL-1 modulators include IL-1 receptor antagonist (IL-1Ra), IL-1 soluble receptor Type I (IL-1sRI), IL-1sRII and IL-1 receptor accessory protein (AcP). Systemic and mucosal levels of IL-1 soluble receptors remain unknown in IBD. Plasma or colonic tissues were obtained from 185 consecutive unselected patients with Crohn's disease (CD) or ulcerative colitis (UC) and from 52 control subjects. Plasma and colonic explant culture supernatants were assessed for IL-1alpha, IL-1beta, IL-1Ra, IL-1sRI and IL-1sRII. Plasma IL-1Ra levels were higher in UC (+93%) than in healthy subjects. IL-1alpha and IL-1beta were not detected. IL-1sRII levels were marginally lower in CD (-10%) and UC (-9%), whereas IL-1sRI levels were elevated in CD (+28%) only. Plasma IL-1sRI levels correlated positively (P < 0.01) with Crohn's disease activity index (r = 0.53), C-reactive protein (r = 0.46) and alpha1-acid glycoprotein (r = 0.42). In colonic explant cultures, IL-1alpha and IL-1Ra levels were elevated in non-lesional (+233% and +185% respectively) and lesional CD (+353% and +1069%), lesional UC (+604% and +1138%), but not in non-lesional UC. IL-1beta was elevated in lesional UC (+152%) and CD (+128%). In contrast, IL-1sRII levels were elevated in non-lesional CD (+65%), but remained unchanged in lesional CD, non-lesional and lesional UC. IL-1sRI levels did not differ between patient and control groups. These results indicate that (i) the proinflammatory moiety IL-1sRI is a systemic marker of inflammation and activity in CD and (ii) local shedding of the functional antagonist IL-1sRII may dampen colonic inflammation in CD, but not in UC.

Differential cytokine expression of human retinal pigment epithelial cells in response to stimulation by C5a

Human retinal pigment epithelial (RPE) cells form part of the blood-retina barrier where they potentially can regulate leucocyte function. RPE cells are known to secrete several cytokines in response to stimulation by other cytokines. Anaphylatoxin C5a, a potent inflammatory mediator produced during complement activation, binds to G-protein coupled C5a receptors (C5aR) on monocytes/macrophages and releases various cytokines from the cells. We previously reported that the human RPE cell line ARPE-19 possesses C5aR and expresses IL-8 mRNA in response to C5a stimulation. In this study, we used a primary human RPE cell line (RPE43) and found that C5a induces increased expression of IL-1beta, IL-6, MCP-1 and GM-CSF mRNAs as well as IL-8 mRNA. ARPE-19 cells showed similar increases in the same cytokines. Interestingly, the kinetics of expression of the various cytokines differed. These results provide further evidence that C5a stimulation of RPE cells may play a role in regulating leucocyte function during ocular inflammation in which there is complement activation.

Cell receptors and cell signalling

All cells in a multicellular organism are constantly exposed to a variety of extracellular signals that they need to interpret and translate into an appropriate response to their environment. These signals can be soluble factors generated locally (for example, synaptic transmission) or distantly (for example, hormones and growth factors), ligands on the surface of other cells, or the extracellular matrix itself. To achieve this, cells maintain a diversity of receptors on their surface that respond specifically to individual stimuli. These receptors fall into families, based primarily on the way in which they generate the intracellular signals that give rise to the particular functional responses. Moreover, the activity of a given receptor can be modulated by other signalling pathways in a variety of ways, generating the flexibility required of such a complex system. This review aims to describe the function of the major classes of receptor, including G protein coupled receptors, receptor tyrosine kinases, ligand gated ion channels, integrins, and cytokine receptors, and to demonstrate the "crosstalk" that exists between these systems.

Cloning of the murine thymic stromal lymphopoietin (TSLP) receptor: Formation of a functional heteromeric complex requires interleukin 7 receptor

The cellular receptor for murine thymic stromal lymphopoietin (TSLP) was detected in a variety of murine, but not human myelomonocytic cell lines by radioligand binding. cDNA clones encoding the receptor were isolated from a murine T helper cell cDNA library. TSLP receptor (TSLPR) is a member of the hematopoietin receptor family. Transfection of TSLPR cDNA resulted in only low affinity binding. Cotransfection of the interleukin 7 (IL-7)Ralpha chain cDNA resulted in conversion to high affinity binding. TSLP did not activate cells from IL-7Ralpha(-/)- mice, but did activate cells from gammac(-/)- mice. Thus, the functional TSLPR requires the IL-7Ralpha chain, but not the gammac chain for signaling.

Essential role for the p55 tumor necrosis factor receptor in regulating hematopoiesis at a stem cell level

Hematopoietic stem cell (HSC) self-renewal is a complicated process, and its regulatory mechanisms are poorly understood. Previous studies have identified tumor necrosis factor (TNF)-alpha as a pleiotropic cytokine, which, among other actions, prevents various hematopoietic progenitor cells from proliferating and differentiating in vitro. However, its role in regulating long-term repopulating HSCs in vivo has not been investigated. In this study, mice deficient for the p55 or the p75 subunit of the TNF receptor were analyzed in a variety of hematopoietic progenitor and stem cell assays. In older p55(-/-) mice (>6 mo), we identified significant differences in their hematopoietic system compared with age-matched p75(-/-) or wild-type counterparts. Increased marrow cellularity and increased numbers of myeloid and erythroid colony-forming progenitor cells (CFCs), paralleled by elevated peripheral blood cell counts, were found in p55-deficient mice. In contrast to the increased myeloid compartment, pre-B CFCs were deficient in older p55(-/-) mice. In addition, a fourfold decrease in the number of HSCs could be demonstrated in a competitive repopulating assay. Secondary transplantations of marrow cells from primary recipients of p55(-/-) marrow revealed impaired self-renewal ability of p55-deficient HSCs. These data show that, in vivo, signaling through the p55 subunit of the TNF receptor is essential for regulating hematopoiesis at the stem cell level.