Decoy receptors: a strategy to regulate inflammatory cytokines and chemokines

Human amnion epithelial cells do not abrogate pulmonary fibrosis in mice with impaired macrophage function

Since current treatments for both acute and chronic lung diseases are less than ideal, there has been recent interest in the use of cell-based therapies for inflammatory lung disease. Specifically, human amnion epithelial cells (hAECs) have been shown to reduce bleomycin-induced lung injury and prevent subsequent loss of respiratory function, primarily through modulation of the host immune response. The precise mechanisms of this effect remain unclear. We aimed to investigate the potential of hAECs to mitigate bleomycin-induced lung injury in surfactant protein C deficient (Sftpc(−/−)) mice, which are highly susceptible to pulmonary injury as a result of impairment of macrophage function. Primary hAECs were administered to wild-type (Sftpc(+/+)) and Sftpc(−/−) mice 24 h after exposure to bleomycin. Compared to Sftpc(+/+) mice receiving bleomycin alone, Sftpc(+/+) mice administered hAECs 24 h after bleomycin exposure had decreased expression of proinflammatory genes, decreased macrophage and neutrophil infiltration, fibrosis, collagen content, and α-smooth muscle actin as well as a significant improvement in lung function. Compared to Sftpc(−/−) mice given bleomycin alone, Sftpc(−/−) mice administered hAECs 24 h after bleomycin did not have a decrease in inflammatory gene expression or a reduction in macrophage pulmonary infiltration. Subsequently, Sftpc(−/−) mice did not show any decrease in pulmonary fibrosis or improvement of lung function after hAEC administration. The ability of hAECs to mitigate bleomycin-induced lung injury is abolished in Sftpc(−/−) mice, suggesting that hAECs require normal host macrophage function to exert their reparative effects.

IL-1 receptor 2 (IL-1R2) and its role in immune regulation

The cytokine IL-1 is critical to the pathogenesis of a variety of human conditions and diseases. Unlike most other cytokines, IL-1 is counterbalanced by two endogenous inhibitors. The functional significance of IL-1 receptor antagonist (IL-1RA) is well documented due to the clinical utilization of the recombinant human IL-1RA analog, anakinra. In contrast, much less is known about the type 2 IL-1 receptor (IL-1R2), which acts as a decoy receptor for IL-1. While IL-1R2 is structurally similar to the type 1 IL-1 receptor (IL-1R1) responsible for IL-1 signal transduction, its truncated cytoplasmic domain and lack of Toll-IL-1 receptor (TIR) region renders IL-1R2 incapable of transmembrane signaling. IL-1R2 competes with IL-1R1 for ligands and for the IL-1R1 co-receptor, IL-1 receptor accessory protein (IL-1RAP). Additionally, IL-1R2 exists in both a membrane bound and soluble form (sIL-1R2) that has biological properties similar to both a decoy receptor and a binding protein. Thus far, IL-1R2 has been implicated in arthritis, endometriosis, organ transplantation, sepsis/sickness behavior, diabetes, atherosclerosis, autoimmune inner ear disease (AIED), Alzheimer's disease and ulcerative colitis. In this review, we will detail the functional properties of IL-1R2 and examine its role in human disease.

IL-1 and T Helper Immune Responses

CD4 T cells play a critical role in mediating adaptive immunity to a variety of pathogens as well as in tumor immunity. If not adequately regulated, CD4 T cells can be also involved in autoimmunity, asthma, and allergic responses. During TCR activation in a particular cytokine milieu, naïve CD4 T cells may differentiate into one of several lineages of T helper (Th) cells, including Th1, Th2, and Th17, as defined by their pattern of cytokine production and function. IL-1, the prototypic proinflammatory cytokine, has been shown to influence growth and differentiation of immunocompetent lymphocytes. The differential expression of IL-1RI on human CD4 T cell subsets confers distinct capacities to acquire specific effector functions. In this review, we summarize the role of IL-1 on CD4 T cells, in terms of differentiation, activation, and maintenance or survival.

Mouse neutrophils express the decoy type 2 interleukin-1 receptor (IL-1R2) constitutively and in acute inflammatory conditions

The proinflammatory activities of IL-1 are tightly controlled at different levels. IL-1R2 acts as a decoy receptor and has been shown to regulate the biological effects of IL-1 in vitro and in vivo. However, little is known about its natural expression in the mouse in physiologic and pathologic conditions. In this study, we examined IL-1R2 mRNA and protein expression in isolated cells and tissues in response to different stimulatory conditions. Data obtained using ex vivo CD11b(+)Ly6G(+) peripheral blood cells and in vitro-differentiated CD11b(+)Ly6G(+) BMG indicated that neutrophils are the major source of constitutively expressed IL-1R2 in the mouse. The expression of IL-1R2 on BMG and ex vivo Ly6G(+) peripheral blood cells was highly up-regulated by HC. IL-1R2 pull-down experiments showed that mouse rIL-1β binds to BMG IL-1R2, whereas binding of IL-1Ra could not be detected. Furthermore, LPS treatment induced shedding of IL-1R2 from the neutrophil membrane in vitro and in vivo, executed mainly by ADAM17. Finally, in in vivo models of inflammation, including thioglycolate-induced acute peritonitis and acute lung injury, infiltrating Ly6G(+) neutrophils, expressed IL-1R2. Our data show that in the mouse, neutrophils mainly express the decoy receptor IL-1R2 under naïve and inflammatory conditions. These data suggest that neutrophils may contribute to the resolution of acute inflammation.

A secreted decoy of InR antagonizes insulin/IGF signaling to restrict body growth in Drosophila

Members of the insulin peptide family have conserved roles in the regulation of growth and metabolism in a wide variety of metazoans. Drosophila insulin-like peptides (Dilps) promote tissue growth through the single insulin-like receptor (InR). Despite the important role of Dilps in nutrient-dependent growth control, the molecular mechanism that regulates the activity of circulating Dilps is not well understood. Here, we report the function of a novel secreted decoy of InR (SDR) as a negative regulator of insulin signaling. SDR is predominantly expressed in glia and is secreted into the hemolymph. Larvae lacking SDR grow at a faster rate, thereby increasing adult body size. Conversely, overexpression of SDR reduces body growth non-cell-autonomously. SDR is structurally similar to the extracellular domain of InR and interacts with several Dilps in vitro independent of Imp-L2, the ortholog of the mammalian insulin-like growth factor-binding protein 7 (IGFBP7). We further demonstrate that SDR is constantly secreted into the hemolymph independent of nutritional status and is essential for adjusting insulin signaling under adverse food conditions. We propose that Drosophila uses a secreted decoy to fine-tune systemic growth against fluctuations of circulating insulin levels.

Duplicate abalone egg coat proteins bind sperm lysin similarly, but evolve oppositely, consistent with molecular mimicry at fertilization

Sperm and egg proteins constitute a remarkable paradigm in evolutionary biology: despite their fundamental role in mediating fertilization (suggesting stasis), some of these molecules are among the most rapidly evolving ones known, and their divergence can lead to reproductive isolation. Because of strong selection to maintain function among interbreeding individuals, interacting fertilization proteins should also exhibit a strong signal of correlated divergence among closely related species. We use evidence of such molecular co-evolution to target biochemical studies of fertilization in North Pacific abalone (Haliotis spp.), a model system of reproductive protein evolution. We test the evolutionary rates (d_N/d_S) of abalone sperm lysin and two duplicated egg coat proteins (VERL and VEZP14), and find a signal of co-evolution specific to ZP-N, a putative sperm binding motif previously identified by homology modeling. Positively selected residues in VERL and VEZP14 occur on the same face of the structural model, suggesting a common mode of interaction with sperm lysin. We test this computational prediction biochemically, confirming that the ZP-N motif is sufficient to bind lysin and that the affinities of VERL and VEZP14 are comparable. However, we also find that on phylogenetic lineages where lysin and VERL evolve rapidly, VEZP14 evolves slowly, and vice versa. We describe a model of sexual conflict that can recreate this pattern of anti-correlated evolution by assuming that VEZP14 acts as a VERL mimic, reducing the intensity of sexual conflict and slowing the co-evolution of lysin and VERL.

Interacting sperm and egg proteins must co-evolve to maintain compatibility at fertilization, so their divergence among species should be correlated—lineages with rapidly evolving sperm proteins should have rapidly evolving egg proteins. We use this expectation to target biochemical studies of fertilization in a model system (abalone). We study a discrete functional domain (ZP-N) found in a pair of duplicated egg coat proteins, and we find the ZP-N motif from both proteins bind sperm lysin (a protein important for sperm passage of the egg coat) in a similar fashion. ZP-N is a feature of vertebrate and invertebrate egg coat proteins, as well as yeast mating recognition proteins, demonstrating its broad significance in sexual reproduction. Unexpectedly, we find that the ZP-N motifs of VEZP14 and VERL exhibit inverse patterns of co-evolution with lysin, suggesting that these duplicates may have opposite functions in fertilization. Using computer simulations, we model a novel explanation for this pattern whereby VEZP14 acts as a decoy of VERL in order to decrease the effective amount of sperm lysin and slow the rate of fertilization. Such molecular mimicry could complement other well-established fertilization blocks that females use to control rates of fertilization and limit polyspermy.

TIR8/SIGIRR is an Interleukin-1 Receptor/Toll Like Receptor Family Member with Regulatory Functions in Inflammation and Immunity

Interleukin-1R like receptors (ILRs) and Toll Like Receptors (TLRs) are key receptors of innate immunity, inflammation, and orientation of the adaptive response. They belong to a superfamily characterized by the presence of a conserved intracellular domain, the Toll/IL-1R (TIR) domain, which is involved in the activation of a signaling cascade leading to activation of transcription factors associated to inflammation. The activation of inflammatory responses and immunity by ILRs or TLRs signaling is potentially detrimental for the host in acute and chronic conditions and is tightly regulated at different levels by receptor antagonists, decoy receptors or signaling molecules, and miRNAs. Recent evidence suggests that the ILRs family member TIR8 (also known as SIGIRR) is a regulatory protein acting intracellularly to inhibit ILRs and TLRs signaling. In particular, current evidence suggests that TIR8/SIGIRR dampens TLRs-mediated activation and inhibits signaling receptor complexes of IL-1 family members associated with Th1 (IL-18), Th2 (IL-33), and Th17 (IL-1) differentiation. Studies with Tir8/Sigirr-deficient mice showed that the ability to dampen signaling from ILRs and TLRs family members makes TIR8/SIGIRR a key regulator of inflammation. Here, we summarize our current understanding of the structure and function of TIR8/SIGIRR, focusing on its role in different pathological conditions, ranging from infectious and sterile inflammation, to autoimmunity and cancer-related inflammation.

Allosteric competitive inactivation of hematopoietic CSF-1 signaling by the viral decoy receptor BARF1

Hematopoietic human colony-stimulating factor 1 (hCSF-1) is essential for innate and adaptive immunity against viral and microbial infections and cancer. The human pathogen Epstein-Barr virus secretes the lytic-cycle protein BARF1 that neutralizes hCSF-1 to achieve immunomodulation. Here we show that BARF1 binds the dimer interface of hCSF-1 with picomolar affinity, away from the cognate receptor-binding site, to establish a long-lived complex featuring three hCSF-1 at the periphery of the BARF1 toroid. BARF1 locks dimeric hCSF-1 into an inactive conformation, rendering it unable to signal via its cognate receptor on human monocytes. This reveals a new functional role for hCSF-1 cooperativity in signaling. We propose a new viral strategy paradigm featuring an allosteric decoy receptor of the competitive type, which couples efficient sequestration and inactivation of the host growth factor to abrogate cooperative assembly of the cognate signaling complex.

In vitro generation of monocyte-derived macrophages under serum-free conditions improves their tumor promoting functions

The tumor promoting role of M2 macrophages has been described in in vivo models and the presence of macrophages in certain tumor types has been linked to a poor clinical outcome. In light of burgeoning activities to clinically develop new therapies targeting tumor-associated macrophages (TAMs), reliable in vitro models faithfully mimicking the tumor promoting functions of TAMs are required. Generation and activation of human monocyte-derived macrophages (MDM) in vitro, described as M1 or M2 macrophages attributed with tumoricidal or tumor-promoting functions, respectively, has been widely reported using mainly serum containing culture methods. In this study, we compared the properties of macrophages originating from monocytes cultured either in media containing serum together with M-CSF for M2 and GM-CSF for M1 macrophages or in serum-free media supplemented with M-CSF or GM-CSF and cytokines such as IL-4, IL-10 to induce activated M2 or LPS together with IFN-γ to generate activated M1 phenotype. We observed differences in cell morphology as well as increased surface receptor expression levels in serum-containing culture whereas similar or higher cytokine production levels were detected under serum-free culture conditions. More importantly, MDM differentiated under serum-free conditions displayed enhanced tumoricidal activity for M1 and tumor promoting property for M2 macrophages in contrast to MDM differentiated in the presence of serum. Moreover, evaluation of MDM phagocytic activity in serum free condition resulted in greater phagocytic properties of M2 compared to M1. Our data therefore confirm the tumor promoting properties of M2 macrophages in vitro and encourage the targeting of TAMs for cancer therapy.

Impaired alternative macrophage differentiation of peripheral blood mononuclear cells from obese subjects

Visceral obesity is a chronic, low-grade inflammatory disease that predisposes people to the metabolic syndrome, type 2 diabetes and its cardiovascular complications. Adipose tissue is not a passive storehouse for fat, but an endocrine organ synthesizing and releasing a variety of bioactive molecules, some of which are produced by infiltrated immune-inflammatory cells including macrophages. Two different subpopulations of macrophages have been identified in adipose tissue: pro-inflammatory 'classical' M1 and anti-inflammatory 'alternative' M2 macrophages, and their ratio is suggested to influence the metabolic complications of obesity. These macrophages derive primarily from peripheral blood mononuclear cells (PBMCs). We hypothesised that obesity and the metabolic syndrome modulate PBMC functions. Therefore, alteration of the monocyte response, and more specifically their ability to differentiate toward alternative anti-inflammatory macrophages, was assessed in PBMCs isolated from lean and obese subjects with or without alterations in glucose homeostasis. Our results indicate that PBMCs from obese subjects have an altered expression of M2 markers and that their monocytes are less susceptible to differentiate toward an alternative phenotype. Thus PBMCs in obesity are programmed, which may contribute to the inflammatory dysregulation and increased susceptibility to inflammatory diseases in these patients.

Interleukin-1 (IL-1) family of cytokines: role in type 2 diabetes

Cytokines are small cell signaling protein molecules which encompass a large and diverse family. They consist of immunomodulating agents such as interleukins and inteferons. Virtually all nucleated cells, especially endo/epithelial cells and macrophages are potent producers of IL-1, IL-6 and TNF-α. IL-1 family is a group of cytokines which play a central role in the regulation of immune and inflammatory responses. Type 2 diabetes (T2D) has been recognized as an immune mediated disease leading to impaired insulin signaling and selective destruction of insulin producing β-cells in which cytokines play an important role. Disturbance of anti-inflammatory response could be a critical component of the chronic inflammation resulting in T2D. IL-1 family of cytokines has important roles in endocrinology and in the regulation of responses associated with inflammatory stress. The IL-1 family consists of two pro-inflammatory cytokines, IL-1α and IL-1β, and a naturally occurring anti-inflammatory agent, the IL-1 receptor antagonist (IL-1Ra or IL-1RN). This review is an insight into the different types of cytokines belonging to IL-1 family, their modes of action and association with Type 2 diabetes.

Interleukin-1 participates in the classical and alternative activation of microglia/macrophages after spinal cord injury

Background

Microglia and macrophages (MG/MΦ) have a diverse range of functions depending on unique cytokine stimuli, and contribute to neural cell death, repair, and remodeling during central nervous system diseases. While IL-1 has been shown to exacerbate inflammation, it has also been recognized to enhance neuroregeneration. We determined the activating phenotype of MG/MΦ and the impact of IL-1 in an in vivo spinal cord injury (SCI) model of IL-1 knock-out (KO) mice. Moreover, we demonstrated the contribution of IL-1 to both the classical and alternative activation of MG in vitro using an adult MG primary culture.

Methods

SCI was induced by transection of the spinal cord between the T9 and T10 vertebra in wild-type and IL-1 KO mice. Locomotor activity was monitored and lesion size was determined for 14 days. TNFα and Ym1 levels were monitored to determine the MG/MΦ activating phenotype. Primary cultures of MG were produced from adult mice, and were exposed to IFNγ or IL-4 with and without IL-1β. Moreover, cultures were exposed to IL-4 and/or IL-13 in the presence and absence of IL-1β.

Results

The locomotor activity and lesion area of IL-1 KO mice improved significantly after SCI compared with wild-type mice. TNFα production was significantly suppressed in IL-1 KO mice. Also, Ym1, an alternative activating MG/MΦ marker, did not increase in IL-1 KO mice, suggesting that IL-1 contributes to both the classical and alternative activation of MG/MΦ. We treated primary MG cultures with IFNγ or IL-4 in the presence and absence of IL-1β. Increased nitric oxide and TNFα was present in the culture media and increased inducible NO synthase was detected in cell suspensions following co-treatment with IFNγ and IL-1β. Expression of the alternative activation markers Ym1 and arginase-1 was increased after exposure to IL-4 and further increased after co-treatment with IL-4 and IL-1β. The phenotype was not observed after exposure of cells to IL-13.

Conclusions

We demonstrate here in in vivo experiments that IL-1 suppressed SCI in a process mediated by the reduction of inflammatory responses. Moreover, we suggest that IL-1 participates in both the classical and alternative activation of MG in in vivo and in vitro systems.

CX3CL1/fractalkine is a novel regulator of normal and malignant human B cell function

CX(3)CL1, or fractalkine, the unique member of the CX(3)C chemokine family, exists as a transmembrane glycoprotein, as well as in soluble form, each mediating different biological activities, and is constitutively expressed in many hematopoietic and nonhematopoietic tissues. CX(3)CR1, the CX(3)CL1 exclusive receptor, is a classical GPCR, expressed on NK cells, CD14(+) monocytes, and some subpopulation of T cells, B cells, and mast cells. A recent paper by our group has demonstrated for the first time that highly purified human B cells from tonsil and peripheral blood expressed CX(3)CR1 at mRNA and protein levels. In particular, tonsil naïve, GC, and memory B cells expressed CX(3)CR1, but only GC centrocytes were attracted by soluble CX(3)CL1, which with its receptor, are also involved in the pathogenesis of several inflammatory disorders, as well as of cancer. Previous studies have shown that CX(3)CR1 is up-regulated in different types of B cell lymphoma, as well as in B-CLL. Recently, we have demonstrated that the CX(3)CL1/CX(3)CR1 axis is involved in the interaction of B-CLL cells with their microenvironment. Taken together, our data delineate a novel role for the CX(3)CL1/CX(3)CR1 complex in the biology of normal B cells and B-CLL cells. These topics are the subject of this review article.

CCL2 binding is CCR2 independent in primary adult human astrocytes

Chemokines are low relative molecular mass proteins, which have chemoattractant actions on many cell types. The chemokine, CCL2, has been shown to play a major role in the recruitment of monocytes in central nervous system (CNS) lesions in multiple sclerosis (MS). Since resident astrocytes constitute a major source of chemokine synthesis including CCL2, we were interested to assess the regulation of CCL2 by astrocytes. We showed that CCL2 bound to the cell surface of astrocytes and binding was not modulated by inflammatory conditions. However, CCR2 protein was not detected nor was activation of the classical CCR2 downstream signaling pathways. Recent studies have shown that non-signaling decoy chemokine receptors bind and modulate the expression of chemokines at site of inflammation. Here, we show that the D6 chemokine decoy receptor is constitutively expressed by primary human adult astrocytes at both mRNA and protein level. In addition, CCL3, which binds to D6, but not CCL19, which does not bind to D6, displaced CCL2 binding to astrocytes; indicating that CCL2 may bind to this cell type via the D6 receptor. Our results suggest that CCL2 binding to primary adult human astrocytes is CCR2-independent and is likely to be mediated via the D6 decoy chemokine receptor. Therefore we propose that astrocytes are implicated in both the establishment of chemokine gradients for the migration of leukocytes into and within the CNS and in the regulation of CCL2 levels at inflammatory sites in the CNS.

IL-1 receptor/Toll-like receptor signaling in infection, inflammation, stress and neurodegeneration couples hyperexcitability and seizures

Increasing evidence supports the involvement of immune and inflammatory processes in the etiopathogenesis of seizures. In particular, activation of innate immune mechanisms and the subsequent inflammatory responses, that are induced in the brain by infection, febrile seizures, neurotrauma, stroke are well documented conditions associated with acute symptomatic seizures and with a high risk of developing epilepsy. A decade ago, pharmacological experiments showed that elevated brain levels of the anti-inflammatory molecule IL-1 receptor antagonist reduced seizures in epilepsy models. This observation, together with the evidence of in situ induction of inflammatory mediators and their receptors in experimental and human epileptogenic brain tissue, established the proof-of-concept evidence that the activation of innate immunity and inflammation in the brain are intrinsic features of the pathologic hyperexcitable tissue. Recent breakthroughs in understanding the molecular organization of the innate immune system first in macrophages, then in the different cell types of the CNS, together with pharmacological and genetic studies in epilepsy models, showed that the activation of IL-1 receptor/Toll-like receptor (IL-1R/TLR) signaling significantly contributes to seizures. IL-1R/TLR mediated pro-excitatory actions are elicited in the brain either by mimicking bacterial or viral infections and inflammatory responses, or via the action of endogenous ligands. These ligands include proinflammatory cytokines, such as IL-1beta, or danger signals, such as HMGB1, released from activated or injured cells. The IL-1R/TLR signaling mediates rapid post-translational changes in voltage- and ligand-gated ion channels that increase excitability, and transcriptional changes in genes involved in neurotransmission and synaptic plasticity that contribute to lower seizure thresholds chronically. The anticonvulsant effects of inhibitors of the IL-1R/TLR signaling in various seizures models suggest that this system could be targeted to inhibit seizures in presently pharmaco-resistant epilepsies.

Coronary atherosclerosis is associated with macrophage polarization in epicardial adipose tissue

OBJECTIVES

The purpose of this report was to assess the link between macrophage polarization in epicardial adipose tissue and atherosclerosis in patients with coronary artery disease (CAD).

BACKGROUND

Macrophage accumulation enhances chronic inflammation in adipose tissue, but macrophage phenotypic change in human epicardial adipose tissue and its role in atherogenesis are unknown.

METHODS

Samples were obtained from epicardial and subcutaneous adipose tissue during elective cardiac surgery (CAD, n = 38; non-CAD, n = 40). Infiltration of M1/M2 macrophages was investigated by immunohistochemical staining with antibodies against CD11c and CD206, respectively. Expression of pro- and anti-inflammatory adipocytokines in adipose tissue was evaluated by real-time quantitative polymerase chain reaction.

RESULTS

Infiltration of macrophages and expression of pro- and anti-inflammatory cytokines were enhanced in epicardial fat of patients with CAD compared with that in non-CAD patients (p < 0.05). The ratio of M1/M2 macrophages was positively correlated with the severity of CAD (r = 0.312, p = 0.039). Furthermore, the expression of pro-inflammatory cytokines was positively correlated, and the expression of anti-inflammatory cytokines was negatively correlated with the ratio of M1/M2 macrophages in epicardial adipose tissue of CAD patients. By contrast, there was no significant difference in macrophage infiltration and cytokine expression in subcutaneous adipose tissue between the CAD and non-CAD groups.

CONCLUSIONS

The ratio of M1/M2 macrophages in epicardial adipose tissue of CAD patients is changed compared with that in non-CAD patients. Human coronary atherosclerosis is associated with macrophage polarization in epicardial adipose tissue.

Are Toll-like receptors and decoy receptors involved in the immunopathogenesis of systemic lupus erythematosus and lupus-like syndromes?

In this paper we focus our attention on the role of two families of receptors, Toll-like receptors (TLR) and decoy receptors (DcR) involved in the generation of systemic lupus erythematosus (SLE) and lupus-like syndromes in human and mouse models. To date, these molecules were described in several autoimmune disorders such as rheumatoid arthritis, antiphospholipids syndrome, bowel inflammation, and SLE. Here, we summarize the findings of recent investigations on TLR and DcR and their role in the immunopathogenesis of the SLE.

Interaction of the receptor FGFRL1 with the negative regulator Spred1

FGFRL1 is a member of the fibroblast growth factor receptor family. It plays an essential role during branching morphogenesis of the metanephric kidneys, as mice with a targeted deletion of the Fgfrl1 gene show severe kidney dysplasia. Here we used the yeast two-hybrid system to demonstrate that FGFRL1 binds with its C-terminal, histidine-rich domain to Spred1 and to other proteins of the Sprouty/Spred family. Members of this family are known to act as negative regulators of the Ras/Raf/Erk signaling pathway. Truncation experiments further showed that FGFRL1 interacts with the SPR domain of Spred1, a domain that is shared by all members of the Sprouty/Spred family. The interaction could be verified by coprecipitation of the interaction partners from solution and by codistribution at the cell membrane of COS1 and HEK293 cells. Interestingly, Spred1 increased the retention time of FGFRL1 at the plasma membrane where the receptor might interact with ligands. FGFRL1 and members of the Sprouty/Spred family belong to the FGF synexpression group, which also includes FGF3, FGF8, Sef and Isthmin. It is conceivable that FGFRL1, Sef and some Sprouty/Spred proteins work in concert to control growth factor signaling during branching morphogenesis of the kidneys and other organs.

Biology of FGFRL1, the fifth fibroblast growth factor receptor

FGFRL1 (fibroblast growth factor receptor like 1) is the most recently discovered member of the FGFR family. It contains three extracellular Ig-like domains similar to the classical FGFRs, but it lacks the protein tyrosine kinase domain and instead contains a short intracellular tail with a peculiar histidine-rich motif. The gene for FGFRL1 is found in all metazoans from sea anemone to mammals. FGFRL1 binds to FGF ligands and heparin with high affinity. It exerts a negative effect on cell proliferation, but a positive effect on cell differentiation. Mice with a targeted deletion of the Fgfrl1 gene die perinatally due to alterations in their diaphragm. These mice also show bilateral kidney agenesis, suggesting an essential role for Fgfrl1 in kidney development. A human patient with a frameshift mutation exhibits craniosynostosis, arguing for an additional role of FGFRL1 during bone formation. FGFRL1 contributes to the complexity of the FGF signaling system.

Human atherosclerotic plaque alternative macrophages display low cholesterol handling but high phagocytosis because of distinct activities of the PPARγ and LXRα pathways

RATIONALE

A crucial step in atherogenesis is the infiltration of the subendothelial space of large arteries by monocytes where they differentiate into macrophages and transform into lipid-loaded foam cells. Macrophages are heterogeneous cells that adapt their response to environmental cytokines. Th1 cytokines promote monocyte differentiation into M1 macrophages, whereas Th2 cytokines trigger an "alternative" M2 phenotype.

OBJECTIVE

We previously reported the presence of CD68(+) mannose receptor (MR)(+) M2 macrophages in human atherosclerotic plaques. However, the function of these plaque CD68(+)MR(+) macrophages is still unknown.

METHODS AND RESULTS

Histological analysis revealed that CD68(+)MR(+) macrophages locate far from the lipid core of the plaque and contain smaller lipid droplets compared to CD68(+)MR(-) macrophages. Interleukin (IL)-4-polarized CD68(+)MR(+) macrophages display a reduced capacity to handle and efflux cellular cholesterol because of low expression levels of the nuclear receptor liver x receptor (LXR)α and its target genes, ABCA1 and apolipoprotein E, attributable to the high 15-lipoxygenase activity in CD68(+)MR(+) macrophages. By contrast, CD68(+)MR(+) macrophages highly express opsonins and receptors involved in phagocytosis, resulting in high phagocytic activity. In M2 macrophages, peroxisome proliferator-activated receptor (PPAR)γ activation enhances the phagocytic but not the cholesterol trafficking pathways.

CONCLUSIONS

These data identify a distinct macrophage subpopulation with a low susceptibility to become foam cells but high phagocytic activity resulting from different regulatory activities of the PPARγ-LXRα pathways.

Global gene expression profile progression in Gaucher disease mouse models

BACKGROUND

Gaucher disease is caused by defective glucocerebrosidase activity and the consequent accumulation of glucosylceramide. The pathogenic pathways resulting from lipid laden macrophages (Gaucher cells) in visceral organs and their abnormal functions are obscure.

RESULTS

To elucidate this pathogenic pathway, developmental global gene expression analyses were conducted in distinct Gba1 point-mutated mice (V394L/V394L and D409 V/null). About 0.9 to 3% of genes had altered expression patterns (≥ ± 1.8 fold change), representing several categories, but particularly macrophage activation and immune response genes. Time course analyses (12 to 28 wk) of INFγ-regulated pro-inflammatory (13) and IL-4-regulated anti-inflammatory (11) cytokine/mediator networks showed tissue differential profiles in the lung and liver of the Gba1 mutant mice, implying that the lipid-storage macrophages were not functionally inert. The time course alterations of the INFγ and IL-4 pathways were similar, but varied in degree in these tissues and with the Gba1 mutation.

CONCLUSIONS

Biochemical and pathological analyses demonstrated direct relationships between the degree of tissue glucosylceramides and the gene expression profile alterations. These analyses implicate IFNγ-regulated pro-inflammatory and IL-4-regulated anti-inflammatory networks in differential disease progression with implications for understanding the Gaucher disease course and pathophysiology.

The role of inflammation in epilepsy

Epilepsy is the third most common chronic brain disorder, and is characterized by an enduring predisposition to generate seizures. Despite progress in pharmacological and surgical treatments of epilepsy, relatively little is known about the processes leading to the generation of individual seizures, and about the mechanisms whereby a healthy brain is rendered epileptic. These gaps in our knowledge hamper the development of better preventive treatments and cures for the approximately 30% of epilepsy cases that prove resistant to current therapies. Here, we focus on the rapidly growing body of evidence that supports the involvement of inflammatory mediators-released by brain cells and peripheral immune cells-in both the origin of individual seizures and the epileptogenic process. We first describe aspects of brain inflammation and immunity, before exploring the evidence from clinical and experimental studies for a relationship between inflammation and epilepsy. Subsequently, we discuss how seizures cause inflammation, and whether such inflammation, in turn, influences the occurrence and severity of seizures, and seizure-related neuronal death. Further insight into the complex role of inflammation in the generation and exacerbation of epilepsy should yield new molecular targets for the design of antiepileptic drugs, which might not only inhibit the symptoms of this disorder, but also prevent or abrogate disease pathogenesis.

Oxidized LDL enhances pro-inflammatory responses of alternatively activated M2 macrophages: a crucial role for Krüppel-like factor 2

OBJECTIVE

Macrophages are key players in atherogenesis because of their properties to form foam cells that produce a large variety of pro-inflammatory mediators. We addressed the potency of phenotypic different macrophages to accumulate oxidized LDL.

METHODS AND RESULTS

Surprisingly, anti-inflammatory M2 macrophages but not pro-inflammatory M1 macrophages rapidly accumulated oxidized LDL. Simultaneously, expression of Krüppel-like factor 2, a nuclear transcription factor known to suppress inflammation in endothelial cells and monocytes, decreased and the functional phenotype of M2 macrophages shifted towards a pro-inflammatory profile, characterized by higher production of IL-6, IL-8 and MCP-1 and lower expression of IL-10 upon stimulation with LPS. In contrast, Krüppel-like factor 2 expression and the phenotype of M1 macrophages remained largely unchanged upon oxidized LDL exposure. Downregulation of Krüppel-like factor 2 expression of M2 macrophages using siRNA technology led to a significant increase of LPS-induced MCP-1 secretion.

CONCLUSIONS

We show that (1) anti-inflammatory M2 macrophages are more susceptible to foam cell formation than pro-inflammatory M1 macrophages, (2) exposure to oxidized LDL renders M2 macrophages pro-inflammatory, and (3) Krüppel-like factor 2 is involved in the enhanced secretion of MCP-1 by M2 macrophages loaded with oxidized LDL. The phenotype switch of M2 macrophages from an anti- to a pro-inflammatory profile may play an important role in pathogenesis of atherosclerosis, and could represent a novel therapeutic target.

Macrophage and dendritic cell phenotypic diversity in the context of biomaterials

Macrophages (Mϕ) and dendritic cells (DCs) are critical antigen presenting cells that play pivotal roles in host responses to biomaterial implants. Although Mϕs have been widely studied for their roles in the inflammatory responses against biomaterials, the roles that DCs play in the host responses toward implanted materials have only recently been explored. DCs are of significant research interest because of the emergence of a large number of combination products that cross-traditional medical device boundaries. These products combine biomaterials with biologics, including cells, nucleic acids, and/or proteins. The biomaterial component may evoke an inflammatory response, primarily mediated by neutrophils and Mϕs, whereas the biologic component may elicit an immunogenic immune response, initiated by DCs involving lymphocyte activation. Control of Mϕ phenotypic balance from proinflammatory M1 to reparative M2 is a goal of investigators to optimize the host response to biomaterials. Similarly, control of DC phenotype from proinflammatory to toleragenic is of interest in vaccine delivery and tissue engineering/transplantation situations, respectively. This review discusses the interconnection between innate and adaptive immunity, the comparative and contrasting phenotypes and roles of Mϕs and DCs in immunity, their responses to biomaterials and the strategies to modulate their phenotype for applications in tissue engineering and vaccine delivery. Furthermore, the collaboration between and unique roles of DCs and Mϕs needs to be addressed in future studies to gain a more complete picture of host responses toward combination products.

Expression of chemokine decoy receptors and their ligands at the porcine maternal-fetal interface

Successful pregnancy requires coordinated maternal-fetal cross-talk to establish vascular connections that support conceptus growth. In pigs, two waves of spontaneous fetal loss occur and 30-40% of conceptuses are lost before parturition. Previous studies associated these losses with decreased angiogenic and increased inflammatory cytokines. Chemokines, a sub-category of cytokines, and decoy receptors control leukocyte trafficking, angiogenesis and development. The availability of chemokines is regulated by three non-signalling decoy receptors: chemokine decoy receptor (D6), Duffy antigen receptor for chemokines (DARC) and Chemocentryx decoy receptor (CCX CKR). We hypothesized that the expression of these receptors and their chemokine ligands regulate the porcine pregnancy success or failure. Here, we describe for the first time the transcription and translation of all three decoy receptors and several chemokine ligands in endometrium and trophoblast associated with healthy and arresting conceptuses at gestation day (gd) 20 and gd50. Among decoy receptors, transcripts for DARC were significantly reduced in endometrium, whereas that for CCX CKR were significantly increased in endometrium and trophoblast at gd50 arresting compared with healthy sites. However, western blot analysis revealed no differences in decoy receptor expression between healthy and arresting tissues. Transcripts for decoy receptor ligands CCL2, CCL3, CCL4, CCL5, CCL11, CCL19, CCL21, CXCL2 and CXCL8 were stable between healthy and arresting littermates. Quantification by SearchLight chemiluminescent protein array confirmed ligand expression at the protein level. These data indicate that decoy receptors and ligands are expressed at the porcine maternal-fetal interface and dysregulation of decoy receptor (DARC and CCX CKR) transcripts occurs at sites of fetal arrest.

The bovine chemokine receptors and their mRNA abundance in mononuclear phagocytes

BACKGROUND

The chemokine and chemokine receptor families play critical roles in both the healthy and diseased organism mediating the migration of cells. The chemokine system is complex in that multiple chemokines can bind to one chemokine receptor and vice versa. Although chemokine receptors have been well characterised in humans, the chemokine receptor repertoire of cattle is not well characterised and many sequences are yet to be experimentally validated.

RESULTS

We have identified and sequenced bovine homologs to all identified functional human chemokine receptors. The bovine chemokine receptors show high levels of similarity to their human counterparts and similar genome arrangements. We have also characterised an additional bovine chemokine receptor, not present in the available genome sequence of humans or the more closely related pigs or horses. This receptor shows the highest level of similarity to CCR1 but shows significant differences in regions of the protein that are likely to be involved in ligand binding and signalling. We have also examined the mRNA abundance levels of all identified bovine chemokine receptors in mononuclear phagocytic cells. Considerable differences were observed in the mRNA abundance levels of the receptors, and interestingly the identified novel chemokine receptor showed differing levels of mRNA abundance to its closest homolog CCR1. The chemokine receptor repertoire was shown to differ between monocytes, macrophages and dendritic cells. This may reflect the differing roles of these cells in the immune response and may have functional consequences for the trafficking of these cells in vivo.

CONCLUSIONS

In summary, we have provided the first characterisation of the complete bovine chemokine receptor gene repertoire including a gene that is potentially unique to cattle. Further study of this receptor and its ligands may reveal a specific role of this receptor in cattle. The availability of the bovine chemokine receptor sequences will allow further characterisation of the function of these genes and will confer wide-reaching benefits to the study of this important aspect of the bovine immune response.

Chronic inflammatory responses to microgel-based implant coatings

Inflammatory responses to implanted biomedical devices elicit a foreign body fibrotic reaction that limits device integration and performance in various biomedical applications. We examined chronic inflammatory responses to microgel conformal coatings consisting of thin films of poly(N-isopropylacrylamide) hydrogel microparticles cross-linked with poly(ethylene glycol) diacrylate deposited on poly(ethylene terephthalate) (PET). Unmodified and microgel-coated PET disks were implanted subcutaneously in rats for 4 weeks and explants were analyzed by histology and immunohistochemistry. Microgel coatings reduced chronic inflammation and resulted in a more mature/organized fibrous capsule. Microgel-coated samples exhibited 22% thinner fibrous capsules that contained 40% fewer cells compared to unmodified PET disks. Furthermore, microgel-coated samples contained significantly higher levels of macrophages (80%) than unmodified PET controls. These results demonstrate that microgel coatings reduce chronic inflammation to implanted biomaterials. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Cardiac allograft rejection: examination of the expression and function of the decoy chemokine receptor D6

BACKGROUND

Inflammatory cell recruitment during allograft rejection is driven by a group of inflammatory cytokines termed chemokines. Chemokines are presented on the surface of the vascular endothelium where they ligate specific receptors expressed on the surface of leukocytes. Recently, a group of nonsignaling chemokine receptors have been described. These bind and internalize chemokines but do not drive leukocyte migration. It is believed that these compete with classical signaling receptors to modulate inflammation.

METHODS

This study describes the first examination of the human decoy chemokine receptor D6 during rejection; D6 binds at least 12 potent proinflammatory chemokines. The expression of D6 by graft infiltrating leukocytes was examined in cardiac allografts by confocal microscopy on biopsy sections (n=19). Cytokine regulation of D6 was examined in vitro, and a chemokine scavenging assay was performed using the prototypical transplant-associated chemokine CCL5/RANTES.

RESULTS

D6 expression was found to be higher in the biopsies taken from more severe cardiac allograft rejection (P<0.01) and was predominantly localized to graft infiltrating CD45(+)CD68(+) leukocytes. In vitro studies demonstrated that the transforming growth factor-beta strongly increased the expression of D6 by monocytes, which significantly enhanced D6-mediated chemokine scavenging (by 85%, P<0.05).

CONCLUSIONS

We present the first examination of the biology of D6 during rejection and identify a transplant-associated cytokine that is able to regulate its expression. These data suggest an exciting new mechanism for the antiinflammatory actions of transforming growth factor-beta. Understanding the expression patterns of D6 may provide important insight into the regulation and control of inflammatory cell recruitment during allograft rejection.

Inflammatory bowel disease and intestinal cancer: a paradigm of the Yin-Yang interplay between inflammation and cancer

Colon cancer represents a paradigm for the connection between inflammation and cancer in terms of epidemiology and mechanistic studies in preclinical models. Key components of cancer promoting inflammation include master transcription factors (for example, nuclear factor kappaB, STAT3), proinflammatory cytokines (for example, tumor necrosis factor, interleukin-6 (IL-6)), cyclooxygenase-2 and selected chemokines (for example, CCL2). Of no less importance are mediators that keep inflammation in check, including IL-10, transforming growth factorbeta, toll-like receptor and the IL-1 receptor inhibitor TIR8/SIGIRR, and the chemokine decoy and scavenger receptor D6. Dissection of molecular pathways involved in colitis-associated cancer may offer opportunities for innovative therapeutic strategies.

The macrophage in HIV-1 infection: from activation to deactivation?

Macrophages play a crucial role in innate and adaptative immunity in response to microorganisms and are an important cellular target during HIV-1 infection. Recently, the heterogeneity of the macrophage population has been highlighted. Classically activated or type 1 macrophages (M1) induced in particular by IFN-γ display a pro-inflammatory profile. The alternatively activated or type 2 macrophages (M2) induced by Th-2 cytokines, such as IL-4 and IL-13 express anti-inflammatory and tissue repair properties. Finally IL-10 has been described as the prototypic cytokine involved in the deactivation of macrophages (dM). Since the capacity of macrophages to support productive HIV-1 infection is known to be modulated by cytokines, this review shows how modulation of macrophage activation by cytokines impacts the capacity to support productive HIV-1 infection. Based on the activation status of macrophages we propose a model starting with M1 classically activated macrophages with accelerated formation of viral reservoirs in a context of Th1 and proinflammatory cytokines. Then IL-4/IL-13 alternatively activated M2 macrophages will enter into the game that will stop the expansion of the HIV-1 reservoir. Finally IL-10 deactivation of macrophages will lead to immune failure observed at the very late stages of the HIV-1 disease.

The senescence-associated secretory phenotype: the dark side of tumor suppression

Cellular senescence is a tumor-suppressive mechanism that permanently arrests cells at risk for malignant transformation. However, accumulating evidence shows that senescent cells can have deleterious effects on the tissue microenvironment. The most significant of these effects is the acquisition of a senescence-associated secretory phenotype (SASP) that turns senescent fibroblasts into proinflammatory cells that have the ability to promote tumor progression.

Azithromycin alters macrophage phenotype and pulmonary compartmentalization during lung infection with Pseudomonas

Infection with mucoid strains of Pseudomonas aeruginosa in chronic inflammatory diseases of the airway is difficult to eradicate and can cause excessive inflammation. The roles of alternatively activated and regulatory subsets of macrophages in this pathophysiological process are not well characterized. We previously demonstrated that azithromycin induces an alternatively activated macrophage-like phenotype in vitro. In the present study, we tested whether azithromycin affects the macrophage activation status and migration in the lungs of P. aeruginosa-infected mice. C57BL/6 mice received daily doses of oral azithromycin and were infected intratracheally with a mucoid strain of P. aeruginosa. The properties of macrophage activation, immune cell infiltration, and markers of pulmonary inflammation in the lung interstitial and alveolar compartments were evaluated postinfection. Markers of alternative macrophage activation were induced by azithromycin treatment, including the surface expression of the mannose receptor, the upregulation of arginase 1, and a decrease in the production of proinflammatory cytokines. Additionally, azithromycin increased the number of CD11b(+) monocytes and CD4(+) T cells that infiltrated the alveolar compartment. A predominant subset of CD11b(+) cells was Gr-1 positive (Gr-1(+)), indicative of a subset of cells that has been shown to be immunoregulatory. These differences corresponded to decreases in neutrophil influx into the lung parenchyma and alteration of the characteristics of peribronchiolar inflammation without any change in the clearance of the organism. These results suggest that the immunomodulatory effects of azithromycin are associated with the induction of alternative and regulatory macrophage activation characteristics and alteration of cellular compartmentalization during infection.

ANG II receptor blockade enhances anti-inflammatory macrophages in anti-glomerular basement membrane glomerulonephritis

Macrophages are heterogeneous immune cell populations that include classically activated and alternatively activated (M2) macrophages. We examined the anti-inflammatory effect of ANG II type 1 receptor (AT(1)R) blocker (ARB) on glomerular inflammation in a rat model of anti-glomerular basement membrane (GBM) glomerulonephritis (GN). The study focused on infiltrating CD8(+) and CD4(+) cells and macrophages, as well as the heterogeneity of intraglomerular macrophages. Wistar-Kyoto rats were treated with high-dose olmesartan (3 mg.kg(-1).day(-1)), low-dose olmesartan (0.3 mg.kg(-1).day(-1)), or vehicle (control) 7 days before induction of anti-GBM GN. Control rats showed mainly CD8(+) cells and ED1(+) macrophages, with a few CD4(+) cells infiltrating the glomeruli. Necrotizing and crescentic glomerular lesions developed by day 7 with the increase of proteinuria. AT(1)R was expressed on CD8(+) and CD4(+) cells and on ED1(+) macrophages. Low-dose ARB had no anti-inflammatory effects in anti-GBM GN. However, high-dose ARB reduced glomerular infiltration of CD8(+) cells and ED1(+) macrophages and suppressed necrotizing and crescentic lesions by days 5 to 7 (P < 0.05). In addition, high-dose ARB reduced the numbers of ED3(+)-activated macrophages, suppressed glomerular TNF-alpha and IFN-gamma production, and downregulated M1-related chemokine and cytokines (monocyte chemoattractant protein type 1, IL-6, and IL-12). High-dose ARB also enhanced ED2(+) M2 macrophages by day 7 with upregulation of glomerular IL-4 and IL-13 and augmented CCL17, IL-1 receptor antagonist, and IL-10. We concluded that high-dose ARB inhibits glomerular inflammation by increasing the numbers of M2 macrophages and upregulation of anti-inflammatory cytokines and by suppressing M1 macrophage development with downregulation of M1-related proinflammatory cytokines.

Chemokine decoy receptors: structure-function and biological properties

Chemokines induce cell migration through the activation of a distinct family of structurally related heterotrimeric G protein-coupled receptors (GPCR). Over the last few years, several receptors in this family that recognize chemokines but do not induce cell migration have been identified. These "atypical" chemokine receptors are unable to activate transduction events that lead directly to cell migration, but appear nonetheless to play a nonredundant role in the control of leukocyte recruitment at inflammatory sites and in tumors by shaping the chemoattractant gradient, either by removing, transporting, or concentrating their cognate ligands.

Understanding gene expression patterns in immune-mediated disorders

Gene expression profiling of peripheral blood cells can provide dynamic information regarding the host response to immune-mediated disorders. AlloMap molecular expression testing from XDx monitors the expression of 20 genes in peripheral blood mononuclear cells (PBMC) to discriminate cardiac allograft recipients of 15 years or greater who are at low risk for acute cellular rejection (ACR). The AlloMap test classifier is based on the expression level of 11 genes, encoding proteins with diverse functions, which are differentially expressed in stable patients with moderate to severe ACR compared to patients without ACR. The nine other test genes are used for normalizing gene expression levels and assuring sample quality. In this work we review the development processes leading to the selection of the 11 informative genes and the derivation of the AlloMap test classifier, and discuss the relationship of peripheral blood gene expression with diverse pathways associated with ACR, including T-cell priming, platelet activation, systemic responses to allograft inflammation, and the overall state of immunosuppression.

The FGFRL1 receptor is shed from cell membranes, binds fibroblast growth factors (FGFs), and antagonizes FGF signaling in Xenopus embryos

FGFRL1 (fibroblast growth factor receptor like 1) is the fifth and most recently discovered member of the fibroblast growth factor receptor (FGFR) family. With up to 50% amino acid similarity, its extracellular domain closely resembles that of the four conventional FGFRs. Its intracellular domain, however, lacks the split tyrosine kinase domain needed for FGF-mediated signal transduction. During embryogenesis of the mouse, FGFRL1 is essential for the development of parts of the skeleton, the diaphragm muscle, the heart, and the metanephric kidney. Since its discovery, it has been hypothesized that FGFRL1 might act as a decoy receptor for FGF ligands. Here we present several lines of evidence that support this notion. We demonstrate that the FGFRL1 ectodomain is shed from the cell membrane of differentiating C2C12 myoblasts and from HEK293 cells by an as yet unidentified protease, which cuts the receptor in the membrane-proximal region. As determined by ligand dot blot analysis, cell-based binding assays, and surface plasmon resonance analysis, the soluble FGFRL1 ectodomain as well as the membrane-bound receptor are capable of binding to some FGF ligands with high affinity, including FGF2, FGF3, FGF4, FGF8, FGF10, and FGF22. We furthermore show that ectopic expression of FGFRL1 in Xenopus embryos antagonizes FGFR signaling during early development. Taken together, our data provide strong evidence that FGFRL1 is indeed a decoy receptor for FGFs.

Receptor-Fc fusion therapeutics, traps, and MIMETIBODY technology

Fc fusion proteins are molecules in which the immunoglobulin Fc is fused genetically to a protein of interest, such as an extracellular domain of a receptor, ligand, enzyme, or peptide. Fc fusion proteins have some antibody-like properties such as long serum half-life and easy expression and purification, making them an attractive platform for therapeutic drugs. Five Fc fusion based drugs are on the market presently, and many more are in different stages of clinical trials, demonstrating that Fc fusion proteins have become credible alternatives to monoclonal antibodies as therapeutics. This review summarizes the Fc fusion proteins that have been approved for use in the clinic and those that are currently in clinical trials, as well as the different approaches to design Fc fusion proteins.

Mapping of the full length and the truncated interleukin-18 receptor alpha in the mouse brain

The cytokine IL-18 acts on the CNS both in physiological and pathological conditions. Its action occurs through the heterodimeric receptor IL-18Ralpha\beta. To better understand IL-18 central effects, we investigated in the mouse brain the distribution of two IL-18Ralpha transcripts, a full length and an isoform lacking the intracellular domain hypothesized to be a decoy receptor. Both isoforms were expressed in neurons throughout the brain primarily with overlapping distribution but also with some unique pattern. These data suggest that IL-18 may modulate neuronal functions and that its action may be regulated through expression of a decoy receptor.

Inflammation, aging, and cancer: tumoricidal versus tumorigenesis of immunity: a common denominator mapping chronic diseases

Acute inflammation is a highly regulated defense mechanism of immune system possessing two well-balanced and biologically opposing arms termed apoptosis ('Yin') and wound healing ('Yang') processes. Unresolved or chronic inflammation (oxidative stress) is perhaps the loss of balance between 'Yin' and 'Yang' that would induce co-expression of exaggerated or 'mismatched' apoptotic and wound healing factors in the microenvironment of tissues ('immune meltdown'). Unresolved inflammation could initiate the genesis of many age-associated chronic illnesses such as autoimmune and neurodegenerative diseases or tumors/cancers. In this perspective 'birds' eye' view of major interrelated co-morbidity risk factors that participate in biological shifts of growth-arresting ('tumoricidal') or growth-promoting ('tumorigenic') properties of immune cells and the genesis of chronic inflammatory diseases and cancer will be discussed. Persistent inflammation is perhaps a common denominator in the genesis of nearly all age-associated health problems or cancer. Future challenging opportunities for diagnosis, prevention, and/or therapy of chronic illnesses will require an integrated understanding and identification of developmental phases of inflammation-induced immune dysfunction and age-associated hormonal and physiological readjustments of organ systems. Designing suitable cohort studies to establish the oxido-redox status of adults may prove to be an effective strategy in assessing individual's health toward developing personal medicine for healthy aging.

Unlike PPARgamma, PPARalpha or PPARbeta/delta activation does not promote human monocyte differentiation toward alternative macrophages

Macrophages adapt their response to micro-environmental signals. While Th1 cytokines promote pro-inflammatory M1 macrophages, Th2 cytokines promote an "alternative" anti-inflammatory M2 macrophage phenotype. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors expressed in macrophages where they control the inflammatory response. It has been shown that PPARgamma promotes the differentiation of monocytes into anti-inflammatory M2 macrophages in humans and mice, while a role for PPARbeta/delta in this process has been reported only in mice and no data are available for PPARalpha. Here, we show that in contrast to PPARgamma, expression of PPARalpha and PPARbeta/delta overall does not correlate with the expression of M2 markers in human atherosclerotic lesions, whereas a positive correlation with genes of lipid metabolism exists. Moreover, unlike PPARgamma, PPARalpha or PPARbeta/delta activation does not influence human monocyte differentiation into M2 macrophages in vitro. Thus, PPARalpha and PPARbeta/delta do not appear to modulate the alternative differentiation of human macrophages.

Tuning inflammation in tuberculosis: the role of decoy receptors

Decoy receptors are "silent scavengers" of CC chemokines and cytokines, which play a key role in damping inflammation and tissue damage. In this review we discuss on recent findings demonstrating that these receptors set the balance between antimicrobial resistance, immune activation and inflammatory response in Mycobacterium tuberculosis infection.

The role of IL-1 in the pathogenesis of heart disease

Interleukin (IL)-1 consists of two distinct ligands, IL-1alpha and IL-1beta, with indistinguishable biological activities that signal through the IL-1 type I receptor (IL-1RI). A naturally occurring IL-1 receptor antagonist (IL-1Ra) binds to IL-1RI without initiating signal transduction and prevents IL-1 signaling, competitively inhibiting IL-1-mediated responses. Emerging evidence suggests that the balance between IL-1 agonists and antagonists plays an essential role in a variety of cardiovascular conditions. IL-1 may play a role in atherothrombotic disease by promoting the formation of atheromatous lesions, enhancing vascular inflammation, and triggering plaque destabilization. Following myocardial infarction, IL-1 critically regulates the inflammatory response and is involved in the development of adverse remodeling by enhancing expression of matrix metalloproteinases. IL-1 signaling may also be an essential mediator in the pathogenesis of heart failure by suppressing cardiac contractility, promoting myocardial hypertrophy, and inducing cardiomyocyte apoptosis. The present review summarizes current available data showing the significant role of IL-1 signaling in heart disease and raising the possibility that IL-1 inhibitors (such as anakinra, a nonglycosylated recombinant human IL-1Ra) may be clinically useful agents in patients with certain cardiovascular conditions.

Immune regulation by non-lymphoid cells in transplantation

Regulatory cells play a crucial role in the induction and maintenance of tolerance by controlling T cell as well as B and natural killer (NK) cell-mediated immunity. In transplantation, CD4+CD25+forkhead box P3+ T regulatory cells are instrumental in the maintenance of immunological tolerance, as are several other T cell subsets such as NK T cells, double negative CD3+ T cells, gammadelta T cells, interleukin-10-producing regulatory type 1 cells, transforming growth factor-beta-producing T helper type 3 cells and CD8+CD28(-) cells. However, not only T cells have immunosuppressive properties, as it is becoming increasingly clear that both T and non-T regulatory cells co-operate and form a network of cellular interactions controlling immune responses. Non-T regulatory cells include tolerogenic dendritic cells, plasmacytoid dendritic cells, mesenchymal stem cells, different types of stem cells, various types of alternatively activated macrophages and myeloid-derived suppressor cells. Here, we review the mechanism of action of these non-lymphoid regulatory cells as they relate to the induction or maintenance of tolerance in organ transplantation.

PPARgamma in Kidney Physiology and Pathophysiology

Involvement of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in kidney physiology has been explored recently. Synthetic PPARγ ligands can ameliorate the diabetic kidney disease through different mechanisms, involving inhibition of mesangial cell growth, reduction of mesangial matrix, and cytokine production of glomerular cells as well as promoting endothelial cell survival within the kidney glomeruli. Activation of PPARγ has additional profibrotic consequences, which can contribute to wound healing in diabetic glomerulonephritis. Beside many beneficial effects, PPARγ activation, however, can lead to severe water retention, a common side effect of thiazolidinedione therapy. This unwanted effect is due to the activation of PPARγ in the mesonephric distal collecting system, where PPARγ positively regulates sodium and water resorbtion leading to the expansion of interstitial fluid volume. Recent studies indicate that PPARγ is also involved in the normal kidney development, renal lipid metabolism, and activation of the renin-angiotensin system. In this paper, we give a synopsis of the current knowledge on PPARγ functions in kidney phyisology and pathophysiology.