The TNF-like protein 1A-death receptor 3 pathway promotes macrophage foam cell formation in vitro.

TNF-like protein 1A (TL1A), a TNF superfamily cytokine that binds to death receptor 3 (DR3), is highly expressed in macrophage foam cell-rich regions of atherosclerotic plaques, although its role in foam cell formation has yet to be elucidated. We investigated whether TL1A can directly stimulate macrophage foam cell formation in both THP-1 and primary human monocyte-derived macrophages with the underlying mechanisms involved. We demonstrated that TL1A promotes foam cell formation in human macrophages in vitro by increasing both acetylated and oxidized low-density lipoprotein uptake, by enhancing intracellular total and esterified cholesterol levels and reducing cholesterol efflux. This imbalance in cholesterol homeostasis is orchestrated by TL1A-mediated changes in the mRNA and protein expression of several genes implicated in the uptake and efflux of cholesterol, such as scavenger receptor A and ATP-binding cassette transporter A1. Furthermore, through the use of virally delivered DR3 short-hairpin RNA and bone marrow-derived macrophages from DR3 knockout mice, we demonstrate that DR3 can regulate foam cell formation and contributes significantly to the action of TL1A in this process in vitro. We show, for the first time, a novel proatherogenic role for both TL1A and DR3 that implicates this pathway as a target for the therapeutic intervention of atherosclerosis.

IL-33 reduces macrophage foam cell formation.

The development of atherosclerosis, a chronic inflammatory disease characterized by the formation of arterial fibrotic plaques, has been shown to be reduced by IL-33 in vivo. However, whether IL-33 can directly affect macrophage foam cell formation, a key feature of atherosclerotic plaques, has not been determined. In this study, we investigated whether IL-33 reduces macrophage foam cell accumulation in vivo and if IL-33 reduces their formation in vitro using THP-1 and primary human monocyte-derived macrophages. In Apolipoprotein E(-/-) mice fed on a high fat diet, IL-33 treatment significantly reduced the accumulation of macrophage-derived foam cells in atherosclerotic plaques. IL-33 also reduced macrophage foam cell formation in vitro by decreasing acetylated and oxidized low-density lipoprotein uptake, reducing intracellular total and esterified cholesterol content and enhancing cholesterol efflux. These changes were associated with IL-33-mediated reduction in the expression of genes involved in modified low-density lipoprotein uptake, such as CD36, and simultaneous increase in genes involved in cholesterol efflux, including Apolipoprotein E, thereby providing a mechanism for such an action for this cytokine. IL-33 also decreased the expression of key genes implicated in cholesterol esterification and triglyceride storage, including Acyl-CoA:cholesterol acyltransferase 1 and Adipocyte differentiation-related protein. Furthermore, using bone marrow-derived macrophages from ST2(-/-) mice, we demonstrate that the IL-33 receptor, ST2, is integral to the action of IL-33 on macrophage foam cell formation. In conclusion, IL-33 has a protective role in atherosclerosis by reducing macrophage foam cell formation suggesting that IL-33 maybe a potential therapeutic agent against atherosclerosis.

Age-dependent maintenance of motor control and corticostriatal innervation by death receptor 3.

Death receptor 3 is a proinflammatory member of the immunomodulatory tumor necrosis factor receptor superfamily, which has been implicated in several inflammatory diseases such as arthritis and inflammatory bowel disease. Intriguingly however, constitutive DR3 expression has been detected in the brains of mice, rats, and humans, although its neurological function remains unknown. By mapping the normal brain expression pattern of DR3, we found that DR3 is expressed specifically by cells of the neuron lineage in a developmentally regulated and region-specific pattern. Behavioral studies on DR3-deficient (DR3(ko)) mice showed that constitutive neuronal DR3 expression was required for stable motor control function in the aging adult. DR3(ko) mice progressively developed behavioral defects characterized by altered gait, dyskinesia, and hyperactivity, which were associated with elevated dopamine and lower serotonin levels in the striatum. Importantly, retrograde tracing showed that absence of DR3 expression led to the loss of corticostriatal innervation without significant neuronal loss in aged DR3(ko) mice. These studies indicate that DR3 plays a key nonredundant role in the retention of normal motor control function during aging in mice and implicate DR3 in progressive neurological disease.

Involvement of the CD200 receptor complex in microglia activation in experimental glaucoma.

The interaction of the myeloid restricted molecule CD200R with its widely expressed ligand CD200 is involved in the down-regulation of microglia activation. In the present study, we examined the involvement of CD200R in microglia activation in experimental ocular hypertension to determine the role of microglia activation in retinal ganglion cell (RGC) death, the key pathological event in glaucoma. Experimental glaucoma was induced in adult Brown Norway rats by sclerosis of the episcleral veins with the injection of hypertonic saline. Immunohistochemical methods were used to determine the involvement of microglia using GFAP, CD45, OX42 and OX41 and the involvement of CD200 and CD200R in the optic nerve head. Our data demonstrate the increased presence of microglia within the optic nerve head during ocular hypertension, identified by positive staining with OX42 and OX41. The peak of microglia correlates with peak in RGC death at days 20-27 (T3) post OHT induction. In addition, CD200 and CD200R positive cells were increased in ocular hypertensive eyes. Increased expression of CD200 was detected in the early phase (days 1-7; T1) of OHT and decreased over time, whilst the expression of CD200R was detected in the middle phase (days 20-27; T3) of OHT, correlating with the increase in microglia markers. Changes in the expression of CD200R/CD200 occur early in experimental glaucoma and precede the peak in microglia infiltration and RGC death, suggesting that CD200R-positive microglia play an important role in the initiation of RGC death during OHT, indicating a potential area for therapeutic intervention in treating glaucoma.

TNFR1 signalling is a critical checkpoint for developing macrophages that control of T-cell proliferation.

Macrophages (Mϕ) are professional antigen-presenting cells, but when they accumulate at sites of inflammation, they can inhibit T-cell proliferation. In experimental autoimmune uveoretinitis, this limits the expansion of T cells within the target organ. To define requirements for the elaboration of this outcome, we have generated populations of Mϕ in vitro that could also regulate T-cell responses; stimulating CD4(+) T-cell activation and cytokine production, but simultaneously suppressing T-cell proliferation. When T cells are removed from the influence of such cells, normal T-cell responses are restored. We show that tumour necrosis factor 1 (TNFR1) signalling is a critical checkpoint in the development of such Mϕ, as TNFR1(-/-) Mϕ are unable to suppress T-cell proliferation. This deficit in antigen-presenting cells results in a lack of production of prostaglandin E(2) (PGE(2)) and nitric oxide, which are critical effector mechanisms that inhibit T-cell division. However, TNFR1 signalling is not required for the inhibitory function of Mϕ because we could circumvent the requirement for this receptor, by maturing Mϕ in the presence of exogenous interferon-γ and PGE(2). This produced TNFR1(-/-) Mϕ that inhibited T-cell proliferation and indicates that TNFR1 delivers a signal that is necessary for the development but not the execution of this function.

Mapping immune responses to mRBP-3 1-16 peptide with altered peptide ligands.

PURPOSE: Experimental autoimmune uveoretinitis (EAU) can be induced in C57BL/6 mice (I-A(b)) using human retinoid-binding protein-3 (hRBP-3, previously IRBP) residues 1-20. This study of a truncated murine peptide (mRBP-3 1-16) was conducted to determine its pathogenic potential and to characterize partially its interaction with specific T cells. METHODS: After immunization with mRBP-3 1-16 or hRBP-3 1-20, EAU was assessed by immunohistochemistry. The immune response was assessed by tritiated thymidine incorporation and cytokine production analyzed by enzyme-linked immunosorbent assay (ELISA). T-cell receptor (TCR)- and major histocompatibility complex (MHC)-binding of mRBP-3 1-16 was studied by modeling and by using altered peptide ligands (APLs) and T-cell clones. RESULTS: mRBP-3 1-16 induced EAU in C57BL/6 mice, with severity and kinetics comparable to that after immunization with hRBP-3 1-20. T cells taken from mice immunized with mRBP-3 1-16 had a Th1 phenotype and proliferated in response to reactivation with mRBP-3 1-16, hRBP-3 1-20, or mRBP-3 1-16 APLs. mRBP-3 1-16 APLs elicited at least five distinct patterns of reactivity when tested with the mRBP-3 1-16-reactive T-cell clones. CONCLUSIONS: mRBP-3 1-16 immunizes and causes EAU in C57BL/6 mice. The studies using T-cell clones and APLs demonstrate that the immune response to mRBP-3 1-16 is drawn from a diverse population of antigen-specific T cells with a Th1 phenotype. Modeling and analysis of clones indicate that nonpathogenic T cells of an mRBP-3 1-16-reactive T-cell line recognize the peptide in a single register.

Murine respiratory tract dendritic cells: isolation, phenotyping and functional studies.

Respiratory tract dendritic cells (RTDC) form a contiguous subepithelial network within the nasorespiratory tract bridging innate and acquired immunity and have been implicated in nasal mucosal tolerance induction. Discrepancies exist between isolation techniques with respect to phenotype and function of RTDC. Therefore, the aim of this study was to modify previous methods to provide a consistent isolation method whilst maintaining good cell viability and enriched cell numbers so as to facilitate further phenotype and functional studies of murine RTDC. RTDCs isolated by enzyme digestion, Percoll density gradient centrifugation and overnight GM-CSF culture followed by MACS separation retain an archetypical immature dendritic cell phenotype, characterised by MHCII(low) CD40(neg) CD86(neg) CD80(neg) CD11c(low) cell surface expression. Splenic-derived DC (SDC) isolated conformed to a day 1 in vitro phenotype; MHCII(low) CD40(neg) CD86(low) CD80(neg) CD11c(low) but can further mature phenotypically in vitro. Both RTDC and SDC processed and presented antigen efficiently to T cells in vitro. Using such modified isolation procedures for RTDCs, we have developed a consistent method of RTDC enrichment, which maintains the immature phenotype and functional antigen presenting capability.

B-cell subsets: cellular interactions and relevance in multiple sclerosis.

There has been longstanding interest in how B-cell responses may contribute to the pathology of neurological diseases. Traditionally, the premise has been that any such contribution relates to the potential of B cells to produce autopathogenic antibodies. Targeting autoantibodies continues to be an important therapeutic approach, particularly in disorders where the role of antibodies is relatively well established, such as in certain inflammatory disorders of peripheral nerves or the neuromuscular junction. In other conditions, such as multiple sclerosis, the role of circulating antibodies targeting the CNS has been less clear, although pathologic studies continue to implicate CNS-reactive antibodies, as well as B cells within the CNS compartment. Recently, new insights into fundamental properties of B cells have suggested that these cells may contribute in an antibody-independent fashion, both to normal immune responses, and in the context of immune mediated diseases. Here, we will consider the potential roles of antibody-dependent as well as antibody-independent B-cell involvement in multiple sclerosis. The topic is of particular interest at a time that B-cell-directed therapies are being evaluated for this and other autoimmune diseases.

Monoclonal antibody-mediated CD200 receptor signaling suppresses macrophage activation and tissue damage in experimental autoimmune uveoretinitis.

Macrophage responses are regulated by multiple secreted factors as well as by cell surface receptors, including the inhibitory signals resulting from ligation of myeloid CD200 receptors (CD200R) by the widely distributed CD200. In the absence of CD200, animals display increased susceptibility to autoimmunity and earlier onset aggressive autoimmune disease. In these current experiments, an agonist monoclonal rat anti-mouse CD200R (DX109) antibody delivered a negative signal to bone marrow-derived macrophages, which suppressed interferon (IFN)gamma-mediated nitric oxide (NO) and interleukin-6 production. Experimental autoimmune uveoretinitis (EAU) was used as a model of organ-specific autoimmunity in the eye, a tissue with extensive neuronal and endothelial CD200 expression. In mice lacking CD200 (CD200(-/-)), increased numbers of retina-infiltrating macrophages displaying heightened NO responses were observed during EAU. In addition, we aimed to suppress disease by maintaining tonic suppression of macrophage activation via CD200R. Systemically administered DX109 monoclonal antibody suppressed EAU despite maintained T-cell proliferation and IFNgamma production. Furthermore, locally administered DX109 monoclonal antibody resulted in an earlier resolution of disease. These experiments demonstrate that promoting CD200R-mediated signaling can successfully prevent full expression of IFNgamma-mediated macrophage activation and protect against tissue damage during autoimmune responses.

Mechanisms for inducing nasal mucosal tolerance in experimental autoimmune uveoretinitis.

Delivering soluble (auto) antigenic peptides via the naso-respiratory route induces tolerance to that peptide and suppression of experimental models of autoimmune disease. In the normal lung, respiratory tract dendritic cells (RTDCs) efficiently endocytose soluble antigens, migrate to regional lymph nodes and present peptide to T cells that subsequently become tolerant. This article describes protocols for inducing tolerance via the naso-respiratory tract in experimental autoimmune uveoretinitis (EAU); for the isolation of RTDCs to facilitate definition of, and conditions for, maturation and activation of cells; and to test RTDC ability to induce tolerance in murine EAU when adoptively transferred.

A selective role for the TNF p55 receptor in autocrine signaling following IFN-gamma stimulation in experimental autoimmune uveoretinitis.

IFN-gamma stimulates macrophage activation and NO production, which leads to destruction of the retina in experimental autoimmune uveoretinitis. In this study, we investigate the mechanism of disease resistance in TNF p55 receptor-deficient animals. We show that although T cell priming is relatively unaffected, macrophages lacking the TNF p55 receptor fail to produce NO following IFN-gamma stimulation because of a requirement for autocrine TNF-alpha signaling through the TNF p55 receptor. In contrast to the impaired activation of NO synthesis, MHC class II up-regulation was indistinguishable in wild-type and TNFRp55-/- mice stimulated with IFN-gamma. These defects could be overcome by stimulating macrophages with LPS. Together, these results show that selected aspects of IFN-gamma activation are controlled by autocrine secretion of TNF-alpha, but that this control is lost in the presence of signals generated by pathogen-associated molecular patterns recognizing receptors.