Leptin promotes systemic lupus erythematosus by increasing autoantibody production and inhibiting immune regulation.

Leptin is an adipocytokine that plays a key role in the modulation of immune responses and the development and maintenance of inflammation. Circulating levels of leptin are elevated in systemic lupus erythematosus (SLE) patients, but it is not clear whether this association can reflect a direct influence of leptin on the propathogenic events that lead to SLE. To investigate this possibility, we compared the extent of susceptibility to SLE and lupus manifestations between leptin-deficient (ob/ob) and H2-matched leptin-sufficient (wild-type, WT) mice that had been treated with the lupus-inducing agent pristane. Leptin deficiency protected ob/ob mice from the development of autoantibodies and renal disease and increased the frequency of immunoregulatory T cells (Tregs) compared with leptin-sufficient WT mice. The role of leptin in the development of SLE was confirmed in the New Zealand Black (NZB) × New Zealand White (NZW)F1 (NZB/W) mouse model of spontaneous SLE, where elevated leptin levels correlated with disease manifestations and the administration of leptin accelerated development of autoantibodies and renal disease. Conversely, leptin antagonism delayed disease progression and increased survival of severely nephritic NZB/W mice. At the cellular level, leptin promoted effector T-cell responses and facilitated the presentation of self-antigens to T cells, whereas it inhibited the activity of regulatory CD4 T cells. The understanding of the role of leptin in modulating autoimmune responses in SLE can open possibilities of leptin-targeted therapeutic intervention in the disease.

IL-17 promotes murine lupus.

The proinflammatory activity of IL-17-producing Th17 cells has been associated with the pathogenesis of several autoimmune diseases. In this article, we provide direct evidence for a role of IL-17 in the pathogenesis of systemic lupus erythematosus (SLE). The induction of SLE by pristane in IL-17-sufficient wild-type mice did not occur in IL-17-deficient mice, which were protected from development of lupus autoantibodies and glomerulonephritis. The protection from SLE in IL-17-deficient mice was associated with a reduced frequency of CD3(+)CD4(-)CD8(-) double-negative T cells and an expansion of CD4(+) regulatory T cells, and did not depend on Stat-1 signaling. These data affirm the key role of IL-17 in the pathogenesis of SLE and strengthen the support for IL-17 blockade in the therapy of SLE.

Laquinimod delays and suppresses nephritis in lupus-prone mice and affects both myeloid and lymphoid immune cells.

OBJECTIVE: Lupus nephritis depends on autoantibody deposition and activation of multiple immune cell types that promote kidney inflammation, including lymphocytes and monocyte/macrophages. Laquinimod, currently in clinical trials for multiple sclerosis and lupus nephritis, reduces infiltration of inflammatory cells into the spinal cord in experimental autoimmune encephalomyelitis. Activated monocyte/macrophages infiltrate the kidneys during nephritis in systemic lupus erythematosus (SLE). We undertook this study to determine whether using laquinimod to reduce monocyte/macrophage-driven tissue damage as well as to alter lymphocytes in SLE nephritis could have greater therapeutic benefit than current treatments that primarily affect lymphocytes, such as mycophenolate mofetil (MMF). METHODS: To test laquinimod efficacy, we used the (NZB × NZW)F1 mouse model of SLE, in which disease manifests as nephritis. Preventive and therapeutic studies were performed to determine whether laquinimod could prevent or delay nephritis, as measured by proteinuria, serum creatinine, survival, and renal pathology. Spleen and kidney leukocyte populations and suppression assays were analyzed by flow cytometry. RESULTS: Laquinimod prevented or delayed lupus manifestations at levels equal to or better than MMF. Laquinimod treatment was associated with reduced numbers of monocyte/macrophages, dendritic cells, and lymphocytes, as well as with induction of myeloid-derived suppressor cells in spleens and kidneys. Laquinimod suppressed macrophage-secreted tumor necrosis factor α and induced production of interleukin-10 (IL-10). In addition, laquinimod suppressed interferon-γ and IL-17 production by lymphocytes and down-regulated expression of activation/costimulatory markers on antigen-presenting cells. CONCLUSION: The effects of laquinimod on myeloid and lymphoid cells may contribute to improvements in (NZB × NZW)F1 mouse survival, proteinuria, and glomerulonephritis. Future development of laquinimod as a therapeutic agent for lupus nephritis is promising.

A panel of biomarkers is associated with increased risk of the presence and progression of atherosclerosis in women with systemic lupus erythematosus.

OBJECTIVE: An increased frequency of atherosclerosis (ATH) in systemic lupus erythematosus (SLE) is well-documented but not fully explained by the presence of traditional cardiac risk factors. Several nontraditional biomarkers, including proinflammatory high-density lipoprotein (piHDL) and leptin, have been individually associated with subclinical ATH in SLE. The aim of this study was to examine whether these and other biomarkers can be combined into a risk profile, the Predictors of Risk for Elevated Flares, Damage Progression, and Increased Cardiovascular Disease in Patients with SLE (PREDICTS), that could be used to better predict future progression of ATH. METHODS: In total, 210 patients with SLE and 100 age-matched healthy control subjects (all women) participated in this prospective cohort study. The longitudinal presence of carotid plaque and intima-media thickness (IMT) were measured at baseline and followup (mean ± SD 29.6 ± 9.7 months). RESULTS: At followup, carotid plaque was present in 29% of SLE patients. Factors significantly associated with plaque, determined using Salford Predictive Modeling and multivariate analysis, included age ≥48 years (odds ratio [OR] 4.1, P = 0.002), high piHDL function (OR 9.1, P < 0.001), leptin levels ≥34 ng/dl (OR 7.3, P = 0.001), plasma soluble TWEAK levels ≥373 pg/ml (OR 28.8, P = 0.004), and history of diabetes (OR 61.8, P < 0.001). Homocysteine levels ≥12 µmoles/liter were also a predictor. However, no single variable demonstrated an ideal combination of good negative predictive values (NPVs), positive predictive values (PPVs), sensitivity, and specificity. A high-risk PREDICTS profile was defined as ≥3 positive biomarkers or ≥1 positive biomarker plus a history of diabetes; for high-risk SLE patients, the PPV was 64%, NPV was 94%, sensitivity was 89%, and specificity was 79%. In multivariate analysis, SLE patients with the high-risk profile had 28-fold increased odds for the longitudinal presence of plaque (P < 0.001) and increased progression of IMT (P < 0.001). CONCLUSION: A high-risk PREDICTS score confers 28-fold increased odds of the presence of any current, progressive, or acquired carotid plaque, both in patients with SLE and in control subjects, and is significantly associated with higher rates of IMT progression.

Natural regulatory T cells in autoimmunity.

The suppressive/immunomodulatory function of CD4(+)CD25(+)FOXP3(+) regulatory T (Treg) cells is crucial for the maintenance of immune homeostasis, which helps to prevent autoimmunity and reduce the inflammation induced by pathogens and environmental insults. This review summarizes the current knowledge on the types and mechanisms of action of Treg cells and their role in the immune tolerance to self-antigens, with a particular focus on naturally occurring Treg cells.

Cyclooxygenase-derived mediators regulate the immunological control of Strongyloides venezuelensis infection.

The aim of this study was to define the immunoregulatory role of prostaglandins in a mouse model of Strongyloides venezuelensis infection. Strongyloides venezuelensis induced an increase of eosinophils and mononuclear cells in the blood, peritoneal cavity fluid, and bronchoalveolar lavage fluid. Treatment with the dual cyclooxygenase (COX-1/-2) inhibitors indomethacin and ibuprofen, and the COX-2-selective inhibitor celecoxib partially blocked these cellular responses and was associated with enhanced numbers of infective larvae in the lung and adult worms in the duodenum. However, the drugs did not interfere with worm fertility. Cyclooxygenase inhibitors also inhibited the production of the T-helper type 2 (Th2) mediators IL-5, IgG1, and IgE, while indomethacin alone also inhibited IL-4, IL-10, and IgG2a. Cyclooxygenase inhibitors tended to enhance the Th1 mediators IL-12 and IFN-gamma. This shift away from Th2 immunity in cyclooxygenase inhibitor-treated mice correlated with reduced prostaglandin E(2) (PGE(2)) production in infected duodenal tissue. As PGE(2) is a well-characterized driver of Th2 immunity, we speculate that reduced production of this lipid might be involved in the shift toward a Th1 phenotype, favoring parasitism by S. venezuelensis. These findings provide new evidence that cyclooxygenase-derived lipids play a role in regulating host defenses against Strongyloides, and support the exploration of eicosanoid signaling for identifying novel preventive and therapeutic modalities against these infections.

Leptin signaling: A key pathway in immune responses.

Leptin is a hormone whose central role is to regulate endocrine functions and to control energy expenditure. After the discovery that leptin can also have pro-inflammatory effects, several studies have tried to address - at the molecular level - the pathways involved in leptin-induced modulation of the immune functions in normal and pathologic conditions. The signaling events influenced by leptin after its binding to the leptin receptor have been under scrutiny in the past few years, and considerable experimental work has elucidated the consequences of leptin effects on immune cells. This review examines the biochemistry, function and regulation of leptin signaling in view of possible intervention on this molecule for a better management and therapy of immune-mediated diseases.

Cutting edge: Regulatory T cells directly suppress B cells in systemic lupus erythematosus.

In systemic lupus erythematosus (SLE), adaptive CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) suppress Th cells that help autoantibody (autoAb)-producing B cells. It is not known whether naturally occurring Tregs can directly suppress B cells in SLE without an intermediate suppression of Th cells. This aspect is important for its implications in the natural course of SLE, because most if not all of the clinical and pathologic effects in SLE are associated with a dysregulated production of autoAbs. In this study, we show that natural Tregs can inhibit B cell activity in vitro and in vivo in SLE through cell contact-mediated mechanisms that directly suppress autoAb-producing B cells, including those B cells that increase numerically during active disease. These results indicate that one way by which natural Tregs attempt to limit humoral autoimmunity in SLE is by directly targeting autoreactive B cells.

Modulation of p38 MAPK activity in regulatory T cells after tolerance with anti-DNA Ig peptide in (NZB x NZW)F1 lupus mice.

Treatment of (NZB x NZW)F(1) (NZB/W) lupus-prone mice with the anti-DNA Ig-based peptide pConsensus prolongs the survival of treated animals and effectively delays the appearance of autoantibodies and glomerulonephritis. We have previously shown that part of these protective effects associated with the induction of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) that suppressed autoantibody responses. Because the effects of pConsensus appeared secondary to qualitative rather than quantitative changes in Tregs, we investigated the molecular events induced by tolerance in Tregs and found that signaling pathways including ZAP70, p27, STAT1, STAT3, STAT6, SAPK, ERK, and JNK were not significantly affected. However, peptide tolerization affected in Tregs the activity of the MAPK p38, whose phosphorylation was reduced by tolerance. The pharmacologic inhibition of p38 with the pyridinyl imidazole inhibitor SB203580 in naive NZB/W mice reproduced in vivo the effects of peptide-induced tolerance and protected mice from lupus-like disease. Transfer experiments confirmed the role of p38 in Tregs on disease activity in the NZB/W mice. These data indicate that the modulation of p38 activity in lupus Tregs can significantly influence the disease activity.

Counterregulation of Th2 immunity by interleukin 12 reduces host defenses against Strongyloides venezuelensis infection.

The aim of this study was to investigate the role of interleukin 12 (IL-12) during Strongyloides venezuelensis infection. IL-12(-/-) and wild-type C57BL/6 mice were subcutaneously infected with 1500 larvae of S. venezuelensis. On days 7, 14, and 21 post-infection, we determined eosinophil and mononuclear cell numbers in the blood and broncoalveolar lavage fluid (BALF), Th2 cytokine secretion in the lung parenchyma, and serum antibody levels. The numbers of eggs in the feces and worm parasites in the duodena were also quantified. The eosinophil and mononuclear cell counts and the concentrations of IL-3, IL-5, IL-10, IL-13, and IgG1 and IgE antibodies increased significantly in infected IL-12(-/-) and wild-type mice as compared with uninfected controls. However, the number of eosinophils and mononuclear cells in the blood and BALF and the Th2 cytokine levels in the lungs of infected IL-12(-/-) mice were greater than in infected wild-type C57BL/6 mice. In addition, serum IgE and IgG1 levels were also significantly enhanced in the infected mice lacking IL-12. Meanwhile, parasite burden and fecal egg counts were significantly decreased in infected IL-12(-/-) mice. Together, our results showed that the absence of IL-12 upregulates the Th2 immune response, which is important for control of S. venezuelensis infection.

Cytokines in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of autoantibodies that can form immune complexes and deposit in tissues, causing inflammation and organ damage. There is evidence that interferons and some interleukins can have an active role in the pathogenesis of SLE and can contribute significantly to the immune imbalance in the disease, whereas the role of some cytokines (such as TNF) is still debated. This review discusses the activity of several cytokines in SLE, their effects on the immune cells in relation to the disease pathogenesis, and the promise and limitations of cytokine-based therapies in clinical trials for lupus patients.

Gender-Based Differences in Leptinemia in Healthy Aging, Non-obese Individuals Associate with Increased Marker of Oxidative Stress.

Aging associates with an increased pro-inflammatory activity that is commonly associated with oxidative tissue damage. One pro-inflammatory molecule that facilitates oxidative stress is leptin, a hormone that regulates metabolism, endocrine and immune functions. To address whether leptin levels correlated with oxidative stress in aging, we performed cross-sectional measurements of circulating plasma leptin in groups of healthy individuals that were divided by age and gender. It was found that leptin levels were comparable between young (N=54) and elderly humans (N=56) in each gender, and women had higher levels than men, irrespectively of age. Interestingly, oxidative stress measured as total glutathione levels correlated positively with elevated leptin levels in elderly women but not in men or in the groups of younger individuals. The data suggest that a gender bias for leptin that is maintained with age can associate with increased propensity to oxidative stress in the elderly.

Myosin Va phosphorylated on Ser1650 is found in nuclear speckles and redistributes to nucleoli upon inhibition of transcription.

Nuclear actin and nuclear myosins have been implicated in the regulation of gene expression in vertebrate cells. Myosin V is a class of actin-based motor proteins involved in cytoplasmic vesicle transport and anchorage, spindle-pole alignment and mRNA translocation. In this study, myosin-Va, phosphorylated on a conserved serine in the tail domain (phospho-ser(1650) MVa), was localized to subnuclear compartments. A monoclonal antibody, 9E6, raised against a peptide corresponding to phosphoserine(1650) and flanking regions of the murine myosin Va sequence, was immunoreactive to myosin Va heavy chain in cellular and nuclear extracts of HeLa cells, PC12 cells and B16-F10 melanocytes. Immunofluorescence microscopy with this antibody revealed discrete irregular spots within the nucleoplasm that colocalized with SC35, a splicing factor that earmarks nuclear speckles. Phospho-ser(1650) MVa was not detected in other nuclear compartments, such as condensed chromatin, Cajal bodies, gems and perinucleolar caps. Although nucleoli also were not labeled by 9E6 under normal conditions, inhibition of transcription in HeLa cells by actinomycin D caused the redistribution of phospho-ser(1650) MVa to nucleoli, as well as separating a fraction of phospho-ser(1650) MVa from SC35 into near-neighboring particles. These observations indicate a novel role for myosin Va in nuclear compartmentalization and offer a new lead towards the understanding of actomyosin-based gene regulation.

Immunization with MIC1 and MIC4 induces protective immunity against Toxoplasma gondii.

Host cell invasion by Toxoplasma gondii is tightly coupled to the apical release of micronemal proteins (MIC). In this work, we evaluated the protective effect encountered in C57BL/6 mice immunized with MIC1 and MIC4 purified from soluble tachyzoite antigens by affinity to immobilized lactose. The immunized mice presented high serum levels of IgG1 and IgG2b specific antibodies. MIC1/4-stimulated spleen cells from immunized mice produced IL-2, IL-12, IFN-gamma, IL-10, but not IL-4, suggesting the induction of a polarized Th1 type immune response. When orally challenged with 40 cysts of the ME49 strain, the immunized mice had 68% fewer brain cysts than the control mice. Immunization was associated with 80% survival of the mice challenged with 80 cysts, contrasting with 100% mortality of the non-immunized mice in the acute phase. In this phase, there was much lower parasitism in the lungs and small intestine of the immunized mice, and they did not exhibit the early-stage signs of intestinal necrosis, which was clearly detected in the control mice. Our data demonstrate that MIC1 and MIC4 triggered a protective response against toxoplasmosis, and that these antigens are targets for the further development of a vaccine.

Leukotrienes play a role in the control of parasite burden in murine strongyloidiasis.

It is clear that leukotrienes mediate inflammatory response; new aspects of leukotriene function have recently been described. In this study, we demonstrate that leukotrienes are key chemical mediators in the control of parasite burdens in mice infected with Strongyloides venezuelensis. High leukotriene levels were detected in the lungs and small intestines of Swiss mice. In infected Swiss mice treated with MK886, a leukotriene synthesis inhibitor, numbers of adult worms, and eggs/g/feces were greater than in infected-only animals. The MK886 treatment inhibited leukotriene B(4) production in the lungs and small intestines, albeit on different postinfection days. Similarly, parasite burdens and eggs/g/feces were greater in 5-lipoxygenase(-/-) mice than in wild-type animals. These observation were confirmed by histopathological study of the duodena. We subsequently observed significant lower numbers of eosinophils and mononuclear cells in the blood, peritoneal cavity fluid, and bronchoalveolar lavage fluid of Swiss mice treated with MK886. In the lung parenchyma of infected animals, MK886 significantly inhibited synthesis of IL-5 at the beginning of infection, whereas levels of IL-12 increased progressively throughout the postinfection period. However, levels of leukotriene C(4), PGE(2), TNF-alpha, IL-3, IL-4, IFN-gamma, and IL-10 were comparable between the treated and untreated groups. Nevertheless, IgE and IgG1 (but not IgG2a) synthesis was also significantly inhibited by MK886 administration. Therefore, in S. venezuelensis-infected mice, adult worm and egg burdens are leukotriene dependent. These findings indicate potential immunostimulatory strategies involving leukotriene administration, and may serve as an alert to physicians treating Strongyloides stercoralis-infected patients presenting asthma-like symptoms because use of 5-lipoxygenase inhibitors may worsen the infection.