| Systemic lupus erythematosus (SLE) is an autoantibody-mediated chronic autoimmune disease characterized by the production of various autoantibodies including antinuclear antibodies, immune complex deposition, vasculitis, arthritis, and glomerulonephritis. SLE affects predominantly women, especially during the childbearing years. Recently, the20-y survival rate of patients with lupus nephritis has been reported as73-81%. Despite significant advances in the treatment of SLE, the length of life of patients with systemic lupus erythematosus is shorter than those of healthy people. Therefore, the study of the pathogenesis of SLE has been a significant issue that has gained much attention from scientists.As a hallmark of SLE, the anti-dsDNA autoantibodies have been proved to be pathogenic and could promote deposition of immune complexes (IC) and tissue damage. Anti-dsDNA antibodies are specific for SLE and its level could reflect disease activity of SLE. Previous studies have indicated that anti-dsDNA antibody production could be induced by self-DNA. However, immunogenicity of mammalian DNA was poor and could not induce the immune response. Therefore, the mechanism for anti-dsDNA antibodies production has long been investigated. In our previous studies, it was found that immunization of mice with activated lymphocyte-derived DNA (ALD-DNA) could induce SLE, which developed anti-dsDNA antibodies, proteinuria, IC deposition, and glomerular nephritis. However, the unactivated lymphocyte-derived DNA (UnALD-DNA) failed to induce SLE disease.The precise etiology of SLE remains unclear; however, inefficient clearance of self nuclear antigens has been an important factor of SLE development. There are many factors that were involved in clearance of apoptotic cells and cellular debris, such as macrophage and complement. Deficiency of complement components, such as mannose-binding lectin (MBL), has been reported to occur in the development of SLE disease. As a secreted pattern recognition receptor (PRR), MBL could bind to the carbohydrates of many microorganisms and activate the complement systems. But whether MBL is involved the development of SLE remains not fully investigated.This study is aimed to investigate the correlation between MBL levels and SLE disease and whether MBL treatment could modulate the DNA-induced immune responses.Part I:Serum MBL levels decrease in lupus mice and have negative relations with SLE.It has been observed that extensive lymphocyte activation and excessive apoptosis have been widely reported in SLE patients, and large amounts of DNA that were released from apoptotic cells might exceed self clearance ability and comprise the important source of autoantigens in SLE disease. Stress, infection, and other danger signals could induce lymphocyte activation, and DNA could be released from these apoptotic lymphocytes, but not always triggering the autoimmunity, which indicated that free DNA could be removed by intrinsic mechanisms. MBL was one of the first defences of the innate immunity. In addition to binding ability of MBL to carbohydrates of many microorganisms, previous studies indicate that MBL could enhance the clearance of apoptotic cells and immune complex by interaction with its receptors. It has been observed that low serum MBL levels or MBL deficiency were reported in SLE diseases. But whether it is involved in SLE development remains unclear.Our previous studies indicated that immunization of BALB/c mice with ALD-DNA could induce SLE. To investigate whether MBL has a correlation with SLE disease, we first investigated the levels of serum MBL of ALD-DNA-induced lupus mice and it was found that the levels of serum MBL slightly increased at week2but sharply decreased from week6. Further study revealed that enhanced levels of circulating DNA were found in the lupus mice. The ratios of MBL to DNA were lower in the lupus mice than those in controls. Importantly, serum MBL levels were negatively correlated with anti-dsDNA antibodies levels and urine protein levels in lupus mice, which indicated MBL was insufficient in SLE mice.Taken together, our data presented in this study indicate that serum MBL levels decreased in SLE mice and were negatively correlated with SLE. Part Ⅱ:The study of the role and mechanism of MBL in the regulation of macrophage polarization induced by ALD-DNAOur previous study revealed that macrophage M2b polarization induced by ALD-DNA was dependent on the activation of MAPK and NF-κB signaling, which played an important role in promoting ALD-DNA-induced SLE disease. As a secreted pattern recognition receptor that has binding ability to DNA, MBL is mainly produced by liver and is proved to be a modulator of inflammation. But whether MBL promotes DNA clearance and regulates the DNA-triggered immune responses remain poorly understood.To examine binding ability of MBL to ALD-DNA, we performed dot blot and it was found that MBL could bind to ALD-DNA in a concentration-dependent manner. Further study revealed that MBL could enhance the macrophage-mediated uptake of ALD-DNA. To determine whether MBL has any influence on the macrophage polarization, we examined the production of cytokines and iNOS, and found that MBL could down-regulate production of the pro-inflammatory cytokines MCP-1, TNF-α, and IL-6while up-regulate greatly the expression of IL-10. Further study indicated that MBL could down-regulate the level of iNOS. These data indicate that MBL could modulate macrophage polarization. Importantly, it was found that the modulation of macrophage polarization by MBL was dependent on the repression of MAPK and NF-κB signaling, and CREB activation.Activated macrophages have acquisition of antigen-presenting features, which could promote Thl and Th17responses. In this study it was found that MBL could down-regulate ability of ALD-DNA-stimulated macrophages to enhance the T cells polarization.Taken together, our results indicate that MBL could modulate macrophage polarization by down-regulating the MAPK and NF-κB signaling pathway while up-regulating activation of CREB; MBL could down-regulate ability of ALD-DNA-stimulated macrophages to enhance T cells polarization.Part Ⅲ:The study of preventive role of MBL in SLEOur previous study has indicated that macrophage M2b polarization played a important role in SLE disease. It has been reported that differentiation of T cells plays a key role in SLE disease. Because MBL could regulate macrophage polarization and down-regulate T cell differentiation, we next tested whether MBL has any influence on lupus nephritis. Lupus mice were treated with pcDNA3.1or pMBL. It was found MBL treatment could modulate the renal macrophage polarization and ameliorate lupus nephritis by down-regulating anti-dsDNA antibodies production and IC deposition. These results indicate that MBL could ameliorate lupus nephritis. |
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