【作者】 刘莹；

【导师】 陈政良；

【作者基本信息】 南方医科大学 ， 免疫学， 2011， 博士

【摘要】 天然免疫系统是由多种识别及效应分子组成的复杂的网络结构,通过模式识别受体如Toll样受体(Toll-like receptor, TLR)、肽聚糖识别蛋白、甘露聚糖结合凝集素(mannan-binding lectin, MBL)等识别病原相关分子模式(pathogen associated molecular patterns, PAMPs),构成机体抗感染的第一道防线；并通过抗原提呈、提供共刺激信号和调节细胞因子的分泌,启动获得性免疫应答并指导其应答的性质和强度。天然免疫对获得性免疫应答的指导作用特别是其分子机制,近年来一直是免疫学研究的热点之一。MBL是由肝细胞分泌的高度保守的血浆蛋白,为C型凝集素超家族中胶凝素(collectins)家族成员。MBL也是一种急性期反应蛋白,在应激(如病原体感染、外科手术等)时,其血浆浓度可升高2-3倍。具有“前抗体”(ante-antibody)之称的MBL通过其糖识别域(carbohydrate recognition domain, CRD)广泛识别分布于多种病原体如细菌、病毒、寄生虫、真菌等表面的糖结构,包括D-甘露糖、L-盐藻糖、N-乙酰葡萄糖胺、N-乙酰甘露糖胺等。其胶原样区(collagen-like region,CLR)结合甘露聚糖相关丝氨酸蛋白酶(MBL-associated serine protease,MASP),激活补体凝集素途径而发挥溶破和间接调理功能；或者与吞噬细胞胶凝素受体结合,以不依赖补体的方式启动调理吞噬。MBL结构基因的3个点突变(CGT52TGT、GGC54GAC和GGA57GAA)以及启动子和5’非翻译区突变所致血浆MBL低下而引起的调理吞噬缺损为迄今所发现的最常见的遗传性免疫缺损病。MBL缺损者终生处于高度的感染风险之中,随时可患各种感染甚至威胁生命的感染,亦易患自身免疫性疾病如系统性红斑狼疮、类风湿关节炎、Sjogren’s综合征等；而凝集素途径活性过强时则可能导致炎症性损伤。随着对MBL研究的不断深入,发现其除了可识别并清除病原体,还具备许多内源性功能(endogenous functions),如结合自身免疫球蛋白；识别缺血再灌注损伤中暴露的自身抗原或疾病状态下修饰的自身抗原；参与对凋亡细胞的吞噬；结合肿瘤细胞并发挥MBL依赖性细胞介导的细胞毒作用;抑制DC特异性结合细胞间黏附分子3的非整合素(DC-specific intercellular adhesion molecule 3-grabbing nonintegrin, DC-SIGN)介导的人类免疫缺陷病毒(human immunodeficiency virus, HIV)对T细胞的感染。因此,MBL作为固有免疫中具有多重功能的模式识别分子,不仅仅参与机体的天然免疫防御,很可能在天然免疫与获得性免疫之间的相互作用中亦发挥作用。研究MBL与获得性免疫的关系,具有重要的科学意义和潜在的医学实践意义。然而,目前国际上对MBL与获得性免疫的关系尚未涉及,其免疫调节作用的研究极少,仅见Fraser等报道,MBL可抑制细菌脂多糖(lipopolysaccharide, LPS)刺激的Mo分泌IL-1而促进其产生IL-10、IL-6; Downing等也发现MBL可与B淋巴细胞结合,认为MBL作为急性期反应蛋白,在炎症发生时,可能在血管外与自身细胞结合,参与抗炎反应。而有关MBL与T淋巴细胞之间的相互作用,目前尚未见报道。本课题组在MBL免疫调节作用的研究中发现,人外周血Mo经常规的GM-CSF+IL-4培养,将其诱导为未成熟DC后,施以MBL可刺激DC分化成熟,包括其表面分子CDla、CD83、CD40、CD80、CD86和MHC-DR表达上调,吞噬酵母多糖颗粒活性降低,激发初始T细胞增殖的能力增强,分泌IL-12增多；但存在LPS时,MBL则以剂量依赖方式抑制其诱导的DC分化成熟,包括下调DC的CD83和CD86表达,增强其摄取酵母多糖颗粒的能力,降低其激发初始T细胞增殖的活性,抑制其LPS诱导的TNF-a和IL-12 p40+p70分泌,这种作用与MBL阻断LPS-TLR4结合而降低NF-κB活性有关。我们还发现了MBL与获得性免疫直接联系的初步证据：MBL可与B细胞系Raji细胞以钙离子依赖方式结合,且高浓度MBL可以抑制Raji的增殖,提示在应急状态下,血液及局部组织MBL浓度增加,不仅可以发挥天然免疫作用,而且可以结合自身淋巴细胞,进而调控获得性免疫应答的发生和发展。为进一步研究MBL对获得性免疫的调节作用,本课题以T细胞为切入点,初步探索MBL对T细胞功能活性的影响及其分子机制。我们首先从新鲜冰冻人血浆中提取高纯度的具有生物学活性的天然MBL,进而探讨MBL对T细胞激活剂刀豆蛋白A(Con A)、抗CD3单抗(anti-CD3 mAb)、抗CD3单抗+抗CD28单抗(anti-CD3 mAb+anti-CD28 mAb)活化的人外周血单个核细胞(peripheral blood mononuclear cell, PBMC)以及纯化T细胞的增殖及分泌细胞因子的影响,并初步探讨了MBL对T细胞直接和间接免疫调节功能的机制。第一章MBL对PBMC增殖及分泌细胞因子的调节作用随着天然免疫研究的深入,发现胶凝素家族的一些成员和获得性免疫之间的联系越来越紧密。如表面活性物质-A (surfactant protein A, SP-A),表面活性物质-D (surfactant protein D, SP-D)不仅可与病原体结合,参与天然免疫防御功能,亦可与多种免疫细胞如单核细胞、树突状细胞、T细胞结合,调节获得性免疫应答。SP-A和SP-D可直接抑制T细胞增殖及其功能,避免由于免疫应答过强造成的肺部损伤。MBL也已证实可与多种免疫细胞结合,调节细胞因子的分泌。根据以上研究结果,以及MBL与SP-A、SP-D的同源性,尤其是其与SP-A在结构上的高度相似,推测MBL很有可能参与获得性免疫应答。本部分工作是研究MBL对T细胞激活剂诱导的PBMC增殖及分泌细胞因子是否有调节作用。首先用传统方法从人冰冻血浆中提取MBL。在提取过程中会污染脂多糖(lipopolysaccharide, LPS),为排除LPS对研究MBL调节功能的干扰作用,应用多粘菌素B凝胶柱去除LPS,经配体结合实验鉴定,MBL仍保持良好的甘露聚糖(mannan)结合活性。取人新鲜外周抗凝血, Ficoll-Hypaque密度梯度离心法分离PBMC,用含10%胎牛血清(fetal bovine serum, FBS)的RPMI-1640培养基培养,同时加入T细胞激活剂Con A、anti-CD3 mAb和不同浓度MBL,于37℃,5%CO2培养。CCK-8法检测PBMC增殖；酶联免疫吸附试验(enzyme-linked immunosorbence assay, ELISA)检测细胞因子的分泌。在流式细胞术(flow cytometry, FCM)分析中,预先将PBMC标记荧光染料乙酰乙酸琥珀酰亚胺酯(Carboxyfluoresceindiacetate succinimidylester, CFDA-SE, CFSE) (2.5μM)后,加入anti-CD3 mAb和MBL,培养4d后,收集细胞,标记APC-anti-human CD4和PE-anti-human CD8,分析CD4+T细胞和CD8+T细胞的增殖动力学模型。CCK-8法结果表明,MBL可明显抑制anti-CD3 mAb诱导的PBMC增殖。FCM结果可见,MBL可抑制anti-CD3mAb诱导的PBMC中CD4+T细胞和CD8+T细胞的增殖。ELISA结果显示,不同浓度MBL均抑制Con A诱导的PBMC分泌IL-2、IL-10与IFN-y,但明显上调IL-6分泌。抗MBL-MASP mAbs可阻断MBL对IL-2、IFN-γ分泌的抑制作用。以上结果提示MBL可抑制T细胞的增殖与活化,为进一步研究MBL对纯化T细胞功能的直接调节作用奠定了基础。第二章MBL对纯化T细胞增殖及分泌细胞因子的调节作用由于PBMC细胞成分的复杂性,无法根据上述结果判断MBL是直接抑制T细胞活性,还是通过其它免疫细胞如抗原提呈细胞(antigen-presenting cell, APC)间接抑制T细胞功能,或二者兼有。本部分工作即分离纯化T细胞,旨在探讨MBL对T细胞增殖及活化的直接调节作用。无菌分离人外周血PBMC,磁式细胞分选器(magnetic activated cell sortor,MACS)负选法纯化CD3+T细胞、CD4+T细胞,培养于Con A+MBL的培养基中,培养72h,CCK-8法检测细胞增殖。在FCM分析中,预先将T细胞标记CFSE后,加入anti-CD3 mAb、anti-CD3 mAb+anti-CD28mAb和MBL,培养4d后检测CD4+T细胞和CD8+T细胞的增殖。ELISA检测MBL在不同时间、对不同剂量的T细胞激活剂诱导T细胞分泌Thl型细胞因子(IL-2、IFN-γ)、Th2型细胞因子(IL-6、IL-10),以及IL-17a的影响。CCK-8法结果表明,MBL可抑制Con A诱导的T细胞增殖。FCM结果分析,MBL可抑制anti-CD3 mAb、anti-CD3 mAb+anti-CD28mAb刺激的CD4+T细胞和CD8+T细胞的增殖。ELISA结果显示,在不同时间,MBL均抑制不同剂量的T细胞激活剂ConA和anti-CD3 mAb+anti-CD28mAb诱导的T细胞分泌IL-2、IL-10、IFN-γ、IL-17a,对IL-6分泌则呈现为正负调节作用。MBL还可抑制ConA诱导的CD4+T细胞分泌IFN-γ。以上结果为MBL直接调节T细胞功能的推断提供了实验依据。尚需要进一步解决的问题是：MBL是否通过直接与T细胞结合而发挥调节作用及其结合特性的测定；与T细胞结合所涉及MBL结构域的初步确定(C型凝集素样结构域或胶原样区)；MBL对T细胞活化的影响；MBL是否还可通过调节APC分泌细胞因子而间接抑制T细胞的功能。第三章MBL对T细胞调节功能的机制初探为初步探讨MBL对T细胞免疫调节功能的机制,首先采用细胞ELISA (Cell-ELISA)和FCM研究MBL与T细胞及Jurkat细胞的结合,以及anti-CRD mAb、anti-MBL-MASP mAb对MBL与T细胞结合的影响。FCM分析MBL对T细胞活化标志CD69和HLA-DR表达的影响。向含有T细胞激活剂和MBL的培养基中加入lOmM Ca++, ELISA检测INF-γ、IL-2的分泌,以明确Ca++对MBL功能的影响。在阻断实验中,将Con A、MBL与anti-MBL-CRD mAb或甘露聚糖(mannan)共同孵育,ELISA检测IFN-γ的分泌。为明确MBL对T细胞的抑制作用是否为IL-2依赖途径,在培养基中加入重组人IL-2 (recombinant humanIL-2, rhIL-2) (1OOIU/ml), ELISA检测IFN--γ的分泌。细胞ELISA和FCM结果均表明,MBL可直接与T细胞以不依赖钙离子的方式结合,anti-MBL-CRD mAb对二者的结合没有影响,而可特异性识别MBL-CLR区的anti-MBL-MASP mAb可抑制MBL与T细胞结合；ELISA结果显示,外源性Ca++对MBL抑制IFN-γ,、IL-2的分泌没有影响,anti-MBL-CRD mAb和甘露聚糖均不能阻断MBL对IFN-γ分泌的抑制作用。以上结果均提示MBL对T细胞的直接调节作用是通过其CLR区而非CRD区。MBL与Con A共同刺激T细胞,T细胞早期活化标志CD69表达下降,晚期活化标志HLA-DR表达没有明显改变；外源性IL-2可阻断MBL的抑制作用,提示MBL通过抑制T细胞活化而非诱导T细胞凋亡而发挥抑制作用。为探讨MBL对APC分泌细胞因子的影响,将LPS与MBL同时加入PBMC,ELISA检测细胞培养上清中炎症细胞因子(TNF-α、IL-6)以及趋化性细胞因子(MCP-1)的表达。或者在体外诱导DC的过程中加入MBL,ELISA检测细胞培养上清中IL-6的分泌。ELISA结果显示,MBL可抑制LPS刺激PBMC分泌TNF-α及MCP-1,促进IL-6分泌；MBL可抑制LPS或TNF-α诱导的成熟DC分泌IL-6,并抑制不成熟DC分泌IL-6。以上结果提示MBL可能通过抑制APC分泌炎症细胞因子,进而抑制T细胞功能。具体机制目前正在研究中。综上,本课题研究发现,MBL可抑制由T细胞激活剂诱导的PBMC及T细胞的增殖及多种细胞因子的分泌,初步获得了MBL与T细胞结合的直接证据,并提出MBL还可能通过调节APC分泌细胞因子进而参与对T细胞的调节。提示MBL在识别外源性抗原或自身凋亡细胞并清除它们的同时,可能向T细胞传递抑制信号,避免由于过强的获得性免疫应答造成的机体损伤。但具体分子机制如MBL对不同活化阶段T细胞的调节作用,T细胞上MBL受体的鉴定,与T细胞结合的MBL结构域的确定,MBL对T细胞活化信号转导途径的影响,以及MBL对不同细胞亚群分化及活性的调节,均需更深入系统的研究。下一步工作将进一步研究MBL对不同亚群T细胞如CD4+、CD8+T细胞的活化、增殖及功能的直接调节作用,并继续探索MBL对APC分化与功能及其对T细胞应答的间接调节作用,揭示天然免疫中重要的模式识别分子MBL与获得性免疫应答的关系。本研究将为天然免疫及其指导获得性免疫应答的基础理论提供实验依据,并为MBL失衡和T细胞功能紊乱有关疾病的防治研究提供新的理论依据和靶点。更多还原

【Abstract】 Innate immunity comprises a sophisticated network of molecules, which recognize pathogens, and effector molecules, working together to establish a quick and efficient immune response to infectious agents. It is considered to be the first line of host by recognizing pathogen associated molecular patterns (PAMPs) through its pattern recognition receptors such as Toll-like receptor (TLR), peptidoglycan recognition molecule, mannan-binding lectin (MBL, also known as mannose-binding lectin), assessing the level of danger, determining the nature and extend of adaptive immune response.The mechanisms of innate immunity in shaping adaptive immunity has been the focus of interest for many research groups around the world.MBL, an evolutionary conserved circulating host defense protein produced mainly by liver, is a member of the family of collectins (C-type lectins with a collagen-like domain). MBL can be considered as an ’ante-antibody’ because it has an important role against infectious agents by recognizing and binding to conserved carbohydrate motifs, such as D-mannose, L-fucose,N-acetyl-D-glucosamine(GlcNAc), N-acetyl-mannosamine(ManNAc) present on the surface of a variety of microorganisms (bacteria,virus,fungi,parasite), via its carbohydrate recognition domain (CRD) in a calcium-dependent manner, and its biological effect is thought to be mediated by collagen-like region (CLR) through binding with MBL-associated serine protease(MASP).It can trigger immediate cellular lysis or phagocytosis by initiating the lectin pathway of complement activation, or promote opsonophagocytosis by direct binding to cell surface receptors without the involvement of complement. A mounting body of evidence suggests that defect opsonophagocytosis resulted from low MBL levels due to gene mutations in MBL coding gene (CGT52TGT, GGC54GAC and GGA57GAA) and promoter as well as 5’-untranslated region appear to be more vulnerable to infections in a number of cliical settings, and more susceptible to autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and Sjogren’s syndrome resulted from phagocytosis defection. On the other hand, exess activation of lectin pathway may result in inflammation disease. MBL is also an acute phase reactant, showing an increase of up to two or three-fold after infection or surgical trauma.Recent work has highlighted that MBL recognizes self-structures, thus extending the role of these molecules beyond the traditional view of first line defense molecules, including binding to immunoglobulins, recognizing exposed self-antigens during ischemia-reperfusion injury as well as modified self-antigens; binding to autologous apoptotic cells and promoting the clearance of cellular debris.It can also bind to monocytes as well as dendritic cells and regulate cytokine secretion. As a multi-functional molecule in innate immunity, MBL has more functions far beyond innate defense against infection, and may be involved in "crosstalk" between innate and adaptive immunity. So it is of great significance in studying the relationship of MBL with adaptive immunity.However, up to now, few reports focus on the functions of MBL on adaptive immunity, especially of it’s regulatory functions. Fraser has claimed that MBL can inhibit IL-1 secretion of lipopolysaccharide (LPS)-stimulated monocyte, but upregulate the secretion of IL-10 and IL-6.Downing et al found that MBL can bind to DC, Mo and B cell, yet the mechanism remains to be evaluated.None of research is about the interation of MBL with T cell.Previous studies by our lab showed that MBL can upregulate the expression of CDla,CD83,CD40,CD80,CD86 and HLA-DR on IL-4+GM-CSF cultured DC, inhibit the uptake of zymosan granules by DCs but enhance the proliferation of naive T cells induced by DCs.While in the presence of LPS, MBL inhibit DC maturation including down-regulate expression of CD83 and CD86 in a dose-dependent manner, enhance the ability to uptake zymozan granules by DCs and decrease the proliferation of naive T cells induced by DCs and inhibit the production of TNF-aand IL-12 p40+p70.These effects are associated with blocking LPS-TLR4 binding to MBL,resulting in decreasing the activity of NF-κB.We also acquired the direct clues of MBL with adaptive immunity by finding that MBL can bind to Raji cell in an Calcium-dependent manner, and high MBL level can inhibit the proliferation of Raji cells, which indicated that under certain situation, MBL concentration in blood and tissue may increase, which lead to the binding of MBL to self immune cells so as to regulate the adaptive immunity.The present study aimed to determine the regulatory roles of MBL on adaptive immunity, especially its regulatory roles on T cell. Firstly, we acquire natural MBL with high purity and bioactivity from freshly frozen human plasma. Then we investigated whether MBL have an effect on ConA-, anti-CD3-mAb-, anti-CD3mAb+anti-CD28 mAb-stimulated proliferative responses and cytokine secretion of human PBMCs as well as purified T cells, and studied preliminarily the mechanisms of its function.PartⅠEffect of MBL on Proliferation and Cytokines Secretion of PBMCsIt is clear that the proteins of collectin family such as surfactant-associated proteins SP-A and SP-D can initiate and shape adaptive immunity.They have been suggested to modulate a variety of immune cell funcions of adaptive immunity beyond binding to pathogens, including Mo, DC, T cell. SP-A and SP-D inhibit lymphocyte proliferation as well as its function, avoiding the lung tissue damage caused by excessive acquire immune response. MBL can also bind to various immune cells and regulate the cytokine secretion.The structural homology of the collectins led us to hypothysize that MBL may have effect on T cells activation that is similar to SP-A and SP-D. In this study, we sought to determine if MBL have functional similarity with SP-A and SP-D. The effects of MBL derived from human plasma on mitogen-stimulated proliferative responses as well as cytokine secretion of human peripheral blood mononuclear cell (PBMC) was examined.PBMCs were isolated from peripheral blood of healthy adult volunteers by Ficoll-Hypaque density gradient centrifugation and cultured with Con A, or anti-CD3 mAb and various concentrations of MBL simultaneously in RPMI 1640 supplemented with 10% fetal bovine serum(FBS) at 37℃in 5% CO2 for 72h. Proliferation of PBMCs were analyzed by CCK-8 incorporation. Supernatants were harvested 24h later and assayed for cytokines secretion.In FCM analysis, PBMCs were stained with CFSE(2.5μM),then cultured with anti-CD3 mAb and MBL for 4d.Cells were labeled with APC-anti-human CD4 and PE-anti-human CD8 and then analyzed the proliferation, especially CD4+T cell and CD8+T cell.Results of CCK-8 analysis indicated that, MBL exibit obvious inhibitory functions in anti-CD3 mAb-stimulating PBMCs proliferation.FCM analysis indicated that MBL can inhibit the proliferation of CD4+T cell and CD8+T cell of anti-CD3 mAb-stimulated PBMCs. Analysis of the supernatant of mitogen-stimulated cell cultures treated with MBL showed decreased amounts of interleukin-2(IL-2), IL-10 and IFN-y, compared to mitogen alone,while enhancement of IL-6 was detected. Anti-MBL-MASP mAbs may block the inhibitory roles of MBL on IL-2 and IFN-yproduction. The results mentioned above indicate that MBL may inhibit the proliferation and activation of T cell, laying the foundation that MBL may have direct regulatory roles on purified T cells.Part II Effect of MBL on Proliferation and Cytokine Secretion of T cellsPrevious studies showing that MBL inhibit lymphocyte proliferation were conducted with mixed populations of lymphocyte and monocyte, it was not clear whether MBL were acting directly on T cell or indirectly via a paracrine effect. So the present study sought to address whether MBL act directly on purified T cells independent of accessory cells as well as to determine the cytokine production.PBMCs were isolated from peripheral blood of healthy adult volunteers by Ficoll-Hypaque density gradient centrifugation and further purified into CD3+ and CD4+T cells with MACS, then cultured with Con A and MBL for 72h, followed by analysis with CCK-8 incorporation. In FCM analysis, T cells were stained with CFSE(2.5μM), then cultured with anti-CD3 mAb or anti-CD3 mAb+anti-CD28 mAb for 4d. Proliferation of CD4+T cells and CD8+T cells were analyzed. Cytokine secretion such as Thl(IL-2, IFN-γ) and Th2(IL-6, IL-10), as well as IL-17a were detected by ELISA. CCK-8 analysis indicated that MBL can inhibit the proliferation of T cells induced by Con A.FCM analysis showed that MBL can inhibit proliferation of anti-CD3 mAb, anti-CD3 mAb+anti-CD28 mAb-stimulated T cell proliferation as well as CD4+T cell and CD8+T cell.MBL can inhibit the secretion of IL-2,IFN-γIL-10 and IL-17a induced by various concentrations of ConA and anti-CD3 mAb+anti-CD28 mAb, yet secretion of IL-6 may be up-regulated or down-regulated. MBL can also inhibit Con A induced IFN-ysecretion by CD4+T cells.The results above support an important role of MBL in direct regulation of T cell function.And it remains to be determined:1) whether MBL regulate the T cell function through direct binding to T cell; 2)the domain involved in the recognition;3)effect of MBL T cell activation;4)whether MBL can regulate T cell throuth regulating cytokines secreted by APC.PartⅢMechanisms of regulatory roles of MBL on T cellThe objective of the current study was to characterize preliminarily mechanisms responsible for inhibitory effects of MBL on T cell. We investigated the interation of MBL with purified T cells and Jurkat T cells by cell-ELISA as well as FCM analysis, and the effect of anti-CRD mAb, anti-MBL-MASP mAb on the binding of MBL with T cells. CD69 and HLA-DR expression of T cell activation marker were analyzed by FCM. Exogenous Ca++ was added into the culture in order to investigate the function is Ca++ dependent or not. In blocking assay, MBL was cocultured with anti-MBL-CRD or mannan, and analyze the secretion of IFN-ywas by ELISA. In order to determine whether the inhibitory activity was dependent upon the IL-2, recombinant human IL-2(rhIL-2) was added in the presence of MBL and Con A, and analyze the secretion of IFN-γwas by ELISA. MBL can bind to Jurakt cell and purifiec T cell by cell-ELISA and FCM in a Ca++ independent manner, exogenous Ca++ have no influence on IL-2 and IFN-ysecretion, anti-CRD mAb and mannan have no effect on its inhibitory role.The results presented here suggest that the inhibitory effects exbited by MBL may have been due to the collagen domain rather than CRD. CD69 expression decreased when MBL is added with T cell mitogen, yet there is no change of HLA-DR expression. Exogenous rhIL-2 significantly reverse the IFN-ysecretion inhibited by MBL, indicated that MBL inhibit T cell function through suppressing activation rather than inducing apoptosis.In order to investigate the effect of MBL on cytokines secretion of MBL on APC, MBL was cocultured with LPS-stimulated PBMCs, proinflammatory cytokines (TNF-α, IL-6) and MCP-1 were detected with ELISA. In an in vitro induced DC, MBL was added with LPS or TNF-a, and IL-6 was detected by ELISA.MBL can inhibit the production of TNF-αand IL-6 secretion induced by LPS. IL-6 secretion was down-regulated by MBL in DC culture, which give a clue that MBL may inhibit the proinflammatory cytokine secretion thus to inhibit the T cell function,or inhibit the T cell function followed by inhibition of inflammatory reactions. The mechanisms and biological significance of MBL involved in T cell function remains to be established.In summary, results above have showed that various concentrations of MBL derived from human plasma suppressed proliferation of stimulated PBMCs and purified T cells in comparison to lectin-stimulated cells alone, including concanavalin A, anti-CD3,anti-C3+anti-CD28.Inhibition was associated with a decreased production of cytokines. Acquire direct clue that MBL can interact with T cell.We also mentioned that MBL may regulate T cell function through direct and indirect mechanism. These data lend further credit to an important physiological role MBL in regulating adaptive immunity. Based on current data,it appears that MBL can dampen lymphocyte responses to exogenous stimuli or apoptotic cells and protect the body against collateral immune-mediated damage. Further studies evaluating the specific mechanisms as followedare required:the receptors involved in binding and the effect of MBL on signal transduction; the effect of MBL on CD4+T cell and CD8+ T cell function as well as differentiation; indirect roles of MBL on T cells mediated by APC. Preliminary results from MBL regulatory functions are encouraging, and extension of the research would provide further credit to an important physiological role of MBL in regulating T cell function through an yet unknown mechanism, and can be used to better understand and treat MBL deficiencies as well as T cell disorder diseases.更多还原