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The Effects of Recombinant Human β2-glycoprotein-Ⅰ and Its Domain Ⅰ on the Endothelial Activation Induced by Sera from Antiphospholipid Antibody Syndrome Patients and Priliminary Approach to β2-glycoprotein-Ⅰ Tolerogens

Author: FuJia
Tutor: TanYan
School: Jilin University
Course: Immunology
Keywords: Antiphospholipid antibody syndrome(APS) endothelial cell β2GPⅠ rhβ2GPⅠDⅠ2 anti β2GPⅠ immunologic tolerance
CLC: R392.32
Type: PhD thesis
Year: 2006
Downloads: 124
Quote: 0
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Abstract


The antiphospholipid antibody syndrome (APS), characterized by vascular thrombosis orrecurrent pregnancy losses, is an autoimmune disorder which involves multiple systems.Laboratory evidence for APA could be detected in the patients. APA are a family ofautoantibodies with heterogenicity that target negative phospholipid and protein cofactors.Many researchers focus on β2GPⅠ since it was thought to be an autoimmue antigen in 1990.?2GPI, also called ApoH , is a highly glycosylated single-chain plasma protein composed of326 amino acids with a molecular mass of 50 kDa. The protein is a member of thecomplement control protein or short consensus repeat (SCR) superfamily, that seems to be themajor, but not the only, cofactor for the recognition of anionic phospholipid by aPL antibodies.High homology between β2GPⅠ from human and that from mouse suggested its importantphysiological functions. High titer anti-β2GPⅠ could be detected in sera of patients withthrombosis and recurrent fetal loss and strong correlation between anti-β2GPⅠ andthrombosis. APA could recognize β2GPⅠ directly in absence of phospholids, if the antigenconcentration in microtiter plates is enough. It has been known that β2GPⅠ plays a role inlipoid metabolism, significantly inhibits intrinsic coagulation pathway and the procoagulantrole of apoptotic cells and is involved in clearance of apoptotic cells、senescent cells、and theextraneous matter. Despite the definite pathogenic mechanisms arenot fully elucidated, the multiple clinicalmanifestations attribute to APA targeting β2GPⅠ. Evidence accumulated from animalmodels of the aPL syndrome indicate that aPL antibodies can play a causal role in thedevelopment of thrombosis and pregnancy loss. Human anti-β2GPI antibodies have beenshown to induce tissue factor at both protein and mRNA level in HUVEC monolayers in vitro.Vascular endothelium which plays a key role in thrmbosis is a major site of regulation ofhemostasis. APA has been found to recognize, injure, and/or activate cultured vascularendothelial cells. Possible pathogenic mechanisms include: activating vascular endothelialcells;Disruption of the Annexin-V Anticoagulant Shield;activating platelet and complement;inducing endothelial cells and monocyte cells to express tissue factor;altering the balance ofeicosanoid synthesis toward prothrombotic moieties;interference with the components of theprotein C pathway and inhibition of the antithrombin-III pathway. Endothelial cells incubatedfin the presence of aPL preparations were shown to up-regulate adhesion molecules(E-selectin, ICAM-1 and VCAM-1) expression and pro-inflammatory cytokines (IL-1b andIL-6) secretion, an effect that is mediated by ?2GPI, and may increase the adhesion ofleukocytes to the vascular wall and promote inflammation and thrombosis. Increased plasmalevels of soluble VCAM-1 were found in primary APSpatients with recurrent thromboticevents.Controversial results have been reported regarding the aPL-specific epitopes of β2GPIthat are crucial in the development of APS. Many groups focused on it and reports aboutdomain Ⅰ、Ⅳ、Ⅴ have been shown. It seems that most aPL antibodies recognize domain I of?2GPI. So we postulated that β2GPⅠDⅠ could bind to pathogenic anti-β2GPⅠ andeliminate the effect of majority of autoantibodies on endothelial cells activation. thrombosis.Current treatment of APS relies on the extensive use of anticoagulants to reduce the riskof thrombotic events, or the use of general immunosuppressants and cytotoxic agents. Despiteits effectiveness, safer approaches are needed since prolonged high-intensity medicinetreatment carries significant risks for side effects, including fever, nausea, vomiting, andserious bleeding events. Thus, the elimination of specific immune responses has been asignificant goal in the treatment of antibody-mediated diseases.The major objective of this article was to investigate the effect of APS sera onexpressions of ICAM-1、MCP-1 and E-selectin in endothlial cells by cultruring primaryHUVEC and EA.hy926 cell line in vitro, based on prokaryotic expression of rhβ2GPⅠ andits domain Ⅰ dimer (rhβ2GPⅠDⅠ2);to observe the inhibition of effect of APS sera onICAM-1、MCP-1 and E-selectin expressions in protein and mRNA levels in HUVEC bydifferent concentrations of rhβ2GPⅠ/rhβ2GPⅠDⅠ2. to verify that APS sera anti-β2GPⅠpositive could activate cultruring endothelial cells in vitro;rhβ2GPⅠ and rhβ2GPⅠDⅠ2could eliminate the activation of cultruring endothelial cells in vitro by APS sera.Oral tolerance was induced by low dose of rhβ2GPⅠ in experimental APS mice.Anti-β2GPⅠ titers in β2GPⅠ immunized mice were decreased, oral tolerance could beefficient when rhβ2GPⅠ was given at an early time point after immunization. Immunologictolerance also be induced by rhβ2GPⅠDⅠ2. given intravenously. Then we examined thesecondary immune responses tolerized mice. The researchs in this article providedexperimental basement for developing β2GPⅠ tolerogens.In this article, The full-length cDNA sequence encodingβ2GPⅠ mature peptide wasamplified by reverse transcription polymerase chain reaction (RT-PCR) from RNA in humanliver cells. rhβ2GPⅠ was expressed by prokaryotic expression vectors pQE30, and waspurified and annealled by using NI metal immobilization affinity chromatography and NImetal gel column renaturation;According to isocaudarner character, rhβ2GPI domain Ⅰdimer (rhβ2GPⅠDⅠ2) was contrusted and expressed. The biologic activities of rhβ2GPⅠand rhβ2GPⅠDⅠ2 were characterized by Western blot. Cell-ELISA was used to investigatethe effect of APS sera on expressions of ICAM-1、MCP-1 and E-selectin in primary HUVECand EA.hy926 cell line, it is verified that APS sera anti-β2GPⅠ positive could activatecultruring endothelial cells in vitro;We found the affinity of rhβ2GPⅠDⅠ2 and anti-β2GPⅠwas higher than that of rhβ2GPⅠ. RT-PCR quntitative analysis was used to study mRNAexpression changes of three molecules in HUVEC by different concentrations ofrhβ2GPⅠDⅠ2, We found that elevated mRNA expressions of three molecules in HUVECwas inhibited as well. So it is confirmed that anti-β2GPⅠ can play a causal role in the APSpathogenic mechanism. It is suggested that rhβ2GPⅠ/rhβ2GPⅠDⅠ2 could bind topathogenic anti-β2GPⅠ antibodies and elimiate their pathopoiesis. APS sera treated bydifferent concentrations of rhβ2GPⅠ/rhβ2GPⅠDⅠ2 were used to observe the change ofmolecules expressed on endothelial cells surface by these sera. It was found that expressionsof ICAM-1、MCP-1 and E-selectin were inhibited increasingly with the elevation ofrhβ2GPⅠ/ rhβ2GPⅠDⅠ2 concentrations.in this article, we studied the change ofanti-β2GPⅠ titers in rhβ2GPⅠ oral tolerance mice, it is found that different doses ofrhβ2GPⅠ inhibited humoral immunity to some degree. Kinetic study of the anti-β2GPⅠtiters in the sera of mice during induction of oral tolerance to rhβ2GPⅠ showed that it wouldbe efficient when oral administration of rhβ2GPⅠ at early stages of APS development.Specific T lymphocyte proliferations in oral tolerized mice were decreased evidently. It issuggested that cellular immunity was down-regulated in oral tolerized mice. Cytokines suchas IL-4, IL-10, TGF-β, IL2, IFN-γ levels showed that the balance of Th1/Th2 switched to Th2,cellular immunity was suppressed. On the bases of constructon of rhβ2GPⅠDⅠ2, we studiedthe specific B cell responses inhibition ability of introvenous rhβ2GPⅠDⅠ2 to β2GPⅠimmunized mice. Different doses of rhβ2GPⅠDⅠ2 decreased anti-β2GPⅠ levels comparedwith control groups evidently;Ratio of anti-β2GPⅠ post-boost to pretreatment withrhβ2GPⅠDⅠ2 in individual mice showed that the treatment reduced circulating anti-β2GPⅠlevels and blocked a secondary immune response,Collectively, these results indicate that causal roles lies in APS sera,rhβ2GPⅠ/rhβ2GPⅠDⅠ2 treating verified it is anti-β2GPⅠ. β2GPⅠ/rhβ2GPⅠDⅠ2 couldlower endothelial activation by anti-β2GPⅠ. Low doses of rhβ2GPⅠ could induce oraltolerance , and it would be efficient at early stage of APS development. The mechanism oftolerance is involved with suppression of cellular immunity, down-regulated Th1 cellsfunctions. Intravenous administration of rhβ2GPⅠDⅠ2 suppressed the specific B cellsresponses.For the first time, we verified anti-β2GPⅠ is an important pathogenic factor bytreatment of APS sera with rhβ2GPⅠ/rhβ2GPⅠDⅠ2;Immunologic tolerance was inducedby oral rhβ2GPⅠ and intravenous rhβ2GPⅠDⅠ2 in experimental APS mice successfully,and studied the relevance of β2GPⅠ tolerogens to APS development. Thus experimetalbasement and theoretical evidence for developing APS tolerogen were provided.

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