高中教材中特异性免疫疑点的解答

高中生物学教材由于课时容量限制,对特异性免疫知识的介绍相对较少,导致学生对特异性免疫存在一些疑问。针对抗原递呈细胞、B细胞、T细胞的种类,抗原递呈的过程,T细胞、B细胞活化的条件以及二次免疫过程抗原递呈存在的疑点进行解答。     

靶向M细胞的抗原递送¾¾增强黏膜免疫应答的关键策略

黏膜是阻止病原入侵的第一道防线,黏膜免疫系统在抵抗感染方面起着至关重要的作用。通过黏膜途径接种疫苗可以同时诱导黏膜和全身免疫反应,因此,理论上针对黏膜的免疫策略是最合理和有效的。但黏膜免疫系统的复杂性和屏障作用造成抗原诱导的免疫应答水平低下,制约了黏膜疫苗的发展。M细胞(Microfoldcells)是黏膜免疫系统所独有的,其具有捕获腔内抗原和启动抗原特异性免疫应答的功能。M细胞摄取抗原的多少直接关系到黏膜疫苗的免疫效力,而利用M细胞配体可将抗原靶向递呈给M细胞,从而实现高效的黏膜免疫应答。靶向M细胞的抗原递送策略及其应用可以提高黏膜免疫应答水平,促进黏膜疫苗的研制。尽管如此,要成功研制安全高效的黏膜疫苗,今后依然有漫长的路要走,这可能有赖于进一步探究M细胞的特性和功能及黏膜免疫机制。     

T细胞抗原识别与活化研究

T细胞是通过其表面受体-T细胞抗原特异性受体（T cell antigen specific receptor,TCR）识别抗原并进行免疫应答的．T细胞如何识别以及清除抗原一直是分子免疫学研究的重点．免疫应答的重要过程是淋巴细胞的活化．而T细胞活化是细胞介导的免疫应答中不可缺少的内容．鉴于T细胞抗原识别和活化在免疫应答中的重要性．对近年来T细胞在抗原识别与活化研究方面所取得的重要进展进行了综述,并展望了T细胞的研究前景．     

诱导免疫应答的肿瘤抗原

肿瘤抗原可以诱导机体的免疫应答,是肿瘤的免疫治疗中多肽疫苗的分子基础,近十年来发展起来的肿瘤疫苗筛选方法,利用肿瘤抗原特异性T细胞或抗体识别肿瘤抗原,为临床肿瘤免疫治疗提供了大量备选抗原分子。文中总结了肿瘤抗原的种类,及迄今几乎所有被证明的含有T细胞识别表位的抗原分子及其血清学反应性,为临床肿瘤疫苗的选择提供了依据。     

融合表达DEC205单链抗体和NS3蛋白的HCV DNA疫苗的免疫原性研究

为研发新型HCV DNA疫苗并探讨优化其免疫原性的策略,我们分析靶向树突状细胞(Dendritic cells,DC)的分子对HCV DNA疫苗免疫原性的影响。我们基于抗小鼠DC细胞表面分子DEC205/CD205的单克隆抗体DEC205的单链分子,构建可单独表达DEC205单链抗体或者与HCV非结构蛋白NS3融合表达的DNA表达质粒,并构建单独表达HCV非结构蛋白NS3的DNA表达质粒;经瞬时转染法鉴定HCV NS3及其与DEC205单链抗体融合蛋白的表达;随后采用注射结合电转的方式免疫Balb/C小鼠并研究各疫苗的体液(NS3特异性IgG抗体)与细胞免疫(IFN-γELISPOT)效果。结果表明:DEC205单链抗体基因与HCV NS3编码基因的融合可显著增强NS3特异的免疫应答;采用皮内注射加卡钳电极电转的方式可以产生最强的NS3特异性抗体和T细胞免疫反应。因此,通过DEC205单链抗体与HCV DNA疫苗靶抗原融合可明显增强免疫应答效果。该策略为HCV及其他类似病原的新型DNA疫苗研制提供重要依据。     

MHC分子抗原递呈机制的研究进展

MHC分子限制性抗原递呈机制在细胞免疫应答中占有绝对重要地位,对MHC抗原递呈机制的研究一直是免疫学研究的热点。尽管抗原分子经过MHC分子递呈和加工机制已经被研究了近40年,且抗原递呈机制的基本途径已经在10年前基本阐明,但近几年仍发现MHC一些新的递呈机制和特点。MHC分子抗原递呈过程十分繁琐,涉及许多蛋白质、分子伴侣等之间的相互作用。现综述了MHC分子所递呈限制性抗原的产生、运输以及抗原交叉递呈等方面的最新研究进展。     

树突状细胞在哮喘慢性气道炎症中的作用

树突状细胞(dendritic cells, DCs)作为专职抗原提呈细胞启动了哮喘初次免疫应答,但是DCs在抗原特异性免疫应答及其引发的哮喘慢性气道炎症反应中的作用存在一定争议,需要重新认识。本文通过综述相关研究,认为DCs在哮喘中的免疫活性并不局限于启动过敏原诱发的初次免疫应答,DCs还可以通过激活记忆性T细胞参与介导抗原特异性免疫应答,并在哮喘慢性气道炎症病理进程中发挥重要作用。此外,在多种因素作用下,哮喘气道DCs可以分化为具有免疫抑制作用或引起免疫耐受的调节性DCs (DCreg)或耐受性DCs (tolDC),抑制哮喘Th2细胞主导的慢性气道炎症。通过调节气道免疫微环境或细胞内源性信号分子,抑制DCs在抗原特异性免疫应答中活化记忆性T细胞的能力,或通过诱导DCreg/tolDC细胞分化,进而控制慢性气道炎症,将是未来防治哮喘新的重要研究方向。     

HIV-1辅助蛋白Vpr多肽抗体的制备与鉴定

预测Vpr蛋白的B细胞抗原表位,并利用合成的B细胞表位肽制备Vpr特异性抗体。应用生物信息学技术获得Vpr蛋白共享氨基酸序列并预测其潜在B细胞抗原表位,与载体蛋白血蓝蛋白(KLH)偶联合成多肽并免疫家兔,鉴定及纯化获得的多肽特异性抗体。软件预测显示,Vpr蛋白N端的第3～19位(N)和C端的第82～95位(C)氨基酸序列为潜在B细胞抗原表位;ELISA检测抗血清中多肽特异性抗体的效价都达到1:105以上;Western-Blotting结果显示,无论对HIV-1B亚型还是CRF07_BC重组型的Vpr蛋白,其多肽N抗体和C抗体均能特异性识别;免疫沉淀结果显示,Vpr多肽N和C抗体也能特异性结合未变性的野生型Vpr或GFP-Vpr融合蛋白。利用生物信息学技术能成功预测Vpr蛋白B细胞抗原表位,免疫所获得的抗体具有较好的特异性和应用性。     

肠道免疫的安全靶向载体:大肠杆菌Nissle1917

长期以来,如何激发高效的肠道黏膜免疫应答来预防肠道感染始终是较为棘手的问题.本文旨在对大肠杆菌(Escherichia coli)Nissle 1917作为肠道黏膜免疫的安全靶向载体,调理胃肠道菌群紊乱、缓解溃疡性结肠炎以及利用益生菌固有特性或优化特性进行治疗的可能性等相关研究进展作一综述.大肠杆菌Nissle 1917(EcN)是一株可口服的优良益生菌,也可作为生物载体活苗候选株,兼有较强的肠道局部定殖能力和无免疫原性的特性.该菌株还可以作为载体靶向递呈TAT-凋亡素融合蛋白治疗结肠直肠癌,并在研发靶向递呈防御素治疗溃疡性结肠炎和克罗恩病上具有重要的功能.其基因修饰株能够原位递呈特定的抗原分子,有效激发特异性的黏膜免疫应答.重组大肠杆菌Nissle-HA 110-120具有体外表达特异性抗原的能力,但EcN菌体本身不会引起黏膜免疫应答,也不影响对自身抗原的外周免疫耐受.同时,EcN具有很好的安全性,尤其是因炎症导致肠道防御屏障破坏的时候,重组大肠杆菌Nissle-HA110-120在健康或患有急性结肠炎的小鼠体内都没有迁移、克隆扩增和激活特异性CD4+T淋巴细胞的作用.     

自身抗独特型抗体的产生及其在免疫应答调节中的作用

自身抗独特型抗体(auto—ald)广泛存在于机体对多种抗原的免疫应答过程中,并通过与独特型(Id)相互作用,参与体液和/或细胞免疫应答的调节。auto-aId的调节作用包括:(1)通过抑制B细胞合成相应的Id抗体或激活Id特异性T细胞,后者作用于效应细胞,而反馈性抑制机体对起始抗原的免疫应答(向下调节);(2)内影像auto-aId模拟抗原,促进相应Id的表达(向上调节)。其调节作用在多数情况下对机体有利,如维持体内Id—抗—Id网络的稳定性,促进某些自身免疫病的恢复等。但在某些情况下则对机体有害,甚至导致某些受体自身免疫病的发生。     

Role of antigen and,antibody in the regulation of the immune response

The enzyme dextranase could degrade antigenic dextran in vivo even when given 6-15 d after the antigen. Dextranase injected after the antigen suppressed the immune response when given 24 but not 48 h after the antigen, indicating that the antigen must interact with the immune system for 48 h to initiate a response. Thereafter, the B cells are independent of further antigen stimulation. To show whether antibody-mediated suppression of the immune response was determinant specific FITC-conjugated SRC were applied as immunogen and antibodies were raised both against the carrier (SRC) and the FITC hapten. When these antibodies were injected 1-3 h after the immunogen they only suppressed the immune response to the corresponding determinant. Anti-carrier antibodies usually enhanced the response to the hapten. Therefore, antibody-mediated suppression of the immune response is determinant-specific and cannot be mediated in vivo to a detectable extent by the Fc part of the antibodies.     

Novel function of complement C3d as an autologous helper T-cell target

The C3d fragment of complement component C3 has been shown to enhance immune responses to antigens that lack T-cell epitopes such as bacterial polysaccharides. C3d binds to the B-cell complement receptor 2 (CR2 or CD21); this binding serves as a co-activation signal to the B cell when the polysaccharide antigen portion binds simultaneously to the B-cell receptor (surface Ig). Bringing together receptor-associated signal transduction molecules CD19 and Igalpha/beta, respectively, results in a lower threshold of activation. Paradoxically, C3d has also been shown to enhance antibody titers in the CD21 knockout (KO) mouse model as well as increase Th1 and Th2 cytokine secretion, suggesting that that an auxiliary CR2-independent pathway of immune activation may exist. We hypothesized that in addition to its molecular adjuvant property that enhances signal 1 during B-cell activation (co-signal 1), C3d also contains T-cell epitopes that are able to stimulate autoreactive C3d peptide-specific helper T cells which we term 'co-signal 2'. Using the EpiMatrix T-cell epitope-mapping algorithm, we identified 11 putative T-cell epitopes in C3d, a very high epitope density for a 302 amino-acid sequence. Eight of these epitope candidates were synthesized and shown to bind a variety of class II HLA-DR molecules of different haplotypes, and to stimulate C3d peptide-specific T cells to secrete pro-inflammatory cytokines in vitro. Further, we demonstrate a C3d-peptide specific increase in CD4(+) intracellular IFN-gamma(+) T cells in peripheral blood mononuclear cells (PBMCs) exposed to C3d peptides in vitro. We believe that the discovery of these autologous T cells autoreactive for C3d provides evidence supporting the 'co-signal 2' hypothesis and may offer a novel explanation of the CD21 KO paradox.     

Trypanosoma cruzi: cross-reactive anti-heart autoantibodies produced during infection in mice

Preimmunization with attenuated Corpus Christi stain Trypanosoma cruzi provides survival to C3H mice and enhances resistance of C57 mice to Brazil strain infection. C3H(He) and C57 B1/6 mice surviving acute infection of T. cruzi are shown to have heart specific autoantibodies through acute and chronic infection. ELISA assays were performed using nondenatured extract of hearts from normal syngeneic mice as target antigen reacted with sera from immunized and/or infected mice. Surviving C3H mice developed a specific anti-heart response as early as Day 21 of infection and this response continued at a high level to Day 300. The response in C57 mice, both immunized-infected and infected only, increased to Day 100 followed by a decline in intensity. The heart specificity of the response in mice was suggested by negligible reaction of sera with smooth muscle preparations and a reduced autoreactivity with skeletal muscle. Laminin, a suggested target of autoimmunity in Chagas' disease, was shown not to be the target of the responses in these mice. Immunoaffinity-purified heart specific antibodies show strong cross-reactivity with parasite antigen and like purified parasite specific antibodies, reacted with heart antigen.     

Modulation of the immune response by anaphylatoxin in the microenvironment of the interacting cells

It was shown that the anaphylatoxins C3a and C5a can modulate in vitro immunological reactivities. C3a suppresses both the in vitro polyclonal antibody response and the specific antibody response to sheep red blood cells (SRBC) of both mouse spleen cells and human peripheral blood cells. The target cell in the mouse for C3a appears to be an Lyt-1+2- suppressor-inducer cell and macrophages appear not to be required. In contrast to C3a, C5a enhances in vitro responses of mice. Both the response to SRBC and the mixed lymphocyte reaction are enhanced by C5a. This enhancement appears to be through an Ia- macrophage that contains receptors for C5a. It appears that enhancement may be brought about by interleukin 1, which is released when Ia- macrophages are pulsed with C5a. It is suggested that these anaphylatoxins, when present in high concentrations in the microenvironment of the interacting cells of the immune system, play a dynamic role in the regulation of the immune response. Peptide fragments cleaved from the Fc portion of antibody, complexed with antigen in this microenvironment, may have a similar regulating role.     

Molecular construction of experimental combined vaccines

A method for designing molecular constructions of combined artificial immunogens mimicking viral particles is proposed. Using this method, it is possible to expose antigenic determinants of any viral protein on the surface of such particles and to deliver plasmids containing genes encoding the synthesis of protein antigens to target cells. This approach was used to create the constructions of combined artificial immunogens inducing the production of specific antibodies to HIV-1 and to evaluate the extent and duration of B-cellular immune response depending on the way of antigen exposure to immunocompetent cells.     

In vitro immune response by murine bone marrow cells stimulated against soluble immune complexes.

Synchronized nonadherent bone marrow lymphocytes were stimulated with soluble immune complexes, in antigen excess formed by C3H/HeJ antibodies and various noncross-reacting protein antigens, in a suspension culture which allowed longterm cultivation. On binding of these complexes, lymphocytes underwent blast transformation with mitosis and formation of plasma cells which secreted specific antibodies to the antigen; a cyclic sequence of lymphocytes, blasts, and plasma cells was observed until the majority of the cell population appeared to be plasma cells. The relative percentage of mature plasma cells then decreased leaving mostly small lymphoid cells among which evidence suggests the presence of memory cells. Complexes at equivalence stimulated for the first few days, whereas antibody excess caused stimulation only initially followed by inhibition of the response. Antibodies passively added to the cultures inhibited the proliferative reaction; free antigen induced a typical secondary-type response.     

A tandem repeat of MUC1 core protein induces a weak in vitro immune response in human B cells

We have recently described an efficient method to study the human humoral immune response in vitro and to generate isotype-switched, antigen-specific human B cells, which has allowed us to produce high-affinity IgG antibodies against different peptides. In an attempt to study the in vitro immune response against self-antigens, such as tumour-associated antigens, this protocol was used to immunise resting human peripheral blood B cells with a peptide epitope from the human-adenocarcinoma-associated antigen, MUC1. After the two-step in vitro immunisation, the secondary immunised cultures were tested for MUC-1-specific antibodies by enzyme-linked immunosorbent assay (ELISA). Phage molecular libraries were subsequently constructed, using the variable parts of Ig genes derived from cells taken from ELISA-positive wells. The libraries were selected on the MUC1 core peptide. Antigen-specific Fab fragments, specific for the self antigen MUC1, were found in the library of secondary immunised IgG⁺ B cells and these antibodies were evaluated by BIAcore analysis. The specific Fab fragments exhibited an unusually rapid dissociation rate constant and the overall response frequency was lower, as compared to other antibodies generated by this protocol, which might be explained by the repetitive nature of the core peptide used for immunisation. Received: 30 June 1998 / Accepted: 24 September 1998     

Tumor vaccine: current trends in antigen specific immunotherapy

Effective cancer treatment to prevent the tumor growth as well as to stop its recurrence is the dream of oncologists. Currently available therapeutic measures like, radiotherapy and chemotherapy, often suffer from severe toxicity and lack of specificity of the drug towards tumor cells. Another promising approach is the 'immunotherapy', in which either the immune system is activated by tumor vaccine to combat the tumor growth or antitumor antibodies can be used. Vaccination can stimulate humoral, cellular and innate immune systems to generate various effector molecules, like antibody, cytotoxic T cells, cytokines etc. In antigen specific immunotherapy, the immune system can be stimulated actively by antigen based tumor vaccine to kill only those tumor cells, having expression of the particular tumor associated antigen. Different experimental, preclinical and clinical studies have proved that generated immune responses are effective to restrict the tumor growth. Useful strategies of antigen specific immunotherapy and outcome of various laboratory and clinic based studies are discussed.     

Inhibition of lymphocyte blastogenesis by C3c and C3d.

The C3 cleavage products C3c and C3d were tested for their ability to alter the immunoproliferative response of human peripheral mononuclear cells to the antigens SLO and SK-SD, and to the mitogens PHA and PWM. It was found that both C3c (30 to 120 micrograms/ml) and C3d (10 to 40 micrograms/ml) inhibited lymphocyte blastogenesis in the presence on antigens but not mitogens, when cells were cultured in either autologous plasma or FCS. Similarly, the response to antigens of cell populations enriched for T lymphocytes was inhibited, whereas the response to optimal or suboptimal doses of mitogens was unaffected. When nonadherent (NA) cells were reconstituted with increasing numbers of adherent (AD) cells to potentiate the proliferative response of NA cells to the antigen SLO, the addition of either C3c or C3d abolished the potentiation of the response at low levels of reconstitution. However, at given dose of C3c or C3d, addition of excess AD cells could restore the proliferative response. These results suggest that both C3c and C3d can inhibit T cell proliferation in response to antigen and that they may act at the level of the monocyte-T lymphocyte interaction to modulate cellular immune responses.