REGULATION OF AUTOIMMUNITY THROUGH EPITOPE SPREADING

描述（由申请人提供）：对几种人类自身免疫性疾病动物模型的研究表明，随着疾病的进展，T细胞对特定自身抗原（分子内）和其他疾病相关自身抗原（分子间）内各种表位的反应发生动态变化。这种现象被称为表位扩散（或反应多样化），在实验模型（如实验性自身免疫性脑脊髓炎（EAE）、非肥胖糖尿病（NOD）小鼠的I型糖尿病和系统性红斑狼疮（SLE）等）和多发性硬化症患者中都观察到了这种现象。在这些疾病中，表位扩散在自身免疫反应的传播中被调用。与此相反，通过大鼠佐剂诱导的人类类风湿关节炎（RA）关节炎（AA）模型，我们观察到，在疾病过程中，涉及T细胞对65-kD分支杆菌热休克蛋白（Bhsp65）反应的表位扩散发生，并且涉及的T细胞表位（即Bhsp65 c末端决定因子；BCTD）本质上具有疾病调节作用。用热致死M. tuberculosis （Mtb）攻毒s.c.诱导Lewis大鼠AA。因此，表位扩散并不总是与自身免疫反应的延续有关；相反，它在本质上也可以起到保护作用。明确表位扩散的机制对于进一步了解自身免疫的发病机制以及为这些疾病设计新的更有效的治疗方法至关重要。AA模型最适合研究免疫调节环境下的表位扩散。然而，有关AA表位扩散的基本机制的信息也适用于其他自身免疫模型。我们假设T细胞对BCTD反应的多样化确实是由自身（大鼠）hsp65 （Rhsp65）在体内触发的。在急性AA的局部炎症/细胞因子环境下，Rhsp65的细胞诱导和表达增强，加上抗原加工机制的上调，导致Rhsp65 c末端决定因子（RCTD）从Rhsp65高效显示，并诱导RCTD反应性T细胞。这些rctd反应性T细胞是同源BCTD通过交叉反应性（分子模仿）募集的T细胞，表现为在AA晚期向Bhsp65扩散表位。我们计划解决以下问题：目标1：确定自身hsp65 （Rhsp65）和分子拟态在AA过程中对疾病调节BCTD的反应多样化（表位扩散）中的作用；目的2：研究新生儿调节性T细胞库耐受对临床疾病和表位扩散的影响，并确定BCTD/ rctd反应性T细胞控制关节炎性表位特异性T细胞活性的机制。这项研究的结果将为表位扩散的机制及其在自身免疫调节中的作用提供新的见解。这反过来将有助于开发新的治疗RA和其他自身免疫性疾病的方法。

DESCRIPTION (provided by applicant): Studies in several animal models of human autoimmune diseases have revealed that with the progression of disease, there is a dynamic shift in the T cell responses to various epitopes within a particular self antigen (intramolecular) as well as to other disease-related self antigens (inter-molecular). This phenomenon has been termed as epitope spreading (or diversification of response), and it has been observed in experimental models [e.g., experimental autoimmune encephalomyelitis (EAE), type I diabetes in the non-obese diabetic (NOD) mouse, and systemic lupus erythematosus (SLE), etc.], and in patients with multiple sclerosis. In these disorders, epitope spreading has been invoked in propagation of the autoimmune response. In contrast to the above, using the rat adjuvant-induced arthritis (AA) model of human rheumatoid arthritis (RA), we observed that epitope spreading involving T cell response to 65-kD mycobacterial heat-shock protein (Bhsp65) occurred during the course of the disease, and that the T cell epitopes involved (namely, Bhsp65 C-terminal determinants; BCTD) were disease-regulating in nature. [AA is inducible in the Lewis rat by challenge s.c. with heat-killed M. tuberculosis (Mtb).] Thus, epitope spreading is not always involved in perpetuation of the autoimmune response; instead it can also be protective in nature. Defining the mechanisms underlying epitope spreading is critical for further understanding of the pathogenesis of autoimmunity, and for devising novel and more effective therapeutic approaches for these disorders. The AA model is most suited for study of epitope spreading in the setting of immune regulation. Nevertheless, information about the basic mechanisms involved in epitope spreading in AA would also be applicable to other models of autoimmunity. We hypothesize that diversification of the T cell response to BCTD is indeed triggered in vivo by self (rat) hsp65 (Rhsp65). It involves the enhanced cellular induction and expression of Rhsp65 coupled with upregulation of the antigen processing machinery under local inflammatory/cytokine milieu of acute AA, leading to efficient display of Rhsp65 C-terminal determinants (RCTD) from Rhsp65 and induction of RCTD-reactive T cells. These RCTD-reactive T cells are the ones that are recruited through crossreactivity (molecular mimicry) by homologous BCTD, manifesting as epitope spreading to Bhsp65 in the late phase of AA. We plan to address the following - Aim 1: To determine the role of self hsp65 (Rhsp65) and molecular mimicry in diversification of response (epitope spreading) to disease-regulating BCTD during the course of AA; and Aim 2: To study the influence on both clinical disease and epitope spreading of neonatal tolerization of the regulatory T cell repertoire, and to define the mechanism by which BCTD/RCTD-reactive T cells control the activity of arthritogenic epitope-specific T ceils. The results of this study would provide novel insights into the mechanisms underlying epitope spreading, and its role in regulation of autoimmunity. This in turn would contribute to developing novel therapeutic approaches for RA and other autoimmune diseases.