ALTERED T-CELL ACTIVATION IN AUTOIMMUNE ARTHRITIS

过度刺激的T细胞活化诱导的细胞死亡(AICD)被认为是体内稳态和预防自身免疫的重要机制。通过T细胞抗原受体(TCR)反复刺激T细胞，诱导T细胞表面Fas和Fas配体(FasL)的共表达，Fas和FasL的相互作用导致T细胞的“自杀”或“自残”。蛋白多糖(PG)诱导的关节炎(PGIA)是一种用PG软骨系统免疫小鼠而形成的新型自身免疫性小鼠模型。在这个模型中，外周CD4+T细胞在体外对TCR刺激的异常增殖是 与关节炎小鼠低水平的AICD和高比率的干扰素(IFN)-γ和白介素4(IL-4)有关。PGIA小鼠的AICD缺陷和CD4+T细胞的过度增殖可能归因于未能诱导细胞Fas相关死亡结构域(FADD)样的IL-1β转换酶(FLICE)抑制蛋白(c-FLIP)降解。与野生型(Wt)BALB/c小鼠相比，IL-4缺陷(IL-4-/-)小鼠的PGIA发生率和严重程度增加，而给BALB/c小鼠注射IL-4可显著减少疾病。此外，PG诱导的IL-4-/-CD4+T细胞不能发生凋亡。基于这些观察结果，我们推测，IL-4的丢失导致c-flip降解失败，进而导致AICD缺陷和周围自身反应性Th1型细胞的过度增殖，从而导致PGIA的发生。为了证实我们的假设，我们提出了三个 具体目标：(1)我们将确定IL-4的丢失是否以及如何导致在IL-4-/-PGIA小鼠体内CD4+T细胞的积聚；(2)我们将研究c-flip是否调节IL-4-/-PGIA小鼠致关节炎的CD4+T细胞的过度增殖和缺陷AICD；以及(3)我们将确定IL-4是否通过调节细胞周期进程来调节自身反应性T细胞对AICD的易感性，并探讨IL-4是否通过控制c-fllip的表达来调节细胞周期进程。这些拟议研究产生的信息将增强我们对IL-4生物学功能的理解，并将有助于开发治疗自身免疫性关节炎的新方法。

Activation-induced cell death (AICD) of over-stimulated T cells has been proposed to be an important mechanism in homeostasis and the prevention of autoimmunity. Repeated stimulation of T cells through T cell antigen receptor (TCR) induces co-expression of Fas and Fas ligand (FasL) on the surface of T cells, and the Fas-FasL interaction leads to the "suicide" or "fratricide" of T cells. Proteoglycan (PG)-induced arthritis (PGIA) is a novel autoimmune murine model induced by systemic immunization of mice with cartilage PG. In this model, an aberrant proliferation of peripheral CD4+ T cells in vitro in response to TCR stimulation was associated with low levels of AICD and a high ratio of interferon (IFN)-gamma to interleukin (IL)-4 in arthritic mice. The defective AICD and hyper-proliferation of CD4+ T cells in mice with PGIA may be ascribed to failure of inducing degradation of cellular Fas-associated death domain (FADD)-like IL-1beta-converting enzyme (FLICE)-inhibitory protein (c-FLIP). The incidence and severity of PGIA is augmented in IL-4-deficient (IL-4-/-) mice in comparison to wild-type (Wt) BALB/c mice, whereas administration of IL-4 to BALB/c mice greatly reduces disease. Moreover, PG-primed IL-4-/- CD4 + T cells fail to undergo apoptosis. Based upon these observations, we hypothesize that loss of IL-4 leads to a failure of inducing c-FLIP degradation which in turn results in defective AICD and hyperproliferation of autoreactive Th1-type cells in the periphery, thus leading to the development of PGIA. To confirm our hypothesis, we propose three specific aims: (1) We will define whether and how loss of IL-4 results in accumulation of CD4+ T cells in IL-4-/- mice with PGIA in vivo; (2) We will investigate whether c-FLIP regulates hyper-proliferation and defective AICD of arthritogenic CD4+ T cells in IL-4-/- mice with PGIA; and (3) We will determine whether IL-4 regulates the susceptibility of autoreactive T cells to AICD by adjusting cell cycle progression, and investigate whether IL-4 regulates cell cycle progression through controlling c-FLIP expression. The information generated by the proposed studies will enhance our understanding of the biological function of IL-4 and will shed light on the development of novel therapeutic approaches to autoimmune arthritis.