Phenotypic And Functional Changes In Circulating T Cells

众所周知，随着年龄的增长，有效免疫反应的能力往往会下降。T细胞表型和功能中存在几种可能相互关联的变化，这些变化可能是衰老中发生的免疫变化的原因或结果。最好描述的变化是CD 4和CD 8 T细胞从幼稚到记忆表型的转变，以及IL-2产生相对于年轻受试者的细胞的下降。这些转变涉及的机制在很大程度上是未知的。为了设计可以开始定义这种机制的实验，有必要能够定义T细胞亚群，以了解它们之间的关系，以及哪些因素调节从一个阶段到下一个阶段的过渡。影响记忆T细胞的发育和细胞因子谱的几种关键细胞因子是IL-2、IL-4、IFN-g和IL-12以及TGF β。各种炎性细胞因子（包括IL-1、IL-6、IL-8、TNF和许多CXC和CC趋化因子）的不受调节的表达已显示参与若干疾病状态，如炎症、自身免疫和一些造血系统恶性肿瘤。使用老年啮齿动物和灵长类动物T细胞进行差异细胞因子产生的几项研究产生了不同的结果。另外的研究已经证明了在衰老过程中从Th 1-Th 0细胞到Th 2细胞的显著转变，而其他研究没有观察到表型Th转换。各种研究报告了老年动物与年轻动物中IFN-g和TNF-a的过度产生，这些差异可能与循环免疫细胞亚群的改变有关。虽然几项人体研究也产生了可变的细胞因子表达结果，但我们已经启动了研究，以检查此类细胞因子的变化（以及其他相关分子的基因和蛋白质表达）使用目前存在的几种独特的分子方法学，包括细胞因子启动子研究，年轻与老年淋巴器官和处于各种激活状态的免疫细胞亚群的基于动力学的微阵列cDNA分析，RNA酶保护测定、定量RT-PCR、使用DNA迁移率变动分析的核结合蛋白分析和DNA甲基化分析。结合使用这些不同的方法，我们应该能够确定在正常和晚期加速（但不是不良）衰老期间细胞因子产生是否有任何改变（例如，虚弱）以及这些变化是否与受试者免疫状态的改变相关。正在进行其他研究，以检查从啮齿动物、人类和不同年龄的灵长类动物中分离的CD 28-/CD 28+和CD 57 +/CD 57- T细胞的原代和克隆培养物的功能作用和细胞因子谱。由于这些免疫亚群在各种疾病状态（包括关节炎，艾滋病和衰老）的循环中急剧增加，我们相信对这些亚群进行更详细的分子和生化分析不仅会产生有关与衰老和疾病相关的免疫缺陷的有价值的信息，而且还可能导致可能的免疫干预措施，以增强免疫反应。

It is well known that the ability to mount effective immune responses often declines with age. There are several, possibly interconnected shifts in T cell phenotype and function that may be either a cause or consequence of immune changes which occur in aging. The best described changes are a shift from naive to memory phenotype among both CD4 and CD8 T cells, and a decline in IL-2 production relative to cells from young subjects. The mechanisms involved in these shifts are largely unknown. To design experiments that can start to define such mechanisms, it is necessary to be able to define T cell subsets to understand the relationships among them, and what factors regulate the transition from one stage to the next. Several key cytokines, which influence the development and cytokine profile of memory T cells, are IL-2, IL-4, IFN-g, and IL-12, as well as TGFb. The unregulated expression of various inflammatory cytokines, including IL-1, IL-6, IL-8, TNF, and many CXC and CC chemokines has been shown to be involved in several disease states such as inflammation, autoimmunity, and some hematopoietic malignancies. Several studies using aged rodent and primate T cells for differential cytokine production have yielded variable results. Additional studies have demonstrated a significant shift from Th1-Th0 cells to Th2 cells over the course of aging while others have observed no phenotypic Th switch. Various studies have reported on the hyperproduction of IFN-g and TNF-a in aged versus younger animals and that these differences may relate to alterations in circulating immune cell subsets. While several human studies have also yielded variable cytokine expression results, we have initiated studies to examine such cytokine alterations (as well as the gene and protein expression of other related molecules) using several unique molecular methodologies currently in place including cytokine promoter studies, kinetic-based microarray cDNA analysis of young versus old lymphoid organs and immune cell subsets in various states of activation, RNAse protection assays, quantitative RT-PCR, nuclear binding protein analysis using DNA mobility shift analysis, and DNA methylation analysis. Using these various methods in combination, we should be able to determine if there are any alterations in cytokine production during normal and advanced accelerated (but not poor) aging (e.g., frailty) and if these changes correlate with alterations in a subjects immune status. Additional studies are underway examining the functional role(s)and cytokine profile of primary and clonal cultures of CD28-/CD28+ and CD57+/CD57- T cells isolated from rodents, humans, and primates of different ages. As these immune subpopulations are dramatically increased in the circulation during various disease states (including arthritis, AIDS, and aging), we believe that more detailed molecular and biochemical analysis of these subsets will not only yield valuable information about the immune deficits associated with aging and disease but may also lead to possible immunotherapeutic interventions to boost immune responses.