Phenotypic And Functional Changes In Circulating T Cells

众所周知，人体产生有效免疫反应的能力往往会随着年龄的增长而下降。在T细胞表型和功能中有几个可能相互关联的变化，可能是衰老过程中发生的免疫变化的原因或结果。最好的描述是CD4和CD8 T细胞从幼稚表型到记忆表型的转变，以及相对于年轻受试者的细胞IL-2产生的下降。这些变化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细胞发育和细胞因子谱的几个关键细胞因子是IL-2、IL-4、IFN-g和IL-12，以及TGFb。各种炎症细胞因子，包括IL-1、IL-6、IL-8、TNF和许多CXC和CC趋化因子的不受调节表达已被证明参与多种疾病状态，如炎症、自身免疫和一些造血恶性肿瘤。几项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生产的研究产生了不同的结果。其他研究表明，在衰老过程中，Th1-Th0细胞向Th2细胞发生了显著的转变，而其他研究则没有观察到表型上的Th开关。各种研究报道了老年动物与年轻动物中IFN-g和TNF-a的过量产生，这些差异可能与循环免疫细胞亚群的改变有关。虽然一些人体研究也产生了不同的细胞因子表达结果，但我们已经开始研究这些细胞因子的改变（以及其他相关分子的基因和蛋白质表达），使用几种独特的分子方法，包括细胞因子启动子研究，基于动力学的微阵列cDNA分析年轻与年老淋巴器官和免疫细胞亚群在各种激活状态下，RNAse保护试验，定量RT-PCR，核结合蛋白分析采用DNA迁移位移分析和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（例如，虚弱）期间细胞因子的产生是否有任何改变，以及这些变化是否与受试者免疫状态的改变相关。进一步的研究正在进行中，以检测从啮齿动物、人类和不同年龄的灵长类动物中分离的CD28-/CD28+和CD57+/CD57- 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与衰老和疾病相关的免疫缺陷的有价值的信息，还可能导致可能的免疫治疗干预，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.