Study on the Specialized Function of Dendritic Cells

树突状细胞(DC)是一种独特的白细胞，是T细胞介导的免疫反应的特异性抗原提呈细胞。它们在周围组织中获得抗原，并迁移到淋巴器官的T区，在那里它们以MHC II类到T细胞的形式提供加工过的多肽。在正常稳定状态下，已有2-3个在表型和功能上可区分的DC亚群定位于淋巴器官，提示它们可能不仅在成熟步骤上不同于前体细胞，而且在发育途径上也不同于前体细胞。因此，我们试图从淋巴结中分离T区树突状细胞，并对其表型、抗原提呈和共刺激功能进行鉴定。我们还研究了体内和体外树突状细胞的发育和功能成熟的特点，以及接种编码CD4T细胞识别的抗原决定簇的DNA后的抗原提呈活性。结果表明：1)T区树突状细胞除MHC-II类分子和多种黏附和共刺激分子外，还呈现高水平的自体多肽，并诱导特异性T-T杂交瘤细胞的凋亡，提示它们调节外周的自身反应性；2)未成熟的早期DC，其中大多数II类细胞内的DC定位于溶酶体内，通过中期成熟变得高度刺激，其中细胞内II类分子存在于外周非溶酶体小泡中。树突状细胞成熟的一个基本特征是II类降解率降低，表面II类分子表达增加；3)从引流淋巴结或皮肤分离的DC向T细胞递呈抗原并携带质粒DNA，提示DC摄取DNA和/或其表达的蛋白质触发了对DNA疫苗的免疫应答。

Dendritic cells (DC) are distinctive leukocytes that are specialized antigen-presenting cells for T cell mediated immune responses. They acquire antigens in peripheral tissues and migrate to T area of lymphoid organs where they present processed peptides in context of MHC class II to T cells. In normal steady state, 2-3 distinguishable subpopulations of DC in respect of phenotype and function have been reported to locate in lymphoid organs, and it is suggested they may be different not only in maturational steps but also in developmental pathways from precursors. Therefore, we attempted to isolate T area DCs from lymph nodes and characterize phenotype and antigen-presenting and costimulatory functions. We also investigated the features of development and functional maturation of DCs in vivo and in vitro, and antigen-presenting activity after inoculating DNA encoding antigenic determinant recognized by CD4 T cells. The results obtained are 1) T area DCs present high levels of self peptides in addition to MHC class II and various adhesion and costimulatory molecules and induce apoptosis of specific T-T hybridomas, suggesting they regulate self reactivity in the periphery ; 2) Immature early-stage of DCs in which most class II are intracellular and localized to lysosomes, undergo maturation to become highly stimulatory through the intermediate stage, in which intracellular class II are found in peripheral non-lysosomal vesicles. The decrease in rate of class II degradation and increase in expression of surface class II is a fundamental feature of DCs maturation and is also exhibited by a very different population of DC ; 3) DCs isolated either from draining lymph nodes or skin present antigens to T cells and carry plasmid DNA,indicating that the uptake of DNA and/or the protein expressed by DCs triggers immune responses to DNA vaccines.