Lahat N, Rahat M A, Sadeh O, Kinarty A, Kraiem Z
Immunology Research Unit, Carmel Medical Center, and Rappaport Faculty of Medicine, Technion, Haifa, Israel.
Thyroid. 1998 May;8(5):361-9. doi: 10.1089/thy.1998.8.361.
The consequence of autoantigen presentation by thyroid cells is dependent on the magnitude of expression of both HLA class II antigens (mainly HLA-DR) and costimulatory molecules, such as B7 (CD80 and CD86). Autoimmune thyrocytes are induced to express HLA-DR by interferon-gamma (IFN-gamma). The costimulatory signal leading to autoantibody production or cytotoxic T-cell immune response could be provided by antigen presenting cells (APCs) attracted to the thyroid by the primary autoimmune stimulus. Malignant thyrocytes can express HLA-DR antigens either constitutively, as a result of a nonimmunologic stimulus, or on induction with IFN-gamma after triggering of an immune response. However, their ability to express B7 molecules, which may determine enhanced antitumoral immune response mainly in the absence of intrathyroidal macrophages, has not yet been studied. The regulation of HLA-DR gene expression in APCs, such as B cells, is mediated by a series of short DNA consensus sequences located in the promoter, termed the W, X, and Y boxes, which bind several known transcription factors. We have previously characterized the expression of HLA-DR in four human thyroid carcinoma cell lines and found differences between constitutive and high- or moderate-induced expression of the protein and mRNA. Evaluation of B7 expression on the surface of thyroid cancer cells and understanding the mechanisms of HLA-DR gene expression may help in designing efficient immune response to thyroid tumors. Using the electrophoretic mobility shift assay (EMSA), we have demonstrated differences between the four thyroid cell lines in the binding of transcription factors to each of the three boxes. The binding to the promoter in each of the cell lines resulted in a single band, probably representing a complex of proteins formed via protein-protein interactions. Using flow cytometry we have shown that the B7 molecule was absent in the four thyroid cell lines and could not be induced by IFN-gamma. The absence of surface B7 molecules from the malignant thyroid cells may lead to either suppression of antitumoral cytotoxic T cell response or demand the cooperation of infiltrating APCs to favor immune response. Differences previously found in HLA-DR expression in the four human malignant thyroid cell lines may be explained by the variation in the binding of transcription factors to the boxes in the HLA-DRalpha promoter. The binding patterns of nuclear proteins derived from the four thyroid cell lines or from the B lymphocyte cell line--Raji--to each of the boxes or to the whole promoter exhibit similarities, thus suggesting similar DNA-protein interactions.
甲状腺细胞呈递自身抗原的结果取决于 HLA II 类抗原（主要是 HLA-DR）和共刺激分子（如 B7，即 CD80 和 CD86）的表达水平。自身免疫性甲状腺细胞可被干扰素-γ（IFN-γ）诱导表达 HLA-DR。导致自身抗体产生或细胞毒性 T 细胞免疫反应的共刺激信号可能由原发性自身免疫刺激吸引至甲状腺的抗原呈递细胞（APC）提供。恶性甲状腺细胞可因非免疫刺激而组成性表达 HLA-DR 抗原，也可在免疫反应触发后经 IFN-γ诱导表达。然而，它们表达 B7 分子的能力（这可能主要在甲状腺内缺乏巨噬细胞的情况下决定增强的抗肿瘤免疫反应）尚未得到研究。APC（如 B 细胞）中 HLA-DR 基因表达的调控由位于启动子中的一系列短 DNA 共有序列介导，这些序列称为 W、X 和 Y 框，它们可结合几种已知的转录因子。我们之前已对四种人甲状腺癌细胞系中 HLA-DR 的表达进行了表征，发现该蛋白和 mRNA 的组成性表达与高诱导或中等诱导表达之间存在差异。评估甲状腺癌细胞表面的 B7 表达并了解 HLA-DR 基因表达的机制可能有助于设计针对甲状腺肿瘤的有效免疫反应。使用电泳迁移率变动分析（EMSA），我们已证明四种甲状腺细胞系在转录因子与三个框中每个框的结合上存在差异。每个细胞系中与启动子的结合产生一条单一的条带，可能代表通过蛋白质-蛋白质相互作用形成的蛋白质复合物。使用流式细胞术我们已表明四种甲状腺细胞系中不存在 B7 分子，且不能被 IFN-γ诱导。恶性甲状腺细胞表面缺乏 B7 分子可能导致抗肿瘤细胞毒性 T 细胞反应受到抑制，或者需要浸润的 APC 进行协作以促进免疫反应。之前在四种人恶性甲状腺细胞系中发现的 HLA-DR 表达差异可能是由于转录因子与 HLA-DRα启动子中框的结合存在差异所致。源自四种甲状腺细胞系或 B 淋巴细胞系——Raji——的核蛋白与每个框或整个启动子的结合模式表现出相似性，因此表明存在相似的 DNA-蛋白质相互作用。
