Possible Role of Gingival Epithelial Cells in Host Immune Response of Periodontal Disease Progression

本研究的目的是阐明牙龈上皮细胞在牙周病进展的宿主免疫反应中的可能作用。由表达MHC II类和B7共刺激分子的专职抗原呈递细胞（APC）呈递的抗原导致CD 4 + T细胞活化。相反，表达MHC II类的非专职APC缺乏共刺激分子的抗原呈递可使CD 4 + T细胞进入无应答状态。通常，B7共刺激分子由专职APC（如巨噬细胞或树突状细胞）表达。双色曝光共聚焦显微镜原位检测到牙周病患者牙龈上皮组织中MHC Ⅱ类分子和B7-1的表达，而健康牙龈组织中未见表达。此外，两个线的大鼠牙龈上皮细胞（GEC）证明组成型表达B7-1，但不B7-2的流式细胞仪分析。相比之下，在IFN-γ刺激后，仅在两种大鼠GEC kline上检测到MHC II类的表达。其他大鼠非专职APC如内皮细胞或成纤维细胞即使在IFN-γ刺激后也不表达B7-1。为了阐明这种异位表达B7-1的免疫学意义，将抗原（伴放线放线杆菌）特异性CD 4 + Th 1 T细胞克隆与IFN-γ/抗原处理的大鼠GEC共培养。因此，T细胞变得对随后的专职APC的抗原刺激无反应，如增殖减少所证明的。在T克隆细胞与IFN-γ/抗原处理的GEC共培养中，抗Ⅱ类抗体或抗CD 80单抗均能抑制GEC对细菌抗原的提呈，从而导致T细胞的下调。这些结果表明，异位表达B7-1的GEC可能发挥调节性T细胞的口腔细菌在局部炎症反应的背景下。

The purpose of the present research project was to clarify the possible role of gingival epithelial cells in host immune response of periodontal disease progression. Antigen presented by professional antigen-presenting cells (APC), which express both MHC class II and B7 costimulatory molecules, results in CD4+ T cell activation. In contrast, antigen presentation by MHC class II expressing non-professional APC which lack costimulatory molecules can render CD4+ T cells into a state of nonresponsiveness. In general, B7 costimulatory molecules are expressed by professional APC, such as macrophages or dendritic cells. Expression of MHC class II and B7-1 was detected on periodontal diseased human gingival epithelial tissue in situ by double color exposure confocal microscopy, but not in healthy gingival tissue. Also, two lines of rat gingival epithelial cells (GEC) demonstrated to constitutively expressed B7-1, but not B7-2 as analyzed by flow cytometry. By contrast, expression of MHC class II was only detected on both rat GEC klines after IFN-γ stimulation. Other rat non-professional APC such as endothelial cells or fibroblasts did not express B7-1 even after stimulation with IFN-γ. In order to elucidate the immunological significance of this ectopic B7-1 expression, antigen (Actinobacillus actinomycetemcomitans)-spedfic CD4+ Th1 T cell clones were cocultured with IFN-γ-/antigen-treated rat GEC. Consequently, the T cells became unresponsive to subsequent antigen-stimulation by professional APC as demonstrated by diminished proliferation. The induction of unresponsiveness was inhibited by anti-class II mAb or anti-CD80 mAb in the coculture of T clone cells and IFN-γ/antigen-treated GEC suggesting that GEC apparently present bacterial antigen, which resulted in T cell down regulation. These results suggest that ectopic expression of B7-1 by GEC may play a regulatory T cell to the commensal bacteria in the oral cavity in the context of a local inflammatory response.