Molecular analysis for TCR-MHC-peptide interaction in thymic selection in vitro and in vivo

T细胞库是通过α - T细胞受体与与自身主要组织相容性复合体（MHC）结合的自肽相互作用形成的正选择和负选择。为了阐明TCR/MHC/肽的相互作用决定了这一相互选择过程，我们试图在体外和体内建立一个单一MHC/肽配体表达的系统。首先，我们开发了一种可溶性MHC分子，其细胞质结构域被糖基-磷脂酰肌醇（GPI）取代。这个分子与一个单一的肽复合物被发现在任何细胞的细胞表面上表达，只要与细胞孵育复合物。然而，在胸腺上皮细胞上表达的GPI锚定的MHC/肽复合物不能支持T细胞分化。其次，我们开发了表达MHC分子在胸腺中以不同水平与单个肽共价结合的转基因小鼠系。通过比较这些细胞系中T细胞的命运，我们发现单个MHC/肽配体可以作为正向和负向选择配体，这取决于其在胸腺中的表达水平。

The T cell repertoire is shaped by positive and negative selection through the interaction of alphabeta T cell receptor with self-peptide bound to self-major histocompatibility complex (MHC). To elucidate TCR/MHC/peptide interaction determining this reciprocal selection process, we have tried to develop in vitro and in vivo system where a single MHC/peptide ligand is expressed.First, we developed a soluble MHC molecule of which cytoplasimic domain has been replaced with glycosyl-phophatidylinositol (GPI). This molecule complexed with a single peptide was found to be expressed on the cell-surface of any cells, by just incubation the complex with cells. However, the GPI anchored MHC/peptide complex expressed on thymic epithelial cells could not support T cell differentiation.Second, we developed transgenic mouse lines expressing MHC molecules covalently bound to a single peptide at different levels in the thymus. By comparing the fate of T cells in these lines, we found that a single MHC/peptide ligand, depending on the expression level in thymus, can serve as both positively and negatively selecting ligand.