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

T细胞谱系是通过α-βT细胞受体与自身主要组织相容性复合体(MHC)结合的自体肽相互作用而形成的。为了阐明TCR/MHC/肽相互作用决定这种相互选择过程，我们试图在体外和体内建立表达单一MHC/肽配体的系统。首先，我们开发了一种可溶性MHC分子，其胞质结构域被糖基磷脂酰肌醇(GPI)取代。通过与细胞孵育，这种与单一多肽形成络合物的分子被发现表达在任何细胞的细胞表面。然而，胸腺上皮细胞表达的GPI锚定的MHC/肽复合体不能支持T细胞分化。其次，我们建立了在胸腺不同水平表达MHC分子的转基因小鼠。通过比较T细胞在这些细胞系中的命运，我们发现单个MHC/肽配体可以作为正负选择配体，这取决于胸腺中的表达水平。

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.