Demotz S
Basel Institute for Immunology, Switzerland.
Eur J Immunol. 1993 Sep;23(9):2100-8. doi: 10.1002/eji.1830230909.
To demonstrate that DR alpha beta dimers still complexed to invariant chain (Ii) have not yet acquired peptides recognized by alloreactive T cells, complexes between DR molecules and Ii isolated from Epstein-Barr-virus (EBV)-transformed B cells were analyzed by affinity chromatography and gel filtration. First, it was shown that DR/Ii complexes inserted into artificial planar membranes (PM) failed to stimulate proliferative response of five alloreactive T cell clones and a polyclonal alloreactive T cell line, while PM bearing mature DR alpha beta dimers from the same EBV-B cells were stimulatory for the T cell clones and the T cell line. These findings indicate that either Ii inhibits binding of peptides to DR molecules or Ii hinders T cells recognition of peptide/DR complexes. Second, to discriminate between these two possibilities, DR alpha beta dimers, which were artificially released from complexes between DR molecules and Ii, were inserted into PM. These DR alpha beta dimers were devoid of alloreactive stimulatory capacity while fully capable of binding and presenting a tetanus toxin synthetic peptide to a specific T cell clone, indicating that DR molecules released from complexes with Ii are empty. This study, by showing that DR molecules bound to Ii do not bear peptides recognized by alloreactive T cells, supports the notion that association of Ii with class II major histocompatibility complex (MHC) molecules prevents premature peptide loading and hence favors encounter with peptides derived from proteins of the extracellular compartment. Since allogeneic class II MHC molecules released from complexes with Ii were not stimulatory for five out of five alloreactive T cell clones and a polyclonal alloreactive T cell line, these data also indicate that, in most cases, alloreactive T cells recognize ligands constituted by complexes between allogeneic class II MHC molecules and specific peptides which derive from the antigen-presenting cells themselves or serum proteins.
为了证明与恒定链（Ii）仍结合在一起的DRαβ二聚体尚未获得同种异体反应性T细胞识别的肽段，通过亲和层析和凝胶过滤分析了从爱泼斯坦-巴尔病毒（EBV）转化的B细胞中分离出的DR分子与Ii之间的复合物。首先，研究表明，插入人工平面膜（PM）中的DR/Ii复合物未能刺激五个同种异体反应性T细胞克隆和一个多克隆同种异体反应性T细胞系的增殖反应，而来自相同EBV - B细胞的带有成熟DRαβ二聚体的PM对T细胞克隆和T细胞系具有刺激作用。这些发现表明，要么Ii抑制肽段与DR分子的结合，要么Ii阻碍T细胞对肽段/DR复合物的识别。其次，为了区分这两种可能性，将从DR分子与Ii的复合物中人工释放的DRαβ二聚体插入PM中。这些DRαβ二聚体没有同种异体反应性刺激能力，但完全能够结合破伤风毒素合成肽并将其呈递给特定的T细胞克隆，这表明从与Ii的复合物中释放的DR分子是空的。这项研究通过表明与Ii结合的DR分子不携带同种异体反应性T细胞识别的肽段，支持了Ii与II类主要组织相容性复合体（MHC）分子的结合可防止肽段过早加载的观点，因此有利于与源自细胞外区室蛋白质的肽段相遇。由于从与Ii的复合物中释放的同种异体II类MHC分子对五个同种异体反应性T细胞克隆中的五个以及一个多克隆同种异体反应性T细胞系没有刺激作用，这些数据还表明，在大多数情况下，同种异体反应性T细胞识别由同种异体II类MHC分子与源自抗原呈递细胞自身或血清蛋白的特定肽段之间的复合物构成的配体。
