Racioppi L, Ronchese F, Schwartz R H, Germain R N
Lymphocyte Biology Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
J Immunol. 1991 Dec 1;147(11):3718-27.
To identify the molecular basis for the effects of MHC molecule polymorphism on T cell responses, we have combined functional T cell response testing with measurements of peptide binding to the class II MHC molecules on transfected cells. Our studies identify a small subset of spatially localized polymorphic residues of the E alpha E beta dimer (strand residue beta 29, and helix residues beta 72 and beta 75) regulating cytochrome c peptide presentation by two distinct mechanisms. The first effect is on quantitative control of net peptide binding. The replacement of the valine found at position beta 29 in E beta k with the glutamic acid found in E beta b results in a selective loss of pigeon cytochrome peptide but not moth cytochrome peptide binding to the resultant mutant E alpha E beta k molecule. Reciprocally, the replacement of glutamic acid at beta 29 in E beta b with valine results in a gain of pigeon peptide binding. These changes in binding parallel changes in T cell responses in vitro to these peptide-E alpha E beta combinations and mirror the in vivo immune response gene phenotypes of mice expressing E alpha E beta k and E alpha E beta b. E alpha E beta s molecules, which have a beta 29 glutamic acid, are nevertheless able to bind and present pigeon cytochrome peptides, and this is due to changes in helix residues beta 72 and beta 75 that compensate for the negative effect of the beta 29 glutamic acid. The second activity is a critical change in the conformation of the peptide bound to the same extent by distinct MHC molecules, as revealed by changes in T cell responses to moth cytochrome peptides presented by two E alpha E beta molecules differing only at position beta 29. Both of these effects can be ascribed to a single polymorphic residue modeled to be inaccessible to TCR contact (beta 29), providing a striking demonstration of how MHC molecule polymorphism can modify T cell-dependent immune responses without direct physical participation in the receptor recognition event.
为了确定MHC分子多态性对T细胞反应影响的分子基础，我们将功能性T细胞反应测试与转染细胞上II类MHC分子肽结合的测量相结合。我们的研究确定了EαEβ二聚体中一小部分空间定位的多态性残基（链残基β29，以及螺旋残基β72和β75）通过两种不同机制调节细胞色素c肽的呈递。第一种效应是对净肽结合的定量控制。Eβk中β29位的缬氨酸被Eβb中的谷氨酸取代，导致鸽细胞色素肽选择性丧失，但蛾细胞色素肽与所得突变EαEβk分子的结合不受影响。相反，Eβb中β29位的谷氨酸被缬氨酸取代，导致鸽肽结合增加。这些结合变化与体外对这些肽 - EαEβ组合的T细胞反应变化平行，并反映了表达EαEβk和EαEβb的小鼠的体内免疫反应基因表型。然而，具有β29谷氨酸的EαEβs分子能够结合并呈递鸽细胞色素肽，这是由于螺旋残基β72和β75的变化补偿了β29谷氨酸的负面影响。第二种活性是与不同MHC分子结合程度相同的肽的构象发生关键变化，这通过对仅在β29位不同的两个EαEβ分子呈递的蛾细胞色素肽的T细胞反应变化得以揭示。这两种效应都可归因于一个被模拟为TCR无法接触的多态性残基（β29），这有力地证明了MHC分子多态性如何在不直接参与受体识别事件的情况下改变T细胞依赖性免疫反应。
