Nathenson S G, Kesari K, Sheil J M, Ajitkumar P
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461.
Cold Spring Harb Symp Quant Biol. 1989;54 Pt 1:521-8. doi: 10.1101/sqb.1989.054.01.062.
MHC variants isolated both in vivo (by tissue graft rejection) and in vitro (by antibody selection) were utilized to study sites on the H-2Kb molecule involved in interaction with antibodies and with the TCR. Kb mutants selected by antibodies were found to have single point mutations, which when analyzed in the context of the three-dimensional structure of a Kb molecule modeled from HLA-A2 coordinates showed that the altered residues were localized mostly to the alpha 1 and alpha 2 helices. The side chains of the variant amino acid residues pointed upward and away from the antigenic site. Analysis of the altered amino acids in the previously described tissue-graft-selected Kb mutants showed that the side chains of the variant residues occur either in the alpha-helical regions or in the beta-pleated-sheet floor of the antigen groove, but every mutant contained at least one and sometimes several acid side chains projecting into the antigen-binding groove. Monoclonal antibody studies showed that the available monoclonal antibodies mapped to discrete domain-specific sites. Analysis of CTL recognition sites using cloned mutant anti-parent or allogeneic combinations showed that all CTL clones examined interacted with amino acid side-chain residues on both the alpha 1 and alpha 2 helices. Thus, we concluded that the CTLs must simultaneously interact with the amino acid residues in both the alpha-helical stretches of the alpha 1 and alpha 2 domains. Our analyses with the point mutants imply that the TCR must interact with the MHC molecule over a relatively large surface area in such an orientation that it interfaces with the two alpha helices, as well as with the foreign or self-peptide in the antigen-binding site between the helices. These findings, together with the observation that several of the in vivo Kb mutants induce strong alloreactions yet have changes only in the bottom of the antigen-binding groove and no alterations in the alpha-helical residues, are consistent with the hypothesis that in some cases alloreaction can be the result of T-cell recognition of an altered pattern on the MHC molecule due to a changed peptide in the antigen groove.
通过体内（组织移植排斥）和体外（抗体选择）分离的MHC变体被用于研究H-2Kb分子上与抗体和TCR相互作用的位点。通过抗体选择的Kb突变体被发现具有单点突变，当根据从HLA-A2坐标建模的Kb分子的三维结构进行分析时，表明改变的残基大多位于α1和α2螺旋上。变体氨基酸残基的侧链向上指向并远离抗原位点。对先前描述的组织移植选择的Kb突变体中改变的氨基酸的分析表明，变体残基的侧链出现在抗原凹槽的α螺旋区域或β折叠底部，但每个突变体至少包含一个，有时包含几个伸入抗原结合凹槽的酸性侧链。单克隆抗体研究表明，可用的单克隆抗体映射到离散的结构域特异性位点。使用克隆的突变体抗亲本或同种异体组合对CTL识别位点的分析表明，所有检测的CTL克隆都与α1和α2螺旋上的氨基酸侧链残基相互作用。因此，我们得出结论，CTL必须同时与α1和α2结构域的α螺旋延伸中的氨基酸残基相互作用。我们对单点突变体的分析表明，TCR必须以与两个α螺旋以及螺旋之间抗原结合位点中的外来或自身肽相互作用的方向，在相对较大的表面积上与MHC分子相互作用。这些发现，连同体内Kb突变体中的几个诱导强烈的同种异体反应但仅在抗原结合凹槽底部有变化而α螺旋残基没有改变的观察结果，与以下假设一致：在某些情况下，同种异体反应可能是T细胞识别由于抗原凹槽中肽的变化而导致的MHC分子上改变模式的结果。
