Institute for Virology, University Medical Center of the Johannes Gutenberg University, Hochhaus am Augustusplatz, 55101 Mainz, Germany.
J Virol. 2010 Feb;84(3):1221-36. doi: 10.1128/JVI.02087-09. Epub 2009 Nov 11.
For recognition of infected cells by CD8 T cells, antigenic peptides are presented at the cell surface, bound to major histocompatibility complex class I (MHC-I) molecules. Downmodulation of cell surface MHC-I molecules is regarded as a hallmark function of cytomegalovirus-encoded immunoevasins. The molecular mechanisms by which immunoevasins interfere with the MHC-I pathway suggest, however, that this downmodulation may be secondary to an interruption of turnover replenishment and that hindrance of the vesicular transport of recently generated peptide-MHC (pMHC) complexes to the cell surface is the actual function of immunoevasins. Here we have used the model of murine cytomegalovirus (mCMV) infection to provide experimental evidence for this hypothesis. To quantitate pMHC complexes at the cell surface after infection in the presence and absence of immunoevasins, we generated the recombinant viruses mCMV-SIINFEKL and mCMV-Deltam06m152-SIINFEKL, respectively, expressing the K(b)-presented peptide SIINFEKL with early-phase kinetics in place of an immunodominant peptide of the viral carrier protein gp36.5/m164. The data revealed approximately 10,000 K(b) molecules presenting SIINFEKL in the absence of immunoevasins, which is an occupancy of approximately 10% of all cell surface K(b) molecules, whereas immunoevasins reduced this number to almost the detection limit. To selectively evaluate their effect on preexisting pMHC complexes, cells were exogenously loaded with SIINFEKL peptide shortly after infection with mCMV-SIINFEKA, in which endogenous presentation is prevented by an L174A mutation of the C-terminal MHC-I anchor residue. The data suggest that pMHC complexes present at the cell surface in advance of immunoevasin gene expression are downmodulated due to constitutive turnover in the absence of resupply.
为了让 CD8 T 细胞识别感染细胞，抗原肽与主要组织相容性复合体 I 类 (MHC-I) 分子结合，呈递在细胞表面。细胞表面 MHC-I 分子的下调被认为是巨细胞病毒编码的免疫逃逸蛋白的标志性功能。然而，免疫逃逸蛋白干扰 MHC-I 途径的分子机制表明，这种下调可能是由于周转率补充中断引起的，并且新生成的肽-MHC (pMHC) 复合物向细胞表面的囊泡运输受阻是免疫逃逸蛋白的实际功能。在这里，我们使用鼠巨细胞病毒 (mCMV) 感染模型为这一假设提供了实验证据。为了在存在和不存在免疫逃逸蛋白的情况下定量感染后细胞表面的 pMHC 复合物，我们分别生成了表达 K(b)呈递肽 SIINFEKL 的重组病毒 mCMV-SIINFEKL 和 mCMV-Deltam06m152-SIINFEKL，用早期阶段动力学取代病毒载体蛋白 gp36.5/m164 的免疫显性肽。数据显示，在不存在免疫逃逸蛋白的情况下，大约有 10000 个 K(b)分子呈递 SIINFEKL，这大约占所有细胞表面 K(b)分子的 10%，而免疫逃逸蛋白将这个数字减少到几乎检测不到的水平。为了选择性地评估它们对预先存在的 pMHC 复合物的影响，在感染 mCMV-SIINFEKA 后不久，用 SIINFEKL 肽对细胞进行外源性加载，其中 C 末端 MHC-I 锚定残基的 L174A 突变阻止了内源性呈递。数据表明，在免疫逃逸蛋白基因表达之前呈递在细胞表面的 pMHC 复合物由于在没有补充的情况下的组成性周转率而下调。
