Well, the way that your immune system recognizes it is that all the cells of our body express a molecule on their surface, a membrane protein called the MHC1 complex.

而免疫系统识别的方法是,身体内所有细胞在其表面表达一种分子,一种叫做MHC1复合体的膜蛋白

耶鲁公开课 - 生物医学工程探索课程节选

Essentially, what they are is it's a protein that spans the membrane of a cell.

本质上来说，它是一个横跨细胞膜的蛋白质。

麻省理工公开课 - 化学原理课程节选