It's a mechanism that they have evolved in order to prevent foreign genes from entering a cell and being expressed.

它们进化出这种机制来,防止异源基因进入细胞并表达

耶鲁公开课 - 生物医学工程探索课程节选

It's the way, for example, that foreign molecules or antigens get presented to cells of your immune system in order to start the process of making an immune response, so sometimes a cell/cell interaction.

通过这种方式,外源分子,或者说抗原,进入到免疫系统的细胞中后,就会开启免疫反应过程,有时候就是细胞之间的相互作用

耶鲁公开课 - 生物医学工程探索课程节选