So, just an introduction to the classes of potential foreign invaders that our immune system tries to defend us against.

所以 我只是简单介绍几类,免疫系统试图抵御的潜在外来侵略者

耶鲁公开课 - 生物医学工程探索课程节选

The reason for that complexity is because your immune system needs to be able to respond to all the potential foreign invaders that we could encounter.

整个系统之所以如此复杂是因为,免疫系统需要应对所有,我们要面对的来犯之敌

耶鲁公开课 - 生物医学工程探索课程节选