It has to be complex, because we're asking the immune system to be able to respond to every potential foreign pathogen that we come into contact with.

免疫系统是十分复杂的,因为我们需要免疫系统,能够对我们身体接触到的,任何潜在的外来病原体进行反应

耶鲁公开课 - 生物医学工程探索课程节选