Last month's murder of both the president and the army chief of staff has heightened the country's political uncertainty at a time when Luciani says the government must move quickly to protect a generation exposed to AIDS.

VOA: standard.2009.04.24

So, every time you're exposed to a new vaccine or a new antigen you go through this primary response before you have the secondary response.

所以,每当你接触到新疫苗或是新抗原,在再次免疫之前,机体将会经历这样的初次免疫过程

耶鲁公开课 - 生物医学工程探索课程节选

When you get exposed to that particular antigen they say, 'I'm on, it's my time'.

等到你暴露在特定的抗原中,它们说,该我了,到我大显身手的时候了

耶鲁公开课 - 生物医学工程探索课程节选