But many here remain deeply traumatized. Today marks the 15th anniversary of the day that former President Juvenal Habyarimana's plane was shot down.

VOA: standard.2009.04.08

Because on second exposure there's another population of cells that I haven't mentioned before that remain after the primary exposure and those are called memory cells, they're down here.

因为在再次免疫中,有另外一些细胞,我之前并没有提到过它们,在初次免疫结束后保留下来的细胞,被称为记忆细胞,它们在下面

耶鲁公开课 - 生物医学工程探索课程节选