Because alveoli serve as critical exchange points between the blood and air from the outside world, they have their own specialized types of white blood cells, or macrophages, which defend against foreign organisms by enveloping and eating them.

因为肺泡相当于血液和来自体外的空气之间的一个临界交换点，它们拥有专门的白血细胞，又名巨噬细胞，这种细胞通过包络和吞噬外来细胞来进行防御。