This is the most common association for the immune system. There are many other phrases that fall into this category; they are army, security guard, mote or maybe cellular submarine force. A more apt association would be the naval association. If face, we are pretty much mostly water, a defensive submarine force is a good visualization.
Feel free to be the first
Please review the linked page for context.
If you can think of something better than this,
please add it to the database