Invading enemies to find,
And protect our body from infection,
It detects a suspect site,
And destroys it with its might,
And it does it with commendable perfection...
But, sometimes, it makes mistakes:
Our own cells for targets takes,
And attempts to kill them, as if they were the foe,
And, though it makes no sense,
There is hardly a defense,
When the immune system misbehaves so...
Then the doctors shake their heads,
And declare, showing some dread,
That they don't quite know just how to ease
Our pain, when the system goes astray
And its forces are arrayed
In what they call auto-immune disease...