something that is “non-self” where it doesn’t
belong, it will perform an immediate
evaluation, which may then trigger one of two
immune responses: a nonspecific suspicion of
something unfamiliar or a specific, aggressive
response to a known troublemaker.
Let’s use another analogy.
If you woke up and found a strange man
hanging out in your kitchen, you’d feel
threatened and anxious. You’d be suspicious
of his motives and would probably react in an
anxious, defensive manner, asking him what
the heck he’s doing in your home, and then
taking appropriate action—inviting him to
stay if you discovered he was a family friend,
or asking him to leave if he didn’t belong
there.
But if this man was in the process of
vandalizing your kitchen, you’d immediately
know he wasn’t a good guy, and would
respond strongly to his presence by calling the