I never get sick. My immune system is ratched up 5 notches higher than what it needs to be. It still attacks the bacteria in my pouch when it shouldn't. The down side is pouchitis, but I never even get a flu shot as I don't get the flu and if I catch something it gets hammered out of my system pretty quick and I never even miss work because of it.
I always thought most of us fall into this category. Biologics ratchet DOWN the immune system from its heightened state so as to stop the response that is causing the inflammation whether it be pouchitis, AS, cuffitis, whatever. Mine definitely needs to be dialed back some.
To the OP, UC is caused by your immune system's aggressive/inappropriate response to bacteria in the lining of your colon, not the lack of a response, which is what your post seemingly implies.