[sanedigital]

Cold & flu weren't the best examples. Here's a more obvious one: getting food poisoning doesn't make you less likely to catch the flu.

Some people treat "the immune system" like a muscle, where stress strengthens. Similar stressors can have cross-reactive effects, but unrelated ones do not.

This can go the other way too: people who have uncontrolled celiac disease (as in, they're still consuming gluten on a regular basis) can also have issues with avenin (a somewhat similar protein in oats) or even lactose. For a lot of folks those sensitivities disappear when they get their gluten consumption down.

[wrycoder]

Interesting comment on gluten consumption. In my case, it appears cumulative. (I'm not celiac, so far as I know.) I've been following a non-gluten diet for fifteen years at this point, and I can now tolerate at least a small amount of gluten without the effects I used to have.

I used to get injections to diminish my hay fever symptoms. I finally mostly grew out of hay fever around the age of forty, though I'm still allergic to horses and cats, if I have direct contact.

Don't those injections comprise increasing challenges to the immune system using the allergens themselves, to make it less prone to mount a histamine response (i.e. runny nose, itchy eyes)?