Those things wouldn’t be good but I don’t know how they affect the immune system specifically. Thing is, I spend more time now outdoors because I had to replace going to the gym with more walking. Our local authorities (NJ, USA) advise (not required) to actually stay indoors as much as possible but I doubt that’s actually necessary, especially given that a lot of people choose not to come out, so it’s easy to keep a safe distance from people on the street. Or to avoid places which attract crowds on nice warm days.
The experts don’t seem to know enough to gtee almost anything about this disease, but my reading is that getting COVID from briefly passing other people several feet away, outdoors, is a very small to negligible risk. I don’t see a good reason to avoid normal exercise, fresh air and sun exposure, unless perhaps one has actual symptoms and/or positive test result.
That’s an interesting idea, especially since the first “vaccination” for small pox was to deliberately infect people with the much milder cow pox. Let’s keep an eye out for research around this.
Your house is full of the more common, conventional germs; it’s getting a good workout. Anyway, your immune system isn’t going to stop working because you aren’t meeting as many people for a few months.