That’s an interesting question – what do you think would happen?
It would interesting to examine – eg astronauts in space don’t have any viruses or bacteria and so on around to infect them. Our immune system is designed to protect us, so parts of this may become redundant. So we could expect some parts of our immunity to eventually stop functioning over time, spefically parts linked to recognising foreign infections, and activating the immune response against these. However, our immune response also helps us heal – eg if we cut a finger, so most of it would still remain.
In the middle of your chest is your thymus – tissue that helps activate our immunity. Scientists have developed mice that have virtually no thymus, so they had a reduced immune system. So would we end up like them? They are called “nude” mice because they have no immunity covering them from infection. Scientists use this to develop therapies for patients who have an ineffective immune response.
There is also the possibility that deprived of something to do our immune systems might start overreacting to things they should ignore.
Our immune system does not just protect us from external threats, it also protects us from the bacteria and fungi that live on and in us. These are a natural part of our bodies but when things get unbalance they can grow where they shouldn’t or grow too much.
Our immune system also protects us from ourselves. It actively fights cancers and disposes of cells that might be becoming cancerous.
So even if we couldn’t get sick form outside sources we’d still need our immune systems!
Perhaps we will get to a stage where diseases are almost eliminated, if this were to happen I think it would be due to prevention rather than cure.