So what happens if you contract Measles and your immune system manages on its own to overcome the illness. Does that mean you’ve acquired an enhanced immune system for the effort?
Depends what you consider enhanced. You will have lifelong immunity, or most people will, there’s always the odd person that won’t develop any immunity. I don’t think anyone is really sure how long immunity from vaccines last. They used to say it was lifelong, but are discovering that is not true, which is one reason that we went from needing only one MMR to now needing two and possibly a booster as we get older.
When your body fights off a disease, you’re left with antibodies to help you fight off further instances of that infection.
An antibody is a y-shaped protein. At the end of the two top ‘prongs’ of the Y there are things called paratopes. These paratopes can be different shapes. The shape of the paratope acts like a key, which will fit into a lock. The lock is a specific molecule of whatever infectious agent (a bacterium or virus for example) the antibody will help fight.
Antibodies find these bacteria and viruses and ‘tag’ them with their paratopes. Once they are tagged, other parts of the immune system kick in to fight off the infection.
So yes, in a way fighting off the infection gives you an ‘advanced’ immune system.
The way vaccines work is they cause your body to produce these antibodies without making you sick with the illness.