From an internet search.
Does exercise help the elderly immune system?
Not only does exercise get the immune cells moving throughout the body during activity, but it also promotes a lasting presence of these immune cells for up to three hours after exercise is completed. This provides extra time for the immune cells to identify unwanted intruders and keep you from getting sick.
frontiersin.org/journals/im...
<== this is a very lengthy dense document
reduces inflammation
the more you do the better the effects