I have a bet with my classmate, he says that sport helps your immune system (as in your white blood cells fight off infections, flu's, and any number of diseases) and i said that he is mistaken and he is getting confused with cholesterol, as in sport helps lower you fat levels and help your heart work better with less risk of developing a heart condition which has nothing to do with white blood cells and/or your immune system because sport helps build and develop muscle and reduce fat levels and releases certain hormones.

P.S. Please do not guess and if you give an answer please post how you found it.