Nana,
If I understood you right, your grandson is dropping 10 mg of prednisone everyday? That does seem pretty quick. When I was on prednisone and doing a stepdown, I was dropping by 5 mg every three days or so.
When the body builds up antibodies, it is building the bodies method of fighting the "invader" (medication, infection, etc.). What that means is that it is possible for the body to withstand the medication and not allow it to function properly in the body. I use this scenario a lot when talking about infections with my athletes: An infection enters your body and starts a reaction of the immune system. The body begins to produce antibodies, or an immunity, to this infection. This allows your body to resist this infection in the future.
I hope this helps.