what does white blood cells have to do with calcium

i went to the doctor and i found out my white blood cell count was low and so they told me to take calcium and vitamin d3 but i dont get what calcium has to do with white blood cells

Why didn't you ask the doctor?

Calcium activates white blood cells.

Your white blood cells use calcium to fight infection.

That's the simple answer.

i guess i didnt really think about it at the time when i was there