garlic is quite potent for increasing white blood cell count. An enzyme in it does this so it has to be eaten raw, crushed. I heard people crush it and put it on bread (it is almost unbearable if eaten on its own). I crush it and mix it with mashed banana..sounds gross but extremely tolerable so I can get in a lot of garlic.
Vitamin a is also great for white blood cell. Due to conflicting evidence for active vitamin A I would just get it from veggies to be on the safe side. carrots,pumpkin,squash,mango,tomatoes