When a new germ enter our body ( a germ or bacteria that your white cells has not seen before ) the white cell is not able to protect itself from it due to the white cells not know what it is. Your immune system also explain the amount of white cells you have. If your immune system is not very good and you have contracted a new bacteria or germ then your white cells can not fight against something they have little to no knowledge/ experience with. Can you put more info in the question? Idk if i answered yours.
