Also called the white blood cells, Leukocytes are important blood components and also play a key role in the immune system. There are several different types of leukocytes, each having a specific function in your body. If you have a high count of leukocytes in your blood, it could be an indication of the presence of an underlying disease or infection. Likewise, when you have a low count (leucopenia), it could be an indicator of some medical problems..