WHITE BLOOD CELLS, sometimes referred to as leukocytes in medical literature, are produced by the immune system to help defend the body against infection. They are formed in the bone marrow and either enter the blood or migrate to key organs, such as the spleen, lymph nodes, or gut. A high white blood cell count likely indicates that an infection is present somewhere in the body, whereas a low number might indicate that an infection or disease (such as HIV or cancer) has slowed the ability of the bone marrow to produce new WBC's.