Diagram of White Blood Cells Leukocytes Key Ring

White blood cells, or leukocytes (also spelled "leucocytes"), are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell. They live for about three to four days in the average human body. Leukocytes are found throughout the body, including the blood and lymphatic system. This file is licensed under the Creative Commons Attribution 3.0 Unported license. Author BruceBlaus