Computer artwork of different types of white blood cells. Top left: basophil, top middle: monocyte, top right: lymphocyte. Bottom left: neutrophil, bottom right: eosinophil. White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from a cell in the bone marrow known as a hematopoietic stem cell. Leukocytes are found throughout the body, including the blood and lymphatic system. All white blood cells have nuclei, which distinguishes them from the other blood cells.