Blood is made up of several different kinds of cells. Erythrocytes, or red blood cells, carry oxygen and give blood its characteristic color. Thrombocytes, or platelets, aid in clotting. Leukocytes, or white blood cells, come in various types and serve different functions.
White blood cells include basophils, eosinophils, lymphocytes, monocytes and neutrophils, according to WebMD. Each of these cells has a different role in protecting the body from disease and infection.
Most white blood cells are produced in the bone marrow: the spongy center of the longer bones. The T and B lymphocytes are produced in the spleen and lymph nodes, and T lymphocytes are also produced by the thymus gland.
When too many white blood cells are produced, or when they do not mature sufficiently before being released into the circulating blood, a person develops a life-threatening condition called leukemia.