The main components of blood are plasma, red blood cells, platelets and white blood cells. White blood cells (WBCs) are created in the bone marrow. In a young child, the majority of bones create blood cells. In adults, these duties are delegated to the larger bones of the body. WBCs, also called leukocytes, are sent into the bloodstream while they are still immature; they live from 13 to 20 days. When needed for inflammation, trauma or infection, the number of white blood cells increases; they can double in number in less than a day. Blood contains immature cells plus five main types of mature WBCs, each with its own specific functions.
Immature Cells
Immature white blood cells are called "bands" or "stabs." They normally compose 3 to 5 percent of the total white blood cell count. If the body has an acute problem, such as a strong infection, the percent will be higher as the bone marrow makes a large number of new cells. Your body makes around 100 billion immature white blood cells each day.
Neutrophils
Neutrophils are the main type of white blood cell in the healthy adult. They have granules inside, making them granulocytes. According to Merck Manual, these cells destroy and ingest fungi and bacteria in the body. They also digest harmful debris, such as dirt that enters a wound. Neutrophils are considered to be infection-fighters. Neutrophils normally compose 50 to 70 percent of the white blood cell count. An elevated neutrophil count is called neutrophilia.
Eosinophils
Eosinophils also have granules, making them granulocytes. These WBCs normally compose 1 to 3 percent of the total white blood cell count. Eosinophils destroy cancer cells and parasites. They also play a complex role in your body's allergic response. A high level of eosinophils in the blood is called eosinophilia.
Basophils
Basophils are the final type of granulocytes. These white blood cells typically compose only 0.4 to 1 percent of total WBCs. Basophils help fight infection and play a complex role in the allergic response. An increase in basophils is called basophilia.
Lymphocytes
Lymphocytes do not contain granules, which means they are part of the kind of white blood cells called agranulocytes. Lymphocytes comprise 25 to 35 percent of the total WBC count in a healthy adult. There are three main types of lymphocytes: B lymphocytes, T lymphocytes and natural killer cells. B lymphocytes, when needed, release a protein called an antibody that fights bacteria, parasites and viruses. B lymphocytes may also attack a transplanted organ, thinking it is a foreign invader. T lymphocytes fight viruses in the body, as do natural killer cells. Both of these lymphocytes can also destroy some types of cancer cells. An elevated level of lymphocytes is called lymphocytosis.
Monocytes
Monocytes are also considered to be agranulocytes. In a healthy adult, 4 to 6 percent of WBCs are monocytes. Merck Manual explains that these WBCs protect you from a large number of infectious organisms in the body and also ingest damaged and dead cells. A high number of monocytes is called monocytosis.
