Each of the various white blood cells has a special role within the immune system. Many are able to transform themselves in different ways.
- Neutrophils, the most common white blood cells, have a short life span - generally less than a day. Once in the blood neutrophils can move through capillary walls into tissue. They are attracted to foreign material. For example, if you get a splinter or a cut, neutrophils are attracted. Once a neutrophil finds a foreign particle or a bacterium, the neutrophils engulfs it, releasing enzymes, hydrogen peroxide and other chemicals to kill it. When there is a serious infection, pus will form. Pus is just dead neutrophils and other debris form cells.
- Eosinophils and basophils are less common than neutrophils. Eosinophils focus on parasites in the skin and the lungs. Basophils carry histamine and are important for causing inflammation. For the immune system, inflammation is good. It brings in more blood and dilates capillary walls so more immune system cells can get to the infection.
- Macrophages are the biggest of all blood cells. Monocytes are released by bone marrow. They float in the bloodstream, enter tissue and become macrophages. Most boundary tissue has its own macrophages. For example, alveolar macrophages keep the lungs clean by ingesting foreign particles like dust and smoke and dust. Macrophages swim freely. One of their jobs is to remove dead neutrophils (or pus) as part of the healing process.
- The lymphocytes handle most bacterial and viral infections. Lymphocytes start in bone marrow. Those that will become B cells develop in the bone marrow before entering the blood. T cells start in the bone marrow but migrate through the bloodstream to the thymus, where they mature. T cells and B cells tend to concentrate in lymph tissue including the lymph nodes, the thymus and the spleen.
- B cells, when stimulated, mature into plasma cells - the cells that produce antibodies. Any specific B cell is in tune with a specific germ. When the germ is present, the B cell clones itself to produce millions of antibodies designed to eliminate the germ.
- T cells actually bump up against cells and kill them. One type of T cell, known as a killer T cell, can detect cells in the body that are harboring viruses. When it detects such a cell it kills it. Other T cells, called Helper and Suppressor T cells, help make killer T cells and control the immune response.