There are many different types of white blood cells. Five of the most common are Monocytes, Lymphocytes, Neutrophils, Eosinophil and Basophil.
Neutrophils are also major players in the body's defense against bacterial infections. Neutrophils are made in the bone marrow and circulate in the bloodstream. Neutrophils move out of the blood vessels into the infected tissue to attack the bacteria. The pus in a pimple (an abscess) is made up largely of neutrophils. Normally a serious bacterial infection causes the body to produce an increased number of neutrophils, resulting in a higher than normal white blood cell count (WBC). When the white blood cell count is low, there may not be enough neutrophils to defend against bacterial infections.
Basophil is a type of granulocyte (a type of white blood cell) that can produce a biologically active substance such as histamine, proteoglycans, or cyclooxigenase products. Basophils are produced continually by stem cells in the bone marrow. The function of basophils is not fully understood, but it is known that they are capable of ingesting foreign particles and produce heparin and histamine (chemicals which induce inflammation), and are often associated with asthma and allergies.
Lymphocytes are a type of leukocyte (white blood cell) present in blood, lymph nodes, the spleen, the thymus gland, the gut wall, and bone marrow. Important to the immune system, lymphocytes come in several varieties, the most common of which are B-lymphocytes, which make antibodies that attack bacteria and toxins, and T-lymphocytes, primarily responsible for cell-mediated immunity (i.e. attacking body cells themselves when they have been taken over by viruses).
The function of Eosinophil is partly understood. They are important at sites of allergic reactions and with parasitic larvae infections ( helminths ). Eosinophil secretory products inactivate many of the chemical mediators of irritation and destroy cancer cells. This phenomenon is most obvious with mast cell-derived mediators Mast cells produce a chemo tactic factor for eosinophils. Produced in the bone marrow, eosinophils then migrate to tissues throughout the body. When a foreign substance enters the body, lymphocytes and neutrophils release certain substances to attract eosinophils which release toxic substances to kill the invader.
Monocytes circulate in the blood after leaving the bone marrow (where it is made). Monocytes usually circulate in the blood for only a day or so before they enter the tissue to mature into macrophages. Monocyte production and release from the bone marrow is increased during an immune response. In addition, monocytes enter the tissues as local cells in various locations . These fixed, local macrophages play an important role in keeping the tissues clear of antigen and rubbish. More monocytes can be recruited as needed to these and other sites.
