White blood cells help the body fight off bacteria, viruses and any cells not recognized as being part of itself. White blood cells are known as leukocytes; your body produces approximately 100 billion white blood cells in the bone marrow every day. The normal white blood cell (WBC) count is 4,000 to 11,000 cells per microliter, the Merck Manual states. There are five different types of white blood cells, each with a different function.
Neutrophils
Neutrophils are the largest group of white blood cells, making up 45 to 75 percent of the white blood count. Neutrophils are phagocytes, major players in fighting off bacterial infections and viruses. A drop in neutrophils below 1,000 cells per microliter increases the risk of developing infections. Neutrophils are the "first responders" in inflammation: the first on the scene to destroy bacteria and viruses. Neutrophils have a short life span, only about 10 hours. Immature neutrophils, called bands, are numerous in an active infection. A decrease in neutrophils is known as neutropenia; causes of neutropenia include chemotherapy treatment, bacterial and viral infections, and allergic reactions.
Lymphocytes
Lymphocytes comprise the second largest group of white blood cells; 20 to 40 percent of white blood cells are lymphocytes, according to Merck. There are three types of lymphocytes: T cells, B cells and natural killer cells. B cells create antibodies that attack foreign antigens. T cells and natural killer cells attack foreign cells and also create toxins that destroy invaders. An increase in lymphocytes usually indicates viral infection or some types of bacterial infection. A decreased number of T cells is found in HIV infection, tumor cells and viruses. Lymphocytes increase in infection and diseases like mononucleosis, the University of Nebraska at Omaha states.
Monocytes
Monocytes make up 1 to 10 percent of white blood cells. Monocytes move out of the bloodstream and into tissue, where they turn into macrophages, large scavenger cells that destroy foreign cells, remove dead tissue and kill cancer cells. Monocytes are elevated in chronic infections and autoimmune disease; chemotherapy may cause decreased levels.
Eosinophils
Eosinophils make up around 7 percent of white blood cells and initiate allergic reactions to allergens. An elevated number of eosinophils most often indicates an allergic reaction response, the University of Texas at Brownsville states; extreme stress or parasitic invasion can also cause an increase in eosinophils.
Basophils
Basophils represent less than 3 percent of the white blood cells. Basophils play a role in allergic reactions by releasing histamine, which causes blood vessels to dilate. Basophils also assist in repairing wounds by releasing heparin, which delays blood clotting so more cells can reach the wound site.
