The human body is able to fight off most infections using its natural immune system. White blood cells, also called leukocytes, play an important role in the body's defense system, according to the Merck Manual. The cells move to where the harmful organism is located and either kill or ingest the foreign life form. There are different kinds of white blood cells, and they each perform very important functions in the immune system. The number and type of leukocytes present in the body are measured using a blood test called the white blood cell count.
Neutrophils
The most numerous white blood cells in the body are the neutrophils. According to the University of Virginia, neutrophils comprise 40 to 75 percent of all white blood cells. In response to an infection, neutrophils are released from the bone marrow and sent to the site of infection. Within 12 hours, the neutrophils have arrived at the infected tissue. These cells destroy the offending organism by engulfing the germ (a process called phagocytosis), and then releasing deadly enzymes that destroy the bacteria.
Eosinophils
Less than two to four percent of all white blood cells are eosinophils, according to Southern Illinois University. Eosinophils are named after a stain called eosin because both appear very pink in color when seen under the microscope. Eosinophils are around the same size as neutrophils, but instead of having multiple nuclei like the neutrophils, the esosinophil has a two-lobed nucleus. Eosinophils are seen in patients with allergies or parasitic infections.
Basophils
Basophils can be recognized by examination under the microscope. These cells stain dark blue under the microscope. Basophils, according to the University of Virginia, have the ability to move themselves and use phagocytosis to destroy harmful organisms. Basophils make up less than one percent of the total white blood cell count.
Monocytes
The biggest white blood cell is the monocyte. This cell only constitutes five percent of the total leukocyte population. These cells use phagocytosis to destroy germs. Monocytes can be found in most tissues of the body, and their number can increase when the tissue becomes inflamed (a sign of infection or injury).
T-Lymphocyte
T-lymphocytes can be divided into two different classes of cells, based on the role the cells play in the immune system. Helper T cells control the immune defense, according to NobelPrize.org. When the helper T cell is presented with a foreign organism, it interacts with other cells in the immune system and helps them become more effective in killing the organism. Without T helper cells, the body's immune system begins to malfunction.
The second division of T-lymphocytes is the killer T cell. These cells, as stated by NobelPrize.org, have been engineered to attack viruses and sometimes bacteria. Killer T cells can recognize cells that have become infected with the virus and kill those infected cells, before the disease has a chance to spread.
B-Lymphocyte
Along with T-lymphocytes, B-lymphocytes comprise 20 to 45 percent of all white blood cells, according to the University of Virginia. NobelPrize.org states that when a B-lymphocyte is exposed to a harmful organism, it begins to clone itself very rapidly. These clones of the original B cell can either produce small attack particles that help kill the germ (antibodies), or become memory B cells. Memory cells allow the immune system to remember the infective agent, so that if there is another infection with the same organism, the body will be able to respond faster.
