White blood cells, or leukocytes, are found in both the blood and the lymphatic system. Their primary function is to battle disease and infection throughout the body. When a foreign substance or invader is encountered by white blood cells, they proliferate and attack the invader, destroying it. According to the Franklin Institute, one drop of blood can contain between 7,000 and 25,000 white blood cells, but when the immune response has been initiated, the population of white blood cells can dramatically increase. The measurement of the white blood cell count is a key indicator of infection. There are several types of white blood cells.
Neutrophils
Neutrophils are the primary first defense in any infection. They are the most common and generally represent 50 to 60 percent of all white blood cells in the body. Their lifespan ranges between a few hours to a few days, and therefore, they are constantly reproducing. Neutrophils are defenders against bacterial and fungal infection and are present in large numbers in any inflammatory reaction. They are capable of engulfing a foreign invader in a process called phagocytosis. Neutrophils are attracted to the site of an injury or a foreign invader within moments and are the primary component of inflammation.
Eosinophils
Eosinophils are white blood cells that make up about six percent of the total white blood cell count and are primarily responsible for allergic reaction modulation, making them a main component of asthma reactions. They also are also involved in the defense against large parasites that may enter the body. Under microscopic observation, eosinophils appear to be granular. These granules contain chemical mediators, such as histamine and proteins that are toxic to parasites. They are released in a process called the granulation.
Basophils
Basophils are similar to eosinophils in function, but are the least common white blood cell, making up only about .1 percent of all white blood cells. Like the eosinophil, basophils are granular and secrete some of the same proteins, including histamine, in their function to modulate allergic reactions. They are heavily involved in asthma attacks. During an allergic reaction, basophils will migrate to the source of the reaction and may leave the blood and enter the tissues to perform their duty.
Lymphocyte
Lymphocytes are another white blood cell, making up 25 to 30 percent of all leukocytes. They are very often found in the lymphatic system, where a great deal of our immune function occurs. There are two common types of lymphocytes with somewhat different functions. B cells are responsible for what is referred to as humoral immunity, meaning it is modulated by antibodies. T cells on the other hand, attack invaders by using what is called cell mediated immunity. Lymphocytes play a key role in the body's immune response by providing very specific defenses against infection.
Monocyte
Monocytes play a couple of very unique roles in the body's immune system. First, they perform phagocytosis in a similar way that Neutrophils do. Second, they also function in harmony with the T cells to identify and destroy pathogens. Monocytes make up about 15 percent of all leukocytes.
