White blood cells, also called leukocytes, are part of the body's defense system. They are responsible for detecting and destroying invading germs and other foreign matter. White blood cells are made from stem cells in the bone marrow and must be present in sufficient numbers in order to ward off disease. These cells communicate with and assist one another in their efforts to keep the body healthy.
Neutrophils
Neutrophils are one of three kinds of white blood cells called granulocytes. They are so named because the substance inside the cell contains granules. The granules of these white blood cells harbor chemical substances that help kill off infectious organisms. In a medical laboratory setting, white cells undergo a staining procedure to help identify the various cell types.
Neutrophils stain a light pink to light purple color. They are the most numerous of all the white cells, making up 60 to 70 percent of the total white blood cell count, according to AnatomyAtlases.org. These cells are particularly suited to fighting against bacteria and are often referred to as the body's first line of defense. Neutrophils are able to navigate to the site of an infection and then proceed to consume the invader in a process called phagocytosis.
Eosinophils
Eosinophils stain red and are much fewer in number compared to neutrophils. They make up only about 5 percent of white blood cells. Eosinophils target parasites and are activated in response to allergic reactions. These granulocytes kill microorganisms by secreting chemical components. They also promote inflammation and can activate other types of white blood cells.
Basophils
Basophils are small in number, making up only about 1 percent of white blood cells. They stain a bluish color. When triggered by an invader, these cells release the contents of their granules which contain histamines and other inflammatory substances. They too become active in response to allergens. They also contain heparin, a component of the blood that keeps the blood from clotting at an excessive rate.
Lymphocytes
Lymphocytes are a type of nongranulocytic white blood cell. The two main types of these are B cells and T cells. The B cell's primary function is to produce antibodies. Antibodies are proteins of the immune system that defend the body against foreign microorganisms. Alternately, T cells travel from the bone marrow and come to maturity in the thymus gland. Most lymphocytes are T cells. Merck Manuals Medical Library notes that there are three types of T cells. Helper T cells promote antibody production from B cells. Cytotoxic T cells release lethal chemicals especially suited to kill cells that are infected with viruses and other invaders. Regulatory T cells help keep the immune system in balance.
Monocytes
Monocytes are one of the nongranular white blood cells. They circulate in the blood stream before moving into the tissues of the body, where they become macrophages. The role of monocytes is to phagocytize foreign material, and decaying or dead cells.
