There are five different types of white blood cells, also called leukocytes, found in the human bodies. White blood cells all help to defend the body from foreign particles in some way. All white blood cells are produced in red bone marrow, with the special type lymphocytes also being formed in lymphatic tissue. White blood cells are not found in the blood in great numbers, instead they leave the blood and defend in the rest of the tissues of the body.
White blood cells are put into two different groups based on appearance in the microscope, agranulocytes and granulocytes. Agranulocytes don't have any type of visual grains in their cells, and are the monocytes and lymphocytes. Granulocytes have visual grains in their cells that help with their specific functions, and are the neutrophils, eosinophils and basophils. Together all these types of white blood cells coordinate a system that defends the body from infection, damage and even cancer.
Neutrophils are the most numerous of the white blood cells. They are often called bacterial slayers because they're usually function is killing foreign bacteria in the body. Neutrophils are the first white blood cell at a cut or when damage is done to the body. They kill bacterial by a process called phagocytosis, where they surround and consume the bacteria. Neutrophils will also release a super oxide burst to kill many bacteria at once.
Eosinophils are usually involved in infections of parasitic worms. Instead of doing phagocytosis, Eosinopils release toxins to kill the parasites They are also involved in allergic reactions.
Basophils in other animals are also called mast cells, which are commonly found in the connective tissues throughout the body. The granules seen in basophils contain histamine and heparin. Basophils are the white blood cell that help with the inflammatory response when tissue is damaged. Histamine dilates blood vessels to bring resources into a site of a damage. Histamine can also be involved in allergies. Heparin is an anti-coagulate and stops the blood from clotting, by not clotting the blood heparin helps to bring in more resources to a damaged area.
Monocytes are the largest white blood cell. When they leave the blood they're called macrophages. Most organs in the body have some type of macrophage that can often go by other names. Macrophages do phagocytosis of foreign particles in the body, such as bacteria. Macrophage also do phagocytosis of dead neutrophils and dead body cells. They are involved with cleaning up at the end of an inflammatory response. Macrophages work with lymphocytes as antigen presenting cells.
Lymphocytes are a special type of white blood cell that are capable of cell division in lymphatic organs and tissues, such as the tonsils, lymph nodes and spleen, in response to specific infections in the body. They are the last step in the immune system and allow to long term resistance to infections the body has seen before. Lymphocytes come in two main types. B lymphocytes differentiate in the bone marrow and produce antibodies and do antibody-mediated resistance. T lymphocytes differentiate in the thymus and perform cell-mediate resistance.