White blood cells are also called leukocytes or immune cells. They help to defend the body against infectious disease and foreign materials as part of the immune system. White cells are also found in large numbers in the lymphatic system, the spleen, and in other body tissues.

Fighting Infection

An infection is the non-beneficial invasion of a foreign species, or pathogen. In infection, the infecting organism seeks to utilize the human body to multiply. The infecting organism, or pathogen, interferes with the normal functioning of the body and can lead to disease, widespread infection and even death. A pathogen is usually considered a microscopic organism such as bacteria, parasites, fungi, viruses, prions, and viroids.

Each of the white blood cell types has a task in helping the body fight infections. The lymphocytes help create antibodies that attack the invaders and mark them for destruction by the neutrophils, monocytes and macrophages.

Here the left caption shows an immune response to infection when compared to the right caption. The left caption shows an increase in the number of neutrophils.

Macrophages (a form of monocyte) engulf invaders and destroy them with powerful enzymes. The macrophage shown at the top of the page is attacking streptococcus bacteria that cause pneumonia.

There are three major types of white blood cells: granulocytes, monocytes and lymphocytes.