Immune Cell
White blood cells or leukocytes are cells of the immune system, which defend the body against both infectious disease and foreign materials. Several different types of leukocytes exist but they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell. Leukocytes are found throughout the body, including the blood and lymphatic system.

Immune system
The immune system is a collection of mechanisms that protects an organism against disease by identifying and killing pathogens and tumour cells. It is able to detect a variety of agents from viruses to bacteria and and needs to distinguish them from the organism's own healthy cells and tissues.

Immunity
The body’s ability to fight infections and disease.

Immunosuppression
When the immune system is weakened and less able to fight infections and disease. Chemotherapy and certain infections can weaken the immune system.

Immunotherapy
The artificial stimulation of the body’s immune system to treat or fight infections. Infection
An infection is a colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to overtake the host's resources to multiply (usually at the expense of the host). The infecting organism, or pathogen, interferes with the normal functioning of the host and can lead to chronic wounds, gangrene, loss of an infected limb, and even death. The host's response to infection is inflammation. The branch of medicine that focuses on infections and pathogens is infectious disease.

Internal central line
In cancer patients, an internal central line is a type of central venous catheter (CVC or central venous line) that is inserted into a large vein near the heart. An internal line is inserted entirely under the skin and is called a Port-a-Cath. It is inserted into the upper part of the child's chest by a surgeon, while the child is under general anaesthesia. To use the internal line, a needle is put through the child's skin into a reservoir. Internal lines cannot be seen once they are under the skin. To prevent infection during the use of the internal line, the skin over it must be washed with an antiseptic soap. A substance called heparin is injected into the port to keep blood clots from blocking the line. See also external line.