Page 176 - 84 human physiolofy part-1

Chapter 9

Immunization

While some infectious diseases are common and can occur many times in the same person, others
can only occur once in a lifetime thanks to the immune system and it's ability to remember the
organism and prevent following infections. To avoid an epidemic of a grave disease such as polio,
before the disease can be acquired, an immunization can create a man-made "memory".

• Active immunization

A person receives an injection (vaccine) that contains dead or harmless living forms of an
organism. The vaccine stimulates the immune system to produce antibodies and memorize the
organism. If there is a later exposure to this organism and subsequent infection, the antibodies will stop
the infection.

• Passive immunization

Blood containing antibodies is taken from animals or humans who have recently had an infection.
Blood serum is made that contains the antibodies, and then injected into the person. The antibodies
either attack an infection that is present or provide short-term protection.

• Genetically engineered viruses

Genetic engineering is a technique that alters or changes the DNA of a plant or animal by inserting
new genetic information from another organism. After these organisms replicate, vaccines and
hormones are made that can help fight disease.

• Hepatitis B vaccine

The gene of the surface antigen of Hepatitis B virus is implanted into the DNA of a single
bacterium. The bacteria produces viral antigens which are then implanted to stimulate the immune
system.

IMMUNE SYSTEM DISORDERS

The immune system is a very complex and highly developed system, yet it has a very simple
mission, seek and destroy invaders. When the immune system does not function properly it leaves the
body open for attacks from an array of diseases. We classify these into three broad categories;
autoimmunity, immunodeficiencies, and hypersensitivities.

Anything that can trigger the immune response is called an antigen. An antigen can be a microbe
such as a virus, or even a part of a microbe. Tissues of cells from another person also carry nonself
markers and act as antigens. This explains why tissue transplants can be rejected. In abnormal
situations, the immune system can mistake self for nonself and launch an attack against the body's own
cells or tissues. The result is called an autoimmune disease. Some forms of arthritis and diabetes are
autoimmune diseases. In other cases, the immune system responds to a seemingly harmless foreign
substance such as a dust mite. The result is allergy, and this kind of antigen is called an allergen.

176 | Human Physiology