Joshua Swift, of Kings High School, asks :-

What is our immune system and what does it do?

Jim Reid, the Associate Dean of Medical Science at the Otago Medical School, responded.

Immunity literally means freedom (originally from taxes), but was first applied in biology to freedom from infection. The human body, as well as other mammals, has mechanisms to defend itself from invasion by micro-organisms. This defence is produced by the immune system. A good example of this is a case of tonsillitis which is ofter caused by a bacteria called a streptococcus. When the tonsils are infected, the lymph glands in the neck swell to produce substances to fight the infection. The lymph glands therefore are part of the immune system.

If a person is infected by bacteria these bacteria are 'recognised' by the immune system and substances known as antibodies are produced. These, in a variety of ways attack the invading organisms in order to protect us from the infection. These antibodies are usually specific to the invading organism. Antibodies may develop not only as a result of infection, but also as the result of challenge with a number of other foreign substances. This is the basis of vaccine production and if either dead organisms, or even the proteins of which they are comprised are introduced into the body, this may stimulate the immune system to produce antibodies. Substances which cause this response are called antigens.

The body also has natural antibodies. These do not arise from any known antigenic stimulus.

If the immune system is overcome or weakened by any sort of illness, then this leaves the body open infection.