The Immune System

The role of the non-specific defence system is to prevent pathogens from entering the body. However, sometimes pathogens are able to breach this first line of defence. The immune system, serving as the second line of defence, can reduce, minimise or stop the infection entirely.

White blood cells play an important role in the immune system and there are two types:

  • Phagocytes
  • Lymphocytes


Phagocytes are a type of white blood cell that can engulf pathogens. They extend their cell membrane around the pathogen and use enzymes to digest (break down) the pathogen. This process is known as phagocytosis.

  • Because phagocytes do not differentiate between various types of pathogens, they are called ‘non-specific’.


Lymphocytes are another type of white blood cell that can destroy pathogens by producing antibodies. The antibodies bind to antigens on the pathogen’s surface, causing them to clump together. This makes it easier for phagocytosis to occur and it prevents the pathogens from entering cells.

  • Since antibodies are specific, the lymphocytes that produce them are also specific

Antibodies can remain in the blood for a long time. Therefore, if the same pathogen enters the body again, the lymphocytes will recognise it and release the specific antibodies.

Certain pathogens produce toxins that can cause illness. Some lymphocytes can produce antitoxins, which neutralise these toxins, preventing them from damaging cells.