The Immune System

The role of the non-specific defence system is to prevent pathogens from entering the body. If a pathogen manages to pass this first line of defence, it causes an infection. The second line of defence is the immune system, which 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.

  • As phagocytes do not differentiate between different 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 attach to antigens on the surface, causing pathogens to stick together. This makes it easier for phagocytosis to occur and it prevents the pathogens from entering cells.

  • The antibodies are specific, so lymphocytes that produced the antibodies are also specific

Antibodies can stay in the blood for a long time, so if the pathogen enters the body again, lymphocytes will identify it and send specific antibodies.

Certain pathogens can produce toxins, which make us ill. Some lymphocytes can produce antitoxins, which neutralise these toxins, preventing them from damaging cells.