The immune system of the human body in defence against disease

An illustrated scene of a phatocyte's cell membrane surrounding a pathogen
Phagocyte engulfing a bacterial cell

If pathogens manage to pass the non-specific first line of defence then they will cause an infection. However, the body has a second line of defence to stop or minimise this infection. This is called the immune system. As a part of this there are two types of white blood cell called phagocytes and lymphocytes.

Phagocytes

Phagocytes are white blood cells that are attracted to pathogens and attach to them. Once they have attached to the pathogen, the phagocyte's cell membrane surrounds the pathogen and engulfs it. This means the pathogen is taken inside of the phagocyte.

Enzymes found inside the phagocyte break down the pathogen and destroy it. Phagocytes do this to all pathogens that they encounter, so they are called 'non-specific'.

Lymphocytes

A scientific impression of a lymphocyte white blood cell

Lymphocytes are another type of white blood cell. They recognise proteins on the surface of pathogens called antigens. Lymphocytes detect that these pathogen antigens are foreign and not naturally occurring within the body, leading the lymphocyte to produce antibodies. This process can take a few days, during which time a person may feel ill. The antibodies are released into the blood and bind to pathogens. This causes the pathogens to stick together, restricting their movement around the body and making it easier for phagocytes to engulf and then destroy them.

Diagram showing how antibodies attach themselves to antigensDiagram showing how antibodies cause pathogens to stick togetherAntibodies released by lymphocytes can attach to pathogens which leads to the destruction of the pathogen

Some pathogens produce toxins which make you feel ill. Lymphocytes can also produce antitoxins to neutralise these toxins. This means that the toxins cannot bind to body cells and cause damage. Both the antibodies and antitoxins are highly specific to the antigen or toxin that is made by the pathogen, therefore the lymphocytes that produce them are called 'specific'.