You know that your body has general defences to prevent pathogens from entering it. However, the body reacts to pathogens that survive through those barriers by using various immune responses to specific antigens. In this activity, you will learn about how the body works to fight diseases that get past the external barriers. 

This image shows antibodies attacking a virus.

 Pathogens carry proteins or other chemicals on their surface called antigens. If they get through your defences, your body recognizes that those proteins or chemicals do not belong in your body. Your body does not like intruders! In response to them, your immune response triggers your cells to create antibodies to defend your body from the antigens.

This process follows these steps:

• When the immune system recognizes that the pathogens are in your body, the white blood cells leave your bloodstream and surround the pathogens.

• The white blood cells signal more cells, called T cells, to work to kill the pathogens.

• Some of the T cells signal B cells to assist in attacking the antigens.

• The B cells produce antibodies that combine with the antigens to make them harmless to your body.

• Some of the antibodies produced by the B cells remain in your blood to protect you in case you come in contact with those antigens again. The image below shows this process.
  

 It's a war in there! These steps are involved in active immunity, which is the process that occurs when your body makes its own antibodies to protect you from a disease. In the next activity, you will learn about passive immunity.