Our defenses against germs
Animation (755KB)Humans possess an excellent natural defense system to fight against undesirable microorganisms. When these microorganisms get inside the body, a whole series of cells and messages come into play to coordinate the efforts to eliminate the intruders. This army that protects us is called the immune system.
Combat units of the immune system
Think of your immune system as an army made up of the following six combat units:
Zoom1) Macrophages
Target: anything they find in their path.
Role: to ingest harmful microorganisms; to activate helper T lymphocytes (TH1 and TH2)
Zoom2) B lymphocytes
Target: microorganisms and infected cells
Role: to secrete antibodies that attach to microorganisms or cells thereby helping to destroy them
Zoom3) Cytotoxic T lymphocytes
Target: infected cell
Role: to kill infected cells
Zoom4) NK cells (natural killer)
Target: infected cells
Role: to kill cells that appear to be abnormal
Zoom5) T helper type 1 lymphocytes (TH1)
Character: Captain of the cytotoxic T lymphocytes (bearing a small crest of a marksman on their sweaters)
Role: to activate cytotoxic T lymphocytes
Zoom6) T helper type 2 lymphocytes (TH2)
Character: Captain of the B lymphocytes (bearing a small crest of Robin Hood on their sweaters)
Role: to activate B lymphocytes
Recognizing the intruder
Each T and B lymphocyte has been trained intensively to recognize molecules that belong to its own organism (the self). Therefore, when it sees a molecule that it does not know (the non-self), it automatically knows that it’s an intruder and sounds the alarm.
Macrophages are able to rid the body of a great number of microorganisms – those whose surfaces contain molecules that the macrophages can bind to. Macrophages are particularly attracted to infected cells and microorganisms covered in antibodies. The collaboration between macrophages and the antibody-producing B lymphocytes increases the effectiveness of the fight against the intruder.
In the case of NK cells, the situation is slightly different since they do not recognize the intruder but rather the effect of the intruder. If the cell appears abnormal, it’s probably because it contains an intruder…This diseased cell must thus be killed before it allows any new intruders to escape!