The two important tasks of the immune system are to kill and to remember. Killing and remembering involves recognizing foreign invaders. Nature is teeming with invaders ready to infect our bodies. Thus, our immune system is equipped to specifically recognize the differences between different invaders referred to as pathogens. All pathogens release certain chemicals and proteins that our immune defense recognizes.
Recognition triggers a kill response.
The cells responsible for killing actually eat and digest the pathogen. When an invader returns, the team members responsible for remembering past invasions sense the invader s chemical signals. The signal stimulates them to produce and excrete chemical tags called antibodies. These antibodies stick to the invaders and enable to killer cells to recognize and kill again. Cells whose duty is to patrol and report do another form of recognition.