Functionally, an immune response can be divided into
two related activities—recognition and response. Immune
recognition is remarkable for its specificity. The immune
system is able to recognize subtle chemical differences that
distinguish one foreign pathogen from another. Furthermore, the system is able to discriminate between foreign
molecules and the body’s own cells and proteins. Once a foreign organism has been recognized, the immune system
recruits a variety of cells and molecules to mount an appropriate response, called an effector response, to eliminate or
neutralize the organism. In this way the system is able to
convert the initial recognition event into a variety of effector
responses, each uniquely suited for eliminating a particular
type of pathogen.
