Once the pathogen has succeeded in overcoming nonspecific defense systems of the body, then the immune systems strategy is a series of well-targeted responses to prevent or limit infection raised by that pathogen. These specific targeted responses constitute the third line of defense in response to an infectious agent. Specific defense mechanism is called as acquired immunity or adaptive immunity.
|Acquired Immunity: An overview|
Characteristics of Adaptive immunity
1) Diversity: they can respond to millions of different Antigens
2) Antigenic specificity: ability of antibody to recognize specific antigen (even antigen molecule differing by a single amino acid). The response is directed only towards the initiated pathogen.
3) Immunologic memory: Once recognized and responded to an Ag, the system is able to respond more strongly on subsequent exposure even after many years.
Reason: memory B cells and T cells are produced during first encounter and has long life span
4) Discrimination between self and non-self or recognizing self-antigen from non self-antigen: It can differentiate self-cells from foreign cells and molecules. Only foreign particles are attacked. Failure of this discrimination results in auto immune diseases.