Adaptive immunity is capable of recognizing and selectively eliminating specific foreign microorganisms and molecules
(i.e., foreign antigens).
Unlike innate immune responses, adaptive immune responses are not the same in all members
of a species but are reactions to specific antigenic challenges.
Adaptive immunity displays four characteristic attributes:
- · Antigenic specificity
- · Diversity
- · Immunologic memory
- · Self/nonself recognition
The antigenic specificity of the immune system permits it to distinguish subtle differences among antigens.
Antibodiescan distinguish between two protein molecules that differ in only a single amino acid.
The immune system is capable ofgenerating tremendous diversity in its recognition molecules,
allowing it to recognize billions of unique structures on foreign antigens.
Once the immune system has recognized and responded to an antigen, it exhibits immunologic memory;
that is, a second encounter with the same antigen induces a heightened state of immune reactivity.
Because of this attribute, the immune system can confer life-long immunity to many infectious agents after an initial encounter.
Finally, the immune system normally responds only to foreign antigens, indicating that it is capable of self/nonself recognition.
The ability of the immune system to distinguish self from nonself and respond only to nonself molecules is essential, for, as described below, the outcome of an inappropriate response toself molecules can be fatal.
Adaptive immunity is not independent of innate immunity.
The phagocytic cells crucial to nonspecific immune responses are intimately involved in activating the specific immune response.Conversely, various soluble factors produced by a specific immune response have been shown to augment the activity of these phagocytic cells.
As an inflammatory response develops, for example, soluble mediators are produced
that attract cells of the immune system.
The immuneresponse will, in turn, serve to regulate the intensity of the inflammatory
Through the carefully regulated interplay of adaptive and innate immunity, the two systems work
together to eliminate a foreign invader.
The Adaptive Immune System Requires Cooperation Between Lymphocytes and Antigen-Presenting Cells