All organisms have "Innate" immune systems which respond to microorganisms or "non-self" or "altered-self" (e.g. cancer cells). The innate responses occur via receptors which detect types or groups of molecules call Pathogen Associated Molecular Patterns or PAMPs. These responses tend to proceed fairly rapidly, but having previously responded to the same substance does not result in a speedier response (i.e. there is no "memory" for it). Innate responses occur via cells such as neutrophils, immune proteins such as complement, antimicrobial peptides, and many other ways which will be explained later in this course.
On the other hand, adaptive immunity is found only in vertebrates. It is characterized by a slower initial "primary" response, but subsequently the adaptive immune response to a given stimulus occurs much more quickly because memory cells were formed. The major effector cells of the adaptive immune response are lymphocytes which have receptors that recognize very specific molecules, rather than patterns of molecules as in the innate system. Table 3 summarizes the two.
Table 3. Innate and Adaptive Immunity.
|Rapid initial response (hours)||Slower initial response (days to weeks)|
|Recognize patterns of molecules||Recognize specific molecules|
|No memory is formed||Memory is formed|
|Found in all organisms||Found only in vertebrates|