The reaction by the immune system to antigens (substances such as bacteria and
viruses) that the body recognizes as foreign is called immune
response.
The immune response can be divided into several phases:
the "innate" first response, mediated by cells able to destroy and
engulf a large range of foreign organisms;
the secondary, "adaptive" response, characterised by the generation of
antibodies and T cells that are specific for the antigen; and
a third, "suppression" phase, where the production of immune cells
reverts to normal, and the information necessary to mount a future immune
response to that antigen is retained in bone marrow memory cells.
