Active Immunity
Active immunity is stimulation of the immune system to
produce antigen-specific humoral (antibody) and cellular
immunity. Unlike passive immunity, which is temporary,
active immunity usually lasts for many years, often for a
lifetime.
One way to acquire active immunity is to survive infection
with the disease-causing form of the organism. In general,
once persons recover from infectious diseases, they will
have lifelong immunity to that disease. The persistence of
protection for many years after the infection is known as
immunologic memory. Following exposure of the immune
system to an antigen, certain cells (memory B cells) continue
to circulate in the blood (and also reside in the bone
marrow) for many years. Upon reexposure to the antigen,
these memory cells begin to replicate and produce antibody
very rapidly to reestablish protection.
Another way to produce active immunity is by vaccination.
Vaccines interact with the immune system and often
produce an immune response similar to that produced by
the natural infection, but they do not subject the recipient
to the disease and its potential complications. Many
vaccines also produce immunologic memory similar to that
acquired by having the natural disease.
Many factors may influence the immune response to
vaccination. These include the presence of maternal antibody,
nature and dose of antigen, route of administration, and the
presence of an adjuvant (e.g., aluminum-containing material