Acquired Immunity
Double headed arrows indicate potential bridging events that
unite innate and acquired forms of immunity
Adaptive immunity has 3 major functions
1. To recognize anything that is foreign to the body
2. To respond to this foreign material
3. To remember the foreign invader
Specific immunity is acquired and require
sufficient time to fully develop
Four characteristics distinguish specific (adaptive) immunity
from nonspecific (innate) resistance:
1. Discrimination between self and nonself.
2. Diversity: it can generate an enormous diversity of
molecules such as antibodies that recognize trillions
of different foreign substances.
3. Specificity. it can be directed against one particular
pathogen or foreign substance (among trillions); the
immunity to this one pathogen or substance usually
does not confer immunity to others.
4. Memory. When re-exposed to the same pathogen or
substance, the body reacts so quickly that there is usually
no noticeable pathogenesis.
By contrast, the reaction time for inflammation and other
nonspecific (innate) defences is just as long for a later
exposure to a given antigen as it was for the initial one.
Naturally acquired Active immunity
• Occurs when an individual’s immune system
contacts a foreign stimulus (antigen) such as a
pathogen that causes an infection.
• The immune system responds by producing
antibodies and activated lymphocytes that
inactivate or destroy the pathogen.
• The immunity produced can be either lifelong
(measles or chickenpox), or last for only a few
years (influenza).
Naturally acquired Passive immunity
• Involves the transfer of antibodies from one host
to another. Mother’s antibodies pass across the
placenta to her fetus.
• If the female is immune to diseases such as polio
or diphtheria, this placental transfer also gives
her fetus and newborn temporary to these
diseases
• Some Abs pass from mother to offspring through
secretions (colostrum)
• Naturally acquired passive immunity generally
lasts only a short time (weeks to months).
Artificially Acquired Active Immunity
It results when an animal is intentionally
exposed to a foreign material and induced to
form antibodies and activated lymphocytes.
This foreign material is called a vaccine and the
procedure is vaccination (immunization).
Artificially acquired Passive immunity
• It results when antibodies or lymphocytes that
have been produced outside the host are
introduced into a host.
• Immunity is immediate, it is short lived, lasting
only a few weeks to a few months.
Eg: botulinum antitoxin produced in a horse and
given to a human suffering from botulism food
poisoning, or a bone marrow transplant given to
a patient with genetic immunodeficiency.
Clonal selection theory