Immunity
Chapter 48
April Sike
AP Biology
April, 2011
Summary
We survive because we have evolved a variety
of defenses against constant attack. The
first line of defense consists the
mechanisms for preventing bacteria from
entering the body. The second line of
defense consists mechanisms for dealing
with any foreign substances in the body. All
organisms have the mechanics to protect
themselves from the onslaught of smaller
organisms and viruses.
Evolutionary development
• Invertebrates
• Vertebrates
Invertebrates
• In 1882 Elie Metchnikoff became the
first to recognize that invertebrate
animals have immune defenses.
• The invertebrate immune response
shares several elements with the
vertebrate one.
Phagocytes
• All animals have phagocytic cells that
attack invading microbes.
• These cells travel through the animal’s
circulatory system.
• In animals that do not have a
circulatory system the phagocytic cells
roam inside the mesoglea.
Distinguishing Self from Nonself
• The ability to recognize the difference
between cells of your own body and cells
from another individual seems to have
evolved early in the history of life.
• Sponges, thought to be the most ancient
animals, attack tissues from other sponges
just like insects and starfish.
• None of these invertebrates seem to show
any evidence of having an immune system.
• Apparently the humoral immune defense did
not evolve until vertebrates.
Lymphocytes
• Lymphocyte – A type of white blood cell
responsible for the immune responses, two
classes; B cells and T cells.
• Invertebrates do not have complementary proteins
or lymphocytes.
• But annelid earthworms and other invertebrates
do have lymphocyte-like cells that may be
evolutionary precursors of lymphocytes.
B and T cells
• B cells: B cells respond to helper T
cells by interleukin-1. B cells have
receptor proteins on their surface, one
type of receptor for each type of B cell.
• T Cells: protect the body from virus
infection and cancer, by killing
abnormal cells.
B Cells: The Humoral Immune
Response
• In this response, the immune system
triggers specific B cells to make large
amounts of their specific antibodies.
These antibodies can fight viruses and
stop infection.
• http://bcs.whfreeman.com/thelifewire/c
ontent/chp18/1802004.html
T Cells: Cellular Immune
Response
• Cells of this system kill cells of the
body that are cancerous. This response
relies on the lethal cytotoxic T cells.
They contain molecules, called
perforin, that they release into target
cells. The perforin pokes holes in the
target cells and kills them.
• http://bcs.whfreeman.com/thelifewire/c
ontent/chp18/1802003.html
Vertebrates
• The earliest vertebrates, the jawless
lampreys first evolved some 500 million
years ago.
• They have an immune system based on
lymphocytes.
• At this early stage of vertebrate evolution,
however, lampreys lack distinct
populations of B and T cells that are found
in all higher vertebrates.
• The modern vertebrate immune system first
arose with the evolution of fish with jaws.
• The oldest surviving group of jawed fishes are
the sharks, which evolved 450 million years
ago. By then the vertebrate immune defense
had been fully evolved.
• Sharks have an immune response similar to
mammals, with a cellular response carried out
by T cell lymphocytes and humoral response
carried out by B cells.
Necessary
• The Immune system is necessary for survival because
without it organisms would not be able to protect
themselves against viruses or diseases. We would be
subject to every infection and disease and not survive.
• There is no example in the world of an organisms
functioning without an immune system, but there are
examples of organisms being born without specific
parts of their immune system, making them susceptible
to infection by certain types of viruses.
Structures and functions of the
system
• Skin:
The first line of defense
• Cellular Counterattack:
2nd line of defense
• The Immune Response:
3rd line of defense
Skin: 1st line of defense
• The largest organ of the vertebrate
body, provides nearly impenetrable
barriers and reinforces defenses with
surface chemical weapons.
• Mucus membranes of the digestive,
and reparatory help trap and get rid of
microorganisms before they invade the
body’s tissue.
Cellular counterattack: 2nd line of
defense
• Macrophages – big phygocytic cells that can
digest invading bacteria.
• Cellular and chemical defenses respond to
any microbial infection.
• Neutrophils (capable of engulfing
microorganisms and other foreign particles)
kill cells of the body infected with viruses.
The Immune Response: 3rd line
of defense
• The pathogen enters the body.
• Macrophages with antigen fragments displayed on
their surfaces are called antigen-presenting cells.
An antigen-presenting macrophage interacts with
a T-helper cell that can recognize the same
antigen.
• During the interaction, the macrophage releases a
chemical alarm signal called interleukin-1, which
stimulates the T-helper cell to secrete interlukin-2.
The Immune response
1.) Damaged tissues
release histamines,
increasing blood
flow to the area.
3.) Phagocytes
engulf bacteria,
dead cells, and
cellular debris.
2.) Histamines cause
capillaries to leak,
releasing phagocytes
and clotting factors into
the wound.
4.) Platelets move out of
the capillary to seal
the wounded area.
Interdependence of this system
with other body systems
The immune system works closely with the
circulatory system for transportation needs by
means of blood cells, allowing the immune cells to
travel throughout the body and survey the body for
infection. The nervous system uses the brain to
help stimulate the defense mechanisms against
infection, and the skeletal system provides the
blood cells that the immune system needs.
The immune System & The
Lymph System
• Lymph organs include the bone marrow, lymph
nodes, spleen, and thymus. Bone marrow contains
tissues that produce lymphocytes.
• B-cells mature in the bone marrow.
• T-cells mature in the thymus gland.
•
Other blood cells like monocytes and leukocytes are
made in the bone marrow.
• The thymus makes the hormone; thymosin, that
causes T-cells to mature in the thymus.
3 types of diseases or disorders
of the system
• T Cell Destruction
• Antigen Shifting
• Autoimmunity and Allergy
T Cell Destruction
• Many helper T Cells and inducer T cells
are CD4+ T cells. Therefore, any pathogen
that inactivates CD4+ T cells leave the
immune system unable to mount a
response from any foreign antigen.
Antigen Shifting
• A pathogen may escape
recognition by the immune system
if it changes its surface antigens.
Such antigen shifting is an
example of evolution by natural
selection.
Autoimmunity and Allergy
• Autoimmunity diseases are produced
by failure of the immune system to
recognize and tolerate self-antigens,
and can result from a variety of
mechanisms.
• Allergies can be divided into immediate
hypersensitivity and delayed
hypersensitivity, both of which can
cause the release of histamine.
• In extreme cases, the widespread
release of histamine can lead to
anaphylactic shock.