Transcript immune system

Introduction
Every organism's body is being attacked and invaded constantly by
viruses and by living organisms such as bacteria, protists, fungi, and
multicellular parasites. Without defenses against the damage, diseases,
and infections caused by the invaders, the attacked organism would soon
die. Organisms have evolved myriad defensive mechanisms to protect
themselves from the invaders; vertebrates have evolved an extremely
sophisticated defense system called the immune system, which is based
on several types of highly specialized white blood cells that search out
and destroy foreign materials that have entered the host's body. Some
of the cells even supply long-term, future protection against reinvasion
by a previously defeated attacker. The recognition of an invading
substance (or organism) by the immune system cells occurs at the
molecular level and is based on the three-dimensional shapes of
particular molecules. The ability to recognize so many different types of
invaders is conferred upon the immune system by a unique form of gene
processing. A disease such as AIDS, which destroys the immune system,
makes us realize with brutal clarity the importance of the immune
system-without it we cannot live. We succumb to the hordes of
attackers.
Types of immunity:
1. Active immunity: production of antibodies by the
organism itself
2. Passive immunity: acquisition of antibodies that
were produced by another organism
--mother to fetus via placenta
--from mother’s colostrum (breast milk produced
late in pregnancy
--injection from antisera (antivenoms)
3. Natural immunity: immunity due to infection
4. Artificial immunity: due to inoculation with a vaccine
*Function: defends the body against foreign invaders
ANALOGY: A castle
First line of defense: Physical barriers
EX: Castle wall, moat
(This is our skin, mucous membranes)
Second line of defense: Non-specific defenses
EX: “Mac” the guard dog. He attacks anything that
doesn’t belong. It could be enemy soldiers, the
mailman, the newspaper carrier-anything that
is not part of the castle. He doesn’t care. He’s
NOT specific in what he attacks.
(This is a group of cell called macrophages, an
inflammatory response, a fever, etc.)
Third line of defense: Specific defenses
EX: Specially trained soldiers that identify specific
enemies and attack them appropriately.
T soldiers are trained in hand-to-hand combat
getting close to the enemy. B soldiers are
trained in attacking at a distance, using weapons
called antibodies.
(This consist of T cells and B cells, which attack
SPECIFIC foreign particles.)
**To avoid not getting attacked, you need to know the
password. If you say the password, you can get
through all of the above. In our bodies, the password
is a set of cell-surface markers (carbs., proteins) such
as the major histocompatability complex MHC.
*Three cooperative lines of defense have evolved to
counter unwanted intruders.
--Two of these are nonspecific - that is, they do not
distinguish one infectious agent from another.
Major Components
1. Leukocytes (White Blood Cells): Macrophages,
T Cells, B cells
2. Proteins: Antibodies, Histamine
3. Organs
--Lymph nodes, spleen, tonsils: filter foreign
particles out of lymph; contain WBC’s that destroy
foreign particles.
--Bone marrow, thymus: produce WBC’s
First line of defense
*We need to get certain substances into our bodies,
such as food, water, and air. The passages through
which these substances pass are obvious places in
which microbes and other foreign particles can enter
our bodies. Thus, we should have defenses through
each of these “openings” to prevent invasion by
microbes. Obviously, none of these defenses are
perfect, as we still get sick.
1. Skin that cannot normally be penetrated by
bacteria or viruses (minute abrasions may allow their
passage).
2. Mucous membranes that line the digestive,
respiratory, and genito/urinary tracts bar the entry of
potentially harmful microbes.
*SKIN: How skin prevents entry of pathogens
--Secretions from sebaceous and sweat glands give
the skin a pH ranging from 3 to 5, which is acidic
enough to prevent colonization by many microbes.
--Antimicrobial proteins found in salivia/tears helps
to keep bacterial growth in check
*Bacteria on skin prevent other bacteria from growing.
*Skin has several tough/keratinized layers
*Lysozyme, is present on the skins surface-- digests
the cell walls of many bacteria, destroying them.
*MUCOUS: sticky, traps bacteria, contains
phagocytes, produces lysozymes
*Cilia sweeps mucous up to be swallowed to kill
bacteria.
Second line of defense
(Nonspecific defenses, Mac the
guard dog)
*Clearly foreign particles are able to slip past our
first line of defenses. We therefore need another
type of defense for when this happens. FIRST,
though, we need to know who is foreign, and who is
self.
Distinguishing Self from Non-self (What’s the password?)
1. All cells have molecules sticking out of their
membranes (carbs, proteins of glycocalyx).
--Immune cells use these to distinguish between self
cells and non-self cells.
2. Major Histocompatability Proteins (MHC)
--One class of of “self” labels
MHC’s cont.
*Bind to foreign particles and “present’ them at the
cell’s surface.
ANALOGY: Someone who’s in a hostage situation may
try to get near the window and hold up a sign saying
“Help! The bad guy’s in here!!!” This is the same thing
these proteins display portions of the the invader so
that other immune cells know what to attack.
1. MHC 1- found on every cell in the body
2. MHC 2- found only on immune system cells
Problems with MHC’s
*Organs and tissue donations rejection by the recipients
immune system.
SOLUTIONS
1. Try to match self-markers between donor
and recipients (using relatives is a common
approach to doing this)
2. Use drugs that suppress the immune system
Second line of defense Defenses
1. Phagocytic leucocytes (macrophages) (type of WBC)
*Chemical recognition of invader
*Moves toward the invader via amoeboid movement
*Ingest a microbe by endocytosis
*Enzymatic digestion (lysososmes)
--Molecular pieces not digested are displayed
on the membrane of the macrophage =
antigen presentation
*NON-SPECIFIC: attack all antigens,
indiscriminately
2. Inflammatory Response:
*Localized response due to tissue damage by a
physical injury or by the entry of microorganisms.
*Damaged cells or bacteria release chemical signals
that cause nearby capillaries to dilate and
become more permeable, leading to clot
formation at the injury.
*Increased local blood supply leads to swelling,
redness, and heat of inflammation.
1. Histamine is released.
--Triggers both dilation and increased permeability
of nearby capillaries.
--WBC’s and damaged tissue cells also discharge
prostaglandins and other substances that promote
blood flow to the site of injury.
2. Clotting elements delivered to the injured area.
--Clotting marks the beginning of the repair
process and helps block the spread of microbes
elsewhere.
3. Migration of phagocytic cells from the blood into
the injured tissues.
--Phagocyte migration usually begins within an hour
after injury.
Third line of defense
(Specific Defenses—trained soldiers)
Mac the guard dog does a decent job protecting us, but
if we know of a specific invader, we want to deal with it
immediately. We do this by sending out soldiers to
specifically search out and destroy these invaders. This
neutralizes the threat much more effectively. So how
does the the body identify and destroy a specific type
of invader?
Players
1. ANTIGEN: molecule that causes antibodies
2. ANTIBODIES: proteins that circulate through the blood
that help recognize antigens.
--Made by lymphocytes and specific to one antigen.
3. White Blood Cells (leucocytes)
B lymphocytes (cells):
-- Only in limited supply since WBC’s make up
only 1% of the total number of cells in the
bloodstream
--Body will clone(mitosis) the appropriate B cell type
*antibody-secreting cells: secrete antibodies
immediately and help fight off the primary
infection
*Memory Cells: do not secrete antibodies after
the first infection, but are long-lived and
circulate through the bloodstream waiting
for a secondary immune response to the pathogen
Helper T Cells: chemically recognizes the antigen
being presented and become activated.
--Turns the immune response from non-self to
antigen-specific as the identity of the antigen
is determine
--Activates specific B cells
Primary Immune Response:
*Clonal selection: antigens activates specific immune
responses
--Individual usually becomes sick while this is
occurring.
Secondary Immune Response:
*Rapid division of memory cells after a second
exposure stronger, more rapid response
--Vaccination: injection of dead or weakened
virus or bacterium; triggers clonal selection and
production of memory cells; if the real virus or
bacteria ever enters the body, these memory
cells rapidly proliferate and destroy it before
the individual gets sick.
Humoral Immune Response (HIR)/Antibody production
*Attacks bacteria, viruses, and toxins moving freely
through the blood; this is like attacking your enemy
at a distance using weapons called antibodies.
1.
Specific antigen is identified
2. Specific B cell is identified producing an antibody that will bind
to the antigen of the invader.
3. B cell clone themselves rapidly increasing the number of the
same type of B cells.
4. Antibody production kicks into high gear producing a lot of
antibodies.
5. Antibodies circulate in bloodstream finding the matching antigen.
6. Antibodies eliminate the pathogen
The humoral immune system
consists of B-cells which originate
in the Bone marrow and stay there
to develop.
The cell-mediated immune system
consists of T-cells which arise in
the bone marrow, but go to the
Thymus to finish their development
B-cells can produce antibodies, but
need exposure to foreign antigens to
do so. These antigens are cell surface
oligosaccharides and proteins which
T-cells are highly-specialized cells
in the blood and lymph to fight
bacteria, viruses, fungi, cancer,
within host cells and react against
foreign matter such as organ
transplants.
There are three kinds of T-cells.
Cytotoxic T-cells directly kill
invaders. Helper T-cells aid B and
other T-cells to do their jobs, and
HIV lives in and kills them.
Suppressor T-cells suppress the
activities of B- and other T-cells so
they don’t overreact. Allergy
injections are supposed to increase
the number of suppressor T-cells
to make the person less sensitive
to allergens.
the cell uses
as “ID tags”.
Antibodies are proteins in blood
plasma and lymph to fight bacteria
and viruses in body fluids. All
daughter cells of a B-cell will be
able to produce the same
antibodies as the mother cell.
Antibodies bind to certain parts of
an antigen to mark it for
destruction (by the T-cells).
Antibiotics: chemicals that take advantage of the
differences between prokaryotic (bacteria)
cells and eukaryotic (our own) cells.
*Block specific metabolic pathways/destroy cell
wall of the bacteria.
*Viruses make use of our own body cells’ metabolism
to create new viruses because they do not have
metabolic pathways
--Host cell not affected by antibiotics
Diseases of the Immune System
1. Allergies: hypersensitive response to environmental
antigens (allergens)
EX: Hay fever is an immune response to pollen
inflammatory response (sneezing, runny nose, teary
eyes, smooth muscle contractions that lead to
difficulty breathing)
Solution: antihistamines-drugs that help this by blocking
histamine(protein that causes the inflammatory
response
EX: Anaphylactic Shock: severe reactionabrupt
dilation of blood vesselsloss of blood
pressuredeath
(peanuts)
Solution: Epinephrine-contricts blood vessels and raises
blood pressure again (“Epi-pens”)
2. Immunodeficiency
EX: SCID (Severe Combined Immunodeficiency Disorder)
--Genetic condition resulting in failure of both branches
of the immune system
Bubble Boy: His parents had a child that died of SCID, so this
time, they decided to raise their child in a “bubble” if he had
the disorder. He did. They raised him for 14 yrs. But then he
died during an attempt at a bone marrow transplant (the
donor tissue had a virus). His whole life, he went without
human touch.
EX: HIV (Human Immunodeficiency Virus)
--Virus that attacks the immune cells (particularly T
helper cells)
--When T helper cells drops below a certain point, we
call it AIDS (Acquired Immunodeficiency Syndrome)
this usually takes 10 yrs.
3. Autoimmune disorder: immune cells attack “self” cells
--Not fully understood
--Multiple sclerosis, Rheumatoid arthritis, Type I
diabetes, Chron’s disease