Download The Immune System

The Immune System
The Body’s Ultimate Defense
Our Lines of Defense
 First Line—Nonspecific—Skin, mucous
membranes, secretions of skin and mucous
membranes
 Second Line—Nonspecific—Phagocytic
WBCs, Antimicrobial proteins, the
inflammatory response
 Third Line—Specific—Lymphocytes and
antibodies
First Line of Defense
 Skin acts as a barrier to invaders—unless it
is cut
 Mucous in openings traps bacteria/viruses
 Secretions such as sweat change pH to
prevent microbial growth
 Salvia, tears, other mucous “wash” away
invaders
 Secretions contain antimicrobial proteins
such as lysozyme
If invaders pass the first line. . .
 Phagocytosis—Ingestion of invading
organisms by certain white blood cells
 Neutrophils (60 – 70% of all WBC’s)—
respond to chemicals released by cells
damaged by invaders
 Neutrophils self-destruct doing their job &
only live a few days
If invaders pass the first line. . .
 Monocytes (5% of leukocytes orWBC’s)—
circulate in blood and develop into
macrophages (“big eaters”)
 Macrophages are the biggest WBC’s and
are long lived.
 Macrophages use pseudopodia to trap
invaders and then digest them
 Especially abundant in the lymph system
and spleen
Figure 43.4
Figure 43.3
If invaders pass the first line. . .
 Eosinophils (1.5% of all WBC’s)—protect
against larger parasitic invaders such as
protists and worms
 Natural Killer Cells (NK cells)—destroy
virus-infected body cells and abnormal
body cells that could become cancerous.
They cause an abnormal cell to lyse.
If invaders pass the first line. . .
 The inflammatory response is evoked
 Arterioles dilate, venules constrict; increasing
blood supply and leaking fluid into the “infected”
tissue
 Chemical signals initiates inflammatory response
 One is histamine released by cells in response to
injury
 Histamine is produced by WBC’s known as
basophils and by mast cells in connective tissue
 Chemokines secreted by vessel tissue attract
phagocytes to the area.
The Inflammatory Response
Why are infected areas
 Red?
 Warm?
 Swollen?
If the injury is severe
 Body issues a systemic nonspecific
response
 Increasing the number of leukocytes
 Raising body temperature (fever) which
inhibits the growth of microbes, facilitates
phagocytosis, and speeds up body reactions
to further healing
If invaders pass the first line. . .
 Antimicrobial proteins are released
 They attack microbes or impede their reproduction
 Complement system—serum proteins that lyse
microbes & attract cells to sites of infection
 Interferon—proteins secreted by virus-infected
cells
 Interferon induce neighboring cells to produce
chemicals that inhibit viral reproduction limiting
the cell to cell spread of viruses—not virus
specific
Specific Immunity
The Third Line of Defense
Specific Defense—The Work of
Lymphocytes
 Two types—B cells & T cells
 Circulate through blood and lymph
 Concentrated in the spleen, lymph nodes, & lymph
tissue
 Recognize & respond to SPECIFIC invaders
 ANTIGEN—foreign molecule that elicits a
response from lymphocytes
 ANTIBODIES—Proteins that interact with
specific antigens
How do cells recognize antigens?
 Antigen receptors are located on cell’s
plasma membranes
 A single lymphocyte has about 100,000
receptors for antigen
 The structure of a lymphocyte’s receptor is
determined by genetic events early in its
development
 Immune system has millions of different
antigenic molecules
Clonal Selection of Lymphocytes
 An antigen binds to a specific receptor on a
lymphocyte
 This activates the lymphocytes specific to that
antigen
 Each activated cell divides giving rise to clones of
thousands of cells specific for that antigen
 Some B cells become memory cells that are longlived and ready to recognize that antigen the next
time
 This confers immunological memory
Clonal Selection of B cells
Immunological Memory—
Primary vs. Secondary response
B cells vs. T cells
 Both originate in the bone marrow from a
pluripotent stem cells
 Some migrate to the thymus for maturation and
become ‘T’ cells
 Some remain in the bone marrow for maturation
and become ‘B’ cells
 B or T cells with antigen receptors specific for
molecules already present in the body are
destroyed (apoptosis) or made nonfunctional
 This allows our immune system to differentiate
between “self” and “non-self”
Insert Figure 43.8
The Types of Lymphocytes
 B cells
– Plasma Cells—Create and release antibodies
– Memory Cells—Circulate in the bloodstream
bearing antigen receptors specific for the same
antigen
 T cells
– Helper T cells—Stimulates other lymphocytes
by releasing chemical signals (cytokines)
– Cytotoxic T cells—Directly kill cancer cells &
cells infected by viruses or other pathogens
Major Histocompatibility
Complex (MHC)
 Glycoproteins inside cells that mark body
cells as “self”
 Class I MHC—found in almost all
nucleated cells
 Class II MHC—found in macrophages, B
cells, activated T cells, and thymus cells
 Cells were first discovered as they were the
cause of rejection of skin grafts
MHC results in antigen
presentation
 Fragment of foreign protein (antigen) inside
the cell associates with MHC molecule
 The MHC molecules transports the antigen
to the cell surface
 The MHC/antigen complex is recognized by
a T cell, alerting it to the infection
 Class I MHC attracts cytotoxic T cells
 Class I MHC attracts Helper T cells
Two Types of Immune Response
 Humoral Immunity—B cell activation resulting
from production of antibodies; usually protects
against free bacteria, toxins, & viruses in body
fluids
 Cell-mediated Immunity—Immunity depending
on the action of T cells; usually protects against
body cells infected with viruses & bacteria, as
well as fungi, protozoa & parasitic worms,
transplanted tissue & cancer cells
The Functions of T cells
The functioning of cytotoxic
T cells
How T cells “help” B cells
Summary of the Immune
Response
Antibody = Immunonglobin
Antibody = Immunonglobin
 IgM—First antibodies to appear. Presence
indicates a current infection. Cannot cross
placenta.
 IgG—Most abundant circulating antibody.
Crosses blood vessels and the placenta
giving fetus passive immunity. Protects
again bacteria, viruses, and toxins; triggers
complement system.
Antibody = Immunonglobin
 IgA—Produced by cells in the mucous
membranes. Prevents the attachment of
viruses & bacteria to epithelial surfaces.
Present in mother’s first milk.
 IgD—Mostly found on surface of B cells.
Probably function as antigen receptors.
Cannot cross placenta.
 IgE—Cause cells to release histamine and
other chemicals causing allergic reactions.
How does the antigen-antibody
complex give immunity?
 Neutralization—antibody binds to & blocks the
activity of the antigen
 The complex enhance macrophage attachment to
and phagocytosis of microbes.
 Because each antibody has two antigen attachment
sites, it can link microbe cells together
(agglutination) which can be eaten by
macrophages.
 Complex signals the release of complement
How does immunity develop?
 Active Immunity—you have infection—you
develop immunity.
 Immunization/Vaccination—The intake of
inactivated bacterial toxins, killed microbes,
parts of microbes and viable but weakened
microbes. They create memory B cells.
 Passive Immunity—When IgG antibodies
of a pregnant woman passes to her child.
Does not last for a long period of time.
ABO Blood Groups
 Blood Types A, B, and AB have RBC that
have antigens on their surface that their
owners recognize as “self”. The immune
system does not attack these cells.
 If transfusions are given that introduce
foreign antigens, the immune system attacks
those RBC.
A mother, a fetus, and Rh factor
 The immune response to ABO blood groups
does not produce immunological memory
SO, a mother can have one blood type and
her baby another blood type without her
immune system attacking the fetus.
 However, if the mother is Rh negative
(lacking the Rh antigen) and she bears an
Rh postive baby there is a problem.
Immunity, Tissue Grafts, and
Organ Transplanation
 Our MHC fingerprint is so unique we
cannot accept foreign cells without evoking
an immune response.
 Close matches are sought.
 The immune system is suppressed with
drugs.
Abnormal Immune Function
 Allergies—Hypersensitive responses to certain
environmental antigens (allergens). Mast cells
produce large amounts of histamine which dilates
& increases blood vessels. This causes sneezing,
runny nose, tearing eyes, and breathing difficulty.
 Anaphylactic shock—Life-threatening reaction to
injected or ingested allergens. Causes immediate
drop in blood pressure; bee venom, penicillin,
peanuts, fish and other foods can cause it.
 Epinephrine—counteracts this response. Allergy
sufferers often carry a “pin” with them!
Abnormal Immune Function
 Autoimmune Disease—When the immune
system loses tolerance for self and turns
against “self” molecules. Lupus,
rheumatoid arthritis, diabetes, multiple
sclerosis
 Immunodeficiency Diseases—Severe
combined immunodeficiency (SCID)