Download lecture # 7 the immune system

Lymphatic and Immune Systems
(Chapter 21)
Lecture # 8: The Immune System
Objectives
1- Identify the body’s three lines
against pathogens.
2- Contrast nonspecific resistance with
immunity.
3- Define specific immunity.
4- Contrast cellular and humoral
immunity.
5- Describe the chemical properties of
antigens.
6- Describe and contrast the
development and functions of T and B
lymphocytes.
Defenses Against Pathogens
Pathogens:
They are environmental agents capable of producing disease
(infectious organisms, toxic chemicals, and radiation).
The human body has three lines of defenses against
pathogens. They may be nonspecific or specific.
a) First line
1- Nonspecific of defense
Resistance
2- Specific
Resistance
External barriers: Skin and mucous
membranes.
b) Second line
of defense
Leukocytes
and
macrophages,
antimicrobial
proteins,
immune
surveillance, inflammation, and fever.
c) Third line
of defense
It is the Immune System, which not
only defeats a pathogen but leaves
the body with a “memory” of it, so it
can defeat it faster in the future.
Nonspecific Resistance
1- Nonspecific Resistance
It guards equally against a broad range of pathogens. Their effectiveness does not depend on prior exposure.
a) First Line of Defense
1- Skin
It makes it mechanically difficult for microorganisms to enter the body
because of the toughness of keratin.
The skin is too dry and nutrient-poor to support microbial growth.
The skin is coated with defensins, peptides that kill microbes by
creating holes in their membranes; and acid mantle, thin film of lactic
acid from sweat which inhibits bacterial growth.
2- Mucous membranes
The digestive, respiratory, urinary, and reproductive tracts are open to
the exterior and protected by mucous membranes. Mucus physically
traps microbes.
Mucus, tears, and saliva contains lysozyme, an enzyme that destroys
bacterial cell walls.
b) Second Line of Defense
It consists of several nonspecific defense mechanisms: Leukocytes
and macrophages, antimicrobial proteins, immune surveillance,
inflammation, and fever.
1-Leukocytes and Macrophages
2- Antimicrobial proteins
3- Immune surveillance
4- Fever
5- Inflammation
A) Interferon
b) Complement System
1-Leukocytes and Macrophages
Neutrophils
They spend most of their life wandering in the
connective
tissue
killing
bacteria
by
phagocytosis and digestion.
When a neutrophil detects bacteria in the immediate area, the
lysosomes migrate to the cell surface and degranulate and discharge
into tissue fluid.
Here the enzymes produce a respiratory burst.
Respiratory Burst:
The neutrophils rapidly absorb oxygen and produce toxic chemicals:
superoxide anion (O2 ) , hydrogen peroxide (H2O2), and hypochlorite
(HClO).
These toxic chemicals form a chemical killing zone around the
neutrophil that destroy more bacteria than the neutrophil can destroy
by phagocytosis. The neutrophil also is killed by these chemicals.
Eosinophils
They are found especially in the mucous
membranes standing guard against parasites,
allergens (allergy causing agents), and other
pathogens.
They kill tapeworms and roundworms by producing superoxide,
hydrogen peroxide, and toxic proteins.
Basophils
Basophils and mast cells (a type of connective
tissue cell), secrete chemicals that aid mobility
and action of other leukocytes:
Leukotrienes that activate and attract neutrophils and eosinophils.
Histamine that is a vasodilator which increases blood flow speeds
delivery of leukocytes to the area.
Heparin, which inhibits the formation of clots that would impede
leukocyte mobility.
Lymphocytes All lymphocytes look more or less alike in blood films,
but there are three basic categories.
The circulating blood contains:
80% T cells, 15% B cells, and 5% NK cells
They have many diverse functions as cells of the
Immune System.
Monocytes
Monocytes are leukocytes that emigrate from the blood
into the connective tissue and transform into
macrophages.
The macrophage system are all the body’s avidly
phagocytic cells, except leukocytes.
Cells of the macrophage system have different
specialized forms in different specific localities:
Histiocytes in loose connective tissue, Microglia in central nervous
system, Alveolar macrophages in lungs, Hepatic macrophages in
liver.
2- Antimicrobial proteins
a) Interferon
b) Complement system
a) Interferons
They are proteins secreted by certain cells infected by viruses. They
are of no benefit to the cell that secretes them, but alert neighboring
cells and protect them from becoming infected.
b) Complement system
It is a group of 30 or more globular proteins that make powerful
contributions to both nonspecific resistance and specific immunity.
The proteins circulate in the blood in inactive form and are activated by
presence of the pathogen.
The activation of complement brings about four methods of
pathogen destruction:
The complement system
may be activated in three
ways:
1- Classical pathway
2- Alternative pathway
3- Lectin pathway
3- Immune surveillance
Natural killer (NK) cells (NK lymphocytes)
They are large lymphocytes that attack and
destroy bacteria, transplanted tissue, and host
cells infected with viruses or that have turned
cancerous. They are responsible for immune
surveillance.
4- Fever
It is an abnormally elevation of body temperature (over 37.0 0C or
98.6 0F). It results from trauma, infections, drug reactions, brain
tumors, and other causes.
Fever is produced by:
Exogenous pyrogens (surface glycolipids of bacteria and viruses).
Endogenous pyrogens (polypeptides produced by macrophages
and neutrophils).
Fever is an adaptive defense mechanism, in moderation, does more
good than harm because:
-Promotes interferon activity.
-Elevates metabolic rate and accelerates tissue repair.
-Inhibits reproduction of bacteria and viruses.
5- Inflammation
Inflammation is a local defensive response to tissue injury of any kind,
including trauma and infection.
The general purposes of inflammation are:
1- To limit spread of pathogens, then destroy them.
2- To remove debris from damaged tissue.
3- To initiate tissue repair.
Four Cardinal Signs of Inflammation:
1- redness 2- swelling 3- heat 4- pain
Inflammation and Immunity are regulated by many chemicals called
cytokines. (Table 21.1)
Cytokines
They are small proteins that serve as a chemical communication network
among immune cells.
Three major processes of inflammation:
1- Mobilization of Defenses
2- Containment and Destruction of Pathogens
3- Tissue Clean up and Repair
1- Mobilization of Defenses
Splinter
Mast cells, endothelial cells and damaged
cells release inflammatory chemicals.
From
damaged
tissue
Basophils and Mast cells
They trigger inflammation by releasing
histamine and leukotrienes (vasodilators),
and heparin (anticoagulant).
Inflammatory
chemicals
Bacteria
Increase blood flow beyond normal
(hyperemia)
From
mast
cells
4
Phagocytosis
From
blood
Neutrophils
3
1- Margination: The ability to adhere to the
wall of blood vessels.
Chemotaxis
Increased
permeability
Mast cells
2- Diapedesis: The ability to crawl thorough
the gaps between the endothelial cells.
3- Chemotaxis: The ability to move toward
inflammatory chemicals.
4- Phagocytosis: The ability to engulf solid
particles.
2
Diapedesis
1
Neutrophils
Margination
Blood capillary
or venule
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2- Tissue Cleanup
Monocytes:
They are the primary agents of tissue cleanup and repair.
◦ arrive in 8 to 12 hours and become macrophages.
◦ engulf and destroy bacteria, damaged host cells, and dead and dying
neutrophils.
Edema
It contributes to tissue cleanup.
swelling compresses veins and reduces venous drainage
forces open valves of lymphatic capillaries promoting lymphatic drainage.
lymphatics collect and remove bacteria, dead cells, proteins, and tissue
debris better than blood capillaries.
Pus
It consists of the accumulation of dead neutrophils, bacteria, other cellular
debris, and tissue fluid form a pool of yellowish fluid.
Abscess
It is the accumulation of pus in a tissue cavity.
3- Tissue Repair
Platelet-derived growth factor secreted by blood platelets and endothelial
cells in injured area:
stimulates fibroblasts to multiply.
synthesize collagen.
Hyperemia delivers oxygen, amino acids, and other necessities for protein
synthesis.
Increased heat increases metabolic rate, speeds mitosis, and tissue repair.
Fibrin clot forms a scaffold for tissue reconstruction.
Pain makes us limit the use of a body part so it has a chance to rest and heal.
Specific Resistance
Specific Resistance:
It results from prior exposure to a pathogen and usually provides future
protection only against that particular one.
Third line of defense. It is the immune system, which not only defeats a
pathogen but leaves the body with a “memory” of it, so it can defeat it faster in
the future.
Specific Immunity
Two characteristics distinguish immunity from nonspecific resistance:
1-Specificity
Immunity is directed against a particular pathogen. Immunity to one pathogen
does not protect against others.
2-Memory
When re-exposed to the same pathogen, the body reacts so quickly that there
is no noticeable illness.
Two Types of Immunity
1- Cellular (cell-mediated) immunity
It employs lymphocytes directly attack and destroy foreign cells or diseased
host cells.
It is a means of ridding the body of pathogens that reside inside human cells,
where they are inaccessible to antibodies . Cellular immunity kills the cells
that harbor the pathogens.
T lymphocytes or T cells are responsible for cellular immunity.
2- Humoral (antibody-mediated) immunity
It is mediated by antibodies that do not directly destroy a pathogen, but tag
them for destruction by other mechanisms.
It can only work against the extracellular stage of infectious micro-organisms.
B lymphocytes or B cells are responsible for humoral immunity
T lymphocytes or T cells are responsible for cellular immunity.
B lymphocytes or B cells are responsible for humoral immunity.
Some B lymphocytes differentiates into plasma cells, which are the cells
responsible for antibody production.
Cellular Immunity
Cellular (cell-mediated) immunity is a form of specific defense in which the
T lymphocytes directly attack and destroy diseased or foreign cells, and the
immune system remembers the antigens and prevents them from causing
disease in the future.
Cellular immunity involves four classes of T cells:
1- Cytotoxic T cells or killer T cells
They are the “effectors” of cellular immunity that carry out attack on enemy cells. They
are called killer T cells, but are not the same as natural killer cells.
2- Helper T cells
They promote cytotoxic T cell and B cell action and nonspecific resistance.
They are destroy by HIV, which affects the central coordinating agent of nonspecific
defense, humoral immunity, and cellular immunity.
3- Regulatory T cells
They inhibit multiplication and cytokine secretion by other T cells and thus limit immune
response.
4- Memory T cells
They descend from the cytotoxic T cells and are responsible for memory in cellular
immunity.
Cytotoxic T cells deliver a lethal hit of toxic chemicals:
1-Perforin and granzymes that kill cells in the same manner as NK cells.
2- Interferons that inhibit viral replication and recruit and activate macrophages.
3- Tumor necrosis factor (TNF) that aids in macrophage activation and kills cancer cells.
Humoral Immunity
Humoral immunity is a more indirect method of defense than cellular
immunity
B lymphocytes of humoral immunity produce antibodies that bind to
antigens and tag them for destruction by other means.
An antibody is a defensive gamma globulin found in the blood plasma,
tissue fluids, body secretions, and some leukocyte membranes.
Some B lymphocytes differentiates into plasma cells,
which are the cells responsible for antibody production.
Once released by plasma cells, antibodies use four mechanisms to render
antigens harmless:
1-Neutralization
Antibodies mask pathogenic
region of antigen.
2-Complement fixation
When antigen binds the antibody changes its shape and initiates complement
binding, which leads to inflammation, phagocytosis, immune clearance, or
cytolysis.
3-Agglutination
Antibody has 2-10 binding sites; binds to
multiple enemy cells immobilizing them from
spreading.
4-Precipitation
Antibody binds antigen molecules (not cells); creates antigen-antibody
complex that precipitates
Antigen: It is any molecule that triggers an immune response
Primary response
The primary immune response is
the immune reaction brought about
by the first exposure to an antigen.
The primary response leaves one
with an immune memory of the
antigen.
Secondary response
The secondary or anamnestic
response is produced by the
reexposition to the same
antigen. It is a greater response
in a much sorter time.
Forms of Immunity
1- Active Immunity
a) Natural Active Immunity
It is the production of one’s own antibodies or specific T cells as
a result of infection or natural exposure to antigen.
b) Artificial Active Immunity
It is the production of one’s own antibodies or specific T cells as
a result of vaccination against disease.
Vaccine
It consists of the administration of dead or attenuated
(weakened) pathogens that stimulate the immune response
without causing the disease.
Booster shots
They are the periodic immunizations to stimulate immune
memory to maintain a high level of protection.
Forms of Immunity
2- Passive Immunity
a) Natural Passive Immunity
It is the temporary immunity that results from antibodies
produced by another person.
Ex: The fetus acquires antibodies from mother through
placenta and milk.
b) Artificial Passive Immunity
It is the temporary immunity that results from the injection of
immune serum (antibodies) from another person or animal.
Ex: Treatment for snakebite, botulism, rabies, tetanus, and
other diseases.
Forms of Immunity
1- Active Immunity
2- Passive Immunity
The body makes its
own antibodies
The body acquires
the antibodies from
another person or
animal
a) Natural Active
Immunity
b) Artificial Active
Immunity
c) Natural Passive
Immunity
d) Artificial Passive
Immunity
It is the production of one’s
own antibodies or T cells
as a result of infection or
natural exposure to
antigen.
It is the production of
one’s own antibodies or
T cells as a result of
vaccination against
disease.
It is the temporary immunity
that results from antibodies
produced by another
person in a natural way.
It is the temporary immunity
that results from the
injection of antibodies from
another person or animal.