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LYMPHATIC SYSTEM,
VIRUSES, AND
IMMUNITY
Body has 3 lines of defense
1. Skin
2. WBC
3. Acquired defenses
Lymphatic System
 In animals is part of the immune system, made up of a
network of conduits that carry a clear fluid called lymph
 It also includes the lymphoid tissue and lymphatic vessels
through which the lymph travels in a one-way system in
which lymph flows only toward the heart.
 Lymphoid tissue is found in many organs, particularly the
lymph nodes, and in the lymphoid follicles associated
with the digestive system such as the tonsils.
 The system also includes all the structures dedicated to
the circulation and production of lymphocytes, which
includes the spleen, thymus, bone marrow and the
lymphoid tissue associated with the digestive system
Function of the lymphatic
 The lymphatic system has multiple interrelated
functions:
 it is responsible for the removal of interstitial fluid from
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tissues
it absorbs and transports fatty acids and fats as chyle to
the circulatory system
it transports immune cells to and from the lymph nodes in
to the bone
The lymph transports antigen-presenting cells (APCs),
such as dendritic cells, to the lymph nodes where an
immune response is stimulated.
The lymph also carries lymphocytes from the efferent
lymphatics exiting the lymph nodes.
Primary lymphoid organs
 The thymus and the bone marrow constitute
the primary lymphoid tissues involved in the
production and early selection of
lymphocytes.
 The thymus has 2 funtions:
 Thymus gland produces thymic hormones to aid
in maturation of T lymphocytes
 Immature I lymphocytes migrate from the bone
marrow through the bloodstream to the thymus
to mature…without mature T cells, the body’s
response to specific pathogens is weak
Secondary lymphoid organs
 Maintain mature naive lymphocytes and initiate an
adaptive immune response. The peripheral lymphoid
organs are the sites of lymphocyte activation by antigen.
 Activation leads to clonal expansion and affinity maturaton
 Provides the environment for the foreign or altered native
molecules (antigens) to interact with the lymphocytes.
 It is exemplified by the lymph nodes, and the lymphoid
follicles in tonsils, Peyer's patches, spleen, adenoids, skin,
etc. that are associated with the mucosa-associated
lymphoid tissue (MALT)
Bacteria
 Single celled prokaryotes that don’t have a nucleus.
 They lack membrane-bound organelles, and can
function and reproduce as individual cells, but often
aggregate in multicellular colonies
 Their genome is usually a single loop of DNA,
although they can also harbor small pieces of DNA
called plasmids.
 Bacteria are surrounded by a cell wall, which provides
strength and rigidity to their cells.
 They reproduce by binary fission or sometimes by
budding, but do not undergo sexual reproduction.
Growth of E. coli
Bacteria can be good
 Microorganisms are used in brewing, winemaking,
baking, pickling, cultured dairy products yogurt and
chesses.
 Specially-cultured microbes are used in the biological
treatment of sewage and industrial waste effluent, a
process known as bioaugmentation
 Microbes can be harnessed for uses such as creating
steroids and treating skin diseases
 The bacteria that live within the human digestive system
contribute to gut immunity, synthesise vitamins such as
folic acid and biotin, and ferment complex indigestible
carbohydrates
Treating a bacteria infection
 Bacterial infections may be treated with antibiotics,
which are classified as bacteriocidal if they kill bacteria,
or bacteriostatic if they just prevent bacterial growth
 Antibiotics are used both in treating human disease and
in intensive farming to promote animal growth, where
they may be contributing to the rapid development of
antibiotic resistance in bacterial populations
(Khachatourians, 1998)
 Disinfectants such as bleach are used to kill bacteria or
other pathogens on surfaces to prevent contamination
and further reduce the risk of infection.
What is a virus?
 A virus particle, or virion, consists of the following:
 Nucleic acid - Set of genetic instructions, either DNA
or RNA, either single-stranded or double-stranded
 Coat of protein - Surrounds the DNA or RNA to
protect it
 Lipid membrane - Surrounds the protein coat (found
only in some viruses, including influenza; these types
of viruses are called enveloped viruses as opposed to
naked viruses)
What is a virus?
 They cannot reproduce on their own, and for
this reason they are not considered alive by
some biologist.
 They can reproduce within cells with
disastrous results to the host organism
Lytic cycle
 A virus particle attaches to a
host cell.
 The particle releases its genetic
instructions into the host cell.
 The injected genetic material
recruits the host cell's enzymes.
 The enzymes make parts for
more new virus particles.
 The new particles assemble the
parts into new viruses.
 The new particles break free
from the host cell.
Once the new viruses are
made, they leave the host
cell in one of two ways:
 They break the host cell open (lysis) and
destroy the host cell.
 They pinch out from the cell membrane and
break away (budding) with a piece of the cell
membrane surrounding them. This is how
enveloped viruses leave the cell. In this way,
the host cell is not destroyed.
How a virus works…
 An infected person sneezes near you.
 You inhale the virus particle, and it attaches to cells lining the sinuses
in your nose.
 The virus attacks the cells lining the sinuses and rapidly reproduces
new viruses.
 The host cells break, and new viruses spread into your bloodstream
and also into your lungs. Because you have lost cells lining your
sinuses, fluid can flow into your nasal passages and give you a runny
nose.
 Viruses in the fluid that drips down your throat attack the cells lining
your throat and give you a sore throat.
 Viruses in your bloodstream can attack muscle cells and cause you to
have muscle aches.
What are some examples of
viruses?
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Common cold
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Influenza and Avian Influenza
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Chickenpox
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Ebola
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AIDS
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HPV
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SARS
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Shingles
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Smallpox
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Human Immunodeficiency Virus (HIV)
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bovine spongiform encephalopathy
("mad cow" disease)
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Viruses that have an association to
cause human cancers include some
genotypes:
human papillomavirus (HPV)
hepatitis B
hepatitis C
Epstein-Barr virus
Kaposi's sarcoma-associated
herpesvirus and human Tlymphotropic virus
How are viruses classified?
They are classified by:
1. Shape
2. Nucleic acid they contain (DNA or RNA)
3. The kind of organism they infect
What do viruses need?
 A virus is a type of parasite—it depends on a
host organism for survival and reproduction
How do viruses behave?
1. A virus may be active
2. A virus can be dormant or latent
Active Virus
1.
ATTACHMENT: A specific virus attaches to the surface of a
specific cell
2.
INVADE: The nucleic acid (DNA or RNA) of the virus is
injected into the cell.
3.
COPY: The viral nucleic acid takes control of the cell an
begins to make new virus particles.
4.
RELEASE: The cell bursts open, hundreds of new virus
particles are released from the cell. These virus particles go
on to infect other cells.
How does our body respond to
viruses?
Immunobiology, 5th ed. Janeway
Reduction of the spread…
 Carrier organisms - mosquitoes, fleas
 The air
 Direct transfer of body fluids from one
person to another - saliva, sweat, nasal
mucus, blood, semen, vaginal secretions
 Surfaces on which body fluids have dried
What are vaccines?
 A vaccine is a substance that stimulates the
body’s immune response.
 The goal of vaccination is to prevent or
control an infection.
Immunity
 Immunity
 The ability of the body to fight infection and/or foreign invaders by
producing antibodies or killing infected cells.
 Immune System
 The system in the body responsible for maintaining homeostasis by
recognizing harmful from nonharmful organisms and produces an
appropriate response.
How acquired defense works
 Our bodies detects a wide variety of agents, from viruses to
parasitic worms, and needs to distinguish them from the organism's
own healthy cells and tissues in order to function properly.
 Detection is complicated as pathogens can evolve rapidly,
producing adaptations that avoid the immune system and allow the
pathogens to successfully infect their hosts.
 The human immune system adapts over time to recognize specific
pathogens more efficiently. This defense system responds to
antigens, molecules the immune system recognizes as foreign to
the body. This adaptation process is referred to as "adaptive
immunity" or "acquired immunity" and creates immunological
memory
 Immunological memory created from a primary response to a
specific pathogen, provides an enhanced response to secondary
encounters with that same, specific pathogen.
Antibodies
 Y-shaped protein molecule.
 Made up of variable and
constant regions.
 Made up of Heavy and
Light chains.
 Produced by BLymphocytes
 Function: Recognize
antigens, bind to and
deactivate them.
 Note: Variable region
recognizes the anitgens.
How an antibody operates/works?
Deactivation of a bacterium by an antibody.
Foreign Invaders
 Called Pathogens
 Viruses, bacteria or
other living thing that
causes disease/immune
response.
 Antigens
 Toxins that pathogens
produce that cause
harm to an organism.
Origin of Viral Diseases
 Viruses that originate in one organism pass to
another, causing a disease in the new host
 New pathogens, emerging viruses, pass in
animals to animals spreading throughout the
world
 Influenza:
 Most lethal virus in human history
 The reservoir of influenza virus is in ducks, chicken,
and pigs in Central Asia
20th Century Flu Statistics
Influenza
Pandemic
Date
U.S.
Worldwide
Deaths
Deaths
Spanish Flu
1918-19 675,000
50 million
Asian Flu
1957-58
70,000
1-2 million
Hong Kong Flu
1968-69
34,000
700,000
AIDS (HIV, Human
immunodeficiency virus)
 This virus first entered humans from
chimpanzees somewhere in Central Africa
probably around the early of the 20th century
 Chimpanzee virus is called simian
immunodeficiency virus (SIV)
 SIV mutates at a rate about 1% per year
 Studies have suggested that the nucleotide
sequence of monkeys that carry SIV are
closely related to other species
AIDS in the US from 1977-2006
Ebola Virus
 Most lethal of emerging viruses from Central
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Africa
Attacks the human connective tissue with
lethality rates up to 50%
One strand of this virus has a lethality rate in
excess of 90%
Transferred through bodily fluids
Victims die too fast to spread the disease very
far
Hantavirus
 Highly fatal hemorrhagic infection “Sin
Nombre” virus in the southwest United States
in 1993
 RNA virus associated with rodents
 Transmitted to humans through fecal
contamination in areas of human habitation
 Deer mouse (1993) was the source
SARS
(Severe acute respiratory syndrome)
 In 2003, a strain of coronavirus emerged to a
worldwide outbreak
 Respiratory infection with pneumonia-like
symptoms that in over 8% of cases were fatal
 This outbreak took 2 years to identify and
virologist identified the Chinese horseshoe
bat as the natural host.
 They were carriers but not sickened by the
virus
West Nile Virus
 Mosquito borne virus
 First detected in humans in Uganda, Africa, in
1937
 First infected people in North America in 1999
 Carried by infected crows and other birds
Chicken Pox - Shingles
 Highly contagious illness caused by primary infection
with varicella zoster virus
 Chicken pox is spread easily through coughs or sneezes
of ill individuals or through direct contact with secretions
from the rash. Following primary infection there is
usually lifelong immunity from further episodes of
chickenpox.
 After a chickenpox infection, the virus remains dormant
in the body's nerve tissues. The immune system keeps
the virus at bay, but later in life, usually as an adult, it can
be reactivated and cause a different form of the virus
called shingles.
How does the body fight infection/foreign invaders?
The Body’s THREE lines of Defense
First Line of Defense – The Skin
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Provides Physical and Chemical barriers
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Physical – hard to penetrate, made of indigestible keratin
Chemical – tears, sweat
Second Line of Defense – Nonspecific Immune
Response
These are defenses the body uses no matter what the invader
may be. These defenses include:
 Phagocytosis – (WBC) done by Macrophages
 Natural Cell Killers
 Inflammation - caused by release of Histamine from leukocytes
 Fever – caused by histamines. The fever (high temp) kills invaders by
denaturing their proteins.
Third Line of Defense – Specific
Immune Response
This is a specific response to a specific
pathogen/antigen.
 The response involves the creation of Antibodies.
The Pathway of Specific Immune Response
Step 1
Pathogens eaten by Macrophage
Step 2
Displays portion of Pathogen
on surface
Step 3
Pathogens
Helper-T cell recognizes
Pathogen
Activates B- Cell
Activates Cytotoxic
T- Cell
Memory T-Cell
Memory B-Cell
Antibodies
Kills Infected Cells
Cellular Immunity .vs. Antibody Immunity
Cellular Immunity
Antibody or Humoral Immunity
 Carried out by T-Cells
 Carried out by B-cells
 Infected cells are killed by
 Antibodies are produced
Cytotoxic T –Cells.
and dumped into blood
stream.
 Antibodies bind to
antigens and deactivate
them.
Immune Response Explained
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Antigen infects cells.
Macrophage ingests antigen and displays portion on its surface.
Helper T- Cell recognizes antigen on the surface of the
macrophage and becomes active.
Active Helper T-Cell activates Cytotoxic T-Cells and B-Cells.
Cytotoxic T-Cells divide into Active Cytotoxic T-cells and Memory T
– Cells.
Active Cytotoxic T-Cells kill infected cells.
At the same time, B-Cells divide into Plasma Cells and Memory BCells.
Plasma cells produce antibodies that deactivate pathogen.
Memory T and Memory B cells remain in the body to speed up the
response if the same antigen reappears.
Supressor T-Cells stop the immune response when all antigens
have been destroyed.
Primary .vs. Secondary Immune Response
 Primary Immune Response
 This is a response to an invader the First time the
invader infects the body.
 No measurable immune response for first few days.
 Next 10 – 15 days antibody production grows steadily
 Secondary Immune Response
 A more rapid response to an invader the 2nd time it
invades the body.
 Antibody production increases dramatically and in a much
shorter time period..
Primary .vs. Secondary Immune Response
Passive .vs. Active Immunity
1. Active Immunity
This is immunity where the body is “actively” producing antibodies to
fight infection.
Ex: You have a throat infection and you are actively creating antibodies
to fight it.
Vaccination: An injection of a weakened strain or DEAD of an
infectious microbe (pathogen) that causes the body to undergo
active immunity (produce antibodies).
2.
Passive Immunity
This is immunity where antibodies are given to a person
from the blood of another person or animal.
This immunity only lasts for a short period of time.
ex: Breastfeeding mothers pass antibodies to their
children through the milk.
Autoimmune Disease
 Autoimmune diseases are diseases where the immune
system begins to attack itself.
 Ex:
 Rheumatoid Arthritis – crippling disease of the
joints.
 Lupus – disease of blood and organs.
 Multiple Sclerosis – disease of nervous system
 Cause(s): unknown
 Cures/Treatments: No known cures. Usually treated with
drugs.
Allergies
Allergy
- An exaggerated response by the immune system to an allergen.
Allergen: a normally harmless substance that causes an allergic
reaction.
ex: dust, pollen, mold, food, insect stings
Types of Allergic reactions
There are two types of allergic reactions.
a. Immediate – occurs within seconds and normally lasts for about
30 mins.
b. Delayed – takes longer to react and can last for a much longer
time.
What happens during an allergic reaction?
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During an allergic reaction antibodies cause histamines to be released
from certain cells.
Histamines cause:
a. Swelling of tissues
b. Release of fluids (runny noses and eyes)
c. muscle spasms (some cases)
Anaphylaxis or anaphylactic shock:
This is the sudden and severe allergic reaction to a substance that can
cause death.
Treatments for Allergies
1.
Avoidance of material – especially food.
2. Epinephrine – “epi – pen”
3. Antihistamines -- benadryl
Epidemiology
 Viral epidemiology is the branch of medical
science that deals with the transmission and
control of virus infections in humans.
Transmission of viruses can be vertical, that is
from mother to child, or horizontal, which
means from person to person
Epidemics and Pandemics
 When outbreaks cause an unusually high
proportion of cases in a population,
community or region they are called
epidemics.
 If outbreaks spread worldwide they are called
pandemics
Treatment
 Because viruses use the machinery of a host
cell to reproduce and reside within them,
they are difficult to eliminate without killing
the host cell.
 The most effective medical approaches to
viral diseases so far are vaccinations to
provide resistance to infection, and antiviral
drugs.