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Lecture 10Immune System

Lecture 10

1. Introduction

2. Nonspecific External Defenses

3. Innate Immune Response

4. Acquired Immune Response

5. Antibiotics and Vaccines

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The not-so-common cold

• A “cold” is an infection of

the mucus membranes of

the respiratory tract by a

rhinovirus.

• Over 100 rhinoviruses have

been identified, which is

one reason why we don’t

become immune to “the

cold.”

Virus vs. Bacteria

• Colds and influenza are

caused by viruses.

• Viruses are non-living

particles that contains genetic

material, they hijack your cells

to reproduce.

• Viruses cannot be “killed”

with antibiotics.

Rhinovirus

Influenza

virus

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Virus vs. Bacteria

• Bacteria are living organisms

that have a metabolism, have

DNA, and can reproduce on

their own.

• Bacteria can be killed with

antibiotics.

E. coli

Streptococcus

Fungi, Protista, & Worms!

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• Viruses, bacteria, fungi, protists, and worms are

everywhere. Some of them want to invade your body.

How does your body defend itself against them?

• Viruses and Bacteria

Immune System

Immune System: Body Defenses

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Defense Against Disease

1. Nonspecific External Barriers

2. Innate Immune System

3. Acquired (Adaptive) Immune System

Nonspecific External Barriers

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First Line of DefenseNon-Specific External Defenses are designed to

prevent infections by viruses and bacteria from

entering the body. These include:

• Intact skin

• Saliva in Mouth

• Mucus and Cilia

• Cough Reflex

• Stomach Acid

• Small Intestine –Bile

The Skin

• Dead skin cells are constantly

sloughed off, making it hard

for invading bacteria to

colonize.

• Sweat and oils contain anti-

microbial chemicals,

including some antibiotics.

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Saliva

Mucus and Cilia

• Mucus contains special enzymes

that destroy bacterial cell walls.

• The normal flow of mucus washes

bacteria and viruses off of mucus

membranes.

• Cilia in the respiratory tract move

mucus out of the lungs to keep

bacteria and viruses out.

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Cough Reflex

Coughing ejects mucus and

foreign matter from the lungs.

Coughs may be voluntary, but

more often in response to

stimulation of receptors in the

respiratory tract.

Stomach Acid

• Low pH. Stomach acid prevents

bacterial and fungal growth.

• When it is properly acidic, bacteria

that are ingested along with food

don’t stand a chance.

• It acts as an acid buffer to protect the

body from pathogens.

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Innate Immune System

Innate Immune System• Innate Immune System (IIS) comprises the cells and

mechanisms that defend the host from infection by other

organisms.

• IIS provides immediate defense against infection.

• The cells of the innate system recognize and respond

to pathogens in a generic way, but,

• IIS does not confer long-lasting or protective immunity to the

host.

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Ouch!

1. Inflammation

Acute inflammatory response is the body’s initial reaction to tissue

damage.

1. Wound occurs!

2. Wounded cells secrete chemicals that stimulate release of

histamine.

3. Histamine causes fluids to collect around an injury to dilute

toxins. This causes swelling.

4. The temperature of the tissues may rise, which can kill

temperature-sensitive microbes.

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2. Phagocytes

• Phagocytes are several types of

white blood cells (including

macrophages and neutrophils) that

seek and destroy invaders.

• Phagocytes are attracted by an

inflammatory response of damaged

cells.

3. Natural Killer Cells

• Are white blood cells

that recognize and

destroy virus-infected

cells or those that have

become cancerous

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Fever

• Fever is a defense mechanism that

can destroy many types of microbes.

• While high fevers can be dangerous,

some doctors recommend letting low

fevers run their course without

taking aspirin or ibuprofen.

Acquired (Adaptive) Immune System

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Acquired Immune System

• AIS gives us immunity to certain diseases.

• In the AIR, the immune system forms a

chemical “memory” of the invading microbe.

• If the microbe is encountered again, the body

reacts so quickly that few or no symptoms are

felt.

Some Vocabulary:

• Antigen (Pathogen) - any substance that

causes an immune system to produce

antibodies against it (e.g. bacteria, virus,

etc.).

• Antibody - a protein produced by the human

immune system to tag and destroy invasive

microbes.

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Acquired Immune System

• Lymphocytes - Main players of the acquired

immune system

− They are white blood cells that circulate in the

bloodstream and lymphatic system

− Two different types:

• T Cells (T Lymphocytes)

• B Cells (B Lymphocytes)

• T Cells - 3 types:

• Helper T Cells - detect the invading pathogen and trigger

production of killer T cells

• Killer T Cells - attack and kill invading pathogen and

infected body cells

• Suppressor T Cells - slow down and halt the immune

response when the threat has been handled

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Acquired Immune System

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Helper T Cells

• The Helper T-Cell is the key cell to signal an

immune response.

• If helper T-cells are disabled, the immune system

will not respond.

• AIDS – Helper T-Cells are disabled

• B Cells - a type of lymphocyte (white blood cell) that

monitor the blood and tissue fluids for antigens.

• Following the body’s first exposure to a pathogen,

the B Cells have a “memory” of the pathogen

• When they encounter a specific invading pathogen

again, they produce antibodies - proteins that bind

to specific invader (antigen)

• Killer T-Cells recognize the antibodies and will kill

the pathogen that is tagged with them.30

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Antibodies

• Antibodies released into the blood

stream will bind to the antigens

(pathogens) that they are specific for.

• Antibodies may disable some microbes,

or cause them to stick together

(agglutinate).

• They “tag” microbes so that the

microbes are quickly recognized by the

Killer t-cells.

1. Antigen invades body for the first time – you get sick

2. T-helper cells recognize threat and trigger the T-killer cells

3. B-cells produce antibodies that mark the antigen so that the t-killer cells

know which cells to attack.

4. Once the t-killer cells have the upper hand, the t-suppressor cells go into

action and begin shutting down the immune response.

5. Your immune system now has a “memory” of the antigen/pathogen. If

the pathogen ever invades again, your immune system is ready to defend

your body against it. When/if it does invade, you never know it

Let’s put it all together…

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Immunity

• After surviving infection by a pathogen, a person

often acquires immunity to future infections by the

same pathogen

• B and T cells become memory cells when exposed to

an infectious agent, allowing recognition and quick

action to destroy the invader before the illness begins

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Human Assist

Antibiotics and Vaccines

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Helping the immune system

• Medical science has

created to systems for

augmenting the human

immune system:

• Antibiotics

• Vaccines

How antibiotics work

• Antibiotics help destroy bacteria

(but not viruses).

• Antibiotics work in one of several

ways:

• Slowing bacteria reproduction.

• Interfering with bacterial cell wall

formation.

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Antibiotic myths

• Antibiotics are not antibodies.

• Antibiotics do not weaken our immune system. They

help it by weakening bacteria.

• Humans do not become “immune” to antibiotics.

Bacteria that resist antibiotics and are not completely

destroyed may multiply, producing more antibiotic-

resistant bacteria.

How vaccines work• Modern vaccines are created from killed bacteria or

viruses, or fragments of proteins from these

microbes.

• The proteins are recognized as antigens by our

immune systems. This causes a mild immune

response.

• Memory T-cells and B-cells remain ready to fight off

the illness if it is encountered again.

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How vaccines work

Vaccine myths

• The flu vaccine does not give you the flu. Some people get the

vaccine too late, or catch a cold and think they have the flu.

• Vaccines are not less effective than a “natural” infection with

the illness. The immunity is the same, and a mild response to a

vaccine is much less risky than a full-blown infection of

measles.

• There is NO link between vaccines and autism.

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Vitamin C for colds?

• Vitamin C is necessary for many

body functions.

• Absorption of Vitamin C increases

during illness. It also has a very

slight antihistamine effect.

• Vitamin C won’t cure a cold, but may

support some aspects of immune

response.

Zinc for colds?

• Some studies have shown that

moderate use of zinc

lozenges slightly decreases

the duration and severity of

colds.

• However, too much zinc can

suppress the immune system,

and can reach toxic levels.

Zinc nasal sprays can destroy

olfactory receptors.

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Vitamin D for colds?

• New research suggests that

Vitamin D plays a role in immune

response, and may be critical for

fighting off viruses.

• Vitamin D is fat-soluble and can

accumulate to toxic levels. A blood

test can determine if a person

needs to take Vitamin D.

Echinacea for colds?

• Echinacea is supposed to

“strengthen” the immune system.

• Studies in petri dishes showed

Echinacea stimulated white blood

cells to produce more virus-killing

peroxides, but controlled human

trials have not had consistent

results.