Transcript Chap. 20 The Immune System

The Immune System
鄭先祐(Ayo) 製作
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The immune system
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There are two basic lines of defense.
– the nonspecific responses
– the specific responses.
Table 20.1 The nonspecific responses
 Barriers of the body covering
 inflammatory response
– clotting mechanisms
– phagocytes engulf invaders.
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Essay 20.1 Lyme disease
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It is a disease caused by a spirochete, a bacterium,
Borrelia burgdorferi, and carried by a tick.
The tick has three stages in its life cycle.
In its larval stage, it mainly infects the whitefooted mouse.
In its nymph stage, it infects a range of mammals,
including dogs, raccoons, and humans.
In its adult stage, it mainly infects white-tailed
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deer.
Lyme disease
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The disease was first identified in 1975 in
Lyme, Connecticut, and has since spread
swiftly throughout the United States.
There may have been 50,000 cases in 1989
alone.
The first sign of the disease may be flu-like
symptoms, including headache, fever,
weakness, and stiff joints.
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Lyme disease
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If antibiotics, such as tetracycline or doxycycline
are administered immediately, the victim is likely
to recover.
As time passes without diagnosis and proper
treatment, a debilitating arthritis(關節炎) may
appear from which the victim may never recover.
The bacterium may invade the brain and spinal
cord, producing dizziness(昏眩), incoherency,
visual problems, and numbness (痲痺).
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The nonspecific responses
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Once any organism invades, it triggers an
inflammatory response (紅腫反應).
It begins as the cells begin to secrete
histamine, which dilates tiny arterioles
bringing more blood to the injured area.
Fever is triggered either by toxins produced
by the invading organism or by pyrogens,
chemicals released by certain white blood
cells as they respond to an invasion.
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Fig. 20.1 Nonspecific responses
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中性球
單核球
嗜鹼球
Fig. 20.2 There are
five major types of
leukocytes.
嗜酸球
淋巴球
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五種白血球的功能
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Phagocytes的有三種：eosinophils,
neutrophils, 和 monocytes.
– Eosinophils primary response to allergies and
parasitic infections.
– Neutrophils are frontline soldiers.They produce
toxic substances against invaders.
– Monocytes arrive next, in great numbers, and
once they encounter the invader they begin to
undergo remarkable changes, growing and
swelling until they become huge macrophages.
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Fig. 20.3 A macrophage capturing
bacteria.
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五種白血球的功能
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Lymphocytes produce both cells and
proteins that interact in both nonspecific
and specific responses.
– The natural killer cell(NK cell) is active in the
nonspecific response. They roam the body.
– When they encounter cancerous cells or cells
harboring viruses, they immediately attack
those cells.
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Basophils secrete histamine that intensifies
the inflammatory response.
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淋巴球的類別與功能
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(cf. Table 20.2)
Cytotoxic T-cell： destroys virus-infected
and cancerous cells.
Helper T-cell：stimulates B-cell and
cytotoxic T-cell proliferation.
Suppressor T-cell ：slows down immune
response.
B-cell：secretes antibodies
Natural killer cell ：directly destroys virusinfected cells and cancerous cells.
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Essay 20.2 allergy (過敏反應)
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The pollen attaches to specific
antibodies on large, granulecontaining "mast cells" that line
the respiratory passages.
The granules are then
explosively released, triggering
the production of histamine and
other chemicals that cause
inflammation.
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Allergic reactions can also produce a dangerous
condition called anaphylactic shock.
This happens when large areas of the body
produce an allergic reaction, as when an
individual allergic to bee stings or penicillin
receives those antigens and they are rapidly
transported throughout the body.
In such a case, capillaries throughout the body
become leaky and blood pressure sudden drops,
reducing blood flow to the brain and heart.
Death can result unless epinephrine (adrenaline)
is quickly administered.
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A historical case
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In the fourteen century, European cities
were crowded, dirty, and filled with
travelers.
Conditions were right for a flea(跳蚤)borne pathogen, Pasteurella, to sweep
repeatedly through the population causing
bubonic plague, or Black Death (黑死病).
Within a few years, one-quarter of the
population of Europe had been killed.
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Specific responses
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Two kinds of lymphocytes play a critical
role in the specific responses.
– These are the B-cells and the T-cells.
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B-cells are specialized to do two things
– plasma cells make antibodies to combat the
invader. (humoral immunity)
– memory B-cells 記憶過去曾經產生過的抗體
資料。
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cellular immunity
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T-cells are involved in cellular immunity.
There are three basic kinds of T-cells.
– Helper T-cells (幫助者), interact with other
cells to enhance the immune response.
– cytotoxic T-cells (殺手), identify infected cells
and rupture their membranes
– suppressor T-cells (壓抑), help call off the
body's defenses.
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抗原-抗體反應
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Antigens are foreign
molecules that elicit
an immune response
in the host organism.
Antibodies are
proteins produced
by the host plasma
cells that identify
and help destroy
antigens, including
the cells that bear
antigens.
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巨喫細胞
Fig. 20.5
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When a specific antigen is encountered, the
recognition regions of the antibody molecules attach
to specific binding sites on the antigen that can be
engulfed by a macrophage.
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Fig. 20.6 In the ongoing
combat against invaders.
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巨喫細胞吞食抗原，
再將抗原送至膜外。
Helper T-cell 受到激
發，分泌interleukin。
Interleukin刺激
cytotoxic T-cells和
memory cells的
production.
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Fig. 20.7
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B-cells begin their own
arousal by capturing antigen
and preparing a recognition
site that will match that of a
chosen helper T-cell.
When they bind together,
interleukin secreted by the
helper T-cell activated the Bcell and plasma, and memory
cells are produced.
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Primary and secondary response
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Those defenses can be divided into two
stages: the primary response and secondary
response.
Primary response occurs when a foreign
substance is encountered for the first time.
The secondary response is the sequence that
is triggered by the army of memory cells
produced by the primary response.
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Self-tolerance and autoimmunity
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All the cells of the body bear their own molecular
"markers" embedded in their membranes.
所有的免疫細胞巡邏全身，只要有這些markers
的細胞，就不會攻擊。
This acceptance by the body's immune cells is
called-tolerance.
In some case, the immune system can turn against
its own body, the reaction is called autoimmunity.
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Interferon (干擾素)
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Interferon causes cells to become resistant to
attacks by other viruses.
It does not act against specific viruses but will
inhibit any viral attack.
Given interferon in a nasal spray 可以避免感冒。
Interferon reduced brain tumor size.
Side effects: it triggers irregular heartbeats, it may
also complicate liver or kidney problems.
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Essay 20.3 How African crocodiles defend
against Texan rabbits
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If you take hemoglobin from a
rabbit and inject it into a crocodile,
the crocodile will form antibodies
against the rabbit hemoglobin.
Why can this be?
There are only about 300 DNA
segments that code for the variable
DNA segments of antibodies.
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Recombination of DNA
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Only 300 DNA segments clearly not enough
to provide an antibody response against
every possible antigen.
However, these regions are extremely
unstable. They break apart and rejoin
endlessly, providing a virtually infinite
number of combinations (in humans, about
180億).
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AIDS
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AIDS：acquired immuno-deficiency
syndrome (後天免疫失調症候群)
The first case of AIDS in the United States
appeared in 1979, followed by a half-dozen
cases reported in Los Angeles in 1981.
In early 1989, the world Health
Organization estimated that over one new
case of AIDS was developing each minute,
worldwide.
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In 1995, it was reported between 63萬 and 89萬7千
人感染AIDS。
It is estimated that between 6 and 10 million people
are presently affected with the virus but do not yet
show symptoms.
Many people carry antibodies to the virus that
causes AIDS, showing that they have been exposed
to it, without developing the symptoms.
The syndrome, once full blown, is incurable and
virtually always cause death within a few years
(fewer than 14% of victims survive past three years).
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 Early signs of AIDS
Fig. 20.8 AIDS manifests
include a series of
itself in numerous ways, all
lingering(慢性的), simple
marked by a deteriorating
immune system.
colds, night sweats,
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persistent fever, swollen
glands, and coughing.
More serious conditions
follow, including at least
three forms of cancer and
destruction of the lungs
and brain (Fig. 20.8)
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Fig.20.9 AIDS is especially prevalent among
needle-sharing addicts.
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Dependence on condoms as a
protection
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Some types of condoms are not completely
effective.
For example, those made of animal
membranes, rather than rubber, do not block
the passage of viruses.
Also some men simply do not know how to
use them safely.(The condom-sheathed
penis must be withdrawn immediately after
ejaculation).
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The geographical source of HIV
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HIV(human immunodeficiency virus)
原本是在African green monkey (West
Africa)身體內的virus 轉入人體。
從西非傳至海地，美國同性戀者渡假地
區。再經由這些同性戀者，傳入美國。
然後，逐漸擴展至全球。
無論是同性或異性戀，都可以傳染。
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Essay 20.4
AIDS
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The infectious
agent of AIDS
was discovered
in 1984.
The virus is
called HIV
(human
immunodeficiency
virus).
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HIV 攻擊 T-細胞
的過程。
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HIV 攻擊 T-細胞的過程。
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The virus attacks the helper T-cell, penetrating
the the cell and releasing a single strand of RNA
and an enzyme, reverse transcriptase, with it.
The enzyme enables the RNA to make a double
strand of complementary DNA, which then
joins the helper T-cell's DNA.
Finally, there are so few helper T-cells in the
blood that no effective immune response can be
mounted against any attack whatsoever.
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AIDS virus seeks out the helper T-cell lymphocytes.
Using the various chemical markers on its surface, the AIDS
virus binds easily to a receptor on the surface of the helper
T-cell.
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The HIV injects RNA and the enzyme transcriptase into T-cell.
The enzyme helps transcribe the invading RNA into DNA.
Once activated, the viral DNA directs the T-cell to make copies of the
virus. Eventually the host cell dies.
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Mind and Body
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People have long noticed a relationship
between mood and illness.
Depressed people seem to get sick more
often than happy, cheerful people.
The link between the mind and the immune
system has even been shown in other species.
But how could mind influence immunity?
The answer isn't clear yet.
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Mind and Body
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Scientists have discovered that
neuropeptides, once believed to be
restricted to the brain, are found throughout
the body.
They are chemically related to substances
that help regulate the immune system.
Some researchers suggest that
neuropeptides are the link between the
immune system and the brain.
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Essay 20.5
The mind-immunity link
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The controversy began in the 1980s when a purported link
between depression and lowered immunity was described.
Correlations were made between the proliferation of white
blood cells, as well as other aspects of the immune response,
and depressed individuals, such as those who were told they
were HIV positive, those caring for spouses with
Alzheimer's disease, those who had lost a mate, or even
those who had moved.
However, the results were not clear-cut.
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The mind-immunity link
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Younger depressed patients retained normal immune
response, while older one saw declines in their
number of helper T-cells and natural killer cells.
Some studies have shown that stress can reactivate
herpes viruses and promote the appearance of cold
sores, genital herpes, and mononucleosis.
The stress in these cases ranged from taking exams,
to becoming divorced, and to caring for the ill.
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The mind-immunity link
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People under high stress often fall victim to
behaviors that lower their resistance to infection,
such as alcohol abuse, smoking and
sleeplessness.
There are those, by the way, who object to the
idea that people can be responsible for their own
illness.
However, the jury is still out on the relationship
of mental attitude and good health.
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Most of us wish to live long and well. But that
implies a continuing existence on an essentially
hostile planet.
Furthermore, that hostility may be increasing,
largely because of our own behavior.
We must rely on new technologies to help us solve
our immediate problems, and the Earth is becoming
permeated with technology's by-products. Many
Chemicals are totally new to environment.
Indeed, our immune systems, and our ability to
withstand, may soon be tested in ways we can only
imagine.
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An ethical concern
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Interleukin-12 (IL-12)is produced normally
by the immune system but can be produced at
great expense by pharmacologists.
When administered to a patient, it "jump
starts" cell-mediated immunity and is
effective against viruses, bacteria, fungi,
protozoa, worms, and possibly AIDS.
Drug companies are hesitant to produce IL-12,
because there will be little profit from the
Third World countries with little money.
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 問題與討論！
[email protected]
Ayo NUTN website:
http://myweb.nutn.edu.tw/~hycheng/
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