Download 中六生物科教材

Body defence
1
Primary immune response and secondary immune response
原發免疫反應和繼發免疫反應
Primary immune response 原發免疫反應：
It is the response that is evoked when an antigen entered into the body for the first time. A few days after
the invasion of the antigens (eg. bacteria), the number of T-cells greatly increases to combat the antigen.
The cell-mediated immune response is being triggered, but is short lived.
它是病原體初次進入身體所引發的免疫反應，抗原(細菌)入侵身體後數天，T-細胞會增加
以對抗抗原，細胞免疫反應被激發，但此種反應很短暫。
Secondary immune response 繼發免疫反應：
The memory cells produced in the primary immune response will remain in the circulation for a long
time. If the antigen invades again, the number of T-cells will increase rapidly. The response is longer
lasting, more rapid and effective, producing greater amounts of T cells. This is due to the presence of
memory cells which can remember the pathogen. This response is called the secondary response.
在原發免疫反應過後會有記憶細胞存於血中一段時期，當抗原再次入侵，可加快 T-細胞及
抗體的產生，免疫反應更強烈及更持久，這是因為記憶細胞可記住病原體，此種反應名為
繼發免疫反應。
The importance of secondary immune response in diseases prevention :
繼發免疫反應的重要性：
Because of the production of memory cells, people can be immunized against certain disease such as
polio and measles.
因為記憶細胞可記住病原體，人類可在某些疾病獲得免疫力，例如小兒麻庳及麻疹。
The functions of immune system :
免疫系統的功能：
The functions of the immune system are to recognize, respond to and eliminate foreign substances
entering the body or arising in the body.
免疫系統可識別外物、對外物作出反應以致最終將它排除，阻止它們進入身體或在身體內
出現。
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Types of immunity 免疫的種類
There are two basic types of immunity, passive immunity and active immunity.
免疫的種類基本有兩種：被動免疫和主動免疫
1. Passive immunity is the passing of the antibodies into an individual in some way
rather than being produced by the individual himself, eg. antibodies can pass across the placenta
froma mother to her foetus, or are passed to the newborn body in the mother’s milk.
被動免疫是抗體非由個體自己產生，而是用某種方法輸入體內，例如透過胎盤將抗體
從母體傳給胎兒，或透過母乳傳給初生嬰兒。
It may be acquired artificially by injection of antibodies from other individual.
eg. in the treatment of tetanus and diphtheria.
抗體亦可透過注射而獲得，例如在預防白喉及破傷風時。
Passive immunity is temporary.
被動免疫只是短暫性的。
2. Active immunity occurs when an organism produces its own antibodies.
主動免疫是指個體自己產生抗體。
It is the result of an infection. Once the body has started to produce antibodies in response to a
disease causing agent, it may continue to do so for a long time (memory effect in secondary immune
response). It is why most people suffered from diseases such as mumps and measles once.
它是感染後的結果，當身體為對付某種病原體而開始產生抗體後，它會繼續如此做一
段長時間 (繼發反應的記憶效應)，這是為什麼感染腮腺炎及麻疹後便不會再受感染的
原因。
It is possible to induce an individual to produce antibodies even without them suffering diseases.
To achieve this, the appropriate antigen must be injected in some way. This is the principal of
immunization (vaccination).
根據此理，我們就算沒有患病，亦可誘發抗體的產生，只要注入適當抗原便可，這便
是免疫接種(打預防針)的科學根據。
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Practical application of immune mechanism (vaccination) :
免疫機制的實際應用(免疫接種)：
1. Passive immunization 被動免疫注射 :
Antibody from infected patients or organisms are inoculated to the client to against the disease
agent. eg. tetanus and diphtheria. This will have a fast action.
從受感染的病人或其他生物處抽取抗體，直接注入接種者，例如白喉和破傷風。
這種免疫力收效快。
2. Active immunization 主動免疫注射 :
Weakened (living, treated by heating) or killed microorganisms are inoculated to the client to
produce immune response. eg. Polio (living), cholera (dead).
接種減弱(活生，但經熱處理)了或已死的微生物來引發繼發免疫反應，例如小兒麻庳(活
生)和霍亂(已死)。
3. Interferon 干擾素 :
It is produced by infected cells which can interfere with the viral replication. Interferon triggers a
series of events which lead to an inhibition of viral protein synthesis, viral RNA transcription,
assembly and release of virus particles. It can inhibit cell growth and is used as an anti-cancer agent
under certain circumstances.
受感染的細胞可產生干擾素以干擾病毒的繁殖，干擾素可激發一連串的反應，引致病
毒蛋白合成、病毒 RNA 轉錄，基因與外殼組合等受到抑制，它可抑制細胞的生長，在某
些情況下可作為抗癌藥使用。
The need of a booster dosage in immunization programs :
為什麼進行防疫注射時，經常要使用加強劑？
The first injection of vaccine brings about a primary immune response which provides low levels of
antibodies and memory B-cells only. However the antibody level is not sufficient to protect the person
from infection. The booster injection stimulates the proliferation of memory B cells and production of
antibodies which stay in the body for a longer period of time. Therefore, further infection is prevented by
the artificial acquired immunization.
首次的防疫注射引起原發免疫反應，只能產生小量抗體和記憶 B-細胞，抗體水平太低不
足以保護身體免受感染，加強劑的使用可刺激身體產生更多的記憶 B-細胞和抗體，而且
效力更持久，故此，可保護身體免受感染。
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The use of drugs 藥物的使用 :
1. Antibiotics 抗生素 :
They are chemicals produced by various fungi and bacteria, which suppress the growth of other
microorganisms or even kill it. e.g. penicillin.
抗生素是由不同的真菌及細菌所產生的化學物品，它可抑制其他微生物的生長，甚或
殺死它們，例如青黴素。
Penicillin inhibits the synthesis of bacterial cell wall. Because bacterial cells are prokaryotic, the
adverse effects of antibiotics will not happen on the eukaryotic cells of the host and so antibiotics
may be safely used throughout the body. Other antibiotics may interfere DNA, RNA, protein
synthesis and cellular metabolism of the microorganisms. They can be used as a drug inside our body
to inhibit the bacterial growth.
青黴素能抑制細菌胞壁的合成，因為細菌是原核生物，青黴素的不良作用不會發生於
宿主的真核細胞中，故抗生素可安全使用於人體中，其他的抗生素可干擾微生物的
DNA、RNA、蛋白合成及代謝作用，它們皆可用於抑制體內的細菌生長。
Antibiotics can be produced by artificial method, eg. technique of recombinant DNA, protein
engineering and cloning.
抗生素可人工的方法產生，如利用 DNA 重組技術、蛋白工程及生物複製技術等。
The consequences of indiscriminate use of antibiotics :
不正當使用抗生素的後果：
(1) Frequently used of antibiotics will lead to decrease in effectiveness of them. It is because
microbes will be immune to the antibiotics through repeated mutations.
經常使用抗生素會引致它失效，因為微生物透過重複的突變可對它產生免疫力。
It was noticed that certain bacterial cells developed resistance to antibiotics, ie. The antibiotics
failed to kill them in the normal way. Resistance is arose by mutation. This mutation allowed
the bacteria to survive in the presence of drugs like penicillin by producing an enzyme to break it
down. In the presence of penicillin, non-resistant forms are destroyed. There is a selection
pressure favouring the resistant types. The greater the dosage and frequency of its use, the
greater are the selection pressures. At last the anti-antibiotic super bacteria are born.
我們發現某些細菌對抗生素產生抵抗力，抗生素不能如常般殺死它，抵抗力從突變
而來，突變使某些細菌產生能分解如青黴素等抗生素的酶，在青黴素的作用下，沒
有抵抗力的種類被殺死，選擇壓力有利於抗藥品種，抗生素的劑量越重，使用越頻
繁，則選擇壓力越大，最後產生能抵抗抗生素的超級細菌‧
When taking antibiotics, it is important to follow the doctor’s instruction to complete the
treatment cycle by finishing the pills all even though there is an apparent recover from the
disease. Otherwise, a little bacteria still survive and are selected to become the resistant strain.
當服用抗生素時，緊記按醫生指示完成整個療程，即就算覺得已復原，也該繼續吃
藥，直至吃完所有藥為止，否則，殘存的細菌會在選擇壓力下，發展為抗藥品種。
(2) Some may affect the synthesis of DNA, RNA, protein synthesis and cellular metabolism of the
patient.
有些抗生素或會干擾病人的 DNA、RNA、蛋白合成及代謝作用，即是有副作用。
2. Sulphonamides 磺醯胺
Sulphonamide can stop bacteria from reproduction and growth. It is an effective drug. This is
because its structure is similar to some metabolite in the bacteria. Hence, it competes with the
metabolite for the active site of bacterial enzymes.
磺醯胺能抑制細菌的生長和繁殖，它是有效的抗菌藥物，因它的結構和細菌的某些代
謝物相似，它會和細菌的代謝物爭奪細菌的酶的活性部位。
Exercise
1. Explain the meaning of the term antibody.
2. Explain the meaning of the term antigen.
3. Explain the meaning of the term lymphocytes.
4. Explain the meaning of the term memory cell.
5. Explain humoral immune response.
6. Explain the action of antibodies produced by plasma cells.
7. Explain cell-mediated immune response.
8. Explain the role of memory cells in the immune response.
9. What are the differences between specific and non-specific immune responses.
10. Explain inflammatory response.
11. Explain the meaning of the term passive immunity.
12. Explain the meaning of the term active immunity.
13. Explain the meaning of the term passive immunization.
14. Explain the meaning of the term active immunization.
Answer
1. Explain the meaning of the term antibody.
A molecule synthesized by an animal in response to antigen (foreign substances).
Antibodies combine with their appropriate antigens and neutralize their action,
preventing them from causing them.
2. Explain the meaning of the term antigen.
Any substance, produced by a microorganism, which will stimulate the production of
antibodies.
3. Explain the meaning of the term lymphocytes.
A type of white blood cell, produced by bone marrow which are important in
immunity of the body.
4. Explain the meaning of the term memory cell.
These are lymphocytes produced during the formation of plasma cells. They greatly
amplify the process of plasma cell formation and antibody secretion when the antigen is
introduced the second time.
5. Explain humoral immune response.
In response to antigens, the B-cells (produced by lymphoid tissue) will differentiate and
proliferate to form a plasma cell clone. The plasma cells can produce antibodies. The
antibodies then attack the antigen. Some memory cells are also produced.
6. Explain the action of antibodies produced by plasma cells.
They are highly specific for the antigens. They speed up phagocytosis, combine with
microorganisms, antigens and clump them together. They also neutralize toxins produced
by microorganisms.
7. Explain cell-mediated immune response.
T-cells produced by thymus gland possessing membrane receptors which recognized
antigen are
stimulated to proliferate and produce two clone of T-cells. One (killer T
cells) can kill antigen
directly. The other (helper T cells) can liberate lymphokines to
activate macrophages to kill the
antigens. In addition, memory cells are also produced.
8. Explain the role of memory cells in the immune response.
The memory cells can speed up the formation of plasma cell and secretion of antibody
when an antigen invades the body the second time.
9. What are the differences between specific and non-specific immune responses.
Specific immune responses differ from non-specific immune responses in
1. Specificity- Non-specific defence mechanism give protection against many types of
pathogens. They include mechanical barriers, enzymes, interferon and phagocytosis.
Specific defence mechanisms confer immunity against the effect of particular pathogens
(eg. The disease caused by a particular virus).
2. Recognition - discrimination between self of non-self molecules
3. Memory - formation of specific memory cells in the immune response so that the second
invasion of the same antigen will result in a more rapid, stronger and long-lasting
response (secondary response).
Memory is absent in non-specific immune response.
10. Explain inflammatory response.
Phagocytosis causes inflammation at the site of infection. The hot and swollen area
contains many dead bacteria and phagocytes which are known as pus. Inflammation
results when histamine is released as a result of injury or infection. This causes dilation
of blood capillaries from which plasma, containing antibodies, escape into tissues.
Lymphocytes also pass through the capillary walls to the infected area.
11. Explain the meaning of the term passive immunity.
Passive immunity is the result of antibodies being passed into an individual in some way
rather than being produced by the individual itself. eg. antibodies pass across the
placenta from a mother to her foetus. It may be acquired artificially by injection of
antibodies from another individual. eg. in the treatment of tetanus. Passive immunity is
only temporary.
12. Explain the meaning of the term active immunity.
Active immunity occurs when an organism manufactures its own antibodies. It is the
result of an infection. Once the body has started to manufacture antibodies in response to a
disease causing agent, it may continue to do so for a long time. It is for this reason that
most people suffer diseases such as mumps and measles only once. It is possible to induce
an individual to produce antibodies even without them suffering diseases. To achieve this,
the appropriate antigen must be injected in some way. This is the basis of immunization
(vaccination).
13. Explain the meaning of the term passive immunization.
Antibody from infected patients or organisms are inoculated to the patient against the
disease agent. eg. Tetanus and diphtheria.
14. Explain the meaning of the term active immunization.
Weakened (living, treated by heating) or killed microorganisms are inoculated to the
patient to produce immune response. eg. Polio (living) ; cholera (dead)