Unit 5 Medical Immunology

Keyto the Exercises

1.Preparation

 

Let'swatch The Jenner Story.

Afterwatching, please answer the following questions.

1 ) Edward Jenner.

2) Vaccination.

3 ) Jenner took some pus from a milkmaid'scowpox\ and rubbed it into two small

scratches on the arm of a boy named JamesPhipps. In a few days, James was poorly

with cowpox9 but he soon got better. Sixweeks later, Jenner took pus from a

smallpox victim and deliberately tried togive James the deadly disease. But James

didn't get smallpox. This experiment showedthat Jenner's vaccination was effective.

 

Script

 

Doctor Jenner was an expert on cuckoos. Hewas also a good scientist because he

asked the right questions. What he reallywanted was to conquer the deadly smallpox.

Cows sometimes caught cowpox. And milkmaidsoften caught cowpox from the cows.

Cowpox didn't do the milkmaids much harm.What interested Jenner was that they

never seemed to catch the deadly smallpox.Thousands used to die from smallpox. Why

not milkmaids? Could it be that cowpox gotin the way? Could catching cowpox stop

them catching smallpox? To test his theory,he needed someone young who hadn't had

either cowpox or smallpox. He chose JamesPhipps aged eight and three quarters. He

told the lad that he thought he could stophim from ever catching smallpox and it

wouldn't hurt-much. Then he took some pusfrom serious cowpox， and rubbed it into

two small scratches on the boy's arm.Cowpox was called vaccinia, so Jenner called his

invention vaccination. In a few days, Jameswas poorly with cowpox, but he soon got

better. Six weeks later, Jenner took pusfrom a smallpox victim and deliberately tried to

give James Phipps the deadly disease. Therewas no cure for smallpox. But James didn't

get smallpox. He lived to a ripe old ageand now smallpox has been wiped out thanks to

Edward Jenner and his vaccination.

 

II.Reading

TextA

ComprehensionCheck

 

pairwork Discuss and answer the following questions. Try not to look back at thetext.

1 ) Lymphocytes? plasma cells? naturalkiller cells, antigen-presenting cells, and

granulocytes are constituents of the humanimmune system. They cooperate well with

their different functions remarkablywell-integrated. ( Para. 1 and the whole text)

 

2) Lymphocytes occupy a very special placeamong the leukocytes that participate in

immune reactions due to their ability tointeract specifically with antigenic substances

and react to nonself antigenicdeterminants. ( Para. 2 )

 

3) B lymphocytes or B cells are sodesignated because in birds the bursa of Fabricius

plays a key role in their differentiation,and T lymphocytes or T cells are so designated

because the thymus plays a key role intheir differentiation. (Para. 3 & 5)

 

4) After proper stimulation, B cellsundergo blastogenic transformation and after several

rounds of division differentiate intoantibody producing cells (plasma cells). (Para. 4)

 

5 ) Because T cells have various effectorfunctions cytotoxicity and lymphokine

production being the main ones) that arethe basis of cell-mediated immunity. ( · Para. 5)

 

6) T lymphocyte activation requires theinteraction of the T cell receptor with an antigen-

derived polypeptide and additionalcostimulatory signals from auxiliary cells. (Para. 6)

 

7) B, C and D. (Para. 8)

8) Macrophages, monocytes, dendritic cellsand activated B lymphocytes. (Para. 4 & 10)

 

9) They ingest with greatest efficiencymicroorganisms and particulate matter coated by

antibody and complement. (Para. 12)

 

10) Eosinophils and basophils. (Para. 13& 14)

 

LanguagePractice

 

1.Read the text carefully and then fill out the missing information in thefollowing short

passage.The beginning letter of each missing word has been given.

1 ) immune 2) response 3 ) antigen 4)lymphocytes

5 ) thymus 6) mediated 7) monocytes 8)activated

9) lymphoid 10) plasma 11 ) immunoglobulins

 

2.Paraphrase the following sentences. Pay special attention to the underlinedparts.

1 ) The lymphocytes can identify theinfected or heterologous cells as unwanted and

remove them without delay.

2 ) An organ with the same function as thebursa of birds has not yet been discovered in

Mammals.

3 ) Activated and differentiated T lymphocytesare unable to be distinguished from a

small, resting lymphocyte by form andstructure.

4 ) The monocyte is regarded as a whiteblood cell transported through the blood.

5 ) The nuclei of granulocytes, which havebeen divided into different parts, take on

variable sizes and shapes.

 

3.Identify the expression from each of the following sentences which correspondsin

 

meaningto one of the Chinese expressions given below. (These sentences are wellwritten.

Itis suggested that you read them aloud and learn them by heart. )

1)in one way or another以这样或那样的方式

2)attribute sth to把······归因于

3)interaction of sth with sth······和······的相互作用

4)(be)bound to结合在······上

5)concentrate sth on sth将······集中在·····。

6) a collection of 群  ·  ·  ·  ·  ·  。

7)(be)designated as被命名为

8)(be)similar to与······相似

with greatest efficiency极为高效地

(be)coated by被······包被着的

9) in high concentration (s) 高浓度

10)evolve from由······演化而来

 

4.Translate the following sentences into English with some expressions you

inexercise 3.

 

1 ) Most of the people would probably agreethat all the unsolved problems in

immunology relate, in one way or another,to the questions of self-tolerance and the

regulation of immune responses.

 

2) Unless treated appropriately, otherseverely affected children who survive until the

third day develop signs of central nervoussystem damage, attributed to the high

concentrations of unconjugated bilirubin.

3) The immune response is triggered by theinteraction of an antigenic determinant

with specific receptors on lymphocytes.

4) A radiolabeled anti-human immunoglobulinwas used to assay the antibody that

becomes bound to the immobilizedantigen.

5) Follicular dendritic cellsconcentrate unprocessed antigen T the membrane and keep

it there for relatively long periods oftime.

6 ) The affected gene is isolated from anappropriate DNA library, a large collection of

Individual DNA sequences representing allor part of an organism’s genome.

7)Bacterial infections associated with theformation of pus are designated as purulent.

8 ) The role of helper T cells in the mixedlymphocyte reaction is likely to be very

similar tothe role of helper T cells that assist B cell responses.

9 ) In order to demonstrate that apatient's serum has an antibody directed against a red

cell sample, indicator red cells coatedby anti-IgG are added with greatest efficiency.

10) Protein is added in relatively highconcentration to the reagent with the purpose of

dissipating the repulsive forces that keepthe red cells apart.

11 ) Leukemic states may evolve froma chronic form to an acute disease, and the type

of proliferating cell may also changeduring the course of the disease.

Note:The underlining points out the expressions identified in exercise 3.

 

TextB

ComprehensionCheck

Answeringthe following questions. Try not to look back at the text.

1)To make a general introduction otimmunology, the author recalls the history from its

its emergence as a discipline to itscurrentinterest of study, explains the general concepts

(specific and nonspecific defenses, stagesof the immune response ) concerning the

mechanisms for protecting human organismagainst infectious agents, and briefly

describes the cells of the immune system.(The whole text)

 

2) The fundamental observation, that anindividual might become resistant for life to a

certain disease after having contracted itonly once\ led to the development of

immunology as a scientific discipline. (para. 1 )

 

3 ) It is the fact, that some infectiousdiseases, such as tetanus, measles, mumps,

Poliomyelitis, and smallpox, are now eitherextinct or very rarely seen, that helps us

Understand that immunization has a powerfuleffect against many infectious diseases.

(Para. 2 )

 

4 ) Nonspecific defenses are innate and genericallyapplicable to many different pathogenic

organisms, while specific defenses areinduced during the life of the individual and

their protective effect is directed to onesingle organism. (Para. 4-6)

 

5) It means that repeated exposure to agiven antigen elicits progressively more intense

specific responses. (Para. 6)

 

6) The red cells are to carry oxygen totissues\ and the white cells are to eliminate

potentially harmful organisms or compounds.(Para. 8)

 

7) Macrophages can trap and present bothnative antigens and antigen fragments in a

most favorable way for the recognition bylymphocytes, deliver activating signals to

lymphocytes engaged in antigen recognition,and eliminate antigens that have elicited

an immune response. (Para. 9 )

 

8) Natural killer cells are very special inthat they have two different mechanisms of

recognition they can identify malignant orviral-infected cells by their decreased

expression of histocompatibility antigens (HI. A ), and they can recognize antibody-

coated cells and mediate ADCC. ( Para. 11 )

 

9) Humoral immunity refers to the immuneresponses in which antibodies play the

principal role as effector mechanism. (Para. 12 )

 

1o) There are four biological consequencesof antigen-antibody reactions neutralization

the activation of the complement system andthe lysis of the offending microbial cell

the destruction of microorganisms due totheir ingestion by phagocytic cells or their

 

destruction by cells mediating ADDC ;certain pathological conditions, such as allergic

reactions. ( Para. 13)

 

LanguagePractice

1. Translatethe following sentences into Chinese.

 

1)使免疫学发展为一门独立自然科学学科的重要发现是一个人在感染某种疾病一次

以后，便可终生具有对该病的抵抗力。

 

2)紧接着，科学家又发现感染性疾病可以通过使易感者暴露于灭活或减毒的传染原生

 

物体或从传染原生物体提取的复合物得到预防。

 

3)保护我们的机体抗传染原的力量涉及很多不同的机制一些非特异性的保护机制(普

遍适用于许多不同病原体)和另一些特异性的保护机制(它们的保护效应仅针对单一

的病原体)。

 

4)此外，这些细胞也向参与抗原识别的淋巴细胞传递活化信号。信号传递方式是以可

溶性介质(白细胞介素类，如1卜1)的形式以及以通过细胞一细胞接触传递的信号的

形式。

5)一个成年人可以识别数百万种不同的抗原，产生抗体(即生物体在感染或免疫接种后

出现在血液中的蛋白质，它们具有与进人该生物体的抗原表位进行特异性反应的能

力)。

6)吞噬作用对于细菌的消除尤为重要，它包括抗体及补体成分结合到传染原的外表面

(调理作用)以及吞噬细胞对结合的抗体和(或)补体成分的识别并将其视作摄人的

信号。

 

2.Paraphrase the following sentences. Pay special attention to the underlinedparts.

1 ) B lymphocytes are the cells from whichantibody-producing cells ( called plasma

cells) are developed.

2) Natural killer cells play two roles ineliminating infected and malignant cells.

3) Antibodies bound to antigens, whichforms a complex, can activate the complement

system.

4) Allergic reactions brought about byantibodies begin rapidly and suddenly, only in a

few minutes, and are known as immediatehypersensitivity reactions.

 

III.Video Watching

ClipOne

Watchthe video clip and do the exercises given below.

1.Watch the clip and answer the following questions.

1 ) The macrophage combines peptidefragments from the invaders with some of its

own proteins.

2) The helper T cells with matchingreceptors will bind to the surface of the

 

macrophage.

 

3 ) the clones are all designed to fightthe specific invader that triggers the response.

 

Script

 

White blood cells called macrophages leadthe body's cell-mediated immune

response by engulfing and digesting borneinvaders. Combining peptide fragments from

the invaders with some of its own proteins,the macrophage builds up a patchwork of

antigen complexes on its surface.

 

When smaller white blood cells calledhelper T cells encounter the macrophage,

those with matching receptors bind to itssurface. These helpers then multiply and

secrete chemicals which call differentcells into battle, especially the cytotoxic or killer T

cells.

 

The macrophage or an infected cellactivates only those cytotoxic cells with

receptors that match the antigen complexes.Stimulated by chemicals from the helper T

cells, these killer T cells rapidly divideinto an army of clones, all designed to fight the

specific invader that triggered theresponse. When killer cells dock with the infected

cell, they bombard it with lethal toxinsthen move on in search of other targets.

 

2.0mitted.

 

ClipTwo

 

Watchthe video clip and do the exercises given below.

 

1.Answer the following questions.

 

1 ) This video clip depicts the body'shumoral or antibody-mediated immune response.

 

2) In the humoral or antibody-mediatedimmune response, the macrophages are joined

by lymphocytes called B cells, which makesthe humoral or antibody-mediated

immune response different from thecell-mediated immune response.

 

3 ) The B cells with matching receptorswith the invading pathogens are activated to

stand ready to fight.

 

2.watch again and fill in the blanks in the following paragraph with the exactwords you hear.

 

1 ) antigen-presenting 2) helper T 3)matching

4 ) activated B 5) Triggered 6) release

7) spur 8) reproduction 9) memory

10) invasion 11) pathogen 12)antibody-producing

13) plasma 14) circulating 15) dock

16) neutralizes 1 7) destruction

 

Script

 

The body's humoral or antibody-mediatedimmune response begins in the same

manner as its cell-mediated response. Buthere the macrophages are joined by

lymphocytes called B cells. The pathogenactivates only those B cells with matching

receptors. These cells stand ready to enterthe battle. Meanwhile ! the antigen-presenting

macrophages activate those helper T cellswith matching receptors. These in turn

rendezvous with activated B cells.Triggered by this meeting, the helpers release

chemicals which spur the selected B cellsinto rapid reproduction. Some B cells become

memory cells, ready to respond to a laterinvasion by the same pathogen, but most

become antibody-producing factories calledplasma cells.

 

Freely circulating in the body, antibodiesdock with pathogens. This neutralizes

them or marks them for destruction by otherweapons in our immunearsenal.

 

ClipThree

 

Watchthe video clip and do the exercises given below.

 

1.What plays each of the following roles according to the clip? Write down theitem in the

blankafter each role.

 

1 ) the thymus gland

2) the helper T cells

3) the lymph glands

4) the B cell

 

2.Watch again, take notes and fulfill the following requirements.

1 ) Omitted.

 

2) 1)The helper T cells incorrectlyidentify a normal healthy cell as a germ. This leads

to the production of antibodies against thehealthy cells and the fighter cells do their

jobs and they kill off the healthy cells.

2)The helper T cells are either too few or not active enough. Thismeans that there

are too few antibodies produced against theillness and the fighter cells do not wake

up to fight the illness.

 

Script

 

MGM presents "YOUR BODY NEEDSYOU", starring "The Immune System".

This is your body. These are the threeareas that are very important to your

immune system-the spine, the thymus gland,and the lymph glands. Your stem cells

are born in bone marrow, such as yourspine. They have no function yet, but can develop

into any cells, like fighter or helpercells. High doses of sugary foods and drinks over a

short period of time causes all productionof stem cells to stop for a full five hours. After

they are born, they travel to the thymusgland at the base of the throat. The thymus

gland is the college for the stem cells,where they are screened and sorted according to

aptitude before being sent for specialisttraining. Some will become your fighter T cells

or CD8s. They train until they are neededto fight infections, and others will become

your helper T cells or CD4s. The helper Tcells are your body's detectives. Before being

sent off into your body, the trainee cellsare tested. If they fail the test, they are killed.

The thymus gland or college shuts down orshrinks when your body does not get enough

zinc. If they qualify, they are sent to thelymph glands. The lymph glands are all over

your body, and are the ary barracks foryour body's immune cells. The helper cells

wander around the body, looking foranything foreign, which they compare to their

memory indentikits of what is part of thebody and what is not. A germ enters your

body—this is an infection. The helper Tcells see this foreign body-the germ-and

scans it against its memory banks. Itrealizes that the germ is dangerous. The helper T

cell runs to the B cell, a smart cell, andshows it the identity of the germ. The B cell then

becomes a mass of factory cell and startsto produce chemicals called antibodies.

Thousands of antibodies go in search of theidentified germ and once they bump into it,

they attach themselves to it like ahandcuff.

 

High doses of sugary foods and drinks alsostop the production of antibodies. A

patrolling fighter cell sees the antibodyhandcuffed to the germ. It races off a wake the

other soldiers, who then also race all overthe body, searching for the germ and they kill

them. When all the germs are dead, theinfection is over. You need to drink lots of water

when fighting an infection to flush thejunk out. An autoimmune illness like arthritis or

multiple sclerosis is caused when thehelper T cells incorrectly identify a normal healthy

cell as a germ. This leads to theproduction of antibodies against the healthy cells and

the fighter cells do their jobs and theykill off the healthy cells. Suppressed immune

system illnesses, like cancer and AIDS, arecaused when the helper T cells are either too

few or not active enough. This means thatthere are too few antibodies produced against

the illness and the fighter cells do notwake up to fight the illness. you have already seen

how certain things such as very high dosesof sugary foods or drinks can harm your

body's ability to fight infections. You'vealso seen how specific substances in food such

as zinc are critical in helping the bodyfight germs.

 

IV.Writing

 

Improvethe following sentences.

1)Liquefied material is removed bylymphatic’s; any particulate residue is removed by

macrophage phagocytosis.

2) vasculitis may be due to direct invasionof vessels by the organism or to production of

toxins.

3) These proteins become insoluble bybinding to the stromal matrix and by forming

cross-links.

4) Community-acquired bacterial infectionsgenerally are associated with a lower

mortality rate than hospital-acquiredinfections both because the host is usually better

able to respond to the infection andbecause the infectious agents are usually more

sensitive to antibiotic therapy.

5)swelling is due to accumulation of fluidpain is due to release of chemicals that

stimulate nerve endings and loss offunction is due to a combination of factors.

6) Fetal healing is characterized by thevirtual absence of acute inflammation, by the

regeneration of skin appendages and by theabsence of TGF-PI in fetal skin.

 

V.Autonomous Learning

 

VocabularyDevelopment

 

1.Fill in each of the following blanks with an appropriate word.

1 ) bone marrow 2) immunity

3) lymphocytes 4) lymph

5) lymph node 6) lymphatic vessels

7) thymus gland 8) tonsils

9) spleen 10) four

 

2.Write the plural form of each of the following words.

1) gingivae 2) mitochondria

3) testes 4) lumina

5) matrices 6) sera

7) meninges 8) foci

9) pelves 10) adenomata

 

3.The suffix-osis added to a root for a type of cell means an increase in thattype of cell in

theblood. Use this suffix to write a word that has the same meaning as each of the

following.

 

1)monocytosis

2 ) granulocytosis

3 ) lymphocytosi

 

70 SupplementaryListening

Script

Activation of the immune response typicallybegins when a pathogen enters the

body. Macrophages that encounter thepathogen ingest, process and display the antigen

fragments on their cell surface.Macrophages with antigen fragments displayed on their

surfaces are called antigen-presentingcells. An antigen-presenting macrophage interacts

with a T-helper cell that can recognize thesame antigen. During the interaction, the

macrophage releases a chemical alarm signalcalled interleukin-1, which stimulates the

T-helper cell to secrete interleukin-2.Interleukin-2 causes the proliferation of certain

cytotoxic T cells and B cells. The immuneresponse from this point follows two paths,

one using cytotoxic T cells and one using Bcells. Normal cells of the body that become

infected can also digest some of thepathogens and display antigen fragments on their cell

surfaces. The body makes millions ofdifferent types of cytotoxic T cells. Each type is

able to recognize a particular antigen. Thecytotoxic T cells that are capable of recognizing

the antigen displayed on the surfaces ofinfected cells bind to the infected cells and

produce chemicals that kill the infectedcell. Death of the infected cells results in

destruction of the pathogen. B cells alsocome in millions of different types\ each able to

recognize a particular antigen. When Bcells become activated by T-helper cells, they

differentiate into plasma cells. Theseplasma cells become antibody-producing factories,

flooding the bloodstream with antibodiesthat can bind to the antigen involved in this

infection. Antibodies bind to the antigenson the surfaces of the pathogens, marking them

for destruction by macrophages. Some of theB cells do not turn into antibody factories,

but instead become memory B cells that maysurvive for several decades. Because of these

memory B cells, the secondary immuneresponse to a future infection by the same

pathogen is swifter and stronger. Thispowerful secondary immune response is what

gives "immunity" to some diseasesafter you have had them once or after you have been

vaccinated.

 

Translationof the Texts

 

TextA

参与免疫应答的细胞

免疫系统的细胞

淋巴细胞

淋巴细胞（图1A）在以这样或那样的方式参与免疫反应的白细胞中占据着特殊的地位，其原因在于它们具有与抗原物质特异性结合并对非己的抗原决定簇做出相应反应的能力。淋巴细胞由胎肝、骨髓以及胸腺中的干细胞分化而来，分为两种主要功能类型。它们分布于外周血和所有的淋巴组织中。

B淋巴细胞

B淋巴细胞或B细胞得名于法氏囊（bursa of Fabricius）——一个紧邻鸟类肠道尾端、在B淋巴细胞的分化中起着关键作用的淋巴器官。在鸟类孵出时或此后不久摘除法氏囊，将导致B淋巴细胞不分化、不成熟以及无法产生抗体。哺乳动物体内尚未找到鸟类法氏囊的对应物。一些研究者相信，骨髓是发生B淋巴细胞分化的最可能的器官，而另一些人认为行使此功能的是肠道周围淋巴组织。

B淋巴细胞细胞膜上具有免疫球蛋白，行使抗原受体的功能。在适当的刺激后，B细胞进行母细胞转化，并在数次分裂后分化成为抗体产生细胞（浆细胞）。活化的B淋巴细胞也可发挥抗原提呈细胞（antigen-presenting cells，APC）的功能，这种功能通常由单核/巨噬细胞行使。

T淋巴细胞

T淋巴细胞或T细胞之所以得名，是由于胸腺（thymus）在其分化的过程中起着关键作用。T淋巴细胞的功能包括调节免疫应答，以及作为细胞免疫基础的各种效应功能（细胞毒性和淋巴因子的产生是其中的主要功能）。T淋巴细胞细胞膜上也具有抗原识别单位——T细胞受体（T cell receptors，TcR）。T细胞受体和免疫球蛋白分子在结构上不相关。

图1 人白细胞的主要类型与形态（A）淋巴细胞（B）浆细胞（C）单核细胞（D）粒细胞

T淋巴细胞活化需要T细胞受体和来自抗原的多肽的相互作用，以及来自辅助细胞的额外共刺激信号。在受到适宜刺激后，小的静息T淋巴细胞迅速通过母细胞转化（过程），成为一个大淋巴细胞（13-15毫米）。这个大淋巴细胞（淋巴母细胞）进而分裂数次，产生一大群具有相同抗原特异性的中型（9-12毫米）和小型（5-8毫米）淋巴细胞。我们无法从形态上区分活化的分化T淋巴细胞与小的静息淋巴细胞。

浆细胞

浆细胞的形态特征是具有浓缩染色质的偏心核以及富含粗面内质网的体积很大的胞浆(图1B)。浆细胞产生并分泌大量免疫球蛋白，但并不表达膜免疫球蛋白。浆细胞几乎不分裂。浆细胞通常分布于骨髓和粘膜周围淋巴组织。

自然杀伤细胞

自然杀伤（NK）细胞在形态上被描述为大颗粒淋巴细胞。这些细胞不具有任何类型的抗原识别受体，但能识别结合在靶细胞上的抗体分子并杀伤这些细胞，其涉及的机制和T淋巴细胞通常采用的细胞毒性机制（抗体依赖的细胞毒性）相同。它们也具有另外一种识别机制令其得以摧毁肿瘤细胞和感染病毒后的细胞。

抗原提呈细胞：单核细胞，巨噬细胞和树突状细胞

单核细胞和巨噬细胞被认为是密切相关的。人们认为单核细胞（图1C）是一种由血液输送的白细胞，一旦定居于组织中，便成为巨噬细胞。单核细胞和巨噬细胞能够摄入颗粒物（微生物、细胞和惰性颗粒），因此被认为具有吞噬功能。巨噬细胞的吞噬活性比单核细胞高。

通过加工处理复杂抗原并将抗原片段集中表达在细胞膜上，巨噬细胞和单核细胞在免疫应答的诱导期扮演着重要的角色。抗原以这种形式被辅助T淋巴细胞识别。因此，这些细胞被称作抗原提呈细胞（antigen-presenting cells，APCs）。最专业有效的抗原提呈细胞是树突状细胞。树突状细胞还具有异源性，至少包括骨髓源性和淋巴源性两个群。一些树突状细胞倾向于出现在诸如肾、脑（小胶质细胞）、毛细血管壁以及粘膜等组织中。在静息状态下，作为抗原提呈细胞的巨噬细胞和单核细胞似乎相当不称职，但在被微生物或其他的刺激激活后，它们迁移到淋巴组织并在此分化为高效抗原提呈细胞，具备激活初始T细胞的能力。

粒细胞

粒细胞是一群胞浆内含有分段或分叶核的白细胞，其胞浆内也含有在特殊染色下清晰可见的颗粒。由于它们的分段核形状和大小不一，这些细胞被归类为多形核白细胞（PMN，图1D）。不同亚群的粒细胞（嗜中性粒细胞、嗜酸性粒细胞和嗜碱性粒细胞）能通过针对胞浆颗粒的鉴别染色法加以区分，反映出它们不同的化学组成。

嗜中性粒细胞

嗜中性粒细胞是白细胞中最大的亚群，有两种胞浆颗粒，颗粒内含有具杀菌活性的复合物。它们生物学上的重要性源于它们的吞噬活性。和大多数其他吞噬细胞相似，它们极为高效地摄取微生物和被抗体和补体包被着的颗粒物质。

嗜酸性粒细胞

嗜酸性粒细胞是含有颗粒的多形核白细胞，这种颗粒可被含有伊红的细胞染料染成橙红色。在过敏反应和寄生虫感染时，这些细胞呈高浓度聚集，它们在这两种情况下的作用将在后面的章节讨论。

嗜碱性粒细胞

嗜碱性粒细胞内存在因含组胺和肝素而具异染性的颗粒。定居于组织中的肥大细胞和嗜碱性粒细胞很相似，尽管它们看似由不同前体细胞演化而来。嗜碱性粒细胞和肥大细胞都参与了抗寄生虫免疫机制，并且在过敏反应中起着关键的致病作用。

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免疫学简介

历史回顾

使免疫学发展为一门独立自然科学学科的重要发现是：一个人在感染某种疾病一次以后，便可终生具有对该病的抵抗力。免疫（immunity）这个术语，来源于拉丁语“immunis”（免除），被用来命名这种自然的获得的对抗诸如麻疹、天花等疾病的保护力。

免疫学作为一门独立的学科出现与微生物学的发展紧密相关。在微生物学的黄金时代，巴斯德、科赫、梅契尼科夫以及许多其他先驱科学家的工作最终导致了对许多新的传染原的迅速鉴定。紧接着，科学家又发现感染性疾病可以通过使易感者暴露于灭活或减毒的传染原生物体或从传染原生物体提取的复合物得到预防。只要我们认真思考以下事实：作为致病和致死的重要原因的破伤风、麻疹、流行性腮腺炎、脊髓灰质炎和天花等感染性疾病现在已经被消灭或极为少见，免疫对抗诸如此类的感染性疾病的强大作用便能被理解。事实上，公正地说，疫苗接种和卫生设施对于人类幸福和平均寿命产生的影响是医学领域迄今为止任何其它进步都无法匹敌的。

在本世纪的后五十年中，免疫学开始超越其早期的界限，成为一个更具综合性的生物医学学科。今天,对于免疫防御机制的研究仍然是一个重要的研究领域，但免疫学家已经投入到更为广泛的问题的研究中去，例如，自我/非我识别、细胞和组织的分化控制、移植、癌症的免疫治疗等等。研究的焦点已经转向对免疫系统工作原理的基本理解，并希望这种理解使人们得以运用新的方法来操纵免疫系统。

基本概念

保护我们的机体抗传染原的力量涉及很多不同的机制：一些非特异性的保护机制(普遍适用于许多不同病原体)和另一些特异性的保护机制(他们的保护效应仅针对单一的病原体)。非特异性防御，这通常是先天的(即所有正常个体与生俱来的)，包括:

• 1．机械屏障，如：表皮和粘膜的完整性

• 2．物理化学屏障,如：胃液的酸性

• 3．存在于外分泌液中的抗菌物质(如溶菌酶，防御素)

• 4．正常肠道运输和支气管分泌物与尿液的正常流动，借以清除各自的系统的传染原

• 5．多种细胞具备的各种吞噬细菌和颗粒物的非免疫机制，在粒细胞发育得尤为完善。

特异性防御，在个体的生命中通常是作为被命名为免疫应答的复杂的事件序列的一部分被诱导的。免疫应答有两个独特特点:

• 1．对于诱导抗原的特异性。例如，接种灭活脊髓灰质炎病毒只能预防脊髓灰质炎，不能同时预防病毒性流感。免疫应答的特异性归因于淋巴细胞上存在的独特的抗原受体。

• 2．记忆性，这意味着再次遇到相同的抗原时，会引起愈发强烈的特定免疫应答。大多数免疫接种涉及免疫复合物的重复给予，旨在建立长效的保护性应答。再次遇到相同的抗原时，免疫应答的强度和持续时间的增加归因于每次接触抗原后引起的抗原特异性淋巴细胞的增殖。

免疫应答的各个阶段

为了更好地理解免疫应答是如何产生的，可以将其按照先后顺序分为不同的阶段。(表1) 第一阶段(识别阶段)涉及一小群有特异受体的淋巴细胞，这些细胞能够识别由被称作抗原提呈细胞的特化细胞产生的抗原或抗原片段。第二阶段(放大阶段)是由活化的抗原提呈细胞和特化的T细胞亚群（辅助性T细胞，见下述定义）介导，它们可以相互促进增殖和分化。随后，将产生效应分子（抗体）或者发生效应细胞（直接或间接介导有害因素的消除的细胞）的分化。因此，最终的结果是通过活化的免疫细胞或者由免疫系统释放的调节因子引发的反应来清除引发免疫应答的生物体或化合物。

表1 免疫应答的三个主要阶段概述

免疫系统的细胞

淋巴细胞及其亚群

外周血含有两大类细胞：即红细胞和白细胞。其中，红细胞的主要生理功能是将氧运输到组织。而白细胞的主要生理功能是清除可能对机体有害的生物体和复合物。在白细胞中，淋巴细胞由于其在免疫应答中的核心作用而显得尤为重要。淋巴细胞的几个亚群已被明确界定：

• 1．B淋巴细胞，它是被称作浆细胞的抗体产生细胞的前体。

• 2．T淋巴细胞，它被分为几个亚群：

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• 辅助性T细胞，它在免疫应答中起着非常重要的放大作用。

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• 细胞毒性T细胞，它是在清除异己或受感染细胞的过程中发挥作用的主要免疫效应细胞。

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• 免疫调节性T细胞，它具有下调免疫应答的能力，主要作用方式是通过释放细胞因子（如IL-10，即白介素10）以及通过表达膜分子（如CTLA4），这些分子与相应受体的相互作用会导致下调信号的释放。

抗原提呈细胞

抗原提呈细胞，例如巨噬细胞、巨噬细胞相关细胞、树突状细胞，在免疫应答的感应阶段发挥着非常重要的作用：它们以最有利于淋巴细胞识别的方式摄入并提呈天然抗原和抗原片段。此外，这些细胞也向参与抗原识别的淋巴细胞传递活化信号。信号传递方式是以可溶性介质（白细胞介素类，如IL-1）的形式以及以通过细胞-细胞接触传递的信号的形式。

吞噬细胞

吞噬细胞，例如单核细胞、巨噬细胞和粒细胞，也在免疫应答中作为效应器发挥着重要作用。它们的主要功能之一是以抗体和补体的方式清除引发免疫应答的抗原物质。但是，如果抗原位于目的细胞表面，抗体便会诱导细胞毒性细胞附着于目的细胞上，从而导致抗体覆盖的细胞的死亡（即抗体依赖的细胞介导的细胞毒作用）。

自然杀伤细胞

自然杀伤细胞在清除受感染细胞和恶性细胞的过程中发挥着双重作用。这类细胞的独特性在于它们有两套不同的识别机制：它们通过组织相容性抗原的表达下降现象来识别恶性或病毒感染的细胞；它们能识别抗体覆盖的细胞并介导抗体依赖的细胞介导的细胞毒作用（ADCC）。

抗原与抗体

抗原通常是外源性物质（细胞、蛋白质和多糖类），它们被淋巴细胞上的受体识别, 从而引发免疫应答。位于淋巴细胞膜上的受体分子与外源细胞或蛋白质中被称为抗原决定簇或表位的部位相互作用。一个成年人可以识别数百万种不同的抗原，产生抗体（即生物体在感染或免疫接种后出现在血液中的蛋白质，它们具有与进入该生物体的抗原表位进行特异性反应的能力）。由于抗体具可溶性并存在于几乎所有体液内，人们用“体液免疫”这一术语来命名以抗体作为主要效应机制发挥作用的一类免疫应答。抗体也被通称为免疫球蛋白。这一术语来源于以下事实：抗体分子在结构上属于被称为球蛋白（即球状蛋白）的蛋白质家族；抗体分子参与机体免疫应答。

• 1．如果抗原是可溶性的，在适宜条件下与特异抗体的反应将导致大块的抗原抗体复合物的沉淀。

• 2．如果抗原表达在细胞膜上，细胞将会通过抗体交联形成可见的团块（凝集）。

在功能上，抗原-抗体反应可根据其生物学后果加以分类：

• 1．病毒与细菌释放的可溶性毒素在与相应的抗体反应后，失去了其传染性和致病性（中和作用）。

• 2．与抗原形成复合物的抗体能激活补体系统。九种被相继激活的主要蛋白质或成分构成了补体系统。一些补体成分能促进吞噬细胞摄入微生物，而另一些会插入并破坏细胞质膜，造成入侵微生物细胞的溶胞（而死亡）。

• 3．抗体能通过促进吞噬细胞的摄入作用或促进介导ADCC（抗体依赖的细胞介导的细胞毒性作用）的细胞的破坏作用导致微生物的破坏。吞噬作用对于细菌的消除尤为重要，它包括抗体及补体成分结合到传染原的外表面（调理作用）以及吞噬细胞对结合的抗体和（或）补体成分的识别并将其视作摄入的信号。

• 4．抗原–抗体反应是某些病理性状况（例如过敏反应）的基础。抗体介导的过敏反应发作迅速（通常在几分钟左右），因此被称作速发型超敏反应。