Unit 11 The Immune Response

Introduction

I. What are the key characteristics of the immune response? Listen to the text and say whether the following sentences are true or false.

1. The Greek physician Thucydides [Өju:saıdıdıs] recognized the essential features of the immune response to the infection more than 2000 years ago. T / F

2. Immunity to one disease always confers no protection against other diseases. T / F

3. We refer to the immune response as a specific defense against invasion. T / F

4. Lymphocytes are distributed throughout the body in the blood. T / F

5. T cells and B cells play similar roles in the immune response. T / F

II. Use the following pairs of words in sentences of your own, compose 2-3 sentences with each of the pairs. Ask your partner to translate them into Russian.

invasion – prevent defenses – impregnable

response – mount protection – confer

immune – become lymphocytes – clustered

bloodstream - released

III. Working in small groups fill in the Table 10.1.

Table 10.1. The Major Molecules and Cells of the Immune Response

Molecules
_________________	Large organic molecules, normally proteins, polysaccharides, or glycoproteins, that can trigger an immune response, typically located on the surface of cells.
Antibodies	_______________________________________________________
Major histocompatibility complex (MHC)	A set of proteins found on the surface of cells that “label” the cell as belonging to a unique individual organism.
Effector molecules	A diverse group of molecules, including histamine and the cell-destroying proteins of killer cells and complement (soluble proteins found in blood).
_________________	Hormonelike molecules produced by cells of the immune system that regulate the immune response.
Cells
Macrophages	_______________________________________________________
____________________	Lymphocytes that produce antibodies; when stimulated, certain of their daughter cells (plasma cells) secrete large quantities of antibodies into the bloodstream.
____________________	A set of lymphocytes that regulate the immune response or kill certain types of cells.
Cytotoxic T cells	Destroy specific targeted cells, normally either foreign eukaryotic cells, infected body cells, or cancerous body cells.
Helper T cells	Stimulate immune responses by both B cells and killer T cells.
Suppressor T cells	Inhibit immune responses by other lymphocytes.
____________________	A subset of the offspring of B and T cells that are long-lived and provide future immunity against a second invasion by the same antigen.

Reading

I. Read and translate the following text.

Cellular Communication during the Immune Response

The immune system is a strange “system”. Unlike the nervous system, for example, it is not composed of physically attached structures. Instead, as befits its mission of patrolling the entire body for microbial invaders, the immune system consists of an army of separate cells. Nevertheless, the army is highly coordinated. This coordination requires complex communications involving antigens, antibodies, hormones, receptors, and cells. For example, when a virus invades the body (step 1), it sets off a cascade of events that can be loosely divided into three components.

I. Activation of Helper T Cells.

One component of the immune response begins when macrophages ingest the virus (step 2) and digest it. Antigens that have been “chewed off” the virus become attached to certain proteins of the macrophage’s major histocompatibility complex (MHC) and are displayed, or presented, on the surface of the macrophage. These antigen-MHC complexes are recognized by virgin helper T cells (step 3). Next, receptors on helper T cells release a hormone called interleukin-2 (step 4). This hormone stimulates cell division and differentiation (step 5) in both the releasing cell and in any other T cells that have bound to an antigen-MHC complex. Some of the resulting daughter helper T cells become memory cells that provide future immunity (step 6); other daughter cells become mature T cells that assist in activating – that is, stimulating the immune response of – cytotoxic T cells and B cells (step 7).

II. Activation of Cytotoxic T Cells: Cell-Mediated Immunity.

Meanwhile, other copies of the virus are infecting ordinary body cells, such as those lining the respiratory tract (step 8). Infected body cells display viral antigens on their surfaces, bound to another set of MHC molecules. Virgin cytotoxic T cells bind to the antigen-MHC complex on the body cells (step 9) and are simultaneously activated by interleukin-2 released by the activated helper T cells. This combination of binding and stimulation causes the cytotoxic T cells to multiply and become activated (step 10). When activated cytotoxic T cells then encounter infected cells presenting the antigen-MHC complex, the T cells release toxic proteins that kill the infected cell by lysis (step 11).

III. Activation of B Cells: Humoral Immunity.

Some B cells bear antibodies on their surfaces that bind antigens on the surface of free viruses that have not yet invaded a body cell (step 12). This antigen-antibody binding stimulates some B cell division and maturation, but full activation of B cells requires a boost from helper T cells. This boost is provided when B cells that have bound antigen ingest that antigen (by receptor-mediated endocytosis), attach the antigen to MHC molecules, and present the antigen-MHC complex on their surfaces. The antigen-MHC complex is recognized by activated helper T cells (step 13), which then release several types of interleukin hormones that stimulate the division and differentiation of antigen-binding B cells (step 14). Some of the progeny become memory cells (step 15); other become plasma cells that secrete antibodies into the bloodstream (step 16).

As you can see, helper T cells are essential in turning on both phases of the immune response. A loss of helper T cells, such as that caused by the virus that causes AIDS, virtually eliminates the immune response to many diseases.

II. This interlocking communication network is quite complex. Try to summarize its essentials in five generalizations.

Language focus 1

Will and Shall

1 In offers, promises, orders and requests, will (or ‘ll) generally expresses willingness or wishes (this is connected with an older use of will to mean ‘wish’ or ‘want’).

This box looks heavy. I’ll help you with it. (offer)

I won’t tell anyone what happened. I promise. (promise)

Will you open the window, please? (request, wish)

Shall expresses obligation (like a more direct form of should) and is used mostly in questions.

What shall we do now?

Compare Shall I …? and Will you… ?:

Shall I shut the door? (= Do you want me to shut it?)

Will you shut the door? (= I want you to shut it.)

2 We can use will to talk about typical behaviour.

She’ll sit talking to herself for hours.

Under these conditions the process will be irreversible.

The door won’t open.

Sulphuric acid will dissolve most metals.

Stressed will can be used to criticize people’s typical behaviour.

She WILL always argue.

Well, if you WILL keep telling people what you think of them…

I. Complete the sentences with I’ll + a suitable verb.

1. ‘Are you coming with us?’ ‘No, thank you. I think I’ll ………. here’.

2. ‘Would you like tea or coffee?’ ‘………. coffee, please.’

3. ‘Do you want me to finish the experiment?’ ‘No, it’s all right. ………. it.’

4. ‘We haven’t got any samples.’ ‘Oh, haven’t we? ………. and get some.’

5. Thank you for lending me your camera. ………. it back to you on Tuesday.

II. What do you say in these situations? Write sentences with Shall I…? or Shall we…?

1. You and your classmates want to do something this evening but you don’t know what. You ask your friends:…………………………………………………….......?

2. It’s your best friend’s birthday. You want to give him/her a present but you don’t know what. Your ask another friend for advice: What…………………………………….…………………………………………?

3. You and a friend are going out. You haven’t decided whether to go by car or to walk. You ask him/her:……………..……………………………………………..?

4. Your boss wants you to phone later. You don’t know what time to phone. You ask him/her:………………………………………………………………………..?

III. Use modal verbs shall and will in short dialogues of your own to express your promise, suggestion, instruction, to say about decisions that have already been made, to inform about some properties and someone’s typical behaviour.

Words, Words, Words

I. Choose the appropriate modal verb while reading the essay.

Flu – The Unbeatable Bug

Every winter, a wave of influenza, or flu, sweeps across the world. Thousands of the elderly, the newborn, and those already suffering from illness succumb, while hundreds of millions more suffer the respiratory distress, fever, and muscle aches of milder cases. Occasionally, devastating flu varieties appear. In the great flu pandemic of 1918, the worldwide toll was 20 million dead in one winter. In 1968, the Hong Kong flu infected 50 million Americans, causing 70,000 deaths in 6 weeks.

Flu is caused by several viruses that invade the cells of the respiratory tract, turning each cell into a factory for manufacturing new viruses. The outer surface of a flu virus is studded with proteins, some of which are recognized by the immune system as antigens. This recognition ensures that most people survive the flu because their immune systems inactivate the viruses or kill off virus-infected body cells before the viruses finish reproducing. This is the same mechanism by which other viruses, such as those that cause mumps or measles, are conquered. So why (must/can’t) we become immune to the flu, as we (can/may) to measles?

The answer lies in a flu virus’s amazing ability to change. Flu virus genes are made up of RNA, which lacks the proofreading mechanisms that reduce mutations in genes made of DNA. Therefore, flu RNA genes mutate rapidly: on average, 10 mutations will appear in every million newly synthesized viruses. Most single mutations do not change the properties of the viral antigens very much. Four or five mutations in the same virus, however, (may/must) alter the surface antigens enough that the immune system does not fully recognize the virus as the same old flu that was beaten off last year. Some of the memory cells do not recognize it at all, and the immune response produced by the rest of the memory cells does not work as well as it (could/should). The virus although slowed down somewhat, gets a foothold in the body and multiplies until a new set of immune cells recognizes the mutated antigens and starts up a new immune response. So you get the flu again this year.

Far more serious are the dramatically new flu viruses that occasionally appear, as in the epidemic of 1918, the Asian flu of 1957, and the Hong Kong flu of 1968. In these viruses, entirely new antigens seem to appear suddenly. The novel antigens are not just slight variations of the old set, but they have distinctive structures that the human immune system has never before encountered. Where do the genes that encode these new antigens come from? Believe it or not, they come from viruses that infect birds and pigs. The intestinal tracts of birds, especially ducks, (can/may) host viruses strikingly similar to human flu viruses, though infected birds suffer from no noticeable disease. The human flu viruses do not infect birds. But both human and bird viruses (can/might) infect pigs, so both viruses (must/can) in some cases simultaneously infect the same pig cell. Once in a great while (perhaps only three times during the twentieth century), new viruses that spring from a double-infected pig cell end up with a mixture of genes from human and bird viruses. Some of these hybrid viruses combine the worst genes (at least from our perspective) of each: from the human virus, the deadly new viruses pick up the genes needed to subvert human cellular metabolism to produce new viruses; from the bird virus, they pick up genes for new surface antigens. The hybrid viruses (can/could) move easily from pigs to humans, because pigs live near humans and, like us, pigs cough when they have the flu.

Have you ever wondered why flu strains are called “Asian” or “Hong Kong”? The reason is that Southeast Asia is usually the place where new strains crop up. Many farmers in Asia, especially in southern China, have “integrated” farms. Crops are grown to feed pigs and ducks, and the feces from the pigs and ducks are used to fertilize fish ponds. This is a very efficient farming practice, but, unfortunately, it also places ideal mixing vessels for flu viruses (pigs) in close proximity to humans and ducks.

If a human is infected by a hybrid virus, the immune system (must/can) start from scratch, selecting out entirely new lines of B cells and T cells to attack the intruder. But in the meantime, the virus multiplies so rapidly that many individuals die or become so weakened that they contract some other fatal disease. Other individuals recover, with immune systems now primed to resist any further assault from the new virus. In subsequent years, a few point mutations (can/might) allow a slightly altered strain of the new virus to infect millions of people, but with a partial immune response ready, few fatalities occur. Once again, for most of us, the flu becomes a routine annoyance. At least until the next time the improbable happens again.

II. Find in the text English equivalents to the following Russian words and word combinations:

• проносится по миру

• причиной гриппа являются

• внедряются в клетки дыхательных путей

• внешняя поверхность

• распознаются иммунной системой

• удивительная способность

• отсутствуют механизмы исправления ошибок (при копировании матрицы)

• получает некую точку опоры в теле

• совершенно новые вирусы гриппа

• никогда ранее не сталкивалась

• поразительно похожие

• по крайней мере, мы так полагаем

• необходимые для разрушения

• совершенно новые линии

• готовые теперь к отражению новых атак

• слегка измененный штамм

III. The essay states that the flu virus is different each year. If that is true, what good is it to get a “flu shot” each winter?

Render in English.

Определены место рождения и возраст вируса птичьего гриппа

Место происхождения вируса птичьего гриппа H5N1 - юго-восток Китая. Основной механизм его распространения - перевозка домашней птицы. Однако в некоторых случаях переносить заболевание могут и перелетные птицы. Эти выводы получены в результате анализа десятков тысяч генетических проб, взятых у птиц в течение полутора лет. Группа И Гуаня (Yi Guan) из Университета китайского города Шаньтоу (Shantou) совместно с коллегами из Гонконга проанализировала образцы, взятые у 13 тысяч перелетных птиц и 50 тысяч домашних птиц на рынках в юго-восточных провинциях Китая. Около 2% внешне здоровых домашних уток и гусей оказались носителями вируса H5N1. Среди кур вирус встречался гораздо реже, тем не менее, практически каждый месяц исследователи выявляли зараженных кур. Забор образцов производился с января 2004 по июнь 2005 года, когда китайское правительство запретило независимым исследователям брать анализы у птиц. Хотя новые образцы поступать перестали, собранного материала оказалось достаточно, чтобы сделать целый ряд интересных выводов. Геном вируса в китайских провинциях Гуандун (Guangdong), Хунань (Hunan) и Юньнань (Yunnan) демонстрирует наибольшие генетические вариации по сравнению с другими территориями. Разные версии вируса образуют географические кластеры. Однако все версии эволюционно восходят к гуандунскому вирусу 1996 года. Все это говорит о том, что в данном районе вирус появился раньше, чем в других, и не менее 10 лет назад. В то же время, само наличие географических кластеров с генетически различными линиями вируса указывает на то, что инфекция редко переносится птицами, совершающими дальние перелеты. Большая часть заражений происходит при перевозке домашней птицы. Тем не менее, в некоторых случаях переносчиками заболевания могут быть и перелетные птицы. Например, в январе-марте 2005 года в образцах, взятых у диких уток на озере Поян (Poyang) в провинции Цзянси (Tzyansi), граничащей с Гуандуном и Хунанем, была найдена особая форма одного из генов. Позднее, при вспышке эпидемии в Турции, у вируса обнаружился такой же ген, что говорит о практически прямом переносе вируса на значительные расстояния.