chapter 12 p4

Question 1

What is Cell-mediated immunity:

Answer 1

In cell-mediated immunity, T lymphocytes respond to the cells of an organism that have been changed in some way, for example by a virus infection, by antigen processing or by mutation (for example cancer cells) and to cells from transplanted tissue.
The cell-mediated response is particularly important against viruses and early cancers.

Question 2

Steps in Cell-mediated immunity:

Answer 2

• In the non-specific defence system, macrophages engulf and digest pathogens in phagocytosis.
  They process the antigens from the surface of the pathogen to form antigen-presenting cells (APCs).
• The receptors on some of the T helper cells fit the antigens.
  These T helper cells become activated and produce interleukins, which stimulate more T cells to divide rapidly by mitosis.
  They form clones of identical activated T helper cells that all carry the right antigen to bind to a particular pathogen.
• The cloned T cells may:
  develop into T memory cells, which give a rapid response if this pathogen invades the body again
  produce interleukins that stimulate phagocytosis
  produce interleukins that stimulate B cells to divide
  stimulate the development of a clone of T killer cells that are specific for the presented antigen and then destroy infected cells.

Question 3

Answer 3

Question 4

Humoral immunity:

Answer 4

• In humoral immunity the body responds to antigens found outside the cells, for example bacteria and fungi, and to APCs.
• The humoral immune system produces antibodies that are soluble in the blood and tissue fluid and are not attached to cells.
• B lymphocytes have antibodies on their cell-surface membrane (immunoglobulin M or IgM) and there are millions of different types of B lymphocytes, each with different antibodies.
• When a pathogen enters the body it will carry specific antigens, or produce toxins that act as antigens.
• A B cell with the complementary antibodies will bind to the antigens on the pathogen, or to the free antigens.
• The B cell engulfs and processes the antigens to become an APC

Question 5

Steps in Humoral immunity:

Answer 5

Activated T helper cells bind to the B cell APC.
This is clonal selection - the point at which the B cell with the correct antibody to overcome a particular antigen is selected for cloning.

Interleukins produced by the activated T helper cells activate the B cells.

The activated B cell divides by mitosis to give clones of plasma cells and B memory cells - This is clonal expansion.

Question 6

the primary immune response in humoral immunity

Answer 6

Cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to the antigens and disable them, or act as opsonins or agglutinins.
it can take days or even weeks to become fully effective against a particular pathogen.
This is why we get ill - the symptoms are the result of the way our body reacts when the pathogens are dividing freely, before the primary immune response is fully operational.

Question 7

the secondary immune response in humoral immunity

Answer 7

Some cloned B cells develop into B memory cells.
If the body is infected by the same pathogen again, the B memory cells divide rapidly to form plasma cell clones.
These produce the right antibody and wipe out the pathogen very quickly, before it can cause the symptoms of disease.

Question 8

Answer 8

Question 9

Autoimmune diseases:

Answer 9

• when the immune system stops recognising ‘self’ cells and starts to attack healthy body tissue.
• There appears to be a genetic tendency in some families, sometimes the immune system responds abnormally to a mild pathogen or normal body microorganisms and in some cases the T regulator cells do not work effectively.
• There are around 80 different autoimmune diseases that can cause chronic inflammation or the complete breakdown and destruction of healthy tissue.
• Immunosuppressant drugs, which prevent the immune system working, may be used as treatments but they deprive the body of its natural defences against communicable diseases.

Question 10

Answer 10

Question 11

Answer 11

Question 12

Chapter 12.7 - Preventing and treating disease

Answer 12

Non-communicable diseases cannot be passed from one person to another.
They include heart disease, most types of cancer and many diseases of the nervous, endocrine and digestive systems.
Communicable diseases are caused by pathogens and can be passed from person to person.
When you come into contact with a foreign antigen, you need some form of immunity to prevent you getting the disease.
There are several ways of achieving this immunity.

Question 13

Natural immunity:

Answer 13

forms of immunity occur naturally in the body:

When you meet a pathogen for the first time

The immune system of a new-born baby is not mature

Question 14

When you meet a pathogen for the first time

Answer 14

When you meet a pathogen for the first time, your immune system is activated and antibodies are formed, which results in the destruction of the antigen
The immune system produces T and B memory cells so if you meet a pathogen for a second time, your immune system recognises the antigens and can immediately destroy the pathogen, before it causes disease symptoms.
This is known as natural active immunity. It is known as active because the body has itself acted to produce antibodies and/or memory cells.

Question 15

The immune system of a new-born baby is not mature

Answer 15

• and it cannot make antibodies for the first couple of months.
• A system has evolved to protect the baby for those first few months of life.
• Some antibodies cross the placenta from the mother to her fetus while the baby is in the uterus, so it has some immunity to disease at birth.
• The first milk a mammalian mother makes is called colostrum, which is very high in antibodies.
• The infant gut allows these glycoproteins to pass into the bloodstream without being digested.
• So within a few days of birth, a breast-fed baby will have the same level of antibody protection against disease as the mother.
• This is natural passive immunity and it lasts until the immune system of the baby begins to make its own antibodies.
• The antibodies the baby receives from the mother are likely to be relevant to pathogens in its environment, where the mother acquired them.

Question 16

Artificial immunity:

Answer 16

Some diseases can kill people before their immune system makes the antibodies they need.
Medical science can give us immunity to some of these life-threatening diseases without any contact with live pathogens.

Question 17

Artificial passive immunity:

Answer 17

For certain potentially fatal diseases, antibodies are formed in one individual (often an animal), extracted and then injected into the bloodstream of another individual.
This artificial passive immunity gives temporary immunity - it doesn’t last long but it can be lifesaving.
For example, tetanus is caused by a toxin released by the bacterium Clostridium tetani, found in the soil and animal faeces.
It causes the muscles to go into spasm so you cannot swallow or breathe.
People who might be infected with tetanus (for example after a contaminated cut) will be injected with tetanus antibodies extracted from the blood of horses, preventing the development of the disease but not providing long-term immunity.
Rabies is another fatal disease that is treated with a series of injections that give artificial passive immunity.

Question 18

Artificial active immunity

Answer 18

the principles of vaccination In artificial active immunity the immune system of the body is stimulated to make its own antibodies to a safe form of an antigen (a vaccine), which is injected into the bloodstream (vaccination).
The antigen is not usually the normal live pathogen, as this could cause the disease and have fatal results.

Question 19

The main steps in artificial active immunity are as follows:

Answer 19

1. The pathogen is made safe in one of a number of ways so that the antigens are intact but there is no risk of infection.
   Vaccines contain:
2. Small amounts of the safe antigen, known as the vaccine, are injected into the blood.
3. The primary immune response is triggered by the foreign antigens and your body produces antibodies and memory cells as if you were infected with a live pathogen.
4. If you come into contact with a live pathogen, the secondary immune response is triggered and you destroy the pathogen rapidly before you suffer symptoms of the disease.
5. The artificial active immunity provided by vaccines may last a year, a few years or a lifetime.
   Sometimes boosters (repeat vaccinations) are needed to increase the time you are immune to a disease.

Question 20

Vaccines contain:

Answer 20

• killed or inactivated bacteria and viruses, for example. whooping cough (pertussis)
• attenuated (weakened) strains of live bacteria or viruses, for example, rubella, BCG against TB, polio (vaccine taken orally)
• toxin molecules that have been altered and detoxified, for example, diphtheria, tetanus
• isolated antigens extracted from the pathogen, for example, the influenza vaccine
• genetically engineered antigens, for example, the hepatitis B vaccine.

Question 21

Vaccines and the prevention of epidemics:

Answer 21

• Vaccines are used to give long-term immunity to many diseases
• However, they are also used to help prevent epidemics.
• An epidemic is when a communicable disease spreads rapidly to a lot of people at a local or national level.
• A pandemic is when the same disease spreads rapidly across a number of countries and continents.
• At the beginning of an epidemic, mass vaccination can prevent the spread of the pathogen into the wider population.
• When vaccines are being deployed to prevent epidemics, they often have to be changed regularly to remain effective.
• When a significant number of people in the population have been vaccinated, this gives protection to those who do not have immunity.
• This is known as herd immunity, as there is minimal opportunity for an outbreak to occur.

Question 22

Case Study: Influenza: p1

Answer 22

Flu is a disease that has caused epidemics at intervals throughout history.
The virus that causes strain A influenza mutates regularly, so the antigens on the surface change too.
Some forms of this virus can cross the species barrier from animals such as birds or pigs to people.
Although people develop resistance to one strain of flu, the next year the antigens on the surface of the virus may have changed so much that the immune system does not recognise it and many of the same people become ill again.
Every year in the UK older people and anyone who has a compromised immune system are given a flu vaccine.

Question 23

Case Study: Influenza: p2

Answer 23

Every year the mixture of flu antigens in the vaccine is different, reflecting the forms of the virus that the World Health Organisation (WHO) predicts will be most common and most likely to cause serious disease.
If a flu epidemic begins, more people are vaccinated to control infection rates.
Because people travel freely and frequently, an epidemic can spread rapidly from one country to another.
People across the world need to be vaccinated to stop the spread of disease and stock piles of vaccines are in place in case this becomes necessary.
SARS was a new flu-like disease that appeared in 2002 and spread from birds to people. It spread rapidly across countries as people travelled around.
However, in spite of a lack of vaccine, careful management of cases by isolation meant the outbreak was contained and quickly closed down with relatively few deaths (Figure 3).

Question 24

Some communicable diseases that cause problems at a global level cannot yet be prevented by vaccination. Examples include:

Answer 24

malaria
HIV, the human immunodeficiency virus that causes AIDS.

So far scientists have been unable to develop a vaccine for these diseases, which between them affect millions of people globally every year.

Question 25

malaria

Answer 25

Plasmodium, the protoctist that causes malaria. It is very evasive - it spends time inside the erythrocytes so it is protected by self antigens from the immune system, and within an infected individual its antigens reshuffle

Question 26

HIV, the human immunodeficiency virus that causes AIDS.

Answer 26

It enters the macrophages and T helper cells, so it has disabled the immune system itself.

Question 27

Medicines and the management of disease:

Answer 27

Medicines can be used to treat communicable and non-communicable diseases. Medicines can be used to treat symptoms and cure them, making people feel better. Common medicines include painkillers, anti-inflammatories and anti-acid medicines (which reduce indigestion). Medicines that cure people include chemotherapy against some cancers, antibiotics that kill bacteria, and antifungals that kill fungal pathogens.

Question 28

Sources of medicines: p1

Answer 28

Penicillin was the first widely used, effective, safe antibiotic capable of curing bacterial diseases. It comes from a mould, Penicillium chrysogenum, famously discovered by Alexander Fleming in 1928, when he found it growing on his Staphylococcus spp. cultures. Fleming saw what the mould did to his bacteria but could not extract enough to test its potential. It needed Howard Florey and Ernst Chain to develop an industrial process for making the new drug, which has since saved millions of lives around the world. The medicines we use today come from a wide range of sources. Scientists design drugs using complex computer programmes.

Question 29

Sources of medicines: p2

Answer 29

They can build up 3-dimensional models of key molecules in the body, and of pathogens and their antigen systems. This allows models of potential drug molecules to be built up which are targeted at particular areas of a pathogen. Computers are also used to search through enormous libraries of chemicals, to isolate any with a potentially useful action against a specific group of feature of a pathogen, or against the mutated cells in a cancer. Analysis of the genomes of pathogens and genes which have been linked to cancer enable scientists to target their novel drugs to attack any vulnerabilities. However, many of the drugs most commonly used in medicine are still either derived from, or based on, bioactive compounds discovered in plants, microorganisms or other forms of life. Table 2 lists some examples.

Question 30

Answer 30