Immunology

Question 1

What is immunity

Answer 1

When the body’s defences prepared for a second infection from the same pathogen and can repel it before it causes any harm

Question 2

Non specific mechanisms

Answer 2

Mechanisms that do not distinguish between one type of pathogen and another but respond to all of them in the same way these mechanisms isms act immediately and take two forms

A barrier to the entry of pathogens
Phagocytosis

Response is immediate and the same for all pathogens

Question 3

Specific mechanisms

Answer 3

Do distinguish between different pathogens. The responses are less rapid but provide long lasting immunity. The responses involve a type of white blood cell called a lymphocyte and take two forms

Cell-mediated responses involving T lymphocytes
Humoral responses involving B lymphocytes

Response is slower and specific to each pathogen

Question 4

What are lymphocytes and why is there a time lag

Answer 4

A type of white blood cell
Specific lymphocytes are not produced in response to an infection, but that they already exist. There’s so many different types that when a pathogen gets into the body one of these lymphocytes will have a protein on its surface that is complementary to one of the proteins of the pathogen. When an infection occurred the one type already present is stimulated to build up its numbers to a level where it can be effective. This explains why there’s a time lag between exposure to the pathogen and body’s defences bringing it under control.

Question 5

What is the first line of defence against disease

Answer 5

Physical or chemical barrier next line of defence is phagocytes and lymphocytes which are types of white blood cells

Examples

• a protective covering - the skin covers the body surface providing a physical barrier that most pathogens find hard to penetrate.
• epithelia covered in mucus - many epithelial layers produce mucus which acts as a further defence against invasion. In the lungs, pathogens stick to this mucus, which is then transported away by cilia, up the trachea to be swallowed into the stomach.
• hydrochloric acid in the stomach this provides such low pH that the enzymes of most pathogens are denatured therefore the organism is killed.

Question 6

What is an antigen

Answer 6

Usually a protein that protrudes from the cell surface membrane and is used in cell recognition . Antigens can be self or non self
They can generate an immune response
Usually found on the surface of cells including r body cells. Antigens that aren’t normally found in the body are called foreign antigens, it’s these antigens that the immune system usually responds to.
The presence of an antigen triggers the production of an antibody as part of the body’s defence system.

Question 7

What is a pathogen

Answer 7

Organisms that cause disease e.g bacteria, virus and fungi. All pathogens have antigens on their surface- these are identified as foreign by immune system cells, which then respond to destroy the pathogen.

Question 8

Abnormal body cells

Answer 8

Cancerous or pathogen- infected cells have abnormal antigens on their surface, which trigger an immune response.

Question 9

Toxins

Answer 9

These are poisons. They’re also molecules, not cells. Some toxins are produced by bacteria e.g clostridium botulinum releases a protein toxin that affects the nervous system, causing the symptoms of botulism. The immune system can respond to toxins as well as the pathogens that release them.
The toxin itself is an antigen it doesn’t have antigens on its surface.

Question 10

Receiving cells from other individuals of the same species

Answer 10

When you receive cells from another person, such as in an organ transplant or blood transfusion, those cells will have antigens that are different to your own( unless the donor is genetically identical to you). The foreign antigens trigger an immune response. This response leads to the rejection of transplanted organs if drugs aren’t taken to suppress the recipients immune system. For blood transfusions the most important antigens are the ABO blood group antigens- if the donated blood contains A or B antigens that aren’t recognised by the recipients immune system, they will generate an immune response.

Question 11

What is phagocytosis Why can’t large particles like bacteria cross the cell surface membrane

Answer 11

They’re to large to cross cell surface membranes by diffusion or active transport. Instead they have to be engulfed by cells in the form of vesicles formed form the cell surface membrane. This is phagocytosis

Question 12

What’s a phagocyte

Answer 12

A white blood cell

Question 13

What’s phagocytosis

Answer 13

A process where a phagocyte engulfs and digests a pathogen

Question 14

Where can phagocytes be found

Answer 14

Blood
In the alveoli
Lymph nodes
In infected tissue

Question 15

What triggers a phagocyte to destroy a pathogen

Answer 15

Chemo attractant

Question 16

What’s a phagosome

Answer 16

Is a vesicle- produced by Golgi , housing an engulfed pathogen that is formed when the cell surface membrane that invaginate sand engulfs

Question 17

Describe the whole process of phagocytosis

Answer 17

1 Chemical products of the pathogen act as attractants, causing phagocytes to move towards the pathogen along a concentration gradient.
2 A phagocyte recognises the foreign antigens on a pathogen
3 Phagocytes attach themselves to the surface of the pathogen
4 the cytoplasm of the phagocyte moves round the pathogen engulfing it.
5 the pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte. Or say they engulf the pathogen to form a vesicle, known as a phagosome.
6 Lysosomes move towards the vesicle and fuse with it . Or say the lysosome fuses with the phagocytic vacuole.
7 lysozymes break down the pathogen. The process is the same as that for the digestion of food in the intestine, namely hydrolysis of larger insoluble food molecules into soluble ones.
8 the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
9 the phagocyte then presents the pathogens antigens- it sticks the antigens on its surface to activate other immune system cells. The phagocyte is acting as an antigen presenting cell.
10 phagocytosis causes inflammation at the site of infection this swollen area contains dead pathogens and phagocytes.

Question 18

What are B lymphocytes

Answer 18

Associated with humoral immunity. Produces antibodies mature in the bone marrow. Responds to foreign material outside body cells
Respond to bacteria and viruses.

Question 19

T lymphocyte

Answer 19

Associated with cell mediated immunity
Mature in the Thymus gland
Responds to foreign material inside body cells
Responds to own cells altered by viruses or cancer and to transplanted tissues.

Question 20

How can a T cell distinguish normal cells from invader cells

Answer 20

Phagocytes that have engulfed and broken down a pathogen present some of the pathogens antigens on their own cell surface membrane
Body cells invaded by a virus also manage to present some of the viral antigens on their own cell surface membrane as a sign of distress
Cancer cells likewise present antigens on their cell surface membranes

Question 21

Why is it called cell mediated immunity

Answer 21

T cells will only respond to antigens that are attached to a body cell not cells within body fluids

Question 22

What do T cells actually do

Answer 22

Has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes. This activated the T cell.
Helper T cells release chemical signals that activate and stimulate phagocytes and cytotoxic T cells which kill abnormal and foreign cells.

Question 23

Cell mediated immunity/ cellular response

Answer 23

Identified with killing infected body cells to free viruses for destruction by antibodies and phagocytosis .
- also works against cancerous/tumour cells and to expose intracellular bacteria hiding between body cells.
Model answer
1 a phagocyte or macrophage engulfs and digests a virus placing viral antigens on its cell surface membrane , its now an antigen presenting cell
2 a body cell becomes infected by the same virus and some viral antigens are placed on its cell surface membrane this body cell is also an antigen presenting cell.
3 a helper T cell specific to that viral antigen binds to the antigen presenting phagocyte.
4 the phagocyte now releases a chemical (called interleukin 1) that activates/stimulates/ triggers the helper T cell.
5 the helper T cell now releases a chemical (interleukin 2) that enters the honours (blood, tissue fluid, lymph) and activates a cytotoxic T cell, also specific to the viral antigen.
6 the cytotoxic T cell divides by mitosis to form many clones some of which travel to the site of infection.
7 each activated cytotoxic T cell binds to an infected cell and releases a chemical perforin that puts holes into the cells membrane and an influx of water bursts the cell, killing it.
8 freed viruses can now be dealt with by the humoral response and phagocytosis.

Question 24

Four things that result from the response of T lymphocytes

Answer 24

• Produces memory cells that circulate in the blood and tissue fluid in readiness to respond to a future infection by the same pathogen.
• stimulates B cells to divide
• stimulates phagocytosis by phagocytes
• kills infected cells by making holes in their cell surface membrane

Question 25

Humoral immunity

Answer 25

Involves antibodies and antibodies are insoluble in blood and tissue fluid of the body
This involves B cells

Question 26

The humoral response / antibody mediated immunity

Answer 26

Involves B cells / lymphocytes
Identified with specific antibody production to immobilise specific pathogens of any type

1 A phagocyte engulfs and digests a pathogen placing pathogenic antigens on its cell surface membrane it’s now an antigen presenting cell
2 A B cell also encounters and engulfs the same type of pathogen presenting antigens bound to specific antibodies that protrude from its cell surface membrane it is now an antigen presenting cell
3 a helper T cell specific to that pathogenic antigen binds to the antigen presenting phagocyte and becomes activated
4 the helper T cell detached and seeks out the specific B cell that can make the appropriate antibodies
5 when encountering the B cell the helper T cell binds to it and activates it.
6 the B cell divides by mitosis to form many clones.
7 some clones will become memory cells that will be used in any possible future infections by the same pathogen.
8 others become plasma cells each of these immediately produces thousands of specific anibodies to enter the body’s humours
9 these antibodies will bind to and immobilise the specific antigen
10the antibodies mark out the pathogen for destruction by a phagocyte

Question 27

What are B cells

Answer 27

Type of white blood cell they’re covered with antibodies - proteins that bind to antigens to form an antigen-antibody complex. Each B cell has a different shaped antibody on its membrane so different ones bind to different shaped antigens

When the antibody on the surface of a B cell meets a complementary shaped antigen it binds to it. This together with substances released from helper T cells activated the B cell. This process is called colonial selection. The activated B cell divides into plasma cells.

The clones of identical B cells produce an antibody that is specific to the foreign antigen.

Question 28

Primary immune response

Answer 28

When an antigen enters the body for the first time it activates the immune system. Called the primary response. The primary response is slow because there aren’t many B cells that can make the antibody needed to bind to it. Eventually the body will produce enough of the right antibody to overcome the infection. Meanwhile the infected person will show symptoms of the disease.

After being exposed to an antigen both T and B cells produce memory cells. These memory cells remain in the body for a long time. Memory T cells remember the specific antigen and will recognise it for a second time round. Memory B cells record the specific