Immune Responses

Question 1

Define antigen?

Answer 1

A large complex molecule i.e. proteins, polysaccharides and glycoproteins which are usually on a cell membrane. Those found on non-self cells generally create an immune response.

Question 2

Define lymphocytes?

Answer 2

Lymphocytes are another type of white blood cell, they are involved in the specific immune response. There are two types T Lymphocytes and B Lymphocytes.

Question 3

What are T Lymphocytes?

Answer 3

They mature in the thymus gland and respond to the body’s own cells infected by a pathogen, diseased or transplanted.

Question 4

What a B Lymphocytes?

Answer 4

They mature in the bone marrow and produce antibodies which respond to foreign material in body fluids e.g. bacteria

Question 5

What must lymphocytes be able to do to defend the body from invasion by foreign materials?

Answer 5

Lymphocytes must be able to distinguish the body’s own cells and chemicals (self) from those that are foreign (non-self). If they could not do this the lymphocytes would destroy the organisms own tissue. They are not produced in a response to an infection but already exist (10 million types). As there are so many it’s likely when a pathogen gets into the body, one of the, will have a protein on its surface which is complementary to one of the pathogens proteins. With so many different lymphocytes there are very few of each type. When an infection occurs the one type already present that has the complementary protein is them stimulated to build up its numbers to a level where it can be effective. This explains the time lag between exposure and response.

Question 6

What happens when a pathogen infects the body?

Answer 6

A range of defence mechanism attempt to prevent it causing disease. There are two types of defence mechanisms specific and non-specific.

Question 7

What is the specific response?

Answer 7

It is a slower and specific response and is both the humoral response and the cell-mediated response. These are able to distinguish between thousands of different pathogens. If these defence mechanisms are successful it is likely that the body will be able to prevent a second infection by the same pathogen, this is known as immunity.

Question 8

What the non specific response?

Answer 8

It is immediate response to anything, it’s both physical barriers and phagocytosis. These are unable to distinguish between different pathogens, they respond to them all in the same response.

Question 9

Define pathogens?

Answer 9

Disease causing microorganisms they will always have non-self antigens.

Question 10

What are physical barriers?

Answer 10

• hydrochloric acid in the stomach
• a protective covering e.g. skin
• epithelia covered in mucus

Question 11

What is phagocytosis?

Answer 11

Specialised white blood cells called phagocytes recognise and engulf pathogens such as bacteria in the blood and tissues.

Question 12

The stages of phagocytosis?

Answer 12

Firstly the phagocyte is attracted to the pathogen by chemo attractants, so it knows it’s non-self. It moves towards the pathogen along a concentration gradient.
Secondly the phagocyte binds to the pathogen.
Next the lysosomes within the phagocyte migrates towards the phagosome formed by engulfing the bacterium.
Next the lysosomes release their lytic enzymes into the phagosome where the break down the bacterium.
Next the broken down products of the bacterium are absorbed by the phagocyte. It can also be released by exocytosis. After destroying the pathogen there is an antigen from the pathogen.

Question 13

What does phagocytosis cause?

Answer 13

It causes inflammation at the site of infection. The swollen area contain dead pathogens and phagocytes. Inflammation is caused by the release of histamine causing dilation of the blood vessels which speeds up the delivery of phagocytes to infection sites.

Question 14

What do T Lymphocytes respond to?

Answer 14

T Lymphocytes respond to body cells which have unusual (non-self) antigens on their surface. There are 4 types of cells that present antigens; cancer cells, transplant cells, cells invaded by a virus and phagocytes that have engulfed and broken down a pathogen.

Question 15

The cell mediated response?

Answer 15

Pathogens invade body cells or are taken in by phagocytes. The phagocyte places antigens from the pathogen on its cell surface membrane. Receptors on certain T-helper cells fit exactly onto these antigen. This activates other T cells to divide rapidly by mitosis forming clones, killer T cells.

Question 16

What do killer T cells do?

Answer 16

• produce memory cells which circulate in the blood and tissue fluid and respond to a future infection by the same pathogen
• stimulates B cells to divide ( the humoral response)
• stimulates phagocytosis by phagocytes
• kills infected cells by making holes in their cell surface membrane.

Question 17

The humoral response?

Answer 17

B lymphocytes produce proteins called antibodies which are soluble in the blood plasma and tissue guild. Each antibody responds to one specific antigen. Each B lymphocyte produces one specific antibody. The antibodies bring about destruction of the foreign antigen by agglutination, inactivation and facilitating phagocytosis. Surface antigens of the invading pathogens are taken up by inactive B cells floating in the blood, B cells process the antigens and present them on their surface. T-helper cell help to activate them, B cells are now activated to divide by mitosis to produce clones called plasma cells. Other B cells develop into memory cells. Plasma cells produce antibodies that exactly fit the antigens on the pathogens surface. Antibodies attach to antigens on the pathogen and destroy them by a primary response e.g. agglutination.

Question 18

Define agglutination?

Answer 18

Agglutination cause bacteria to form clumps which are more easily destroyed by white blood cells.

Question 19

What is inactivation?

Answer 19

Where bacterial toxins are neutralised.

Question 20

What are plasma cells?

Answer 20

They secrete antibodies into the blood stream.

Question 21

What are memory cells?

Answer 21

They don’t produce antibodies but remain in the blood stream for long periods of time and mount a secondary immune response, if the same microorganisms re-infect the body.

Question 22

What is the primary immune response?

Answer 22

The primary immune response destroys the microorganisms and create memory cells. These cells are immunological memory cells and recognise the same antigen if it enters the body again this causes a secondary immune response.

Question 23

What is a secondary immune response?

Answer 23

The secondary immune response is quicker and more effective as the memory cells are present in large numbers. Memory B Cells form antibody secreting plasma cells in greater numbers and quicker to produce antibodies in higher concentrations. Memory T cells form killer T cells in greater numbers and quicker which bind with and destroy more infected cells.

Question 24

The humoral response simplified?

Answer 24

Main cells involved? B lymphocytes
Where do the cells develop? bone marrow
Does it have antibodies? Yes
How are pathogens identified? Antigens free in blood
How are pathogens killed? Antibodies
How do cells divide once stimulated? Plasma and memory cells

Question 25

The cell mediated response simplified?

Answer 25

Main cells involved? T lymphocytes
Where do the cells develop? Thymus Gland
Does it have antibodies? No
How are pathogens identified? Antigens presented on cell membrane
How are pathogens killed? Killer T cells
How do cells divide once stimulated? Killer, helper and memory T cells

Question 26

Define passive immunity?

Answer 26

Antibodies are not produced due to interaction with a pathogen, immunity is acquired immediately. However, no memory cells are produced and once plasma cells are broken down, immunity is lost e.g. Mother to foetus.

Question 27

Define active immunity?

Answer 27

Immunity is acquired from contact with the pathogen, immunity is achieved but it takes time, there are two types natural and artificial.

Question 28

What is active natural immunity?

Answer 28

From an infection with a pathogen, a secondary response.

Question 29

What is active artificial immunity?

Answer 29

The basis of vaccinations.

Question 30

Define herd immunity?

Answer 30

Since vaccines reduce the chances of getting a disease those who are not vaccinated also have a reduced risk of catching the disease as there are fewer animals to catch it from.