Chapter 5: Cell Recognition And Immune Response

Question 1

How can the body determine self and non-self cells?

Answer 1

Each cell has specific molecules on its surface which are of most types. They are mostly proteins with enormous variety and highly specific tertiary structure.

Question 2

What are types of non self cells?

Answer 2

• pathogens
• cells from other organisms of the same species
• toxins produced by certain pathogens
• abnormal body cells

Question 3

How could the immune system be destructive?

Answer 3

Cells in humans given by tissue or organ transplants could be killed
To minimise the effect, transplants are usually given by close relatives to minimise rejection

Question 4

What do phagocytes do?

Answer 4

Phagocytes ingest and destroy pathogens by phagocytosis

Question 5

How do phagocytes carry out the process of phagocytosis?

Answer 5

1. The phagocyte is attracted to the pathogen by chemical products of the pathogen along a concentration gradient
2. The phagocyte has several receptors on its cell surface membrane that attach to chemicals on the surface of the pathogen
3. Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium
4. The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium.
5. The hydrolysis products of the bacterium are absorbed by the phagocyte

Question 6

What is an antigen?

Answer 6

An antigen is any part of an organism or substance that is recognised as non self - proteins that are part of the cell membrane.

Question 7

What are B lymphocytes?

Answer 7

They are made in the bone marrow. It is associated with humoral immunity involving antibodies that are present in body fluids.

Question 8

What are T lymphocytes?

Answer 8

They are made in the thymus gland. They are associated with cell mediated immunity involving body cells.

Question 9

What are cells that display foreign antigens on their surface called?

Answer 9

Antigen presenting cells

Question 10

How do T lymphocytes respond to an infection by a pathogen?

Answer 10

1. Phagocytes engulf pathogen and then present its antigens on its surface
2. Receptors on the T helper cells are specific and fit exactly on to these antigens
3. This activates the T cell to divide rapidly by mitosis to form clones with the same receptors
4. The cloned cells turn into:
   
   • memory cells for rapid response
   • stimulate phagocytes to engulf pathogens
   • stimulate B cells to divide and secrete their antibodies
   • activate cytotoxic T cells

Question 11

What is Immunity?

Answer 11

The body’s defences seem to be better prepared for a second infection of the same pathogen and can kill it before it causes harm

Question 12

How do cytotoxic T cells kill infected cells?

Answer 12

They produce a protein called perforin which makes holes in the cell surface membrane of the pathogen. This makes the walls freely permeable to substances (allowing water in and bursting the cell)

Question 13

Why are T cells most effective against viruses?

Answer 13

Viruses use body cells to replicate so by killing the body cells, the T cells prevent viruses from multiplying and infecting more cells

Question 14

What is the humoral response?

Answer 14

It involves antibodies which are soluble in blood and tissue fluid in the body

Question 15

What do B cells produce?

Answer 15

B cells produce antibodies and memory cells

The antibodies are specific to the antigen of the pathogen - they are complementary

Question 16

How do B cells work?

Answer 16

1. The antigen enters the B cell by endocytosis and get presented on the surface
2. The T helper cells bind to the processed antigens and stimulate the B cell so it can replicate by mitosis to form clones (clonal selection)
3. The cloned plasma cells secrete specific antibodies to destroy them

If a toxin is also released by a pathogen then B cells produce clones of another antibodies

Question 17

What are plasma cells and what type of response do they provide?

Answer 17

They secrete antibodies into the blood which destroy the antigens. They only survive a few days
They are part of the primary immune response

Question 18

What are memory cells and what response do they provide?

Answer 18

They circulate the body and its fluids so when the same antigen occurs again, they will divide rapidly and develop into plasma cells and more memory cells. They provide long term immunity and are part of the secondary immune response.

Question 19

What is the secondary response?

Answer 19

The antibodies are produced at a faster rate
The antibodies stay in the blood for a longer time
More antibodies are produced
Therefore they pathogen may be killed without any symptoms being felt

Question 20

What are antibodies made of and what are their structures?

Answer 20

Antibodies are made of polypeptide chains- two heavy and light chains. Each antibody has a specific binding site that fits the specific antigen to form an antigen-antibody complex. The binding site is different on different antibodies so it is called the variable region. The rest of the structure is called the constant region.
Binding site is specific due to specific 3D structure

Question 21

What is agglutination?

Answer 21

Antibodies clump bacterial cells together so the phagocytes can locate and ingest them easily.

Question 22

What are the two ways antibodies work?

Answer 22

• agglutination

- markers

Question 23

How are antibodies markers?

Answer 23

They serve as markers that stimulate phagocytes to engulf bacterial cells to which they are attached

Question 24

What are monoclonal antibodies?

Answer 24

An antibody specific to an antigen that has been isolated and cloned

Question 25

What is direct monoclonal antibody therapy?

Answer 25

Antibodies specific to antigens on cancer cells are given to patient. They attach to the surface of their cancer cells and block chemical signals to inhibit uncontrolled growth