Cell recognition and the immune system

Question 1

Describe the principle of cell recognition

Answer 1

-In order to defend an organism during invasion by foreign material, lymphocytes must be able to distinguish between the bodys own cells and molecules ( self cells) and ones that are foreign (non self cells)
-All cells have specific molecules on its surface used to identify it, including proteins
- These proteins have enormous variety and a highly specific tertiary structure
- These can identify pathogens, toxins, abnormal body cells and cells from other organisms of the same species

Question 2

How does the mechanism of cell recognition impact those who have had tissue or organ implants?

Answer 2

-Immune system will recognise the transplant as non self even though they have come from an organism of the same species
- It therefore attempts to destroy the transplant
- Doctors therefore match a transplant as close to a recipent as possible
- Immnosupressant drugs are also administered

Question 3

What is a non specific defence mechanism give e.g

Answer 3

• Response is immediate and the same for all pathogens e.g physical barriers (skin) or phagocytosis

Question 4

What is a specific defence mechanism give e.g

Answer 4

• Response is slower and different for all pathogens e.g a cell mediated response ( T lymphocytes) or a humoural response ( B lymphocytes)

Question 5

Why is there a time lag between exposure to the pathogen and the bodys defences bringing it under control?

Answer 5

• When the infection occurs, the one type of lymphocyte which has complementary proteins to the pathogen present is stimulated to divide to build up its number to a level of which it can be effective in destroying the pathogen

Question 6

Describe the process of phagocytosis

Answer 6

Chemical products of pathogens, or dead, abnormal cells act as attractants , causing phagocytes to move towards the pathogens
Phagocytes have several receptors on their cell surface membrane that recognise, and attach to the chemicals on the surface of the pathogen
They engulf the pathogen to form a vesicle called a phagosome
Lysosomes move towards the vesicle and fuse with it
Enzymes in the lysosomes called lysozymes destory the ingested bacteria by hydrolysis of cell walls
The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte

Question 7

Define immunity

Answer 7

The ability of an organism to resist infection by protecting against disease causing micro-organisms or their toxins that invade their bodies, involves the recognition of antigens

Question 8

Define antigen

Answer 8

Any part of an organism or substance that is recognised as non self by the immune system and stimulates an immune response, triggers an antibody

Question 9

Give examples of antigens

Answer 9

Usually proteins that are part of the cell surface membranes or cell walls of invading cells such as micororganisms or abnormal body cells such as cancer cells

Question 10

What is a lymphocyte?

Answer 10

One type of white blood cell which are produced by stem cells in the bone marrow

Question 11

What is a B lymphocyte ( B cell)?

Answer 11

They mature in the bone marrow
Associated with the humoural immunity( antibodys present in bodily fluids e.g blood plasma)

Question 12

What is a T lymphocyte ( T cell)?

Answer 12

Mature in the thymus gland
Associated with cell-mediated immunity

Question 13

How are T lymphocytes able to distinguish between invader cells and self cells?

Answer 13

• Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogens antigens on their own cell surface membrane
• Body cells infected by a virus present some of the viral antigens on their own cell surface membrane
• Transplanted cells from organisms of the same species present different antigens on their cell surface membrane due to a difference in genetic material
  -Cancer cells are different from normal body cells and present antigens on their cell surface membranes

Question 14

What is an antigen presenting cell?

Answer 14

Cells that present forigen antigens on their surface

Question 15

Describe the process of the cellular 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 a specific helper t cell fit exactly onto these antigens
This attachment activates the T cell to divide rapildy by mitosis and form a clone of genetically identical cells
The cloned T cells have functions ( diff flashcard)

Question 16

What do the clones T cells do in the cellular response?

Answer 16

-Develop into memory cells that enable a rapid response to future infections by the same pathogen
-Stimulates phagocytes to engulf pathogens by phagocytosis
-Stimulate B cells to divide and secrete their antibody
-Activate cytotoxic T cells

Question 17

Describe the function of cytotoxic T cells

Answer 17

-Kills abnormal cells and body cells that are infected by pathogens
-Does this by producing a protein called perforin that makes holes in the cell surface membrane
-Holes mean cell membrane becomes freely permeable and cells die as a result

Question 18

Explain the role of B cells in humoural immunity

Answer 18

-Each B cell produces a specific antibody which responds to one specific antigen
- When an antigen ( foriegn cell,toxin,damaged/ abnormal cell) enters blood or tissue fluid, there will be a B cell which has a complementary antibody to the antigen on its surface
- The antibody therefore attaches to the complementary antigen
- The antigen then enters the B cell by endocytosis and gets processed ( presented on the surface)
- TH cells bind to these processed antigens and stimulate this B cell to divide by mitosis to form a clone of identical B cells all of which produce the antibody that is specific to the foriegn antigen
This is clonal selection

Question 19

During clonal selection, which are the different types of monoclonal antibodies that can be produced?

Answer 19

Plasma cells- secrete antibodies into blood plasma, only survive for a few days but many are made, these destroy antigens
Plasma cells are responsible for the immediate defence system
Memory cells- These live for decades, dont produce antibodies directly, but they circulate in the blood and tissue fluid. When they encounter the sqme antigen at a later date, divide rapidly and produce more plasma cells and more memory cells. Plasma cells made from this then produce the antibodies needed to destroy the pathogen
Inc quantity of antibodies is secreted at a faster rate than the primary immune response, ensures a new infection is destroyed before it can cause any more harm

Question 20

Define antibody

Answer 20

-Antibodies are proteins with specific binding sites synthesised by B cells

Question 21

Describe the structure of antibodies

Answer 21

-Made up of 4 polypeptide chains
- Chains of one pair are long and called heavy chains, chains of the other pair are short and called light chains
- Specific binding site which attaches to a specific antigen
- Forms antigen antibody complexes
-Binding site is variable, has a sequence of amino acids forming a specific 3d shape
- Rest of the antibody is the constant region, binds to receptors on b cells

Question 22

How does the antibody lead to the destruction of a bacterial cell ( agglunation)

Answer 22

• They prepare the antigen for destruction by clumping bacteria cells together
• This makes it easier for phagocytes to locate them as they are less spread out within the body

Question 23

How does an antibody lead to the destruction of a bacterial cell by markers?

Answer 23

-They serve as markers which stimulate phagocytes to engulf the bacterial cells when they are attached

Question 24

How are monoclonal antibodies used in targeting specific cell types by attaching medication to an antibody? Etc cancer antigens

Answer 24

-Monoclonal antibodies are produced which are specific to antigens on cancer cells
- These antibodies are given to a patient and attach themselves to receptors on cancer cells
- They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrolled growth

Question 25

Describe the advantages of direct monoclonal antibody therapy

Answer 25

-Since the antibodies are not toxic and highly specific, they lead to fewer side effects than other forms of therapy

Question 26

Describe the principle and advantages of indirect monoclonal antibody therapy

Answer 26

-Involves attach a radioactive or cytotoxic drug to the monoclonal antibody. When the antibody attaches to the cancer cells it kills them -They can be used in smaller doses which makes them alot cheaper and reduces side effects which the drug may have

Question 27

Describe ethical issues of using monoclonal antibodies

Answer 27

-Producing them involves the use of mice. These mice are used to produce both antibodies and tumour cells, this means cancer is induced by the scientists into the rats, people have reservations of using the mice in this way - Although they have been used to treat a number of diseases, including cancer and diabetes saving lives, people have died associated with their use in treatment of scleorosis, shows need for informed consent - During research and testing the use of new monoclonal antibodies, voulunteers have experienced organ failures and complications causing controversy

Question 28

Describe the principle of passive immunity

Answer 28

-Produced by the introduction of antibodies from an outside source into an individual -No direct contact with the pathogen or its antigen is needed to induce immunity - As the antibodies are not being produced by the organism itself, antibodies are not replaced when broken down, and no memory cells are produced

Question 29

Describe the principle of active immunity

Answer 29

-When the production of the organisms own antibodies from its immune system is stimulated - Direct contact with the pathogen or its antigen is needed - Has two forms, natural active immunity and artificial active immunity

Question 30

Describe what natural active immunity is

Answer 30

- Results from an individual becoming infected with a disease under normal circumstances - Body produces its own antibody and continues to do so for many years

Question 31

Describe what artificial active immunity is

Answer 31

-Forms the basis of vaccination -Involves inducing an immune response in an individual without them suffering symptoms of the disease

Question 32

Describe how a vaccine works

Answer 32

-Introduction of the appropriate disease antigens into the body either by injection or by mouth - Stimulates an immune response against a specific disease -Contains one or more types of antigen from the pathogen - Response is slight as only a small amount of an antigen has been introduced -Memory cells are produced which stay in the blood and allow a greater more immediate response produced upon re infection, infection is overcome before any harm is done

Question 33

Describe features of a successful vaccination programme

Answer 33

- A suitable vaccine must be economically available in sufficient quantities to immunise most of the population - Few side effects to prevent discouragement from getting vaccinated - Means of producing storing and transporting the vaccine must be available - Must be means of administering the vaccine properly at an appropriate time, involves training staff with needed skills -Must be possible to vaccinate the vast majority of the vunerable population

Question 34

Describe the principle of herd immunity

Answer 34

-Arises when a sufficientley large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population - As pathogens are passed from individual to individual when in close contact, if most of the population is made immune, its unlikely an infected person will come into contact with an uninfected person - This means individuals who are not immune to the disease are protected

Question 35

Describe the importance of herd immunity

Answer 35

-Its impossible to vaccinate everyone in a population has babies and young children are not vaccinated as their immune systems are not developed and there can be risks with vaccinating them -

Question 36

Why may vaccination not eliminate a disease

Answer 36

-Vaccination to induce immunity in certain individuals for example people with defective immune systems - Individuals may develop the disease straight after the vaccination before their immunity levels are high enough to prevent it, causing infection to others -Pathoegn may mutate frequently so its antigens change suddenly, new vaccines become ineffective as new antigens on the pathogen are not recgonised easily, so new antibodies are not produced to destroy the pathoegn - Individuals may have objections to vaccinations for ethical or religous reasons

Question 37

Describe ethical issues of using vaccines

Answer 37

-Production of vaccines may involve use of animals - Vaccines have side effects that sometimes may cause long term harm -Questions arise on who should take in part in clinical trials for them -Is it right that vaccines should be compulsory, or does this have to be only before an epidemic or all the time? And should people be able to opt out if they want to? - Should expensive vaccination programmes continue when a disease is almost eradicated, reducing the budget used for other treatments? - -

Question 38

Describe the structure of HIV

Answer 38

- Surrounded by a lipid envelope -Attachment proteins are embedded in the lipid envelope - Inside the envelope is a capsid which encloses 2 single strands of RNA and enzymes - Reverse transcriptase is one of these enzymes, and it catalyses the production of DNA from RNA - Due to the presence of this enzyme, HIV belongs to a group of viruses called retroviruses

Question 39

Describe how HIV replicates itself

Answer 39

- Following an infection HIV enters the bloodstream and circulates around the body -A protein on the HIV readily binds to a protein called CD4 which is found on many cells,or a T helper cell - The rotein capsid fuses with the cell surface membrane, RNA and enzymes of HIV enter the T helper cells -The HIV transcriptase converts the viruses RNA into DNA -The newly made DNA is moved into the T helper cells nucleus where it is inserted into the cells DNA -HIV DNA in the nucleus creates mrna using cells enzymes and this contains the instructions for making new viral proteins and the rna to go into the new HIV -Mrna passes out of the cells nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles -HIV particles break away from T helper cell using abit of its csm surrounding them which forms their lipid enveleope

Question 40

How does HIV lead to the symptoms of AIDS?

Answer 40

-HIV attacks specifically T helper cells - These helper T cells are important in cell-mediated immunity, without a specfic number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or the cytotoxic T cells which kill cells infected by pathogens -Memory cells may also become infected and destroyed - This means the body cannot provide a sufficient immune response and therefore is more prone to other infections and cancers, its these secondary diseases that cause death

Question 41

Describe the use of antobodies in the ELISA test

Answer 41

-Uses antibodies to detect the presence of a protein in a sample and the quantity - Procedure as follows -Apply the sample to a surface for example a slide, to which all the antigens in the sample will attach -Wash the surface several times to remove any unattached antigens -Add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together -Wash the surface to remove excess antibody - Add a second antibody which binds to the first antibody, this second antibody has an enzyme attached to it -Add the colourless substrate of the enzyme -Enzyme acts on the substrate to change it into a coloured product -The amount of the antigen present is the relative to the intensity of the colour that develops -

Question 42

Why are antibiotics ineffective against viral diseases such as AIDS

Answer 42

Viruses rely on the host cells to carry out their metabolic activities and therefore lack their own metabolic pathways and cell structures This means antibiotics are ineffective as there are no metabolic pathways or structures to distrupt Viruses also have a protein coat rather than a muerin cell wall and so do not have sits where antibiotics can work