Cell recognition and the immune system

Question 1

what is the definition of immunity?

Answer 1

the means by which the body protects itself from infection

Question 2

what is non specific defence?

what are two examples?

Answer 2

response is immediate and the same for all pathogens
physical barriers (skin)
phagocytosis

Question 3

what is specific defence?

what are two mechanism examples?

Answer 3

response is slower and specififc to each pathogen
cell-mediated responses involving T-lymphocytes
humoral responses involving B lymphocytes

Question 4

what allows for your body to recognise your own cells?

Answer 4

each type of cell, self or non-self, has specific molecules on its surface that identifies it - these protein molecules allow the immune system to identify pathogens, non-self material, toxin and abnormal body cells

Question 5

how do lymphocytes work to recognise cells belonging to the body?

Answer 5

lymphocytes in fetus collide with self cells, and some lymphocytes will have recpeotrs that exactly fit the body cells.
lymphocytes either die or are suppressed
only ones remaining are those that might fit foreign material, therefore only respond to foreign material.
any lymphocytes that show an immune response to these self-antigens undergo programmed cell death (apoptosis) before they differentiate into mature lymphocytes

Question 6

what are the five steps of phagocytosis?

Answer 6

1. phagocyte attracted to pathogen by chemical products of pathogen. moves towards the pathogen along a conc. gradient
2. phagocyte has several receptors onits cell-surface membrane that attach to chemicals of the surface of the pathogen
3. lysosomes within 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 7

what is an antigen?

Answer 7

proteins on the cell-surface membrane of invading cells, that stimulate an immune response

Question 8

what are the two types of lymphocytes?

Answer 8

B lymphocytes - mature in bone marrow, involving antibodies in body fluids
T lymphocytes - mature in thymus gland, involving body cells

Question 9

what are antigen-presenting cells?

Answer 9

cells that display foreign antigens on their surface

Question 10

explain cell-mediated immunity involving T lymphocytes?

Answer 10

• 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 rapidly by mitosis and form a clone of genetically identical cells
• the cloned T cells :
• develop into memory cells that enable rapid response to future infections by the same pathogen
• stimulate phagocytes to engulf pathogens by phagocytosis
• stimulate B cells to divide and secrete their antibody
• activate cytotoxic T cells

Question 11

how do cytotoxic T cells kill infected cells?

Answer 11

produce a protein called perforin that makes holes in the cell-surface membrane - it is then freely permeable to all substances and dies
most effective against viruses as viruses replicate inside cells

Question 12

what do plasma cells do?

Answer 12

they secrete antibodies usually into blood plasma - lead to the destruction of the antigen
the production of antibodies and memory cells is known as the primary immune response

Question 13

what do memory cells do?

Answer 13

they are responsible for the secondary immune response. live considerably longer than plasma cells, often for decades.
circulate in blood + tissue fluid - don’t directly produce antibodies.
memory cells circulate in readiness for any future infection.

Question 14

how do B cells work in humoral immunity?

Answer 14

• surface antigens of an invading pathogen are taken up by a B cell
• the B cell processes the antigens and presents them on its surface
• helper T cells attach to the processed antigens on the B cell thereby activating the B cell.
• the B cell is now activated to divide by mitosis to give a clone of plasma cells
• the cloned plasma cells produce and secrete the specific antibody that firs the antigen of the pathogen’s surface
• the antibody attaches to antigens on the pathogen and destroys them
• some B cells develop into memory cells. can respond to future infections by dividing rapidly into plasma cells that produce antibodies - secondary immune response

Question 15

what is the structure of an antibody?

Answer 15

four polypeptide chains - one pair is heavy chains, other pair is light chains
specific binding sites that fits very precisely onto a specific antigen, forming the antigen-antibody complex
binding site is called the variable region
rest of the antibody is called the constant region

Question 16

how do antibodies lead to the destruction of an antigen?

Answer 16

• cause agglutination of the bacterial cells - makes it easier for phagocytes to locate them as they are less spread-out
• serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

Question 17

what are monoclonal antibodies?

Answer 17

when a single type of antibody can be isolated and cloned

Question 18

how are monoclonal antibodies used to target medication to specific cell types by having a therapeutic drug attached to them?

Answer 18

commonly used to target cancer cells

• monoclonal antibodies produced that are specific to antigens on cancer cells
• antibodies given to patient and attach themselves to the receptors on their cancer cells
• attach to surface of cancer cells and block the chemical signals that stimulate their uncontrolled growth.

Question 19

what is indirect monoclonal antibody therapy?

Answer 19

attaching an radioactive or cytotoxic drug to the monoclonal antibody. when the antibody attaches to the cancer cells, it kills them

Question 20

what else are monoclonal antibodies used for?

Answer 20

medical diagnosis
pregnancy testing (hCG hormone in pregnant women)

Question 21

what are three ethical issues with using monoclonal antibodies?

Answer 21

mice are used, to produce the antibodies and tumour cells.
some deaths have been associated with them in the treatment of multiple sclerosis - needs informed consent
testing presents certain dangers - conduct must be thorough

Question 22

what is passive immunity?

Answer 22

produced by the introduction of antibodies into individuals from an outside source (eg. from mother to child in placenta)

Question 23

what is active immunity and what are the two types?

Answer 23

produced by stimulating the production of antibodies by the individuals’ own immune system
natural active immunity - being infected w/ disease normally
artificial active immunity - vaccination

Question 24

what are four factors that confirm a successful vaccination programme?

Answer 24

• economically available in sufficient quantities
• few side-effects, if any
• means of producing, storing and transporting the vaccine must be available.
• must be means of administering it properly
• must be possible to vaccinate vast majority to produce herd immunity

Question 25

what is herd immunity and why is it important?

Answer 25

when a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population.
important because it is never possible to vaccinate everyone in a large population - babies and very young children are not vaccinated because their immune systems are not fully functioning

Question 26

what are 6 factors as to why vaccination may not eliminate a disease?

Answer 26

• fails to induce immunity in certain individuals
• individuals may develop the disease immediately after vaccination
• pathogen may mutate –> antigenic variability
• may be so many varieties of a particular pathogen that is almost impossible to develop a vaccine
• certain pathogens ‘hide’ from the body’s immune system
• individuals may have objections to vaccination for religious, ethical or medical reasons

Question 27

structure of HIV

Answer 27

lipid envelope, attachment proteins, capsid, RNA, reverse transcriptase

Question 28

what can we say about HIV if it can make DNA from RNA?

Answer 28

it is a retrovirus

Question 29

how does HIV replicate?

Answer 29

virus, so can’t replicate itself.

• enters bloodstream following infection and circulates around the body
• protein on HIV readily binds to protein called CD4
• protein capsid fuses with cell-surface membrane. RNA and enzymes of HIV enter the helper T cell
• HIV reverse transcriptase converts the virus’s RNA into DNA
• newly made DNA moved into helper T cell’s nucleus where it is inserted into the cell’s DNA
• HIV DNA creates mRNA using cell’s enzymes - contains the instructions for making new viral proteins
• mRNA passes out of nucleus through nuclear pore - makes HIV particle
• HIC particles break away from helper T cell

Question 30

how does HIV cause symptoms of AIDS?

Answer 30

specifically attacks helper T cells, kills or interferes with the normal functioning of helper T cells - those infected by HIV are unable to respond effectively to other pathogens, causing ill health + eventual death

Question 31

what does the ELISA test detect?

give the steps

Answer 31

detects the presence of a protein in a sample but also quantity

• apply sample to surface
• wash several times to remove unattached antigens
• add specific antibody + leave two to bind
• wash surface to remove excess antibody
• add second antibody that binds with the first antibody
• add colourless substrate of enzyme
• amount of antigen present is relative to the intensity of colour that develops

Question 32

why are antibiotics ineffective against viral diseases like AIDS?

Answer 32

because there are no metabolic mechanisms or cell structures for them to disrupt