Chapter 5 - Cell recognition and the immune system

Question 1

two lymphocyte responses?

Answer 1

• cell-mediated (T-lymphocytes)

- humoural responses (B-lymphocytes)

Question 2

definition of a pathogen?

Answer 2

any foreign body/microorganism that causes disease

Question 3

how are pathogens identified as non self?

Answer 3

specific molecules on cell surface membrane

Question 4

what molecules would be identified by the body? (4)

Answer 4

• pathogens e.g. viruses
• cells from other organisms
• toxins
• abnormal body cells e.g. cancers

Question 5

how do lymphocytes recognise own cells in adults? (3)

Answer 5

• lymphocytes produced in bone marrow only encounter self antigens
• any lymphocytes which show an immune response towards self-antigens undergo apoptocis
• no clones of anti-self lymphocytes appear in blood

Question 6

how do lymphocytes recognise own cells in a fetus?(1)

Answer 6

• anti self lymphocytes die or are suppressed

Question 7

outline phagocytosis (5)

Answer 7

• Phagocyte attracted to pathogen by chemical products along concentration gradient
• phagocyte receptors bind to antigens on surface of pathogen
• lysosomes in phagocyte migrate to the phagosome which is forming
• lysosomes release lysozymes into phagosome, which hydrolyses the pathogen
• products of hydrolysis are absorbed by phagocyte

Question 8

definition of an antigen

Answer 8

part of an organism/substance that is recognised as non-self by the body to trigger an immune response e.g. cell surface proteins on a pathogen

Question 9

what are the two types of lymphocyte?

Answer 9

B lymphocytes

T lymphocytes

Question 10

where do the two main types of lymphocyte form/mature?

Answer 10

B - in the bone marrow (humoural immunity)

T - in the thymus gland (cell mediated immunity)

Question 11

How are T-lymphocytes able to recognise invading cells? (4)

Answer 11

• phagocyte present antigens of engulfed pathogens on their surface
• or cells invaded by a virus present antigens on their surface
• transplanted cells have different antigens
• cancer cells have different antigens

Question 12

Why is it that T-lymphocytes are said to be involved in cell-mediated immunity?

Answer 12

they only respond to antigens presented on cells rather than in fluids

Question 13

outline the response of a T-lymphocyte to the detection of a pathogen (4)

Answer 13

• phagocyte engulfs pathogen and presents antigens on its surface
• receptors on specific T helper cells fit exactly onto these antigens
• attachment prompts T cell to divide rapidly by mitosis
• these daughter cells; stimulate phagocytes to carry out phagocytosis, stimulate B-cells to divide and produce antibodies - develop into memory cells, activate cytotoxic T cells.

Question 14

How do cytotoxic T cells kill infected cells? (3)

Answer 14

• produce protein called perforin
• this makes many holes in the CSM
• cell becomes freely permeable to everything and dies

Question 15

What are antibodies?

Answer 15

specific protein produced by B cells in response to the presence of the appropriate antigen

Question 16

outline the process of humoural immunity by B-lymphocytes (4)

Answer 16

• B-cell with complimentary antibody attaches to antigen
• antigen enters by endocytosis and is presented on cell surface
• T helper cells bind to processed antigens triggering B cells to divide by mitosis
• all clones produce same antibody therefore known as monoclonal (variety of monoclonal antibodies used to fight one type of pathogen due to antigenic variability)

Question 17

what do the cells of B cell clones develop into? (2)

Answer 17

plasma cells - secrete antibodies directly into blood plasma
memory cells - responsible for secondary immune response, able to divide rapidly

Question 18

how do antibodies assist in the destruction of pathogens? (2)

Answer 18

• cause agglutination, clumps them together making it easier for phagocytes to engulf
• mark pathogens of phagocytes to engulf

Question 19

What are monoclonal antibodies?

Answer 19

• specific to one antigen

- produced by a single clone

Question 20

outline how monoclonal antibody therapy can be used to treat cancer (3)

Answer 20

• monoclonal antibodies produced specific to antigens of cancer cells
• antibodies given to patient to attach to cancer
• stop chemical signals that stimulate uncontrolled growth and replication of cancer

Question 21

why might monoclonal antibody therapy be a better treatment than other cancer treatments e.g. chemo?

Answer 21

• specific to patient

- less side effects, own antibodies

Question 22

give 2 examples of diseases that can be diagnosed using antibody testing

Answer 22

influenza
hepititus
chlamydia
prostate cancer

Question 23

how is early pregnancy detected?

Answer 23

• hormone HCG released from placenta in urine

- binds to antibody-colour complex causing a colour change

Question 24

state 3 ethical issues for the use of monoclonal antibodies

Answer 24

• production uses mice who have cancer deliberately induced
• patients must have informed consent
• drugs trials are not always safe

Question 25

what is passive immunity? (2)

Answer 25

- introduction of antibodies from outside e.g. antivenom | - not long lasting

Question 26

what is active immunity? (2)

Answer 26

- stimulation of antibody production from own immune system | - natural active immunity, artificial active immunity

Question 27

what is natural active immunity?

Answer 27

when an individual is naturally infected with a disease which stimulates an immune response which leaves memory cells

Question 28

what is artificial active immunity?

Answer 28

vaccination - purposeful introduction of disease causing an immune response and memory cells

Question 29

what is vaccination?

Answer 29

introduction of appropriate disease (or/including antigens) into body to induce artificial immunity

Question 30

what do vaccines aim to produce on the body?

Answer 30

immunity to secondary exposure through memory cells

Question 31

state the features of a successful vaccination programme (5)

Answer 31

- economically viable on a large scale - few side effects so people aren't discouraged - means of production, storage, transport - proper administering equipment e.g. needles - possible to vaccinate majority for herd immunity

Question 32

what are the reasons a vaccination might not lead to a disease being eliminated? (6)

Answer 32

- not all become immune, faulty immune systems - may develop disease just after vaccination but before immunity - pathogen may frequently mutate (antigenic variability) - too many strains of pathogen to vaccinate against them all - pathogens may hide from immune system - people may object to vaccination programs

Question 33

ethics of vaccination? (7)

Answer 33

- production , animals - side effects, long term harm - informed consent in human testing not totally possible - use of countries in which disease is widespread to trial vaccine - compulsory vaccination - expensive vaccination for almost eradicated diseases - individual health risks vs population health

Question 34

how does HIV replicate? (6)

Answer 34

- HIV binds to CD4 on (usually) T helper cells - capsid fuses to CSM, RNA and enzymes enter T helper cell - HIV reverse transcriptase makes HIV DNA - DNA inserted into T helper cell nucleus - nucleus the makes mRNA as if it were the cells own DNA - HIV breaks way with part of CSM forming its lipid envelope

Question 35

How does HIV cause symptoms of AIDS? (3)

Answer 35

- killing/interferring with normal functions of T helper cells - T helper cells not available for cell mediated immunity - means no B cells produced of cytotoxic T cells, means the body can't respond to any infection

Question 36

technique for ELISA test? (7)

Answer 36

- apply sample to surface and allow binding - wash away unattached antigens - add specific antibody - wash away excess antibody after time for binding - add second antibody that binds to first one - add colourless substrate of enzyme - amount of antigen present is relative to the intensity of colour which develops

Question 37

Why do viruses not respond to antibiotics? (2)

Answer 37

- rely on host cells for metabolic activities (antibiotics usually work by disrupting metabolic activities) - protein coat rather than murien cell wall means antibiotics can't break down