Cell recognition and the immune system

Question 1

What is a pathogen?

Answer 1

• a disease causing micro-organism
• e.g. bacteria, virus, fungi
• bacteria cause disease by producing toxins
• virus cause disease by dividing in cells causing them to burst

Question 2

Body’s defence against pathogens

Answer 2

• I, Barriers (prevents pathogens entering the body)
• II, Phagocytes (perform phagocytosis and stimulate specific response)
• III, specific response (uses lymphocytes to produce memory cells and antibodies)

Question 3

What are barriers?

Answer 3

• skin, impermeable barrier made of keratin
• cilia and mucus in lungs
• stomach acid (denatures/breakdown pathogens

Question 4

describe the process of phagocytosis

Answer 4

• pathogen releases chemicals
• this attracts the phagocyte
• the phagocyte binds to the pathogen
• the phagocyte engulfs the pathogen
• forms a phagosome around the pathogen
• lysosomes inside the phagocyte release digestive enzymes into the phagosome
• breaking down the pathogen by hydrolysis

Question 5

Describe the specific response

Answer 5

• phagocytes perform phagocytosis without destroying the antigen, they place antigens on their surface, they present antigens
• t lymphocytes (T cells) bind to the antigen and become stimulated
• they divide by mitosis to form 3 types of cells: t helper, t killer, t memory
• t helper cells stimulate b lymphocytes
• t killer cells kill infected cells
• t memory cells provide long term immunity
• b lymphocytes engulf and present antigens on their surface, the t helper cells bind to this
• the B cells become stimulated and divide by mitosis to make 2 types of cells: plasma cells and B memory cells
• plasma cells make antibodies
• B memory cells provide long term immunity

Question 6

What is an antigen?

Answer 6

A protein on the surface of a pathogen that stimulates an immune response

Question 7

How does the immune response lead to production of antibodies?

Answer 7

The phagocyte stimulate the T cells, the T cells form t helper cells , the t helper cells stimulate the B cells, the B cells form plasma cells, the plasma cells make antibodies

Question 8

what is an antibody?

Answer 8

• a globular protein
• made by plasma cells
• has 3 regions: variable region, hinge region, constant region
• variable region has a different shape in each antibody, contains the antigen binding sites these bind to complementary antigens (on a pathogen) to form an antigen-antibody complex, destroying the pathogen
• hinge region the same shape in all antibodies, binds to phagocytes to help with phagocytosis

Question 9

How do memory cells work?

Answer 9

• made during the specific immune response after a new infection by a pathogen
• B and T memory cells remain in the blood
• if person is reinfected by the same pathogen the memory cells will recognise the pathogen and produce antibodies rapidly and to a large amount
• therefore the pathogen is killed before it can cause harm = immunity

Question 10

How does a vaccine produce immunity?

Answer 10

Involves giving an injection that contains dead/wakened pathogens that carry antigens stimulates the immune response leading to production of antibodies & memory cells

Question 11

Active vs passive immunity

Answer 11

• Active = individual has memory cells - can make their own antibodies & provides long term immunity
• passive = person given antibodies, these work then die, no long term immunity, no memory cells

Question 12

How does activity immunity occur?

Answer 12

Naturally = by primary infection

Artificially = by vaccination

Question 13

How does passive immunity occur?

Answer 13

Naturally = from mother to baby

Artificially = by injection

Question 14

Successful vaccination programme

Answer 14

• produce suitable vaccine

- herd immunity

Question 15

What is herd immunity?

Answer 15

When a large proportion of the population is vaccinated, therefore most people will be immune, only a few will not be a immune, increases chance of non-immune person coming into contact with immune person, so the pathogen has no where to go, so it dies out

Question 16

Problems with vaccination programmes

Answer 16

• vaccine does not work
• vaccine not safe
• many strains of pathogen
• cannot achieve herd immunity
• antigenic variability

Question 17

What is antigenic variability?

Answer 17

The pathogen mutates, the antigen changes shape, so the memory cells no longer complementary - do not recognise the pathogen, therefore the pathogen can reharm

Question 18

What is a monoclonal antibody?

Answer 18

One type of antibody, complementary to one type of antigen, made by one type of plasma cell

Question 19

What are monoclonal antibodies used for?

Answer 19

Identify specific antigens or antibodies in person’s blood, or pregnancy tests

Question 20

How do monoclonal antibodies identify specific antigens in the blood?

Answer 20

• identify TB antibodies in the blood
• place antigen complementary to TB antibodies on test plate
• add person’s blood to test plate
• if TB antibodies are present in blood, they will bind to the antigen
• then a set of monoclonal antibodies complementary to the TB antibodies are added
• if the TB antibodies are present, the monoclonal antibodies will attach
• if the TB antibodies are not present, the monoclonal antibodies will not attach
• the test plate is then washed
• if the TB antibodies are present, the monoclonal antibodies will attach, this will not be washed away, so the enzyme will be present
• if the TB antibodies are not present, the monoclonal antibodies will not attach, this will be washed away, so the enzyme will be washed away
• a colourless substrate is then added, if the enzyme is present it will breakdown the substrate causing a colour change, if the enzyme is not present there will be no change
• therefore: colour change occurs = enzyme present, no colour change = no enzyme present

Question 21

How are monoclonal antibodies used in pregnancy testing?

Answer 21

• pregnant women produce HCG hormone in their urine
• test strip has 3 parts to it (1st: start contains antibodies complementary to HCG: 2nd: middle contains antibodies complementary to HCG-antibody complex, 3rd: end contains antibodies complementary to HCG antibodies
• if woman is pregnant, HCG in the urine binds to antibodies on 1st part forming a HCG-antibody complex, the HCG-antibody complex then binds to antibodies on the 2nd part forming a blue line, HCG antibodies also bind to 3rd part as a control
• if woman is not pregnant, no HCG in urine so nothing binds to HCG antibodies in 1st part, is nothing binds to antibodies in 2nd part leaving no blue line, the HCG antibodies still bind to 3rd part for the control

Question 22

What is HIV/AIDs?

Answer 22

• HIV = Human Immunodeficiency Virus
• AIDs = Acquired Immunodeficiency Syndrome
• HIV is the pathogen, AIDs is the infectious disease
• HIV is spread by fluid to fluid contact
• HIV damages and destroys T helper cells, therefore person no longer produces immune response and has no defence against pathogens/infections = AIDs
• with AIDs, individual at risk from all sorts of pathogens/infections called opportunistic infections