12 Immunity

Question 1

what is the immune response?

Answer 1

a response to the presence of a foreign antigen involving the activation of lymphocytes and the production of antibodies

Question 2

what is the definition of the primary defences?

Answer 2

mechanisms that have evolved to prevent the entry of pathogenic organisms

Question 3

give some examples of barrier defences

Answer 3

skin

• keratinocytes prevent entry of pathogens
• blood clotting prevent entry of pathogens to blood

eye
- conjunctiva protected by lysozyme

airways

stomach

• mucus layer
• HCl to maintain optimum enzyme pH and destroying pathogens in food

vagina
- low pH

Question 4

give some examples of inflammatory defences

Answer 4

tissue injury –> release of histamine

dilation and leaking of local arterioles

capillaries become more permeable

Question 5

outline the process of phagocytosis

Answer 5

{phagocytes = neutrophils + macrophages}

pathogens release chemicals/damaged mammalian cells release cytokines

phagocyte moves down chemical concentration gradient towards pathogen via chemotaxis

pathogen is attached to receptors on CSM of phagocyte

phagocyte surrounds and engulfs the pathogen in a phagosome

lysosomes containing hydrolytic enzymes fuse with the phagosome creating a phagolysosome

enzymes break down and digest the pathogen

useful products absorbed; unwanted are exocytosed

antigens presented on CSM to alert T helper cells

Question 6

where are T cells produced and matured?

Answer 6

produced in bone marrow

matured in thymus gland

Question 7

where are B cells produced and matured?

Answer 7

produced AND matured in bone marrow

Question 8

what is maturation of B and T cells?

Answer 8

addition of receptors

Question 9

what are the four types of T cells?

Answer 9

helper

• detect antigens and secrete cytokines
• stimulates B lymphocytes to produce B plasma and memory cells in clonal selection and expansion

killer
- destroy infected cells by producing a protein that punches a hole in the CSM

regulatory

• supressor - maintain tolerance to self-antigens
• prevent AI diseases

memory

• remain and circulate in blood and tissues
• co-ordinate a response on reinfection

Question 10

what is the function of B cells? what are the two types?

Answer 10

to search for the antigen that matches their receptors (clonal selection)

stimulated by T helper cells to divide in clonal expansion

plasma
- produce monoclonal antibodies which bind with the antigen to form an antigen-antibody complex, immobilising the antigen

memory
- recognise pathogens and co-ordinate more antibodies for response to secondary infection

Question 11

what are antibodies?

Answer 11

soluble glycoproteins that bind to complementary antigens on the surface of the pathogen

Question 12

where do antibodies come from?

Answer 12

B plasma cells

Question 13

what is neutralisation?

Answer 13

antibodies combine with viruses/bacterial toxins to prevent them entering/damaging cells

Question 14

what is agglutination?

Answer 14

antibodies immobilise pathogens by clumping them together to stop them entering the cell and making them easier to be phagocytosed

Question 15

what is immobilisation?

Answer 15

antibodies stop movement of bacteria by attaching to flagella

Question 16

what are lysis-antibodies?

Answer 16

antibodies that bind to foreign bodies and attract complement proteins which ‘punch’ pores in the CSM

Question 17

what is opsonisation?

Answer 17

the constant region of the antibodies attaches to receptors on CSM on phagocyte

the variable region attaches to antigens on pathogen ∴ it can be engulfed

Question 18

why is a secondary immune response more effective than primary immune response?

Answer 18

clonal selection and expansion takes a long time

differentiation of T/B cells takes time

production of antibodies by plasma cells

more memory cells @ secondary response

Question 19

what is the Mantoux/tuberculin test used to diagnose?

Answer 19

tuberculosis

Question 20

in the Mantoux test, how big must the induration be for a normal healthy person to have TB?

Answer 20

> 15 mm

Question 21

in the Mantoux test, how big must the induration be for someone with a weakened immune system to have TB?

Answer 21

> 5 mm

Question 22

what are the two ways in which we screen for HIV?

Answer 22

point of care

• finger prick/mouth swab
• results in 11 - 28 days

blood samples

• tests for both antigens and antibodies
• results in 11 - 28 days

Question 23

outline the ELISA test

Answer 23

capture molecule is fixed to a surface

target antigens bind to a capture molecule

detecting antibodies added and bound

solution rinsed - non-captured detecting antibodies washed away –> negative result

if not, substrate added and bound

enzyme changes colour –> positive result

change in colour marked in optical density

antigen concentration x optical density plotted in calibration curve

Question 24

what is hypersensitivity?

Answer 24

an undesirable reaction produced by the immune system

Question 25

what is sensitisation?

Answer 25

initial contact with the allergen triggers the primary immune response

plasma cells produce ImmunoglobulinE antibodies, which bind to receptors on mast cells

Question 26

how does exposure to an allergen cause an inflammatory response?

Answer 26

allergen binds to variable region on IgE on mast cells

stimulated to produce histamines

blood vessels vasodilate and ‘leak’ plasma

Question 27

what is active immunity?

Answer 27

activation of B and T lymphocytes in response to the presence of pathogenic antigens, resulting in the production of antibodies and memory cells

Question 28

what is the difference between natural and artificial active immunity?

Answer 28

natural = primary immune response to natural infection to a pathogen

artificial = deliberate introduction of antigens to stimulate primary immune response (i.e. vaccination)

Question 29

what is passive immunity?

Answer 29

no activation of lymphocytes and no memory cells produced

presence of antibodies ONLY

Question 30

what is the difference between natural and artificial passive immunity?

Answer 30

natural = e.g. from mother to foetus across placenta/breast milk

artificial = injection of antibodies from another source