Defensive functions of mammalian blood

Question 1

Types of defence mechanisms

Answer 1

non-specific
*response is immediate and same for all pathogens
- physical barriers
- phagocytosis

specific
*response is slower and specific for each pathogen
- cell-mediated response (T-cells)
- humoral response (B-cells)

Question 2

What happens when lymphocytes recognise cells belonging to the body?

Answer 2

in fetus:
- infections occur rarely
- lymphocytes collide with body cells
- lymphocytes with receptors that fit body cells die

in adults:
- lymphocytes form in bone marrow
- those who show an immune response to self-antigens undergo cell death - apoptosis
- therefore they don’t mature

Question 3

Describe the process of phagocytosis

Answer 3

1. Chemical products from the pathogen are recognised, phagosome moves towards the pathogen - chemotaxis
2. Receptors on the cell membrane of the phagocyte attach to the antigens on the pathogen
3. Phagocyte engulfs the pathogen forming a vesicle - phagosome
4. Lysosome moves towards the phagosome and fuses with it
5. Lysozymes break down the pathogen by hydrolysing its cell wall
6. Soluble products are absorbed or released by exocytosis

Question 4

Immunity -

Answer 4

Immunity - the ability of an organism to resist infection by protecting against disease-causing microorganisms and toxins that invade the body

Question 5

Antigen -

Answer 5

Antigen - a substance that is recognised as foreign by the immune system and stimulates an immune response.

Question 6

Antibody -

Answer 6

Antibody - a protein produced by lymphocytes in response to the presence of a specific antigen.

Question 7

Differences between T lymphocytes and B lymphocytes

Answer 7

B lymphocytes
- produced in bone marrow, mature in Bone marrow
- humoral immune response
- respond directly to antigens in the blood

T lymphocytes
- produced in bone marrow, mature in Thymus gland
- cell-mediated immunity
- respond to APCs (antigen-presenting cells)

Question 8

Cell-mediated immunity -

Answer 8

Cell-mediated immunity - response to cells infected by pathogens (mainly viruses)

APCs: phagocytes that engulfed and hydrolysed a pathogen, body cells invaded by a virus, transplanted cells, cancer cells - all display antigens on their cell-surface membrane

Question 9

Describe cell-mediated immunity

Answer 9

1. Macrophages engulf and digest pathogens / pathogens invade body cells
2. ATPs present antigens on their cell-surface membrane
3. Receptors on a specific T helper cell attach to the antigens
4. attachment activates T helper cells to divide rapidly by mitosis forming clones
5. The cloned T helper cells:
   a) develop into memory cells
   b) stimulate phagocytosis
   c) stimulate B cells to divide and secrete antibodies
   d) activate cytotoxic T cells

Question 10

How do cytotoxic cells kill infected cells?

Answer 10

• produce a chemical perforin that makes holes in the cell-surface membrane of cells
• cells become freely permeable and die

Question 11

Describe humoral immunity

Answer 11

1. B cell takes up surface antigen of the pathogen, processes and presents it on its surface
2. Helper T cell attach to the antigens activating the B cell
3. B cells divide rapidly by mitosis into plasma cells
4. Plasma cells produce antibodies specific to the antigen
5. Antibodies attach to antigens and help destroy it by phagocytosis
6. B cells also develop into memory B cells

Question 12

Why do memory cells provide a faster immune response to future infections by the same pathogen?

Answer 12

• for secondary immune response
• memory cells circulate in the blood until future infection by the same pathogen
• they divide rapidly to develop plasma cells that produce antibodies

Question 13

Structure of an antibody

Answer 13

• 2 heavy chains and 2 light chains
• variable and constant regions
• antigen binding site
• receptor binding site

the shape of the antigen binding site has specific protein structure that makes the antibody complementary to the antigen

Question 14

How antibodies lead to destruction of pathogens?

Answer 14

• agglutination - clumps of bacterial cells make it easier for phagocyte to locate and destroy them
• neutralisation

Question 15

Active and passive immunity -

Answer 15

Active immunity - stimulation of the production of antibodies.
Passive immunity - introduction to antibodies from another source.

Question 16

Natural and artificial active immunity -

Answer 16

Natural active immunity - contracting a disease, immune system producing antibodies

Artificial active immunity - vaccination inducing an immune response

Question 17

Vaccination -

Answer 17

Vaccination - the introduction of a vaccine containing appropriate disease antibodies to the body in order to induce artificial immunity

Question 18

Herd immunity

Answer 18

• when sufficiently large population is vaccinated so the infection can’t spread
• works because If pathogen enter a vaccinated person it can’t be passed on

Question 19

Features of a successful vaccination programme

Answer 19

• economically available to most population
• few side effects
• producing, storing and transporting the vaccine is possible
• training staff
• able to vaccinate the vast majority of population to achieve herd immunity

Question 20

The ethics of vaccination

Answer 20

• fails to induce immunity in certain individuals, e.g. with defective immune systems
• may develop disease right after vaccination, spread to others
• antigenic variability due to mutations = not always effective
• pathogens ‘hide’ in body cells
• other religious, ethical, or medical reasons

Question 21

Primary non-specific defence mechanisms

Answer 21

skin
mucous membranes
expulsive reflexes - coughing, sneezing
lysozymes
HCl in the stomach
commensal microorganisms - ‘healthy’ bacteria, compete with pathogenic
inflammation