6.7 Response to infection

Question 1

Describe the mode of action of macrophages

Answer 1

-monocytes migrate to tissues and become macrophages
-macrophage engulfs pathogen, enclosed in a phagosome
-phagosome fuses with a lysosome (phagolysosome) - lysozymes break down pathogen - not destroy
-MHC (major histocompatibility complex) formed - antigens displayed on pathogen’s surface
-MHC can be recognised by lymphocytes

Question 2

Describe the mode of action of neutrophils

Answer 2

-cytokines signal neutrophils to site of infection
-N move to pathogens which may be covered in antibodies
-N have receptor proteins that recognise antibodies and attach to them
-once attached to pathogen, N engulfs it - trapping in a phagosome(phagocytic vacuole) - endocytosis
- lysosome fuses, lysosymes released to break down pathogen
-after killing pathogen, neutrophil dies
-pus is sign of dead neutrophils

Question 3

Describe the mode of action of lymphocytes

Answer 3

made in white bone marrow of long bones
B cells:
- produce antibodies and memory cells
-activated by T helper cells

T cells:
-mainly kill pathogens and activate B cells
- mature in thymus
-activated by APCs
-activate B cells and cytokines

Question 4

What is the role of B effector cells?

Answer 4

divide and differentiate to form the plasma cell clones

Question 5

What is the role of plasma cells?

Answer 5

produce antibodies to particular antigens at a rate of 2000 antibodies/second

Question 6

What is the role of B memory cells?

Answer 6

provide the immunological memory to a specific antigen, allowing the body to respond rapidly to a pathogen carrying the same antigen

Question 7

What is the role of T killer cells?

Answer 7

produce chemicals to destroy infected body cells

Question 8

What is the role of T helper cells?

Answer 8

activate plasma cells to produce antibodies against antigens
secrete opsonins to label pathogen for phagocytosis by other white blood cells

Question 9

What is the role of T memory cells?

Answer 9

long lived cells that make up part of the immunological memory.
when they meet a pathogen for the 2nd time they divide rapidly - forming large clone of T-killer cells which quickly destroy the pathogen

Question 10

What are the 2 types of immune responses?

Answer 10

humoral response:
- T helper activation
- the effector stage

cell mediated response

Question 11

Describe the stages of T helper activation

Answer 11

1. bacterium with antigens on surface
2. bacterium engulfed by macrophage
3. Mphage presents antigens on MHCs - becoming APC
4. Mphage APC binds to T helper cell to activate it
5. once activated, it divides to form clone T helper and T memory cell

Question 12

Describe the stages of the effector stage

Answer 12

1. bacterium with antigens on surface
2. antigen binds to B cell (with complementary receptor) and it engulfs bacterium through endocytosis - enzymes break it down, leaving antigen fragments
3. MHC forms with antigen - B cell is APC
4. activated T helper cell (with complementary receptor) binds to APC - cytokines produced to stimulate B cell
5. B cell divides to form clone B memory and B effector cells
6. B effector cells differentiate into plasma cells
7. plasma cells secrete antibodies - bind to antigens on similar pathogens so they are easier to destroy

Question 13

What are the 3 ways antibodies destroy a pathogen?

Answer 13

agglutination
opsonisation
neutralisation

Question 14

What is agglutination?

Answer 14

when antibodies bind to the antigens on pathogens, the microorganisms agglutinate (clump up). this prevents them spreading through the body and makes it easier for them to be engulfed by phagocytes

Question 15

What is opsonisation?

Answer 15

when the antibody acts as an opsonin - makes the antigen or pathogen more easily recognised by phagocytes

Question 16

What is neutralisation?

Answer 16

when antibodies neutralise the effects of bacterial toxins by binding to them

Question 17

Describe the stages of the cell-mediated response

Answer 17

[usually in viral infections]
1. bacterium infects a host cell
2. host cell presents antigens on MHCs - becomes APC
3. T killer cell with complementary receptor binds to APC - cytokines from activated T helper cell released
4. stimulated by T helper cells, T killer cells divide and differentiate to form 2 clones.
5. clone T memory cells formed
6. clone active T killer cells formed - bind to infected cells presenting antigens on MHCs
7. T killer cells release chemicals, causing lysis in infected cell as pores form in its membrane. the infected cell dies

Question 18

What are the roles of B and T memory cells in a secondary immune response?

Answer 18

B memory cells are long-lived - help quickly produce antibodies against a pathogen you have already had

T memory cells stay in the blood so the body can produce a rapid response if the same pathogen invades again. - these release T killer cells to engulf and destroy pathogen

Question 19

What is natural active immunity?

Answer 19

when body produces its own antibodies to an antigen encountered naturally - like catching the pathogen

Question 20

What is natural passive immunity?

Answer 20

when antibodies made by the mother are passed down to the baby via breastmilk or the placenta

Question 21

What is artificial active immunity?

Answer 21

when the body produces its own antibodies to an antigen acquired through a vaccination

Question 22

What is artificial passive immunity?

Answer 22

when antibodies are extracted from one individual and injected into another e.g. the tetanus vaccine

Question 23

What is herd immunity?

Answer 23

when a high proportion of a population is immune to a pathogen, usually by vaccination, lowering the risk of infection to all.
unvaccinated people are also less likely to encounter the pathogen

Question 24

How can a vaccination control a disease and develop herd immunity?

Question 25

What are potential issues in populations that choose not to vaccinate?

Answer 25

• a tiny minority of children become extremely ill after a vaccination - an extreme immune response
  they may die or be left severely brain damaged
• mass vaccination programmes are linked to the recent rise in childhood asthma and allergies