6.7 Response to infection

Question 1

what is the bodies first line of defence?

Answer 1

• surface of body (skin)
• lungs
• intestine

Question 2

what is the body’s second line of defence?

Answer 2

inflammatory response

Question 3

define inflammation

Answer 3

rapid, localised response of our tissues to damage

Question 4

what triggers inflammation

Answer 4

when cells are damaged, they release ‘alarm’ chemicals including histamine

Question 5

inflammatory response

what does histamine do?

Answer 5

• the smooth muscle of arterioles relaxes, increasing blood flow to that area.
• cells in the walls of capillaries draw away from one another (diapedesis), so that the capillaries become ‘leaky’, forming more tissue fluid than usual. This extra tissue fluid causes local swelling of the infected area. (oedema)
• sensory neurones become more sensitive
• complement proteins of plasma activated

Question 6

inflammation

what is the effect of increased blood flow + leakage of plasma

Answer 6

• dilution and removal of toxins from invading microorganisms and from damaged cells
• more plasma + white blood cells

Question 7

what two leucocytes are involved inflammatory response

what do each do

Answer 7

• neutrophils (short-lived) engulf bacteria identified by opsonins
• macrophages engulf lather debris and damaged cells

Question 8

what are the two main steps necessary for phagocytosis

Answer 8

1. must distinguish foreign cells from the body’s own cells
2. engulfs and destroys foreign cell

Question 9

what do neutrophils and macrophages have in common?

Answer 9

both are phagocytic leucocytes

Question 10

what are the things that help pahocytes identify foreign cells (to engulf)

and where did they come from

Answer 10

complement proteins

histamines causes them to be activated in plasma

Question 11

3 effects of complement proteins:

Answer 11

• attracting more phagoctyes to the site of infection
• binding to and forming pores in the surface membrane of foreign cells, leading to lysis of these cells
• binding to surface membranes of foreign cells thus aiding the attatchment of the surface membrane of a phagocyte to a foreign cell. These proteins are called opsinins.

Question 12

describe phagocytosis

Answer 12

1. phagocytic leucocyte detects presence of bacterium
2. bacterium becomes attatched to receptor molecules on the cell surface membrane of leucocyte
3. trapped bacterium engulfed in a food vacuole in the cytoplasm of leucocyte
4. lysosomes in the cytoplasm fuse with the vacuole and discharge hydrolytic enzymes
5. bacterium broken up into its constituent molecules and these are dispered into the cytoplasm (of leucocyte)

Question 13

what are cytokines

Answer 13

a group of small proetins released by one type of cell that affects the behaviour of other cells

Question 14

non specific still

what are interferons

what do they do

Answer 14

a group of cytokines called interferons are released by cells infected by viruses

these interferons bind to neighbouring healthy cells and trigger synthesis of antiviral proteins - as a reslut viral replication is slowed or halted.

Question 15

what are the two types of leucocyte that are specific

Answer 15

lymphoctes:
- B lymphocytes (B cells) - humoral
- T lymphotes (T cells) - cell-mediated

bees make you laugh… humoural

Question 16

where do both lymphocytes come from and where do they mature

Answer 16

both are produced by multipotent stem cells in marrow of some bones, t cells leave bone marrow to mature in the thymus gland whereas b cells stay in the bone marrow to mature.

Question 17

define antigen

what molecules classify

Answer 17

any molecule that can stimulate an immune response.
small molecules like amino acids and sugars do not cause an immune response
large molecules like glycoproteins, glycolipids, proteins do.
The cell surface surface of the cell is coated in antigens

Question 18

why are glycoproteins useful

Answer 18

they are highly variable and help to identify cells so are called markers

Question 19

define MHC

Answer 19

Major Histocompatability complex (MHC) protiens
Glycoproteins found on the cell surface membrane of a cell membrane of a cell that are unique to that individual. In humans, these are often called human leucocyte associated antigens (HLA).
**They help identify cells **
are types of antigen

Question 20

what do B and T cells have on their surface that allow them to recognise cells

Answer 20

antigen receptor molecules
( molecules that are complementary to very specific antigens )

Question 21

what is the consequence of the antigen-receptors on B/T cells being complementary to a specific antigen?

Answer 21

each lymphoctye can only recognise one type of antigen

Question 22

what are antibodies

Answer 22

the antigen receptor molecules of a B cell that are released.

Question 23

what are the two most common antibodies?

what are they

Answer 23

igG
igM

they are a type of protein, immunoglobin (ig)

Question 24

describe the structure of igG

Answer 24

four polypeptides linked by disulfide bridges to form a Y shape, two cghains are large (the heavy chains) and two are small (light chains)

Question 25

define self-antigen | and why do they not trigger immune response against themselves

Answer 25

a glycoprotein on the cell surface membrane of one of the body's own cells. (The ability of this glycoprotein to cause an immune response is reduced by the body destroying any randomly produced lymphocytes with a complementary antigen-receptor. )

Question 26

what is the humoral response

Answer 26

response involving the release of antibodies by B-cells.

Question 27

outline the humoral response

Answer 27

1. antigen to antibody on the B cell surface membrane 2. antigen taken up by exocytosis and is expressed on the cell surface membrane at the MHC protien 3. Meanwhile.. macrophages engulf antigens by endocytosis and then express this antigen on their MHC proteins on the cell surface membrane = antigen presentation 4. T cell binds (briefly) to macrophage that presents an antigen and is activated- it is now an activated T helper cell 5. activated T helper cell now binds to B cell with the same antigen expressed-immediately the B cell is activated = activated B cell 6. activated B divides rapidly forming a clone of plasma cells - each containg lots of rER now mass producing antibody molcules that are secreted by exocytosis 7. (some activated B cells and T cells surviuve in the body as memory cells, and are able to initiate a more speedy response in the event of re-infections antibodies overcome antigen eg by neutralising it by causing clumping together of cells to aid engulfing by other macrophages

Question 28

outline the cell mediated response

Answer 28

1. complementary T cell binds to macrophae presenting complementary antigen = activated T helper cell 2. T helper cells release cytokines that stimulate T helper cell to divide repeatedly to form clones clone could be three types of T helper cell

Question 29

3 types of T cell (from clone)

Answer 29

- T killer cells- destroy body cells infected by virus or other cells carrying for example TAA (tumor associated antigens) - T helper cells- release cytokines that stimulate the production of B cells - Memory cells- remain in the body and bring about the secondary response (re-infection).

Question 30

contrast primary and secondary immune reponse (re-infection)

Answer 30

secondary is - faster rate of antibody production - shorter time lag between exposure an antibody production - higher concentration of antibodies - antibdoy level remains higher after the secondary response - pathogen usually destroyed before any symptoms

Question 31

similarities between passive and active immunity

Answer 31

- both involve antibodies - both can be natural or arificial

Question 32

give examples of passive and active immunity

Answer 32

passive natural: antibodies in breast milk passive artificial: anti-venom active natural: humoral response to infection active artificial: vaccination

Question 33

contrast passive and active immunity

Answer 33

passive: - no memory cells and antibodies not replaced when broken down= short term - immediate - antibodies from external source - direct contact with antigen not necessary active: - memory cells produced = long-term memory - time lag - lymphocytes produce antibodies - direct contact with the antigen necessary

Question 34

explain the principles of vaccination

Answer 34

1. vaccine contains dead/inactive form of a pathogen or antigen 2. triggers primary immune reponse 3. memory cells are produced and remian in the bloodstream so secondary response is rapid and produce higher conc of antibodies 4. pathogen is destroyed before it causes symptoms.

Question 35

what is herd immunity?

Answer 35

vaccinating 80-90% of population reduces available carriers of the pathogen to control disease transmission protects individuls who have not been vaccinated eg: those with a weak immune system.