Antigens & phagocytosis

Question 1

Pathogen definition?

Answer 1

any disease causing microorganism (disrupts the normal physiology of the infected organism)

Question 2

Immune response?

Answer 2

If pathogen gets past chemical and physical barriers (e.g. skin and stomach acid) and enters the blood then next line of defence - white blood cells…
Phagocytes- non-specific
Lymphocytes- specific

Question 3

First line of defence - barriers to infection?

Answer 3

Physical:
- skin
- membrane linings
- cilia
Chemical:
- sweat & oils
- saliva
- stomach acid
-urine
- tears
- mucus

Question 4

Difference between non-specific & specific defence mechanisms?

Answer 4

• non: response is immediate & the same for all pathogens - physical barriers & phagocytosis
• specific - response is slower & specific to each pathogen - cell-mediated response (T lymphocytes) & humoral response (B lymphocytes)

Question 5

Identifying self and non-self cells?

Answer 5

• using lymphocytes
• each type of cell has specific molecules on surface that identify it
• these molecules r usually proteins - as 3D tertiary structure enables lots of unique & identifiable shapes to be made
• aka antigens

Question 6

types of cells that trigger immune response?

Answer 6

• if non-self cell detected - response triggered to destroy cell e.g.
• pathogens e.g. bacteria/fungi/viruses
• cells from other organisms of same species (e.g. organ transplants)
• abnormal body cells (e.g. cancer cells)
• toxins

Question 7

antigen definition?

Answer 7

a molecule (often protein) that the body recognises as ‘foreign’ and so triggers an immune response

Question 8

How lymphocytes recognise cells

Answer 8

10 mil diff type types of lymphocytes in your body - each can recognise a diff shaped antigen
- made when foetus - when developing in womb u r unlikely to be exposed to any cells other than self cells
- lymphocytes complementary to antigens on self cells will die/production will be suppressed - to prevent ur lymphocytes from attacking ur own cells so…
- lymphocytes remaining r complementary to pathogenic & non-self cells
- same process occurs after birth in bone marrow (any new lymphocytes made in the bone marrow which are complementary in shape to antigens on self-cells will be destroyed
- if process doesn’t work properly - lymphocytes which will attack self-r produced - causes symptoms of autoimmune diseases

Question 9

Antigen variability?

Answer 9

• pathogens’ DNA can mutate frequently - if mutation occurs in gene which codes for antigen - shape of antigen change
• any previous immunity to pathogen - no longer effective as - all memory cells in blood hv memory of old antigen shape
• aka antigen variability - influenza virus mutates & changes its antigens very quickly - y a new flu vaccine has to be created each yr

Question 10

Phagocyte definition?

Answer 10

a macrophage (type of white blood cell) that carries out phagocytosis.
- are found in the blood and in tissues.

Question 11

Phagocytosis

Answer 11

(non-specific)
1. chemicals/debris r released by pathogen
2. phagocytes r attracted to chemicals & move towards pathogen
3. The phagocyte engulfs the pathogen into a vesicle called a phagosome (by endocytosis)
4. Lysosomes found in the phagocyte move towards the vesicle and fuse with the phagosome
5. Lysozymes (hydrolytic enzymes) in the lysosomes digests the pathogen
6. The phagocyte displays the important antigens on its cell surface membrane