Antigens/ Phagocytosis

Question 1

What cells identify foreign substances in the body?

Answer 1

• Lymphocytes will identify foreign substances in body.

Question 2

What does each type of cell have on its membrane?

Answer 2

• Each type of cell has specific molecules on its surface that identify it.

Question 3

Why are molecules on surface of cells (used to identify cells) often proteins?

Answer 3

• Because protein’s 3D structures allow for many unique, identifiable shapes to be made.

Question 4

What 4 different types of foreign substances can be identified by immune system by the molecules on their surface?

Answer 4

1.) Pathogens
2.) Cells from other organisms of the same species ie. transplants.
3.) Abnormal body cells ie. cancer cells.
4.) Toxins (which some pathogens release.)

Question 5

How do lymphocytes not destroy self-cells in body?

Answer 5

• Lymphocytes, in foetus, complementary to antigens on self-cells will die/ production will be suppressed (prevents lymphocytes from attacking own cells.)
• Only lymphocytes remaining are complementary to antigens on non-self cells.
• Same process after birth in bone marrow (any new lymphocytes comp to antigens on self- cells will be destroyed.)

Question 6

How do autoimmune diseases actually occur?

Answer 6

• Lymphoytes comp to antigens on self- cells aren’t destroyed, so lymphocytes destroy its own cells.

Question 7

What are antigens?

Answer 7

• Antigens are molecles that generate an immune response by lymphocyte cells when detected in body.
• Usually proteins located on surface of cells.

Question 8

What is antigen variability? What is the effect of antigen variability on disease prevention?

Answer 8

• When pathogens mutate, gene that codes for antigen will change/ shape of antigen will change.
• Any previous immunity is no longer effective - as memory cells in blood can only identify old antigen shape.

Question 9

Give an example of chemical/ physical barrier pathogen would need to get past in order to enter bloodstream.

Answer 9

• Chemical: hydrochloric acid.
• Physical: skin.

Question 10

What is the next line of defence against pathogen/ foreign substance after chemical/ physical barriers? What two types of responses occur?

Answer 10

• White blood cells destroying the foreign substance.
• Phagocytes will carry out non-specific response
• Lymphocytes will carry out specific response.

Question 11

What is a phagocyte? Where is it found?

Answer 11

• A phagocyte is a macrophage (type of WBC) that carried out phagocytosis.
• Found in blood/ tissues.

Question 12

What is meant when we say: “phagocytosis is a non-specific response?”

Answer 12

• Any non-self cell (regardless of antigens on surface) will be engulfed in the exact same way to destroy it.

() - extra info

Question 13

Steps of phagocyotis of pathogen.

Answer 13

1.) Any chemicals/ debris released by pathogens attract the phagocytes/ they will move towards these cells.
2.) Many receptor binding sites on surface of phagocytes. They will attach to chemicals/ antigens of pathogen.
3.) Phagocyte changes shape/ engulfs pathogen.
4.) Pathogen is contained within vesicle - called phagosome.
5.) Lysosome will fuse with phagosome and release contents into phagosome.
6.) Lysozyme enzymes released into phagosome- this hydrolyses/ destroys the pathogen.
7.) Soluble products are absorbed and used by phagocyte/ antigens (of broken down pathogen) are displayed on cell-surface membrane. Phagocyte becomes APC.

() - extra info for clarification.