IMMUNITY- phagocytosis,cell mediated and humoural response, active and passive immunity

Question 1

what is an antigen?

Answer 1

-Cell-surface molecule which stimulates immune response.
-glycoprotein or glycolipids or polysaccharide.

-The immune system recognises as ‘self-cells’ or ‘non-self cells’ which enables identification of cells from other organisms of same species, pathogens, toxins and abnormal body cells.

Question 2

How does phagocytosis destroy pathogens?

Answer 2

1. phagocyte moves towards pathogen by chemotaxis - the phagocyte is attracted to the cytokines secreted by pathogen.
   2.phagocyte engulfs pathogen by endocytosis to form a phagosome.
2. The pathogen is now trapped inside the phagocyte and forms a phagocytic vesicle.
3. lysosomes are attracted towards the phagosome
4. the lysosome fuses with the phagosome, forming a phagolysosome.
   6.Lysozyme hydrolyses/digests the pathogen
   7.The phagocyte absorbs the products from the pathogen hydrolysis.
5. The phagolysosome move towards the cell membrane and performs exocytosis. Phagocyte is exocytosed out of the cell.

Question 3

explain the role of APC’s?

Answer 3

APC - antigen presenting cells
After hydrolysis in phagocytosis, the macrophage presents antigens of the pathogen on its surface.
Once the surface receptor of the T cell binds to the specific complementary antigen (on the antigen-presenting cell) it becomes sensitised and starts dividing to produce a clone of cells.

Question 4

name 2 types of specific immune responses?

Answer 4

cell mediated
humoral

Question 5

outline the process of cell mediated response?

Answer 5

1. complementary T-helper cells bind to the foreign antigen on the APC.
   2.T-helper cells release cytokines that stimulate:
   a) the clonal expansion of complementary T-helper cells by rapid mitosis which then become memory cells or stimulate the b cells
   b) clonal expansion of cytotoxic t-cells ( t-killer cells)- which secrete the enzyme perforin the destroy infected cells

Question 6

outline the process of the humoral response?

Answer 6

1. complementary t helper cells bind to the foreign antigens on the APC.
   2.T cells release cytokines which stimulates clonal expansion of complementary b-cells.
2. b cells differentiate into plasma cells or memory b cells
3. plasma cells secrete antibodies with complementary variable region to the antigen.

Question 7

What is an antibody?

Answer 7

• protein secreted by plasma cells
• quaternary structure: 2 light chains held together by disulfide bridges, and 2 longer heavy chains
• binding site is on the variable region of light chain
• variable region has very specific tertiary structure complementary to the antigen
• rest of the molecule is known as a constant region

Question 8

How does antibody lead to the destruction of an antigen?

Answer 8

formation of the antigen-antibody complex results in agglutination, which enhances phagocytosis.

Question 9

What are monoclonal antibodies?

Answer 9

Antibodies produced from a single clone of B-cells.

Question 10

What are memory cells?

Answer 10

• specialised B cells produced from the primary immune response
  -remain in low levels of the blood
  -can divide rapidly by mitosis if organisms encounters the same pathogen again.

Question 11

compare the primary and secondary immune response?

Answer 11

secondary response -
- faster rate of antibody production
- shorter time between exposure and antibody production
- higher concentration of antibodies
- AB levels remain higher after the secondary response
-pathogen is usually destroyed before any symptoms

Question 12

what causes antigen variability?

Answer 12

Random genetic mutation changes in the DNA base sequence of antigen results in different sequence codons on mRNA. There is a different primary structure of the antigen as there are different hydrogen bonds, ionic bonds and disulphide bridges forming in different places in tertiary structure. Therefore the antigen is a different shape.

Question 13

Explain how antigen variability affects the incidence of disease?

Answer 13

The memory cells are no longer complementary to the antigen so the body is not immune and catch the disease more than once.
Many varieties of the pathogen makes it more difficult to produce a vaccine containing all antigen types.

Question 14

what is active immunity?

Answer 14

the body makes antibodies after being exposed to an antigen. Long term protection because memory cells are produced

Question 15

what is passive immunity?

Answer 15

the body is given the antibody that is made by a different organisms. Short term as no immune response is involved and no memory cells are produced.

problems - protection is temporary and only lasts a few months after birth

Question 16

compare passive and active immunity?

Answer 16

both involve antibodies
can both be natural or artificial

passive natural: antibodies in breast milk/ across placenta
passive artificial: anti-venom, needle stick injections
active natural: humoural response to infection
active artificial: vaccination