Immune system

Question 1

What is a pathogen?

Answer 1

Any disease causing microorganism

Question 2

What are the 4 types of cellular (living) pathogens?

Answer 2

Fungi
Protozoa
Parasites
Prokaryote

Question 3

What are the 2 types of acellular (non-living) pathogens?

Answer 3

Virus
Prion

Question 4

What are the first defences that the body has to pathogens?

Answer 4

Tears
Cilia
Mucus
Skin surface
Stomach acid (pH 2)

Question 5

What is the body’s second line of defence?

Answer 5

White blood cells

Question 6

What white blood cells have a specific response?

Answer 6

Lymphocytes

Question 7

What white blood cells have a non-specific response?

Answer 7

Phagocytes

Question 8

How are self and non-self cells distinguished?

Answer 8

Identifiable proteins on the cell surface

Question 9

What is an antigen?

Answer 9

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

Question 10

Process of phagocytosis

Answer 10

1. Chemicals released by the pathogen
2. The phagocytes are attracted to these chemicals (foreign substances) and move towards the 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

Question 11

What is an antibody?

Answer 11

A protein with specific binding sites complementary to a specific antigen, synthesised and secreted by plasma cells.

Question 12

Formation of an antigen-antibody complex

Answer 12

● An antibody has a specific tertiary structure
● The antigen binding sites on the variable regions of the antibody are only complementary to one specific antigen (because they are made up of a specific amino acid sequence)
● They will only bind to and form an antigen-antibody complex with this specific antigen

Question 13

Describe agglutination and subsequent phagocytosis

Answer 13

Antibodies each bind to an antigen on two separate pathogens, causing the pathogens to clump together via a network of antigen-antibody complexes.
This clump is then easier for phagocytes to locate and engulf. The antibodies also serve as a marker for the phagocyte to commence phagocytosis of the bacteria.

Question 14

What are monoclonal antibodies?

Answer 14

Antibodies with the same tertiary structure produced from a genetically identical set of plasma cells. These antibodies are all specific to the same antigen.

Question 15

What cells does the cell mediated response require?

Answer 15

T lymphocytes

Question 16

What cells does the humoral response require?

Answer 16

B lymphocytes

Question 17

Industrial/medical uses of monoclonal antibodies:

Answer 17

Targeting medication to specific cell types
Medical testing
Medical diagnosis using ELISA

Question 18

Direct monoclonal antibody therapy

Answer 18

• Monoclonal antibodies are produced specific to the antigens on the target cells (eg. cancerous cells)
• The antibodies are given to a patient
• The antibodies attach to the antigens on the surface of the target cells &
  prevent their uncontrolled growth (by blocking signalling pathways in them)

Question 19

Indirect monoclonal antibody therapy

Answer 19

• A cytotoxic drug (a drug that kills cells) is attached to the monoclonal
  antibodies
• The antibodies are given to the patient
• When the antibodies attach to the antigens on the target cells it kills the cells

Question 20

Components of a pregnancy test

Answer 20

Reaction Site - free antibody (traps hCG)
Test Site - fixed antibody (traps hCG)
Control Site- fixed antibody (traps free antibody)

Question 21

Stages of ELISA

Answer 21

1. Antigen coated well
2. Wash
3. Add patient’s sample
4. Wash
5. Add enzyme-conjugated secondary antibody
6. Wash
7. Add substrate and measure colour

CAN USE ANTIBODY COATED WELL AND ADD ANTIGEN THEN ENZYME CONJUGATED ANTIBODY

Question 22

Ethical questions about monoclonal antibodies

Answer 22

● Mice used to produce both the monoclonal antibodies and the tumour cells - involves deliberately inducing cancer in mice (animal cruelty)
● Although monoclonal antibodies have successfully treated a number of diseases there have also been some deaths to do with their use
● It’s important people are clear on the risks as well as the benefits before agreeing
● Testing the safety of new drugs in trials can be dangerous
● Maybe drug trials should be limited to volunteers who are terminally ill with a condition that the monoclonal antibody is designed to treat?

Question 23

What is a vaccination?

Answer 23

Involves injection of antigens that have been isolated from a dead/attenuated microorganism. This induces a primary immune response in an individual (production of memory cells), without them suffering the symptoms of the disease.

Question 24

What is herd immunity?

Answer 24

When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread even to those not immunised.

Question 25

When can vaccines be ineffective?

Answer 25

When antigens on the pathogen mutate

Question 26

Ethical concerns of using vaccines

Answer 26

- Use of animals - Side effects - Who should it be tested? - Should trials only occur in specific countries? - Should it be compulsory? - Economical concerns - The greater good versus individual health risks

Question 27

What is passive immunity?

Answer 27

Introducing/inserting monoclonal antibodies into an organism from an outside source - no contact with the pathogen or its antigens

Question 28

What is active immunity

Answer 28

Involves direct contact with the pathogen or its antigens, stimulating the body’s immune system to produce its own antibodies

Question 29

Differences between passive and active immunity

Answer 29

Passive: - Antibodies introduced to body - Short term (antibodies break down) - Fast acting Active: - Antibodies secreted by plasma cells - Longer term - Takes longer to develop

Question 30

Features of a successful vaccination

Answer 30

● Must be financially available ● Must have few side-effects - if any ● Must be ways of producing, storing and transporting the vaccine ● Must be ways of administering the vaccine properly - may involve training staff ● Must be available in sufficient quantities to vaccinate most of the population to result in herd immunity

Question 31

When might vaccines not work?

Answer 31

- Certain individuals with defective immune systems may either not develop immunity or may develop the disease - Individuals may have objections against vaccines - religious, ethical or medical reasons - When pathogens mutate frequently it’s difficult to develop a vaccine against them

Question 32

Antigenic variability

Answer 32

A pathogen may mutate frequently, which can cause its surface antigens to change. The vaccine then suddenly becomes ineffective because the antibodies of the immune system can no longer recognise (are no longer complementary to) the antigens

Question 33

Replication of the HIV virus

Answer 33

● HIV infects a person’s blood through sex/sharing needles/blood transfusion. ● It cannot reproduce itself - it requires a host cell to replicate inside of. ● It instructs the host cell to produce the components of new HIV viruses. ● The specific host cells for HIV viruses are T helper cells.

Question 34

Process of HIV infection

Answer 34

● HIV enters the bloodstream, it circulates around the body ● Virus binds (using attachment proteins) to receptor proteins (CD4) on the surface of a t-helper cells ● The virus lipid envelope fuses with the cell surface membrane ● The capsid breaks down and this releases the genetic material & enzymes into the cell ● Reverse transcriptase converts RNA to DNA ● The viral DNA moves into the nucleus through a nuclear pore and is inserted into the host cell DNA by integrase ● The HIV DNA is transcribed into mRNA & then translated into viral proteins ● These new viral particles are assembled and bud off from the cell surface membrane to infect more cells - this destroys T helper cells

Question 35

How HIV causes aids

Answer 35

● Someone infected with HIV is described as HIV positive. ● Uninfected person- between 800 and 1200 helper T cells in each mm3 of blood ● Infected person - When the amount of helper T cells falls below 200 cells/mm3 a person may receive an AIDS diagnosis (critical value) ● Immune system stops functioning normally - is unable to produce an adequate immune response ● Individual becomes more susceptible to other infections ● Leads to AIDS - Acquired Immune Deficiency Syndrome (really low T helper cell count = damaged immune system) ● Symptoms are related to the infections a person develops as a result of having a damaged immune system - can’t fight off infections as well ● It is the secondary infections/diseases that cause death (not the HIV virus itself) ● To make matters worse, AIDS patients have a much higher cancer risk, since a healthy immune system plays a role in detecting and killing cancer cells.

Question 36

What are aseptic techniques?

Answer 36

Practices and procedures to handle bacterial cultures in a way to prevent contamination by unwanted microorganisms. It involves applying the strictest rules to minimize the risk of infection

Question 37

Aseptic techniques:

Answer 37

• Cuts should be covered with a dressing • No eating or drinking • Windows & doors closed to avoid airborne contamination • Wash hands • Bench wiped down with disinfectant before & after use • Report spillages immediately • Equipment must be sterilised before use, using appropriate methods - eg. heating to a high temperature in a bunsen burner until red hot (blue flame) - NOT glass rod! • Necks of containers passed through the flame - sterilises neck & prevents contaminated air entering • Keep lids off things for a minimum amount of time • Growth media (agar) & petri dishes must be sterilised before use (agar is boiled before use) • Work as close as possible to the flame • Open dishes/ hold containers at an angle • Tape dishes on each side after inoculation • Never remove lid of sealed Petri dish • Never incubate microorganisms above 30•C (25•C in schools/labs) • All cultures/bacterial growth in Petri dishes to be place in autoclavable bag & autoclaved after

Question 38

How do antibiotics work?

Answer 38

- Work in a number of ways - one way is preventing bacteria from making normal cell walls - Tough cell walls prevent bacterial cells from bursting/lysis - Penicillin inhibits enzymes involved in the synthesis & assembly of the bacterial cell wall (made of murein) - When water enters, the bacterium bursts and dies