Immune System Part 2

Question 1

Transplanted organs will produce an immune response in the recipient due to the presence of non-self antigens on the transplanted tissue-what are the key stages in transplant rejection?

Answer 1

-T-lymphocytes are sensitised by the non-self antigens in transplanted tissue.
-T-lymphocytes are cloned to produce Killer T-cells (cytotoxic cells) (& other T cells)
-Killer T-cells destroy the transplanted tissue, by releasing perforins, resulting in lysis of transplanted cells

Question 2

Describe 3 ways in which the problems of tissue rejection can be overcome

Answer 2

-Tissue Typing-> matching the donor and recipient antigens so that there is as good as match as possible
-Immunosuppression Techniques-> drugs to inhibit DNA replication and therefore preventing the cloning of T-lymphocytes. No Killer T-cells produced to destroy transplanted tissue.
-X Rays-> irradiation of bone marrow inhibit production of lymphocytes

Question 3

Outline 2 problems that could arise from the treatments used to prevent tissue rejection

Answer 3

-Recipient’s immune system compromised by immunosuppression-susceptible to infection
-Unpleasant side effects of X rays and irradiation

Question 4

What methods can be used to support the immunocompromised transplant patient?

Answer 4

-Anti-viral drugs
-Anti-bacterial mouthwashes
-Monoclonal antibodies

Question 5

What blood group is the universal donor?

Answer 5

Blood group O. This is because blood group O does not have any A or B antigens on the surface of the red blood cells, therefore will not react/agglutinate with the antibodies in the recipients blood.

Question 6

What blood group is the universal recipient?

Answer 6

Blood group AB. This is because blood group AB lacks both antibodies.

Question 7

What does the term agglutination mean?

Answer 7

The formation of clumps that occurs when an antigen-antibody reaction takes place. This could be when:
1. Antibodies attach onto antigens on bacterial cells forming an antigen-antibody complex, immobilising the pathogen, which can then be engulfed by polymorphs.
2. In a blood transfusion, when a person with blood group A donates to a recipient with blood group B- the A antigens would attach to the anti-a antibodies in the recipients blood. The donor red blood cells would agglutinate. This agglutination could block capillary networks and lead to organ failure and death.

Question 8

What would happen if blood was donated from a donor with blood group A to a recipient with blood group B?

Answer 8

-The donor’s red blood cells have antigen A on their surface
-The recipient’s plasma contains anti-a antibodies
-An antigen-antibody reaction would take place. The donor’s red blood cells would be agglutinated by the recipients anti-a antibodies.
-This could block capillary networks and lead to organ failure and death.

Question 9

Why are the antibodies unimportant in the donor’s blood

Answer 9

Donated blood is mainly red blood cells. The amount of donated plasma (containing the antibodies) is insignificant.

Question 10

What does Rh+ mean?

Answer 10

The red blood cells’ cell surface membrane has the rhesus antigen (also called antigen D) Rhesus positive

Question 11

What does Rh- mean?

Answer 11

The red blood cells’ cell surface membrane does not have the rhesus antigen. Rhesus negative.

Question 12

What is another name for rhesus antibodies?

Answer 12

Anti-D antibodies

Question 13

Do Rh- individuals have anti-D antibodies?

Answer 13

No
But they will produced anti-D antibodies of their blood comes in contact with blood containing antigen D
eg 1: blood transfusion (extremely rare)
eg 2: when a Rh- mother has a Rh+ baby

Question 14

Why is it dangerous for a Rh- mother to be pregnant with a Rh+ foetus?

Answer 14

During birth some foetal Rh+ RBC may leak into the mother’s circulation, causing the Rh- mother’s immune system to produce anti-D antibodies (not usually a threat to first pregnancy)
In subsequent pregnancies that are Rh+, B lymphocytes are not already sensitised and large numbers of anti-D antibodies can be produced immediately if foetal Rh+ cells get into the mother’s circulation. The anti-D antibodies can cross the placenta and cause agglutination of foetal red blood cells.

Question 15

What is haemolytic disease of the newborn (HDN)?

Answer 15

When the mother’s anti-D antibodies cross the placenta and cause agglutination of foetal (Rh+) red blood cells .

Question 16

Why is HDN rare today?

Answer 16

-Mother’s blood types are known
-Rh- mothers at risk during pregnancy are given an injection of anti-D antibodies at 30 weeks and again following birth
-These anti-D antibodies will attach to any foetal Rh+ blood cells that have entered the mother’s circulation before B lymphocytes are stimulated to produce anti-D antibodies.

Question 17

What is an antibiotic?

Answer 17

Drugs that kill bacteria

Question 18

How do antibodies kill bacteria?

Answer 18

1. Disrupt cell wall formation (inhibition of an enzyme involved in the wall making process). Bacteria are killed by lysis
2. Inhibit bacterial cell metabolic processes eg protein synthesis

Question 19

What do we mean by the term antibiotic resistant bacteria?

Answer 19

When one or more antibodies no longer have any effect on the bacterial cells, ie they are not killed by the antibiotic . This is usually as a result of a mutation in the bacterial genome.

Question 20

What is an epidemic?

Answer 20

When a disease spreads rapidly through a small region (usually within one country) and affects a higher proportion of the population than normal.

Question 21

What is a pandemic?

Answer 21

When a disease affects many thousands of people or several countries at the same time

Question 22

Why are viruses often the causal agents of widespread infection?

Answer 22

1. Viruses have small genomes that are prone to mutation
2. Many disease causing viruses are retroviruses with RNA in the genome- these viruses are less stable than those with a DNA genome
3. Antibiotics are not effective against viruses

Question 23

What do we mean by the term animal reservoir?

Answer 23

Animal species that harbour viruses that subsequently cause disease in humans
Eg
Avian flu
Swine flu
Ebola
Zika

Question 24

Suggest two reasons why viruses which are carried by bats may pass relatively easily to human populations

Answer 24

-have similar physiology to humans
-fly which gives them a large range
-social animals/ have contact with large numbers of other bats and therefore a large pool is infected
-carrier animal/ bushmeat
-encroachment / urbanisation so contact more likely

Question 25

What are antimicrobial drugs?

Answer 25

Drugs that are effective against a broader range of microbes than antibiotics, ie they are effective against pathogens that antibiotics cannot combat.