Immune System

Question 1

What are antigens?

Answer 1

Antigens are molecules/proteins located on the surface of cells that generate an immune response when detected in the body.

Question 2

What is antigen variability?

Answer 2

Pathogens DNA can mutate frequently, if the mutation occurs in the antigens coding genes, the shape of the antigen may change shape. Previous immunity to this pathogen if no longer effective as the memory cells have memory of the old antigen shape.
Or the pathogen can have multiple shaped antigens on their surface.

Question 3

What is a lymphocyte?

Answer 3

A lymphocyte is a type of white blood cell that is part of the immune system.

Question 4

What is a phagocyte?

Answer 4

A phagocyte is a macrophage, a type of white blood cell that carries out phagocytosis, a non-specific response (engulfment of pathogens). They are found in the blood and tissues and are the first cells to respond to an immune system trigger within the body.

Question 5

What is the process of phagocytosis in large amounts of detail?

Answer 5

1. Any chemicals or debris released by pathogens or non-self-cells attract the phagocytes.
2. The chemicals or antigens on the pathogen will bind to the receptors on the phagocyte.
3. The phagocyte will change shape to move around the pathogen and engulf it.
4. Once engulfed, the pathogen is contained in a phagosome vesicle.
5. A lysosome within the cell will fuse with the phagosome and release its contents.
6. A lytic enzyme from the lysosome will hydrolyse, break down and destroy the pathogen.
7. The soluble products are absorbed and used by the phagocyte
8. The phagocyte presents the pathogens antigens on its surface to activate other immune system cells, and antigen-presenting cell.

Question 6

What response do the T cells create?

Answer 6

Cell mediated response.

Question 7

What is the cell mediated response?

Answer 7

1. Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface, this is now called an antigen presenting cell.
2. Helper T-Cells have receptors on their surface which can attach to the antigens on the APC
3. Once attached this activates the helper T-Cells to divide by mitosis to replicate and make large numbers of clones.
4. Cloned helper T-Cells differentiate into different cells
   Helper T-Cells, some stimulate macrophages to perform more phagocytosis, memory cells, cytotoxic T-Cells (killer T-Cells)

Question 8

How do B cells work?

Answer 8

1. B cells are activated when chemicals are released from T helper cells. They are also activated when the antibody molecules on their cell surface bind to a complementary antigen.
2. Once they are activated, the B cells divide by mitosis and differentiate into two kinds of cell: plasma cells and memory cells.

Question 9

What are plasma cells?

Answer 9

Plasma cells are very short lived, and they produce antibodies with a complementary shape to the antigen. They carry out the primary immune response as they are an immediate response.

Question 10

What are memory cells?

Answer 10

Memory cells remain in the bloodstream in low levels in case reinfection occurs, and they can live for decades. If the memory cells detect the same antigen, they will quickly divide by mitosis into plasma cells. This will result in large numbers of antibodies being produces so rapidly that the pathogen is destroyed before any symptoms can occur. They carry out the secondary immune response, provide long-term immunity but take longer.

Question 11

What is an antibody?

Answer 11

A Y shaped protein that is produced/secreted by B cells/plasma cells.

Question 12

What is the structure of an antibody?

Answer 12

Antibodies have a quaternary structure made up of four polypeptide chains (two heavy chains and two light chains) held together by disulfide bridges. Variable region where the antigen-binding site is located. Constant region contains another binding site which allows the antibody to bind to immune system cells, such as B cells or phagocytes. Hinge region which provides the antibody with flexibility.

Question 13

What is aggulation?

Answer 13

Antibodies each contain two antigen-binding sites which means they can bind to two pathogens at the same time. This causes pathogens to become clumped together. Phagocytes can then engulf and digest lots of pathogens at the same time, which makes phagocytosis more efficient.

Question 14

What is the primary immune response?

Answer 14

The primary immune response occurs when you are infected with a pathogen for the first time.This process is slow because it takes time for the correct B cell to be activated and divide into lots of plasma cells to produce antibodies with a complementary shape to the antigen. The infected person will experience symptoms while the T and B cells mount an immune response and produce memory cells.

Question 15

What is the secondary response?

Answer 15

It is a much quicker response if you are re-infected with the same pathogen in the future, the T and B memory cells will recognise the antigen and start dividing. T memory cells will divide into the correct type of T killer cell to kill any cells that are infected with the pathogen. B memory cells will divide into plasma cells to produce many antibodies which is complementary to the antigen molecules on the pathogen. The pathogen is suppressed before you can experience symptoms - you are immune to the pathogen.

Question 16

What is the structure of HIV?

Answer 16

Contain a core of genetic material.
Capsid, an outer protein coat.
Proteins attachments.
An envelope taking from host cell.

Question 17

How is HIV replicated?

Answer 17

1. HIV is transported around in the blood until it attached to a receptor molecule on the helper T cell (CD4 protein).
2. The HIV protein capsule then fuses with the helper T cell membrane enabling the RNA and enzymes from HIV to enter.
3. The HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the helper T cell nucleus, this is why it is called retrovirus.
4. Double stranded DNA is made and inserted into the human DNA.
5. Here mRNA is transcribed, and the helper T cell starts to create viral proteins to make new viral particles.
6. The viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells

Question 18

What is the acute phase of HIV?

Answer 18

May suffer fever, sweats, headaches, sore throat, swollen lymph nodes. Lasts 3-12 weeks after infection. Rapid viral multiplication + loss of T helper cells

Question 19

What is the latency/chronic phase?

Answer 19

Can last for many years. Reduced immune system efficiency, latent diseases like tb or shingles may reactivate.

Question 20

What is an opportunistic infection?

Answer 20

Infections normally controlled in healthy people but potentially life-threatening in HIV infected people.

Question 21

How do antibiotics work?

Answer 21

Antibiotics work by interfering with bacterial cell walls and ribosomes, either killing the bacteria or stopping its growth.

Question 22

What is AIDS?

Answer 22

When the patient’s immune system has weakened to a particularly low level (this is seen by a low T helper cell count in hospital blood tests), the patient has developed a disease called acquired immunodeficiency syndrome (AIDS).

Question 23

Why don’t antibiotics work on our own cells or viruses?

Answer 23

Because human cells ad viruses do not have cell walls.

Question 24

What can ELISA tests be used for?

Answer 24

Medical diagnosis and animal testing.

Question 25

What is the direct ELISA test?

Answer 25

1. A single antibody is used that complement the antigen you are testing for.
2. Antigens from the patient sample is bound to the inside of a well in a well plate.
3. A detection antibody that’s complimentary with an attached enzyme are added.
4. Any antigen present will be immobilised in the well and the detection antibody will attach.
5. The well is then washed out to remove any unbound antibodies.
6. A substrate solution is added that will react with the enzyme on the antibody and produce a colour change.

Question 26

What is the indirect ELISA test?

Answer 26

1. Is used to test for HIV and uses two different antibodies.
2. The HIV antigen is bound to the base of a well in a well plate.
3. Patients’ blood plasma is added. Any HIV-specific antibodies will bind to the antigen.
4. The well is then washed out.
5. A secondary antibody with a specific enzyme is added, this can bind to the HIV-specific antibody.
6. The well is then washed out again.
7. A solution is added to the well containing a substrate that reacts with the enzyme attached to the secondary antibody and a colour product is produced.
8. If the colour changes this indicates that the patient has HIV-specific antibodies in their blood plasma and are infected with HIV.

Question 27

What is a monoclonal antibody?

Answer 27

Monoclonal antibodies are antibodies which have the same tertiary structure and are produced from a genetically identical single B-cell clone.

Question 28

How is a monoclonal antibody formed?

Answer 28

1. An antigen is injected into a mouse
2. The mouse naturally produces lymphocytes, which produce antibodies specific to the antigen
3. Spleen cells which produce the lymphocytes are removed during a small operation
4. The spleen cells are fused with human cancerous white blood cells called myeloma cells to form hybridoma cells which divide indefinitely
5. These hybridoma cells divide and produce millions of monoclonal antibodies specific to the original antigen

Question 29

What are the 4 uses of monoclonal antibodies?

Answer 29

Separation of chemicals in a mixture, immunoassay, cancer treatment and transplant surgery.

Question 30

How are monoclonal antibodies used in pregnancy tests?

Answer 30

Monoclonal antibodies are attached to the end of a pregnancy test stick onto which a woman urinates. If she is pregnant, HCG will be present in her urine and will bind to the monoclonal antibodies on the test stick. This will cause a change in colour or pattern which will indicate pregnancy.