Immunology 4

Question 1

What is the role of T helper cells?

Answer 1

To activate B cells, phagocytes and help one another. Activation leads to:
Chemoattraction – other cells respond to the signal and migrate to the infection
Autoactivation – increase activation
Augmentation of inflammation
Stimulation of Ab production by B cells

Question 2

What is the role of T cytotoxic cells?

Answer 2

Effective at killing viral infected cells.

Question 3

How do T cytotoxic cells kill infected cells?

Answer 3

Inducing apoptosis - by secreting perforin and granzyme B into infected cells.

Question 4

What is the role of regulatory cells?

Answer 4

Regulate or suppress other cells in the immune system and prevent autoimmune diseases.

Question 5

Which cell is CD4 positive?

Answer 5

T helper cells

Question 6

Which cell is CD8 positive?

Answer 6

T cytotoxic cells

Question 7

Which receptor is associated with CD3 molecule?

Answer 7

T cell receptor

Question 8

How do Th recognise antigen presenting cells?

Answer 8

APC cells present the foreign peptide to together with MHC class II to Th cells. These cells do not kill the APC, but release cytokines to trigger an immune response.

Question 9

How do Tc recognise infected cells?

Answer 9

Tc cells carry the CD8 receptor that interacts with MHC class I molecules. Remember- viral antigens are presented with MHC class I molecules to the T cell by an infected cell. The result is that the Tc cell will kill the infected cell.

Question 10

What is anergy?

Answer 10

T cell anergy is a tolerance mechanism in which the lymphocyte is intrinsically functionally inactivated following an antigen encounter, but remains alive for an extended period of time in a hyporesponsive state.

Question 11

What further stimulation is needed for T cell activation?

Answer 11

Recognition of a CD28 molecule on the T cell by a CD80 molecule on the APC cell.

Question 12

Why are is the reason for co-stimulation on T cells?

Answer 12

The reason for this is to prevent T cells being activated by the body’s own (host) antigens, which would lead to an autoimmune response. If a Th cell recognised a host peptide that was being presented with an MHC molecule on the surface of a cell, that could lead to such a response. Only when the presentation is made by an APC, with the necessary CD80 molecule as well, will the Th cell be activated.

Question 13

What is the function of cytokines?

Answer 13

• Drives class-switching and so has auto-signalling effects
• Chemo-attraction
• Activate T cells
• Activate B cells and cause Ab production
• Activate macrophages (which can then release monokines such as IL1 and so stimulate B cells to proliferate and mature)

Question 14

What is the function of Th1?

Answer 14

Activate cell-mediated immunity. Releases cytokines such as IL2, IL15, IFN-g

Question 15

what is the function of Th2?

Answer 15

Responsible for antibody production. Releases IL4, IL10 and IL13

Question 16

How can cytokines be used clinically?

Answer 16

In treatment such as in multiple sclerosis - this however can result in the development of Graves’ disease.

Question 17

How is the name of the HIV antigen?

Answer 17

gp120

Question 18

How does HIV infect cells?

Answer 18

HIV antigen binds to CD4 and so gets close enough to enter the cell. Virus injects its RNA and reverse transcriptase into the cell (transforms RNA to DNA) and forces the cell to make viral genes and forget about its own function, with the net result of HIV replication

Question 19

Can T cells recognise linear interaction? i.e Do the peptides need to be folded?

Answer 19

Yes

Question 20

What is central tolerance?

Answer 20

A way in which the immune system is educated not to react to own cells.

Question 21

Where does Central tolerance occur?

Answer 21

T cells - In the thymus

B cell - Bone marrow. There is also the process of receptor tolerance.

Question 22

What is positive and negative selection?

Answer 22

Positive selection: Only cells that respond to antigens presented on MHC are selected.

Negative selection: Those cells that amount a response against own cells are destroyed.

Question 23

What is peripheral tolerance?

Answer 23

It takes place in the immune periphery (after T and B cells egress from primary lymphoid organs). Its main purpose is to ensure that self-reactive T and B cells which escaped central tolerance do not cause autoimmune disease.

Question 24

Give examples of methods of peripheral tolerance?

Answer 24

Regulatory T cells that eliminate immune cells directed against self antigens

Absence of second signal when lymphocytes are activated (immune cell anergy)

Anatomical barriers and immune privileged areas:
Inside the eyes (injury to one eye can cause immune destruction to the other eye – complete tragedy)

Question 25

What is the cause of autoimmune disease?

Answer 25

Autoimmune disease occur if self tolerance against a body antigen is broken.

Question 26

How are antibodies produced?

Answer 26

1. Upon antigen binding, the memory B cell takes up the antigen through receptor-mediated endocytosis, degrades it, and presents it to T cells as peptide pieces in complex with MHC-II molecules on the cell membrane. In other cases, the B cell receptor binds to the antigen in clonal selection.
2. The B cell then displays antigen fragments bound to its own distinctive MHC molecules.
3. The combination of antigen fragments and MHC molecule attracts the help of a mature, matching T cell.
4. Lymphokines secreted by the T cell allows the B cell to multiply and mature into antibody-producing plasma cells.
5. Released into bloodstreams antibodies lock into matching antigens. These antigen-antibody complexes are soon eliminated, either by the complement cascade or by the liver and the spleen.

Question 27

what is sympathetic ophthalmia?

Answer 27

Occurs when someone injures one eye, antigens are exposed, the immune system starts to react to the self antigens. This amounts an immune response in the healthy eye, destroy it and lead to blindness.