T cells

Question 1

What are the two main types of T cells? How are they identified. (2)

Answer 1

CD4 (helper cells) and CD8 (cytotoxic).

CD stands for cluster determinant. It is a marker on surface of leukocytes.

Question 2

What are the functions of T cells? (2)

Answer 2

1. CD4 - They orchestrate immune response.

2. CD8 - They kill viral infected cells, as they can enter cell membrane.

Question 3

Where do T cells mature and how? (2)

Answer 3

1. They mature in Thymus gland.

2. The cells are clonally selected and self reactive cells are removed.

Question 4

Draw and label a T cell receptor (7)

Answer 4

Allocate:

1. Alpha Chain
2. Beta Chain
3. Variable Region
4. Constant Region
5. Disulphide bond
6. Hinge
7. Transmembrane region and Cytoplasmic tail.

Question 5

How does a T cell recognise an antigen? (2)

Answer 5

1. The Antigen-presenting cell has a HISTOCOMPATIBILITY molecule that attaches to antigen peptide.
2. The T cell receptor binds to the Histocompatibility molecule.

Question 6

What can CD8 cells recognise that innate immune cells cannot. (2)

Answer 6

1. Antibodies and innate immune cells cannot easily recognise virus-infected cell.
2. Viral Cell produce markers (viral peptides) on surface which CD8 cells recognise.

Question 7

Describe how MCHI (class 1 protein presenting molecule) present antigens in Viral infected cells.

How are they recognised by CD8 T cells. (4)

Answer 7

1. The Viral cell is synthesising viral proteins using ER and Golgi and assembled in cytoplasm.
2. Proteosome in cell collects samples of viral proteins, chops them into peptides and transports back into ER via TAP transporter.
3. In the ER, the peptides are loaded unto MHCI molecules.
4. CD8 with corresponding receptor recognises viral peptide in MCHI as foreign and kills target cell.

Question 8

How do CD4 cells work? (2)

Answer 8

1. They direct immune response.
2. They recognise viral peptides on SPECIALISED antigen-presenting cells with MCHII (class two) molecules.
3. They inform specialised cells what action to take.

Question 9

What Specialied Cells have MCHII molecule for antigen presenting?

How do MCHII (class 2 protein presenting molecule) presents antigens? (4)

Answer 9

1. Antigen is taken up from extracellular space by Macrophages and Dendritic cells. B-Cells do this by using antibody on surface.
2. These are degraded by proteases and loaded unto MCHII molecule (which are located in endosomes) to be presented to CD4 cells.

Question 10

How do CD4 cells help B cells mature? (3)

Answer 10

1. The B cell presents antigen to T cell.
2. The T cell uses cytokines (via Juxtacrine signalling) to signal B cell.
3. The T cell stimulates the B cell to take action such as response to antigen, affinity maturation, and what type of isotope to use.

Question 11

How do CD4 help Macrophages infected with Mycobacterium Tuberculosis?

What is this seen as on an X-ray?

Answer 11

1. The infected cell presents TB on MCHII on surface.
2. CD4 with corresponding TB affinity uses cytokines to signal cell to take action. e.g response to antigen, affinity maturation, and what type of isotope to use.
3. This is seen as granuloma in X-rays when Macrophages are activated and fuse to form multi-nucleated GIANT cells.

Question 12

What is the difference between T cells and B cells following clonal selection? (1)

Answer 12

T cells do not mutate their receptors. (1)