Immunology 6 - T lymphocytes and antigen recognition

Question 1

What are the 2 major subsets of T cells?

Answer 1

• Use CD4 co-receptor, and see peptide on MHC class II (class II restricted)
• Use CD8 co-receptor, and see peptide on MHC class I (class I restricted)

Question 2

What is the function of CD8 cells?

Answer 2

• Most are cytotoxic and kill target cells
• Secrete cytokines
• Induce apoptosis in the target cell (programmed cell death, suicide)

Question 3

What is the function of the CD4 cells?

Answer 3

• T helper cells
• Secrete cytokines
• Recruit effector cells of innate immunity
• Help activate macrophages
• Amplify and help Tc and B cell responses

Question 4

Describe the development of T helper cells in the Thymus.

Answer 4

1) T cell contains no CD4 or CD8
2) pre TCR+ receptor added
3) Cell contains CD4 and CR8
4) Cell contains either CD4 or CD8 with the TCR receptor (only step in the medulla)

Question 5

Describe the process of recombination during T cell development.

Answer 5

There are three different types of genes. V (variable), D (diversity) and J (joining) regions. The V and J regions are present in both the b chain and the a chain, but the D region is only present in the b chain.

Question 6

What occurs at the pre-TCR checkpoint?

Answer 6

• Checks if the new B chain is functional - if not there is death by apoptosis.
• Must bind to MHC but not too loosely or too weakly.

Question 7

Describe the structure of the T cell receptor

Answer 7

• a chain and B chain
• The a chain contains beta and gamma subunits.
• Both have a variable region, where the processed antigen binds, and a constant region.
• Both cross the membrane, with a cytoplasmic tail

Question 8

What are MHC molecules?

Answer 8

• Display internal cell contents at the cell surface to T cells
• Markers of self, indicating the health of cells
• Continuously present peptides, even in the absence of infection

Question 9

What are the classes of MHC?

Answer 9

• MHC class 1 (transplantation agents) which control the ability for an antibody response.
• MHC class 2

Question 10

What is the structure of MHC class 1?

Answer 10

• 3 a sections, and one small B subunit
• Contains a peptide binding region (a1 and a2) a immunoglobulin like region (B2 and a3)
• The a-chain only has a transmembrane and cytoplasmic region

Question 11

What is the structure of MHC class II?

Answer 11

• Both the B chain and a chain have 2 sections - symmetrical
• Both a and B chain have transmembrane and cytoplasmic regions

Question 12

What kind of gene expression occurs in MHC?

Answer 12

Codominant.

Question 13

Where is MHC class I present?

Answer 13

MHC class I: all nucleated cells, although at various levels: levels may be altered during infection, or by cytokines

Question 14

Where is MHC class II present?

Answer 14

MHC class II: normally only on professional antigen presenting cells: may be regulated by cytokines

Question 15

What is a MHC haplocyte?

Answer 15

A group of MHC alleles - as human MHC genes are highly polymorphic.

Question 16

What is HLA?

Answer 16

Human MHC

Question 17

What are the two types of antigen processing and presentation?

Answer 17

• Endogenous antigens are synthesised in the cytoplasm

- Exogenous are captured from the external environment.

Question 18

Which cells use endogenous antigens?

Answer 18

Class I restricted CD8 T cells

Question 19

Which cells use exogenous T cells?

Answer 19

Class II restricted CD4 T cells

Question 20

What is the pathway of APCs presenting MHC type I?

Answer 20

Uses TAP transporters (associated with antigen processing) and displays the processed MHC on the cell surface following peptide production.

Question 21

What is the pathway of APCs presenting MHC type II?

Answer 21

Exogenous involves endocytosis of the antigen, which is then processed using CLIP (class II associated invariant chain peptide).

Question 22

What do the CD3 polypeptides on T lymphocytes form?

Answer 22

Form a non-variable constant region important in cell signalling.

Question 23

What is the main difference between antigen recognition between BCRs and TCRs?

Answer 23

• BCRs involve direct recognition of intact extracellular antigens.
• TCRs involve recognition of processed antigens by MHC molecules

Question 24

Which MHC types does CD8 and CD4 T lymphocytes bind to?

Answer 24

• CD8 is class I restricted

- CD4 is class II restricted