T lymphocytes

Question 1

What is a T lymphocyte?

Answer 1

Lymphocye that detects and combats INTRACELLULAR processed pathogens

Does this by seeing through TCR

Question 2

HOw does a TCR ‘see’ antigen?

Answer 2

It is presented by MHC onto its receptor - activating it by increasing AVIDITY

Question 3

Describe the structure of a T-cell receptor

Answer 3

Analgous to CONSTANT region of antibody - Fc

It is a HETERODIMER - alpha and beta unit

CD3 receptors are part of it too, as co-receptors, transmitting signal from TCR into cell

Question 4

WHat are the two main types of T-cell?

Answer 4

Those that use CD8 co-recptor, seeing MHC CLass I

Those that use CD8 and MHC I

Question 5

What is the function of CD8 T-cells?

Answer 5

They are cytotoxic, involved in killing target cells via:

• perforin
• cytokines
• induction of apoptosis

Question 6

What is the function of CD4 T-cells?

Answer 6

Known as T-helper cells

Secrete cytokines
Recruit effector cells
Activate macrophages

Question 7

How are T-cells developed?

Answer 7

In the thymus, precursors arrive immature, from BONE MARROW - no CD4/8 or TCR

Then, pre-T cell receptor is added (beta chain)
This is then checked and if functional, it can pass on

Then an alpha chain is added.
Important checkpoint
- if bind too tightly
- can't see MHC
- bind to self
They are apoptosed

Then, CD4 AND 8 receptors are added.

Selection of CD4 or 8 is done in THYMUS MEDULLA

Question 8

How is TCR diversity established?

Answer 8

Ig gene rearrangement

- each chain coded for by different groups of genes

Question 9

What are MHC molecules?

Answer 9

Major histocompatibility complex

• Molecules that display a sample of cell’s contents at surface for immune response
• – continuously, even if not infected

Question 10

What is the MHC?

Answer 10

A group of tightly linked proteins, aka HLA

Responsible for immune response and presentation of antigens to T lymphocytes via MHC molecules.

Question 11

Describe the types of MHC molecule

Answer 11

Class I

• 3 alpha, 1 beta chain
• CD8 binds to alpha 3

Class II

• 2 alpha, 2 beta
• CD4 binds to beta 2

alpha 3 and beta 2 are Ig like

the others are peptide bind regions

Question 12

What is the difference in MHC molecules?

Answer 12

Class I presents peptides upto 10 AAs long

Class II presents longer

Question 13

How many HLA are there?

Answer 13

SIx, three for each class of MHC, meaning they are polygenic

Question 14

HOw are HLA genes expressed?

Answer 14

They are codominant

Question 15

On which cells are MHC Class I and II present?

Answer 15

Class I
- On every nucleated cell

Class II
- ‘Professional APC - give example’

Question 16

Give examples of APCs

Answer 16

Dendritic cells

B cells

Activated macrophages

Question 17

What are APCs

Answer 17

Cells that present peptides to T cells in order to start adaptive immune response

Question 18

Where are APCs located

Answer 18

Dendritic - skin, mucus

B cells - lymphoid

Macrophage - lymphoid

Question 19

What are the two ways APCs present antigens?

Answer 19

Endogenously (CD1) and exogenously (CD8)

Question 20

How do Class 1 MHCs present antigens?

Answer 20

TAP - transporter associated with antigen processing

Antigen is in cell, joins after being broken by proteasome

MHC in ER via TAP, presented on surface via vesicle

Question 21

How do Class II MHCs present antigens?

Answer 21

CLIP - CLass II associated invariant chain peptide

Exogenous AG enters cell,

MHC fuses with endosome, forming complex

The MHC is formed with an invariant peptide, keeping it intact till antigen comes, but CLIP replaces this bfore