Day 21 - 13/10/14

Question 0

What are Alpha-Beta T Cells called before they recognise their SPECIFIC foreign antigen?

Answer 0

Naive

Question 1

What is the percentage of T-Lymphocytes and alpha-beta-T-Lymphocytes respectively?

Answer 1

70% of lymphocytes are T-Lymphocytes

95% of T-Lymphocytes are Alpa-Beta Lymphocytes

Question 2

What happens when T cells recognise their specific foreign antigen on APCs?

Answer 2

1) T Cells undergo cell division called CLONAL EXPANSION

2) Then they DIFFERENTIATE in to EFFECTOR CELLS

Question 3

What can you say about TCR and BINDING?

Answer 3

TCR cannot bind on its own

CO-STIMULATORY molecules

• allow TCR to bind to APC
• initiate important signalling

Question 4

What structure forms at the point of contact between APC and TCR?

Answer 4

IMMUNE SYNAPSE

Question 5

What is the structure of IMMUNE SYNAPSE?

Answer 5

1) ADHESION MOLECULES such as LFA-1 , ICAM-1
form a TIGHT RING on the T CELL and APC membranes

2)The TCR and the COSTIMULATORY molecules are held in place at the centre

Question 6

What can you say about COSTIMULATORY MOLECULES in context of their presence in cells?

Answer 6

They are INVARIENT

-do not differ on different cells and are NOT specific

Question 7

Name major and additional COSTIMULATORY Molecules.

Answer 7

CD3
CD4
CD8

CD28
CD80
CD86

Additional
CD40
OX40
ICOS

Question 8

What does CD3 do?

Answer 8

CD3 has long CYTOPLASMIC TAILS which bind and activate TYROSINE KINASES.

This initiates INTRACELLULAR SIGNALLING after specific antigen detection.

Question 9

What does CD4 do?

Answer 9

CD4 binds to CLASS 2 MHC to make the TCR to PEPTIDE-MHC binding better.

CD4 also drags the enzyme: Ick
to CD3.

CD3 can then begins to RECRUIT SIGNALLING ENZYMES
inside the T CELL.

Question 10

What does CD8 do?

Answer 10

Same as CD4, but binds to

CLASS 1 MHC and Ick

Question 11

What does CD28 do?

Answer 11

Binds to CD80 and CD86 on the APC.

This LIGATION triggers signalling which is essential to TRANSCRIBE and make INTERLEUKIN 2 (IL2)

Question 12

What does IL2 do?

Answer 12

IL2 and IL2 RECEPTOR is made by CD4+ cells.
AUTOCRINE interaction between these two result in
CLONAL EXPANSION

Question 13

What happens if you don’t have COSTIMULATORY MOLECULES?

Answer 13

T-Cells become TOLERANT of antigens and is unable to respond to them in the future.

Question 14

What do CD40ligand, OX40 and ICOS do?

Answer 14

After CLONAL EXPANSION, differentiation of the TCELL occurs.

Question 15

What APC presents antigens in a way that PRIMES NAIVE CD4+ T Cells?

Answer 15

Dendritic Cells

Question 16

Dendritic Cells are SENTINELS.

What does this entail?

Answer 16

Sample the environment by

• Endocytosis
• Pinocytosis
• phagocytosis

Question 17

What happens when Dendritic Cells find antigens?

Answer 17

Dendritic Cells leave the tissue via AFFERENT LYMPHATICS and then enter the T-Cell area of the LYMPH NODES.

There they activate the corresponding CD4+ NAIVE T CELLS

Question 18

How is the Dendritic Cells activated?

Answer 18

Dendritic Cell is ACTIVATED by DANGER SIGNALS such as picking up components of Bacteria/Viruses with the TOLL LIKE RECEPTORS (TLR)

Question 19

What do the DANGER SIGNALS do?

Answer 19

Increase ANTIGEN PROCESSING

and CCR7 CHEMOKINE RECEPTOR needed to drive Dendritic Cells to the LYMPH NODES

Increase expression COMPLIMENTARY MOLECULES
CD40
CD80
CD86

Question 20

Define Immunological Tolerance

Answer 20

A state of antigen specific unresponsiveness to an antigen which
Under other circumstances can stimulate an active immune response.

Question 21

What happens if Tolerance doesn’t work?

Answer 21

AUTOIMMUNITY

Question 22

What does Tolerance usually happen to?

Answer 22

Food Proteins
Commensal Microbes
Foetus

Question 23

Give examples of Tolerance diseases

Answer 23

Coeliac disease - allergic for wheat protein

Crohn’s disease - allergic to commensals

Question 24

What are the two types of tolerance?

Answer 24

• Central
• Peripheral

(tolerance)

Question 25

What is CENTRAL tolerance?

Answer 25

Tolerance against SELF ANTIGENS

Affected Cells- T&B lymphocytes

Affected Organs- THYMUS & BONE MARROW

Question 26

What is PERIPHERAL tolerance?

Answer 26

Tolerance against

• HARMLESS FOREIGN ANTIGENS
• SPECIFIC SELF ANTIGENS (e.g. During lactation milk/Sex hormones)

Affected Cells - MATURE LYMPHOCYTES
Affected Organs - Secondary Lymphatic organs

Question 27

What are the 4 cellular mechanisms of Tolerance?

Answer 27

Ignorance
Clonal Deletion
Clonal Anergy
Active Regulation

Question 28

When does IGNORANCE occur?

Answer 28

Lymphocytes which aren’t usually exposed to tissue antigens and so cannot make an immune response.

(Such as lens of the eye/testis)

Question 29

When does CLONAL DELETION occur?

Answer 29

When MATURING lymphocytes encounter SELF ANTIGENS in the THYMUS/BONE MARROW.

Self-Reactive T-Cells die.

Question 30

When does CLONAL ANERGY occur?

Answer 30

Occurs when MATURE T LYMPHOCYTES
encounter SELF/FOREIGN ANTIGENS
presented by APC
in the ABSENCE of COSTIMULATORY molecules

Can happen in BONE MARROW or
PERIPHERAL IMMUNE SYSTEM

Question 31

When does ACTIVE REGULATION occur?

Answer 31

REGULATORY T CELLS
against SELF ANTIGENS in THYMUS
or FOREIGN ANTIGENS in PERIPHERAL NERVOUS SYSTEMS