MIIM - Ocular Defences: The Immune System III - Week 4

Question 1

Is the MHC marker and peptide recognition by a T cell alone enough to activate it?

Answer 1

No

Question 2

Which cell is the best antigen presenting cell?

Answer 2

Dendritic cell

Question 3

In non-inflamed tissue, how efficient are dendritic cells at capturing antigens and stimulating naïve T cells?

Answer 3

Highly efficient at capturing antigens but poor stimulators of naïve T cells.

Question 4

Do dendritic cells have a high or low level of MHCII on their plasma membrane?

Answer 4

Low

Question 5

What is secreted by dendritic cells?

Answer 5

TGF-β

Question 6

Can dendritic cells migrate easily to lymph nodes?

Answer 6

No, its restricted

Question 7

What initiates dendritic cell maturation, and what is it essential for?

Answer 7

Initiated when it binds pathogens.

Essential for naïve T cell activation.

Question 8

Name 6 maturation events for dendritic cells.

Answer 8

Migration of the cell to draining lymphoid tissue
Increased antigen processing
Increased MHCI and MHCII expression
Increased surface espression of adhesin
Expression of co-stimulatory molecules
Secretion of cytokines

Question 9

Do maturing dendritic cells gain or lose capacity to capture antigens?

Answer 9

Lose

Question 10

Name the three molcules involved in the best characterised co-stimulatory signal.

Answer 10

CD80 and CD86 on the surface of the APC, and CD28 which is found on all T cells.

Question 11

Define signal 1.

Answer 11

The antigen specific recognition by a T cell

Question 12

Define signal 2.

Answer 12

A co-stimulatory signal needed in addition to signal 1, given by mature dendritic cells.

Question 13

Define signal 3.

Answer 13

Secretion of selected cytokines by the mature antigen presenting cell that has successfully activated and costimulated a naïve T cell.

Question 14

Once a naïve CD4 T cell receives signals 1 and 2, what does it express (2) and secrete? What else?

Answer 14

It expresses CD40L and IL-2R.

It secretes IL-2 and now proliferates.

Question 15

What happens to a CD4 T cell with signal 3?

Answer 15

It differentiates, and performs its effector function.

Question 16

What does signal 3 facilitate in CD4 T cells?

Answer 16

Facilitates differentiation along several possible pathways, each leading to a cell with a particular function.

Question 17

Where do mature APCs interact with CD8 T cells?

Answer 17

Secondary lymphoid tissue

Question 18

If a B cell binds an antigen in the lymphoid tissue, can it both release antibodies as well as act as an APC?

Answer 18

Yes

Question 19

When a B cell act as an APC, which MHC marker does the antigen end up on?

Answer 19

Class II

Question 20

What do activated T cells expressing CD40L do with it? What happens after this (4)? What kind of cell additionally arises from this?

Answer 20

It binds B cells that display CD40 and antigen peptides on their MHC.
The B cells proliferate, isotype switch, and undergo affinity maturation, and secrete their antibodies.
Some of these B cells differentiate into memory B cells.

Question 21

Are CD80 and CD86 constitutively expressed on APCs? What about CD40L on T cells?

Answer 21

No, none of them are constitutively expressed (only weakly expressed).

Question 22

Define PAMP.

Answer 22

Pathogen associated molecular pattern

Question 23

What interaction is a major signal to induce expression of CD80 and CD86?

Answer 23

Their interaction with PAMPs

Question 24

Can T cells become activated in the absence of co-stimulation?

Answer 24

No

Question 25

Can T cells express CD40L if they are not activated?

Answer 25

No

Question 26

Can B cells be fully activated in the absence of CD40 ligation by CD40L?

Answer 26

No

Question 27

Once CD4 T cells are activated and migrated to the infection site, what two things do they do there?

Answer 27

Activate tissue macrophages

Activate other cell types such as fibroblasts, neutrophils, and keratinocytes.

Question 28

What molecule do cytotoxic T cells use to kill infected cells?

Answer 28

Perforin

Question 29

Name three ways T cell activation can be inhibited, and give one example for each.

Answer 29

Immunosuppressive drugs - inhibiting IL-2 production
Antibodies - block T and APC/T and B cell interactions
Soluble ligands - block co-stimulatory interactions

Question 30

Describe briefly how the innate and adaptive immune systems activate each other (5).

Answer 30

Innate activates adaptive by increasing co-stimulation via APC action and producing cytokines inducing T cell differentiation.
Adaptive activates innate by producing antibodies that act as opsonins triggering phagocytosis and complement cascades, and producing cytokines recruiting macrophages and other phagocytes.

Question 31

Name the cytokine responsible for upregulating the production of the following antibodies:
IgA
IgG
IgE

Answer 31

IgA - TGFβ
IgG - IFNγ
IgE - IL-4