Lecture 7 - T Cell Activation

Question 1

What class of MHC molecules are exogenous antigens presented on? What cells do this? Which T cells interact with these?

Answer 1

APCs like dendritic cells present Class II MHCs with exogenous peptides to CD4+ T cells.

Question 2

What class of MHC molecules are endogenous antigens presented on? What cells do this? Which T cells interact with these?

Answer 2

All host cells present endogenous antigens on Class I MHCs to CD8+ T cells.

Question 3

How can a virally infected host cell induce T cell activation?

Answer 3

The virally infected cell presents viral proteins on its MHC Class I molecules, which interact with and activate CD8+ T cells.

Question 4

What role does the proteasome play in viral protein presentation in a host cell?

Answer 4

The proteasome cuts up the protein so that it can be taken to the ER and put on a MHC Class I molecule.

Question 5

Can several different peptides bind a single MHC molecule (at different times)?

Answer 5

Yes.

Question 6

How many signals are required to activate a naive T cell?

Answer 6

Two. One from the TCR-CD4/8 co-receptor complex and another from the co-stimulators.

Question 7

What are co-stimulators?

Answer 7

Signal transduction molecules found on APCs and T cells that interact with each other during antigen presentation.

Question 8

Name two co-stimulator pairs.

Answer 8

1. B7 on APC interacts with CD28 on T cells

2. CD40 on APC interacts with CD40 ligand on T cells

Question 9

What changes occur after an immature dendritic cell phagocytizes and processes an antigen?

Answer 9

In becoming a mature DC, the cell becomes peptide loaded, and expresses high levels of MHC II and B7. It also makes IL-12 and other cytokines to activate T cells. It them migrates out of the tissue and goes to a draining lymph node.

Question 10

Do immature dendritic cells express MHC II and B7?

Answer 10

Yes but low levels.

Question 11

What is ZAP-70?

Answer 11

T cell intracellular tyrosine kinases that interact with zeta signal transduction molecules. They start the intracellular signaling cascade in T cell activation.

Question 12

What does intracellular Ca2+ release trigger in T cell activation?

Answer 12

Leads to elevated calcineurin –> activation of transcription factors for IL-2 and IL-2 receptor.

Question 13

What does cyclosporin do?

Answer 13

Blocks calcineurin. It is a drug used in organ transplantation.

Question 14

What do co-stimulators do in upregulation of IL-2 transcription in T cell activation?

Answer 14

They enhance stability of IL-2 mRNA (CD28 especially)

Question 15

What is IL-2?

Answer 15

A T-cell growth factor.

Question 16

What is a superantigen?

Answer 16

Antigens that activate a huge number of alpha and beta T cells leading to massive proliferation and high levels of cytokines. They bind to MHC II molecules outside the binding cleft, which cross-link T cells with the MHC II molecules. Can be fatal. Enterotoxins are an example.