T Cell Activation

Front 1

T cells recognize antigens via their ____________

Back 1

TCR

Front 2

What is clonal selection?

Back 2

Only mature T cells whose TCR binds a certain MHC-peptide complex can be activated

Front 3

T cells are subdivded into which two populations and how?

Back 3

T cells are divided into CD4 T cells or CD8 T cells based on the exprssion of CD4 membrane of CD8 membrane proteins

Front 4

How do CD4 T cells function as and what antigenic peptides do they recognize?

Back 4

They have TCR that recognize antigenic peptides that are presented by MHC class II proteins
-CD4 T cells function as T Helper cells

Front 5

How do CD8 T cells function and what antigenic peptides do they recognize?

Back 5

CD8 T cells have TCRs that recognize antigenic peptides that are presented by MHC class I proteins
-CD8 T cells function as cytotoxic cells

Front 6

CD4 and CD8 are known as___________

Back 6

co receptors

Front 7

What do CD4 and CD8 recognize

Back 7

They recognize a conserved region of the MHC molecule that is presenting the antigenic peptide to the TCR but these molecules do not influence antigen secificty of the TCR, but they do strengthen the interaction between the TCR and the MHC-peptide complex of the TCR

Front 8

What does full activation of a T cell require?

Back 8

Two signals

Front 9

What are the Two signals that fully activate a T cell?

Back 9

1) INteraction of T cell's TCR with the MHC/peptide complex on the antigen-presenting cells
2) Interaction of an accessory molecule CD28 on the T cell with a co-stimulatory molecule B7 on the APC

Front 10

What provides the B7 co-stimulatoion function?

Back 10

Antigen presenting cells provide this necessary co-stimulatory function (expression B7) so only antigen presenting cells can activate T cells

Front 11

What is clonal anergy?

Back 11

IT is when the T cell receives only the first signal and fails to receive the co-stimulatory signal and thus the T cell enters a state of non responsiveness known as clonal anergy.

Front 12

List the stages in T cell development

Back 12

1) Least mature thymocyte do not express with CD4 or CD8 are referred to as double negative DN thymocytes. They do not have alpha beta TCRs
2) DN thymocytes develop into DP (CD4+ CD8+) thymocytes and at this immature stage they express alpha beta TCR
3) Immature DP thymocytes that are positvely selected by MHC class I/peptide complexes develop into CD8 T cells (lose CD4) and those that are positvely selected by MHC class II peptide complexes develop into CD4 T cells (lose CD8)

Front 13

What are CD8 T cells positvely selected by?

Back 13

Self peptides that are presented by self-MHC class I molecules

Front 14

What are CD4 T cells positvely selected by?

Back 14

Self-peptides that are presented by self-MHC class II molecules

Front 15

What are CD8 T cells most effective in combating?

Back 15

Pathogens that replicate in the cytosol (viruses)
-Controls viral infections
-MOUses that lack this cell get killed by viruses

Front 16

What are CD4 T cells most affect against?

Back 16

Depending aggainst pathogens that replicate in intracellular vesicles (Mycobacterium tuberculosis)

Front 17

How are autoreactive T cells generated?

Back 17

Since the immature tymocytes express a randomly generated TCR repertoire a small proportion of these TCRs will possess high affinity for self-peptide/ self-MHC complexes. These cells will become self-reactive if they are not elimianted

Front 18

How does negative selection occur?

Back 18

Cells that have high affinity TCRs for self-peptide/self-MHC complexes are killed at either the immature DP or the mature SP stage

Front 19

What provides signal 1

Back 19

Non professional APCS such as endothelial cells can provide signal 1 but endothelial cells are less effeicent at proving signal 2

Front 20

What completely activates T cells?

Back 20

Professioanl antigen-presenting cells such as dendritic cells, macrophages and B cells are able to present antigenic peptides complexed with MHC II proteins and provide the co stimulatory signal necessary to completely activate T cells
-In order words only they provide both signal 1 and signal 2

Front 21

What does signal 2 involve?

Back 21

It involves B7 which is a set of cell surface protein that binds to the CD28 protein on the T cell to provide a co-stimulatory signal

Front 22

What do dendritic cells express?

Back 22

They express high levels of MHC class I and II proteins and B7 proteins and are very good activators of T cells

Front 23

What do Resting macrophages express?

Back 23

-Low levels of MHC class II proteins and do not express B7 proteins thus cannot activate naive T cells
-When macrophage is stimulated by phagocytosis of an antigen or Interaction of PRR/PAMP, it increases its expression of both MHC class II and B7 proteins

Front 24

What do Resting B cells express?

Back 24

Low levels of MHC class II proteins but do not express B7 proteins
-Binding of antigen to B cell receptor activates a B cell and the PRR/PAMP interaction also activates B cell
-B cell increases its expression of MHC class II proteins and begins to express B7

Front 25

There are two forms of dendritic cells what are they called?

Back 25

Immature and Mature Forms

Front 26

What are the characteristics of the immature form of Dendritic Cells?

Back 26

They are highly phagocyotic, express TLR and other PRR's
-Called Langerchans cell
-Reside in skin due to skin being common infection site

Front 27

Explain how dendritic cells would be involved in a bacteria infection

Back 27

Infection in skin- bacteria get underskin and replicate
-They then get phagocytosed by DC
-The DC react with Pamps on the pathogen and differientiate to mature DC
-INteraction of pathogen causes DC to mature which has MHC and B7
-This migrates to draining lymph nodes
-IF DC is not infected it will exprss survival signal
-At lymp nodes, it scans for DCS for peptide complxeses, if high affinity they bind with T cells
-Mature DC can provide signal 1 and 2 to naive T cell to trigger T cell activation