L16 - Antigen Presenting Cells / Innate Recognition Flashcards
What are the features of a naive T cell?
- Has not experienced antigen
- No effector function
- Circulates between blood and lymphoid organs
- Need to acquire effector function
How long does it take for naive T cells to survey all the lymph nodes in the body?
Roughly 24 hours
How do naive T cells get in touch with cognate antigen when most pathogens invade via the periphery?
Through dendritic cells which are found in most tissues. Uptake material, enter lymph vessels, migrate to paracortext where naive T cells congregate
What are the general differences between extracellular and intracellular antigen presentation?
Extracellular generally are presented on MHC II molecules, intracellular MHC I
What is cross presentation?
Presentation of MHC II on MHC I by dendritic cells
Why is cross presentation important
Viruses may infect peripheral tissue. Cross presenting cells are able to utilize the MHC I pathway to remain uninfected while still triggering an adaptive immune response of activated CD8+ T cells against peripheral tissue cells
What drives dendritic cells to the lymph node / T cell zone?
It’s CCR7 receptor
What ligands does CCR7 recognize?
CCL19 and CCL21
How does the phenotype of dendritic cells change?
Exist in immature state of high phagocytic activity but poor capacity to present antigen to T cells. Stimulation induces maturation, changing functional orientation towards antigen presentation
What receptor do immature dendritic cells express?
Some B7 and low levels of MHC molecules
How does the phenotype of dendritic cells change as it enters the lymph node?
Upregulation of B7 to co-receptor CD28 from T-cells, and upregulation of MHC II for presentation
What are the three signals APCs deliver to naive T cells and what do they do (roughly)?
Signal 1 - TCR - MHC interactions
Signal 2 - Costimulatory molecules (B7/CD28)
Signal 3 - Soluble factors such as cytokines
