Initiation of lymphocyte response Flashcards
(25 cards)
What morphological changes do B cells undergo after cell mediated immunity?
- The cell body enlarges
- Increased cytoplasm and organelles
- Highly developed endoplasmic reticulum
What morphological changes do T cells undergo after cell mediated immunity?
- The cell body enlarges
- Increased cytoplasm and organelles
- Highly developed endoplasmic reticulum not as big as B cell though
What is the purpose of dendritic cells in lymph nodes?
It expresses required surface molecules to activate naive T cells
What is cross-presentation?
A process by which primarily dendritic cells, present exogenous antigens on MHC class I molecules, which typically present endogenous (self-generated) antigens
How does cross-presentation enable CD8+ T cell activation?
In cross-presentation, dendritic cells present exogenous antigens on MHC class I molecules, triggering CD8+ T cells to attack the pathogen
Why is cross-presentation important for immune surveillance?
It enables dendritic cells to present exogenous antigens on MHC class I molecules, activating CD8+ T cells against pathogens or cancers that aren’t directly infecting the dendritic cells
What are the two possible pathways of cross presentation?
- Cytosolic pathway
- Vacuolar pathway
What happens in the cytosolic pathway?
Exogenous antigens are transferred to the cytosol
What happens in the vacuolar pathway?
Exogenous antigens are internalised into vesicles and processed in the acidic vesicle
What antigens are commonly processed via the cytosolic pathway?
Viruses and tumor antigens
What antigens are commonly processed via the vacuolar pathway?
Bacteria and extracellular pathogens
What do dendritic cells do in response to danger signals?
They are activated and migrate away from the periphery to draining lymph nodes
What is the immunological synapse?
The interface between antigen presenting cells and T cells
What are the four steps of T cell activation?
- Antigen recognition
- Co-receptors
- Adhesion molecules
- Co-stimulation
What are two important notes about the recognition of peptide + MHC?
- Two or more T cell receptors must be engaged for several minutes to commence activation
- This interaction is weak on its own
Why is it important that the initial recognition of peptide + MHC is weak on its own?
It prevents accidental activation which prevents autoimmune diseases
What is the purpose of co-receptors?
Help stabilise the weak binding between the TCR and MHC
What is the purpose of adhesion molecules?
They strengthen the connection between T cells and antigen presenting cells so activation signals last long enough
What binds to what with adhesion molecules?
LFA-1 on the T cell binds to the ICAM-1 on the APC
What are the two signals for activation of T cells?
- Signal 1 = antigen recognition
- Signal 2 = co-stimulatory signal from dendritic cells
Where does the second signal come from and what does it do for T cell activation?
Second signal comes from B7 molecules on the antigen presenting cell which binds to CD28 on the T cell
What are the two inhibitor receptors to prevent T cell overreaction?
- CTLA-4
- PD-1
What does the inhibitory receptor CTLA-4 do?
Competes with CD28 to bind B7 molecules preventing excessive activation
What does the inhibitory receptor PD-1 do?
Binds to PD-L1/PD-L2 on APCs to help turn off the immune response after infection is controlled
