Antigen Processing and Presentation - Bittencourt Flashcards
What do dendritic cells present to?
Naive T cells and CD8+ T cells
dendritic cells initiate T cell response
What do macrophages present to?
CD4+ cells in the effector stage of cell mediated immunity
What do B cells present to?
CD4+ cells during humoral immunity
What are some non professional APCs?
- Neutrophils
- NK cells
- T cells
- Basophils
What is it called when APCs provide additional stimulus to T cells?
Co-stimulation
What is the sequence of events for processing of an endocytosed antigen?
MHC II pathway
- Uptake of extracellular pathogen
- Processing in endosome/lysosome vesicles
- Biosynthesis and transport to of MHC II molecules to endosomes
- Association of processed peptides with MHC II molecules in vesicles
- Expression of peptide-MHC II complex to APC surface to CD4+ T cells
What are the most important proteolytic enzymes involved in protein degradation?
cathpesin
What is the variable region of the MHC II molecule?
alpha 1 + beta 1 = peptide binding cleft
Where do CD4+ T cells bind to on MHC II molecules?
beta 2 non variable region
Where do CD8+ T cells bind to on MHC I molecules?
alpha 3 non variable region
What is the variable region of the MHC I molecule?
alpha 1 + alpha 2 = peptide binding cleft
Where does the association of processed peptides with MHC II molecules take place?
endosomes
Where does proteolytic degradation take place in the MHC I pathway?
Proteosomes
In which pathway are proteins ubiquitinated for proteosomal degradation?
MHC I pathway
The TAP transport system is involved in which MHC pathway?
MHC I
What is the purpose of TAP?
mediates the transport of peptides entering into the ER
Exogenously acquired proteins will generate peptides that activate?
CD4+ T cells
Endogenously acquired proteins will generate peptides that activate?
CD8+ T cells
What is the predominant type of TCR and where is it found?
alpha/beta TCR
found in lymphoid tissues
Where are yQ TCRs found?
in mucosal surfaces
Which TCR is MHC dependent?
alpha/beta TCR
Which TCR is MHC independent?
yQ TCR
What do most T lymphocytes recognize?
Peptides
Which T cell recognizes peptides of 8-10 AA ?
CD8+ cells on MHC I
Which T cells recognize peptides > 13 AA ?
CD4+ T cells on MHC II
True or False: T cells may be specific for haptens
TRUE
What is closely associated with the TCR and helps to confirm its ID as a T cell?
CD3 complex
CD3 complex
closely associated to the TCR
transduces activation signals
invariant, doesnt contribute to T cell specificity but is needed to generate a response
What is MHC restriction?
When T cells only recognize things displayed to them on SELF MHC
Prevents autoimmunity
Which receptor is not restricted by MHC presentation?
BCR on B cells
What do B cells recognize?
- Peptides
- Proteins
- Nucleic acids
- Polysaccharides
- Lipids
What are the differences between TCR and BCR’s?
- BCR has 2 Ag binding sites
- BCR does not interact w MHC molecules
- B cells can recognize soluble antigens
How are lipids presented to T cells?
Through CD1 on NKT cells
What 2 signals are required for T cell activation?
- SPECIFIC SIGNAL - where MHC-peptide complex binds to TDR-CD3 complex
- CO-STIMULATORY SIGNAL - where CD28 on T cell interacts with B7 (CD80/CD86) on APC
What happens when T lymphocytes are stimulated without a co-stimulatory signal?
Clonal anergy occurs
A state of no responsiveness, does not generate immune response
What are the activating receptors on T cells?
CD28 and ICOS
What are the inhibitory receptors on T cells?
PD-1 and CTLA-4
CD28 on CD4+T cells bind to __________ on APC’s
B7 (CD80/CD86)
*** costimulatory transduction to activate naive T cells
What makes dendritic cells most effective for initiating T cell responses?
- Located at sites where microbes enter
- Expresses high levels of co-stimulatory molecules needed to activate Naive T cells
- Captures and transports antigens to draining lymph nodes
When do dendritic cells express a lot of co-stimulatory molecules?
Once activated
after capturing Ag high co-stimulatory molecules are expressed to activate Naive T cells
When do dendritic cells express a lot of Fc and mannose receptors?
When resting in tissue waiting to capture Ag
Do resting dendritic cells or activate dendritic cells have a longer half life?
Activated
Macrophages and dendritic cells are inducible by _______
IFN-y
What do dendritic cells present to CD8+ T cells?
infected cells or tumor cells
What is cross-presentation / cross - priming?
Ability of dendritic cells to present to naive CD4+ T cells and CD8+ T cells
