Lec 9: Antigen recognition Flashcards
What is an antigen
and antigen is a substance that stimulates an immune response.
They contain intact epitopes that are recognized by BcR
They contain processed peptide epitopes that are recognized by TcR
What type of antigens do B cells recognize
intact antigens
What type of antigens do T cells recognize?
processed antigens
What might hide a liner or conformational epitope from its binding domain?
Either protein is denatured, or the native folding of the protein hides the linear domain
Epitope
Ag-Ab interaction
the epitope is the portion of the antigen recognized by the antibody
-> antigenic determinant
Paratope
Ag-Ab interaction
the paratope is the portion of the antibody that binds an epitope
-> antigen binding site
Multivalent antigen
contains more than one identical epitope
Purpose of a multivalent antigen
can incrementally stablize BcR or antibodies bound to FcR on the cell membrane
Multivalent antigens can cluster reeceptors
envelope or capsid proteins on viruses
cell surface proteins
stabilize BcR bound to FcR and cluster them on the cell surface
-> activation and cell signalling
Procesed antigen
Antigen bound to MHCII and presented to TcR on a CD4 cell
intact antigen
soluable antigen binding to a B cell
What is the difference in the way T cells and B cells recognize antigen? **
B cells = intact
T cells = processed
What types of antigens does MHC class I recognize
endogenous Ag
(and exogenous antigen cross-presented by CD8+ DCs only)
MHC I peptide\CD8+ cells
What types of antigens do CD1d recognize
endogenous and exogenous lipid Ag
NKT cells
MHC class II
exogenous and endogenous Ag
MHC II-peptide
CD4+ T cells
BcR and antibodies
intact Ag
B cells and cells expressing FcRs
Which cells are MHC I expressed on
all nucleated cells
Which cells are MHC II expressed on
APCs ie DCs, peptide is not fully in the pocket
Which is the only type of cell that can activate a naive T cell
DC
name all of the APCs
DC macrophage monocyte B cell epitheliad cell] eosinophil
Purpose of shutting off cellular proteasome
means that MHCI antigen presentation is stopped
-> inhibition to mask cytocolic antigens
CD8+ DCs can cross-present antigen
cross-presentation occurs when exogenous antigens are transferred to the MHCI pathway
what the fuck is cross presentation
idk
Antigen cross-presentation assists when MHCI pathways are compromised
disruption of the proteasome can disrupt MHCI presentation in APCs
Transfering exogenous antigen to MHCI can overcome this deficiency
What is the difference in early TLR responses between DCs and macrophages
DC -> pepides stay on the surface
macrophages -> transient peptides
DC-T cell interactions
T cells activate by way of multipe antigen recognition events, and stable synapses only form at specific stages of Ag presentation
T cells sampling DC with no antigen in lymph node = short contact
T cells sampling DC with antigen in lymph node = long contact
-> binds MHC and waits for co-stimulation
The Tcr-CD3 complex
only processed antigen will do
assessing self vs non-self by peptide sampling
mature T cells weakly recognize MHC and only activate if presented with cognate ligans
T cells also require co-stimulation to activate
Co-stimulaton via cytokines
T cells need cytokine-mediated co-stimulation as a final act
-> secreation of IL-2 = clonal proliferation
Co-stimulation of T cells with CD80/CD86 via CD23/CTLA-4 ligand
directs howe a T-cell will proliferate and differentiate
DC microenviroment sets the stage for T cell programming
DC microenvironment sets the stage for T cell programming
Resting = Low Ag, no costimulation
-> short contacts and leads to tolerance
Active = high Ag, high costimulation and cytokines
-> long contacts and leads to effectors
Exhausted DC= high Ag, High costimulation
-> short contacts and leads to memory
DC instruction of T cells determines
ON or OFF
Type of response
Population size of Activated T cells
Multiple signals drive T cell subtype differentation
signal 1 = MHC: TcR
singla 2 = costimulation
signal 3 = cytokine and cellular context
Define the follownig:
Antigen
epitope
paratope
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How does the type of epitope impact antibody binding?
give an example
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Compare and contrast:
MHCI antigen processing pathway
MHCII antigen processing pathway
Cross-presentation
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What are the 3 signals required for a DC to activate a naive T cell?
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