10 T and B cell effectors Flashcards
what expresses MHC 1
nucleated cells (and APC)
what expresses MHC 2
APC
where are cytosolic pathogens degraded
cytosol
what do cytosolic pathogens bind to
MHC 1
what are cytosolic pathogens presented to
effector CD8 T cells
what is the effect on presenting cytosolic pathogens to cell
cell death
where are cross-presentation of exogenous antigens degraded
cytosol (by retrotranslocation)
what do cross-presentation of exogenous antigens bind to
MHC 1
what are cross-presentation of exogenous antigens presented to
naive CD8 T cells
what is the effect when cross-presentation of exogenous antigens are presented to cell
the presenting cell usually a dendritic cell, activates CD8 T cell
where are the intravesicular pathogens
endocytic vesicles (low pH)
what do the intravesicular pathogens bind to
MHC 2
what are the intravesicular pathogens presented to
effector CD4 T cells
what is the effect when intravesicular pathogens are presented
activation to kill intravesicular bacteria and parasites
where are the extracellular pathogens and toxins degraded in
endocytic vesicles (low pH)
what are the peptides that the extracellular pathogens and toxins bind to
MHC 2
what are the extracellular pathogens and toxins presented to
effector CD4 T cells
what is the effect of extracellular pathogen and toxins when presented to cell
activation of B cells to secrete Ig to eliminate extracellular bacteria/toxins
cellular response
Cytotoxic t cell CD8 release perforin – causes target cell to lyse
humoral response
Helper CD4 cell
types of uptake
cellular and humoral
cellular immune response
antigen as intracellular
humoral immune response
antigen is extracellular
cellular response
Cytotoxic t cell CD8 release perforin – causes target cell to lyse
humoral response
Helper CD4 cell
types of uptake
cellular and humoral
cellular immune response
antigen as intracellular
humoral immune response
antigen is extracellular
Antigen presenting: Cellular response
Partly folded MHC class 1 in ribosome binds a proteins. Cytosolic proteins and defective ribosomal products degraded are taken to ER Peptide bins MHC class 1, completes folding, MHC released from TAP to go to cell membrane
Antigen presenting: Humoral response
- invariant chain (li) forms complex with MHC class 2 molecule, blocking peptides binding and misfolded proteins
- li is cleaved in an acidified endosome, leaving short peptide fragment, CLIP, still bound to the MHC 2
- endocytosed antigens degraded to peptides in endosomes, CLIP peptide blocks binding of peptides to MHC 2
- HLA-DM binds to MHC 2 releasing CLIP, allowing other peptides to bind. MHC 2 travels to cell surface
Activation phase (MHC 2) Immune system cells - Bacterium
- Bacterium infects macrophage and enters vesicle, producing peptide fragments
- Bacterial fragments bound by MHC class 2 in vesicles
- Bound peptides transported by MHC class 2 to the cell surface
Activation phase (MHC 2) Immune system cells - antigen
- Antigen bound by B-cell surface receptor
- Antigen internalized and degraded to peptide fragments
- Fragments bind to MHC class 2 and transported to cell surface
how are macrophages activated
TH1 cell recognises complex of bacterial peptide with MHC class 2 and activates macrophages
how are B cells activated
Helper T cell recognises complex of antigenic peptide with MHC class 2 and activates B cell CD4 T cells MHC 2
Activation phase (MHC 1) – All cells
Virus infects cell
Viral proteins synthesised in cytosol
Peptide fragments of viral proteins bound by MHC class 1 in ER
Bound peptides transported by MHC class 1 to cell surface
Effector phase (MHC 1)
Cytotoxic T cell recognises complex of viral peptide with MHC class 1 and kills infected cell CD8 T cells MHC 1
positive selection
not viable if do not bind to a specific peptide
negative selection
bind too tightly so die)
Positive negative selection
Not all combinations of MHC loaded peptides and T cell are possible
Selection for affinity and self must take place
what occurs in positive and negative selection
- T-cell precursor rearranges its T-cell receptor genes in thymus
- Immature T cells that recognise self MHC receive signals for survival. Those that interact with self-antigen are removed
- mature T cells encounter foreign antigens in peripheral lymphoid organs and are activated
- activated T cells proliferate and eliminate infection
