2-3 T Cell Receptor & MHC Flashcards
List some of the differences between TCRs and BCRs as it relates to:
Diversity
Binding affinity
Signal transduction
TCRs are much more diversity than BCRs
BCRs bind antigens more tightly than TCRs
TCR is found as a complex associated with CD3s because TCRs cannot transduce a signal on its own.
CD8+ T cells are also known as what? What class of MHC does it bind? Which chain is responsible for the variability?
CD8+ T cells are also known as cytotoxic T cells
Binds to Class I MHC
Alpha chain is responsible for variability
CD4+ T cells are also known as what? What class of MHC does it bind? Which chain is responsible for the variability?
CD4+ T cells are also known as Helper T cells
Binds to Class II MHC
Beta chain is most variability
Where do peptides presented by MHC I come from:
What type of pathogens?
Where are these peptides degraded?
What cell type presents these peptides to MHC I?
What are the effects on the presenting cell?
Cytosolic pathogens
Degraded in cytoplasm
Presented by CD8+ T cells
Effects on presenting cell is cell death
Where do peptides presented by MHC II come from:
What type of pathogens?
Where are these peptides degraded?
What cell type presents these peptides to MHC II?
What are the effects on the presenting cell?
Pathogens can be intravesicular (macrophage) or can be extracellular pathogens and toxins.
Both types of pathogens are degraded in endocytic vesicles (low pH)
Presented by CD4+ T cells
macrophages are activated to kill intravesicular pathogens, while the activation of B cells to secrete Ig to eliminate extracullular bacteria/toxins
How are antigens processed for presentation by Class I MHC?
Fragmented into peptides by proteasome (polyubiquitination). Framents attach to TAP protein in membrane of ER and moves into the lumen of ER where peptides are placed in binding groove of MHC class I (displacing self-peptide)...then classI:peptide goes to cell surface for presentation
How are antigens processed for presentation by Class II MHC?
Ingested antigens are taken to phagolysosome and fragmented by proteases. Peptides move to endosomal compartments and placed in binding grove of class II MHC (displacing CLIP) then class II:peptide carried to cell surface
On what cell types are MHC class I molecules expressed?
ALL nucleated cells…therefore not RBCs
What are anchor residues and why are they important?
Anchor residues (contact residues) conserved for binding of the peptide to the molecule…once it is bound, the other amino acids can be presented
Peptides only need to have specific anchor residues to bind to those regions on the MHC
The anchor residues will be buried inside of the groove on the MHC binding site and the other amino acids will be presented on the surface to the TCR
On what cell types are MHC class II molecules expressed?
MHC class II molecules presents antigen that are found on intravesicular pathogens, such as intracellular bacteria (mycobacteria)…and also pathogens that are taken up from the extracellular environment through RME or phagocytosis and presented to CD4+ T Cells
What is cross penetration?
Cross Presentation is the process that allows processing of antigen for binding to both Class I and Class II MHC in antigen-presenting cells
Which MHC binds shorter peptides?
MHC I binds shorter peptides, while peptides that bind to MHC II can be longer
Which type of receptor is both membrane bound and soluble?
BCR is both. TCR is ONLY membrane bound.
Describe the difference between BCR and TCR with respect to somatic hypermutations and class switching
Unlike BCR, with TCR there is no somatic hypermutations or class switch of constant regions.
What is MHC haplotype and why is it important for immunity?
The complete set of alleles (variant genes that can occupy a single locus) found within an animals MHC is called its MHC haplotype…everyone in the room will have a different MHC haplotype…it is important/beneficial to have more MHC heterozygosity because that means you will be able to recognize and present more foreign antigens on cell surface…more heterozygosity can activate more pathogen specific T cells.
One MHC allele is inherited from each parent are expressed codominantly…and both alleles will allow presentation of more peptides from any pathogen than more related haplotypes so are able to activate more pathogen-specific T cells and better protect against infection
