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30 Cards in this Set
- Front
- Back
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BCR properties
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- 2 binding sites, bivalent
- recognize large molecules, lipids, NA, small chemicals in their native form with pathogen (conformational and linear epitopes) - 10^9 specificity - Consists of a light and heavy chain |
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TCR properties
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- 1 binding site
- strict peptide size is recognized and only when presented with APC - 10^11 specificity - consists of an alpha and beta chain |
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What does the BCR need to send signal?
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- IgAlpha and IgBeta chain
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What does the TCR need to send a signal?
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- CD3
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Are lymphocyte receptors able to transmit signals?
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- no, cytoplasmic tail of receptor is insignificant, receptor must rely on accessory molecules for signal transmission
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What are the 2 major regions of Ig? What chains make up these portions?
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- Fab region consisting of the variable and constant light and heavy chains
- Fc region consisting of the constant heavy regions |
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What chains of the Fab region are used for Ag-binding?
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- Variable light and heavy chains
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IgA has how many parts and for what function?
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- dimer
- mucosal immunity |
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IgE has how many parts and what function
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- monomer
- immediate hypersensitivity |
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IgG has how many parts and what function?
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- monomer
- opsonization - most frequent in serum |
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IgM has what form and function?
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- pentamer
- complement activation - also in serum |
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What are Fc roles?
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- NK cells have FC receptors that are activated to kill tumor cells
- toxins bind to FCR and are neutralized - bacteria in extracellular space are opsonized by Ig with FC on them, targeted for macrophages - complement activation of bacteria in plasma |
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Binding factors for Ab/Ag besides shape.
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- electrostatic
- hydrogen - Van der Waals - hydrophobic |
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What are hypervariable regions?
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- regions within the light variable chains that are for Ag specificity
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What does the TCR consist of? What are the regions called?
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- Variable alpha and beta chains (Ag-recognition)
- Constant alpha and beta chains - Just one region: Fab |
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Is the BCR or TCR always membrane bound?
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- TCR
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BCR/Tcr development
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- Pro-B/T cell
- express heavy/beta chain (u) - rearrange genes - express light/alpha chain - any receptor that binds strongly to self is negatively selected - T cells that do not respond to self peptides at all fail positive selection |
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What is VDJ recombination?
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- DNA rearrangement in the light/alpha or heavy/beta chain that generates great diversity for possible Ag binding sequences in CDR region
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VDJ recombination for the light/alpha chain.
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- VJC (gene order)
- DNA is spliced out between V and J and J and C |
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VDJ recombination for the heavy/beta chain
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- VDJC ( more Cs)
- DNA spliced out between different regions so they form one continuous gene |
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what are RSSs and what do they do?
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- Recombination switch sequences
- recruit Rag1/2 recombination enzymes to promote recombination between the V and J regions of the light/alpha chains and the V/D/J regions of the heavy/beta chain |
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Describe the process of Junctional diversity
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- Rag 1 and 2 bind to RSS (regions of 23 or 12 bp after/before the v/D/J)
- Bring together the 2 RSS sequences so one continuous gene, (remove exon) - Rag complex forms, cleaves RSS sequence out - forms hairpin - brings in complex of proteins to facilitate the joining of the 2 areas - Ku70 and 80 bind to ends of V and J (or whatever the 2 genes are) - Artemis and DNA-PK cleave the hairpin - Tdt process cut DNA - DNA ligase fills in gaps |
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What is the purpose of junctional diversity?
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- creates regions of DNA that are not encoded in the germline, thus completely random and greatly increases diversity
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Junctional diversity creates what region on the hypervariable region?
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- CDR3 loop that interacts with the peptide
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What does the CDR1 and 2 are in contact with what?
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- MHC molecule
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How is the CDR1/2/3 arranged in the TCR/BCR?
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- CDR1/2 are on the outside (where MHC binds)
- CDR3 are on the inside (Where peptide binds) |
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What is combinatorial diversity? How many possible combinations does this create?
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- combination of different V/J/D/C
- Ig: 10^6 - TCR- 3 x 10^6 |
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How many possible combinations does junctional diversity create?
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- Ig: 10^11
- TCR: 10^18 |
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When does Ig expression (state of the receptor) first occur?
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- Pre-B stage when Heavy chain recombines and the cytoplasmic u and pre-B receptor
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What is allelic exclusion and what is associated with this?
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- only genes of one parent are expressed per cell
- Heavy/beta and light/alpha chains are each expressed by either the maternal/paternal gene - but every cell can have a different configuration |
