7 - B/T Lymphocyte Receptors and Diversity - Partridge Flashcards
Draw a diagram of the B cell receptor, highlighting the main structure and additional proteins that are associated
311 - 7
word
How many aa are present at the C terminal end of the BCR and how many residues are exposed on the cytoplasmic side?
approx 26 residues at the C terminus. these span the membrane as well as 3 aa being exposed in the cytoplasm
What are the main Ig classes that are found on the surface of B cells and can these be expressed together?
IgM and IgD are the main classes on B cells. although most Ig type can be expressed on surface and act as a B cell receptor
How does the B cell receptor generate a signal?
the cytoplasmic domains (because theyre so short) are not enough to generate a signal. need to associate e/ Iga and IgB. their cytoplasmic domains are longer and have an ITAM section (immunoreceptor tyrosine activation motif) allowing a signal to be generated once the BCR binds to antigen
Briefly describe T lymphocyte receptor and what subsets of T cells they exist on
only expressed on cell surfaces and cannot exist as soluble proteins. same TCR structure exists on both T cytotoxic cells (CD8+ve) and T helper cells (CD4+ve)
Generally outline the functions of CD8/4+VE T cells
CD8+ve;
specifically kills infected host cells
CD4+ve;
augment immune responses
Describe the TCR extracellular domains in relation to immunoglobulins
V and C region of the TCR are homologous to the V and C region of immunoglobulin domains. each V region contains 3 HVRs
There is an alternative subset of T cells that express a different receptor. what is this receptor made up of? does this receptor show the same diversity as the aB receptor?
- where does this alternative subset exist?
gamma theta V and C domains. (1-5%)
less diverse compared to aB
- found in mucosal surfaces
What type of infections do B cells provide immunity against?
extracellular pathogen
eg fungi, parasites, extracellular bacterial
What does it mean when stated that B cells bind free and native antigen
free - free bacterium/soluble protein/carbohydrate
native - has not been processed/modified in anyway
What type of infections do T cells provide immunity against?
defence against intracellular pathogens.
How do T cells recognise intracellular antigens?
infected cells have the pathogenic protein within them. broken down -> peptide. processed, associates w/ MHC and taken to surface where recognised by specific T cell.
overall; T cells recognise cell associated, processed antigens
What region of the V regions of the a B subunits are the most variable?
CDR3 region has been shown to be the most variable
What do the CDR1/2/3 regions of the TCR bind to?
CDR3 -> foreign peptide. CDR1/2 -> self-MHC
Draw the full complex of the TCR, including any bonds, associations with other proteins
311 - 7 word
What do the additional subunits associated with the TCR allow it do?
allows the TCR to be expressed at the cell surface and signal efficiently
What do the CD3 subunits contain that allow it to signal?
ITAM motifs in cytoplasmic regions
Approximately, how many combinations of each antibody receptor and T cell receptor are there?
Antibody = 10^14 TCR = 10^18
What are the main determinants of STRUCTURAL diversity in Abs?
the length and sequence of the CDRs of which CDR3 is the most variable (in both length and sequence)
In Abs, which chain the H/L chain is said to be more variable and why?
Heavy chain > variable. this chain contributes > to antigen binding
What were the initial hypotheses that tried to explain the occurrence of this huge amount of diversity in Abs?
multiple genes
somatic mutations
somatic recombination
Why was it initially thought of as strange to have so much diversity?
the human genome only codes for 25,000 genes therefore how can it produce this much diversity
How does this much diversity actually occur?
mutation and recombination of inherited gene segments which make up the V region
What were the 2 hypotheses proposed by Dreyer and Bennett (1965) and Tonnegawa (1976)?
D&B;
immunoglobulins encoded for by separate C region and multiple V region genes
Tonnegawa;
Ig genes are rearranged during B cell development
How were the Dreyer and Bennett and Tonnegawa hypothesis proved?
2 cells tested. Mouse embryo cell and and mouse myeloma cell.
- DNA was extracted from both, restriction digests and separated by gel electrophoresis
- radioactive probes complementary to V and C regions were added and hybridised at location in the gel where the V/C regions were
- see diagram on word 311 - 7
- the embryo pattern was seen in ALL cells apart from the B cell lineages (which were differentiated cells producing specific Ab)
What are the 3 sets of immunoglobulin genes and on which chromosomes are they found?
H chain; chromosome 14
K chain; chromosome 2
lambda; chromosome 22
Describe each locus in terms of how many genes the V and C regions have and how many they are encoded by
each locus has MULTIPLE V region genes and one or a few C region genes.
the V region is encoded by at least 2 exons.
Draw diagrams showing both the DNA and protein sequences of L and H chain configurations and the exons that encode them
311 - 7 word
Which chain (C/V and H/L) of which Ab class is expressed first on differentiating B cells?
the Cu (IgM heavy chain) is always expressed first on B cells. because it is found closest to DNA that makes up the V region?
When does the structural rearrangement of the light and heavy chain genes occur during the lifetime of a B cell?
during B cell differentiation creating permanent changes in the DNA
What is the name of the process that removes certain segments of DNA in order to join others together? Briefly describe this process
somatic recombination. certain DNA fragments are excised from the DNA and certain fragments (eg V/J fragments are spliced together)
Draw a diagram to highlight the rearrangement of the light chain kappa
311 - 7. word
What does the enhancer region allow to happen?
V region promoter now closer to the enhancer region allows for their transcription
Draw a diagram indicating the light chain locus lambda
word
Draw a diagram highlighting the recombination that occurs in the heavy chain
word
state which segments encode the CDR1/2 regions and the CDR3 regions
CDR1/2; encoded for V segments w/n germline
CDR3; encoded for by VDJ/VJ segements. hence why we see > variability in this section
Which of these light/heavy chain process rearrangements occur first?
heavy chain rearrangement occurs first over either light chain type.
IgM Cu region is expressed first
