7 - B/T Lymphocyte Receptors and Diversity - Partridge

Question 1

Draw a diagram of the B cell receptor, highlighting the main structure and additional proteins that are associated

Answer 1

311 - 7

word

Question 2

How many aa are present at the C terminal end of the BCR and how many residues are exposed on the cytoplasmic side?

Answer 2

approx 26 residues at the C terminus. these span the membrane as well as 3 aa being exposed in the cytoplasm

Question 3

What are the main Ig classes that are found on the surface of B cells and can these be expressed together?

Answer 3

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

Question 4

How does the B cell receptor generate a signal?

Answer 4

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

Question 5

Briefly describe T lymphocyte receptor and what subsets of T cells they exist on

Answer 5

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)

Question 6

Generally outline the functions of CD8/4+VE T cells

Answer 6

CD8+ve;
specifically kills infected host cells
CD4+ve;
augment immune responses

Question 7

Describe the TCR extracellular domains in relation to immunoglobulins

Answer 7

V and C region of the TCR are homologous to the V and C region of immunoglobulin domains. each V region contains 3 HVRs

Question 8

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?

Answer 8

gamma theta V and C domains. (1-5%)
less diverse compared to aB
- found in mucosal surfaces

Question 9

What type of infections do B cells provide immunity against?

Answer 9

extracellular pathogen

eg fungi, parasites, extracellular bacterial

Question 10

What does it mean when stated that B cells bind free and native antigen

Answer 10

free - free bacterium/soluble protein/carbohydrate

native - has not been processed/modified in anyway

Question 11

What type of infections do T cells provide immunity against?

Answer 11

defence against intracellular pathogens.

Question 12

How do T cells recognise intracellular antigens?

Answer 12

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

Question 13

What region of the V regions of the a B subunits are the most variable?

Answer 13

CDR3 region has been shown to be the most variable

Question 14

What do the CDR1/2/3 regions of the TCR bind to?

Answer 14

CDR3 -> foreign peptide. CDR1/2 -> self-MHC

Question 15

Draw the full complex of the TCR, including any bonds, associations with other proteins

Answer 15

311 - 7 word

Question 16

What do the additional subunits associated with the TCR allow it do?

Answer 16

allows the TCR to be expressed at the cell surface and signal efficiently

Question 17

What do the CD3 subunits contain that allow it to signal?

Answer 17

ITAM motifs in cytoplasmic regions

Question 18

Approximately, how many combinations of each antibody receptor and T cell receptor are there?

Answer 18

Antibody = 10^14
TCR = 10^18

Question 19

What are the main determinants of STRUCTURAL diversity in Abs?

Answer 19

the length and sequence of the CDRs of which CDR3 is the most variable (in both length and sequence)

Question 20

In Abs, which chain the H/L chain is said to be more variable and why?

Answer 20

Heavy chain > variable. this chain contributes > to antigen binding

Question 21

What were the initial hypotheses that tried to explain the occurrence of this huge amount of diversity in Abs?

Answer 21

multiple genes
somatic mutations
somatic recombination

Question 22

Why was it initially thought of as strange to have so much diversity?

Answer 22

the human genome only codes for 25,000 genes therefore how can it produce this much diversity

Question 23

How does this much diversity actually occur?

Answer 23

mutation and recombination of inherited gene segments which make up the V region

Question 24

What were the 2 hypotheses proposed by Dreyer and Bennett (1965) and Tonnegawa (1976)?

Answer 24

D&B;
immunoglobulins encoded for by separate C region and multiple V region genes
Tonnegawa;
Ig genes are rearranged during B cell development

Question 25

How were the Dreyer and Bennett and Tonnegawa hypothesis proved?

Answer 25

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)

Question 26

What are the 3 sets of immunoglobulin genes and on which chromosomes are they found?

Answer 26

H chain; chromosome 14
K chain; chromosome 2
lambda; chromosome 22

Question 27

Describe each locus in terms of how many genes the V and C regions have and how many they are encoded by

Answer 27

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.

Question 28

Draw diagrams showing both the DNA and protein sequences of L and H chain configurations and the exons that encode them

Answer 28

311 - 7 word

Question 29

Which chain (C/V and H/L) of which Ab class is expressed first on differentiating B cells?

Answer 29

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?

Question 30

When does the structural rearrangement of the light and heavy chain genes occur during the lifetime of a B cell?

Answer 30

during B cell differentiation creating permanent changes in the DNA

Question 31

What is the name of the process that removes certain segments of DNA in order to join others together? Briefly describe this process

Answer 31

somatic recombination. certain DNA fragments are excised from the DNA and certain fragments (eg V/J fragments are spliced together)

Question 32

Draw a diagram to highlight the rearrangement of the light chain kappa

Answer 32

311 - 7. word

Question 33

What does the enhancer region allow to happen?

Answer 33

V region promoter now closer to the enhancer region allows for their transcription

Question 34

Draw a diagram indicating the light chain locus lambda

Answer 34

word

Question 35

Draw a diagram highlighting the recombination that occurs in the heavy chain

Answer 35

word

Question 36

state which segments encode the CDR1/2 regions and the CDR3 regions

Answer 36

CDR1/2; encoded for V segments w/n germline

CDR3; encoded for by VDJ/VJ segements. hence why we see > variability in this section

Question 37

Which of these light/heavy chain process rearrangements occur first?

Answer 37

heavy chain rearrangement occurs first over either light chain type.
IgM Cu region is expressed first