Antibody Recombination

What isVDJ recombination

somatic recombination of variable, diverse and joining gene segments

What type of recombination occurs in the heavy chain?

DJ then VJD

What type of recombination occurs in the light Chain

V recombination only

What is meant by CDR3

complementarity determining region 3

which segments encode CDR1 and CDR2

V segments

Which genes define antibody isotype upon class switching

9 constant gene regions

How many different specificities generated by combinatorial diversity

1.6 million

How is the joining of VH to JH prevented?

spacers of 12 - 23 base pairs

What is RSS

Recombination signal sequence

Describe the RSS

Heptamer and roamer motifs signal V(D)J recombinase to specific gene segments

What are RAGs

Recombinase activating genes

where do RAG1 and 2 bind?

RSS

What other enzymes does RAG complex for recombination

ubiquitous DNA Repair Enzymes

What are the sources of variation in recombination

N-nulcleutode additions by Tdt to hairpin regions

What is meant by N-nucleotide

Not gremline-encoded

what is the consequence of unproductive recombination

B cells dies

Tdt

terminal deoxynucleotide transferase

What is somatic hypermutation

point mutations across v domain coding sequence, particularly in CDR3Ho

How is somatic hypermutation induced?

AID converts cytosine to uracil in DNA during transcription, which can then be converted to any of the 4 bases by subsequent enzymatic action

what is AID

Activation-induced Cytidine Deaminse

where is AId expressed

exclusively in proliferating B cells

how many specificfites from recombination

10⁶

how many variants from mutation

10⁹

How are IgM and IgD expressed in Naive B cell

Alternative Splicing

IgM transcript contains only Cμ with pAμ

IgD contains Cμ and Cδ with pAδ

What is CSR

Class switch DNA Recombination

Where is CSR induced by AID for class switching

Switch regions

Where are switch regions

uostream of c region gene apart from Cδ

in which art of the GC does CSR and somatic hypermutation occur?

dark zone

in which part of the GC does selection for antibodies occur

light zone

what types of cells to selected high affinity B cells differentiate into

memory B cells or plasma cells

How is class switch and somatic hypermutation initiated?

B cells internalise antigen bound B cell receptor and present on MHCII for CD4+ T cells to recognise. T cells support differentiation with cytokines (IL-4, IL21), and stimulate CD40 pathway leading to class switch

describe the process of antigen entry to differentiate B cell

What s the benefit of allelic exclusion?

only 1 variant produced

if one rearrangement possible to try recombination of other gene before apoptosis

what is allelic exclusion

ensuring only one allele rearranged and the other is silenced.

How are B cell receptors transported form the ER to the cell membrane?

with the Igalpha/IgBeta receptor

What s the difference between membrane bound and secreted antibodies?

Membrane bound antibodies will have MC, Secreted will have Sc sequence

What are the secreted antibody types?

IgA, IgD

What are the membrane bound antibody types?

IgG, IgA, IgE

What is the difference between MC and SC

in Cμ4 exon, MC has hydrophobic amino acid region insertion encoded by M1 and M2 exons of embedded in S exon of Cμ.

How is cytokine signalling crucial to antibody make up?

cytokines regulate switching to specific Ch genes, dependent on pathogens and cytokine environment.

How are C genes targeted by AID

switch sequences find at 5’ side of heavy chain C chains apart from delta

Describe the distribution of cells in the thymus cortex

tightly packed immature proliferating thymocytes

Describe the distribution of cells in the thymus medulla

Loosely packed mature thymocytes

what is a thymocyte

thymic T cell

What is the site of positive selection in the thymus

Cortex

What is the site of negative selection on the medulla

Medulle

What is the role of positive selection in the thymus

enable cells that are capable of weakly recognising self MHCII too survive

what is the role of negative selection in the thymus

enliminate T cells that strongly bind to self antigens to prevent autoimmunity

How is variation in T cells achieved?

random rearranegement of TCR genes - subjection to positive and negative selection

Show the developmental stage of a double negative T cell

DN CD4- CD8-

show the developmental stage of a double positive T cell

DP CD4+, CD8+

She the developmental state for a single possible T cell

SP CD4+ or SP CD+

what is central tolerance

removal of autoreactive T cells which could dodge the immune system

Which chains make T cell receptors

T cell receptor chains alpha and beta

which regions does the TCR alpha have

V, J

Which regions does the TCR beta have

VDJ

What is the estimated average clonal size for a T cell

100 - 200 cells per clone

how many variable region combinations in T cells

1.5 million

How many T cell junctional diversities

1 × 10¹⁵

Summarise the stges of T cell development

double-positive CD3+ thymocytes - sub capsular zone (proliferation & diff)

Double positive CD3+ thermocsytes in the thymic cortex (positive slsecton)

Double positive CD3+ in cortex (negative selection)

Mature CD4/CD8 cells leave through blood venues