Genetics Diversity and Antibody Structure

Question 1

how do human genes code for Ig?

Answer 1

genetic recombination in B cells

Question 2

what are the structural configurations of Ig?

Answer 2

either lamba or kappa

Question 3

what are the two regions of the peptide structural confirmation of the light chain?

Answer 3

variable light (VL) and constant light constant (CL)

Question 4

what two regions is the VL region coded by?

Answer 4

V and J

Question 5

what gene is the CL region coded by

Answer 5

C

Question 6

what is unique to B cells prior to transcription?

Answer 6

V and J genes are cut allowing for the different exons for each gene to recombine via V(D)J recombinase then joins them back to the C region to form the final B cell DNA of the light chain

Question 7

when does the synthesis of the antibody molecule of the light chains of the take place?

Answer 7

during development of B cell prior to B cell maturation

Question 8

what are the two enzymes in the nucleus of developing B cells?

Answer 8

RAG-1 and RAG-2 (recombination-activating (gene))

Question 9

what happens once the kappa DNA rearrangement is completed?

Answer 9

it undergoes transcription yielding the primary complete RNA segment containing 5’ cap, both exons and introns and polyA tail

Question 10

what happens after the splicing in the nucleus to remove the introns?

Answer 10

mature mRNA strand is transferred to the rough ER

Question 11

what happens in the rough ER and and lumen of the ER?

Answer 11

it is synthesized (translated) by the ribosomes into the lumen of the ER, where the signal peptide is cleaved into a protein peptide awaiting assembly with a new heavy chain

Question 12

what are recombination recognition sequences?

Answer 12

serve as a beacons for the V(D)J recombinase to bind and cleave the V-J DNA loop

Question 13

how do we know that RAG-1 and RAG-2 have a role in the cleavage step?

Answer 13

effects in the RAG-1 and RAG-2 genes that code for enzymes have been linked to a primary immune deficiency called severe combined immune deficiency (SCID) (both the B and T cells are absent or non-functional)

Question 14

true or false: genes that code for the lambda light chain is found on the same chromosomes as the genes for the kappa light and heavy chains

Answer 14

false

Question 15

during B cell development the synthesis of which light chain is initiated first?

Answer 15

kappa before lambda

Question 16

what is the difference between the lambda and kappa light chains?

Answer 16

λ light chain is that the λ DNA germline has ~30 Vλ segments, 4λ segments and 4Cλ segments. This would suggest it has the capacity for an even larger protein peptide diversity

Question 17

what are similarities of heavy and light chain peptide synthesis?

Answer 17

on the DNA locus, the variable and constant segments and a variable gene segment recombination event occurs prior to transcription.

Question 18

what are the major differences between heavy and light chains?

Answer 18

the heavy chain has an additional D-diversity gene segment coding for the variable region, post- transcription alternative splicing of the primary RNA transcript occurs resulting in a μ and δ heavy chain peptide with identical antigen epitope specificity.

Question 19

the C region genes are identified with greek letter of the isotypes or subisotypes, why?

Answer 19

to re-enforce the point that the heavy chains
define the isotype or sub-isotype of the antibody molecule

Question 20

what happens when gene expression is initiated in heavy chains?

Answer 20

V D J segments undergo rearrangement

Question 21

what is the two step process of the V D J rearrangement?

Answer 21

1. D and J segments are joined first
2. then V-segment is joined

Question 22

what does transcription of heavy chain result in?

Answer 22

primary RNA transcript containing
the 5’cap, leader sequence, polyA tail, rearranged variable region VDJ segment, extra J segment and the 2 closest C-region genes (μ and δ).

Question 23

what is the result of alternative splicing of the primary RNA transcript of heavy chain?

Answer 23

results in 2 separate mRNA trans with identical variable region RNA, but different constant
region RNA.

Question 24

what happens when the regions are transferred to the rough ER during heavy chain peptide synthesis?

Answer 24

they synthesize 2 heavy peptide chains with
variable regions specific for the same antigen epitope, but one having a μ constant heavy
peptide structure and the other having a δ constant heavy peptide structure.

Question 25

what is allelic exclusion?

Answer 25

During B cell development, a particular B cell will use only one of the parental chromosomes for the synthesis of an Ig peptide, while the other chromosome is silenced.

Question 26

how does allelic exclusion enhance diversity?

Answer 26

since the genes that code for the whole Ig are on different chromosomes, it is possible for one peptide chain of the Ig to be from the mother and the other from the father

Question 27

what is the result of all of the genetic events to form the mature B cell?

Answer 27

synthesis of antibodies that is highly specific for a particular antigen epitope.

Question 28

what is the isotype for a newly minted naïve
mature B cell, and the isotype on the surface that can be co-expressed?

Answer 28

IgM
IgD

Question 29

what is the suggested role of IgD?

Answer 29

inhibit autoreactive B cells

Question 30

during B cell development what is the first immunoglobulin isotype produced as a BCR and secretory Ig?

Answer 30

IgM

Question 31

how are other isotopes produced?

Answer 31

isotype or class switching/class switch recombination

Question 32

what is class switch recombination limited to?

Answer 32

heavy chain constant gene segments.

Question 33

why is heavy chain of the antibody necessary for class switch recombination?

Answer 33

because the heavy chain of the antibody is
responsible for the biologic activity of the antibody.

Question 34

what is the best isotype to deal with if the antigen target is a respiratory virus?

Answer 34

IgA

Question 35

is infection is localized more into the interstitial space and is more systemic, which antibody would be more effective?

Answer 35

IgG

Question 36

when is the only time isotype switches occur?

Answer 36

• when mature B cells are activated by antigen epitope to replicate or produce clones
  or
• B cell needs to receive signals from a T cell

Question 37

Not all activated B cells encounter T cells, so these cells would not undergo isotype switching resulting in a measurable ___ peak

Answer 37

IgM

Question 38

what helps explain the different antibody peaks following a primary and secondary vaccine booster?

Answer 38

If the B cell does not receive a signal from a T cell, then isotype switching does not occur.

Question 39

where do the mature B cells reside that are stimulated via antigen recognition through BCR?

Answer 39

germinal center of the secondary lymphoid tissues

Question 40

what are switch regions?

Answer 40

collection of repeating bases in the heavy chain DNA germline locus of the activated B cell that are upstream of each C region gene, except for the δ gene that’s clustered with the μ gene

Question 41

what happens to the B cell in the absence of T cell signaling?

Answer 41

switch associated with the μ−δ cluster is retained, and the IgM isotype is synthesized yielding a B cell clone identical to the parent IgM B cell

Question 42

what allows the switch region of specific C region gene is rearranged so that the downstream C-region gene is positioned next to the rearranged VDJ genes?

Answer 42

T cell signalling of the γ1 C-region gene (IgG1)

Question 43

what enzyme is required for the γ1 C-region gene (IgG1) rearrangement?

Answer 43

activation-induced cytidine deaminase found in the germinal centers.

Question 44

describe H and L chain random assortment

Answer 44

Any light chain produced can be assembled with any heavy chain. Thus, random assortment of the newly synthesized H & L chains can also contribute to variation in the V regions, which contributes to diversity in antigen epitope recognition

Question 45

describe junctional diversity

Answer 45

Diversity is increased via the addition of P-nucleotides and N-nucleotides and mediated by an enzyme called terminal deoxynucleotidyl transferase (TdT). As this recombination event takes place in the variable regions including the hypervariable regions where the CDRs are located, this further promotes diversity in antigen recognition

Question 46

what is somatic hypermutation?

Answer 46

process that occurs continually during a B cell’s existence, in which point mutations occur and accumulate in the V-regions of both the heavy and light chains at a rate of 104 to 106-fold higher than the normal background mutation rate of other genes.

Question 47

following a primary immune response, the responding antibodies bind to the antigen epitope with a _____ affinity.

Answer 47

weak

Question 48

it is believed that when the activated B cells clonally expand in the germinal centers, the new clones that are in the _________ stage of B cell differentiation the V genes undergo hypermutations.

Answer 48

centroblast

Question 49

what is affinity maturation?

Answer 49

new B cell clone with a modified antigen- binding site that has enhanced affinity for the original antigen epitope