Thrush - Genetics of Ig's

Question 1

what are the multiple gene segments of the heavy chain

Answer 1

V + D + J

Question 2

what are the multiple gene segments of the light chain

Answer 2

V+ J

Question 3

Genes must be rearranged in order to be functional coding for an Ab. ____ of the genes used is ___ and occurs before Ag stimulation. After Ag stimulation, a mature B cell can change the isotype which is called:

Answer 3

Selection; random; class switching.

Question 4

what is the reason why we could produce a lot of antibodies

Answer 4

B cell picks one of each for heavy chain and light chain

Question 5

To achieve Ig specificity, only one ____ can be expressed at once. ____ exclusion occurs during the process of Ig gene rearrangement when the first allele is successful, then the process stops. The process of gene rearrangement is tightly controlled and occurs in a very specifc order. ___ chain first, then ___ light chain, then ___ light chain (if needed)

Answer 5

allele; allelic; Heavy; kappa, lambda

Question 6

Describe Ig gene rearangement

Answer 6

1. Heavy chain first by yielding a VDJ DNA seq.
2. First constant region is IgM followed by coexpression of IgD.
   * Only time that a B cell expresses two isotypes
3. DNA gets transcribed to mRNA and gets processed
4. Produce IgM or IgD

Question 7

How to select one V region and not two or more?

Answer 7

There are recognition sequences; recombination signal sequences (RSS) that tell the enzymes where to bind and which genes to pull together.
*12/23 rule bp rule: a 12 bp seq. can join with a 23 bp sequence

Question 8

What do RAG (recombination activating genes do) enzymes do?

Answer 8

bring together the 12/23 sequences; expressed only in B and T cells

Question 9

____ recombinase is the complex of enzymes impt in recognizing and excising the intervening sequences.

Answer 9

VDJ

Question 10

what is Terminal deoxynucleotidyl transferase (Tdt)

Answer 10

adds back nucleotides in the “joining” region; Non germline bases = N nucleotides

Question 11

what contributes to Ig diversity

Answer 11

1. Multiple germ-line gene segments (V, D, J)
2. Combinatorial V D J joining
3. combinatorial association of light and heavy chain: an Ag can interact with either the L chain, the H chain or the combination of the two.
4. junctional flexibility (variability): imprecise joining together of the VDJ or VJ regions;
5. P region nucleotide addition: addition of bases by the repair enzymes
6. N region nucletide addition: addition of bases by Tdt
7. Somatic hypermutation: results in affinity maturation; mutation that occurs in a mature B cell (after Ig gene rearrangment)

Question 12

What is somatic hypermutation. Where is localized?

Answer 12

a mutation that occurs after B cell recognizes antigen and is basically becoming a memory cell; a very high rate of mutation every time a B cell replicates; goal is to make better antibody molecule. Lovalizd to the CDRs –> CDR3 bc it tends to make the most contact with antigen in case of heavy chain and CDR1 in light chain

Question 13

Igs with highest affinity for Ag will be selected which is referred to:

Answer 13

immunodominance

Question 14

we are supposed to make roughly ___ million Ab, but with all of the variabilities, the potential number or Ab’s is estimated to be ____

Answer 14

9; 10^15

Question 15

How does the expression of Ig genes determine whether the protein will be membrane bound or secreted?

Answer 15

By differential RNA processing of heavy chains at the mRNA level; allows for simultaneous exp of IgM and IgD

Question 16

How can a single B cell express a protein with its membrane bound or secrete it?

Answer 16

Start off with rearranged DNA–> transcribe to mRNA–> if ending part of mRNA remain in transcript after mRNA processing, the membrane spanning region –> protein embedded in membrane –> travel to surface of B cell to become membrane bound

If membrane spanning portion is cut –> secreted protein

Question 17

How does coexpression of IgM and IgD occur

Answer 17

The primary transcript has both IgM and IgD sequences. The mRNA is processed to remove one or the other.

Question 18

A mature cell will express ___ and ___ on its surface. Upon Ag recognition, the B cell can develop into a ____ cell and secrete the Ab or become a ____ cell and class switch.

Answer 18

IgM and IgD; plasma; memory

Question 19

class switching only occurs in ____ chain and are controlled by _____.

Answer 19

heavy; cytokines

Question 20

___ is a major cytokine for production of IgE

Answer 20

IL-4

Question 21

T/F once switch to a downstream isotype, you cannot go back.

Answer 21

true

Question 22

why are IgM and IgD expressed first

Answer 22

they are the constant region sequences closest to the VDJ sequences; via differential mRNA processing

Question 23

___ play the major role in class switching and it only occurs once. ____ and ___ cells produce different cytokines

Answer 23

Cytokines; Th1 and Th2

Question 24

Ab diversity is generated primarily bc of Ig gene rearrangement and occurs before exposure to _____

Answer 24

antigen

Question 25

Somatic hypermutation can increase the affinity of a given Ab for its Ag and this occurs ___ recognition of Ag–> generation of memory cells.

Answer 25

after