Ig genes 2

Question 1

what kind of antibodies does the following produce

immature B cell
mature B cell
memory B cell
plasma Cell

secreted or membrane bound?

Answer 1

immature B cell –> can only produce MB IgM
mature B cell –> can only produce MB IgM and IgD
memory B cell –>MB GAMED
plasma Cell –> secretory GAMED depending on specialization

Question 2

What two antibodies are made without constant segment gene rearrangements?

Answer 2

IgM and IgD

Question 3

t or false, in a mature B cell IgM and IgD are made simultaneously

Answer 3

true

Question 4

What is differential RNA splicing

Answer 4

this permits IgM and IgD to be made simultaneously within a cell. After DNA VDJ rearrangements, if the antibody is going to be M or D the gene gets transcribed there and then. After, RNA splicing occurs randomly to excise out either the IgD portion or IgM portion.

Question 5

what are the M1 and M2 segments of constant regions?

Answer 5

these are membrane exons. When these are included within the transcript the antibody will be membrane bound such as in mature B cells.

Question 6

What are poly-adenylation sites on constant regions of a gene?

Answer 6

after every constant gene region (for GAMED) there are two poly A sites where cleaving can occur.

Poly A site 1 –> occurs right after the gene for conserved regions
Poly A site 2 –> after poly A site one and includes M1 nad M2 membrane exons

Question 7

how do we create a membrane bound IgM antibody?

Answer 7

IgM –> the VDJ—-constant regions M,D,etc. gets transcribed. then the transcript undergoes differential mRNA splicing where it is cleaved at poly-A site 2!! This includes the M1 and M2 exons which causes this antibody to be membrane bound.

Question 8

how do we create a membrane bound IgD antibody?

Answer 8

To make an IgD antibody membrane bound; differential splicing cleaves at poly A site 4.

Question 9

how do we create secretory IgM and IgD

Answer 9

plasma cell: differential splicing occurs at

IgM –> poly A site one (membrane exons excluded)
IgD –> poly A site 3 (“”)

Question 10

true or false, to make a membrane bound antibody for any of the 5 antibodies known we must cleave at the poly A site 2.

Answer 10

false, this is true for all antibodies except for IgD which must be cleaved at site 4.

Question 11

where do naive B cells cleave? plasma cells?

Answer 11

naive = MB = poly A site 2 and 4 
plasma = secretory = Poly A site 1 and 3

Question 12

what enzyme facilitates class switching?

Answer 12

AID –> activation induced cytidine.

class switching = DNA rearrangements to make other antibody constant regions

Question 13

explain how class switching works starting from heavy chain VDJ rearrangement.

Answer 13

• heavy chain undergoes two rearrangements to form VDJ
• the first antibody to be made would be IgM and then IgD –> these are produced and are MB
• antigen binds a MB antibody
• signals tell the cell to make a specific antibody. call it IgE
• switch sequence of IgE loops around and connects to the switch sequence of IgM. This loop is cleaved (i.e. IgM gene and any genes prior to IgE gene are cleaved).
• now IgE gene is directly downstream from VDJ
• RNA processing

Question 14

true or false, we can make IgM from IgA

Answer 14

false. Only down stream class switching can occur.

Question 15

antibody diversity:

multiple germ line genes?

Answer 15

stating there are many genes to choose form –> many variable genes, many diversity genes, etc.

Question 16

antibody diversity:

combinatorial diversity?

Answer 16

explains that the combination of D to J and V to DJ and V to J (light chain) contributes to diversity.

Question 17

antibody diversity: junctional diversity

- junctional flexibility / RSS cleavage?

Answer 17

antibodies become more diverse when they are cut by Rag 1 and 2 enzymes in different nucleotide locations at RSS sequences. Differing by one or two nucleotides may affects the Ag binding region.

Question 18

antibody diversity: junctional diversity

- P-nucleotide addition

Answer 18

p = palindromic

once Rag cuts between V and J regions or D and J regions or etc. DNA repair must occur.

P- addition adds a palindromic sequence

Question 19

antibody diversity: junctional diversity

- N-nucleotide addition

Answer 19

TdT enzyme randomly adds nucleotides to cut region after RSS is been cleaved.

Question 20

antibody diversity:

somatic hypermutation?

Answer 20

random point mutations occurring at hyper-variable regions (occur 100,000 times more here then anywhere else).

AID enzyme creates knicks in DNA for class switching but also sometimes creates knicks in hyper-variable regions which leads to hypermutations.

Question 21

what is affinity maturation and what causes it?

Answer 21

increase in AB affinity for an Ag. –> caused by somatic hypermutation.

Question 22

antibody diversity:

combinatorial association of H and L

Answer 22

refers to genetic diversity of combining light and heavy chains