Lecture 16: Antibodies

Question 1

What three things is an antibody composed of?

Answer 1

Heavy chain, light chain, disulfide bonds

Question 2

What are three C (constant) names for the heavy chain?

Answer 2

IgM, IgD, IgG1

Question 3

What does junctional diversity do?

Answer 3

Creates additional antibody variation. Variation in the V(D)J joint increases diversity

Question 4

What three mechanisms is junctional diversity generated by?

Answer 4

• junctional flexibility
• P-nucleotide addition
• N-nucleotide addition

Question 5

What is junctional flexibility?

Answer 5

The imprecise joining of the V(D)J segments. It is generally not a perfect cut and some nucleotides get deleted or a changed reading frame occurs creating diversity

Question 6

What is P-nucleotide addition?

Answer 6

When two strands are connected, one block on top of the other, the loop is not always cut evenly resulting in the gain/loss of nucleotides. Palindromic sequence, same when you read it from 5’-3’ on one strand and the same on the other.

Question 7

What is N-nucleotide addition?

Answer 7

Up to 15 nucleotides can be added to the end of a gene segment by terminal deoxyribonucleotidyl transferase. They’re randomly added and called non-templated.

Question 8

When does Ig rearrangement begin?

Answer 8

Early in B-cell development

Question 9

What is the process of Ig rearrangement? (3)

Answer 9

• RAG complex (recombination activating gene (1-2))
• recognizes the borders of the gene segment and cuts it
• DNA ligase and other enzymes are also used

Question 10

If there is deficiency in RAG genes what results?

Answer 10

Severe combined immunodeficiency phenotype

Question 11

Draw and label Ig gene rearrangement and B cell development

Answer 11

I did

Question 12

What is the surrogate light chain a product of?

Answer 12

Two conserved genes Vpre-b and lambda5

Question 13

How does RAG know where to cut?

Answer 13

The gene segment is flanked by short conserved sequences known as recombination signal sequences

Question 14

What are recombination signal sequences made of?

Answer 14

• heptamer
• 12 or 23 spacer sequence
• nonamer

Question 15

What is the 12/23 rule

Answer 15

Rearrangement always occurs between a RSS with a 12 bp spacer and a RSS with a 23 bp spacer

Question 16

Draw a rearrangement signal sequence

Answer 16

I did

Question 17

What is allelic exclusion

Answer 17

When one allele is rearranged successfully it prevents the other from being rearranged. Potentially due to signalling through the Pre-B cell receptor that stops heavy chain rearrangement

Question 18

If an activated B cell encounters certain signalling molecules what do they undergo?

Answer 18

They undergo antibody class switching to produce IgG, IgA or IgE antibodies

Question 19

Does class switch recombination affect antigen specificity? Why or why not

Answer 19

During class switch recombination the constant region portion of the antibody heavy chain is changed but the variable region of the heavy chain stays the same thus class switching does not affect antigen specificity

Question 20

What are antibody isotypes

Answer 20

Antibodies can come in different varieties known as isotypes which refer to the genetic variation in the constant region of the heavy and light chains

Question 21

Describe how a B cell goes from naive to differentiated

Answer 21

• immature B cells that have never been exposed to an antigen are known as naive B cells and express only the IgM isotype
• B cells began to both IgM and IgD when they reach maturity and are then ready to respond to an antigen
• when an antibody binds with an antigen it is activated and it starts to divide and differentiate, it becomes a plasma cell

Question 22

Why does class switching occur?

Answer 22

Since it does not change the variable region the antigen specificity stays the same but the antibody can now interact with different effector molecules

Question 23

What happens during class switching

Answer 23

Parts of the antibody heavy chain are removed from the chromosome and the gene segments surrounding the deleted portion are rejoined to retain a functional antibody gene that produces antibodies of a different isotype. Double stranded breaks are made at switch regions.

Question 24

What enzyme is required for class switch

Answer 24

Activation-induce cytosine deaminase, induces single strand breaks in the DNA.