Lecture 16: Antibodies Flashcards
What three things is an antibody composed of?
Heavy chain, light chain, disulfide bonds
What are three C (constant) names for the heavy chain?
IgM, IgD, IgG1
What does junctional diversity do?
Creates additional antibody variation. Variation in the V(D)J joint increases diversity
What three mechanisms is junctional diversity generated by?
- junctional flexibility
- P-nucleotide addition
- N-nucleotide addition
What is junctional flexibility?
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
What is P-nucleotide addition?
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.
What is N-nucleotide addition?
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.
When does Ig rearrangement begin?
Early in B-cell development
What is the process of Ig rearrangement? (3)
- 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
If there is deficiency in RAG genes what results?
Severe combined immunodeficiency phenotype
Draw and label Ig gene rearrangement and B cell development
I did
What is the surrogate light chain a product of?
Two conserved genes Vpre-b and lambda5
How does RAG know where to cut?
The gene segment is flanked by short conserved sequences known as recombination signal sequences
What are recombination signal sequences made of?
- heptamer
- 12 or 23 spacer sequence
- nonamer
What is the 12/23 rule
Rearrangement always occurs between a RSS with a 12 bp spacer and a RSS with a 23 bp spacer
Draw a rearrangement signal sequence
I did
What is allelic exclusion
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
If an activated B cell encounters certain signalling molecules what do they undergo?
They undergo antibody class switching to produce IgG, IgA or IgE antibodies
Does class switch recombination affect antigen specificity? Why or why not
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
What are antibody isotypes
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
Describe how a B cell goes from naive to differentiated
- 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
Why does class switching occur?
Since it does not change the variable region the antigen specificity stays the same but the antibody can now interact with different effector molecules
What happens during class switching
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.
What enzyme is required for class switch
Activation-induce cytosine deaminase, induces single strand breaks in the DNA.
