Quiz 3 Part 3 Flashcards
What is the 1st antibody to be produced in an antibody response
IgM
What are the 2 antibodies on the B cell surface
IgM and IgD (BOTH CANT BE ON SAME ANTIBODY —- 1 OR THE OTHER)
What genes are transcribed FIRST
C mu and C delta
What is allelic exclusion?
allelic exclusion refers to the fact that we only want to make ONE type of antibody at a time, so 1 chromosome is suppressed and one is activated.
1 type of antibody to a single antigen
Where does the uniqueness exist between antibodies?
ALWAYS IN VDJ
However, the idea is that we can attach different constant regions to work with different kinds of effector molecules
Explain the process of making IgM and IgD and how they get to the surface of the B cell
VDJ has already been joined
transcription occurs through C mu and C delta. Through alternate splicing, either C mu or C delta is chosen to be attached to the VDJ region.
Attached to VDJ and the C mu or C delta is a AAA region. this AAA makes a molecule that has a hydrophobic transmembrane domain to stick into the plasma membrane of the B cell
After the antibody is formed, it has issues getting to the surface of the B cell. Iga and IgB deliver the B cell receptor (the antibody) to the membrane. Iga and IgB have tails that allow for intracellular signaling
When IgM/IgD is being spliced to attach to VDJ, is the DNA being spliced or mRNA?
mRNA is being spliced
What happens when B cell receptors bind to an antigen?
this binding triggers proliferation and differentiation of B cells into antibody secreting plasma cells
What is somatic hypermutation?
somatic hypermutation introduces POINT MUTATIONS (addition/deletion/changing of a single base) throughout rearranged variable regions.
If this mutation increases affinity for the antigen, the B cell is selected to mature into plasma cells that begin secreting antibodies
Somatic hypermutation is dependent on…..
AID activity (activation-induced cytidine deaminase)
Activation-induced cytidine deaminase is ONLY produced in proliferating B cells (those that have been activated by antigen)
Due to somatic hypermutation, antibodies of increasingly higher affinity for the antigen are produced. what is the term for this?
AFFINITY MATURATION
Explain the difference between the B cell receptor IgM and the secreted IgM
the B cell receptor IgM is a monomer while the secreted form is a circular pentamer
the secreted IgM is not very effective. It is a bulky molecule with low-affinity sites. It has a small hinge region, and is so big that it has issues moving around efficiently
Secreted (pentameric) IgM coordinates with….
J chain
Is IgM heavily involved in the antibody response?
no — it is really only a receptor.
the secreted version is too bulky to be involved
What part of an antibody gives it the ability to interact with different effector molecules?
the constant region
What is isotype switching
Switching IgM for something more useful
When does isotype switching occur? What is isotype switching dependent on?
isotype switching ONLY occurs in B cells in response to an antigen.
like somatic hypermutation, it is also dependent on AID ( activation-induced cytidine deaminase)
In isotype switching, is the variable region being changed?
NO—–only the constant region (C region)
Isotype switching is regulated by….
cytokine signaling.
Cytokines stimulate different transcription factors. They stimulate SPECIFIC transcription
VDJ ALWAYS GIVES…..
antigen specificity
In somatic hypermutation, AID causes the ___ to become ____
C’s to become U’s
Explain how isotype switching is done
CYTOKINES turn promoters in the switch region ON. This causes AID to add in the U’s at the switch regions which causes a break in the DNA. a loop is formed and a circular piece of all the unneeded things breaks off and the new constant region is now attached to VDJ and transcription occurs
is isotype switching done on DNA or RNA
DNA
Is spacing a concern in isotype switching?
NO
