Which antibody is the only one that is NOT secreted?
IgD (does not play a role in fighting pathogens, cancer cells or parasites, instead, it is expressed on B cell surface to indicate it is mature)



What is class switching?
Class switching involves changing the constant region of the B cell receptor to switch from a membrane-bound form to a secreted form. This allows them to differentiate into antibody-secreting plasma cells and make other antibody types (like IgE, IgA, and IgG) needed in different locations in the body.



What region of an antibody is involved in class switching?
What is the importance of class switching?
Only the heavy chain CONSTANT region

Different effector functions of the antibody allow for improved response to eliminate different pathogens.



What are the two types of class switching?
minor and major 



Minor class switching occurs between which two antibodies?
IgM and IgD


What is the difference between 'minor' and 'major' class switching?
Minor class switching occurs at the mRNA level (differential splicing) and does not affect the DNA of the B cell. 

Major class switching results in DNA recombination (no undo button).



Mature naive B cells express both IgM and IgD, how?
Differential (alternative) splicing


Give examples of major class switching
IgM -> IgG, IgA, IgE

IgG -> IgA, IgE



How do B cells know which antibody class to switch to?
Cytokine signalling: produced by T helper cells that act on B cells, this indicates the type of pathogen it is exposed to

CD40L/CD40 signalling: confirms that b cells are interacting with T cells



Major class switching requires a mechanism known as class switch recombination (CSR). What 3 things are required for CSR?

1) Cytokine signal
2) Switch regions (recombination occurs here)
3) AID and DSB repair proteins


Why are IgM antibodies able to undergo class switching to IgG, IgA and IgE but not the reverse?
Switching only proceeds downstream

i.e. the μ gene segment comes before the γ, α, and ε segments

-it is non-reversible: once IgM switches to IgG, the segment preceding γ is removed



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