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16 Cards in this Set

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Expression of Ig genes - How is it similar and differet
Ig genes go through normal transcription translation processessing as do other eukaryotic genes. mRNA are processed by cutting out introns and expressing exons. A 5'cap and 3' poly A tail is added.

There is a DIFFERENTIAL processing of mRNA with regard to the Heavy chain that determines whether the protein will be MEMBRANE bound or SECRETED

and that allows for SIMULTANEOUS IGM & IGD expression.
How do membrane and secreted IgG differ in the their gene expression
Transmembrane IgMs express anchor residues and hydrophobic membrane spanning sequence

Secreted IgMs express "secreted" sequence with no expression of membrane spanning sequence
Secreted Ig undergo the following steps:

1) Protein assembled along ______.
2) H / L chains assemble in ______.
3) Ig travels in vesicles to _____ and underges:
________of H chain
4) Vesicle leaves Golgi and fuses with _________
5) Ab secreted
RER
ER
Golgi
glycosylation
plasma membrane
The only difference in membrane bound Igs.
As the Ig travels from the ER to the Golgi it is anchored to vesicle membrane
Describe co-expression of IgM and IgD and
the primary transcript has BOTH IgM and IgD sequences.
The mRNA is ‘processed’ to remove one or the other.
Describe expression of Ig genes
A mature (naïve) B cell will express IgM and IgD on it’s surface
Upon Ag recognition, the B cell can develop into a plasma cell and secrete the Ig OR a memory cell
Describe the life of a plasma cell
focuses on secreting Ab (and then dies within a few days)
Describe the life of a memory cell
memory cell will usually CLASS SWITCH (dependent upon cytokines)upon next Ag exposure, B cell can develop into plasma cell secreting another IG ISOTYPE
SOMATIC HYPERMUTATION will occur with selection of higher affinity Abs
Describe class switching of Ig genes
Occurs in H chain – constant region genes

Controlled by cytokines
-Switch factors: mostly produced by Th cells that cause a B cell to rearrange Ig CH genes

not completely understood
In class switching of Ig genes the _______ is induced to become a ________ and then a __________
Activated B cell (centroblast)
Proliferating B cell (centrocyte)
Plasma cell
What are the PROLIFERATING cytokines involved in turning an activated B cell to a Proliferating B cell
IL-2
IL-4
IL-5
What are the DIFFERENTIATION cytokines involved in turning a proliferating B cell into a IgG2a or IgG3
IFN-gamma
What are the DIFFERENTIATION cytokines involved in turning a proliferating B cell into a IgA or IgG2b
TNF-Beta
What are the DIFFERENTIATION cytokines involved in turning a proliferating B cell into a IgE or IgG1
IL-4
What are the DIFFERENTIATION cytokines involved in turning a proliferating B cell into a IgM
IL-2
IL-4
IL-5
Describe Class switching of genes
Once switch to a downstream isotype, cannot go back. In other words a B cell can never produce an upstream isotype.

Cytokines play the major role in class switching.
Th1 and Th2 cells produce different cytokines
these “classes” of cytokines play a role in determining which isotypes are most needed:
-IgA in secretory areas
-IgG to cross the placenta
-IgE against multicellular pathogens (parasitic worm, allergies)