Lecture 7 - Humoral Immune Responses Flashcards
(26 cards)
What are the three co-receptors on B-cells?
CD 19, CD 21, and CD 32
What is the function of CD 19?
It is the dominant signaling component of B cells. It is in complex with CD 81
What is CD 21 also known as?
Complement receptor 2 (CR2)
What do CD 21/CD 19 while working together?
They are co-receptors that positively regulate B cell activation and they SERVE to lower the Ag threshold for B cell activation
What is CD 32 also known as?
FGÿRIIB
What is the function of CD 32?
It contain an ITIM and negatively regulates BCR signaling
What is an ITAM?
A tyrosine activation motif
B cells express a complex made up of what CDs?
CD 21 (CR2) and CD 19 - CD 81 which contain an ITAM
What binds to CR2 on B cells?
Microbial Ags opsonized by C3d
The signaling cascades from what 2 complexes on B cells greatly enhance B cell activation.
Ag interaction with the BCR and the CR2 complex
What is the function of C3 in B cell stimulation?
C3 is cleaved into C3b which is further degraded into C3d. C3d remains bound to the Ag-Ab surface or on the microbial surface. This then binds to CR2 as the Ag binds to the BCR
What is another name for the CD19 CD81 complex?
TAPA-1
What is another name for the CR2-CD19-CD81 complex?
The B cell coreceptor complex
After C3d binds to CR2, what happens?
The CD19 cytoplasmic tail become tyrosine phosphorylated
Do B cells respond to PAMPs? How do they respond (receptor)?
Yes. Via TLRs.
What happens when a PAMP binds to a B cell? What is the outcome?
PAMPs engage the TLR which activates NFKB. B-cell proliferation and differentiation into plasma cells
What are the functional consequences of Ag-Mediated B cell activation? (picture from slides)
- ) Increased survival and proliferation via expression of proteins
- ) Interaction with helper T cells via increased B7 expression
- ) Responsiveness to cytokines via increased amount of cytokine receptors
- ) Migration from follice to T cell zone via increased expression of CCR7
- ) Antibody secretion by becoming plasma cell
How do B Cells present to T cells?
Protein Ags recognized by membrane Ig are endocytosed and processed. The peptide fragments are presented in association with class II MHC molecules.
Helper T cells recognize MHC-peptide complexes and then stimulate B cell responses.
What is the mechanism of T Cell-Mediated activation of B Cells?
- ) When helper T cells are activated by recognizing Ags presented by B cells, they express CD40L.
- ) CD40L binds to CD40 on B cells and stimulates B cell proliferation and differentiation
- ) Cytokines produced by helper T cells also contribute
What is the general function of Tfh cells?
They play a role in germinal center (GC) formation and function.
What 4 things do Tfh cells express?
ICOS (inducible costimulator), PD-1 (programmed death 1), IL-21, and Bcl-6 (transcription repressor).
What is cytokine IL-21 important for?
It is released by Tfh cells which results in the development of B Cells and subsequent isotype switching, affinity maturation, and antibody production.
What are the three zones of the GC?
Dark, light, and mantle zone.
Where does isotype switching primarily occur? What cells drive this?
In the germinal centers. Tfh cells.
