B cell development III Flashcards
When looking at the anti-HEL Ab binding to WT and Ig-transgenic mice, what are some differences between the two groups?
WT have more diversity and therefore fewer BCRs that bind to HEL; whereas the transgenic had many BCRs that bind to HEL
How are self-reactive B cells produced, why is it important that they are removed, what is the process of removal called?
produced = random nature of V(D)J recombination results in some B cells expressing BCRs that recognize self-Ag.s
importance of removal = autoimmunity can result if they are not removed
process = negative selection
What is central tolerance, and where does this occur for B cells and T cells?
removal of self-reactive lymphocytes in primary lymphoid organs
- B cells = bone marrow
- T cells - thymus
What are three mechanisms of negative selection in central tolerance?
- anergy
- clonal deletion
- receptor editing
What is peripheral tolerance (why is it a thing), what mechanisms does it involve and what happens to self-reactive T1 cells that bind to self Ag.s?
peripheral tolerance = not all self-Ags are present in the bone marrow; therefore, other mechanisms outside of the bone marrow to deal with the issue
mechanisms = anergy, clonal deletion, and perhaps receptor editing
T1 cells = undergo apoptosis
What is clonal deletion, how is it anti-inflammatory?
clonal deletion = self-reactive cells undergo programmed cell death, primarily apoptosis
anti-inflammatory = apoptosis is anti-inflammatory and this is important because inflammation in the bone marrow is harmful
What is function anergy (anergy), and what effects does it have on B cells?
anergy = self-reactive cells become non-responsive to Ag. via impaired signaling when Ag. binds BCR (e.g. upon ligand binding: no activation, no proliferation, no differentiation)
effects = shorter half-life, phenotypically different (e.g down-regulate IgM)
What determines whether a cell undergoes clonal deletion or anergy?
Strength of BCR signaling
- mutlivalent self-Ag: membrane bound self-Ag.s will cause simultaneous clusters of many BCRS on the cells surface and induces a strong signal
- monovalent self-Ag: soluble self-Ag. engages fewer BCRs and induces a weaker BCR signal
How was clonal deletion and anergy studied?
Using the anti-HEL BCR transgenic to study negative selection:
- crossed an anti-HEL BCR transgenic mouse with a transgenic mouse expressing soluble HEL (HEL tansgenic) to study anergy
- creates a double trangenic that carries both HEL and anti-HEL transgenes
Why would using a BCR transgenic be useful to study negative selection?
- all B cells are of the same specificity
- you know the specificity of the transgenic BCR
What were the results of the HEL transgenic vs WT experiment, where the mice were injected with HEL? What was the conclusion?
Results:
- non-Tg (control) when injected with HEL had a high anti-HEL titre
- HEL-Tg when injected with HEL had little Ab response
Conclusion: the HEL transgenic do no respond to HEL; tolerant to HEL
What were the results and conclusions when a double trangenic mouse that carries both HEL and anti-HEL transgenes when probed with a allotype (transgenic BCR) Ab.s, when compared to WT and anti-HEL transgenic? What question resulted from this study>
Results:
- WT = few BCRs that bind to the a allotype
- anti-HEL transgenic = lots of BCRS that bind the a allotype
- double transgenic = lots of BCRs that recognize the a allotype; however, there were fewer IgM than the single transgenic which is an anergic phenotype (low IgM, high IgD)
Conclusion:
- B cells in double transgenic have an anergic phenotype
Question:
- are these cells truly anergic?
When anti-HEL transgenics and double transgenics were injected with HEL what was the results and conclusion?
results:
- anti-HEL: had a high Ab response to HEL
- double tg: had a low Ab repsonse to HEL
conclusion: the double tg.s do not make anti-HEL Ab.s; therefore, anti-HEL B cells in db tg are anergic
How could the anti-HEL transgenic system be used to study clonal deletion?
Make HEL memb-bound
In the HEL/anti-HEL system, where some cells should be deleted, there was a small number of mature B cells found, what was a characterisitc of their BCR?
express a transgenic heavy chain and endogenous light chain - receptor editing
