Populational change is Darwin’s hypothesis that evolution occurs by changes in the proportions (frequencies) of different variant kinds of individuals within a population.

TLS Online TPP Program

#Id: 10346

#Unit 4. Cell Communication and Cell Signaling

T1 cells are mIgMhi, mIgD -/lo, CD21-, CD23-, CD24+, and CD93+. 

T2 cells differ from T1 cells in having higher levels of mIgD and in expressing CD21 and CD23. 

TLS Online TPP Program

#Id: 10347

#Unit 4. Cell Communication and Cell Signaling

Transitional B cells bound for a follicular fate undergo positive and negative selection in the spleen.

TLS Online TPP Program

#Id: 10348

#Unit 4. Cell Communication and Cell Signaling

BAFF-R expression is first detected in T1 B cells and increases steadily there after.

Signaling through the BAFF/BAFF-R axis promotes survival of transitional B cells by inducing the synthesis of anti-apoptotic factors such as Bcl-2, Bcl-xl, and Mcl-1

TLS Online TPP Program

#Id: 10349

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 10350

#Unit 4. Cell Communication and Cell Signaling

B cells migrate to the lymphoid follicles. They are directed there by chemokine interactions between CXCL13, which is secreted by follicular dendritic cells (FDCs).

TLS Online TPP Program

#Id: 10351

#Unit 4. Cell Communication and Cell Signaling

B-cell survival in the follicle is dependent on access to the TNF-family member cytokine B-cell activation factor (BAFF), otherwise known as B lymphocyte survival factor (BLyS), which is secreted by the FDCs.