| B cells are an important population of lymphocytes that can secrete antibody and thus play a critical role in humoral immune response. The development of B cells is a multi-step, gradually-progressed and strictly-regulated process. The embryonic B cell development occurs in the fetal liver, while in the adult the majority of B cells come from bone marrow. In the bone marrow, B cells undergo three developmental stages: pro-B, pre-B, immature B cells and then migrate into peripheral lymphoid organs, such as spleen. In the spleen, immature B cells further transit into transitional B cells and finally become mature naive B cells. Mature B cells are capable of binding to antigen and then become activated. Activated B cells undergo a serial of molecular up-regulation or down-regulation and fully differentiate into the powerful antibody-secreting cells:plasma cells. While another proportion of activated B cells will differentiate into memory B cells, which are responsible for the rapid immune response after secondary challenge.How do B cells avoid attacking the "self" while at the same time do not compromise the ability to take rapid response to foreign pathogens? Clonal deletion, receptor edition and anergy serve as the three major mechanisms for negative selection to ensure the self-tolerance is effectively launched.It is generally thought that the signals from self-antigen binding to BCR provide the decision-making choice.In the first party of my thesis, we studied the role of Bcl10in regulating the negative selection mechanisms. Bcl10deficient mice have less anergic B cell in the spleen. Within all the splenic B cell populations, anergic B cells specifically show a higher level of cell apoptosis with Bcl10, indicating that the deficiency of Bcl10selectively affect the survival of anergic B cell population. Moreover, using IgHELtgsHELtg mice model to study self-reactive B cells, we observed the total B cell loss and higher cell apoptosis in Bcl10deficient IgHELtgsHELtg mice, further demonstrating that Bcl10is involved in regulating the survival of self-reactive B cells. Bcl10-null B cells also displayed higher apoptosis level under in vitro stimulation with anti-IgM or HEL. Moreover, while wild type B cells can successfully induce the up-regulation of pro-survival molecules:BcI-XL and Al, but Bcl10deficient B cell failed to do so. Therefore, all our data demonstrated that Bcl10plays a decisive role in the negative selection mechanisms of self-reactive B cells.The second part of my thesis is focusing on the role of PLCyl in B cell development and function. As one of the two isoforms of PLCy, PLCyl is generally thought be involved in TCR and growth factor receptor signaling. However, high expression level could be detected in early developmental stages of B cells, implying its possible role in regulating B cell development. Using the mixed bone marrow cells from PLCglf/-MxCre mice and μMT mice as bone marrow donor, we generated chimera mice that possess B cell specific deletion of PLCγ1. After examine the development of different stages of B cells, we found that both the number and percentage of mature B cells in bone marrow and spleen are reduced after PLCγ1is deleted. However, within the mature B cell population, the ratio of GC B cells is increased in PLCyl deficient mice. Challenged with ARS-CGG antigen, PLCyl B-cell-specific deficient mice displayed an overactive response to ARS, possibly due to the increase of GC B cells in the spleen. Moreover, Hep2cells staining for detecting anti-ANA antibody and IgH chain CDR3sequencing results demonstrate that PLCγ1B-cell-specific mice displayed a higher tendency of autoantibody production and autoimmune symptoms. |
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