| Research Abstract |
The major Purpose of this project is to understand cellular and molecular basis which regulates the early process of B cell differentiation in murine bone marrow. Before this project had started, we demonstrated that the entire process of B lineage differentiation from phuripotent hematopoietic stem cells to smu^+ mature B cells is supported by interleukin-7 (IL-7) and IL-7 negative stromal cell clone PA6. Using these two signals separately, intramarrow B lineage cells are divided into 4 distinct differentiation stages ; 1) B-pro-I which proliferates on the PA6-layer in the absence of IL-7, 2) B-pro II whose proliferation requires both PA6 and IL-7, 3) CFU-IL7 which proliferates in response to IL-7, and mature B cell which does not react to any of stromal cell-derived growth factors. On this basis, we next focused on following two subjects ; the role of c-kit and its ligand SLF in the stromal cell dependent B cell differentiation, and signals which triggers B cell differentiation. Foll
… More
owings are the summaries on the results obtained from this two year study.
1) There exists a distinct B lineage population which coexpresses c-kit and a B lineage marker, B220. From in vitro culture of FACS purified stem cell enriched population, B lineage differentiation proceeds from c-kit^+lin^- stem cell through c-kit^+B220^+ stage to c-kit^-B220^+ stage.
2) In vitro development of B lineage cells from c-kit^+lin^- stem cells is severely suppressed by addition of monoclonal antibody antagonistic to c-kit function. This suggests that c-kit on the early B cell surface in functional.
3) Most of B lineage cells in the bone marrow of scid mouse which is unable to express functional mu-chain express c-kit, while in the scid mouse carrying mu-chain transgene the most B cells do not express c-kit. This result suggests that c-kit expression is downregulated upon expression of mu-chain.
4) The frequency analysis of B-pro-II and CFU-IL7 in mu-transgenic mouse and k-transgenic mouse demonstrated that B-pro-II is selectively reduced in mu-transgenic mouse, while CFU-IL7 is selectively reduced in k-transgenic mouse. This result strongly suggests that the differentiation of B cells is directed by the expression of immunogrlobulin gene. Less
|
