已知前体干细胞是在胚胎肝被诱导开始B细胞的分化。在发育后期骨髓承担了生成B细胞克隆的功能,并将细胞输送到全身其他组织。前B细胞是B细胞系发育过程中最早被识别的细胞,前B细胞在有些方面显著不同于B细胞的子代细胞。在妊娠第八周的胎儿肝脏中出现前B细胞,其特点是:分裂快;大的淋巴样细胞;胞浆中含有IgM重链;没有表面Ig以及C_3和Ig的Fc段受体。大的前B细胞进一步发展为小的前B细胞,除大小不同外,两者很相似,后者是开始出现表面IgM的不成熟B细胞的直接前体。发生克隆多样性所需的大多数基因决定在前B细胞的分化阶段表达出来。由于前B细 It is known that precursor stem cells are induced in the embryonic liver to initiate B cell differentiation. Bone marrow undergoes the function of generating B cell clones in the late stages of development and transports the cells to other tissues throughout the body. Pre-B cells are the earliest recognized cells in the development of B-cell lines, which in some respects are significantly different from the progeny of B-cells. Pre-B cells appear in the fetal liver at the eighth week of gestation and are characterized by rapid division; large lymphoid cells; the IgM heavy chain is contained in the cytoplasm; there are no surface Ig and Fc receptor of C_3 and Ig. Large pre-B cells further develop into small pre-B cells that are similar in size except for the direct precursors of immature B cells that begin to develop surface IgM. Most of the genes required for clonal diversity are expressed at the stage of differentiation of pre-B cells. Because of the former B fine