Microenvironmental niches in the bone marrow required for B-cell development.

B-cell development is known to occur in a complex bone-marrow microenvironment but its functional organization remains unclear. It is thought that bone-marrow stromal cells create distinct microenvironments, known as niches, that provide support for haematopoiesis and B-cell development. Although it has been more than 20 years since the development of a culture system that allows the growth of B-cell progenitors on bone-marrow-derived stromal cells in vitro, it is only recently that studies have provided a novel basis for understanding the nature of the niches for B-cell development in vivo. This article summarizes the recent advances in research on the earliest B-cell precursors, their requisite environmental factors and the cellular niches that supply these factors and maintain B cells during their development.