Cytokine and Stromal Influences on Early B-Cell Development

Abstract

Mammalian bone marrow (BM) is a complex milieu of rare pluripotent stem cells, developmentally restricted stem cells, a range of immature to mature cells in distinct lymphohematopoietic lineages, and nonlymphohematopoietic cells (1). The latter category consists of several cell types, including adventitial reticular cells, barrier cells, endothelial cells, adipocytes, osteoblasts, and osteoclasts. The adventitial reticular cells line the abluminal surface of the marrow vascular sinus, and the cytoplasmic processes that extend from these cells are in direct contact with lymphohematopoietic cells (2). Whether adventitial reticular cells constitute a single cell type with origin in a common mesenchymal precursor is not known, but they manifest many attributes of fibroblast-like cells (3). The term BM stromal cells is also used to describe the adherent cell population established from the in vitro culture of BM, and the predominant cell present in such an adherent cell population is generally the adventitial reticular/fibroblast-like cell. In this chapter, the authors will employ the term BM stromal cell to describe the adventitial reticular/fibroblast-like cell that predominates cultures established from mouse or human BM plated in tissue culture medium supplemented with fetal bovine serum.