Galectin-1 expressing stromal cells constitute a specific niche for pre-BII cell development in mouse bone marrow

In the bone marrow (BM), stromal cells constitute a supportive tissue indispensable for the generation of pro-B/pre-BI, pre-BII and immature B lymphocytes. IL7 producing stromal cells constitute a cellular niche for pro-B/pre-BI cells but no specific stromal cell microenvironment was identified for pre-BII cells expressing a functional pre-B cell receptor (pre-BCR). However expression of the pre-BCR represents a crucial checkpoint during B cell development. We recently demonstrated that the stromal cell derived-galectin1 (GAL1) is a ligand for the pre-BCR, involved in the proliferation and differentiation of normal mouse pre-BII cells. Here we show that non-hematopoietic osteoblasts and reticular cells in the BM express GAL1. We observed that pre-BII cells, unlike the other B cell subsets, were specifically localized in close contact with GAL1+ reticular cells. We also determined that IL-7+ and GAL1+ cells represent two distinct mesenchymal populations with different BM localization. These results demonstrate the existence of a pre-BII specific stromal cell niche and indicate that early B cells move from IL7+ to GAL1+ supportive BM niches during their development.