Osteoblasts release a soluble factor that modulates immunoglobulin secretion by mature B cells.

An osteogenic member, MBA-15 cell line, from marrow stroma compartment, was examined for its ability to regulate mature lymphoma B cell line functions. The effect of MBA-15 cell secreting factor/s on cell proliferation, immunoglobulin secretion and isotype switch of 29M4.1 IgM+ mature B cell line was examined. The factor causes temporal arrest in cell proliferation, augments immunoglobulin secretion and has no effect on isotype switching. The results revealed a direct effect of the MBA-15 factors on the B cell functions. Factors secreted by other osteoblastic cells (ROS 17/2.8 and MC-3T3-E1) possess the same biological activities. In contrast, factors secreted by an endothelial adipocyte stromal cell line 14F1.1 lack these properties.