BST-1 (bone marow stromal antigen-1) has been identified as a surface molecule that is GPI-anchored to the cell membrane of stromal cells. Both ADP-ribosyl cyclase and cADPR hydrolase activites have been demonstrated by BST-1. cADPR activity is a potential regulator of insulin secretion in pancreatic beta cells. Most pancreatic islet cells express BST-1, indicating a link between BST-1 and insulin secretion. BST-1 expression has also been found in a wide range of tissues including umbilical vein endothelial cells, monocytes and granulocytes. BST-1 expression in thymus tissue and on B and T cell progenitors undergoing gene rearrangement implicates BST-1 as a useful marker for lymphoid progenitor cells that are initiating gene rearrangement of their antigen receptors. BST-1 has also been shown to facilitate B cell growth and may act as a receptor.