In the bone marrow (BM) hematopoietic microenvironment, stromal cells play crucial roles. Stromal cells secrete a variety of cytokines and express cell surface molecules that regulate the growth of hematopoietic cells. BM stromal cell lines derived from patients with rheumatoid arthritis (RA) have augmented ability to support the growth of a murine pre-B cell line, DW34. BST-1 (bone marrow stromal cell antigen-1) is expressed on BM stromal cell lines and is responsible for an augmented ability to support pre-B cell line growth. BST-1 is also expressed by RA-derived synovial cell lines, a myelomonocytic cell lines, and HUVEC, suggesting that BST-1 has other functional roles than just supporting pre-B cell growth.Synonyms: ADP-ribosyl cyclase 2, BST-1, Bone marrow stromal antigen 1, Cyclic ADP-ribose hydrolase 2, cADPr hydrolase 2