The activation antigen BLAST-2, when shed, is an autocrine BCGF for normal and transformed B cells.

A shed form of the membrane-bound B cell activation marker, BLAST-2 (Epstein-Barr virus cell surface, CD 23) was immune-affinity purified from Epstein-Barr virus-transformed lymphoblast conditioned medium. SDS-PAGE analysis revealed a complex of two polypeptides, mol. wts 25,000 and 12,000, here termed s-BLAST-2. We show that this complex, when purified to homogeneity, can act as a growth factor for EBV-infected B lymphoblasts and normal receptor-stimulated B cell blasts. It has no effect on resting B or T cells. These data suggest that the BLAST-2 antigen has a role in autocrine B cell growth. Additionally, this complex is a co-mitogen for PHA-stimulated murine thymocytes, a property of interleukin-1.