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.