TRANSMEMBRANE SIGNALING THROUGH CD80 (B7-1) INDUCES GROWTH ARREST ANDCELL SPREADING OF HUMAN B-LYMPHOCYTES ACCOMPANIED BY PROTEIN-TYROSINEPHOSPHORYLATION

We addressed the issue of the role for CD80 (B7-1) expressed on human B cells in transmembrane signaling. Cross-linking of CD80 on B lymphom a Raji cells induced tyrosine phosphorylation in 160-, 120-, 55-, 46- and 44-kDa proteins, which was inhibited by genistein. CD80-mediated s ignaling resulted in the inhibition of DNA replication of B cells and induced the changes in morphology like macrophages or fibroblasts. Thi s cell spreading was inhibited by the pre-treatment of the cells with genistein. These results suggest that the CD80 antigen is involved in transmembrane outside-in signaling in B cells and its biological effec ts appear to be mediated by tyrosine kinases.