Transmembrane signaling through CD80 (B7-1) induces growth arrest and cell spreading of human B lymphocytes accompanied by protein tyrosine phosphorylation

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 lymphoma Raji cells induced tyrosine phosphorylation in 160-, 120-, 55-, 46- and 44-kDa proteins, which was inhibited by genistein. CD80-mediated signaling resulted in the inhibition of DNA replication of B cells and induced the changes in morphology like macrophages or fibroblasts. This 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 effects appear to be mediated by tyrosine kinases.