Evidence for LFA-1/ICAM-1 dependent stimulation of protein tyrosine phosphorylation in human B lymphoid cell lines during homotypic adhesion

JK32.1 and SKW6.4 are Epstein-Barr virus (EBV)-positive human B cell lines that undergo spon- taneous, lymphocyte function-associated antigen 1 (LFA-1) dependent homotypic adhesion in culture. This process is associated with induction of tyrosine phos- phoproteins of molecular mass 90, 106, and 120 kDa and could be reproduced when these cells were centrifugation- ally aggregated. Antibodies to the /32 (CD18) chain of LFA-1 interfered with induction of p120, p106, and p90 during cellular aggregation. Response induction was abrogated when cells were incubated with protein tyro- sine kinase (PTK) inhibitors (erbstatin, genistein, and geldanomycin) or cytochalasin B prior to aggregation. An in vitro kinase assay did not reveal activation of focal adhesion kinase. Although the role of LFA-1-dependent tyrosine phosphorylation in B cells is uncertain, patients with the leukocyte adhesion defect (LAD) exhibit hu- moral abnormalities. Moreover, aggregation did not in- duce specific tyrosine phosphoproteins in an EBV- transformed B cell line from a LAD patient. These results suggest that an LFA-1-dependent PTK pathway may play an important role in human B cell function. J. Leukoc. Biol. 57: 343-351; 1995.