Effector-target co-aggregation as a crucial step in the neutrophil-mediated tumour cell lysis

The Daudi cell lysis by human neutrophils, incubated with phorbol myristate acetate (PMA), was inhibited by amino acids (taurine, methionine), consistent with the involvement of hypoclorous acid (HOCl) in the lytic process. Also, the lysis was inhibited by a monoclonal antibody (mAb J-90) directed against the leukocyte function-associated antigen-1 (LFA-1). The inhibition of the target cell lysis by mAb J-90 is not due to a HOCl-scavenging mechanism, as suggested by the use of control mAb Dako M-1 (anti CD-15). As detected by the microscopic examination of samples from test tubes and measured by monitoring the light transmission from the cell suspensions, neutrophils and Daudi cells were found to co-aggregate during the lytic reaction. Co-aggregation was efficiently inhibited by the mAb J-90. The results suggest that tumour cell lysis by PMA-triggered human neutrophils involves at least two events: production of HOCl and LFA-1-mediated effector-target adhesion.