Target-cell membrane alterations induced by lymphotoxin. Ultrastructural observations.

Upon in vitro stimulation by antigens or mitogens, lymphocytes release a series of lymphokines. One such lymphocyte mediator is lymphotoxin, which appears to be responsible for in vitro lymphocyte-mediated cytolysis. Employing immuno-electron microscopy with ferritin- or peroxidase-labeled antibody, we observed patchy localization of the mediator on the plasma membranes of target L cells exposed to lymphotoxin, often in areas overlying a microfilament web. When studying lymphotoxin-affected cells by electron microscopy of freeze-fracture replicas, we observed aggrlasma membrane, with intervening areas which were frequently particle free. Sometimes the affected cells revealed plasma-membrane lesions suggesting intramembranous "blisters."