The Roles of β-Lymphotoxin in antibody Dependent Cell-mediated Cytotoxicity

Abstract

We investigated roles of α- and β-lymphotoxins in antibody dependent cell-mediated cytotoxicity(ADCC) utilizing a homologous human system; skin fibroblasts with known HLA type, allo-antiserum and blood lymphocytes. Under assay conditions using optimal amounts of priming anti-HLA antibody, maximal killing of 60-80% was achieved within 6 hours. At this time, only β-LT was present in supernatants of lytic culture; α-LT was not detected. The amounts of β-LT, as well as the kinetics of appearance, paralleled the extent and kinetics of ADCC killing by lymphocytes. Allo-antibody directed to HLA determinants not on the target cells elicited neither lysis nor β-LT release. Antisera were prepared to β-LT-containing supernatants or to partially purified α-LT. Anti-β-LT serum inhibited essentially only β-LT. Anti-α-LT inhibited from 13-38% of the total activity of standard β-LT preparations. We interpret this as either indicating a 13% contamination of the anti-α-LT with anti-β-LT activity or a 13% contamination of the standard β-LT preparation with α-LT. Both immune sera inhibited EA-rosette formation. In addition, anti-α-LT serum inhibited E-rosette formation. Anti-β-LT serum was markedly effective in inhibiting ADCC. Inhibition by anti-α-LT correlated with its anti-β-LT titer rather than with its anti-α-LT titer. Adsorptions to spleen cells essentially did not reduce the ability to block ADCC and totally removed EA-rosette inhibiting activity. These data suggest that β-LT plays a important role in ADCC target destruction.