Use of the defined antigen substrate spheres system as a model for analysing possible mechanisms of inhibition-blockade of anti-tumour lymphocytotoxicity.

The defined antigen substrate spheres (DASS) system was employed for analysing reactions between solid state antibody or antigen and soluble immune complexes. Sepharose beads covalently coupled with ovalbumin were used to represent tumour cells and beads coupled with antibody against ovalbumin were used to represent anti-tumour lymphocytes; the ovalbumin and corresponding antibody simulated tumour-derived antigen and antibody to tumour respectively. Binding of soluble complexes to the beads was measured by fluorimetry and/or radiometry of fluorescein or 125-I-labelled ovalbumin or antibody. Antigen-antibody complexes in antibody excess bound less effectively to the antibody beads than antigen alone, but complexes in slight or moderate antigen excess bound more effectively. Complexes in antibody excess were most effective in the complex before levelling off and then decreased in extreme antibody excess. The model demonstration of augmentation by antibody of antigen binding to solid state antibody might by analogy reflect a mechanism of inhibition of lymphocyte cytotoxicity. Complexes in a wide range of antibody excess should also be effective in blocking lymphocytotoxicity at the target cell level.