The goal of the proposed research is to understand the molecular events which comprise antibody dependent immune recognition. For this study the antigen will be synthetic lipid bilayers containing spin label hapten covalently bound to the lipid head groups. The antibody-liposomal antigen interactions will be studied for both fluid and solid liposomal membranes. These liposomal-antigen-antibody complexes will then be used to activate the first component of complement (Cl) and to activate neutrophils. Both Cl and neutrophil activation will be studied in order to understand the effect that the physical state of the liposomal membrane has on the degree of activation of these systems. Dissociation rates for monovalent and divalently bound antibodies will be determined, using fluorescently labeled antibodies and a cell sorter in the cytofluorograph mode, as a function of the physical state of the membrane. Equilibrium binding data for antibodies on liposomes will be determined by fluorescence methods. From these data the mean residence time for a bivalently bound antibody will be calculated. The kinetics of activation of radioiodinated Cl will be measured by measuring the rate of production of radioactive Cls fragments. An assay for the rapid measurement of neutrophil activation will be developed based on redistribution of membrane potential sensitive fluorophors. With this assay the kinetics of neutrophil activation can be studied in parallel to that of Cl activation. These activation kinetics will be compared with the kinetics of antibody interaction with hapten-containing liposomes in the fluid and solid state in order to determine the requirements for antibody dependent immune recognition in these two systems.