Glycolipid and monoclonal immunoglobulin-glycolipidic liposomes spread onto high ionic strength buffers: Evidence for a true monolayer formation

The kinetics of the formation of an interfacial film obtained after spreading synthetic glycolipid and monoclonal immunoglobulin-glycolipidic liposomes onto high ionic strength buffered subphases were studied by measuring the evolution of the surface pressure with time, and the experimental data were analyzed theoretically according to a model previously proposed.(1) The spreading kinetics of the multilamellar glycolipidic vesicles can be explained by the mechanistic scheme described for small unilamellar phospholipidic vesicles(2-4) and based on a double control process (irreversible diffusion into the subphase and interfacial transformation of the closed vesicles in the surface film). In addition, the specific behavior of the glycolipidic liposomes, observed within the first minute after spreading, reveals that these liposomes exhibit surface-active properties related to their efficient interfacial disintegration. The theoretical analysis applied to the experimental data suggests that the multilamellar liposomes disintegrate at the interface into a true monomolecular film with a high rate constant of transformation. The insertion of a monoclonal immunoglobulin (IgG(1)) into these liposomes does not fundamentally modify their interfacial behavior and simply accelerates their disintegration. The formation of a true monolayer has been evidenced also in the presence of the immunoglobulin. The antibody insertion, characterized through transmission electron microscopy, leads to a structural modification of the liposomal membranes. This modification, weakening the membranous system, induces an additional retrodiffusion of the proteo-glycolipidic liposomes toward the interface and enhances their disintegration. The presence of the immunoglobulin in the glycolipidic film has been characterized by front face fluorescence emission spectroscopy with a mixed fluorescently labeled IgG-glycolipid film transferred onto a quartz plate. The occurrence of the interactions between the immunoglobulin and the glycolipid in the Liposomal membrane prior to the monolayer formation appeared as a key step enabling the protein to stay included in the lipidic matrix during both monolayer formation and compression.