Binding of immunoglobulin G to phospholipid vesicles by sonication.

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Purified goat immunoglobulin G (IgG) does not bind to sonicated phospholipid vesicles. However, when IgG is sonicated together with phospholipids, 4 to 40% of the IgG can be bound to the vesicles, depending on the experimental conditions. The extent of binding depends on the period and power of sonication, the IgG to lipid ratio, and the lipid composition. Anionic phospholipids such as phosphatidylglycerol and phosphatidylserine, but not cholesterol, enhance binding about 50% over that obtained with the neutral phosphatidylcholine. Binding of IgG causes extensive aggregation of vesicles, as shown by electron microscopy, and aggregates can be separated from unbound IgG by molecular-sieve chromatography on Sepharose 4B or by sucrose density gradient centrifugation. The IgG-vesicle aggregates remain stable in either phosphate-buffered saline or 50% fetal calf serum up to 20 h at 37/sup 0/C, although substantial lipid degradation in 50% fetal calf serum was observed. The use of goat IgG containing antibody to a purified protein antigen allowed quantitation of antibody activity of these preparations. Immune IgG sonicated alone shows 100% of the original antigen binding capacity while vesicle-bound IgG retains 30 to 50%. Antigen binding capacity of bound IgG is not increased when vesicles are lysed by 1.5% NP-40, suggestingmore » all of the bound IgG is exposed on the outer surfaces of the vesicles. IgG's of human, mouse, and rabbit, as well as the purified goat F(ab')/sub 2/ fragments, also bind with vesicles by cosonication.« less