Visualization of specific antibody and C1q binding to hapten-sensitized lipid vesicles.

Abstract

Specific Ig[immunoglobulin]G antibodies directed against the spin-label nitroxide group present as a lipid hapten in single-compartment lipid vesicles were visualized using freeze-etch electron microscopy. Indvidual particles with diameters of the order of 20 nm were identified as single IgG molecules bound to lipid hapten. No significant aggregation of these IgG molecules was observed over a period of 1 h in a dipalmitoyl phosphatidylcholine vesicle at 22.degree. C. Binding of the human complement component Clq results in the formation of large (.apprx. 50-100 nm) asymmetric particles having a partially resolved substructure that may arise from individual IgG molecules bound to the membranes and to Clq. The binding of Clq appears to result in a clustering of membrane-bound IgG molecules. Samples containing a serum factor (perhaps anti-IgG antibodies) exhibit some IgG clustering distinct from that produced by Clq.