Phospholipid membranes form specific nonbilayer molecular arrangements that are antigenic

Hexagonal phase (H-II)-preferring lipids such as phosphatidate, cardiolipin , and phosphatidylserine form nonbilayer molecular arrangements in lipid bi layers. While their presence in biological membranes has not been establish ed, in vitro studies suggest that alterations in membrane properties modify their function. In this study, antiphospholipid monoclonal antibodies were developed against nonbilayer structures. One of the monoclonal antibodies identifies nonplanar surfaces in Liposomes and in membranes of cultured cel ls. These results are the first evidence that natural membranes maintain a fragile balance between bilayer and nonbilayer Lipid arrangements. Therefor e, these antibodies can be used to evaluate the role of H-II-preferring lip ids in the modulation of membrane activities, Our studies demonstrated that nonplanar surfaces are highly immunogenic, Although these structures are n ormally transient, their formation can be stabilized by temperature variati ons, drugs, antibiotics, apolar peptides, and divalent cations, Our studies demonstrated that abnormal exposure of nonbilayer arrangements may induce autoimmune responses as found in the antiphospholipid syndrome.