Immune reactions of liposomes containing cardiolipin and their relation to membrane fluidity

The relation between the immune reactions of phosphatidylcholine liposomes containing cardiolipin with or without cholesterol and the physical state of the liposomes was studied. In egg yolk phosphatidylcholine liposomes, both immune agglutination and complementmediated immune damage occurred irrespective of the presence of cholesterol. Immune agglutination also occurred at all temperatures tested (0--40 degrees C). On the other hand, in dipalmitoylphosphatidylcholine liposomes, both reactions depended on the cholesterol content, but immune agglutination occurred even in the absence of cholesterol above the phase transition temperature at which liposomal membranes became fluid. The finding of antibodies to liposomes was found to be independent of the physical state of the liposomal membranes. The requirement of the fluid state of liposomal membranes for immune reactions is discussed.