On the mode of incorporation of human transplantation antigens into lipid vesicles.

Highly purified HLA (A and B) antigens in octylglucoside were quantitatively incorporated into egg lecithin vesicles, and it was demonstrated that vesicles of different densities could be prepared by varying the ratio of lipid to protein. The HLA antigens were bound to the vesicles by the hydrophobic stretch of amino acids normally integrated into the plasma membrane, and most if not all HLA antigens in the lipid vesicles occurred in the right-side-out orientation, as demonstrated by pronase digestion and by quantitative radioimmunoassay determinations on intact HLA antigen-containing vesicles. Both the lipid and the HLA antigens aggregated at octylglucoside concentrations below the critical micelle concentration. The protein aggregates appeared stable and could be incorporated into preformed lipid vesicles. It is suggested that vesicle formation preceeds the incorporation of protein into the lipid vesicles.