Influence of vesicle size on complement-dependent immune damage to liposomes

Area of Science:

• Lipid bilayer research
• Immunology
• Biophysics

Background:

• Complement-dependent antibody-mediated damage typically releases 50-60% of trapped markers from multilamellar lipid vesicles (MLVs).
• This is often attributed to complement attacking only the outermost layers of MLVs.

Purpose of the Study:

• To investigate the influence of vesicle size and type on complement-mediated damage.
• To test the hypothesis that vesicle size affects the extent of marker release.

Main Methods:

• Complement lysis assays were performed on large unilamellar vesicles (LUVs) prepared by different methods (REVs and LUVETs).
• Multilamellar lipid vesicles (MLVs) were separated into size populations using a fluorescence-activated cell sorter.
• Marker release and glucose uptake were quantified after complement-mediated lysis.

Main Results:

• LUVs released only 25-40% of trapped markers, less than expected.
• Marker release from MLVs was inversely proportional to vesicle size.
• No glucose uptake was observed when glucose was only external to liposomes during lysis.

Conclusions:

• Vesicle size significantly influences the extent of complement-mediated marker release.
• Results support the hypothesis that complement channels are transiently open in liposomes.
• Loss of channel patency may result from channel closing or physical loss of channels.