Interaction of immunoglobulins with liposomes.
Liposomes were used as model targets to test the effect of immunoglobulins on biomembranes. Heat-aggregated immunoglobulins (Ig) exceeded native immunoglobulins in their capacity to release anions and glucose from model liposomes (either lecithin-dicetyl-phosphate-cholesterol or lecithin-stearylamine-cholesterol in molar ratios of 7:2:1). This interaction was not dependent upon the presence of cholesterol in the membrane. Mild heat-aggregation (10 min at 61.5 degrees C) increased the membrane-perturbing activity of certain Ig. Activity varied among classes and subclasses: IgG1 > pooled IgG > IgG4 > IgA1 > IgG3. IgG2, IgA2 and IgM were inert. Fc fragments of IgG were as active as IgG1, whereas Fab fragments were inactive. Prolonging aggregation to 60 min destroyed the activity of Ig. Membrane-activity could not be induced in non-Ig molecules (such as bovine serum albumin) by 10 or 60 min heat-aggregation. Density gradient centrifugation of IgG1 molecules indicated that membrane perturbing activity was associated with 15-20-s aggregates. Sepharose 4B chromatography demonstrated preferential interaction between cationic membranes and aggregated Ig, whereas anionic membranes interacted nonselectively with both native and aggregated Ig via salt-like interactions. One explanation for these data is that heat aggregation induces a conformational change in the Fc regions of certain Ig permitting them to interact with liposomes, presumably by enhancing their hydrophobic associations with membrane phospholipids.
Weissmann
G
G
Department of Medicine, Rheumatic Diseases Study Group, and Irvington House Institute, New York University School of Medicine, New York 10016, USA.
Brand
A
A
Franklin
E C
EC
D000818:Animals; D000838:Anions; D002412:Cations; D002840:Chromates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007136:Immunoglobulins / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000378:metabolism
D000838:Anions; D002412:Cations; D002840:Chromates; D007136:Immunoglobulins; D008051:Lipid Bilayers; D008081:Liposomes; D012710:Serum Albumin, Bovine; D005947:Glucose