Lateral hapten mobility and immunochemistry of model membranes.
A study has been made of the interaction of specific anti-nitroxide (anti-spin label) IgG antibodies, Fab fragments, complement, and liposomes containing dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, and dipalmitoylphosphatidylcholine plus 0-50 mole % cholesterol, together with various concentrations of a head group spin-labeled phospholipid (0.5-0.01 mole % in the plane of the membrane). The spin-labeled lipid is the amide formed from the reaction of an iodoacetamide spin label, N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodoacetamide, with dipalmitoylphosphatidylethanolamine. We have reached two conclusions: (i) complement fixation depends on the lateral mobility of the lipid hapten at low hapten concentrations in the plane of the membrane (less than or equal 0.1 mole %) and does not depend strongly on this mobility at high hapten concentrations; (ii) cholesterol may have two distinct effects on complement fixation, one arising from an enhancement of hapten exposure to antibody binding sites and a second due to a modulation of membrane fluidity.
D000906:Antibodies; D000937:Antigen-Antibody Reactions; D002462:Cell Membrane / Q000276:immunology*; D002784:Cholesterol / Q000502:physiology*; D003165:Complement System Proteins / Q000502:physiology*; D003497:Cyclic N-Oxides / Q000276:immunology; D006241:Haptens; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G / Q000378:metabolism; D008081:Liposomes / Q000276:immunology; D013113:Spin Labels
D000906:Antibodies; D003497:Cyclic N-Oxides; D006241:Haptens; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D008081:Liposomes; D013113:Spin Labels; D003165:Complement System Proteins; D002784:Cholesterol