Specific antibody-dependent interactions between macrophages and lipid haptens in planar lipid monolayers

The binding of guinea pig peritoneal macrophages to planar lipid monolayers on alkylated glass is shown to be highly specific, requiring lipid hapten in the monolayer and specific anti-hapten IgG antibody. This is true for both "fluid" and "solid" monolayer membranes, in which the lateral diffusion coefficients of fluorescent lipid probes and bound fluorescent antibodies differ by at least two orders of magnitude. The region of the (macrophage membrane)--(monolayer membrane) contact is readily observed by using an epifluorescence microscope and fluoresceinated IgG antibodies or fluorescent lipids. The fluorescence intensity of IgG antibodies bound to lipid haptens in fluid monolayer membranes in the region of the (macrophage membrane)--(monolayer membrane) contact was significantly enhanced in the early stages of binding (first 10 min at 24 degrees C), due to a diffusive flux of the fluorescent antibodies into the region of membrane--membrane contact. Cellular activation takes place immediately during a 10-min warm-up to 37 degrees C and can be recognized by rapid symmetrical cell spreading, the formation of "black holes" around the cells (probably due to superoxide-facilitated photochemical bleaching of the fluorophore), and the release of the lysozomal enzyme cathepsin B. Specific antibody-dependent [1-14C]-glucose oxidation by these macrophages on fluid and solid monolayers is quite similar to that reported previously for fluid and solid bilayer vesicle target membranes. These results are significant for understanding the molecular interactions between membranes that are necessary for a macrophage cytotoxic response.