Preparation of colloidal gold-labeled agarose-gelatin microspherules for electron microscopic studies of phagocytosis in cultured cells.

Agarose-gelatin microspherules about 0.5 micron or larger are prepared with emulsification of 4% agarose-gelatin sol containing 0.2 M N-octylglucoside in an organic phase composed of cyclohexane, egg lecithin, Span 80, and ethanol, followed by extraction of lipophilic components with cyclohexane and ether. Colloidal gold particles are then introduced into microspherules using gold chloride reacting at room temperature with tannic acid in a specified concentration range. After they have been coated with bovine serum albumin or mouse IgG, colloidal gold-labeled microspherules can be readily phagocytized by mouse L-cells and P388 cells after incubation for several hours. In addition to their use as a novel marker for phagocytosis, we discuss other potential uses for these colloidal gold-labeled microspherules.