Antibody coated gold particles containing radioactive gold in the demonstration of cell surface molecules

Gold particles of varying size which contain either 195Au of 198Au were prepared using white phosphorus or sodium citrate as the reducing agent. After coating with specific antibody to blood group A antigen or human IgG, these particles were used to determine the number of particles binding to the surface of A1 RBC's or rat RBC's to which human IgG had been attached. The number of particles binding to the surface of cells correlated with the number of antibody coated gold particles in the fluid bathing the cells as well as the number of antigen molecules on the cell surface. That is, the number of particles binding increased as the particle density of the suspension increased and as the cell surface antigen density increased. Under the conditions of the experiments, both blood group A antigen and human IgG appeared to be randomly distributed over the surface of the cells in TEM and SEM preparations. This approach permitted the quantitation of the number of gold particles bound per cell and at the same time, the examination of the distribution of the particles over the surface of the same cell population by TEM and SEM.