Immunoelectron microscopic demonstration of tissue antigens with monoclonal antibodies.

Two methods of demonstrating tissue antigens by ultrastructural enzyme immunohistochemistry were tested. The monoclonal antibodies Ki-M1 and Ki-M4 were chosen for testing the methods because Ki-M1 identifies a relatively stable, and Ki-M4 a very unstable antigen. The two antibodies react selectively with human macrophages and interdigitating reticulum cells or dendritic reticulum cells of lymphoid follicles. The Ki-M1 reaction product is confined to the surface membrane. Ki-M4 reactivity is located on the surface membrane and, less often and to a lesser extent, in the cytoplasm. The technical prerequisites for reliable conservation of the antigens identified by these two antibodies were standardized. The results indicated that prior fixation in 4% paraformaldehyde is preferable for optimum preservation of stable antigens. Application of the primary antibody prior to fixation was found to be the best procedure for demonstrating unstable antigens, although nonspecific reactions were seen more often with this method.