The use of a peroxidase-anti-peroxidase complex for the visualization of monoclonal antibodies on the ultrastructural level.

Human peripheral blood mononuclear cell (PBMC) were treated with a panel of monoclonal antibodies (MoAbs) for the demonstration of membrane antigens at the ultrastructural level. The bound MoAbs were linked by rabbit anti-mouse IgG to a peroxidase-anti-peroxidase (PAP) complex composed of monoclonal mouse anti-peroxidase antibodies and horse radish peroxidase. This labelling method with a three step incubation procedure resulted in clear demonstration of the membrane antigens. Moreover, the use of the PAP complex as marker permitted the recognition of monocytes not only by morphology but also by their endogenous peroxidase pattern. In addition, it was observed that the MoAbs used, supposedly specific for T lymphocytes, reacted to a certain degree with monocytes.