Combination of the APAAP and the IGSS techniques for double-labeling with two different monoclonal antibodies.

Cryostat sections were incubated with two different monoclonal antibodies directed either against two different cells or against the same cell. For visualization of the first antibody, the alkaline phosphatase-antialkaline phosphatase (APAAP) technique was used, which rendered a bright red reaction product. For visualization of the second monoclonal antibody, the immunogold-silver-staining (IGSS) technique was used, which resulted in a black reaction product. The combination of an enzyme technique with a technique involving metals (gold and silver) seemed ideal since the reaction product of either technique could be detected easily.