Use of horseradish peroxidase to block nonspecific enzyme uptake in immunoperoxidase microscopy.

Intrinsic tissue peroxidase activity can be more or less successfully destroyed by methanol-H2O2 treatment. It has been found, however, in our laboratory that horseradish peroxidase (HRP) coupled to antibody will bind to some tissue components on a nonspecific basis and remain to take part in the histochemical stain. This contributes considerably to the background. This difficulty can be largely overcome if the tissues are pretreated with a solution of horseradish peroxidase which binds with nonspecific tissue sites. The adsorbed enzyme, along with the intrinsic peroxidase, can then be successfully inactivated by methanol-H2O2 treatment. By this method of blocking, there is considerable reduction in background staining.